US20060142820A1 - Antenna systems for implantable medical device telemetry - Google Patents

Abstract

An implantable medical device system includes an implanted device communicating with an external device via telemetry. The implanted device and the external device each have a telemetry module connected to an antenna system to support a radio-frequency (RF) telemetry link. The antenna system of the external device has a manually or automatically controllable directionality. The controllable directionality is achieved, for example, by using two or more directional antennas, one non-directional antenna and one or more directional antennas, or an electronically steerable phased-array directional antenna.

Description

CROSS REFERNCE TO RELATED APPLICATION(S)
• This application is a continuation of U.S. patent application Ser. No. 10/309,337, filed on Dec. 3, 2002, the specification of which is incorporated herein by reference.
TECHNICAL FIELD
• This document relates generally to implantable medical devices and particularly, but not by way of limitation, to such a device including a telemetry system allowing communication with an external device.
BACKGROUND
• Medical devices are implanted in human bodies for monitoring physiological conditions, diagnosing diseases, treating diseases, or restoring functions of organs or tissues. Examples of such implantable medical devices include cardiac rhythm management systems, neurological stimulators, neuromuscular stimulators, and drug delivery systems. Because such a device may be implanted in a patient for a long time, the size and power consumption of the device are inherently constrained. Consequently, an implantable device may depend on an external system to perform certain functions. Communication between the implantable device and the external system is referred to as telemetry. Examples of specific telemetry functions include programming the implantable device to perform certain monitoring or therapeutic tasks, extracting an operational status of the implantable device, transmitting real-time physiological data acquired by the implantable device, and extracting physiological data acquired by and stored in the implantable device.
• One particular example of implantable medical devices is a cardiac rhythm management device implanted in a patient to treat irregular or other abnormal cardiac rhythms by delivering electrical pulses to the patient's heart. Such rhythms result in diminished blood circulation. Implantable cardiac rhythm management devices include, among other things, pacemakers, also referred to as pacers. Pacemakers are often used to treat patients with bradyarrhythmias, that is, hearts that beat too slowly or irregularly. Such pacemakers may coordinate atrial and ventricular contractions to improve the heart's pumping efficiency. Implantable cardiac management devices also include defibrillators that are capable of delivering higher energy electrical stimuli to the heart. Such defibrillators may also include cardioverters, which synchronize the delivery of such stimuli to portions of sensed intrinsic heart activity signals. Defibrillators are often used to treat patients with tachyarrhythmias, that is, hearts that beat too quickly. In addition to pacemakers and defibrillators, implantable cardiac rhythm management systems also include, among other things, pacer/defibrillators that combine the functions of pacemakers and defibrillators, drug delivery devices, and any other implantable systems or devices for diagnosing or treating cardiac arrhythmias.
• An implantable cardiac rhythm management device typically communicates with an external device referred to as a programmer via telemetry. One type of such telemetry is based on inductive coupling between two closely-placed coils using the mutual inductance between these coils. This type of telemetry is referred to as inductive telemetry or near-field telemetry because the coils must be closely situated for obtaining inductively coupled communication. One example of such an inductive telemetry is discussed in Brockway et al., U.S. Pat. No. 4,562,841, entitled “PROGRAMMABLE MULTI-MODE CARDIAC PACEMAKER,” assigned to Cardiac Pacemakers, Inc., the disclosure of which is incorporated herein by reference in its entirety.
• In one example of inductive telemetry, an implantable device includes a first coil and a telemetry circuit, both sealed in a metal housing (referred to as a “can”). The external programmer provides a second coil in a wand that is electrically connected to the programmer. During device implantation, a physician evaluates the patient's condition, such as by using the implanted device to acquire real-time physiological data from the patient and communicating the physiological data in real-time to the external programmer for processing and/or display. The physician may also program the implantable device, including selecting a pacing or defibrillation therapy mode, and parameters required by that mode, based on the patient's condition and needs. The data acquisition and device programming are both performed using the inductive telemetry. If the patient's condition is stable after implantation, he or she needs no attention from the physician or other caregiver until a scheduled routine follow-up. During a routine follow-up, for example, the physician reviews the patient's history with the implantable device, re-evaluates the patient's condition, and re-programs the implantable device if necessary.
• One problem with inductive telemetry is its requirement that the two coils are closely placed. This typically requires placing the wand on the body surface over the implantable device. Because the wand is electrically connected to the programmer using a cable, the inductive telemetry limits the patient's mobility.
• To improve communication range and patient mobility, a far-field radio-frequency (RF) telemetry may be used, in which an RF transceiver in the implantable device is used to communicate with an RF transceiver in the external programmer. With a far-field RF telemetry, the patient is typically free of any body surface attachment that limits mobility. However, the far-field RF telemetry between the implantable device and the external programmer may operate in an environment where one or more sources of interferences exist. Such sources of interferences include, for example, magnetic resonance imaging (MRI) machines, cellular phones, and other devices emitting electromagnetic waves. Such sources of interferences may also include another pair of implantable cardiac rhythm management device and external programmer communicating via far-field RF telemetry operating at the same or similar frequencies.
• For these and other reasons, there is a need for ensuring the quality of far-field RF telemetry between an external system and an implanted device when interference is present.
SUMMARY
• An implantable medical device system includes an implanted device communicating with an external device via telemetry. The implanted device and the external device each have a telemetry module connected to an antenna system to support an RF telemetry link. The antenna system of the external device has a manually or automatically controllable directionality. The controllable directionality is achieved, for example, by using two or more directional antennas, one non-directional antenna and one or more directional antennas, or an electronically steerable phased-array directional antenna.
• In one embodiment, a system for communicating with an implantable medical device includes an external device that is coupled to the implantable medical device via RF telemetry. The external device includes a transceiver, an antenna system, an antenna interface circuit, and a directionality controller. The antenna system includes at least two antennas each having a predetermined directionality characteristic. The antenna interface circuit electrically connects the transceiver and the antenna system. The directionality controller connects to the antenna interface circuit and controls a directionality of the antenna system.
• In one embodiment, one or more RF signals are received from an implantable medical device using one or more antennas of an antenna system, where the one or more antennas each have a predetermined directionality characteristic. A quality of each of the one or more RF signals is analyzed. A directionality of the antenna system is controlled based on an outcome of the RF signal quality analysis.
• This Summary is an overview of some of the teachings of the present application and not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details about the present subject matter are found in the detailed description and appended claims. Other aspects of the invention will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which are not to be taken in a limiting sense. The scope of the present invention is defined by the appended claims and their equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
• In the drawings, which are not necessarily drawn to scale, like numerals describe similar components throughout the several views. Like numerals having different letter suffixes represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
• FIG. 1 is a schematic illustration of an embodiment of portions of an implantable medical device system and portions of an environment in which it is used.
• FIG. 2 is a schematic/block diagram illustrating one embodiment of portions of the implantable medical device system with radio-frequency telemetry.
• FIG. 3 is an illustration of a radiation pattern of a non-directional antenna.
• FIG. 4 is an illustration of a radiation pattern of a directional antenna.
• FIG. 5 is a structural diagram illustrating one embodiment of an external device having multiple directional antennas.
• FIG. 6 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 5.
• FIG. 7 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 5.
• FIG. 8 is a structural diagram illustrating one embodiment of an external device having one non-directional antenna and multiple directional antennas.
• FIG. 9 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 8.
• FIG. 10 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 8.
• FIG. 11 is a structural diagram illustrating one embodiment of an external device having one non-directional antenna and one directional antenna.
• FIG. 12 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 11.
• FIG. 13 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 11.
• FIG. 14 is a structural diagram illustrating one embodiment of an external device having a phased-array directional antenna.
• FIG. 15 is an illustration of radiation patterns of a four-element phased array directional antenna and a two-element phased array directional antenna.
