CN102607734A - Temperature measuring method and device based on nuclear magnetic resonance principle - Google Patents
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Abstract
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Description
Translated fromChinese技术领域technical field
本发明涉及一种温度测量方法和使用了该温度测量方法的装置。The invention relates to a temperature measuring method and a device using the temperature measuring method.
背景技术Background technique
温度测量是测量领域最重要的功能之一，随着科学技术的发展和现代工业技术的需要，测温技术也不断地改进和提高。目前传统的温度测量方法包括如下几种：热辐射温度测量、电阻温度测量、热电偶温度测量、热胀冷缩的原理的温度测量等。现有的温度测量技术存在灵敏度不高的问题，以常用的铂电阻温度传感器为例，在273K时，铂电阻每欧姆温度系数大约为0.00392Ω·K-1。此温度下电阻为25Ω的铂电阻温度计，温度系数大约为0.1Ω·K-1，欲使所测温度能准确到0.001K，测得的电阻值必须精确到±10-4Ω以内。由于测量电路的限制，测量温度的灵敏度很难提高。Temperature measurement is one of the most important functions in the field of measurement. With the development of science and technology and the needs of modern industrial technology, temperature measurement technology is constantly improving and improving. At present, the traditional temperature measurement methods include the following: thermal radiation temperature measurement, resistance temperature measurement, thermocouple temperature measurement, temperature measurement based on the principle of thermal expansion and cold contraction, etc. The existing temperature measurement technology has the problem of low sensitivity. Taking the commonly used platinum resistance temperature sensor as an example, at 273K, the temperature coefficient of platinum resistance per ohm is about 0.00392Ω·K-1 . A platinum resistance thermometer with a resistance of 25Ω at this temperature has a temperature coefficient of about 0.1Ω·K-1 . To make the measured temperature accurate to 0.001K, the measured resistance value must be accurate within ±10-4 Ω. Due to the limitations of the measurement circuit, it is difficult to improve the sensitivity of measuring temperature.
中国发明专利200980101841.9公开了一种温度测量方法，采用温度敏感的磁性材料放置在被测量位置，通过测量磁场来测量温度的变化。该方法的灵敏度主要由磁场测量灵敏度决定，目前的磁场测量方法除了核磁共振方法外，其它方法灵敏度均较低，因此温度测量的灵敏度也较低。超导量子干涉仪虽然灵敏度较高，但是只适用于对弱磁场的测量，并受环境磁场的严重影响，因此不适用于该方法的温度测量。Chinese invention patent 200980101841.9 discloses a temperature measurement method, which uses a temperature-sensitive magnetic material to be placed at the position to be measured, and measures the temperature change by measuring the magnetic field. The sensitivity of this method is mainly determined by the sensitivity of the magnetic field measurement. Except for the nuclear magnetic resonance method, the current magnetic field measurement methods have low sensitivity, so the sensitivity of temperature measurement is also low. Although the superconducting quantum interferometer has high sensitivity, it is only suitable for the measurement of weak magnetic fields and is seriously affected by the environmental magnetic field, so it is not suitable for the temperature measurement of this method.
发明内容Contents of the invention
为了克服现有技术的缺点，本发明提供一种温度测量方法及其温度测量装置，本发明采用核磁共振原理进行温度测量，可获得非常高的温度测量灵敏度。In order to overcome the shortcomings of the prior art, the present invention provides a temperature measuring method and a temperature measuring device thereof. The present invention adopts the principle of nuclear magnetic resonance for temperature measurement, which can obtain very high temperature measurement sensitivity.
