Radio-frequency oscillator, liquid electrical parameter measurement circuit, and SAR test device

Abstract

A radio-frequency oscillator, a liquid electrical parameter measurement circuit using same, and an SAR test device, used for testing electrical parameters of a liquid. The radio-frequency oscillator comprises a dielectric resonator (31) and a dielectric test tube (32) connected to the dielectric resonator (31); the dielectric resonator (31) has a test hole (316) penetrating through two ends, two first ports (314), and one second port (315), wherein the first ports (314) are used for accessing a voltage-controlled oscillator loop, and the second port (315) is used for connecting a variable capacitance diode; the dielectric test tube (32) is used for containing a liquid to be tested, and the dielectric test tube (32) penetrates through the test hole (316) of the dielectric resonator (31). The parameter fluctuation of a tissue fluid can influence the oscillation frequency and phase noise level of the oscillator, and the dielectric constant and loss parameter change of the tissue fluid can be calculated by measuring the oscillation frequency and the phase noise level, thereby achieving the purpose of real-time monitoring.

Description

RF oscillator, liquid electrical parameter detection circuit and SAR test equipment Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave detection, and in particular to a radio frequency oscillator, a liquid electrical parameter detection circuit and SAR testing equipment. Background Art

[0002] With the rapid development of communication technology, various electronic devices, especially handheld electronic devices and wearable electronic products, have emerged in an endless stream. This has led to increasingly serious electromagnetic radiation around the human body and an increasing level of radiation, which can pose a threat to human health. Under the influence of external electromagnetic fields, the human body will generate an induced electromagnetic field in its tissues, forming an electric current, which causes electromagnetic waves to be absorbed and dissipated in the body. The human body's absorption intensity of electromagnetic waves is defined as the specific absorption rate (SAR), which specifically means the electromagnetic power absorbed or consumed by a unit mass of human tissue. The equipment that tests the specific absorption rate is called SAR test equipment. SAR test equipment is specifically used to evaluate the electromagnetic radiation levels of mobile phones and tablets. All handheld electronic products must pass SAR testing and certification before they can obtain a marketing license.

[0003] SAR testing equipment primarily consists of a human body phantom, a scanning and positioning device, an electromagnetic sampling device, and data post-processing. The phantom consists of a plastic shell (either a head or abdomen phantom) and simulated tissue fluid. An RF probe or sampling array is placed within the tissue fluid to sample the electromagnetic field within the fluid. Test sampling reveals that the electrical parameters of the fluid, particularly the dielectric constant and loss, significantly influence the distribution and dissipation of the electromagnetic field within the fluid. Only when the fluid electrical parameters meet specific values ​​can the electromagnetic probe's electromagnetic field sampling be accurate, and the resulting SAR value be valuable.

[0004] In early SAR test equipment, the tissue fluid was stored in an open container. Long-term use can lead to changes in concentration due to evaporation, and foreign substances can easily intrude and cause contamination. Furthermore, tissue fluid contains organic substances such as sugar and ethylene glycol, which inevitably deteriorate over time. These factors can cause changes in the fluid's electrical parameters. Deteriorated tissue fluid needs to be discarded and replaced.

[0005] The new international standard (IEC 62209-3) currently stipulates that tissue fluid should be sealed and internalized, which can prevent external contamination to a certain extent, thus extending the shelf life.

[0006] However, whether in an open or closed configuration, whether and when to replace tissue fluid is often determined empirically. If the tissue fluid is deteriorating and not replaced promptly, the SAR results will be completely unreliable. Furthermore, within the microwave frequency range, the dielectric constant of tissue fluid varies with temperature, decreasing by 0.5% for every degree Celsius increase in temperature. Therefore, during SAR testing, the temperature of the fluid must not fluctuate by more than 2°C. To ensure that tissue fluid electrical parameters remain within acceptable ranges, they should be monitored periodically, ensuring that tissue fluid monitoring and SAR testing are completed within 24 hours. Technical issues

[0007] The purpose of the present invention is to provide a radio frequency oscillator that can improve the accuracy of liquid electrical parameter detection, and a liquid electrical parameter detection circuit and SAR testing equipment using the radio frequency oscillator. Technical Solutions

[0008] To achieve the above objectives, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a radio frequency oscillator for testing the electrical parameters of a liquid, comprising a dielectric resonator and a dielectric test tube connected to the dielectric resonator; the dielectric resonator has a test hole running through both ends, two first ports and a second port, wherein the first port is used to connect to a voltage-controlled oscillator loop, and the second port is used to connect to a varactor diode; the dielectric test tube is used to hold the liquid to be tested, and the dielectric test tube is passed through the test hole of the dielectric resonator.

