技术领域technical field
本发明涉及一种多稳态超声检测传感器，主要用于超声检测和超声成像，具体地说，是利用控制电路在同一个超声换能器单元上实现压电式超声传感和电容式超声传感相互组合的多稳态工作方式，适用于水中声波探测、生物医学成像及工业超声无损检测等领域。The invention relates to a multi-stable ultrasonic detection sensor, which is mainly used for ultrasonic detection and ultrasonic imaging. Specifically, it uses a control circuit to realize piezoelectric ultrasonic sensing and capacitive ultrasonic sensing on the same ultrasonic transducer unit The multi-stable working mode combined with sensing and sensing is suitable for underwater acoustic wave detection, biomedical imaging and industrial ultrasonic non-destructive testing and other fields.
背景技术Background technique
超声波是一种频率高于听阈的弹性波，具有声能集中、方向性良好、穿透力强、水中传播距离远等特点，在医学诊断治疗、工业无损检测、水中声波探测、超声波成像等方面具有广阔的应用背景。超声波换能器是在超声频率范围内将交变的电信号转换成声信号或者将外界声场中的声信号转换成电信号的能量转换器件，按照电声转换原理的不同，超声换能器主要包括压电式超声换能器和电容式超声换能器等。Ultrasound is an elastic wave with a frequency higher than the hearing threshold. It has the characteristics of concentrated sound energy, good directionality, strong penetrating power, and long propagation distance in water. Has a broad application background. Ultrasonic transducers are energy conversion devices that convert alternating electrical signals into acoustic signals or convert acoustic signals in the external sound field into electrical signals within the ultrasonic frequency range. According to the different principles of electroacoustic conversion, ultrasonic transducers mainly Including piezoelectric ultrasonic transducers and capacitive ultrasonic transducers.
压电式超声换能器是利用压电元件受力或电激励后产生的的正或逆压电效应来实现超声波的发射与接收的，目前使用最为广泛，具有机电转换效率高、加工工艺简单、技术实现方便、价格低廉和性能可靠等优点，且压电材料的声阻抗与固体材料的声阻抗在相同数量级上。但是，该换能器也具有很突出的缺点，如压电材料声阻抗很大而与气、液体介质声阻抗失配，带宽低，高频换能器的压电薄膜不易加工，在恶劣环境中性能差甚至无法工作等。目前解决压电薄膜与介质之间的阻抗失配的方法是在中间增加一个阻抗匹配层，但由于匹配层不能加工太薄而进一步限制换能器的工作频率不能很高，且牺牲换能器的带宽，增加结构的复杂性和生产成本。Piezoelectric ultrasonic transducers are used to transmit and receive ultrasonic waves by using the positive or inverse piezoelectric effect generated by the piezoelectric element after being subjected to force or electric excitation. It is currently the most widely used, with high electromechanical conversion efficiency and simple processing technology. , convenient technical implementation, low price and reliable performance, etc., and the acoustic impedance of piezoelectric materials is on the same order of magnitude as that of solid materials. However, this transducer also has very prominent shortcomings, such as the piezoelectric material has a large acoustic impedance that does not match the acoustic impedance of the gas or liquid medium, the bandwidth is low, and the piezoelectric film of the high-frequency transducer is not easy to process. Neutral performance is poor or even not working etc. The current method to solve the impedance mismatch between the piezoelectric film and the medium is to add an impedance matching layer in the middle, but because the matching layer cannot be processed too thin, the operating frequency of the transducer cannot be further limited, and the transducer is sacrificed. The bandwidth increases the complexity of the structure and the production cost.
电容式超声换能器是利用平板电容两电极板之间的静电力和顶部电极(带有薄膜)自身的结构应力之间的力平衡原理制成的。通过在电容上施加一定频率的交流电压信号使薄膜发生振动而产生超声波，或者当薄膜接收到超声波时因声压作用而产生相应超声波频率的机械振动，在平板电容两端加上一定的直流偏置电压，则此时由于薄膜的振动而产生变化的电流，从而换能器实现超声波的发射和接收。电容式超声换能器具有阻抗与气、液体介质阻抗易匹配，带宽高，工作频率范围大，可制造成一维线阵列和二维面阵列，且易于与电子电路集成，可适应恶劣环境(如高温)等特点，但也存在寄生电容大、输出声压低等问题。The capacitive ultrasonic transducer is made by using the principle of force balance between the electrostatic force between the two electrode plates of the flat capacitor and the structural stress of the top electrode (with a thin film) itself. By applying an AC voltage signal of a certain frequency on the capacitor to vibrate the film to generate ultrasonic waves, or when the film receives ultrasonic waves, the mechanical vibration of the corresponding ultrasonic frequency is generated due to the action of sound pressure, and a certain DC bias is added to both ends of the plate capacitor. If the voltage is set, a changing current is generated due to the vibration of the film at this time, so that the transducer realizes the transmission and reception of ultrasonic waves. Capacitive ultrasonic transducers have the advantages of easy matching between impedance and gas and liquid medium impedance, high bandwidth, and large operating frequency range. They can be manufactured into one-dimensional line arrays and two-dimensional surface arrays, and are easy to integrate with electronic circuits. High temperature) and other characteristics, but there are also problems such as large parasitic capacitance and low output sound pressure.