本发明温度测量方法的原理是，将一个内置有信号源的射频线圈放入一个由具有温度敏感性的永久磁体产生的均匀的静磁场中，所述的永久磁体放置在需要测量温度之处。给射频线圈施加一个脉冲功率，该射频线圈产生一个射频场，所述的射频场照射内置的所述的信号源，信号源中的原子核由于核磁共振而受到激发。撤除所述的射频场后，所述的信号源中被激发的原子核辐射出射频信号，所述的射频信号由所述的射频线圈接收，射频信号经过放大和数字滤波，并经过傅立叶变换，可获得所述信号源所辐射的射频信号的频率。由于信号源所辐射的射频信号频率与其所在位置的磁场强度成比例，因此所述信号源所辐射的射频信号的频率可转换为其对应的磁场强度。又因为磁场强度与所述的永久磁体的温度相关，其对应关系可事先标定。将测量得到的磁场强度数据和已标定的温度与磁场强度的对应关系进行比对，经过差值处理，可获得所述的永久磁体当前的温度，以所述的永久磁体当前的温度得到上述需要测量温度之处的温度，从而实现温度测量。The principle of the temperature measurement method of the present invention is that a radio frequency coil with a built-in signal source is placed in a uniform static magnetic field generated by a temperature-sensitive permanent magnet, and the permanent magnet is placed at a place where temperature needs to be measured. A pulse power is applied to the radio frequency coil, and the radio frequency coil generates a radio frequency field, and the radio frequency field irradiates the built-in signal source, and the nuclei in the signal source are excited by nuclear magnetic resonance. After the radio frequency field is removed, the excited nuclei in the signal source radiate radio frequency signals, the radio frequency signals are received by the radio frequency coils, the radio frequency signals are amplified and digitally filtered, and undergo Fourier transform, which can be The frequency of the radio frequency signal radiated by the signal source is obtained. Since the frequency of the radio frequency signal radiated by the signal source is proportional to the strength of the magnetic field at its location, the frequency of the radio frequency signal radiated by the signal source can be converted to its corresponding magnetic field strength. And because the magnetic field strength is related to the temperature of the permanent magnet, the corresponding relationship can be calibrated in advance. Comparing the measured magnetic field strength data with the calibrated corresponding relationship between temperature and magnetic field strength, after difference processing, the current temperature of the permanent magnet can be obtained, and the above-mentioned requirements can be obtained by using the current temperature of the permanent magnet The temperature is measured where the temperature is, thereby enabling temperature measurement.
信号源所辐射的射频信号的频率与磁场关系是：The relationship between the frequency and magnetic field of the radio frequency signal radiated by the signal source is:
λ＝γBλ=γB
其中：λ为磁共振信号频率，γ为旋磁比，B为磁感应强度。Among them: λ is the magnetic resonance signal frequency, γ is the gyromagnetic ratio, and B is the magnetic induction intensity.
基于上述原理，本发明提供一种温度测量方法，其特征在于，将具有温度敏感性的永久磁体放置在需要测量温度的位置，所述的永久磁体用以产生均匀的静磁场，并在所述的永久磁体内放置有包含信号源的射频线圈，测量时，给所述的射频线圈施加一个脉冲功率，使射频线圈产生一个射频场，所述的射频场激励射频线圈内的信号源，信号源辐射射频信号，采集所述的射频信号，放大并转换为数字信号，经过傅立叶变换转换成频率域信号，频率域信号峰值所对应的频率就是所述永久磁体磁场强度所对应的核磁共振频率，通过比对已标定的核磁共振频率与温度的关系，可得到所述的永久磁体的温度，也即上述需要测量温度位置处的温度。Based on the above principles, the present invention provides a temperature measurement method, which is characterized in that a permanent magnet with temperature sensitivity is placed at the position where the temperature needs to be measured, and the permanent magnet is used to generate a uniform static magnetic field, and in the A radio frequency coil containing a signal source is placed in the permanent magnet. During measurement, a pulse power is applied to the radio frequency coil, so that the radio frequency coil generates a radio frequency field, and the radio frequency field excites the signal source in the radio frequency coil, and the signal source Radiate the radio frequency signal, collect the radio frequency signal, amplify and convert it into a digital signal, and convert it into a frequency domain signal through Fourier transform. The frequency corresponding to the peak value of the frequency domain signal is the nuclear magnetic resonance frequency corresponding to the magnetic field strength of the permanent magnet. By comparing the relationship between the calibrated nuclear magnetic resonance frequency and temperature, the temperature of the permanent magnet can be obtained, that is, the temperature at the above-mentioned position where the temperature needs to be measured.