• FIG. 16 is an illustration of radiation patterns of a two-element phased array directional antenna when driven out of phase.
• FIG. 17 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 14.
• FIG. 18 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 14.
• FIG. 19 is a flow chart illustrating another embodiment of the method corresponding to the embodiment ofFIG. 14.
DETAILED DESCRIPTION
• In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
• This document discusses, among other things, antennas and antenna systems for a medical device that communicates with an implantable medical device via telemetry. The present methods and apparatuses will be described in applications involving implantable cardiac rhythm management systems such as systems including pacemakers, cardiac resynchronization therapy (CRT) devices, cardioverter/defibrillators, and pacer/defibrillators. However, it is to be understood that the present methods and apparatuses may be employed in other types of implantable medical devices, including, but not being limited to, neurological stimulators, neuromuscular stimulators, drug delivery systems, and various types of physiological signal monitoring devices.
• FIG. 1 is a schematic illustration of an embodiment of portions of an implantablemedical device system100 and portions of an environment in which it is used. In one embodiment,system100 is a cardiac rhythm management system including, among other things, an implanteddevice110 and anexternal device120. Implanteddevice110 is implanted within a patient'sbody101 and coupled to the patient'sheart102 by alead system105. Examples of implanteddevice110 include pacemakers, CRT devices, cardioverter/defibrillators, pacemaker/defibrillators, and drug delivery devices.External device120 provides a user interface forsystem100. The user interface allows a physician or other caregiver to interact with implanteddevice110 through a wireless telemetry link. In this embodiment, the wireless telemetry link is a radio-frequency (RF)telemetry link190 supported by RF transceivers residing in implanteddevice110 andexternal device120.RF telemetry link190 provides for bi-directional data communication between implanteddevice110 andexternal device120.
• In one embodiment,RF telemetry link190 provides for data transmission from implanteddevice110 toexternal device120. This may include, for example, transmitting real-time physiological data acquired by implanteddevice110, extracting physiological data acquired by and stored in implanteddevice110, extracting therapy history data stored in implanteddevice110, and extracting data indicating an operational status of implanted device110 (e.g., battery status and lead impedance). In a further embodiment,RF telemetry link190 provides for data transmission fromexternal device120 to implanteddevice110. This may include, for example, programming implanteddevice110 to acquire physiological data, programming implanteddevice110 to perform at least one self-diagnostic test (such as for a device operational status), and programming implanteddevice110 to deliver at least one therapy.
• In one embodiment,RF telemetry link190 is a far-field telemetry link. A far-field, also referred to as the Fraunhofer zone, refers to the zone in which a component of an electromagnetic field produced by the transmitting electromagnetic radiation source decays substantially proportionally to 1/r, where r is the distance between an observation point and the radiation source. Accordingly, far-field refers to the zone outside the boundary of r=λ/2π, where λ is the wavelength of the transmitted electromagnetic energy. In one embodiment, a communication range of RF telemetry link190 (a distance over which data is capable of being wirelessly communicated) is at least ten feet but can be as long as allowed by the communication technology utilized. Unlike an inductive telemetry link using a wand placed near implanteddevice110, typically attached to the patient, and electrically connected toexternal device120 with a cable, usingRF telemetry link190 frees the patient from any physical restraints caused by the wand and the cable. On the other hand, while a relatively short communication range associated with the inductive telemetry provides for a relatively good immunity to environmental interferences, the relatively long communication range associated with the RF telemetry raises a concern thatexternal device120 may be sensitive to interferences such as electromagnetic waves radiated from other medical devices, such as MRI machines, and/or personal items such as cellular phones. In addition, several patients carrying the same of similar types of implantable devices may be examined, in the same area or even the same room in a cardiovascular clinic, using the same of similar types of external programmers. Under such circumstances, multiple RF telemetry links may operate within the communication ranges of each other and therefore interfere with the operations of each other. To allowRF telemetry link190 to operate within such environments, one approach is to control its directionality.
• FIG. 2 is a schematic/block diagram illustrating one embodiment of portions ofsystem100. In this embodiment, implanteddevice110 includes an implantedtelemetry module112 and an implantedantenna system114.External device120 includes anexternal telemetry module122 and anexternal antenna system124. Implantedtelemetry module112 andexternal telemetry module122 respectively refer to portions of implanteddevice110 andexternal device120 that communicate with each other viaRF telemetry link190. In one embodiment, implantedtelemetry module112 andexternal telemetry module122 each include a transceiver. In one embodiment, implantedantenna system114 andexternal antenna system124 each include a single antenna. In an alternative embodiment, implantedantenna system114 andexternal antenna system124 each include two or more antennas. In another alternative embodiment, implantedantenna system114 includes a single antenna, andexternal antenna system124 comprises two or more antennas.
• In one embodiment, implantedtelemetry module112 includes an RF test signal generator to generate an RF test signal and send it toexternal device120 viaRF telemetry link190. The RF test signal is used in processes of antenna selection or orientation that are discussed below. In one embodiment, the RF signal is modulated with a predetermined binary code to allow for analysis of data integrity byexternal telemetry module122. In one embodiment, the RF signal has a duration of about 50-100 ms. In one embodiment, implanteddevice110 has an operation mode being a telemetry testing mode during which the RF test signal is sent toexternal device120. In a further embodiment,external device120 sends a command to implanteddevice110 to cause it to operate in the telemetry testing mode. In one embodiment, ifexternal device120 sends the command during an ongoing telemetry session, the telemetry session is interrupted during the telemetry testing mode and resumed automatically upon completion of the telemetry testing mode operation.
• FIG. 3 is an illustration of a radiation pattern of a non-directional antenna. A non-directional antenna, also referred to as an omnidirectional antenna, is an antenna that transmits electromagnetic waves with equal energy to all directions and/or receives electromagnetic waves equally well from all directions, at least on one plane. Aradiation pattern321 illustrates a directionality characteristic of a non-directional antenna having an approximately uniform gain in all directions in one plane (non-directional plane). In this document, a non-directional antenna refers to an antenna having a predetermined directionality characteristic shown by a radiation pattern with less than 6 dB of signal strength difference between any two directions in the non-directional plane. In one embodiment, the non-directional antenna is a single dipole antenna. In a further embodiment, the dipole antenna is a single planar dipole antenna and can be printed on a printed circuit board.Radiation pattern321 illustrates the directionality of the single planar dipole antenna in the plane perpendicular to the planar sides of the antenna. In another embodiment, the non-directional antenna is a loop antenna. In a further embodiment, the loop antenna is formed with a wire or printed on a printed circuit board.Radiation pattern321 illustrates the directionality of the loop antenna on the plane of the loop. In yet another embodiment, the non-directional antenna is a single monopole antenna. In a further embodiment, the monopole antenna is a single planar monopole antenna and can be printed on a printed circuit board.Radiation pattern321 illustrates the directionality of the single planar monopole antenna in the plane perpendicular to the planar sides of the antenna.
• A non-directional antenna is suitable for use in an environment where no significant interference exists and only a single RF telemetry link is active. No antenna orientation is needed. However, an RF telemetry link may be required to operate in a busy clinical environment where multiple physicians and/or other caregivers evaluate multiple patients simultaneously. This may require several RF telemetry links to operate in the same area or even in the same room. If the several RF telemetry links operate in substantially the same or similar frequency bands, each RF telemetry link using non-directional antenna may interfere with other RF telemetry links. Moreover, electromagnetic energy radiated from sources such as other electronic medical equipment in all directions in the clinical environment may be received by a non-directional antenna as a noise interfering with the RF telemetry supported partially by the non-directional antenna.