由于MEMS微加工技术具有较高的准确度和重复性以及良好的一致性等优点，成为加工超声换能器的一种新的技术途径，基于MEMS制作工艺的压电式微加工超声换能器(Piezoelectric Micromachined Ultrasonic Transducer,pMUT)和电容式微加工超声换能器(Capacitive Micromachined Ultrasonic Transducer,cMUT)逐渐成为研究热点。Since MEMS micromachining technology has the advantages of high accuracy, repeatability and good consistency, it has become a new technical approach for processing ultrasonic transducers. The piezoelectric micromachining ultrasonic transducer based on MEMS manufacturing technology ( Piezoelectric Micromachined Ultrasonic Transducer (pMUT) and Capacitive Micromachined Ultrasonic Transducer (cMUT) have gradually become research hotspots.
目前国内外对于pMUT和cMUT的研究基本上都停留在对超声换能器单一稳态的设计分析，即要么采用pMUT及其阵列(Qiu Y,Gigliotti J V,Wallace M,etal.Piezoelectric micromachined ultrasound transducer(pMUT)arrays forintegrated sensing,actuation and imaging[J].Sensors,2015,15(4):8020-8041.)，要么采用cMUT及其阵列(Zhang R,Zhang W,He C,et al.Underwater Imaging Using a 1×16cMUT Linear Array[J].Sensors,2016,16(3):312.)，加工后的换能器单元工作方式单一固定。传感器工作频率低虽然可实现较长的检测深度，但是分辨率较低，反之，传感器工作频率高虽然可实现较高的分辨率，但是检测深度较短，无法做到兼顾检测深度和分辨率，或者采用多种传感器集成增加了器件体积与复杂性，传感器及其阵列具有pMUT或cMUT固有的缺陷。At present, the research on pMUT and cMUT at home and abroad basically stays in the design and analysis of the single stable state of the ultrasonic transducer, that is, either using pMUT and its array (Qiu Y, Gigliotti J V, Wallace M, et al.Piezoelectric micromachined ultrasound transducer( pMUT) arrays for integrated sensing, actuation and imaging[J].Sensors,2015,15(4):8020-8041.), or cMUT and its arrays (Zhang R, Zhang W, He C, et al. Underwater Imaging Using a 1×16cMUT Linear Array[J].Sensors,2016,16(3):312.), the working mode of the processed transducer unit is single and fixed. Although the sensor operating frequency is low, it can achieve a longer detection depth, but the resolution is low. On the contrary, although the sensor operating frequency is high, although it can achieve higher resolution, but the detection depth is short, it is impossible to achieve both detection depth and resolution. Or the integration of multiple sensors increases the size and complexity of the device, and the sensors and their arrays have inherent defects of pMUT or cMUT.
因此，需要研究一种多稳态的超声检测传感器，结合pMUT和cMUT的优点，利用MEMS微加工技术制作超声换能器，在一个单元中实现pMUT和cMUT两种工作方式，以实现体积小易于集成阵列、器件设计灵活、工作频率可调、可广泛应用于工业、农业、交通运输、生活医疗及军事等领域的微型超声检测传感器为目标。虽然压电式微加工超声换能器可实现弯曲振动和厚度振动两种工作模式(Hedegaard T,Pedersen T,Thomsen E V,et al.Screenprinted thick film based pMUT arrays[C]//2008IEEE Ultrasonics Symposium.IEEE,2008:2126-2129.)，但是一个换能器单元只能选择其中一种模式工作，无法选择性切换，具有压电式超声换能器固有的缺点，且两种工作模式增加了器件阻抗匹配的难度，进一步影响传感器的性能。Therefore, it is necessary to study a multi-stable ultrasonic detection sensor, combine the advantages of pMUT and cMUT, use MEMS micromachining technology to make ultrasonic transducers, and realize two working modes of pMUT and cMUT in one unit, so as to realize small size and easy operation. Integrated arrays, flexible device design, adjustable operating frequency, and miniature ultrasonic detection sensors that can be widely used in industry, agriculture, transportation, life, medical and military fields are targeted. Although the piezoelectric micro-machined ultrasonic transducer can realize two working modes of bending vibration and thickness vibration (Hedegaard T, Pedersen T, Thomsen E V, et al.Screenprinted thick film based pMUT arrays[C]//2008IEEE Ultrasonics Symposium.IEEE, 2008:2126-2129.), but a transducer unit can only select one of the modes to work, and cannot be selectively switched, which has the inherent disadvantages of piezoelectric ultrasonic transducers, and the two working modes increase the impedance matching of the device The difficulty further affects the performance of the sensor.
发明内容Contents of the invention
本发明针对上述现有技术方案中存在的不足，在其基础上提出一种多稳态超声检测传感器，利用控制电路在同一个超声换能器单元上可实现压电式超声传感和电容式超声传感相互组合的多稳态工作方式，兼顾了超声检测的深度和分辨率，工作原理如图1所示。本发明的技术方案如下：The present invention aims at the deficiencies in the above-mentioned existing technical solutions, and proposes a multi-stable ultrasonic detection sensor on the basis of it, and the piezoelectric ultrasonic sensing and capacitive ultrasonic sensing can be realized on the same ultrasonic transducer unit by using the control circuit. The multi-stable working mode of ultrasonic sensing combined with each other takes into account the depth and resolution of ultrasonic detection. The working principle is shown in Figure 1. Technical scheme of the present invention is as follows:
一种多稳态超声检测传感器，包括声阻匹配层、金属电极、压电薄膜、耐高压绝缘层、空腔密封层、背衬层和机电控制电路板。按压电式超声传感和电容式超声传感稳态工作频率的不同，整体结构有两种形式，如图2和图3所示。A multi-stable ultrasonic detection sensor includes an acoustic resistance matching layer, a metal electrode, a piezoelectric film, a high-voltage insulating layer, a cavity sealing layer, a backing layer and an electromechanical control circuit board. According to the difference in the steady-state operating frequency of the piezoelectric ultrasonic sensor and the capacitive ultrasonic sensor, the overall structure has two forms, as shown in Figure 2 and Figure 3.
