A material complex dielectric constant measurement system

Abstract

A material complex dielectric constant measurement system belongs to the field of microwave dielectric measurement technology. The system includes: a self-resonant oscillator, a phase-locked loop and an envelope detector. The self-resonant oscillator includes a resonator, a first radio frequency amplifier and a first power divider; the two ends of the resonator are respectively connected to the output end of the first radio frequency amplifier and the input end of the first power divider; the phase-locked loop includes a mixer, a low-pass filter and a voltage-controlled oscillator. The phase-locked loop and the envelope detector are used to demodulate the signal and map the signal frequency and power to a DC voltage. The phase-locked loop control voltage and the envelope detector output voltage are measured using a voltmeter to obtain the relationship between the material complex dielectric constant and the voltage. The phase-locked loop control voltage can be measured from the voltage control end of the voltage-controlled oscillator. This solution has a simple structure, a small size and is easy to carry. It is suitable for rapid on-site measurement and mobile applications. The measurement results are more comprehensive and the system has higher measurement accuracy and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave dielectric measurement, and in particular relates to a material complex dielectric constant measurement system. Background Art

[0002] In the field of engineering, dielectric constant is an important representation of material properties, which can often provide us with a lot of valuable information. Therefore, accurate dielectric constant measurement has also brought many wide applications, such as food quality testing, biomaterial testing, blood sugar testing, etc. Among them, dielectric detection methods based on microwave technology, such as the resonant cavity perturbation method, have received increasing attention in recent years due to their unique non-contact and non-destructive characteristics.

[0003] At present, there are two main methods for dielectric constant measurement: one is the passive method: this method is mainly to indirectly derive the dielectric constant by measuring the absorption and reflection of the material to the microwave resonator transmission signal. In recent years, compact planar sensors such as split ring resonator (SRR), microstrip LC resonator, complementary split ring resonator (CSRR) and substrate integrated waveguide (SIW) cavity have been proposed. However, these passive sensors must be connected to a vector network analyzer (VNA) to obtain the magnitude of the resonant frequency or transmission coefficient to calculate the complex dielectric constant. For Internet of Things (IOT) or sensor network applications, these VNA-based sensing solutions are expensive. The second is the active method: its purpose is to avoid the use of VNA. Common methods include active sensors with capacitive sensors, sensor voltage-controlled oscillators (VCOs) with phase-locked loops (PLLs), microwave dielectric constant sensors based on CMRC structures, and liquid dielectric constant measurement systems based on SIW resonators. However, since the phase-locked loop is used to transfer the frequency deviation to a DC voltage, sensors based on the phase-locked loop can only measure the real part of the dielectric constant. However, the dielectric constant consists of a real part and an imaginary part, and the limited measurement capability, that is, only measuring the real part of the dielectric constant, makes it difficult to characterize the complete liquid properties. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention provides a material complex dielectric constant measurement system, which has a simple structure, a compact size and is easy to carry, is suitable for on-site rapid measurement and mobile applications, has more comprehensive measurement results, and has higher measurement accuracy and stability.

[0005] In order to achieve the purpose of the present invention, the following scheme is proposed:

[0006] A material complex dielectric constant measurement system, comprising: an autoresonant oscillator, a phase-locked loop and an envelope detector;

[0007] The self-resonant oscillator includes a resonator, a first radio frequency amplifier and a first power divider; the resonator is used to generate a resonant frequency, and its two ends are respectively connected to the output end of the first radio frequency amplifier and the input end of the first power divider, and an output end of the first power divider is connected to the first radio frequency amplifier;

[0008] Another output end of the first power divider is connected to a second radio frequency amplifier and a second power divider in sequence, and one output end of the second power divider is connected to an envelope detector;

[0009] The phase-locked loop includes a mixer, a low-pass filter and a voltage-controlled oscillator, the other output end of the second power divider is connected to the radio frequency input end of the mixer, the radio frequency output end of the mixer is connected to the input end of the low-pass filter, the output end of the low-pass filter is connected to the voltage control end of the voltage-controlled oscillator, and the output end of the voltage-controlled oscillator is connected to the intrinsic input end of the mixer;

[0010] The phase-locked loop and envelope detector are used to demodulate the signal and map the signal frequency and power to a DC voltage. A voltmeter is used to measure the phase-locked loop control voltage and the envelope detector output voltage to derive the relationship between the material's complex dielectric constant and voltage. The phase-locked loop control voltage can be measured from the voltage control terminal of the voltage-controlled oscillator.

