Apparatus and method for improving precision of measuring permittivity of sample material

Abstract

An apparatus and method for improving the precision of measuring the permittivity of a sample material. The apparatus for improving the precision of measuring the permittivity of a sample material comprises a voltage-controlled crystal oscillator, a modulation synthesizer, an amplitude stabilization module, a resonant cavity module, a microwave frequency multiplication module and a processor; the voltage-controlled crystal oscillator is used for outputting a first signal of a preset frequency, and separately transmitting to the modulation synthesizer, the microwave frequency multiplication module and the processor the first signal as an external reference signal thereof; the modulation synthesizer is used for receiving the first signal, using the first signal as an external source, and generating an FSK signal on the basis of a control instruction of the processor, the center frequency of the FSK signal being x.****MHz, and x being an odd number less than 10; the amplitude stabilization module is used for receiving the FSK signal output by the modulation synthesizer and measuring the amplitude, so as to output a frequency signal of a stable amplitude to the microwave frequency multiplication module.

Description

Device and method for improving dielectric constant measurement accuracy of sample materials Technical Field

[0001] The present invention relates to the field of circuit technology, and in particular to a device and method for improving the measurement accuracy of the dielectric constant of a sample material. Background Art

[0002] In the traditional resonant cavity indirect method for measuring the dielectric constant of the sample material, as shown in Figures 1 to 3, a microwave signal is usually fed into the resonant cavity using a frequency sweep method under the conditions of the resonant cavity being empty and with the sample added. The corresponding resonance curve is then obtained through resonant detection, and the dielectric constant of the sample material is then indirectly calculated using the characteristic values ​​in the corresponding resonance curve. However, the accuracy of the entire measurement depends to a large extent on the accuracy of f0 and fS.

[0003] As shown in Figure 1, f0, f s are the resonance frequencies of the cavity when empty and with a sample, respectively. f1 and f2 are the half-power point frequencies. The quality factor Q0 of the cavity is defined as: Q s for: Where (f1, f2) and (f3, f4) are the half-power point frequencies of the resonant cavity when it is empty and when the sample to be tested is inserted, respectively.

[0004] However, in reality, the resonance curve of the resonant cavity is not as sharp as in theory, but as shown in Figure 2. As can be seen from Figure 2, the measured f0, f S The value cannot truly reflect the actual resonant frequency value of the resonant cavity center, which will cause errors in the subsequent dielectric constant ε value.

[0005] The above content is only used to assist in understanding the technical solution of the present invention and does not constitute an admission that the above content is prior art.

[0006] Summary of the Invention

[0007] The main purpose of the present invention is to provide a device and method for improving the measurement accuracy of the dielectric constant of a sample material, aiming to solve or partially solve the above-mentioned problems.

[0008] To achieve the above-mentioned object, the present invention provides a device for improving the measurement accuracy of the dielectric constant of a sample material, the device for improving the measurement accuracy of the dielectric constant of a sample material comprising a voltage-controlled crystal oscillator, a modulation synthesizer, an amplitude stabilization module, a resonant cavity module, a microwave frequency multiplication module, and a processor;

[0009] The voltage-controlled crystal oscillator is used to output a first signal of a preset frequency, and transmit the first signal to the modulation synthesizer, the microwave frequency multiplication module, and the processor respectively as their external reference signals;

[0010] The modulation synthesizer is used to receive the first signal and use the first signal as an external source, and generate an FSK signal according to the control instruction of the processor, wherein the center frequency of the FSK signal is x.****MHz, where x is an odd number less than 10;

[0011] The amplitude stabilization module is used to receive the FSK signal output by the modulation synthesizer and perform amplitude detection to output a stable amplitude frequency signal to the microwave frequency multiplication module;

[0012] The resonant cavity module is used to place the sample to be tested and send the detection signal to the processor;

[0013] The processor is configured to generate three low-frequency signals of the same frequency, one of which is a modulation signal and is transmitted to the modulation synthesizer, and the other two are synchronous phase-locked reference signals; the processor is further configured to perform synchronous phase-locked detection on the detection signal received from the resonant cavity module under the action of the synchronous phase-locked reference signal and obtain a correction signal, and transmit the correction signal to the voltage-controlled crystal oscillator to change the frequency of the first signal output by the voltage-controlled crystal oscillator, wherein the frequency of the low-frequency signal is an odd number between 70 Hz and 100 Hz;

[0014] The microwave frequency doubling module receives the amplitude frequency signal sent by the amplitude stabilization module, changes the frequency of the output microwave resonance signal, and transmits the microwave resonance signal to the resonant cavity module.

[0015] Preferably, in the device for improving the measurement accuracy of the dielectric constant of a sample material, the SCLK terminal of the processor is connected to an external clock source; the modulation synthesizer is connected to the processor via its FSELECT terminal, two frequency control registers are provided inside the modulation synthesizer, and the two frequency control registers respectively store two preset signal frequencies F0 and F1, the PSEL0 terminal and PSEL1 terminal of the modulation synthesizer are phase adjustment terminals of the two signal frequencies F1 and F0, respectively, the PSEL0 terminal and PSEL1 terminal are grounded, and the modulation synthesizer further includes an FSYNC terminal and an SDATA terminal respectively connected to the processor;

[0016] The modulation synthesizer is further configured to:

[0017] When a square wave signal is input to the FSELECT terminal, the IOUT terminal of the modulation synthesizer will read the value of F1 or F0 from the two frequency control registers as output, and the phase of the signal will remain unchanged.