所述的多稳态超声检测传感器，按照结构如图2所示，其特征在于：所述多稳态超声检测传感器可按照pMUT和cMUT两种方式组合工作，pMUT工作方式通过上层压电薄膜来实现，该压电薄膜上、下两端为金属电极，顶端电极上面为声阻匹配层，底端电极下面为上层空腔密封层；cMUT工作方式通过下层压电薄膜和下层空腔密封层来实现，下层压电薄膜上、下两端为金属电极，顶端电极上面为耐高压绝缘层，底端电极下面为下层空腔密封层，该空腔层下面为耐高压绝缘层，该绝缘层下面为金属电极，在金属电极下面为背衬层，在背衬层下面为机电控制电路板。The multi-stable ultrasonic detection sensor, according to the structure as shown in Figure 2, is characterized in that: the multi-stable ultrasonic detection sensor can work in combination according to pMUT and cMUT, and the pMUT working mode is realized by the upper piezoelectric film. Realization, the upper and lower ends of the piezoelectric film are metal electrodes, the top electrode is an acoustic resistance matching layer, and the bottom electrode is an upper cavity sealing layer; the cMUT works through the lower piezoelectric film and the lower cavity sealing layer. Realization, the upper and lower ends of the lower piezoelectric film are metal electrodes, the top electrode is a high-voltage insulating layer, the bottom electrode is a lower cavity sealing layer, and the cavity layer is a high-voltage insulating layer. It is a metal electrode, the backing layer is under the metal electrode, and the electromechanical control circuit board is under the backing layer.
所述如图2所示的多稳态超声检测传感器，其超声检测的工作原理为：Described multi-stable ultrasonic detection sensor as shown in Figure 2, the operating principle of its ultrasonic detection is:
(1)在pMUT工作方式下，将A、B、C、D金属电极通孔引线级联在一起作为供电地线，若在E金属电极上施加适当大小的高频电压信号，则由于逆压电效应使得压电薄膜发生振动而发射超声波，若压电薄膜接收到超声波则会按照相应的频率振动，由于正压电效应，薄膜的振动将产生相应频率的电压并经放大以后被检测，此过程中下层压电薄膜无振动；(1) In the pMUT working mode, the through-hole leads of the metal electrodes A, B, C, and D are cascaded together as the power supply ground wire. If a high-frequency voltage signal of an appropriate size is applied to the metal electrode E, due to the reverse voltage The electric effect causes the piezoelectric film to vibrate and emit ultrasonic waves. If the piezoelectric film receives ultrasonic waves, it will vibrate according to the corresponding frequency. Due to the positive piezoelectric effect, the vibration of the film will generate a voltage of the corresponding frequency and be detected after being amplified. The lower piezoelectric film has no vibration during the process;
(2)在cMUT工作方式下，将D、E金属电极通孔引线级联在一起，在上层空腔上、下两端电极(构成平板电容)间施加足够强度的电压，由于两金属电极板之间的静电力大于结构应力，上层压电薄膜与下层压电薄膜吸合在一起作为新压电薄膜(图4)，将A金属电极作为供电地线，若在下层空腔密封层上、下两端电极(构成平板电容)间施加适当大小的高频电压信号，新压电薄膜由于交变的静电力作用而产生超声波并发射出去，若新压电薄膜接收到超声波，薄膜由于一定频率的声压作用而产生相应频率的振动，此时在下层空腔密封层上、下两端电极间施加一定大小的直流偏置电压并并联一定大小的电容，则由于压电薄膜的振动最终产生相应的可测电流，实现超声波的接收和检测。(2) In the cMUT working mode, the D and E metal electrode through-hole leads are cascaded together, and a sufficient voltage is applied between the upper and lower electrodes (forming a plate capacitor) of the upper cavity, because the two metal electrode plates The electrostatic force between them is greater than the structural stress, the upper piezoelectric film and the lower piezoelectric film are attracted together to form a new piezoelectric film (Figure 4), and the A metal electrode is used as the power supply ground wire. If the lower cavity sealing layer, A high-frequency voltage signal of appropriate size is applied between the electrodes at both ends of the lower end (forming a flat plate capacitor). The new piezoelectric film generates ultrasonic waves due to the action of alternating electrostatic force and emits them. If the new piezoelectric film receives ultrasonic waves, the film due to a certain frequency The vibration of the corresponding frequency is generated by the action of the sound pressure of the lower cavity. At this time, a certain size of DC bias voltage is applied between the upper and lower electrodes of the lower cavity sealing layer and a certain size of capacitance is connected in parallel. The vibration of the piezoelectric film will eventually produce The corresponding measurable current realizes the reception and detection of ultrasonic waves.