[0011] The beneficial effects of the present invention are:

[0012] 1. The resonator adopts a multi-coupling complementary open-loop structure design, and optimizes the performance of the resonator by using multi-coupling and complementary design. Compared with the traditional single resonator structure, this design can provide higher measurement sensitivity, accuracy and more concentrated electric field distribution. The resonator can more accurately measure the complex dielectric constant of the material in the microwave circuit, significantly improving the accuracy and reliability of material analysis. Through complementary design and multi-coupling strategy, the resonator provides excellent frequency stability, reduces frequency drift caused by environmental changes or device aging, and thus improves the reliability of long-term measurement.

[0013] 2. The complex dielectric constant can be measured simultaneously, solving the problem of incomplete dielectric information characterization in traditional PLL sensor-based solutions. This solution uses a new microwave measurement system that can accurately measure the complex dielectric constant of materials. Unlike traditional PLL sensor-based methods that can only measure the real part, this solution can simultaneously obtain the real and imaginary parts of the dielectric constant, thereby improving the integrity and accuracy of dielectric performance characterization.

[0014] 3. The measurement accuracy and stability of the system are significantly improved by using a feedback self-resonant oscillator to generate the modulation signal, a phase-locked loop and an envelope detector to jointly demodulate the technology, and an active low-pass filter with a high-precision op amp. The phase-locked loop technology effectively stabilizes the signal frequency, reduces frequency drift and phase noise, thereby improving the accuracy of the system and reducing the impact of interference. The active low-pass filter achieves effective suppression of high-frequency noise and interference signals through a high-precision op amp, further optimizing the signal-to-noise ratio of the measured data. In addition, the envelope detector plays a role in demodulating power information, enabling the system to achieve accurate demodulation of dual-channel signals. This comprehensive application significantly improves the overall performance of the system, meets the needs for high-precision and high-stability measurements, and is suitable for demanding application scenarios.

[0015] 4. Make the dielectric measurement device low-cost and portable. The device of the present invention has a simple design structure, a small size and is easy to carry, and is suitable for on-site rapid measurement and mobile application.

[0016] 5. Real-time measurement function: The self-resonance signal is converted into a DC signal through a phase-locked loop and an envelope detector. The measurement result is directly displayed as the complex dielectric constant or concentration of the substance using AD sampling in conjunction with the single-chip microcomputer MCU.

[0017] 6. Rich test objects, diverse detection objects, and diverse application scenarios. In addition to detecting the dielectric constant of liquid materials, solid materials can also be placed directly on the resonator to detect changes in the solid dielectric constant. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present invention.

[0019] Figure 1 Shown is a system block diagram of the present application.

[0020] Figure 2 The simulated and measured images of the resonator are shown.

[0021] Figure 3 The results of resonator measurements of methanol and ethanol are shown.

[0022] Figure 4 The methanol and ethanol spectra of the autoresonant oscillator output are shown.

[0023] Figure 5 The graph shows the test results of the self-resonant oscillator on methanol and ethanol.

[0024] Figure 6 The circuit test results of the phase-locked loop are shown.

[0025] Figure 7A graph showing overall test results for methanol and ethanol is shown.

[0026] Figure 8 The fitting curves of the real part of the methanol dielectric constant and the methanol loss tangent are shown.