[0018] When FSYNC is high, the SCLK and SDATA terminals are in high impedance state;

[0019] When FSYNC is low, the modulation synthesizer will be in the communication state. At this time, when there is a falling edge pulse at the SCLK terminal, the DATA on the data bus SDATA will be written into the data buffer of the modulation synthesizer. Until the last DATA is written, the modulation synthesizer will select F1 or F0 as the output of the IOUT terminal according to the state on the FSELECT terminal.

[0020] Preferably, in the device for improving the measurement accuracy of the dielectric constant of the sample material, the modulation signal is a square wave signal with a duty cycle of 1:1, and the square wave signal is sent to the FSELECT terminal of the modulation synthesizer; the synchronous phase-locked reference signal is used for the synchronous phase-locked reference signal of the servo loop, and the synchronous phase-locked reference signal is a rectangular pulse and has a fixed phase relationship with the square wave signal, but the duty cycle of the synchronous phase-locked reference signal is not 1:1.

[0021] Preferably, in the device for improving the measurement accuracy of the dielectric constant of a sample material, the amplitude stabilization module includes an amplitude detection module and a compensation module, and the amplitude detection module is used to receive the FSK signal output by the modulation synthesizer and perform amplitude detection;

[0022] The compensation module is used to compensate the FSK signal to ensure that the amplitudes of F1 and F2 in the compensated FSK signal are consistent, and to transmit the amplitude frequency signal to the microwave frequency multiplication module.

[0023] Preferably, the device for improving the measurement accuracy of the dielectric constant of a sample material further comprises a D / A control module and an A / D sampling module, wherein two ends of the D / A control module are respectively connected between the voltage-controlled crystal oscillator and the processor, and two ends of the A / D sampling module are respectively connected between the resonant cavity module and the processor;

[0024] The processor is used to transmit the correction signal to the D / A control module in ascending order, so that the voltage-controlled crystal oscillator can realize the output frequency sweep function under the action of the external voltage, and obtain the microwave resonance signal acting on the resonant cavity module after passing through the microwave frequency multiplication module;

[0025] The resonant cavity module is detected by a crystal and then converted by an A / D sampling module to obtain a resonance curve.

[0026] Preferably, in the device for improving the measurement accuracy of the dielectric constant of a sample material, the crystal detection module is further connected between the resonant cavity module and the A / D sampling module, and a programmable gain operation module is further connected between the processor and the D / A control module;

[0027] The programmable gain calculation module is used to perform calculations based on A*U, where A is a fixed parameter whose size is determined by the voltage control slope of the voltage controlled crystal oscillator, and U is the voltage;

[0028] The programmable gain operation module is used to determine an operation value based on the voltage-controlled slope of the voltage-controlled crystal oscillator, so that the operation value is converted by the D / A control module and the output voltage acts on the voltage-controlled crystal oscillator each time, causing the output signal frequency to change. At the same time, the detection frequency of the microwave resonance signal falls within the effective peak range of the resonance curve of the resonant cavity module, that is, is located around the center frequency of the resonant cavity.

[0029] Preferably, in the device for improving the measurement accuracy of the dielectric constant of the sample material, the external voltage of the voltage-controlled crystal oscillator is changed through the D / A control module to change its output frequency, so that the detection frequency of the microwave resonance signal changes, so as to obtain the resonance curve of the resonant cavity module around the center frequency of the resonant cavity.

[0030] Preferably, in the device for improving the measurement accuracy of the dielectric constant of a sample material, the detection signal sent by the resonant cavity module is sampled by the A / D sampling module to obtain voltage values ​​U1 and U2 of the detection signal respectively;

[0031] When U1>U2, U=U2-U1<0, it means that the microwave resonance signal frequency f is greater than the atomic center reference frequency f0 in the resonant cavity module, and the voltage-controlled crystal oscillator needs to be negatively corrected. At this time, the value of A*U is applied to the voltage-controlled crystal oscillator through the programmable gain operation module through the output voltage of the D / A control module, so that its output signal frequency becomes smaller.

[0032] When U1<U2,U=U2-U1> 0, indicating that the microwave resonance signal frequency f is less than the atomic center reference frequency f0 in the resonant cavity module, that is, the voltage-controlled crystal oscillator needs to be positively corrected; at this time, the programmable gain operation module causes the value of A*U to act on the voltage-controlled crystal oscillator through the output voltage of the D / A control module, thereby increasing the output signal frequency.

[0033] Preferably, in the device for improving the measurement accuracy of the dielectric constant of the sample material, when U1=U2, U=U2-U1=0, it means that the microwave resonance signal frequency f has been aligned with the center frequency f0 of the resonant cavity module, that is, there is no need to correct the voltage-controlled crystal oscillator. At this time, the programmable gain operation module makes the value of A*U act on the voltage-controlled crystal oscillator through the output voltage of the D / A control module, so that its output signal frequency does not change.

[0034] In order to achieve the above object, the present invention also provides a method for improving the measurement accuracy of the dielectric constant of a sample material, using the apparatus according to any one of claims 1 to 9 to obtain the parameters in the following formula;

[0035] The calculation formula is as follows: ε=ε′-jε″; (3)

[0036] Where V0, V S are the volumes of the rectangular resonant cavity and the sample to be measured respectively;

[0037] Q0 is:

[0038] Q s for:

[0039] f1 and f2 are the half-power point frequencies of the resonant cavity module when it is idle;

[0040] f3 and f4 are the half-power point frequencies after the resonant cavity module is inserted into the sample to be tested;

[0041] ε is the dielectric constant of the sample material.