[0010] In one embodiment, a plurality of dielectric resonators are provided, each dielectric resonator is stacked and has a different resonant frequency, and the dielectric test tube is passed through the test hole of each dielectric resonator to connect the dielectric resonators in series.

[0011] In one embodiment, the dielectric resonator includes a metal box and a dielectric resonator body arranged in the metal box, the first port and the second port are opened on the outer periphery of the metal box, the metal box and the dielectric resonator body are both provided with through holes, and the through holes of the metal box and the dielectric resonator body jointly define the test hole.

[0012] In one embodiment, the metal box is circular, the first ports are located at both ends of the diameter of the metal box, and the second port is equidistant from the two first ports.

[0013] In one embodiment, the medium testing tube is a capillary tube made of glass.

[0014] In one embodiment, there are seven dielectric resonators, whose central operating frequencies are 0.5 GHz, 1 GHz, 2 GHz, 3 GHz, 4 GHz, 5 GHz, and 6 GHz, respectively.

[0015] As a second aspect, the present invention provides a liquid electrical parameter detection circuit, including a phase detector, a loop filter, a frequency divider, a voltage-controlled oscillator, a control voltage detection unit and a phase-locked loop, wherein the phase detector is used to access a test signal, the input end of the loop filter is connected to the output end of the phase detector, the input end of the control voltage detection unit is connected to the output end of the loop filter, the voltage-controlled oscillator includes the above-mentioned radio frequency oscillator and an amplifier, the input end of the radio frequency oscillator is connected to the output end of the loop filter, the output end of the radio frequency oscillator is connected to both the phase-locked loop and the frequency divider, and a feedback loop is also formed between the amplifier and the radio frequency oscillator.

[0016] In one embodiment, the control voltage detection unit includes a DC branch, an AC branch and an AD sampling chip, the DC branch includes a low-pass filter, and the low-pass filter is connected between the loop filter and the AD sampling chip; the AC branch includes a narrowband filter and a detector, the input end of the narrowband filter is connected to the loop filter, the input end of the detector is connected to the output end of the narrowband filter, and the output end of the detector is connected to the AD sampling chip.

[0017] In one embodiment, when the radio frequency oscillator is provided with multiple dielectric resonators, it further includes a radio frequency switch, the radio frequency switch including an input end and multiple output ends, the input end of the radio frequency switch is connected to the frequency divider; the multiple output ends of the radio frequency switch are connected to each of the dielectric resonators in a one-to-one correspondence, and each dielectric resonator is connected to a phase-locked loop and a loop filter.

[0018] As a third aspect, the present invention also provides a SAR testing device, comprising a simulated spherical shell, an electromagnetic field sampling array and the above-mentioned liquid electrical parameter detection circuit; the simulated spherical shell is a closed structure, used to accommodate simulated liquid simulating human tissue fluid; the electromagnetic field sampling array and the liquid electrical parameter detection circuit are both arranged in the simulated spherical shell and immersed in the liquid during testing, and the liquid electrical parameter detection circuit is arranged close to the electromagnetic field sampling array, wherein the liquid to be tested in the dielectric test tube is the simulated liquid. Beneficial effects

[0019] The technical solution provided by the present invention has the following beneficial effects: the radio frequency oscillator of the present invention is composed of a dielectric resonator and a test tube. The tissue fluid to be tested is contained in the test tube and constitutes a part of the oscillator. The parameter fluctuations of the tissue fluid will affect the oscillation frequency and phase noise level of the oscillator. By detecting the oscillation frequency and phase noise level, the dielectric constant and loss parameter changes of the tissue fluid can be calculated, thereby achieving the purpose of real-time monitoring and improving the accuracy of SAR testing.

[0020] By passing the test tube through multiple dielectric resonators, it is ensured that the tissue fluid to be tested in each dielectric resonator is the same, thereby ensuring the accuracy of the test result.

[0021] By integrating a tissue fluid electrical parameter detection circuit near the SAR radio frequency probe, the health of the tissue fluid can be assessed promptly while reducing the need for temperature fluctuations. This detection circuit can monitor the tissue fluid electrical parameters in real time, ensuring that the tissue fluid is in good working condition. It also measures the dielectric constant and loss of the tissue fluid in real time, providing data for post-processing and bias compensation in SAR testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments of the present invention.

