Method for realizing dual and three parameter measurement by utilizing PT symmetric LC sensing system

Abstract

The invention discloses a method for realizing dual and three parameter measurement by using a PT symmetric LC sensing system, and relates to the technical field of LC sensors. The method comprises the following steps: constructing a reading circuit which is in PT symmetry with an LC sensor, wherein the LC sensor and the reading circuit form a PT symmetric LC passive wireless sensing system; two minimum values of an amplitude-frequency characteristic curve of a reflection coefficient S11 of the passive wireless sensing system measured by a single port of a reading circuit are obtained, frequencies corresponding to the two minimum values are two resonant frequencies of a measurement system, and capacitance and resistance values of the sensing system are obtained through decoupling of the two frequency equations; three resonant frequencies are correspondingly obtained through the zero phase of the phase frequency characteristic curve of the reflection coefficient S11, three frequency equations are solved, and capacitance, resistance and coupling coefficient values of the sensing system are obtained. According to the method, the number of observable parameters can be increased under the condition that the sensor node space is not increased.

Description

Technical Field

[0001] The present invention relates to the technical field of LC sensors, and in particular to a method for realizing dual and triple parameter measurement by using a PT symmetrical LC sensing system. Background Art

[0002] Passive wireless LC sensors typically consist of a spiral inductor and a sensing capacitor connected to form an LC resonator. The capacitance changes in response to the parameter of interest, causing the resonant frequency of the LC resonator to shift. To wirelessly interrogate the LC sensor, an external readout coil is magnetically coupled to the sensor and the sensor's resonant frequency is detected by monitoring the return loss of the readout coil. The inherent passive wireless nature makes LC sensors useful in situations where wired connections are difficult or even impossible, such as rotating parts and sealed environments. With the rapid development of IoT technology and its increasing applications in portable and wearable devices, it requires multiple parameters to be monitored simultaneously through a single chip, which requires miniaturization while achieving multifunctionality.

[0003] In order to achieve effective integration of multi-parameter LC sensors, researchers have explored a variety of schemes based on the design of LC sensor nodes and external readout circuits. Temperature and humidity are measured through a single LC resonator using the resonant frequency and the amplitude of the impedance. However, this approach is limited to dual-parameter detection and requires a known coupling coefficient. By interacting with two separate LC resonators, it can be used to monitor dual parameters, but the measurement range is limited due to the mutual coupling between the overlapping inductors. Then, a symmetrical dual-resonance circuit is proposed to optimize the above problems, but this greatly increases the complexity of the sensor structure. Multiple sensitive capacitors are connected in parallel with a planar inductor, and a relay switch is used to control the sensor to work in different modes. In theory, this scheme can achieve simultaneous measurement of multiple parameters, but the introduction of multiple active devices limits its application. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to provide a method for realizing dual and triple parameter measurement by using a PT symmetrical LC sensing system, which can increase the number of observable parameters without increasing the sensor node space.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system, comprising the following steps:

[0006] A readout circuit is constructed which is PT-symmetrical with the LC sensor, and the LC sensor and the readout circuit constitute a PT-symmetrical LC passive wireless sensing system;

[0007] Obtain the reflection coefficient S of the passive wireless sensor system measured by the single port of the readout circuit11 The two minimum values ​​of the amplitude-frequency characteristic curve, the frequencies corresponding to the two minimum values ​​are the two resonant frequencies of the measurement system, and the two frequency equations are decoupled to obtain the capacitance and resistance values ​​of the sensor system;

[0008] The reflection coefficient S 11 The zero phase of the phase-frequency characteristic curve corresponds to three resonant frequencies, and the three frequency equations are solved to obtain the capacitance, resistance and coupling coefficient values ​​of the sensing system.

[0009] The beneficial effect of adopting the above technical solution is that the method described in this application applies the parity-time (PT) symmetry in quantum mechanics to LC passive wireless sensing, and by observing the frequency response of the reflection coefficient at the end of the readout circuit, two or even three parameters can be monitored simultaneously. In particular, for three-parameter detection, the three resonant frequencies of the system are extracted through the phase-frequency characteristics of the reflection coefficient to respond to changes in three parameters in the environment. It has been theoretically and experimentally proved that by using a series LCR circuit as a sensor and a symmetrical adjustable LCR circuit as a readout circuit, a PT-symmetrical LC sensor can achieve multi-parameter measurement. This method increases the number of observable parameters without increasing the sensor node space. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0011] Figure 1 is a flow chart of the measurement method according to an embodiment of the present invention;

[0012] Figure 2a is a simplified circuit model diagram of a PT symmetrical LC sensing system in the method according to an embodiment of the present invention;

[0013] Figure 2b is an equivalent circuit diagram of a single-port measurement PT symmetrical LC sensing system in the method according to an embodiment of the present invention;

[0014] Figure 2c is the eigenfrequency w in the method described in the embodiment of the present invention 1,2 The real part of ;

[0015] Figure 2d is the eigenfrequency w in the method described in the embodiment of the present invention 1,2 The imaginary part of is a function of the capacitance and resistance, assuming L = 5μH, k = 0.1

[0016] Figure 3a 1 is a simulated reflection spectrum under different capacitances in an embodiment of the present invention, and the resistance Rs=10Ω.