• FIG. 4 is an illustration of a radiation pattern of a directional antenna. Using a directional antenna provides, among other things, a solution to the problems associated using a non-directional antenna as described above. A directional antenna is an antenna that transmits electromagnetic waves with more energy in one direction than in another direction and/or receives electromagnetic waves more readily from one direction than from another direction in a plane (directional place). In this document, a directional antenna refers to an antenna having a predetermined directionality characteristic shown by a radiation pattern with at least6 dB of signal strength difference between at least two directions in the directional plane. The directionality (or directionality characteristic) of a directional antenna is measured or defined by beamwidth, which is the angle of the directional antenna's signal coverage, i.e., the angle within which the directional antenna transmits and receive signals. In one embodiment, as illustrated inFIG. 4, aradiation pattern421 shows a directionality characteristic of a directional antenna having a half-power beamwidth of about 80 degrees in one plane and a highest gain in one direction referred to as the forward direction of the directional antenna. To achieve more directionality, the gain within the half-power beamwidth can be increased by decreasing the beamwidth. In one embodiment, the directional antenna is a planar patch antenna. In a further embodiment, the planar patch antenna is printed on a printed circuit board.Radiation pattern421 illustrates the directionality of the planar patch antenna in the plane perpendicular to the planar sides of the antenna. In another embodiment, the directional antenna is a slot antenna being a planar conductive patch with a nonconductive hole or rectangular slot. The slot antenna has directionality characteristics similar to those of the patch antenna, as illustrated byradiation pattern421. Other examples of the directional antenna include, but are not limited to, parabolic reflector (dish) antenna, Uda-Yagi antenna, and helical antenna. In one embodiment, the beamwidth of the directional antenna is chosen based on a compromise among competing design considerations including relative immunity to interferences, ease of aiming, and complexity and cost of circuitry. Narrower beamwidths provide better immunity to interferences. On the other hand, large beamwidths provide ease of aiming or, alternatively, require few patch antennas to cover all directions.
• With a limited beamwidth, a directional antenna is less likely to act as a source of interference to RF telemetry links associated with other antennas. This allows multiple RF telemetry links to be established for concurrent communications between multiple pairs of external devices and implanted devices, even within a small area. The directional antenna may also allow a user to locate a source of interference to avoid it. In one embodiment, the user sweeps the directional antenna over all directions to identify sources of interference.
• Using the same level of electrical power, a directional antenna achieves higher gain in its forward direction as compared to the uniform gain of a non-directional antenna. This allows a longer communication range allowingexternal device120 to communicate with implanteddevice110 over a greater distance, as compared with the non-directional antenna, unless it also results in a radiation energy level that exceeds a limitation imposed by pertinent government regulations or other safety standards. A directional antenna generally has a higher signal-to-noise ration (S/N) as compared to a non-directional antenna because of the higher gain applied to a signal and lower gains applied to noises coming from directions outside the directional antenna's beamwidth.
• The directionality ofRF telemetry link190 is controllable by controlling a directionality of implantedantenna system114 and/or a directionality ofexternal antenna system124. In one embodiment, the directionality ofRF telemetry link190 is controllable by controlling the directionality ofexternal antenna system124. Implanteddevice110 andexternal device120 send signals to each other. A noise radiated from a source of interference is received by both implanteddevice110 andexternal device120. Because body tissue absorbs RF electromagnetic energy, implantedantenna system114 receives the signals and the noise that are both attenuated by body tissue surrounding implanteddevice110. On the other hand, whileexternal antenna system124 receives signals that are attenuated when being transmitted from implanteddevice110 through the surrounding body tissue, the noise radiated from the source of interference is not attenuated by body tissue. Thus, an S/N associated withexternal antenna system124 is more degraded by the presence of noise from the source of interference than an S/N associated with implantedantenna system114. Furthermore, the complexity of implanteddevice110 is limited by size and power consumption restraints for an implant. Because many more units of implanteddevice110 are produced than units ofexternal device120, a cost increase associated with implanteddevice110 is more of a concern than a cost increase associated withexternal devices120. For at least these reasons, controlling the directionality ofexternal antenna system124 is a more efficient approach as compared to controlling the directionality of implantedantenna system114 or both antenna systems.
• FIG. 5 is a structural diagram illustrating one embodiment of an external device having multiple directional antennas. In one embodiment,external device120 is a computer-based device that controls operation of implanteddevice110 and receives data indicative of a patient's physiological and/or pathological conditions, and/or an operational status of implanteddevice110, from implanteddevice110 throughRF telemetry link190 during an RF telemetry session. In one embodiment,external device120 is constructed on a notebook computer. In one embodiment,external device120 is a medical device programmer operated by a user, such as a physician or other caregiver, to communicate with implanteddevice110 viaRF telemetry link190. In another embodiment,external device120 is a monitor communicating with implanteddevice110. In one embodiment, the monitor stores the received data for review by the user at a later time. In an alternative embodiment, the monitor relays the received data to a device in a remote location for review by the user. In one embodiment,external device120 includes adisplay screen530, which constitutes a portion of a user interface allowing the user to observe conditions of the patient and to monitor and control the operation of implanteddevice110. During a telemetry operation,display screen530 is set to be about perpendicular to the base of the external device, and hence perpendicular to a floor during the RF telemetry session.
• In the embodiment ofFIG. 5,antenna system124 ofexternal device120 has, by way of example, but not by way of limitation, twodirectional antennas541A and541B, each having a half-power beamwidth of less than or equal to about180 degrees. In one embodiment,directional antennas541A and541B are planar patches. In one embodiment, the planar patches each have a square shape. In an alternative embodiment, the planar patches each have a trapezoidal shape. In one embodiment, the planar patches each have sides that are two to three centimeters long. In another embodiment,directional antennas541A and541B are slot antennas each including a planar conductive patch with a nonconductive hole or rectangular slot in it. In one embodiment,directional antenna541A and541B are printed on a printedcircuit board525 located behind, and parallel to,display screen530.Display screen530 is about perpendicular to the base of the external device, and hence, about perpendicular to the floor during the RF telemetry session. Other examples ofdirectional antennas541A and541B include, but are not limited to, parabolic reflector (dish) antenna, Uda-Yagi antenna, and helical antenna.Directional antenna541A transmits signals to, and receives signals from, substantially all directions behinddisplay screen530, anddirectional antenna541B transmits signals to, and receives signals from, substantially all directions in front ofdisplay screen530. In an alternative embodiment,antenna system124 has more than two directional antennas for a finer directionality control. In one embodiment,antenna system124 has three directional antennas each having a half-power beamwidth of about120 degrees.
• In one embodiment, the user selects one ofdirectional antennas541A and541B for an RF telemetry session. For example, whendirectional antenna541A covers substantially all directions behinddisplay screen530 anddirectional antenna541B covers substantially all directions in front ofdisplay screen530, the user selectsdirectional antenna541A if the patient is behind the screen, ordirectional antenna541B if the patient is in front of the screen. In another embodiment, the user observes the quality of communication, such as indicated by signals received by each ofdirectional antennas541A and541B and displayed ondisplay screen530, to determine which antenna to select. In another embodiment, one ofdirectional antennas541A and541B is automatically selected, as discussed below with reference toFIGS. 6 and 7.
• In an alternative embodiment,antenna system124 has a single directional antenna. While using a single directional antenna provides the simplest and leastexpensive telemetry module122 having a directional antenna system, the user would have to alignexternal device120 with implanteddevice110. This may require several position adjustments forexternal device120 beforeRF telemetry link190 is established.
• FIG. 6 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 5. The circuit constitutes portions ofexternal telemetry module122 and anantenna system124.External telemetry module122 includes atransceiver660, acontroller670, and aswitching circuit650.Transceiver660 further includes atransmitter663, areceiver664, and a transmit-receiveswitch662.Transmitter663 receives data from another portion ofexternal device120 in a form of a bit stream, modulates an RF carrier signal with the data, and transmits the modulated RF signal to implanteddevice110 throughantenna system124.Receiver664 receives modulated RF signals throughantenna system124, demodulates the modulated RF signal to recover data transmitted from implanteddevice110, and sends the recovered data in a format of a bit stream to another portion ofexternal device120. Transmit-receiveswitch662 controls a connection betweenantenna system124 and one oftransmitter663 andreceiver664.Transceiver660 allows for one of transmission and receiving at any instant.
• Controller670 controls whethertransceiver660 transmits or receives RF signals. In the embodiment in which one ofdirectional antennas541A and541B is automatically selected, controller679 also includes asignal analyzer672 and anantenna selector674. The signal analyzer analyzes signal quality of the RF signals received through each ofdirectional antennas541A and541B. In one embodiment,signal analyzer672 measures the strength (amplitude) of each of the RF signals received through each ofdirectional antennas541A and541B. In a further embodiment,signal analyzer672 examines integrity of the data recovered bytransceiver660 and generates a data integrity indicator.Antenna selector674 is a directionality controller ofantenna system124. It controls the directionality ofantenna system124 by selecting one or more of its antennas having different orientation and/or directionality characteristics. In the embodiment ofFIG. 6,antenna selector674 generates an antenna selection control signal based on comparing the outcome of analyzing the signal quality of RF signals received by each ofdirectional antennas541A and541B.Switching circuit650, in response to the antenna selection control signal, makes an electrical connection betweentransceiver660 and one ofdirectional antennas541A and541B. In one embodiment, switchingcircuit650 is a multiplexer.