[0042] The present invention has at least the following beneficial effects:

[0043] The device for improving the measurement accuracy of the dielectric constant of a sample material provided by the present invention comprises a voltage-controlled crystal oscillator, a modulation synthesizer, an amplitude stabilization module, a resonant cavity module, a microwave frequency doubling module and a processor; the voltage-controlled crystal oscillator is used to output a first signal of a preset frequency, and transmit the first signal to the modulation synthesizer, the microwave frequency doubling module and the processor respectively as their external reference signal; the modulation synthesizer is used to receive the first signal and use the first signal as an external source, and generate an FSK signal according to the control instruction of the processor, wherein the center frequency of the FSK signal is x.****MHz, where x is an odd number less than 10; the amplitude stabilization module is used to receive the FSK signal output by the modulation synthesizer, and perform amplitude detection, so as to output a stable amplitude frequency signal to the microwave frequency doubling module; the resonant cavity module It is used to place the sample to be tested and send the detection signal to the processor; the processor is used to generate three low-frequency signals with the same frequency, one of which is a modulation signal and is transmitted to the modulation synthesizer, and the other two are synchronous phase-locked reference signals; the processor is also used to perform synchronous phase-locked detection on the detection signal received from the resonant cavity module under the action of the synchronous phase-locked reference signal and obtain a correction signal, and send the correction signal to the voltage-controlled crystal oscillator to change the frequency of the first signal output by the voltage-controlled crystal oscillator, and the frequency of the low-frequency signal is an odd number between 70Hz and 100Hz; the microwave frequency multiplication module receives the amplitude frequency signal sent by the amplitude stabilization module, changes the frequency of the output microwave resonance signal, and transmits the microwave resonance signal to the resonant cavity module, so as to achieve improved accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a resonance curve diagram of a resonant cavity under an ideal state in the prior art;

[0045] FIG2 is a resonance curve diagram of a resonant cavity in the prior art;

[0046] FIG3 is a schematic diagram of a device for measuring the dielectric constant of a sample material in the prior art;

[0047] FIG4 is a schematic diagram of a device for improving the measurement accuracy of the dielectric constant of a sample material according to the present invention;

[0048] FIG5 is a DDS serial communication timing diagram of the present invention;

[0049] FIG6 is a phase relationship diagram of several signals generated by the processor of the present invention;

[0050] FIG7 is a schematic diagram of an embodiment of the amplitude stabilization module in FIG4 ;

[0051] FIG8 is a resonance curve diagram provided by the present invention;

[0052] FIG9 is a comparison diagram of various signals provided by the present invention;

[0053] FIG10 is a schematic diagram of another embodiment of a partial structure in FIG4 .

[0054] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0055] In embodiments of the present invention, the term "and / or" describes the association relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0056] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0057] In the embodiments of the present invention, the term "plurality" refers to two or more than two, and other quantifiers are similar.

[0058] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in the embodiments of the present invention, many technical details are provided to enable the reader to better understand the present invention. However, even without these technical details and the various changes and modifications based on the following embodiments, the technical solutions claimed in the present invention can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with each other and referenced to each other under the premise that there is no contradiction.

[0059] The present invention provides a device for improving the measurement accuracy of the dielectric constant of a sample material. Referring to FIG4 , the device for improving the measurement accuracy of the dielectric constant of a sample material includes a voltage-controlled crystal oscillator, a modulation synthesizer, an amplitude stabilization module, a resonant cavity module, a microwave frequency multiplication module, and a processor.

[0060] The voltage-controlled crystal oscillator (VCXO) is used to output a first signal of a preset frequency, and transmit the first signal to the modulation synthesizer, microwave frequency multiplication module, and processor respectively as their external reference signal, thereby achieving synchronization of the entire system. In this embodiment, the output frequency of the VCO is 20 MHz (i.e., the frequency of the first signal is 20 MHz); in other embodiments, the output frequency of the VCO can be set according to other requirements, for example, the output frequency of the VCO can also be 12 MHz, 15 MHz, etc., which is not specifically limited here.

[0061] The modulation synthesizer is used to receive the first signal and use the first signal as an external source of the internal DDS, and generate FSK signals (F1, F2) according to the control instructions of the processor. The center frequency of the FSK signal is x.****MHz, where x is an odd number less than 10. It should be noted that ".****" means that the decimal point of the center frequency is four digits. The center frequency x is an odd number less than 10, for example, it can be 1, 3, 5, 7, or 9. For example, the center frequency of the FSK signal is 3.1234MHz. The voltage-controlled crystal oscillator outputs a 20MHz frequency signal. The modulation synthesizer uses the 20MHz frequency signal output by the voltage-controlled crystal oscillator as the external source of the internal DDS, is controlled by the processor, generates F1 and F2, whose center frequency is 7.1234MHz, and sends them to the amplitude stabilization module.

[0062] The amplitude stabilization module is used to receive the FSK signal output by the modulation synthesizer and perform amplitude detection to output a stable amplitude-frequency signal to the microwave frequency multiplication module. The amplitude stabilization module can perform amplitude detection on the F1 or F2 signal to output a stable amplitude-frequency signal to the microwave frequency multiplication module.