[0017] Figure 3bThe theoretical (blue and orange lines) and simulated (blue and orange symbols) frequency responses as a function of the varying capacitance Cs in the embodiment of the present invention are shown in FIG. Figure 3a Extracted from;

[0018] Figure 3c 1 is the theoretical (blue and orange lines) and simulated (blue and orange symbols) frequency response as a function of the varying resistance Rs, Cs=10 pF, in an embodiment of the present invention.

[0019] Figure 3d is a response diagram of the frequency f1 as the capacitance Cs and the resistance Rs change in the embodiment of the present invention;

[0020] Figure 3e is a response diagram of the frequency f2 as the capacitance Cs and the resistance Rs change in the embodiment of the present invention;

[0021] Figure 4a is the reflection spectrum under different capacitances in the embodiment of the present invention;

[0022] Figure 4b is the reflection spectrum under different resistances in the embodiment of the present invention;

[0023] Figure 4c is the reflection spectrum under different coupling coefficients in the embodiment of the present invention;

[0024] Figure 4d is a graph showing changes in the reflection spectrum with changes in capacitance Cs, resistance Rs and coupling coefficient k in an embodiment of the present invention;

[0025] Figure 5a is a diagram of an experimental apparatus in an embodiment of the present invention;

[0026] Figure 5b is an experimental circuit diagram in an embodiment of the present invention;

[0027] Figure 6a is a graph showing the change of the capacitance C2 value with humidity in an embodiment of the present invention;

[0028] Figure 6b is a curve diagram showing the change of the resistance value R2 with the illumination in the embodiment of the present invention;

[0029] Figure 6c is a curve diagram showing the variation of the coupling coefficient k with the coupling distance d in an embodiment of the present invention;

[0030] Figure 7a is the reflection spectrum under different relative humidity in the embodiment of the present invention;

[0031] Figure 7b is the reflection spectrum under different illuminations in the embodiment of the present invention;

[0032] Figure 7cis the reflection spectrum at different coupling distances in the embodiment of the present invention;

[0033] Figure 7d It is the reflection spectrum that changes with relative humidity, illumination and coupling distance in the embodiment of the present invention; wherein: 1. LC sensor 2. readout circuit. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] like Figure 1 As shown, the embodiment of the present invention discloses a method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system, comprising the following steps:

[0037] S1: construct a readout circuit 2 that is PT-symmetrical with the LC sensor 1, and the LC sensor 1 and the readout circuit 2 constitute a PT-symmetrical LC passive wireless sensing system;

[0038] S2: Obtain the reflection coefficient S of the passive wireless sensor system measured by the single port of the readout circuit 2 11 The two minimum values ​​of the amplitude-frequency characteristic curve, the frequencies corresponding to the two minimum values ​​are the two resonant frequencies of the measurement system, and the two frequency equations are decoupled to obtain the capacitance and resistance values ​​of the sensor system;

[0039] S3: The reflection coefficient S 11 The zero phase of the phase-frequency characteristic curve corresponds to three resonant frequencies, and the three frequency equations are solved to obtain the capacitance, resistance and coupling coefficient values ​​of the sensing system.

[0040] Figure 2aThis is a basic structural diagram of the PT-symmetrical LC passive wireless sensing system proposed in the application, which includes a pair of inductively coupled LCR resonators, one with gain (-R) and the other with equal loss (R). Since the LC sensor is a passive device with a positive resistance Rs (usually the parasitic resistance of the inductor), it serves as an energy loss end. The other circuit has a negative resistance -Rr, which provides energy as a readout circuit. The inductor Ls is connected in series with the sensitive variable capacitor Cs and the sensitive variable resistor Rs to form a dual-parameter sensitive sensor. In order to satisfy the PT symmetry, the relationship between the inductance, capacitance, and resistance in the two circuits is required to be: Lr=Ls=L, Cr=Cs=C, Rr=Rs=R. M is the mutual inductance between the two inductors, Where k is the inductive coupling coefficient, which is a coefficient between 0 (no coupling) and 1 (maximum coupling). In addition to the variable capacitor Cs and the variable resistor Rs, the coupling coefficient k can be used as the third sensitive variable parameter in the system.