所述的多稳态超声检测传感器，按照结构如图3所示，其特征在于：所述多稳态超声检测传感器可按照pMUT和cMUT两种方式组合工作，pMUT工作方式通过下层压电薄膜来实现，该压电薄膜上、下两端为金属电极，顶端电极上端为耐高压绝缘层，该绝缘层上面为上层空腔密封层，底端电极下面为下层空腔密封层，该空腔层下面为背衬层，在背衬层下面为机电控制电路板；cMUT工作方式通过上层压电薄膜和上层空腔密封层来实现，上层压电薄膜上、下两端为金属电极，顶端电极上面为声阻抗匹配层，底端电极下面为下层空腔密封层，下层空腔密封层上、下两端分别为上层压电薄膜底端电极和耐高压绝缘层。The multi-stable ultrasonic detection sensor, according to the structure shown in Figure 3, is characterized in that: the multi-stable ultrasonic detection sensor can work in combination according to pMUT and cMUT, and the pMUT working mode is realized by the lower piezoelectric film. Realization, the upper and lower ends of the piezoelectric film are metal electrodes, the upper end of the top electrode is a high-voltage insulating layer, the upper layer of the insulating layer is the upper cavity sealing layer, and the bottom electrode is the lower cavity sealing layer, the cavity layer The bottom is the backing layer, and the electromechanical control circuit board is under the backing layer; the working mode of cMUT is realized by the upper piezoelectric film and the upper cavity sealing layer. The upper and lower ends of the upper piezoelectric film are metal electrodes, and the top electrode is above It is the acoustic impedance matching layer, the bottom electrode is the lower cavity sealing layer, and the upper and lower ends of the lower cavity sealing layer are the upper piezoelectric film bottom electrode and the high voltage insulating layer respectively.
所述如图3所示的多稳态超声检测传感器，其超声检测的工作原理为：Described multi-stable ultrasonic detection sensor as shown in Figure 3, the working principle of its ultrasonic detection is:
(1)在cMUT工作方式下，将A、B金属电极通孔引线级联在一起作为供电地线，若在上层空腔上、下两端电极(构成平板电容)间施加适当大小的高频电压信号，上层压电薄膜由于交变的静电力作用而产生超声波并发射出去，若上层压电薄膜接收到超声波，薄膜由于一定频率的声压作用而产生相应频率的振动，此时在上层空腔密封层上、下两端电极间施加一定大小的直流偏置电压并并联一定大小的电容，则由于压电薄膜的振动最终产生相应的可测电流，实现超声波的接收和检测，此过程中下层压电薄膜无振动。(1) In the cMUT working mode, the through-hole leads of the A and B metal electrodes are cascaded together as the power supply ground wire. If an appropriate high frequency is applied between the upper and lower electrodes (forming a plate capacitor) Voltage signal, the upper piezoelectric film generates ultrasonic waves due to the action of alternating electrostatic force and emits them. If the upper piezoelectric film receives ultrasonic waves, the film will vibrate at a corresponding frequency due to the action of sound pressure at a certain frequency. A certain size of DC bias voltage is applied between the upper and lower electrodes of the cavity sealing layer and a certain size of capacitance is connected in parallel, and the corresponding measurable current is finally generated due to the vibration of the piezoelectric film to realize the reception and detection of ultrasonic waves. The lower piezoelectric film does not vibrate.
(2)在pMUT工作方式下，在B、C金属电极两端(构成平板电容)施加足够强度的电压，由于两金属电极板之间的静电力大于结构应力，上层压电薄膜与下层压电薄膜吸合在一起作为新压电薄膜(图5)，将A金属电极作为供电地线，若在下层压电薄膜上、下两端电极间施加适当大小的高频电压信号，则上层压电薄膜相当于负载作用在下层压电薄膜上端，由于逆压电效应使得新压电薄膜发生振动而发射超声波，若新压电薄膜接收到超声波则会按照相应的频率振动，由于正压电效应，薄膜的振动将产生相应频率的电压并经放大以后被检测。(2) In the pMUT working mode, a voltage of sufficient strength is applied to both ends of the B and C metal electrodes (forming a plate capacitor). Since the electrostatic force between the two metal electrode plates is greater than the structural stress, the upper piezoelectric film and the lower piezoelectric film The films are sucked together to form a new piezoelectric film (Figure 5), and the metal electrode A is used as the power supply ground. If a high-frequency voltage signal of an appropriate size is applied between the upper and lower electrodes of the lower piezoelectric film, the upper piezoelectric film will The film is equivalent to the load acting on the upper end of the lower piezoelectric film. Due to the inverse piezoelectric effect, the new piezoelectric film vibrates and emits ultrasonic waves. If the new piezoelectric film receives ultrasonic waves, it will vibrate at the corresponding frequency. Due to the positive piezoelectric effect, The vibration of the membrane will generate a voltage of corresponding frequency and be detected after being amplified.
所述的多稳态超声检测传感器(图2、图3)按照pMUT方式工作时，其一阶弯曲振动频率可以确定为：其中，αp1为pMUT方式下的一阶振动因子，tp为压电薄膜的厚度，A为压电薄膜的表面积，Y0为压电薄膜的杨氏模量，ρ为压电薄膜的密度，ν为压电薄膜的泊松比。When the multi-stable ultrasonic detection sensor (Fig. 2, Fig. 3) works according to the pMUT mode, its first-order bending vibration frequency can be determined as: Among them, αp1 is the first-order vibration factor in the pMUT mode, tp is the thickness of the piezoelectric film, A is the surface area of the piezoelectric film, Y0 is the Young’s modulus of the piezoelectric film, and ρ is the density of the piezoelectric film , ν is the Poisson's ratio of the piezoelectric film.