[0063] The resonant cavity module is used to place the sample to be tested and send the detection signal to the processor; in addition, the resonant cavity module can also receive the microwave resonance signal output by the microwave frequency doubling module.

[0064] The processor is configured to generate three low-frequency signals of the same frequency, one of which is a modulation signal and is transmitted to the modulation synthesizer, and the other two are synchronous phase-detection reference signals. The processor is also configured to perform synchronous phase-detection on the detection signal received from the resonant cavity module, using the synchronous phase-detection reference signal, to obtain a correction signal, and transmit the correction signal to the voltage-controlled crystal oscillator to change the frequency of the first signal output by the voltage-controlled crystal oscillator. The low-frequency signal has an odd frequency between 70 Hz and 100 Hz. For example, the low-frequency signal has an odd frequency between 70 Hz and 100 Hz, such as 71 Hz, 73 Hz, 75 Hz, 77 Hz, 79 Hz, 81 Hz, 83 Hz, 85 Hz, 87 Hz, and so on. In this embodiment, three low-frequency signals of 99 Hz are generated, one of which is transmitted to the modulation synthesizer, and the other two are used as reference detection signals. Furthermore, the processor also controls the modulation synthesizer to output an FSK signal, which in turn acts on the microwave frequency-doubling module, causing the frequency of the microwave resonance signal output by the microwave frequency-doubling membrane to change, thereby achieving a frequency sweep function.

[0065] The microwave frequency doubling module receives the amplitude frequency signal sent by the amplitude stabilization module, changes the frequency of the output microwave resonance signal, and transmits the microwave resonance signal to the resonant cavity module.

[0066] In order to more clearly embody the present invention, various aspects are described in detail below.

[0067] (1) Generation of a signal with a center frequency of x.****MHz

[0068] It should be noted that since the resonance center frequency f0 of the resonant cavity module is not an integer value, for example, the resonance center frequency of the resonant cavity module is 7.1234 GHz, the present invention can be more accurate by changing the frequency value of the first signal output by the modulation synthesizer to an adjustable specific value with 4 decimal places, 7.****MHz.

[0069] Specifically, the SCLK terminal of the processor is connected to an external clock source; the modulation synthesizer is connected to the processor through its FSELECT terminal, and two frequency control registers are provided inside the modulation synthesizer. The two frequency control registers respectively store two preset signal frequencies F0 and F1. The PSEL0 and PSEL1 terminals of the modulation synthesizer are phase adjustment terminals of the two signal frequencies F1 and F0 respectively. The PSEL0 and PSEL1 terminals are grounded. The modulation synthesizer also includes an FSYNC terminal and an SDATA terminal respectively connected to the processor;

[0070] More specifically, the present invention connects the SCLK terminal of the processor to an external clock source, ensuring that the stability of the frequency signal at the output terminal IOUT of the modulation synthesizer DDS is consistent with the external clock source. For DDS chips without an internal PLL frequency multiplication link, the frequency of the SCLK terminal input clock source should generally be higher than four times the frequency of the IOUT terminal output signal. For example, if the output signal frequency is 5MHz, the signal frequency of the SCLK clock terminal should be greater than 20MHz to achieve better phase noise. After passing through an external filtering circuit, a relatively pure signal spectrum can be obtained. The FSELECT terminal is the keyed frequency modulation signal input terminal, that is, the modulated square wave signal input terminal. The DDS has two frequency control registers within it, which store pre-set frequency values ​​F0 and F1 in the registers through programming. When a square wave signal is input to the FSELECT terminal (i.e., a rising or falling edge transition), the DDS IOUT terminal will subsequently read the value of F1 or F0 from the frequency control register as output, while maintaining the signal's phase unchanged. PSEL0 and PSEL1 are used to adjust the phase of the two frequency signals F1 and F0. We intend to maintain phase continuity between F1 and F0 during switching, so PSEL0 and PSEL1 are directly grounded in the design. The DDS's primary communication with the outside world (such as the F1 and F0 values) is accomplished via the FSYNC, SCLK, and SDATA terminals. The serial communication timing is shown in Figure 5.

[0071] The modulation synthesizer is further configured to:

[0072] When a square wave signal is input to the FSELECT terminal, the IOUT terminal of the modulation synthesizer will read the value of F1 or F0 from the two frequency control registers as output, and the phase of the signal will remain unchanged.

[0073] When FSYNC is high, the SCLK and SDATA terminals are in high impedance state;

[0074] When FSYNC is at a low level, the modulation synthesizer DDS will be in a communication state. At this time, when there is a falling edge pulse at the SCLK terminal, the DATA hanging on the data bus SDATA will be written into the data buffer of the modulation synthesizer. Until the last DATA is written, the modulation synthesizer will select F1 or F0 as the output of the IOUT terminal according to the state on the FSELECT terminal.