• FIG. 7 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 5. At700,external telemetry module122 receives an RF signal throughdirectional antenna541A. The RF signal is modulated with binary data and transmitted from implanteddevice110. In one embodiment,external telemetry module122 receives the RF signal after it sends out a command causing implanteddevice110 to operate in the telemetry testing mode. In this mode, the RF signal is a portion of the RF test signal generated by the RF test signal generator of implantedtelemetry module112. At710,external telemetry module122 receives a further RF signal throughdirectional antenna541B. The further RF signal is substantially similar to the RF signal received at700 in that both RF signals are generated from the same implanteddevice110 at substantially the same distance and modulated with data in substantially the same format. In one mode, the RF signal is a further portion of the RF test signal generated by the RF test signal generator of implantedtelemetry module112. In one embodiment, At720,signal analyzer672 analyzes signal quality of both the RF signals received at700 and710. In one embodiment,signal analyzer672 examines data integrity of each of the received RF signals by performing error-checking in accordance with a predetermined protocol. In an additional embodiment,signal analyzer672 measures the amplitude of each of the received RF signals. At730,antenna selector674 selects one ofdirectional antennas541A and541B based on an outcome of720. In one embodiment,antenna selector674 selects one ofdirectional antennas541A and541B that provides a satisfactory data integrity according to a predetermined data integrity standard. In an additional embodiment, whendirectional antennas541A and541B both provide a satisfactory data integrity,antenna selector674 selects one ofdirectional antennas541A and541B providing a higher received RF signal strength. Once an antenna is selected,antenna selector674 sends the antenna selection control signal to switchingcircuit650 to electrically connect one ofdirectional antennas541A and541B to transceiver660, thereby establishingRF telemetry link190. At740, if an RF session has not already been started,controller670 issues a signal to start an RF telemetry session betweenexternal device120 and implanteddevice110. If the RF session has been started, it is continued with the directional antenna just selected at730. In one embodiment, the RF telemetry session is started during an operation for implanting implanteddevice110 intobody101. The RF telemetry session allowsexternal device120 to monitor a patient's physiological conditions and/or an operational status of implanteddevice110 and set parameters for a desired performance of implanteddevice110. In an alternative embodiment, the RF telemetry session is started during a postoperative patient examination. The RF telemetry session allowsexternal device120 to monitor the patient's physiological conditions and/or the operational status of implanteddevice110 and, if necessary, adjust parameters for the desired performance of implanteddevice110.
• In one embodiment, after the RF telemetry session is started at740,controller670 starts to repeat steps700-740, at750, on a predetermined periodic basis during the RF telemetry session. In another embodiment, after the RF telemetry session is started at740,signal analyzer672 monitors the quality of the RF signal on a continuous or periodic basis. At750,controller670 starts to repeat steps700-740 wheneversignal analyzer672 determines that the quality of the RF signal is no longer satisfactory during the RF telemetry session. In one embodiment, steps700-740 are repeated while the RF telemetry operation is ongoing without significant interruptions to the RF telemetry session. In one embodiment,external device120 sends a command to implanteddevice110 to start to repeat steps700-740 by causing implanted device to operate in the telemetry testing mode. In this embodiment, the RF telemetry operation is interrupted at least for the period during which implanteddevice110 operates in the telemetry testing mode. At the end of each repetition of steps700-740, if a different directional antenna is selected, the telemetry session continues with the different directional antenna. This ensures thatRF telemetry link190 remains functional throughout the RF telemetry session, even when, for example, implanteddevice110 changes position because the patient carrying it moves. The RF telemetry session concludes when all the data transmissions for the session are completed or stopped by an unintended interruption.
• FIG. 8 is a structural diagram illustrating one embodiment of an external device having one non-directional antenna and a plurality of directional antennas.External device120 includes substantially the same structural components, arranged in substantially the same way, as in the embodiment ofFIG. 5. In addition,antenna system124 has anon-directional antenna842. In one embodiment, as illustrated inFIG. 5,antenna system124 hasdirectional antennas541A and541B andnon-directional antenna842. In one embodiment,non-directional antenna842 is a single planar dipole antenna. In another embodiment,non-directional antenna842 is a single planar monopole antenna. In one embodiment,directional antennas541A and541B andnon-directional antenna842 are all printed on printedcircuit board525. Size of the dipole or monopole depends on the permittivity of printedcircuit board525. In one embodiment, the printed dipole or monopole is about four to eight centimeters in length. Whendisplay screen530 is positioned about perpendicular to the floor,non-directional antenna842 is substantially non-directional on a plane parallel to the floor. In another embodiment, non-directional antenna is a loop antenna. In one embodiment, the loop antenna is formed with wire and placed withinexternal device120, with the plane of the loop being parallel to the base ofexternal device120. In another embodiment, the loop antenna is printed on a printed circuit board withinexternal device120 and parallel to the base ofexternal device120. In one embodiment,non-directional antenna842 is non-directional on a plane parallel to a floor on which clinical facilities are established for the user to see patients and perform medical examinations.Directional antennas541A and541B are each directional on the same plane on whichnon-directional antenna842 is non-directional.
• FIG. 9 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 8. The circuit has substantially the same functional blocks as in the embodiment ofFIG. 6. In addition,antenna system124 hasnon-directional antenna842. Each functional block inFIG. 9 has substantially the same type of circuitry as its corresponding functional block inFIG. 6, but modified to accommodate the additional antenna.
• FIG. 10 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 8. At1000,external telemetry module122 receives an RF signal throughnon-directional antenna842. The RF signal is modulated with binary data and transmitted from implanteddevice110. In one embodiment,external telemetry module122 receives the RF signal after it sends out a command causing implanteddevice110 to operate in the telemetry testing mode. In this mode, the RF signal is a portion of the RF test signal generated by the RF test signal generator of implantedtelemetry module112. At1010,signal analyzer672 analyzes quality of the RF signal received at1000. In one embodiment,signal analyzer672 examines data integrity of the received RF signal by performing error-checking in accordance with a predetermined protocol. If the quality of the RF signal is found satisfactory under the predetermined protocol at1020,controller670 issues a signal to start an RF telemetry session betweenexternal device120 and implanteddevice110 usingnon-directional antenna842. If the quality of the RF signal is found unsatisfactory at1020,controller670 issues a signal to switch to a directional antenna to receive further RF signals.
• At1030,external telemetry module122 receives a further RF signal throughdirectional antenna541A. The further RF signal is substantially similar to the RF signal received at1000 in that both RF signals are generated from the same implanteddevice110 at substantially the same distance and modulated with data in substantially the same format. In one mode, the RF signal is a further portion of the RF test signal generated by the RF test signal generator of implantedtelemetry module112. At1040,external telemetry module122 receives a still further RF signal throughdirectional antenna541B. The still further RF signal is also substantially similar to the RF signal received at1000. In one mode, the RF signal is a still further portion of the RF test signal generated by the RF test signal generator of implantedtelemetry module112. At1050,signal analyzer672 analyzes signal quality of both the further and still further RF signals received at1030 and1040. In one embodiment,signal analyzer672 examines data integrity of each of the received RF signals by performing error-checking in accordance with the predetermined protocol. In an additional embodiment,signal analyzer672 measures the amplitude of each of the received RF signals. At1060,antenna selector674 selects one ofdirectional antennas541A and541B based on an outcome of analyzing the signal quality of the RF signal at1050. In one embodiment,antenna selector674 selects one ofdirectional antennas541A and541B that provides a satisfactory data integrity according to the predetermined standard. In an additional embodiment, whendirectional antennas541A and541B each provide a satisfactory data integrity,antenna selector674 selects one ofdirectional antennas541A and541B providing a higher received RF signal strength. Once a directional antenna is selected,antenna selector674 sends the antenna selection control signal to switchingcircuit650 to electrically connect one of thedirectional antennas541A and541B to transceiver660, thereby establishingRF telemetry link190. At1070, if an RF telemetry session has not been started,controller670 issues a signal to start an RF telemetry session betweenexternal device120 and implanteddevice110. If the RF session has been started, it is continued with the antenna just selected at1020 or1060.