所述的多稳态超声检测传感器(图2、图3)按照cMUT模式工作时，其一阶弯曲振动频率可以确定为：其中，αc1为pMUT方式下的一阶振动因子，tc为压电薄膜的厚度，A为压电薄膜的表面积，Y0为压电薄膜的杨氏模量，ρ为压电薄膜的密度，ν为压电薄膜的泊松比。由空腔密封层上、下两端电极构成的平板电容发生吸合时的塌陷电压为：其中，k为压电薄膜的弹性系数，d0为空腔层初始高度，ε0为真空中的介电常数，A为压电薄膜的表面积。压电薄膜的位移形变与施加的激励电压之间的关系为：当时平板电容发生吸合。When the multi-stable ultrasonic detection sensor (Fig. 2, Fig. 3) works according to the cMUT mode, its first-order bending vibration frequency can be determined as: Among them, αc1 is the first-order vibration factor in the pMUT mode, tc is the thickness of the piezoelectric film, A is the surface area of the piezoelectric film, Y0 is the Young’s modulus of the piezoelectric film, and ρ is the density of the piezoelectric film , ν is the Poisson's ratio of the piezoelectric film. The collapse voltage of the plate capacitor formed by the electrodes at the upper and lower ends of the cavity sealing layer is: Among them,k is the elastic coefficient of the piezoelectric film, d0 is the initial height of the cavity layer,ε0 is the dielectric constant in vacuum, and A is the surface area of the piezoelectric film. The relationship between the displacement deformation of the piezoelectric film and the applied excitation voltage is: when When the plate capacitor pulls in.
所述的多稳态超声检测传感器，机电控制电路板用来控制超声检测传感器的工作方式和超声换能器发射与接收模式，可以是一层或多层电路板，可以使用印制电路板或者柔性电路板，电路板可以采用铜箔或其他导电材料代替。此外，电路板可以固定在背衬层表面、金属电极表面或压电薄膜的表面。In the multi-stable ultrasonic detection sensor, the electromechanical control circuit board is used to control the working mode of the ultrasonic detection sensor and the transmitting and receiving mode of the ultrasonic transducer. It can be one or more layers of circuit boards, and can use printed circuit boards or For flexible circuit boards, the circuit board can be replaced by copper foil or other conductive materials. In addition, the circuit board can be fixed on the surface of the backing layer, the surface of the metal electrode, or the surface of the piezoelectric film.
所述的多稳态超声检测传感器，耐高压绝缘层的作用是在电容极板发生吸合时防止电学短路并避免被高压击穿。In the multi-stable ultrasonic detection sensor, the function of the high-voltage-resistant insulating layer is to prevent an electrical short circuit and avoid high-voltage breakdown when the capacitor plates are pulled together.
所述的多稳态超声检测传感器，压电薄膜为一层或由多层叠加而成，压电材料选自压电陶瓷、压电单晶、压电复合材料或压电聚合物。其中，压电陶瓷可以是PZT、AlN或ZnO。In the multi-stable ultrasonic detection sensor, the piezoelectric film is formed by one layer or stacked by multiple layers, and the piezoelectric material is selected from piezoelectric ceramics, piezoelectric single crystals, piezoelectric composite materials or piezoelectric polymers. Wherein, the piezoelectric ceramic can be PZT, AlN or ZnO.
所述的多稳态超声检测传感器，声阻抗匹配层为一层或由多层叠加而成，本超声检测传感器不对声阻抗匹配层的材料具体限定，声阻抗匹配层的厚度由换能器设计的声学要求所决定。In the multi-stable ultrasonic detection sensor, the acoustic impedance matching layer is one layer or stacked by multiple layers. The ultrasonic detection sensor does not specifically limit the material of the acoustic impedance matching layer, and the thickness of the acoustic impedance matching layer is determined by the transducer design. determined by the acoustic requirements.
所述的多稳态超声检测传感器，其结构外形可以为圆形、方形或者多边形平面元件，换能器的尺寸由工作频率所决定，换能器的表面积越大，厚度越薄，则换能器的一阶谐振频率越低，反之则一阶谐振频率越高。换能器可以根据应用需求设计不同稳态工作频率组合的传感器，比如pMUT稳态工作方式下超声频率为5MHz、cMUT稳态工作方式下超声频率为20MHz的超声检测传感器(图2)，或者cMUT稳态工作方式下超声频率为5MHz、pMUT稳态工作方式下超声频率为20MHz的超声检测传感器(图3)。在一些具体实施方式中，所述多稳态超声检测传感器可以为1D、2D等阵列超声换能器，其中，1D阵列换能器是指换能器单元沿着长度方向直线排列，2D阵列换能器是指换能器单元沿着长度和宽度方向直线排列。The multi-stable ultrasonic detection sensor can have a structural shape of a circular, square or polygonal planar element, and the size of the transducer is determined by the operating frequency. The lower the first-order resonance frequency of the device is, the higher the first-order resonance frequency is. The transducer can design sensors with different steady-state operating frequency combinations according to application requirements, such as an ultrasonic detection sensor with an ultrasonic frequency of 5MHz in pMUT steady-state operation mode and an ultrasonic frequency of 20MHz in cMUT steady-state operation mode (Figure 2), or cMUT An ultrasonic detection sensor with an ultrasonic frequency of 5MHz in steady-state operation and an ultrasonic frequency of 20MHz in pMUT steady-state operation (Figure 3). In some specific implementation manners, the multi-stable ultrasonic detection sensor can be a 1D, 2D, etc. array ultrasonic transducer, wherein, a 1D array transducer means that the transducer units are arranged in a straight line along the length direction, and a 2D array transducer The transducer means that the transducer units are arranged in a straight line along the length and width directions.
所述的多稳态超声检测传感器，传感器可以为单阵元换能器或由多个阵元按同心圆的方式排列的超声换能器。As for the multi-stable ultrasonic detection sensor, the sensor can be a single array element transducer or an ultrasonic transducer with multiple array elements arranged in concentric circles.