[0075] For DDS chips without an internal PLL multiplication module, the external clock frequency input to the SCLK terminal is the system clock frequency. For example, for a 5MHz output signal, the SCLK clock input signal frequency is 20MHz. The DDS internally has two 32-bit frequency control registers (F0 and F1). In the above serial communication timing, the DATA bit should be 32 bits. Therefore, when the SCLK external input clock frequency is 20MHz, the minimum frequency resolution of the DDS is:

[0076] When IOUT outputs 20MHz, the corresponding 32-bit frequency control register value is all 1s. When outputting 5MHz, the corresponding value is (5MHz / 20MHz)*232. The resulting decimal value is converted to binary, representing the corresponding 32-bit frequency control register value. Based on the serial communication timing, the microprocessor writes the corresponding 32-bit value to the corresponding frequency control register (e.g., F0). Similarly, a 32-bit value can be written to the corresponding frequency control register (e.g., F1) for the other modulated single frequency using a similar method. By varying the level of the DDS pin FSELECT, switching between the internal frequencies F0 and F1 is achieved, thereby outputting a keyed FM signal. The signal that changes the level of the FSELECT pin is generated by the processor.

[0077] (2) Low-frequency signal formation with odd frequency values ​​between 70 Hz and 100 Hz

[0078] To implement keyed frequency modulation and synchronous phase detection, it is necessary to generate a modulation signal and two synchronous phase detection reference signals with a clear and adjustable phase relationship. These signals are generated by a microprocessor using appropriate clock interrupts or frequency division techniques. In this embodiment, three low-frequency signals with the same frequency are shown in Figure 6. As shown in Figure 6, A is the modulation signal, and B and C are the two synchronous phase detection reference signals.

[0079] In this embodiment, the modulation signal is a square wave signal with a duty cycle of 1:1, which is sent to the FSELECT terminal of the modulation synthesizer. The synchronous phase-locked reference signal, used for servo loop synchronous phase-locked detection, is a rectangular pulse with a fixed phase relationship with the square wave signal, but the duty cycle of the synchronous phase-locked reference signal is not 1:1. Taking Figure 6 as an example, in Figure 6, A is a square wave signal with a duty cycle of 1:1, which acts on the FSELECT terminal of the DDS. Signals B and C used for servo loop synchronous phase-locked detection are also rectangular pulses with a fixed phase relationship with signal A, and their duty cycles are not 1:1.

[0080] In this embodiment, the aforementioned signals are implemented using a 16-bit timer within the processor. The machine cycle of the processor used is 0.2 milliseconds. For example, a variable T is defined and looped to implement square wave A in Figure 6 on the corresponding processor pin (e.g., P2.0). Simply invert the level of pin P2.0 (P2.0 = !P2.0) in the corresponding 16-bit timer overflow interrupt response function. Similarly, square wave signals B and C can be implemented on two other processor pins (P2.2 and P2.3). However, signals B and C are phase-shifted relative to P2.0, and their duty cycle is not a 1:1 square wave. This is achieved through "delay," or digital phase shifting. "Delay" is implemented in the processor through fixed machine execution cycle statements. The machine cycle mentioned above is determined by the frequency of the external clock signal added to the processor clock end. In fact, the execution of each statement also involves an execution cycle. Different statements may have 1, 2, or 4 machine cycles depending on the executed command behavior. However, the execution cycle of the same statement is fixed, which provides a guarantee for the "delay" mechanism.

[0081] It should be noted that during the execution of the processor, since many functional statements are inserted into the timer interrupt function, such as "edge judgment" and "assignment", this will result in inconsistent statements to be executed each time the timer interrupt function responds, that is, the total number of machine cycles experienced is inconsistent. From the perspective of stability, this will inevitably cause the generated signals to be unstable. However, since the servo phase-locked reference pulse (P2.2, P2.3) and the keyed frequency modulation signal (P2.0) are closely related in the generation process, even if the frequencies of the signals change, the phase relationship between the synchronous phase-locked reference pulse and the square wave modulation signal is always stable, which is very important for the servo circuit.

[0082] (3) Amplitude stabilization module

[0083] In this embodiment, referring to FIG7 , the amplitude stabilization module includes an amplitude detection module and a compensation module. The amplitude detection module is used to receive the FSK signal output by the modulation synthesizer and perform amplitude detection.

[0084] The compensation module is used to compensate the FSK signal to ensure that the amplitudes of F1 and F2 in the compensated FSK signal are consistent, and to transmit the amplitude frequency signal to the microwave frequency multiplication module.

[0085] Specifically, for FSK-modulated composite signals F1 and F2, the amplitudes of F1 and F2 can first be detected using existing techniques. For example, if the amplitude of F1 is V1 and the amplitude of F2 is V2, then a stable amplitude value V is set in the compensation module. This value is chosen to be (V1 + V2) / N, where N is a multiple greater than 1, such as N = 5. Once this specific V value is determined, it will not change. Because the amplitudes V1 and V2 of the F1 and F2 signals output each time are significantly greater than this value V, this ensures that the amplitudes of F1 and F2 remain consistent after compensation.

[0086] (4) Microwave resonance signal

[0087] The device for improving the measurement accuracy of the dielectric constant of a sample material also includes a D / A control module and an A / D sampling module. The two ends of the D / A control module are respectively connected between a voltage-controlled crystal oscillator and the processor, and the two ends of the A / D sampling module are respectively connected between the resonant cavity module and the processor. The processor is used to transmit the correction signal to the D / A control module in ascending order, so that the voltage-controlled crystal oscillator can realize an output frequency sweep function under the action of an external voltage, and obtain a microwave resonance signal acting on the resonant cavity module after passing through the microwave frequency multiplication module. After the resonant cavity module is subjected to crystal detection, it is converted by the A / D sampling module to obtain a resonance curve.