[0027] Fig. 9 The fitting curve of the real part of the ethanol dielectric constant and the ethanol loss tangent is shown. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present invention more clear, the implementation modes of the present invention are described in detail below with reference to the accompanying drawings. However, the embodiments described in the present invention are only part of the embodiments of the present invention, rather than all the embodiments.

[0029] Embodiment 1, as Figure 1 As shown, a material complex dielectric constant measurement system includes: an autoresonant oscillator, a phase-locked loop, an envelope detector and a human-computer interaction part.

[0030] The self-resonant oscillator includes a resonator, a first radio frequency amplifier and a first power divider; the resonator is used to generate a resonant frequency, and its two ends are respectively connected to the output end of the first radio frequency amplifier and the input end of the first power divider through a 50-ohm coaxial line, and one output end of the first power divider is connected to the first radio frequency amplifier through a 50-ohm coaxial line. The operating voltage of the first radio frequency amplifier is 5V, and the gain flatness is less than 0.1dB in the system operating frequency band, providing a 20dB measurement power gain. It is used to compensate for the loss caused by the resonator and meet the loop gain requirements of the Barkhausen oscillation criterion. In the prior art, a voltage-controlled oscillator is usually used to generate a signal. The signal stability generated by this type of structure is relatively low. The circuit of the self-resonant oscillator of this scheme uses a self-excited oscillation feedback circuit to generate a signal, and the signal is stabilized by introducing positive feedback. A container is provided on the top of the resonator for carrying the medium to be tested. Preferably, the container is made of 3D printing.

[0031] The other output end of the first power divider is connected to the second RF amplifier and the second power divider in sequence. Specifically, the other output end of the first power divider is connected to the input end of the second RF amplifier, the output end of the second RF amplifier is connected to the input end of the second power divider, and one output end of the second power divider is connected to the envelope detector.

[0032] The phase-locked loop includes a mixer, a low-pass filter and a voltage-controlled oscillator (VCO). The other output end of the second power divider is connected to the RF input end of the mixer, and the RF output end of the mixer is connected to the input end of the low-pass filter. Preferably, in this solution, the low-pass filter adopts an active low-pass filter, and the output end of the low-pass filter is connected to the voltage control end of the voltage-controlled oscillator, and the output end of the voltage-controlled oscillator is connected to the intrinsic input end (LO) of the mixer.

[0033] The phase-locked loop and envelope detector are used to demodulate the signal and map the signal frequency and power to a DC voltage. The phase-locked loop control voltage and the envelope detector output voltage are measured using a voltmeter to obtain the relationship between the material's complex dielectric constant and voltage, thereby avoiding the use of a vector network analyzer. The phase-locked loop control voltage can be measured from the voltage control terminal of the voltage-controlled oscillator.

[0034] The human-computer interaction part is equipped with a display device and an MCU that collects and processes the demodulator output signal, and displays it clearly and in real time through an OLED display. Specifically, the MCU uses an STM32F103C8T6 microcontroller, which can also be replaced by other processor models. The processor provides powerful computing performance with a main frequency of up to 72MHz. Its integrated 12-bit analog-to-digital converter (ADC) has a 4096-level resolution, ensuring extremely high-precision sampling of the sensor output voltage.

[0035] Preferably, the resonator is an open-loop structure, which includes at least three coupling rings arranged from the inside to the outside, and the coupling points on adjacent coupling rings are staggered. The use of the above-mentioned multi-coupling design can effectively reduce the impact of external interference on the measurement results and provide more accurate complex dielectric constant data. In addition, the open-loop resonator structure simplifies the system design, reduces complexity and cost. This technology shows extremely high performance advantages in microwave circuit material measurement and provides a reliable solution for high-precision material analysis and optimization.

[0036] Specifically, the resonator is made of RO4350 plate with a thickness of less than 1 mm, and the bottom thereof is a copper-clad area. In this embodiment, a Rogers RO4350 plate with a thickness of 0.762 mm is used.