对于1H原子核，旋磁比γ＝42.58MHz/T。For 1H nuclei, the gyromagnetic ratio γ=42.58MHz/T.
该发明的温度测量灵敏度推算如下：对于一个1000Gs的磁场，其对应的信号频率λ＝4.258MHz。若磁场的温度变化为0.5％/C°，则信号频率的变化为Δλ＝21290Hz。接收电路的频率分辨率很容易达到1Hz，因此温度灵敏度可达到4.7×10-5C°。The temperature measurement sensitivity of the invention is estimated as follows: for a 1000Gs magnetic field, its corresponding signal frequency λ=4.258MHz. If the temperature change of the magnetic field is 0.5%/C°, the signal frequency change is Δλ=21290Hz. The frequency resolution of the receiving circuit can easily reach 1Hz, so the temperature sensitivity can reach 4.7×10-5 C°.
由于本发明的温度测量过程是将模拟电平信号通过傅立叶变换转换成频率域信号，因此电路在放大等环节的误差都不影响测量结果，因此温度测量具有很高的精确度。Since the temperature measurement process of the present invention converts the analog level signal into a frequency domain signal through Fourier transform, the errors of the circuit in the amplification and other links will not affect the measurement result, so the temperature measurement has high accuracy.
由于模拟信号是通过傅立叶变换转换成频率域信号的，因此信号线宽会对测量的准确度有一定的影响，因此需要信号的线宽尽量窄。缩小线宽的根本方法就是让静磁场更加均匀，因此在所述永久磁体中设置有匀场装置。基本的匀场装置是采用铁片贴在所述永久磁体的两极上，以此改变磁场的分布，使磁场更加均匀。另一种使磁场均匀的方法是采用多组线圈，调节不同线圈的电流来改变线圈所产生的磁场，从而补偿静磁场的不均匀性，达到改善磁场均匀度的目的。Since the analog signal is converted into a frequency domain signal through Fourier transform, the line width of the signal will have a certain impact on the accuracy of the measurement, so the line width of the signal needs to be as narrow as possible. The fundamental way to reduce the line width is to make the static magnetic field more uniform, so a shimming device is provided in the permanent magnet. The basic shimming device is to stick iron sheets on the two poles of the permanent magnet, so as to change the distribution of the magnetic field and make the magnetic field more uniform. Another way to make the magnetic field uniform is to use multiple sets of coils and adjust the currents of different coils to change the magnetic field generated by the coils, thereby compensating for the inhomogeneity of the static magnetic field and achieving the purpose of improving the uniformity of the magnetic field.
本发明对温度的测量方法，是通过使永久磁体的磁场强度随温度变化来实现的，因此要求该永久磁体所产生的静磁场的强度能够随外界温度的变化而改变。稀土永磁材料一般都具有较大的温度系数，比如一种钕铁硼NdFeB材料的温度系数达到0.3％，也就是外界温度每变化1度，其剩磁Br变化0.3％。从温度测量的角度上讲，需要磁性材料的温度系数越大越好，核磁共振温度传感器的温度灵敏度公式为：The temperature measuring method of the present invention is realized by making the magnetic field strength of the permanent magnet change with temperature, so it is required that the strength of the static magnetic field generated by the permanent magnet can be changed with the change of the external temperature. Rare earth permanent magnet materials generally have a large temperature coefficient. For example, the temperature coefficient of a neodymium-iron-boron NdFeB material reaches 0.3%, that is, when the external temperature changes by 1 degree, its remanence Br changes by 0.3%. From the perspective of temperature measurement, the larger the temperature coefficient of the magnetic material, the better. The temperature sensitivity formula of the NMR temperature sensor is:
η＝1/δγBη=1/δγB
η为温度灵敏度，δ为磁场的温度系数，γ为旋磁比，B为磁感应强度。为使η更小，即灵敏度更高，应使B和δ更大。为此，本发明采用高温度系数的稀土永磁材料，如N35牌号的钕铁棚材料等来制造永久磁体，使用这种材料的另一个好处是比较容易得到高的磁场强度，对提高灵敏度有利。η is the temperature sensitivity, δ is the temperature coefficient of the magnetic field, γ is the gyromagnetic ratio, and B is the magnetic induction. In order to make η smaller, that is, the sensitivity is higher, B and δ should be made larger. For this reason, the present invention adopts the rare-earth permanent magnet material of high temperature coefficient, as the neodymium-iron shed material of N35 brand etc. to manufacture permanent magnet, another benefit of using this material is that it is easier to obtain high magnetic field strength, which is beneficial to improving sensitivity .