• In one embodiment, after the RF telemetry session is started at1070,controller670 starts to repeat steps1000-1070, at1080, on a predetermined periodic basis during the RF telemetry session. In another embodiment, after the RF telemetry session is started at1070,signal analyzer672 monitors the quality of the RF signal on a continuous or periodic basis. At1080,controller670 starts to repeat steps1000-1070 wheneversignal analyzer672 determines that the quality of the RF signal is no longer satisfactory during the RF telemetry session. In one embodiment, steps1000-1070 are repeated while the RF telemetry operation is ongoing without significant interruptions to the RF telemetry session. In one embodiment,external device120 sends a command to implanteddevice110 to start to repeat steps1000-1070 by causing implanted device to operate in the telemetry testing mode. In this embodiment, the RF telemetry operation is interrupted at least for the period during which implanteddevice110 operates in the telemetry testing mode. At the end of each repetition of steps1000-1070, if a different directional antenna is selected, the telemetry session continues with the different directional antenna. This ensures thatRF telemetry link190 remains functional throughout the RF telemetry session, even when, for example, implanteddevice110 changes position because the patient carrying it moves. The RF telemetry session concludes when all the data transmissions for the session are completed or stopped by an unintended interruption.
• FIG. 11 is a structural diagram illustrating one embodiment of an external device having one non-directional antenna and one directional antenna.External device120 has substantially the same structural components as in the embodiment ofFIG. 5 except thatantenna system124 hasnon-directional antenna842 and adirectional antenna1143. In one embodiment,directional antenna1143 is a hand-held device connected toexternal device120 using a cable. In one embodiment,directional antenna1143 is a parabolic reflector (dish) antenna. In another embodiment,directional antenna1143 is a planar patch antenna discussed above with reference toFIG. 4. In yet another embodiment,directional antenna1143 is a slot antenna discussed above with reference toFIG. 4. A user controls the forward direction ofdirectional antenna1143 by manually aimingdirectional antenna1143 to implanteddevice110. In one embodiment, the user may placedirectional antenna1143 on the patient over implanteddevice110. In one further embodiment,directional antenna1143 is a detachable antenna connected toexternal device120 using a cable with a detachable connector.Non-directional antenna842 is used whendirectional antenna1143 is not connected toexternal device120. Wheneverdirectional antenna1143 is connected toexternal device120,non-directional antenna842 is not used. Embodiments using hand-helddirectional antenna1143 are suitable, and may be necessary, whenRF telemetry link190 is to be established in a noisy environment where the embodiments described above do not allow the user to establish an RF telemetry link successfully or easily. For example, a postoperative examination of a patient carrying implanteddevice110 may occur in a busy clinic where multiple patients wearing similar implantable devices are examined simultaneously in the same room. The busy clinic may also include electronic devices radiating electromagnetic energy, such as MRI machines and cellular phones. This necessitates a high directionality forantenna system124 that would require a complicated and expensive circuit having a large number of antennas each having a very narrow beamwidth. Under such circumstances, hand-helddirectional antenna1143 provides an inexpensive solution. When hand-helddirectional antenna1143 is placed on the patient over implanteddevice110, or otherwise placed near implanteddevice110,RF telemetry link190 has a high S/N because of the high signal strength associated with the short transmission distance, as compared to the S/N associated withnon-directional antenna842. Thus, hand-helddirectional antenna1143 need not have a very narrow beamwidth. In this embodiment,non-directional antenna842 eliminates the need of manual aiming when the environment does not necessitate the use of a directional antenna.
• FIG. 12 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 11. The circuit has substantially the same functional blocks as in the embodiment ofFIG. 6, except thatantenna system124 hasnon-directional antenna842 and hand-helddirectional antenna1143.
• FIG. 13 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 11. At1300,external telemetry module122 receives an RF signal throughnon-directional antenna842. The RF signal is modulated with binary data and transmitted from implanteddevice110. In one embodiment,external telemetry module122 receives the RF signal after it sends out a command causing implanteddevice110 to operate in the telemetry testing mode. In this mode, the RF signal is the RF test signal generated by the RF test signal generator of implantedtelemetry module112. At1310,signal analyzer672 analyzes signal quality of the RF signal received at1300. In one embodiment,signal analyzer672 examines data integrity of the received RF signal by performing error-checking in accordance with a predetermined protocol. If the quality of the RF signal is found satisfactory under the predetermined protocol at1320,controller670 issues a signal at1370 to start an RF telemetry session betweenexternal device120 and implanteddevice110. If the quality of the RF signal is found unsatisfactory at1320, further RF signals will be received throughdirectional antenna1143.
• At1330,external telemetry module122 receives a further RF signal throughdirectional antenna1143. The further RF signal is substantially similar to the RF signal received at1300 in that both RF signals are generated from the same implanted device and modulated with data in substantially the same format. In one embodiment, wheredirectional antenna1143 is a detachable antenna,directional antenna1143 is connected toexternal device120 beforeexternal telemetry module122 receives the further RF signal at1330. At1340,signal analyzer672 analyzes signal quality of the further RF signal received at1330. In one embodiment,signal analyzer672 examines data integrity of the further RF signal by performing error-checking in accordance with a predetermined protocol. If the quality of the RF signal is found satisfactory under the predetermined protocol at1350,controller670 issues a signal at1370 to start an RF telemetry session betweenexternal device120 and implanteddevice110. If the quality of the RF signal is found unsatisfactory at1350, the user adjusts the orientation ofdirectional antenna1143 by re-aiming it to implanteddevice110. Steps1330-1360 are repeated until the quality of the RF signal is found satisfactory at1350. At1370,controller670 issues a signal to start an RF telemetry session betweenexternal device120 and implanteddevice110.
• In an alternative embodiment, wheredirectional antenna1143 is a detachable antenna, the user starts to usedirectional antenna1143 by connecting it toexternal device120 at any time. In one embodiment, the user starts to usedirectional antenna1143 upon his judgment on the presence and magnitude of the interference. In one specific embodiment, the user makes the judgment based on observations of cardiac signals displayed byexternal device120. In another embodiment, the user starts to usedirectional antenna1143 whenexternal device120 indicates an unacceptable amount or rate of data transmission errors. In one specific embodiment, implanteddevice110 andexternal device120 each include error-checking modules to ensure the integrity of data transmitted in both directions viaRF telemetry link190. When the number and/or frequency of errors detected exceed a predetermined threshold,external device120 provides a signal to the user to replacenon-directional antenna842 withdirectional antenna1143 ifnon-directional antenna842 is being used, or to repositiondirectional antenna1143 if it is being used.
• FIG. 14 is a structural diagram illustrating one embodiment of an external device having a phased-array directional antenna.External device120 has substantially the same structural components, arranged in substantially the same way, as in the embodiment ofFIG. 5, except thatantenna system124 has adirectional antenna1444, which is the phased-array directional antenna.Directional antenna1444 includes two or more antennas acting its antenna elements. In one embodiment, the antenna elements are each a planar dipole antenna. In one further embodiment,directional antenna1444 is printed on printedcircuit board525. Size of each of the dipole antennas depends on the permittivity of printedcircuit board525. In one embodiment, each of the dipole antennas is about four to eight centimeters in length. An effective forward direction, or effective orientation ofdirectional antenna1444 and alsoantenna system124, is controlled by electronically driving the antenna elements out of phase. In one embodiment, the antenna elements are driven out of phase by introducing a weighting factor into an RF signal transmitted or received through each of the antenna elements. Each weight factor is a vector including an amplitude and a phase angle. The weighting factors are multiplied with the RF signals to modify a phase angle of each RF signal. The effective orientation ofantenna1444 is steered by controlling one or more phase angles of the RF signals transmitted or received through the antenna elements. In an alternative embodiment, the antenna elements are driven out of phase by introducing different transmission delays to the antenna elements. Because RF signals transmitted or received through the plurality of antenna elements each has a phase angle depending on the conduction delay, the effective orientation ofantenna1444 can be steered by adjusting the transmission delays. In one embodiment, the plurality of antenna elements are each connected to a delay line. In one embodiment, each delay line is a conductive path being a wire or a metal path on printedcircuit board525. The transmission delay of each delay line is proportional to its length. Thus, the effective orientation ofantenna1444 can be steered by adjusting how the delay lines and the antenna elements are paired.
• In one embodiment, as illustrated inFIG. 14,directional antenna1444 has, by way of example, but not by way of limitation, fourantenna elements1444A-D. In an alternative embodiment,directional antenna1444 has two antenna elements. In another alternative embodiment,directional antenna1444 has more than four antenna elements. The number of antenna elements included indirectional antenna1444 is chosen based on a compromise among factors including cost, circuit complexity, and desirable degree of directionality.