通过本设计实现的多稳态超声检测传感器具有体积小易于集成、功耗低、性能可靠、工作频率可调、超声检测方式可自由切换等优势，通过不同的外封装形式，该器件可以在真空、空气、水下等多种不同环境进行超声检测。与现有的方法相比，本发明设计的多稳态超声检测传感器具有以下特点：The multi-stable ultrasonic detection sensor realized by this design has the advantages of small size, easy integration, low power consumption, reliable performance, adjustable operating frequency, and free switching of ultrasonic detection methods. Through different external packaging forms, the device can operate in a vacuum , air, underwater and other environments for ultrasonic testing. Compared with existing methods, the multi-stable ultrasonic detection sensor designed by the present invention has the following characteristics:
(1)通过适当的结构设计将压电式微加工超声换能器(pMUT)和微电容超声换能器(cMUT)两种类型的换能器工作方式结合在一起，突破传统器件只能以单一稳态方式工作的局限，实现多稳态超声检测；(1) Combining the two types of transducers, the piezoelectric micromachining ultrasonic transducer (pMUT) and the microcapacitance ultrasonic transducer (cMUT), through appropriate structural design, breaks through the traditional devices that can only be used in a single The limitations of steady-state work, to achieve multi-stable ultrasonic testing;
(2)通过调整换能器的结构参数，可实现对任意超声频率组合的多稳态超声检测，比如可以通过机电控制电路实现低频超声传感和高频超声传感，兼顾了超声检测的深度与分辨率，结构设计灵活，应用前景广泛；(2) By adjusting the structural parameters of the transducer, multi-stable ultrasonic detection for any combination of ultrasonic frequencies can be realized. For example, low-frequency ultrasonic sensing and high-frequency ultrasonic sensing can be realized through electromechanical control circuits, taking into account the depth of ultrasonic detection and resolution, flexible structure design, wide application prospects;
(3)本器件兼具pMUT和cMUT的优点，可灵活应用于气态、液态、固态媒体介质的超声探测，阻抗匹配简单，甚至不需要匹配层；(3) This device has the advantages of both pMUT and cMUT, and can be flexibly applied to ultrasonic detection of gaseous, liquid, and solid media. The impedance matching is simple, and even no matching layer is required;
(4)本器件采用微纳加工技术制作，体积小，功耗低，有利于器件的批量化生产，器件生产成本低，性能一致性好；(4) The device is made by micro-nano processing technology, which is small in size and low in power consumption, which is conducive to the mass production of the device, with low production cost and good performance consistency;
(5)该器件可以广泛应用于水中声波探测、生物医学成像及工业超声无损检测等多种领域(5) The device can be widely used in various fields such as underwater acoustic wave detection, biomedical imaging, and industrial ultrasonic nondestructive testing.
附图说明Description of drawings
图1：多稳态超声检测传感器工作原理图；Figure 1: Working principle diagram of multi-stable ultrasonic detection sensor;
图2：pMUT稳态频率为5MHz、cMUT稳态频率为20MHz的超声检测传感器侧面结构示意图(结构一)；Figure 2: Schematic diagram of the side structure of an ultrasonic detection sensor with a steady-state frequency of pMUT of 5 MHz and a steady-state frequency of cMUT of 20 MHz (structure 1);
图3：cMUT稳态频率为5MHz、pMUT稳态频率为20MHz的超声检测传感器侧面结构示意图(结构二)；Figure 3: Schematic diagram of the side structure of an ultrasonic detection sensor with a steady-state frequency of cMUT of 5 MHz and a steady-state frequency of pMUT of 20 MHz (structure 2);
图4：结构一所示的传感器在两层压电薄膜发生吸合时示意图；Figure 4: Schematic diagram of the sensor shown in Structure 1 when the two piezoelectric films are pulled together;
图5：结构二所示的传感器在两层压电薄膜发生吸合时示意图。Figure 5: Schematic diagram of the sensor shown in Structure 2 when the two piezoelectric films are pulled together.
附图中的标号分别为：1、机电控制电路板，2、背衬层，3、耐高压绝缘层，4、金属电极，5、空腔密封层，6、压电薄膜，7、声阻抗匹配层。The labels in the accompanying drawings are: 1. Electromechanical control circuit board, 2. Backing layer, 3. High voltage insulating layer, 4. Metal electrode, 5. Cavity sealing layer, 6. Piezoelectric film, 7. Acoustic impedance matching layer.
具体实施方式Detailed ways
本发明提供一种多稳态超声检测传感器，包括机电控制电路板1、背衬层2、耐高压绝缘层3、金属电极4、空腔密封层5、压电薄膜6和声阻抗匹配层7。下面结合附图和实施例来说明本发明的具体实施方法。The present invention provides a multi-stable ultrasonic detection sensor, comprising an electromechanical control circuit board 1, a backing layer 2, a high-voltage insulating layer 3, a metal electrode 4, a cavity sealing layer 5, a piezoelectric film 6 and an acoustic impedance matching layer 7 . The specific implementation method of the present invention will be described below in conjunction with the drawings and embodiments.
本实施例提供的一种多稳态超声检测传感器，其具体的技术实施思路：采用机电控制电路控制多稳态超声检测传感器的工作方式，根据实际应用需求在pMUT和cMUT两种方式之间切换，再根据所需换能器的工作模式选择发射或接收超声波，如图1所示。A multi-stable ultrasonic detection sensor provided in this embodiment, its specific technical implementation ideas: use an electromechanical control circuit to control the working mode of the multi-stable ultrasonic detection sensor, and switch between pMUT and cMUT according to actual application requirements , and then choose to transmit or receive ultrasonic waves according to the working mode of the required transducer, as shown in Figure 1.