[0037] The above system works as follows:

[0038] First, the resonant frequency is generated by the resonator of the passive device. By placing the material to be tested with different complex dielectric constants (ε' and ε'') inside or on it, its frequency and power response can be changed. This change in frequency and power response will cause the output signal frequency and power of the self-resonant oscillator to change, thereby obtaining different output frequencies and powers. Here, the self-resonant oscillator is used as a signal generating device. Then, the phase-locked loop and envelope detector are used as signal demodulators, where the phase-locked loop is used for FM demodulation and the envelope detector is used for AM demodulation, and the signal frequency and power are mapped to the DC voltage. The voltage information is collected and data processed using AD sampling in conjunction with the STM32F103C8T6 microcontroller; finally, the complex dielectric constant or concentration relationship of the material can be directly displayed through the OLED.

[0039] Embodiment 2: The self-resonant oscillator as a signal generating device mainly includes two working contents: a sensing unit and a signal generating unit.

[0040] The sensing unit, including a resonator with a multi-coupled complementary open-loop structure, is suitable for measuring the complex dielectric constant of materials in microwave circuits. The main advantages of the resonator include its high sensitivity, superior frequency stability and excellent measurement accuracy. Because of the multi-coupling design, the resonator can effectively reduce the impact of external interference on the measurement results and provide more accurate complex dielectric constant data. In addition, the open-loop resonator structure simplifies the system design, reduces complexity and cost. This technology shows extremely high performance advantages in the measurement of microwave circuit materials and provides a reliable solution for high-precision material analysis and optimization. The resonator model uses Rogers RO4350 sheet with a thickness of 0.762mm and a copper-clad area at the bottom; the fine-tuning size can be replaced with a cheaper fr4 sheet to further reduce costs. The multi-coupling design means that the resonator includes three coupling rings arranged on the inner and outer sleeves, and the coupling points of the coupling rings are staggered with each other. The resonator is simulated and verified, and the results are as follows Figure 2 As shown, it is shown that the resonance points corresponding to S11 and S21 of the resonator are at 2.56g.

[0041] In order to verify the response of the resonator to solutions with different complex dielectric constants, a vector network analyzer (VNA) was used to measure the S parameters of the resonator. During verification, the two ports of the resonator were connected to the vector network analyzer (VNA), and the solution to be tested was injected into the container above the resonator. In this embodiment, methanol and ethanol solutions were used for verification. The forward transmission coefficient S21 was measured using a vector network analyzer. The measurement results are shown in Figure 2. Figure 3 As shown. The experimental results show that as the concentration of the solution increases, the resonant frequency of the resonator increases, while the forward transmission coefficient decreases. This shows that the frequency of the signal output will increase with the increase of concentration, while the output power will decrease accordingly. This phenomenon is particularly obvious in the application of the self-resonant oscillator as a signal generating device, which is reflected in the increase of the signal output frequency and the decrease of the output power. This change can be attributed to the influence of the complex dielectric constant of the solution on the electromagnetic field distribution inside the resonator and its electrical properties, thereby affecting the working state and signal characteristics of the resonator. The real part of the dielectric constant will affect the resonant frequency of the resonator. The larger the real part, the lower the resonant frequency; the change of the loss tangent will affect the size of the forward transmission coefficient S21. The larger the loss tangent, the greater the corresponding loss, and the smaller the forward transmission coefficient S21.

[0042] Signal generation, in order to realize a self-resonant oscillator with dielectric sensing capability, Figure 1 The resonator in the sensor oscillator design is considered as the frequency selective element, which acts like a bandpass filter. The circuit of the sensor oscillator developed based on the feedback loop oscillator is shown in Figure 1. Figure 1As shown in the self-resonant circuit. Figure 1 The self-resonant oscillator shown is composed of a resonator, a first radio frequency amplifier, and a first power divider, wherein the two ends of the resonator are connected to the output end of the first radio frequency amplifier and the input end of the first power divider through a 50-ohm coaxial line, and one output end of the first power divider is connected to the input end of the first radio frequency amplifier through a 50-ohm coaxial line. The operating voltage of the first radio frequency amplifier is 5V, and the gain flatness is 0.1dB within the system operating frequency band. A measured power gain of 20dB is provided. It is used to compensate for the loss caused by the resonator and meet the loop gain requirements of the Barkhausen oscillation criterion. Similarly, the coaxial line connected to the resonator and the first radio frequency amplifier is designed to meet the ring phase requirements.