• FIG. 15 is an illustration of radiation patterns of a four-element phased array directional antenna and a two-element phased array directional antenna. Aradiation pattern1581 illustrates an example of a directionality characteristic ofdirectional antenna1444, whenantenna elements1444A-D are not driven out of phase, in a plane perpendicular tocircuit board525 and hence about parallel to the floor. In one embodiment,radiation pattern1581 is obtained by applying equal weighting factors to all ofantenna elements1444A-D. In an alternative embodiment,radiation pattern1581 is obtained by introducing the same transmission delay to each ofantenna elements1444A-D.
• Adirectional antenna1544 is substantially the same asdirectional antenna1444 except thatantenna1544 has two, instead of four, antenna elements1544A and1544B. Aradiation pattern1582 illustrates an example of a directional characteristic ofdirectional antenna1544, when antenna elements1544A and1544B are not driven out of phase, in the plane perpendicular tocircuit board525, and hence about parallel to the floor during an RF telemetry session. As illustrated byradiation patterns1581 and1582, having more antenna elements provides for a narrower beamwidth centered at each effective orientation, thereby enhancing the advantage of the directional antenna in reducing chance of interference and increasing the communication range in the direction aligned with the effective orientation of the directional antenna. On the other hand, fewer antenna elements require a simpler electronic steering system.
• FIG. 16 is an illustration of radiation patterns of a two-element phased array directional antenna when driven out of phase. Same as inFIG. 15,directional antenna1544 hasradiation pattern1582 when it is not driven out of phase.Radiation patterns1582A and1582B illustrate the effect of drivingdirectional antenna1544 out of phase. The effective orientation ofdirectional antenna1544 is the direction at whichdirectional antenna1544 has the highest gain. Thus,radiation patterns1582,1582A, and1582B are each related to a different effective orientation ofdirectional antenna1544. In one embodiment,directional antenna1544 is driven out of phase when the two weighting factors introduced to antenna elements1544A and1544B have at least a relatively different phase angle. The effective orientation ofdirectional antenna1544 is steered by adjusting at least the relative phase difference between the two weighting factors. In an alternative embodiment,directional antenna1544 is driven out of phase when antenna elements1544A and1544B are tuned to introduce different phase angles to the RF signals transmitted or received through antenna elements1544A and1544B.
• Directional antenna1444 or1544 allows electronic alignment betweenexternal antenna system124 and implantedantenna system114 to establishRF telemetry link190. This eliminates the need for physically positioningexternal device120. As compared to an antenna system having two or more planar patch or slot directional antennas, a phased-array directional antenna is potentially more suitable when relatively fine directionality is required or desired. In other words, a phased-array directional antenna is suitable for establishingRF telemetry link190 in a clinical environment where narrow antenna beamwidth is necessary or desired.
• FIG. 17 is a schematic/block diagram illustrating one embodiment of a circuit corresponding to the embodiment ofFIG. 14. The circuit constitutes portions ofexternal telemetry module122 and anantenna system124. In one embodiment,antenna system124 has, by way of example, but not by way of limitation, a phased-array antenna1444 havingantenna elements1444A-D.External telemetry module122 includes atransceiver660, acontroller670, and anantenna interface circuit1752.Transceiver660 is substantially the same as, or substantially similar to, the same element as in the embodiment ofFIG. 6.
• Controller670 controls whethertransceiver660 transmits or receives RF signals and includes asignal analyzer672 and anantenna steerer1776. The signal analyzer analyzes signal quality of RF signals received at a plurality of effective orientations ofdirectional antenna1444. In one embodiment,signal analyzer672 measures the amplitude of the RF signal received at each of the plurality of effective orientations. In a further embodiment,signal analyzer672 examines integrity of the data recovered bytransceiver660 and generates a data integrity indicator.Antenna steerer1776 is a directionality controller ofantenna system124. In the embodiment ofFIG. 17,Antenna steerer1776 controls the directionality ofantenna system124 by determining the effective orientation associated with the best signal quality, steeringdirectional antenna1444 to that effective orientation, and lockingdirectional antenna1444 in that effective orientation. In one embodiment,antenna system124 is coupled totransceiver660 throughantenna interface circuit1752, which is an antenna orientation circuit allowing effectively orientation ofdirectional antenna1444. In one embodiment,antenna interface circuit1752 includes individual interface circuits1752A-D respectively connected toantenna elements1444A-D. In one embodiment, interface circuits1752A-D are multipliers allowing the weighting factors to be multiplied with RF signals received throughantenna elements1444A-D, respectively. In one embodiment, a table containing the weighting factors defining the plurality of effective orientations ofdirectional antenna1444 is stored in amemory1771.Antenna steerer1776 applies the weighting factors to sweep through the plurality of effective orientations to testdirectional antenna1444 at each of the plurality of effective orientations. In an alternative embodiment, interface circuits1752A-D are delay elements each having an adjustable transmission delay. In one embodiment, delay elements1752A-D each include wires or other metal paths of different length. The transmission delay is adjusted by selecting one of the wires or other metal paths to connect to the corresponding antenna element.Antenna steerer1776 controls the transmission delay of each of delay elements1752A-D to result in the plurality of effective orientations at whichdirectional antenna1444 will be tested. In one embodiment, a table containing transmission delays defining the plurality of effective orientations is stored inmemory1771. In another embodiment,interface circuit1752 includes an array of delay lines each associated with a different transmission delay. The number of the delay lines in the array is equal to or more than the number of antenna elements inantenna1444.Antenna steerer1776 includes a delay line selector that selects delay lines from the array of delay lines and selectively couples each of the selected delay lines between one ofantenna elements1444A-D andtransceiver660. Delay elements1752A-D represent these selected delay lines.Antenna elements1444A-D and the array of delay lines are connected in a plurality of combinations to result in the plurality of effective orientations at whichdirectional antenna1444 will be tested.
• FIG. 18 is a flow chart illustrating one embodiment of a method corresponding to the embodiment ofFIG. 14.Directional antenna1444 is tested at a predetermined number (N) of effective orientations. The number of effective orientations to be tested depends on the beamwidth ofdirectional antenna1444 and the total range of directions to be tested. In one embodiment, the predetermined total range of directions is 0°-360°, i.e., the N effective orientations cover a 360° space in one plane. In another embodiment, the total range of directions includes one or more portions of 0°-360°, i.e., the N effective orientations cover one or more less-than-360° spaces in one plane. In one embodiment, the total range of directions is equally divided over the first to Nth effective orientations, resulting in first through Nth spaces. In one specific embodiment,directional antenna1444 has a constant beamwidth, and N equals approximately 360° divided by that beamwidth (in term of degrees).
• At1800,directional antenna1444 is tested for a first effective orientation. The first effective orientation is the first of the predetermined number of effective orientations at whichdirectional antenna1444 will be tested. Testingdirectional antenna1444 at the first effective orientation includes at least four steps1801-1804. At1801,antenna steerer1776 electronically steersdirectional antenna1444 to a first effective orientation. In one embodiment,directional antenna1444 is electronically steered by applying the weighting factors to RF signals received through each ofantenna elements1444A-D. In another embodiment,directional antenna1444 is electronically steered by adjusting the transmission delays associated withantenna elements1444A-D. At1802,external telemetry module122 receives an RF signal throughdirectional antenna1444. The RF signal is modulated with binary data and transmitted from implanteddevice110. In one embodiment,external telemetry module122 receives the RF signal after it sends out a command causing implanteddevice110 to operate in the telemetry testing mode. In this mode, the RF signal is at least a portion of the RF test signal generated by the RF test signal generator of implantedtelemetry module112. At1803,signal analyzer672 analyzes signal quality of the RF signal received at1802. In one embodiment,signal analyzer672 examines data integrity of the received RF signal by performing error-checking in accordance with a predetermined protocol. In an additional embodiment,signal analyzer672 measures the amplitude of the received RF signal. At1804, one or more quality indicators associated with the first effective orientation, as an outcome of analyzing the quality of the RF signal at1803, are recorded. The recording of the one or more quality indicators associated with the first effective orientation concludes the test ofdirectional antenna1444 for the first effective orientation.