本实施例提供两种不同结构的多稳态超声检测传感器：pMUT稳态工作超声频率为5MHz、cMUT稳态工作超声频率为20MHz的超声检测传感器，结构侧面如图2所示；cMUT稳态工作超声频率为5MHz、pMUT稳态工作超声频率为20MHz的超声检测传感器，结构侧面如图3所示。This embodiment provides two multi-stable ultrasonic detection sensors with different structures: the ultrasonic detection sensor with pMUT steady-state working ultrasonic frequency of 5 MHz and cMUT steady-state working ultrasonic frequency of 20 MHz, the structure side is shown in Figure 2; cMUT steady-state working The structure of an ultrasonic detection sensor with an ultrasonic frequency of 5 MHz and a pMUT steady-state operating ultrasonic frequency of 20 MHz is shown in Figure 3.
在结构一所示的多稳态超声检测传感器(图2)中，pMUT方式下的超声换能器主要包括五层，即上层压电薄膜6、上层压电薄膜顶端和底端金属电极4、顶端金属电极上层为声阻抗匹配层7、底端金属电极下层为上层空腔密封层5，其余部分对于传感器工作状态无影响，可不作考虑。当换能器以发射模式工作时，在上层压电薄膜两端金属电极间施加适当大小的高频激励电压，当换能器以接收模式工作时，在上层压电薄膜两端金属电极间输出超声波相应频率的电压信号。cMUT方式下的超声换能器需先在上层空腔密封层两端金属电极(C、D)间施加足够强度的电压使得上层压电薄膜与下层压电薄膜发生吸合(塌陷模式下的换能器侧面结构如图4所示)，金属电极E与金属电极D级联，下层压电薄膜顶端电极C的上端为耐高压绝缘层3，下层压电薄膜底端电极B的下端为下层空腔密封层，该空腔密封层下端为耐高压绝缘层，绝缘层覆盖在金属电极A的上面，金属电极A的下端为背衬层2，其沉积在机电控制电路板1的上面。当换能器以发射模式工作时，在下层空腔密封层两端金属电极(A、B)间施加适当大小的高频激励电压，当换能器以接收模式工作时，在金属电极A和B间输出超声波相应频率的电流信号。In the multi-stable ultrasonic detection sensor shown in structure 1 (Fig. 2), the ultrasonic transducer in the pMUT mode mainly includes five layers, namely the upper piezoelectric film 6, the top and bottom metal electrodes 4 of the upper piezoelectric film, The upper layer of the top metal electrode is the acoustic impedance matching layer 7, and the lower layer of the bottom metal electrode is the upper cavity sealing layer 5, and the remaining parts have no influence on the working state of the sensor and can be ignored. When the transducer works in transmitting mode, an appropriate high-frequency excitation voltage is applied between the metal electrodes at both ends of the upper piezoelectric film. The voltage signal corresponding to the frequency of the ultrasound. The ultrasonic transducer in the cMUT mode needs to apply a voltage of sufficient strength between the metal electrodes (C, D) at both ends of the upper cavity sealing layer to make the upper piezoelectric film and the lower piezoelectric film absorb (transition in the collapse mode The side structure of the energy device is shown in Figure 4), the metal electrode E is cascaded with the metal electrode D, the upper end of the top electrode C of the lower piezoelectric film is a high-voltage insulating layer 3, and the lower end of the bottom electrode B of the lower piezoelectric film is the lower space. Cavity sealing layer, the lower end of the cavity sealing layer is a high-voltage insulating layer, the insulating layer covers the metal electrode A, and the lower end of the metal electrode A is the backing layer 2, which is deposited on the electromechanical control circuit board 1. When the transducer works in the transmitting mode, a high-frequency excitation voltage of appropriate size is applied between the metal electrodes (A, B) at both ends of the lower cavity sealing layer. When the transducer works in the receiving mode, between the metal electrodes A and B Room B outputs the current signal of the corresponding frequency of the ultrasonic waves.