本发明温度测量装置采用以下技术方案：The temperature measuring device of the present invention adopts the following technical solutions:
本发明温度测量装置主要由以下部件组成：一个永久磁体，在所述的永久磁体空气隙中产生一个均匀的静磁场，在永久磁体的空气隙中放置一个射频线圈，射频线圈调谐在静磁场所对应的磁共振频率上。射频线圈内置有信号源，信号源是含1H原子核的液体，比如水或者脂肪等物质。一个脉冲发生器输出射频脉冲信号，该射频脉冲信号通过射频功率放大器的信号输入接口进入射频功率放大器，驱动射频功率放大器输出功率脉冲，射频功率放大器与射频线圈连接，该功率脉冲馈入射频线圈，使得射频线圈产生一个射频磁场，用来激发信号源中的1H原子核；被激发的信号源中的1H原子核向外辐射射频脉冲，所辐射的射频脉冲频率就是1H原子核的磁共振频率，该射频脉冲信号由射频线圈接收并经过信号放大与采集处理电路将信号放大，转换为数字信号，经过傅立叶变换为频率域信号，频率域信号频谱的峰值所对应的频率就是磁共振信号的频率。由于磁共振信号的频率跟磁场强度成正比，因此，测量磁共振信号的频率就可得到磁场的强度。而永久磁体的磁场强度是随温度变化的，因此微小的温度变化就可引起磁共振信号频率的变化。信号放大与采集处理电路与射频线圈连接，信号放大与采集处理电路中预先内置有频率与温度对应关系的标定数据表，该信号放大与采集处理电路将所测得信号的频率数据与所存储的标定数据表比较，并通过差值计算，可以获得该频率所对应的温度值，即为所测量的温度。本发明所涉及的永久磁体采用温度系数较高的磁性材料制成，比如稀土永磁材料或铁氧体永磁材料。磁体结构上可采用带轭铁的二极磁体，也可采用halbach结构，其目的是在磁体中央的空气隙中产生均匀的静磁场。为了提高温度的响应速度，尽可能减小磁体的体积，以减少热惯性。减小磁体的空气隙可以有效减小磁体体积，当然，本发明的方法不限于此，即使是大的磁体体积也可以用于温度测量。The temperature measuring device of the present invention is mainly composed of the following components: a permanent magnet, a uniform static magnetic field is generated in the air gap of the permanent magnet, a radio frequency coil is placed in the air gap of the permanent magnet, and the radio frequency coil is tuned to the position of the static magnetic field. corresponding to the magnetic resonance frequency. The RF coil has a built-in signal source, which is a liquid containing 1H nuclei, such as water or fat. A pulse generator outputs a radio frequency pulse signal, the radio frequency pulse signal enters the radio frequency power amplifier through the signal input interface of the radio frequency power amplifier, drives the radio frequency power amplifier to output power pulses, the radio frequency power amplifier is connected with the radio frequency coil, and the power pulse is fed into the radio frequency coil, Make the radio frequency coil generate a radio frequency magnetic field to excite the 1H nucleus in the signal source; the 1H nucleus in the excited signal source radiates radio frequency pulses, and the frequency of the radiated radio frequency pulse is the magnetic resonance frequency of the 1H nucleus. The signal is received by the radio frequency coil and amplified by the signal amplification and acquisition processing circuit, converted into a digital signal, and transformed into a frequency domain signal by Fourier transform. The frequency corresponding to the peak value of the frequency domain signal spectrum is the frequency of the magnetic resonance signal. Since the frequency of the magnetic resonance signal is directly proportional to the strength of the magnetic field, the strength of the magnetic field can be obtained by measuring the frequency of the magnetic resonance signal. The magnetic field strength of a permanent magnet varies with temperature, so a small temperature change can cause a change in the frequency of the magnetic resonance signal. The signal amplification and acquisition processing circuit is connected with the radio frequency coil. The calibration data table of the corresponding relationship between frequency and temperature is built in the signal