[0043] In order to test the designed self-resonant oscillator and verify the relationship between the output signal and the solution concentration (dielectric constant), a spectrum analyzer test is used for verification. First, the solution to be tested is injected into the container and measured using a spectrum analyzer. The output spectrum of methanol and ethanol at different concentrations is measured using a spectrum analyzer. Figure 4 The measurement results are shown in Figure 5 As shown. The results show that as the concentration of the solution increases, the frequency of the output signal of the self-resonant oscillator increases and the power decreases. The reason for this result is that as the concentration of the solution increases, the real part of the dielectric constant will decrease, thereby increasing the resonant frequency of the resonator; and its loss tangent will increase, so the change in the loss tangent will reduce the forward transmission coefficient S21 of the resonator, so the output power will become smaller. These phenomena are Figure 3 The figure shows the change of the resonator S parameter with the complex dielectric constant of the solution, which specifically verifies the effect of solution concentration on the resonator performance. The self-resonant oscillator of this scheme uses a self-excited oscillation feedback circuit to generate signals. By introducing positive feedback, the signal is made more stable. Compared with the method of using a voltage-controlled oscillator to generate signals, the signal is more stable.

[0044] In Embodiment 3, the principle of demodulating the signal by the phase-locked loop and the envelope detector is as follows:

[0045] The phase-locked loop demodulates the FM signal. As a frequency demodulator, the phase-locked loop can be understood as a circuit that stabilizes the oscillation frequency. It can adjust the oscillation frequency of the voltage-controlled oscillator by outputting a feedback voltage, so that the phase-locked loop is fixed at a fixed frequency. When the output frequency of the voltage-controlled oscillator is equal to the output signal frequency of the self-resonant oscillator, the phase-locked loop circuit reaches a stable locked state, and the feedback voltage remains stable. In this state, the phase-locked loop reaches a locked state, and the output frequency of the voltage-controlled oscillator is stabilized at a value equal to the output frequency of the self-resonant oscillator. The control voltage of the voltage-controlled oscillator in the locked state corresponds to the high or low frequency of the signal, and the high or low frequency is determined by the real part of the complex dielectric constant, so that the original complex dielectric constant real part information can be mapped to the voltage. In this embodiment, the voltage-controlled oscillator is designed using YSGM232508 of Innoson, and the power supply voltage is 5V; the low-pass filter is an active type, and the operational amplifier OPA627AP is used to optimize the gain stability and noise performance of the filter, and improve its ability to suppress high-frequency signals, so as to achieve more accurate frequency response control and lower total harmonic distortion, and significantly improve the quality and stability of the signal. This design makes the filter perform well in the application scenarios of high-precision measurement systems.

[0046] When verifying the phase-locked loop, use a 50-ohm coaxial line to connect the microwave signal source to the RF input of the mixer, connect the RF output of the mixer to the input of the active low-pass filter, connect the output of the active low-pass filter to the voltage control terminal of the voltage-controlled oscillator, and connect the output of the voltage-controlled oscillator to the intrinsic input of the mixer. Use a multimeter to measure the control voltage of the voltage-controlled oscillator. The test results are as follows: Figure 6 As shown in the figure, the results show that when the input power is kept at 8dBm, the frequency of the input signal is changed, and the control voltage of the voltage-controlled oscillator increases approximately linearly with the increase of frequency, so the designed phase-locked loop can map the change of signal frequency to voltage approximately linearly. This relationship verifies the rationality of the phase-locked loop as a signal demodulator, which can map the frequency deviation of the output signal of the self-resonant circuit caused by the change of the real part of the material dielectric to the voltage deviation.