• At1810,directional antenna1444 is tested, one at a time, at each of the predetermined number (N) of effective orientations covering a predetermined total range of directions. This includes repeating the test procedure of1801-1804 for a second through Nth effective orientations. In one embodiment,external telemetry module122 starts testing the first effective orientation after it sends out a command causing implanteddevice110 to operate in the telemetry testing mode. In a further embodiment, implanteddevice110 operates in the telemetry testing mode until the Nth effective orientation has been tested. In this mode, the RF signal in each repetition of steps1801-1804 is a portion of the RF test signal generated by the RF test signal generator of implantedtelemetry module112. As a result, N sets of quality indicators are recorded, corresponding to the N effective orientations. At1820,antenna steerer1776 compares among the N sets of quality indicators. In one embodiment,antenna steerer1776 compares the amplitudes of the RF signals received at the N effective orientations to determine the effective orientation providing the largest RF signal amplitude. In an alternative embodiment,antenna steerer1776 compares the amplitudes of the RF signals received at the effective orientations at which the data integrity is satisfactory to determine the effective orientation providing the largest RF signal amplitude and a satisfactory data integrity. At1830,antenna steerer1776 selects an effective orientation at which an RF telemetry session will be started, based on an outcome of the comparison among the quality indicators at1820. In one embodiment,antenna steerer1776 selects the effective orientation providing the largest RF signal amplitude. In another embodiment,antenna steerer1776 selects an effective orientation providing a satisfactory data integrity. In a further embodiment,antenna steerer1776 selects the effective orientation providing the largest RF signal amplitude while providing a satisfactory data integrity. After the effective orientation is selected at1830,antenna steerer1776 electronically steersdirectional antenna1444 to the selected effective orientation and locksdirectional antenna1444 in that effective direction at1840. At1850,controller670 issues a signal to start an RF telemetry session betweenexternal device120 and implanteddevice110.
• In one embodiment, after the RF telemetry session is started at1850,controller672 starts to repeat steps1800-1850, at1860, on a predetermined periodic basis during the RF telemetry session. In a further embodiment, at1860,controller670 starts to repeat steps1800-1850 on the predetermined periodic basis with a different set ofeffective orientations1 to N that is limited to cover a vicinity of the effective orientation thatdirectional antenna1444 has been locked into. This enables the effective orientation ofdirectional antenna1444 to track, for example, the direction of the patient moving within a limited area, such as running on a treadmill. In another embodiment, after the RF telemetry session is started at1850,signal analyzer672 monitors the quality of the RF signal on a continuous or periodic basis. At1860,controller670 starts to repeat steps1800-1850 wheneversignal analyzer672 determines that the quality of the RF signal is no longer satisfactory during the RF telemetry session. In one embodiment, steps1800-1850 are repeated while the RF telemetry operation is ongoing without significant interruptions to the RF telemetry session. In one embodiment,external device120 sends a command to implanteddevice110 to start to repeat steps1800-1850 by causing implanted device to operate in the telemetry testing mode. In this embodiment, the RF telemetry operation is interrupted at least for the period during which implanteddevice110 operates in the telemetry testing mode. At the end of each repetition of steps1800-1850, if a new effective orientation is selected,directional antenna1444 is locked in the new effective orientation. This ensures thatRF telemetry link190 remains functional throughout the RF telemetry session, even when, for example, implanteddevice110 changes position because the patient carrying it moves. The RF telemetry session concludes when all the data transmissions for the session are completed or stopped by an unintended interruption.
• FIG. 19 is a flow chart illustrating another embodiment of the method corresponding to the embodiment ofFIG. 14. In this embodiment, an operating beamwidth is predetermined fordirectional antenna1444. The operating beamwidth applies throughout an RF telemetry session except for periods during which an effective orientation is being tested. The predetermined total range of directions is first divided into two spaces corresponding to effective orientations A and B. In one embodiment, the predetermined total range of directions is first equally divided into two spaces, such thatdirectional antenna1444 has the same beamwidth to cover each of the effective orientations A andB. Steps1900,1910,1920, and1930 are substantially the similar tosteps1800,1810,1820, and1830, respectively, expect thatdirectional antenna1444 is tested for only one effective direction (B) at1910. As a result, two sets of quality indicators are recorded, corresponding to the effective orientations A and B. At1920,antenna steerer1776 compares among the two sets of quality indicators.Step1920 is substantially similar to step1820 with N equal to two. At1930,antenna steerer1776 selects one of the effective orientations A and B based on an outcome of the comparison among the quality indicators at1920. The criteria for the selection are substantially similar to the criteria discussed above with respect to step1830. At1935, if the selected effective orientation corresponds to a range of directions equal to or narrower than the predetermined operating beamwidth ofdirectional antenna1444,antenna steerer1776 electronically steersdirectional antenna1444 to the selected effective orientation if it has not already pointed to that direction, and locksdirectional antenna1444 in that effective direction at1940. If the selected effective orientation corresponds to a range of directions wider than the predetermined operating beamwidth ofdirectional antenna1444, the range of directions covered by the selected effective orientation is further divided into a new set of effective orientations A and B at1936. In one embodiment, the range of directions covered by the selected effective orientation is equally divided into two spaces, such thatdirectional antenna1444 has the same beamwidth to cover each of the new set of effective orientations A and B. Steps1900-1935 are repeated until the selected effective orientation corresponds to a range of directions equal to or narrower than the predetermined operating beamwidth ofdirectional antenna1444. At1950, if an RF session has not been started,controller670 issues a signal to start an RF telemetry session betweenexternal device120 and implanteddevice110. If the RF session has been started, it is continued with directional antenna being locked on the latest selected effective orientation.
• In one embodiment, after the RF telemetry session is started at1950,controller670 starts to repeat steps1900-1950, at1960, on a predetermined periodic basis during the RF telemetry session. In a further embodiment, at1960,controller670 starts to repeat steps1900-1950 on the predetermined periodic basis with the effective orientations A and B being limited to a vicinity of the effective orientation thatdirectional antenna1444 has been locked into. This enables the effective orientation ofdirectional antenna1444 to track, for example, the direction of the patient moving within a limited area, such as running on a treadmill. In another embodiment, after the RF telemetry session is started at1950,signal analyzer672 monitors the quality of the RF signal on a continuous or periodic basis. At1960,controller670 starts to repeat steps1900-1950 wheneversignal analyzer672 determines that the quality of the RF signal is no longer satisfactory during the RF telemetry session. In one embodiment, steps1900-1950 are repeated while the RF telemetry operation is ongoing without significant interruptions to the RF telemetry session. In one embodiment,external device120 sends a command to implanteddevice110 to start to repeat steps1900-1950 by causing implanted device to operate in the telemetry testing mode. In this embodiment, the RF telemetry operation is interrupted at least for the period during which implanteddevice110 operates in the telemetry testing mode. At the end of each repetition of steps1900-1950, if a new effective orientation is selected,directional antenna1444 is locked in the new effective orientation. This ensures thatRF telemetry link190 remains functional throughout the RF telemetry session, even when, for example, implanteddevice110 changes position because the patient carrying it moves.
• If dividing the predetermined total range of directions by two results in two spaces each being wider than the maximum beamwidth ofdirectional antenna1444, portions of the methods ofFIG. 18 andFIG. 19 are to be combined. The predetermined total range of directions is first divided by N to result in N equal spaces each being no wider than the maximum beamwidth ofdirectional antenna1444. One of the N equal spaces is selected as the effective orientation by performing1800-1830 discussed above with reference toFIG. 18. This effective direction then serves as the predetermined total range of directions that is to be divided by two to result in the effective orientations A and B of the method ofFIG. 19. Then, the method ofFIG. 19 is performed. In one specific embodiment, as an example, the predetermined total range of directions includes a 360° space.Directional antenna1444 has a maximum beamwidth of 120°. The 360° space is first divided into three 120° spaces, corresponding to theeffective orientations1 to N (N=3) that are tested at1800-1830. Then, one of the three 120° spaces is selected at1830. If the operating beamwidth ofdirectional antenna1444 is predetermined to be narrower than 120°, the selected 120° space is divided into two 60° spaces, corresponding to the effective orientations A and B that are tested by performing1900-1930. At1930, one of the two 60° spaces is selected. If the predetermined operating beamwidth ofdirectional antenna1444 is narrower than 60°, the selected 60° space is divided into two 30° spaces, corresponding to a new set of effective orientations A and B that are tested by repeating1900-1930. The process proceeds to step1940 if the operating beamwidth ofdirectional antenna1444 is predetermined to be at least 30°. In general, this loop of repeated testing and selection (1900-1930) ends when the effective orientation selected at1930 corresponds to an angular space equal to or narrower than the operating beamwidth ofdirectional antenna1444.
• It is to be understood that the above detailed description is intended to be illustrative, and not restrictive. For example, the implantable device can be any implantable medical device having an active electronic circuit. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims (21)