amplification and acquisition processing circuit in advance. The signal amplification and acquisition processing circuit compares the frequency data of the measured signal with the stored The temperature value corresponding to the frequency can be obtained by comparing the calibration data tables and calculating the difference, which is the measured temperature. The permanent magnets involved in the present invention are made of magnetic materials with high temperature coefficients, such as rare earth permanent magnet materials or ferrite permanent magnet materials. The magnet structure can be a dipole magnet with a yoke or a halbach structure, the purpose of which is to generate a uniform static magnetic field in the air gap in the center of the magnet. In order to improve the temperature response speed, the volume of the magnet should be reduced as much as possible to reduce thermal inertia. Reducing the air gap of the magnet can effectively reduce the volume of the magnet. Of course, the method of the present invention is not limited thereto, and even a large magnet volume can be used for temperature measurement.
本发明所涉及的磁体一般都需要进行磁场均匀的过程，因此需要在磁体的内部设置磁场均匀装置。该磁场均匀装置通过调节匀场片的位置和尺寸，使得空气隙中的磁场更加均匀。另外，可在空气隙的周围布置多组的匀场线圈，通过改变线圈的电流达到调节磁场均匀性的目的。The magnets involved in the present invention generally require the process of making the magnetic field uniform, so it is necessary to install a magnetic field uniforming device inside the magnet. The magnetic field uniform device makes the magnetic field in the air gap more uniform by adjusting the position and size of the shims. In addition, multiple sets of shim coils can be arranged around the air gap, and the purpose of adjusting the uniformity of the magnetic field can be achieved by changing the current of the coils.
通过磁场的均匀过程，可将磁场的均匀性调整到可以获得较窄线宽的程度，比如20ppm或更好，则线宽小于42Hz，若采样100个点，频率分辨率可达到0.42Hz，可获得很高的温度分辨率。Through the uniform process of the magnetic field, the uniformity of the magnetic field can be adjusted to the extent that a narrow line width can be obtained, such as 20ppm or better, the line width is less than 42Hz, and if 100 points are sampled, the frequency resolution can reach 0.42Hz, which can obtain very high temperature resolution.
本发明中在磁体的空气隙中放置有射频线圈，所述的射频线圈的内部有一个信号源。射频线圈的作用是产生射频磁场，用来激发信号源中的1H原子核。射频线圈是一个高频振荡器，具有高的品质因数，线圈的形式可以是螺线管，也可以是鞍形，或者螺线管与鞍形的正交线圈。线圈通过调谐匹配电路工作在谐振频率处，并用来产生射频磁场和接收信号源发出的射频信号。为获得高的效率，信号源应该充满射频线圈的内腔。In the present invention, a radio frequency coil is placed in the air gap of the magnet, and there is a signal source inside the radio frequency coil. The role of the radio frequency coil is to generate a radio frequency magnetic field to excite the 1H nuclei in the signal source. The RF coil is a high-frequency oscillator with a high quality factor. The form of the coil can be a solenoid, a saddle, or a quadrature coil of a solenoid and a saddle. The coil works at the resonant frequency through a tuned matching circuit, and is used to generate a radio frequency magnetic field and receive a radio frequency signal from a signal source. For high efficiency, the signal source should fill the cavity of the RF coil.