[0023] FIG1 is a schematic structural diagram of a SAR testing device provided by an embodiment of the present invention;

[0024] FIG2 is a schematic structural diagram of a dielectric resonator provided by an embodiment of the present invention;

[0025] FIG3 is a cross-sectional view of the dielectric resonator shown in FIG2 ;

[0026] FIG4 is a schematic structural diagram of a radio frequency oscillator provided by an embodiment of the present invention;

[0027] FIG5 is a circuit block diagram of a liquid electrical parameter detection circuit provided by an embodiment of the present invention;

[0028] FIG6 is a circuit block diagram of a liquid electrical parameter detection circuit provided by another embodiment of the present invention;

[0029] FIG7 is a circuit block diagram of a control voltage detection unit provided by an embodiment of the present invention;

[0030] FIG8 is a functional relationship diagram of the RF oscillator frequency and the voltage-controlled voltage provided by an embodiment of the present invention;

[0031] FIG9 is a graph showing the functional relationship between the dielectric constant of tissue fluid and the voltage control voltage;

[0032] FIG10 is a schematic diagram showing the relationship between the control voltage noise power spectrum and the quality factor of the RF oscillator;

[0033] FIG11 is a schematic diagram showing the relationship between the quality factor of the radio frequency oscillator and the tissue fluid loss parameter. Modes for Carrying Out the Invention Implementation Method

[0034] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0035] It should be understood that the various steps described in the method embodiments of the present invention may be performed in different orders and / or in parallel. In addition, the method embodiments may include additional steps and / or omit the steps shown. The scope of the present invention is not limited in this respect.

[0036] As used herein, the term "including" and its variations are open-ended, meaning "including but not limited to." The term "connected" may refer to a direct connection or an indirect connection via intermediate components (elements). The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; and the term "some embodiments" means "at least some embodiments." Other terms are defined below.

[0037] It should be noted that the concepts of "first" and "second" mentioned in the present invention are only used to distinguish devices, modules or units, and are not used to limit these devices, modules or units to be different devices, modules or units, nor are they used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0038] The present invention adopts the resonance method to measure the dielectric constant of the medium. The resonance method is one of the methods for measuring the dielectric constant of the medium. The resonance method establishes a functional relationship between the characteristic frequency and quality factor of the resonator and the electrical parameters of the measured material. By measuring the characteristic frequency and quality factor of the resonator, the dielectric constant and loss parameters of the measured material are calculated.

[0039] 1 to 11 , the present invention provides a radio frequency oscillator and a liquid electrical parameter detection circuit and SAR testing equipment using the radio frequency oscillator. The liquid electrical parameter detection circuit can detect electrical parameters of tissue fluid, such as dielectric constant and loss parameters, to improve the accuracy of SAR testing.

[0040] The RF oscillator includes a dielectric resonator 31 and a dielectric test tube 32 connected to the dielectric resonator. The dielectric resonator has test holes 316 extending through both ends, two first ports 314, and a second port 315. The first port 314 is used to connect to the voltage-controlled oscillator loop, and the second port 315 is used to connect to a varactor diode. The dielectric test tube 32 is used to hold the liquid to be tested and is inserted through the test hole 316 of the dielectric resonator. Optionally, the dielectric test tube is a glass capillary tube with a diameter of 1 mm.

[0041] When the liquid electrical parameter detection circuit 3 is immersed in the tissue fluid in FIG. 1 , once the medium test tube 32 contacts the tissue fluid, the liquid will be absorbed and filled into the medium test tube due to capillary action.

[0042] 4 , in one embodiment, a plurality of dielectric resonators 31 are provided, each dielectric resonator is stacked and has a different resonant frequency, and the dielectric test tube is passed through the test hole of each dielectric resonator to connect the dielectric resonators in series.

[0043] In one embodiment, there are seven dielectric resonators, whose central operating frequencies are 0.5 GHz, 1 GHz, 2 GHz, 3 GHz, 4 GHz, 5 GHz, and 6 GHz, respectively. The dielectric test tube and the liquid poured therein are connected in series with all seven resonators.

[0044] In one embodiment, the dielectric resonator includes a metal box and a dielectric resonator body 313 disposed within the metal box. The first port and the second port are disposed on the outer periphery of the metal box. Both the metal box and the dielectric resonator body are provided with through holes, and the through holes of the metal box and the dielectric resonator body together define the test hole. The metal box is defined by a cavity 311 and a cover 312.