1. A system for communicating with an implantable medical device, the system comprising:

an external device adapted to be communicatively coupled to the implantable medical device via radio-frequency (RF) telemetry and adapted to control operation of the implantable medical device and receive data from the implantable medical device, the external device comprising:

a transceiver;

a phased-array directional antenna;

an antenna interface circuit coupled between the transceiver and the phased-array directional antenna; and

a controller coupled to the antenna interface circuit, the controller adapted to control an effective orientation of the phased-array directional antenna.

2. The system ofclaim 1, wherein the phased-array directional antenna comprises two or more substantially identical planar antennas.

3. The system ofclaim 2, wherein the two or more substantially identical planar antennas comprise two or more substantially identical planar dipole antennas.

4. The system ofclaim 2, wherein the two or more substantially identical planar antennas are printed on a circuit board housed in the external device.

5. The system ofclaim 1, wherein the controller comprises:

a signal analyzer coupled to the transceiver, the signal analyzer adapted to analyze a quality of each of RF signals received at a plurality of effective orientations of the phased-array directional antenna; and

an antenna steerer adapted to control the effective orientation of the phased-array directional antenna based on the quality of the each of the RF signals.

6. The system ofclaim 5, wherein the antenna steerer is adapted to determine a first effective orientation associated with the best signal quality from the plurality of effective orientations of the phased-array directional antenna, to steer the phased-array directional antenna to the first effective orientation, and to lock the directional antenna in the first effective orientation.

7. The system ofclaim 5, wherein the signal analyzer comprises a peak detection circuit adapted to determine an effective orientation of the plurality of effective orientations of the phased-array directional antenna at which a maximum amplitude is measured.

8. The system ofclaim 5, wherein the antenna interface circuit comprises a multiplier adapted to multiply weighting signals with antenna elements of the phased-array directional antenna, and the electronic steerer comprises a weighting signal generator adapted to generate a plurality of weighting signals each corresponding to one of the antenna elements to control the effective orientation of the phased-array directional antenna.

9. The system ofclaim 5, wherein the antenna interface circuit comprises a plurality of delay lines, and the electronic steerer comprises a delay line selector adapted to control the directionality of the phased-array directional antenna by selecting one of the plurality of delay lines to be coupled between each of antenna elements of the phased-array directional antenna and the transceiver.

10. The system ofclaim 9, wherein each delay line of the plurality of delay lines comprises a conductive path having a predetermined length.

11. A method for communicating with an implantable medical device via radio-frequency (RF) telemetry, the method comprising:

steering a phase-array directional antenna electronically to a plurality of effective orientations;

receiving an RF signal from the implantable medical device using the phase-array directional antenna at each effective orientation of the plurality of effective orientations;

analyzing a quality of the received RF signal to produce a set of one or more quality indicators associated with each effective orientation of the plurality of effective orientations; and

selecting an effective orientation from the plurality of effective orientations based on the sets of one or more quality indicators associated with the plurality of effective orientations.

12. The method ofclaim 11, wherein the plurality of effective orientations includes effective orientations each corresponding to a range of directions, and further comprising:

dividing the selected effective orientation into a further plurality of effective orientations if the range of directions associated with the selected effective orientation is wider than a predetermined operating beamwidth of the phase-array directional antenna;

repeating the steering, the receiving, and the analyzing for the further plurality of effective orientations; and

selecting a further effective orientation from the further plurality of effective orientations based on the sets of one or more quality indicators associated with the further plurality of effective orientations.

13. The method ofclaim 12, further comprising repeating the dividing the selected effective orientation into the further plurality of effective orientations, the repeating the steering, the receiving, and the analyzing for the further plurality of effective orientations, and the selecting the further effective orientation until the range of directions associated with the selected further effective orientation is not wider than the predetermined operating beamwidth of the phase-array directional antenna.

14. The method ofclaim 11, wherein analyzing the quality of the received RF signal comprises performing an error-checking to examine data integrity of the received RF signal.

15. The method ofclaim 14, wherein analyzing the quality of the received RF signal comprises measuring an amplitude of the received RF signal, and selecting the effective orientation from the plurality of effective orientations comprises selecting the effective orientation associated with the largest amplitude of the received RF signal and a satisfactory data integrity.

16. The method ofclaim 11, wherein steering the phase-array directional antenna electronically comprises:

applying weighting factors to a plurality of antenna elements of the phase-array directional antenna; and

adjusting the values of the weighting factors to steer the phase-array directional antenna electronically to each effective orientation of the plurality of effective orientations.

17. The method ofclaim 11, wherein steering the phase-array directional antenna electronically comprises:

controlling transmission delays each associated with one antenna element of a plurality of antenna elements of the phase-array directional antenna; and

adjusting the transmission delays to steer the phase-array directional antenna electronically to each effective orientation of the plurality of effective orientations.

18. An external system for communicating with an implantable medical device via radio-frequency (RF) telemetry, the system comprising:

a phased-array antenna;

means for electronically steering the phased-array antenna to a plurality of effective orientations;

means for receiving an RF signal from the implantable medical device using the phased-array antenna;

means for analyzing a quality of the RF signal associated with each effective orientation of the plurality of effective orientations; and

means for selecting an effective orientation based on the quality of the RF signal associated with the each effective orientation of the plurality of effective orientations.

19. The system ofclaim 18, wherein the phased-array antenna comprises a plurality of antenna elements printed on a circuit board.

20. The system ofclaim 19, wherein the plurality of antenna elements comprises planar antennas.

21. The system ofclaim 18, further comprising means for storing information used to electronically steer the phased-array antenna to the plurality of effective orientations.

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