本发明包括脉冲序列发生器和射频功率放大器，其中脉冲序列发生器产生一个特定形状、大小和宽度的射频脉冲，驱动射频功率放大器；射频功率放大器与射频线圈连接，将射频功率馈送给射频线圈。一般地，为获得较高的磁共振信号，可将所有信号源的1H原子核激发，由于磁场有一定的不均匀性，需要一个有一定激发带宽的射频脉冲，比如宽度1ms的脉冲，可激发大约1Hz的宽度，对于20ppm以下的磁场均匀度，则可将所有1H核激发，产生足够的信号强度。脉冲序列发生器的脉冲形状可采用固定波形，也可采用外部控制的可编程波形，其大小和宽度也同样固定或可控。The invention includes a pulse sequence generator and a radio frequency power amplifier, wherein the pulse sequence generator generates a radio frequency pulse of a specific shape, size and width to drive the radio frequency power amplifier; the radio frequency power amplifier is connected with the radio frequency coil, and feeds the radio frequency power to the radio frequency coil. Generally, in order to obtain higher magnetic resonance signals, the 1H nuclei of all signal sources can be excited. Due to the inhomogeneity of the magnetic field, a radio frequency pulse with a certain excitation bandwidth is required, such as a pulse with a width of 1ms, which can excite about With a width of 1 Hz, for a magnetic field uniformity below 20 ppm, all 1H nuclei can be excited to generate sufficient signal strength. The pulse trainer can have a fixed waveform or an externally controlled programmable waveform with the same fixed or controllable size and width.
本发明的射频线圈为收发一体的线圈形式，即线圈兼有产生射频场和接收磁共振信号的功能。射频功率放大器通过一个TX/RX开关与射频线圈连接，射频线圈接收的磁共振信号经过一个四分之一波长线与信号放大和采集处理电路连接，将信号输入到信号放大器。The radio frequency coil of the present invention is in the form of a coil integrating transceiver, that is, the coil has the functions of generating a radio frequency field and receiving magnetic resonance signals. The RF power amplifier is connected to the RF coil through a TX/RX switch, and the magnetic resonance signal received by the RF coil is connected to the signal amplification and acquisition processing circuit through a quarter-wavelength line, and the signal is input to the signal amplifier.
本发明包括一个信号放大和采集处理电路，由射频线圈输出的信号输入到信号放大和采集处理电路中。信号放大和采集处理电路主要由A/D转换器，数字正交解调器和傅立叶变换器构成，信号放大和采集处理电路受脉冲发生器的时序控制，并接收脉冲发生器产生的本振信号。射频线圈输出的信号进入到信号放大和采集处理电路的A/D转换器变为数字信号，A/D转换器后面跟随一个数字正交解调器，数字信号进入数字正交解调器后，转换为两路基带正交信号，进入与之相连的傅立叶变换器，变换为频率域信号，并计算出信号的频率，转换为温度值。The invention includes a signal amplification and acquisition processing circuit, and the signal output by the radio frequency coil is input into the signal amplification, acquisition and processing circuit. The signal amplification and acquisition processing circuit is mainly composed of A/D converter, digital quadrature demodulator and Fourier transformer. The signal amplification and acquisition processing circuit is controlled by the timing of the pulse generator and receives the local oscillator signal generated by the pulse generator. . The signal output by the radio frequency coil enters the A/D converter of the signal amplification and acquisition processing circuit to become a digital signal. The A/D converter is followed by a digital quadrature demodulator. After the digital signal enters the digital quadrature demodulator, Convert to two baseband quadrature signals, enter the Fourier transformer connected to them, transform into frequency domain signals, and calculate the frequency of the signals, and convert them into temperature values.
附图说明Description of drawings
图1为核磁共振温度测量装置结构图，图中：101永久磁体，102磁场均匀磁装置，103射频线圈，104信号源，105射频功率放大器，106脉冲发生器，107信号放大和采集处理电路，108TX/RX开关。Fig. 1 is the structural diagram of the nuclear magnetic resonance temperature measuring device, in the figure: 101 permanent magnet, 102 magnetic field uniform magnetic device, 103 radio frequency coil, 104 signal source, 105 radio frequency power amplifier, 106 pulse generator, 107 signal amplification and acquisition processing circuit, 108TX/RX switch.