[0045] In one embodiment, the metal box is circular, the first ports are located at both ends of the diameter of the metal box, and the second port is equidistant from the two first ports.

[0046] A radio frequency oscillator is constructed using a dielectric resonator perfused with tissue fluid. As the dielectric constant of the tissue fluid changes, the free-flowing frequency of the RF oscillator also changes synchronously. A phase-locked loop (PLL) forces the oscillator's output frequency to be N times that of a reference crystal oscillator, thus outputting a control voltage to maintain the RF oscillator's frequency constant. The relationship between the change in free-flowing frequency caused by the dielectric constant of the tissue fluid and the control voltage as a function of the oscillator's frequency is monotonic. This establishes a one-to-one correspondence between the dielectric constant of the tissue fluid and the control voltage. Accurately measuring the control voltage allows calculation of the current dielectric constant of the tissue fluid.

[0047] By testing several liquids with known parameters, a functional relationship between the characteristic frequency and quality factor of the RF oscillator and the electrical parameters of the material being tested is established. Then, for the actual tissue fluid to be tested, the characteristic frequency and quality factor of the RF oscillator can be tested to reversely deduce the electrical parameters of the tissue fluid to be tested.

[0048] As a second aspect, the present invention provides a liquid electrical parameter detection circuit 3, including a phase detector 33, a loop filter 34, a frequency divider 35, a voltage-controlled oscillator (VCO), a control voltage detection unit, and a phase-locked loop. The phase detector is used to access a test signal, the input end of the loop filter is connected to the output end of the phase detector, the input end of the control voltage detection unit is connected to the output end of the loop filter, the voltage-controlled oscillator includes the above-mentioned radio frequency oscillator and a radio frequency amplifier 37, the input end of the radio frequency oscillator (mainly a dielectric resonator) is connected to the output end of the loop filter, the output end of the radio frequency oscillator is connected to both the phase-locked loop and the frequency divider, and a feedback loop is also formed between the radio frequency amplifier 37 and the dielectric resonator 31 of the radio frequency oscillator.

[0049] In one embodiment, the control voltage detection unit includes a DC branch, an AC branch and an AD sampling chip 44, the DC branch includes a low-pass filter 41, and the low-pass filter is connected between the loop filter and the AD sampling chip 44; the AC branch includes a narrowband filter 42 and a detector 43, the input end of the narrowband filter 42 is connected to the loop filter, the input end of the detector 43 is connected to the output end of the narrowband filter, and the output end of the detector is connected to the AD sampling chip.

[0050] The VCO (voltage-controlled oscillator) consists of a dielectric resonator 31, an RF amplifier 37, and a feedback loop. The dielectric resonator shown in Figure 2 has three ports: two first ports 314 connected to the voltage-controlled oscillator loop, and a second port 315 connected to a varactor diode. An external control voltage can adjust the resonator frequency (and thus the oscillator frequency) by varying the reactance of the varactor diode. When the parameters of the tissue fluid perfusing the resonator change, the oscillator frequency also changes accordingly.

[0051] A phase-locked loop (PLL) is used to lock the VCO frequency to a reference crystal oscillator. Therefore, the PLL's output frequency is N times the reference frequency, where N is the division ratio of the PLL's frequency divider. When the parameters of the tissue fluid perfusing the dielectric resonator change, the frequency of the RF oscillator also changes accordingly. However, the PLL forces the oscillator's output frequency to be N times the reference crystal oscillator's. Therefore, the control voltage output by the PLL, via the phase detector and loop filter, changes the reactance of the VCO's varactor diode, thereby maintaining the oscillator's output frequency. This shows that the effects of the VCO control voltage and changes in tissue fluid parameters on the resonator cancel each other out, meaning that the VCO control voltage information can reflect changes in tissue fluid parameters.

[0052] Since the tissue fluid 200 in the glass tube is part of the resonator, the dielectric constant of the liquid affects the characteristic frequency of the resonator. The higher the dielectric constant of the liquid, the lower the characteristic frequency. Prepare a standard tissue fluid sample with a known dielectric constant, use the circuit shown in Figure 5 to perform an open-loop test, and establish the function curve of the oscillator frequency and voltage control voltage as shown in Figure 8. For example, if the dielectric constants of the tissue fluid samples are 45, 46, and 47, three voltage control function curves can be established. The output frequency of the phase-locked loop (closed loop) is , thus obtaining the control voltage parameters under tissue fluid sample: 、 and . Control voltage 、 and The value of reflects the dielectric constant of the tissue fluid sample (45, 46 and 47). 、 、 The functional relationship between the control voltage and the dielectric constant can be fitted by using the dielectric constants 45, 46, and 47, as shown in FIG9 . For a liquid with unknown parameters, the control voltage is tested and the dielectric constant of the liquid can be deduced using the curve.