[0047] The microwave envelope detector demodulates the AM signal. The microwave envelope detector is an electronic device used to detect and measure the amplitude change of microwave signals. Its working principle is similar to that of the envelope detector in ordinary electronics, but it is suitable for higher frequency microwave signals. The basic principle of the microwave envelope detector is to convert the high-frequency microwave signal into a DC signal, so that the envelope of the signal (i.e., the amplitude change) passes through a low-pass filter, and a DC signal is obtained, whose amplitude changes with the amplitude change of the input microwave signal, that is, the envelope of the input microwave signal. In this way, the change of the original dielectric constant loss tangent can be corresponded to the change of the detector voltage value.

[0048] The above-mentioned frequency demodulator based on phase-locked loop and the power demodulator based on microwave envelope detector form a dual-channel demodulator to demodulate the FM and AM modulation signals generated by the self-resonant oscillator signal. Specifically, the frequency modulation signal is converted into a voltage corresponding to the real part of the complex dielectric constant, and the amplitude modulation signal is also converted into a voltage corresponding to the imaginary part of the complex dielectric constant. In the existing technology, only the real part of the dielectric constant is usually detected, and the dielectric property characterization is incomplete. And the use of a phase-locked loop as a demodulator greatly improves the accuracy and stability of demodulation.

[0049] By measuring the phase-locked loop control voltage and the envelope detector output voltage with a voltmeter, the relationship between the complex dielectric constant and the voltage can be obtained, thus avoiding the use of a vector network analyzer. Figure 1 The two output voltages (ADC) are measured, the solution to be tested is injected into the container, and the voltage of the phase-locked loop control voltage and the envelope detector measured by the digital multimeter are read. The overall test results are as follows: Figure 7 As shown, is the control voltage of the phase-locked loop, which corresponds to the change in the real part of the dielectric constant, that is, the change in frequency. is the output voltage of the envelope detector, which corresponds to the change in the loss tangent, that is, the change in power. The test results show that as the concentration of the solution increases, the output voltage of the phase-locked loop increases and the output voltage of the envelope detector decreases. This also verifies that the frequency of the output signal of the self-resonant oscillator increases and the power decreases as the concentration of the solution increases. Here, the signal of the self-resonant oscillator is successfully demodulated to voltage, which conforms to the law of the output signal of the self-resonant circuit.

[0050] Embodiment 4, human-computer interaction and data processing, in order to make the measuring device more portable and easy to use, an MCU is used to collect and process the demodulator output signal.

[0051] The data processing content is as follows. In order to predict the dielectric constant of the unknown solution, the sensor needs to be calibrated. Therefore, the complex dielectric constant information corresponding to 20%, 40%, 60%, 80%, and 100% concentrations of methanol and ethanol are used to perform curve fitting of the real part and loss tangent. The results are as follows: Figure 8 , Fig. 9 As shown,

[0052] The real part fitting curve equation of methanol dielectric constant is: , where A1=2200.389, A2=-48.787, x0=2.629, d x =0.157.

[0053] Methanol loss tangent fitting curve equation: , where A1=0.580, A2=0.120, x0=1.698, dx =0.035.

[0054] The real part fitting curve equation of ethanol dielectric constant is: , where A1=129.369, A2=7.593, x0=3.127, d x =0.034.

[0055] Ethanol loss tangent fitting curve equation: , where A1=43.368, A2=-0.679, x0=1.025, d x =0.186.

[0056] The voltage back-calculation verification was performed at 10%, 30%, 50%, 70%, and 90% concentrations, and compared with the measurement values ​​of existing commercial dielectric probes. The error results are shown in Tables 1 and 2. The existing commercial dielectric probe uses KEYSIGHT (N1501A). The results show that the maximum errors of the real and imaginary parts of methanol are 3.96% and 2.99%, and the maximum errors of the real and imaginary parts of ethanol are 3.14% and 3.42%.