图2是磁体结构原理图；Fig. 2 is a schematic diagram of the magnet structure;
图3是本发明工作原理图。Fig. 3 is a working principle diagram of the present invention.
具体实施方式Detailed ways
以下结合附图和具体实施方式进一步说明本发明。The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.
图1所示为本发明的温度测量装置结构图。其中，磁体结构如图2所示。磁体是由磁性材料和轭铁构成，或者由不同磁化方向的磁性材料按一定方式排列组成，在空气隙中形成均匀的静磁场。在极板201上，或围绕halbach磁体内腔的圆周布置有磁场均匀装置102。Fig. 1 shows the structure diagram of the temperature measuring device of the present invention. Wherein, the magnet structure is shown in FIG. 2 . The magnet is composed of magnetic material and yoke iron, or is composed of magnetic materials with different magnetization directions arranged in a certain way, forming a uniform static magnetic field in the air gap. On the
在磁体的空气隙中安装射频线圈103，其中在射频线圈103中放置有信号源104，信号源104中充满水或脂肪等包含1H原子核的物质。射频线圈103通过一个TX/RX开关与射频功率放大器105连接，同时通过一根四分之一波长线与信号放大和采集处理电路107连接。脉冲发生器106发出具有特定时序的射频脉冲波形，并控制信号放大和采集处理电路107的工作。A
所述的信号源104中的1H原子核将受到极化，1H原子核的磁矩将围绕外磁场方向进动，1H原子核的磁矩围绕外磁场进动的频率就是拉莫尔频率，拉莫尔频率与外磁场的大小成正比。脉冲发生器106产生一个射频脉冲，驱动射频功率放大器105，将射频功率脉冲传输到射频线圈103上。射频线圈所产生的射频场将1H原子核的磁矩打到垂直于外磁场的横向位置。射频脉冲结束后，1H原子核的磁矩向外磁场方向恢复，并在此过程中在射频线圈上感应出信号，信号的频率就是外磁场对应的拉莫尔频率。The 1H nucleus in the signal source 104 will be polarized, and the magnetic moment of the 1H nucleus will precess around the direction of the external magnetic field. The frequency at which the magnetic moment of the 1H nucleus precesses around the external magnetic field is the Larmor frequency. proportional to the size of the external magnetic field. The
所述的信号经放大后，进入该信号放大采集处理电路的A/D转换器301转换为数字信号，再经过数字正交解调单元302，将高频信号转换为基带信号，同时生成了两路正交信号，两路正交信号通过傅立叶变换单元303，将时域信号变换到频域信号，即可读出信号的频率值。After the signal is amplified, it enters the A/D converter 301 of the signal amplification acquisition processing circuit and converts it into a digital signal, and then passes through the digital quadrature demodulation unit 302 to convert the high-frequency signal into a baseband signal, and simultaneously generates two Two orthogonal signals pass through the Fourier transform unit 303 to transform the time domain signal into a frequency domain signal, and then the frequency value of the signal can be read out.