[0053] The dielectric constant of the liquid is measured using the DC component of the control voltage. The AC component (high-frequency component) also contains important information. The power spectrum of the control voltage is shown in Figure 10. This spectrum is closely related to the quality factor of the voltage-controlled oscillator. A high quality factor results in a low power spectrum amplitude, while a low quality factor results in a high power spectrum amplitude. The loss parameters of the tissue fluid perfused in the resonator affect the quality factor of the voltage-controlled oscillator. Therefore, the loss parameters of the tissue fluid can be inferred by measuring the power spectrum of the control voltage.

[0054] Using several tissue fluid samples with known loss parameters, we obtained multiple power spectrum curves, as shown in Figure 10. This allowed us to establish a functional relationship between sample loss and quality factor, as shown in Figure 11. For liquids with unknown parameters, we obtained the power spectrum of the control voltage and calculated the oscillator's quality factor. This curve can then be used to deduce the liquid's loss parameters.

[0055] The N-fold frequency-divided signal of the oscillator is phase-detected with the reference crystal oscillator to generate a phase detection signal proportional to the phase difference, which is then passed through a loop filter to obtain the control voltage of the oscillator. In one embodiment, the control voltage is obtained by sampling using the circuit shown in Figure 7, where the DC portion of the control voltage is filtered by a low-pass filter and sampled by an AD sampling chip. And then calculate the current dielectric constant of the tissue fluid.

[0056] The AC portion of the control voltage is extracted by a narrowband filter, subjected to power detection by an RMS detector, and then sampled and calculated by an AD sampling chip to obtain the narrowband power value, thereby determining the quality factor of the current oscillator. The skirt noise of the control voltage contains information about the phase noise of the voltage-controlled oscillator, which is closely related to the quality factor (Q value) of the resonator. By extracting the skirt noise from the control voltage through a narrowband filter and then passing it through an RMS detector to obtain the noise power, the tissue fluid loss parameters can be inferred.

[0057] In one embodiment, when the radio frequency oscillator has multiple dielectric resonators, for example, seven, it also includes a radio frequency switch, the radio frequency switch including an input end and multiple output ends, the input end of the radio frequency switch is connected to the frequency divider; the multiple output ends of the radio frequency switch are connected to each of the dielectric resonators in a one-to-one correspondence, and each dielectric resonator is connected to a phase-locked loop and a loop filter.

[0058] This embodiment uses seven radio frequency oscillators with different frequency bands, and the oscillation frequencies are set to 0.5GHz, 1GHz, 2GHz, 3GHz, 4GHz, 5GHz, and 6GHz respectively. The crystal oscillator used is 10MHz, and the divider of the phase-locked loop is a digitally controlled adjustable divider. The division ratios are set to 50, 100, 200, 300, 400, 500, and 600, which correspond one-to-one to the oscillation frequencies of the oscillators.

[0059] Seven voltage-controlled oscillators (VCO1-7) are constructed using dielectric resonators of seven different frequency bands. These are selected by a radio frequency switch 36 and connected to a peripheral circuit to form a phase-locked loop circuit. The output control voltage is fed into a detection circuit to measure the DC voltage and quality factor. This allows for precise testing of the dielectric constant and loss parameters of tissue fluid at these frequencies, and the electrical parameters at other frequencies to be obtained using data fitting methods.

[0060] As a third aspect, referring to FIG1 , the present invention further provides a SAR testing device comprising a simulated spherical shell, an electromagnetic field sampling array 2, and the aforementioned liquid electrical parameter detection circuit 3. The simulated spherical shell is a closed structure for containing a simulated liquid simulating human tissue fluid; the electromagnetic field sampling array and the liquid electrical parameter detection circuit are both disposed within the simulated spherical shell and immersed in the liquid during testing, with the liquid electrical parameter detection circuit disposed proximate to the electromagnetic field sampling array. The liquid to be tested in the dielectric test tube is the simulated liquid.

[0061] By immersing the electromagnetic field sampling array in the tissue fluid of a simulated spherical shell simulating the head or abdomen, the liquid electrical parameter detection circuit of the tissue fluid is placed near the sampling array. The local tissue fluid electrical parameters detected by the detection circuit can characterize the tissue fluid electrical parameters around the sampling array, avoiding detection errors caused by different tissue fluids and improving the accuracy of SAR test results.