[0088] The detection signal output by the resonant cavity module is fed to the A / D sampling module for electrical inverse processing, resulting in the resonance curve shown in Figure 8. In Figure 8, F represents the modulation signal x.****MHz (7.****MHz in this embodiment) for the aforementioned integrated modulation control. The frequency of the square wave FM signal (e.g., 99Hz) applied to the FSELECT terminal of the DDS to implement keyed FM determines the speed at which the frequency signal is switched to and from the resonant cavity center frequency.

[0089] For example, taking the resonant cavity center frequency f0 = 6GHz as an example, the processor transmits the signal to the D / A control module in ascending order, and then the voltage-controlled crystal oscillator VCXO realizes the output frequency f under the action of the external voltage. VCXO Sweep function (e.g. f VCXO =20MHJz-23MHz), after passing through the microwave frequency multiplication module, we can obtain f=f VCXO *B (B = 300) = A resonance detection signal of 6 GHz to 6.9 GHz is applied to the resonant cavity module; then, after being detected by a crystal, it is converted by an A / D sampling module to obtain the resonance curve shown in FIG8 .

[0090] It should be noted that, for the sake of convenience, the following uses the modulation signal A frequency of 99Hz and the modulation depth of 7.****MHz as an example, but this does not mean that the frequency of A is limited to 99Hz and the modulation depth is limited to 7.****MHz. In the above process, f is a single frequency. Since the modulation technology is used in the scheme, the modulation signal A frequency is 99Hz and the modulation depth is 7.****MHz. Therefore, after the A / D sampling module converts it, the sampling signal display module displays a modulated waveform. However, when f<f0,f=f0,f> When f0, the obtained sampling signal and the modulation signal acting on the input f have phase and frequency changes.

[0091] As shown in Figure 9, the sampled signal has a similar waveform to the previously described 99Hz modulation signal A, differing only in phase and frequency. By synchronizing the high levels of phase-locked reference signals B and C to sample and compare the levels at points X1 and X2, the processor can determine the relationship between the corresponding feed microwave frequency f and the resonant cavity center frequency f0.

[0092] (5) Program-controlled amplification

[0093] The crystal detection module is also connected between the resonant cavity module and the A / D sampling module, and a programmable gain operation module is also connected between the processor domain and the D / A control module; the programmable gain operation module is used to perform operations based on A*U, where A is a fixed parameter, the size of which is determined by the voltage-controlled slope of the voltage-controlled crystal oscillator, and U is the voltage; the programmable gain operation module is used to determine the operation value based on the voltage-controlled slope of the voltage-controlled crystal oscillator, so that the voltage output by the operation value converted by the D / A control module changes its output signal frequency each time it acts on the voltage-controlled crystal oscillator, and at the same time, the detection frequency of the microwave resonance signal falls within the effective peak range of the resonance curve of the resonant cavity module, that is, is located around the center frequency of the resonant cavity.

[0094] The detection signal sent by the resonant cavity module is sampled by the A / D sampling module to obtain the voltage value of the detection signal. Taking Figure 9 as an example, the detection signal Y from the resonant cavity module is sampled by the A / D sampling module according to X1 and X2 in Figure 9, and the corresponding voltage values ​​U1 and U2 are obtained respectively. The processor reads two synchronous phase-locked reference signals (for example, 99Hz signals), and the voltage values ​​U1 and U2 of the detection signal Y corresponding to the rising edges of B and C. Using U = U2 - U1, the corresponding numerical value and operation symbol can be obtained.

[0095] The programmable gain calculation module performs calculations based on A*U. A is a fixed parameter, and its value is determined by the voltage control slope of the VCXO. That is, the value of A*U should be set based on the specific voltage control slope of the VCXO. When the value of A*U is converted into an output voltage by the D / A control module and applied to the VCXO, the output signal frequency changes, and f=f VCXO *B (B=300) detection frequency falls within the effective peak range of the resonance response curve of the resonant cavity, that is, around the center frequency f0 of the resonant cavity.

[0096] Specifically, it includes the following:

[0097] 1) Open-loop frequency sweep: The D / A control module changes the external voltage of the voltage-controlled crystal oscillator to make its output frequency f VCXO The frequency of the microwave resonance signal changes so that the detection frequency of the microwave resonance signal changes, so as to obtain the resonance curve of the resonance cavity module around the center frequency of the resonance cavity.

[0098] 2) When U1>U2, U=U2-U1<0, it means that the microwave resonance signal frequency f is greater than the atomic center reference frequency f0 in the resonant cavity module, and the voltage-controlled crystal oscillator needs to be negatively corrected. At this time, the value of A*U is applied to the voltage-controlled crystal oscillator through the programmable gain operation module through the output voltage of the D / A control module, so that its output signal frequency becomes smaller.

[0099] 3) When U1<U2,U=U2-U1> 0, indicating that the microwave resonance signal frequency f is less than the atomic center reference frequency f0 in the resonant cavity module, that is, the voltage-controlled crystal oscillator needs to be positively corrected; at this time, the programmable gain operation module causes the value of A*U to act on the voltage-controlled crystal oscillator through the output voltage of the D / A control module, thereby increasing the output signal frequency.

[0100] 4) When U1=U2, U=U2-U1=0, it means that the microwave resonance signal frequency f has been aligned with the center frequency f0 of the resonant cavity module, that is, there is no need to correct the voltage-controlled crystal oscillator. At this time, the programmable gain operation module makes the value of A*U act on the voltage-controlled crystal oscillator through the output voltage of the D / A control module, so that its output signal frequency does not change.