在结构二所示的多稳态超声检测传感器(图3)中，cMUT方式下的超声换能器主要包括六层，即上层空腔密封层5、该空腔密封层顶端为金属电极4、金属电极C的上端为上层压电薄膜6，该压电薄膜的上端为声阻抗匹配层7，耐高压绝缘层3在上层空腔密封层和金属电极B中间，其余部分对于传感器工作状态无影响，可不作考虑。当换能器以发射模式工作时，在上层空腔密封层两端金属电极间施加适当大小的高频激励电压，当换能器以接收模式工作时，在金属电极B和C间输出超声波相应频率的电流信号。pMUT模式下的超声换能器需先在上层空腔密封层两端金属电极(B、C)间施加足够强度的电压使得上层压电薄膜与下层压电薄膜发生吸合(塌陷模式下的换能器侧面结构如图5所示)，下层压电薄膜顶端为金属电极B，下层压电薄膜的底端为耐高压绝缘层，该绝缘层覆盖在金属电极A的上端，金属电极A的下端为背衬层2，其沉积在机电控制电路板1的上端。当换能器以发射模式工作时，在下层空腔密封层两端金属电极(A、B)间施加适当大小的高频激励电压，当换能器以接收模式工作时，在金属电极A和B间输出超声波相应频率的电压信号。In the multi-stable ultrasonic detection sensor shown in structure 2 (Fig. 3), the ultrasonic transducer in the cMUT mode mainly includes six layers, that is, the upper cavity sealing layer 5, the top of the cavity sealing layer is a metal electrode 4, The upper end of the metal electrode C is the upper piezoelectric film 6, the upper end of the piezoelectric film is the acoustic impedance matching layer 7, the high-voltage insulating layer 3 is between the upper cavity sealing layer and the metal electrode B, and the rest has no effect on the working state of the sensor , may not be considered. When the transducer works in transmitting mode, a high-frequency excitation voltage of appropriate size is applied between the metal electrodes at both ends of the upper cavity sealing layer. When the transducer works in receiving mode, ultrasonic waves are output between metal electrodes B and C correspondingly. Frequency current signal. The ultrasonic transducer in the pMUT mode needs to apply a voltage of sufficient strength between the metal electrodes (B, C) at both ends of the upper cavity sealing layer to make the upper piezoelectric film and the lower piezoelectric film absorb (transition in the collapse mode The side structure of the energy device is shown in Figure 5), the top of the lower piezoelectric film is a metal electrode B, the bottom of the lower piezoelectric film is a high-voltage insulating layer, the insulating layer covers the upper end of the metal electrode A, and the lower end of the metal electrode A is the backing layer 2 , which is deposited on the upper end of the electromechanical control circuit board 1 . When the transducer works in the transmitting mode, a high-frequency excitation voltage of appropriate size is applied between the metal electrodes (A, B) at both ends of the lower cavity sealing layer. When the transducer works in the receiving mode, between the metal electrodes A and B Room B outputs a voltage signal corresponding to the ultrasonic frequency.
需要说明的是，每一层材料均可以是一层或有多层叠加而成，例如声阻抗匹配层可以有一层或多层，压电薄膜也可以有一层或多层。机电控制电路板的位置不限于在背衬层的底端，例如可以将其设置在压电薄膜的侧面，电路板中可以加入控制换能器发射和接收的专用集成电子电路芯片(ASIC)。It should be noted that each layer of material may be formed by one or more layers, for example, the acoustic impedance matching layer may have one or more layers, and the piezoelectric film may also have one or more layers. The position of the electromechanical control circuit board is not limited to the bottom of the backing layer, for example, it can be arranged on the side of the piezoelectric film, and an application-specific integrated circuit chip (ASIC) for controlling the transmission and reception of the transducer can be added to the circuit board.
本实施例中所述的压电薄膜，其材料可以是压电陶瓷、压电单晶、压电复合材料或压电聚合物等。其中，压电陶瓷可以是PZT、AlN、ZnO或者其他压电材料。压电薄膜外形可以为圆形、方形或者多边形平面元件。The piezoelectric thin film described in this embodiment may be made of piezoelectric ceramics, piezoelectric single crystals, piezoelectric composite materials or piezoelectric polymers. Wherein, the piezoelectric ceramics may be PZT, AlN, ZnO or other piezoelectric materials. The shape of the piezoelectric film can be a circular, square or polygonal planar element.
在实施例中，耐高压绝缘层没有具体限定，只要能起到在电容极板发生吸合时防止短路并避免被高压击穿即可，例如聚氟乙烯、聚乙烯、聚乳酸等材料。In the embodiment, the high-voltage insulating layer is not specifically limited, as long as it can prevent short circuit and avoid high-voltage breakdown when the capacitor plates are pulled together, such as polyvinyl fluoride, polyethylene, polylactic acid and other materials.
本实施例中器件参数的选择可根据实际应用中所需工作频率的要求以及加工工艺的水平来设定，工作频率越高则换能器单元整体尺寸越小。例如，若要求换能器在pMUT模式下的工作频率为3.5MHz左右(按照结构一设计)，压电薄膜选择AlN材料，则方形薄膜的边长和厚度可以分别为：50μm和0.5μm，70μm和1μm，或者85μm和1.5μm。The selection of device parameters in this embodiment can be set according to the requirements of the working frequency required in practical applications and the level of processing technology. The higher the working frequency, the smaller the overall size of the transducer unit. For example, if the working frequency of the transducer in pMUT mode is required to be about 3.5MHz (according to the design of structure 1), and the piezoelectric film is made of AlN material, the side length and thickness of the square film can be respectively: 50μm and 0.5μm, 70μm and 1 μm, or 85 μm and 1.5 μm.
综上所述，本发明将pMUT和cMUT两种类型的超声换能器工作方式结合在一起，实现多稳态超声检测，可以通过机电控制电路进行低频超声传感和高频超声传感，兼顾了超声检测的深度和分辨率，可以广泛应用于工业、医疗、军事、农业等领域。In summary, the present invention combines the working modes of pMUT and cMUT two types of ultrasonic transducers to realize multi-stable ultrasonic detection, and can perform low-frequency ultrasonic sensing and high-frequency ultrasonic sensing through electromechanical control circuits, taking into account It improves the depth and resolution of ultrasonic detection, and can be widely used in industrial, medical, military, agricultural and other fields.
以上实施例仅用以说明本发明的技术方案，并没有详细叙述所有的细节，也不限制本发明为所述的具体实施方式。显然，根据本说明书的内容可以做很多修改和变型。倘若对于本发明的这些修改和变型属于本发明权利要求及其等同技术的范围之内，则本发明也意图包含这些改动和变型在内。The above examples are only used to illustrate the technical solutions of the present invention, and do not describe all the details in detail, nor limit the present invention to the described specific implementation modes. Obviously, many modifications and variations are possible from the contents of this specification. If these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies, the present invention also intends to include these modifications and variations.
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