[0057] Table 1: Comparison of the measurement values ​​of methanol solution by this solution and the existing dielectric probe

[0058]

[0059] Table 2: Comparison of the measurement values ​​of ethanol solution by this solution and the existing dielectric probe

[0060]

[0061] In this embodiment, MCU adopts STM32F103C8T6 microcontroller. The human-computer interaction part accurately calculates and processes the collected voltage data, and this system can accurately derive the value of the complex dielectric constant, and display it clearly and in real time through the OLED display. This configuration not only significantly improves the accuracy and response speed of data acquisition, but also greatly enhances the interactive experience between the user and the system, making the operation more intuitive and efficient. This solution directly displays the measured values ​​of the real and imaginary parts of the dielectric constant on the display screen after collecting voltage through MCU and then processing, eliminating cumbersome substitution calculation functions, and truly realizing the real-time measurement and portable measurement of the complex dielectric constant, and at a lower cost.

[0062] The above description is only a preferred embodiment of the present invention, and is not intended to be the only one or to limit the present invention. Those skilled in the art should understand that various changes or equivalent substitutions made to the present invention without departing from the scope of the present invention are within the scope of protection of the present invention.

Claims

1. A material complex dielectric constant measurement system, characterized in that: include: Autoresonant oscillator, phase-locked loop and envelope detector; The self-resonant oscillator includes a resonator, a first radio frequency amplifier and a first power divider; The resonator is used to generate a resonant frequency, and its two ends are respectively connected to the output end of the first radio frequency amplifier and the input end of the first power divider, and one output end of the first power divider is connected to the first radio frequency amplifier; Another output end of the first power divider is connected to a second radio frequency amplifier and a second power divider in sequence, and one output end of the second power divider is connected to an envelope detector; The phase-locked loop includes a mixer, a low-pass filter and a voltage-controlled oscillator, the other output end of the second power divider is connected to the radio frequency input end of the mixer, the radio frequency output end of the mixer is connected to the input end of the low-pass filter, the output end of the low-pass filter is connected to the voltage control end of the voltage-controlled oscillator, and the output end of the voltage-controlled oscillator is connected to the intrinsic input end of the mixer; The phase-locked loop and envelope detector are used to demodulate the signal and map the signal frequency and power to a DC voltage. A voltmeter is used to measure the phase-locked loop control voltage and the envelope detector output voltage to derive the relationship between the material's complex dielectric constant and voltage. The phase-locked loop control voltage can be measured from the voltage control terminal of the voltage-controlled oscillator.

2. A material complex dielectric constant measurement system according to claim 1, characterized in that: The operating voltage of the first RF amplifier is 5V, the gain flatness is 0.1dB within the system operating frequency band, and a measured power gain of 20dB is provided.

3. A material complex dielectric constant measurement system according to claim 1, characterized in that: The resonator is an open-loop structure, which includes at least three coupling loops arranged from the inside to the outside, and the coupling points on adjacent coupling loops are staggered.

4. A material complex dielectric constant measurement system according to claim 1 or 3, characterized in that: The resonator is made of RO4350 board with a thickness of less than 1mm and a copper-clad area at the bottom.

5. A material complex dielectric constant measurement system according to claim 1 or 3, characterized in that: A container is provided on the top of the resonator for carrying the medium to be measured.

6. A material complex dielectric constant measurement system according to claim 1, characterized in that: It also includes a human-computer interaction part, which is equipped with a display device and an MCU. The MCU is used to collect and process the demodulator output signal, and display the processing result through the display device. The data processing includes curve fitting of the real part and loss tangent of the complex dielectric constant information corresponding to the material concentration.

7. A material complex dielectric constant measurement system according to claim 1, characterized in that: The phase-locked loop is used for FM demodulation and the envelope detector is used for AM demodulation.

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