[0062] The above description is merely a preferred embodiment of the present invention and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of the present invention is not limited to technical solutions formed by specific combinations of the aforementioned technical features. It also encompasses other technical solutions formed by any combination of the aforementioned technical features or their equivalents, without departing from the aforementioned inventive concept. For example, a technical solution formed by replacing the aforementioned features with (but not limited to) technical features with similar functions in the present invention.

[0063] Although the subject matter has been described in language specific to structural features and / or methodological logical acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are merely example forms of implementing the claims.

Claims

1. A radio frequency oscillator for testing the electrical parameters of a liquid, characterized in that: It comprises a dielectric resonator and a dielectric test tube connected to the dielectric resonator; the dielectric resonator has test holes running through both ends, two first ports and a second port, wherein the first port is used to access a voltage-controlled oscillator loop, and the second port is used to connect a varactor diode; the dielectric test tube is used to hold a liquid to be tested, and the dielectric test tube is passed through the test hole of the dielectric resonator.

2. The radio frequency oscillator according to claim 1, characterized in that: There are a plurality of dielectric resonators, each of which is stacked and has different resonant frequencies. The dielectric test tube is passed through the test holes of each dielectric resonator to connect the dielectric resonators in series.

3. The radio frequency oscillator according to claim 2, characterized in that: The dielectric resonator includes a metal box and a dielectric resonator body arranged in the metal box, the first port and the second port are opened on the outer periphery of the metal box, the metal box and the dielectric resonator body are both provided with through holes, and the through holes of the metal box and the dielectric resonator body jointly define the test hole.

4. The radio frequency oscillator according to claim 3, characterized in that: The metal box is circular, the first ports are arranged at two ends of the diameter of the metal box, and the distance between the second port and the two first ports is equal.

5. The radio frequency oscillator according to claim 2, characterized in that: The medium testing tube is a capillary tube made of glass.

6. The radio frequency oscillator according to claim 2, characterized in that: There are seven dielectric resonators, and their central operating frequencies are 0.5 GHz, 1 GHz, 2 GHz, 3 GHz, 4 GHz, 5 GHz, and 6 GHz respectively.

7. A liquid electrical parameter detection circuit, characterized in that: The invention comprises a phase detector, a loop filter, a frequency divider, a voltage-controlled oscillator, a control voltage detection unit and a phase-locked loop, wherein the phase detector is used to access a test signal, the input end of the loop filter is connected to the output end of the phase detector, the input end of the control voltage detection unit is connected to the output end of the loop filter, the voltage-controlled oscillator comprises the radio frequency oscillator and the amplifier according to any one of claims 1 to 6, the input end of the radio frequency oscillator is connected to the output end of the loop filter, the output end of the radio frequency oscillator is connected to both the phase-locked loop and the frequency divider, and a feedback loop is also formed between the amplifier and the radio frequency oscillator.

8. The liquid electrical parameter detection circuit according to claim 7, characterized in that: The control voltage detection unit includes a DC branch, an AC branch and an AD sampling chip, the DC branch includes a low-pass filter, and the low-pass filter is connected between the loop filter and the AD sampling chip; the AC branch includes a narrowband filter and a detector, the input end of the narrowband filter is connected to the loop filter, the input end of the detector is connected to the output end of the narrowband filter, and the output end of the detector is connected to the AD sampling chip.

9. The liquid electrical parameter detection circuit according to claim 7, characterized in that: When the radio frequency oscillator has multiple dielectric resonators, it also includes a radio frequency switch, which includes an input end and multiple output ends, and the input end of the radio frequency switch is connected to the frequency divider; the multiple output ends of the radio frequency switch are connected to each of the dielectric resonators in a one-to-one correspondence, and each dielectric resonator is connected to the phase-locked loop and the loop filter.

10. A SAR test device, characterized in that: It comprises a simulated spherical shell, an electromagnetic field sampling array and a liquid electrical parameter detection circuit as described in any one of claims 7 to 9, wherein the simulated spherical shell is a closed structure for containing simulated liquid simulating human tissue fluid, the electromagnetic field sampling array and the liquid electrical parameter detection circuit are both arranged in the simulated spherical shell and immersed in the liquid during testing, and the liquid electrical parameter detection circuit is arranged close to the electromagnetic field sampling array, wherein the liquid to be tested in the medium test tube is the simulated liquid.

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