[0101] 5) Closed-loop detection state: According to the above steps 2), 3), and 4) the processor autonomously changes the external voltage value of the VCXO and obtains 100 groups of f values ​​(i.e., f0 values) f1, f2, f3, ..., f100 and then obtains the corresponding average value through arithmetic averaging

[0102] From the above three points, combined with Figure 1, we can know:

[0103] (a) When the microwave resonance signal f moves away from the center frequency f0 of the resonant cavity module (either too low or too high), theoretically, we expect the VCXO to change significantly, causing the microwave resonance signal to approach the center frequency f0 of the resonant cavity more quickly. According to the aforementioned servo locking scheme, the absolute value of the difference U = U2 - U1 will be very large, and the A*U obtained by the programmable gain calculation module will also be very large. The output voltage of the digital-to-analog converter, when applied to the VCXO, will cause its output signal frequency to change significantly, thus satisfying the aforementioned theoretical requirement.

[0104] (b) When the microwave resonance signal f approaches the center frequency f0 of the resonant cavity module (whether it is slightly lower or higher), theoretically, if a large gain correction is applied at this moment, causing the VCXO to undergo a large change, it will be difficult to lock the center frequency value f0. At this time, it is desirable for the VCXO to perform a small gain correction to more accurately bring the microwave resonance signal closer to the center frequency f0 of the resonant cavity module. According to the above servo locking scheme, the absolute value of the difference U = U2 - U1 will be very small at this time, and the A*U obtained by the programmable gain calculation module will also be very small. After the output voltage of the digital-to-analog converter is applied to the VCXO, its output signal frequency will change slightly, thus satisfying the above theoretical requirements.

[0105] In this way, the intelligent program control of the servo gain of the present invention is achieved.

[0106] The present invention also provides a method for improving the measurement accuracy of the dielectric constant of a sample material, using the above-mentioned device to obtain the parameters in the following formula:

[0107] The calculation formula is as follows: ε=ε′-jε″; (3)

[0108] Where V0, V S are the volumes of the rectangular resonant cavity and the sample to be measured respectively;

[0109] Q0 is:

[0110] Q s for:

[0111] f1 and f2 are the half-power point frequencies of the resonant cavity module when it is idle;

[0112] f3 and f4 are the half-power point frequencies after the resonant cavity module is inserted into the sample to be tested.

[0113] ε is the dielectric constant of the sample material.

[0114] The dielectric constant of the sample material can be calculated using the above formula.

[0115] It should be noted that the embodiments of the method for improving the measurement accuracy of the dielectric constant of the sample material provided by the present invention include the embodiments of the above-mentioned device for improving the measurement accuracy of the dielectric constant of the sample material; the beneficial effects of the above-mentioned device for improving the measurement accuracy of the dielectric constant of the sample material can be applied to the method for improving the measurement accuracy of the dielectric constant of the sample material.

[0116] Obviously, the embodiments described above are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, those skilled in the art may make other different forms of changes or modifications without making any creative work, and all of these should fall within the scope of protection of the present invention.

Claims

1. An apparatus for improving the measurement accuracy of the dielectric constant of a sample material, characterized in that, It includes a voltage-controlled crystal oscillator, a modulation synthesizer, an amplitude stabilization module, a resonant cavity module, a microwave frequency multiplier module, and a processor; Among them, the voltage-controlled crystal oscillator is used to output a first signal with a preset frequency, and send the first signal to the modulation synthesizer, the microwave frequency multiplier module, and the processor respectively, as their external reference signal; The modulation synthesizer is used to receive the first signal and use the first signal as an external source, and generate an FSK signal according to the control instruction of the processor. The center frequency of the FSK signal is x.****MHz, where x is an odd number less than 10; The amplitude stabilization module is used to receive the FSK signal output by the modulation synthesizer, and perform amplitude detection, so as to output a stable amplitude-frequency signal to the microwave frequency multiplier module; The resonant cavity module is used to place the sample to be measured, and send a detection signal to the processor; The processor is used to generate three low-frequency signals with the same frequency. One of them is a modulation signal and is sent to the modulation synthesizer, and the other two are synchronous phase discrimination reference signals; the processor is also used to, under the action of the synchronous phase discrimination reference signals, perform synchronous phase discrimination on the received detection signal sent by the resonant cavity module and obtain a correction signal, and send the correction signal to the voltage-controlled crystal oscillator, so that the frequency of the first signal output by the voltage-controlled crystal oscillator changes. The frequency of the low-frequency signal is an odd number between 70Hz and 100Hz; The microwave frequency multiplier module receives the amplitude-frequency signal sent by the amplitude stabilization module, changes the frequency of the output microwave resonance signal, and sends the microwave resonance signal to the resonant cavity module.

2. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 1, characterized in that, The SCLK terminal of the processor is connected to an external clock source; the modulation synthesizer is connected to the processor through its FSELECT terminal. There are two frequency control registers inside the modulation synthesizer. The two frequency control registers respectively store two preset signal frequencies F0 and F1. The PSEL0 terminal and the PSEL1 terminal of the modulation synthesizer are the phase adjustment terminals of the two signal frequencies F1 and F0 respectively. The PSEL0 terminal and the PSEL1 terminal are grounded. The modulation synthesizer also includes an FSYNC terminal and an SDATA terminal respectively connected to the processor; The modulation synthesizer is further configured as: When a square wave signal is input to the FSELECT terminal, the IOUT terminal of the modulation synthesizer will respectively read the values of F1 or F0 from the two frequency control registers as the output, and will keep the phase of the signal unchanged; When FSYNC is at a high level, the SCLK terminal and the SDATA terminal are in a high-impedance state; When FSYNC is at a low level, the modulation synthesizer will be in a communication state. At this time, when there is a falling-edge pulse on the SCLK terminal, the DATA hanging on the data bus SDATA will be written into the data buffer of the modulation synthesizer. Until the last DATA is written, the modulation synthesizer will select F1 or F0 as the output of the IOUT terminal according to the state on the FSELECT terminal.

3. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 1, wherein, The modulation signal is a square wave signal with a duty cycle of 1:1, and the square wave signal is sent to the FSELECT terminal of the modulation synthesizer; the synchronous phase discrimination reference signal is used for synchronous phase discrimination in the servo loop. The synchronous phase discrimination reference signal is a rectangular pulse and has a fixed phase relationship with the square wave signal, but the duty cycle of the synchronous phase discrimination reference signal is not 1:

1.

4. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 1, characterized in that, The amplitude stabilization module includes an amplitude detection module and a compensation module. The amplitude detection module is used to receive the FSK signal output by the modulation synthesizer and perform amplitude detection. The compensation module is used to compensate the FSK signal to ensure that the amplitudes of F1 and F2 in the compensated FSK signal are the same, and send the amplitude-frequency signal to the microwave frequency multiplication module.

5. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 1, characterized in that, It also includes a D / A control module and an A / D sampling module. Two ends of the D / A control module are respectively connected between the voltage-controlled crystal oscillator and the processor, and two ends of the A / D sampling module are respectively connected between the resonant cavity module and the processor. The processor is used to transmit the correction signal to the D / A control module in ascending order, so that the voltage-controlled crystal oscillator realizes the output frequency sweeping function under the action of an external voltage, and obtains a microwave resonance signal acting on the resonant cavity module after passing through the microwave frequency multiplication module. After the resonant cavity module is detected by a crystal detector, a resonance curve is obtained through conversion by the A / D sampling module.

6. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 5, characterized in that, A crystal detector module is also connected between the resonant cavity module and the A / D sampling module, and a programmable gain operation module is also connected between the processor and the D / A control module. The programmable gain operation module is used to perform an operation according to A*U, where A is a fixed parameter, and its value is determined by the voltage control slope of the voltage-controlled crystal oscillator, and U is the voltage. The programmable gain operation module is used to determine the operation value according to the voltage control slope of the voltage-controlled crystal oscillator, so that each time the voltage output after the operation value is converted by the D / A control module acts on the voltage-controlled crystal oscillator to change its output signal frequency, the detection frequency of the microwave resonance signal falls within the effective peak range of the resonance curve of the resonant cavity module, that is, around the center frequency of the resonant cavity.

7. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 6, characterized in that, By changing the external voltage of the voltage-controlled crystal oscillator through the D / A control module to change its output frequency, so as to change the detection frequency of the microwave resonance signal, so as to obtain the resonance curve of the resonant cavity module around the center frequency of the resonant cavity.

8. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 6, characterized in that, The detection signal sent by the resonant cavity module is sampled by the A / D sampling module to obtain the voltage values U1 and U2 of the detection signal respectively. When U1>U2, U = U2 - U1 < 0, it means that the microwave resonance signal frequency f is greater than the atomic center reference frequency f0 in the resonant cavity module, and negative correction needs to be performed on the voltage-controlled crystal oscillator; at this time, the value of A*U is output through the D / A control module by the programmable gain operation module to act on the voltage-controlled crystal oscillator, so that its output signal frequency becomes smaller. When U1 < U2 and U = U2 - U1 > 0, it indicates that the microwave resonance signal frequency f is less than the atomic center reference frequency f0 in the resonant cavity module, that is, positive correction needs to be performed on the voltage-controlled crystal oscillator; at this time, after the value of A*U by the programmable gain operation module is output as a voltage through the D / A control module and acts on the voltage-controlled crystal oscillator, the output signal frequency of the voltage-controlled crystal oscillator becomes larger.

9. The device for improving the measurement accuracy of the dielectric constant of a sample material according to claim 8, characterized in that, When U1 = U2 and U = U2 - U1 = 0, it indicates that the microwave resonance signal frequency f has been aligned with the center frequency f0 of the resonant cavity module, that is, no correction needs to be performed on the voltage-controlled crystal oscillator. At this time, after the value of A*U by the programmable gain operation module is output as a voltage through the D / A control module and acts on the voltage-controlled crystal oscillator, the output signal frequency of the voltage-controlled crystal oscillator does not change.

10. A method for improving the measurement accuracy of the dielectric constant of a sample material, characterized in that, The dielectric constant uses the device described in any one of claims 1 to 9 to obtain the parameters in the following formula; The calculation formula is as follows: ε = ε′ - jε″; (3) where V0 and V S are the volumes of the rectangular resonant cavity and the sample to be measured, respectively; Q0 is: Q s is: f1 and f2 are respectively the half-power point frequencies when the resonant cavity module is empty; f3 and f4 are respectively the half-power point frequencies after the test sample is inserted into the resonant cavity module; ε is the dielectric constant of the sample material.

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