图2是永久磁体101的结构，图2(A)是带铁轭的二极磁体，图2(B)是Halbach结构的二极磁体。在图2(A)中铁轭202起导磁的作用，极板201对磁场进行均匀作用，在图2(B)中，磁场通过磁性材料的不同磁化方向和一定的排列顺序形成均匀磁场。在两种磁体中，起温度敏感作用的是磁性材料，采用NdFeB永磁材料，具有比较大的温度系数，或者专门制作具有高的温度系数的磁性材料，一般温度系数达到0.1％以上，就具有很高的温度灵敏度，本发明的这一要求与通常的永久磁体正好相反，常规的永久磁体需要温度系数越低越好。当然，一切具有高的温度系数的材料都可以用于本发明中。在磁体结构上，带铁轭的二极磁体具有稳定的磁场均匀性，信号的线宽容易控制，但是重量比halbach结构的要重。Halbach磁体结构轻巧，但是磁场均匀度的稳定性不如带铁轭的二极磁体。两种结构的磁体均可用于温度测量。Fig. 2 is the structure of the
图3是本发明的工作原理图。永久磁体空气隙中产生一个均匀的静磁场，在永久磁体的空气隙中放置一个射频线圈，射频线圈调谐在静磁场所对应的磁共振频率上。射频线圈内置有信号源，信号源是含1H原子核的液体，比如水或者脂肪等物质。一个脉冲发生器与射频功率放大器连接，输出射频脉冲信号，该射频脉冲信号驱动射频功率放大器输出功率脉冲；射频功率放大器与射频线圈连接，该功率脉冲经过一个TX/RX开关馈入射频线圈，使得射频线圈产生一个射频磁场，用来激发信号源中的1H原子核；被激发的信号源中的1H原子核向外辐射射频脉冲，所辐射的射频脉冲频率就是1H原子核的磁共振频率，该射频脉冲信号由射频线圈接收，经过TX/RX开关和一段四分之一波长线，进入一个放大器，信号经过放大，通过A/D转换器转换为数字信号，在经过数字正交解调，进行傅立叶变换，变换为频率域信号，频率域信号频谱的峰值所对应的频率就是磁共振信号的频率。由于磁共振信号的频率跟磁场强度成正比，因此，测量磁共振信号的频率就可得到磁场的强度。而永久磁体的磁场强度是随温度变化的，因此微小的温度变化就可引起磁共振信号频率的变化。信号处理电路中预先内置有频率与温度对应关系的标定数据表，该信号处理电路将所测得信号的频率数据与所存储的标定数据表比较，并通过差值计算，可以获得该频率所对应的温度值，即为所测量的温度。由于温度测量需要信号处理电路有高的稳定性，因此采用数字化的正交解调技术，其电路的频率分辨率高于0.1Hz，可满足温度测量的要求，由于传统的模拟正交解调电路的不稳定，不适合在温度测量中的应用。Fig. 3 is a working principle diagram of the present invention. A uniform static magnetic field is generated in the air gap of the permanent magnet, and a radio frequency coil is placed in the air gap of the permanent magnet, and the radio frequency coil is tuned to the magnetic resonance frequency corresponding to the static magnetic field. The RF coil has a built-in signal source, which is a liquid containing 1H nuclei, such as water or fat. A pulse generator is connected with the radio frequency power amplifier, outputs radio frequency pulse signal, and this radio frequency pulse signal drives the radio frequency power amplifier output power pulse; The radio frequency power amplifier is connected with the radio frequency coil, and this power pulse is fed into the radio frequency coil through a TX/RX switch, makes The radio frequency coil generates a radio frequency magnetic field to excite the 1H nucleus in the signal source; the 1H nucleus in the excited signal source radiates radio frequency pulses outward, and the frequency of the radiated radio frequency pulse is the magnetic resonance frequency of the 1H nucleus. The radio frequency pulse signal It is received by the radio frequency coil, passes through the TX/RX switch and a quarter-wavelength line, and enters an amplifier. The signal is amplified and converted into a digital signal through the A/D converter. After digital quadrature demodulation, Fourier transform is performed. Transformed into a frequency domain signal, the frequency corresponding to the peak value of the frequency domain signal spectrum is the frequency of the magnetic resonance signal. Since the frequency of the magnetic resonance signal is directly proportional to the strength of the magnetic field, the strength of the magnetic field can be obtained by measuring the frequency of the magnetic resonance signal. The magnetic field strength of a permanent magnet varies with temperature, so a small temperature change can cause a change in the frequency of the magnetic resonance signal. The calibration data table of the corresponding relationship between frequency and temperature is built in the signal processing circuit in advance. The signal processing circuit compares the frequency data of the measured signal with the stored calibration data table, and through the difference calculation, the frequency corresponding to the frequency can be obtained. The temperature value is the measured temperature. Since temperature measurement requires high stability of the signal processing circuit, digital quadrature demodulation technology is adopted, and the frequency resolution of the circuit is higher than 0.1Hz, which can meet the requirements of temperature measurement. The instability is not suitable for the application in temperature measurement.
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