[0041] Applying Kirchhoff's laws in two series circuits,

[0042]

[0043] Among them, I r and I s are the currents in the gain (readout circuit) slot and the loss (LC sensor) slot, respectively, and w is the system frequency. The natural frequency of the LC resonator is, (1a)–(1b) can be rewritten as:

[0044]

[0045] From the above equation, we can see that the system satisfies PT symmetry, that is, equation (2) remains unchanged after exchanging the subscripts r and s (representing P inversion) and changing the polarity of the imaginary unit i (representing T inversion). This linear system has four eigenfrequencies:

[0046]

[0047] Define the dimensionless number of non-Hermitian parameters or the gain / loss parameter system in the above system,

[0048]

[0049]

[0050] when When the system is in the PT symmetric precise region, w 1,2 are two unequal real eigensolutions.

[0051] when When 1,2Converge at the singular point (EP).

[0052] when When the system is in the PT symmetry breaking region, w 1,2 are a pair of conjugate complex numbers.

[0053] To more clearly understand the variation of eigenfrequency with capacitance and resistance, Figure 2c and Figure 2d The real and imaginary parts of the eigenvalues ​​w are given separately 1,2 When the real part has two unequal frequencies, the imaginary part of the frequency is 0, which means that it satisfies γ<γ EP In addition, with the change of resistance and capacitance, both low frequency w1 and high frequency w2 change significantly. As the resistance R increases, when the system satisfies γ>γ EP hour, Figure 2c The double real frequencies in disappear, Figure 2d The imaginary part of the frequency begins to appear in . Therefore, two unequal frequencies w can be measured 1,2 The changes in the PT symmetric precision area reflect the changes in sensitive resistance and capacitance parameters, ultimately achieving the purpose of passive wireless detection.

[0054] By decoupling formula (4), the capacitance and resistance values ​​of the system can be obtained:

[0055]

[0056] Figure 2b Equivalent circuit model of a PT symmetric system for single-port measurements. By connecting a vector network analyzer (VNA) to the readout circuit, the reflection coefficient S of the sensing system can be monitored. 11 , and obtain the frequency w to be measured 1,2 In the closed-loop analysis of the readout system, the VNA with a characteristic impedance Z0 of 50Ω can be simulated as a negative resistor -Z0 because it provides energy to the system. At the same time, in order to satisfy the PT symmetry of the system, a variable resistor R is added to the readout circuit. r =Z0-R s , so that the total equivalent series resistance is -R s , to match the variable resistor R in the sensor circuit s =R. In addition, Lr = Ls = L, Cr = Cs = C. Input impedance Z at the readout circuit port in for:

[0057]

[0058] Reflection coefficient S 11 As a function of input impedance Zin, it is expressed as:

[0059]

[0060] Its amplitude (in dB) varies with frequency,

[0061]

[0062] S 11 The amplitude is differentiated with respect to the frequency w, that is Get S 11 The resonant frequency at the amplitude minimum,

[0063]

[0064] As you can see, S 11 The frequency corresponding to the minimum value (10) is equal to the system resonant frequency (3), so it can be obtained by S 11 The frequency sweep curve obtains the system eigenfrequency w 1,2 .

[0065] Three parameter measurement:

[0066] For three-parameter measurement, the above two resonant frequencies cannot respond to three unknown parameters. Therefore, this application also proposes a new signal detection method for the PT symmetric LC sensing system. Figure 2b The single port reflection coefficient S 11 The phase-frequency characteristics, there are three corresponding resonant frequencies at zero phase, which are related to the system parameters. Therefore, by decoupling the three frequency equations of capacitance, resistance, and coupling coefficient in the system, three unknown parameters can be obtained. For practical applications in sealed spaces, in addition to sensitive variable resistors and capacitors, the coupling coefficient corresponding to the coupling distance is usually unknown. At present, the coupling coefficient in existing research must be a fixed and known quantity, so only the detection method proposed in this application can be used, which expands the application scope of LC passive wireless sensors. The circuit model theory is the same as the previous article, and we will directly analyze the S parameter phase-frequency characteristics.

[0067] Formula (8) gives the reflection coefficient S 11 The functional relationship between the phase and the frequency is as follows:

[0068]

[0069] By solving the equation Φ=0, we can get 11 The resonant frequency corresponding to the zero phase is

[0070]

[0071] It can be seen that S in formula (12b) 11 The frequency of zero contact w 1,2It is the system resonant frequency w in equation (3) 1,2 , and the additional frequency w0 in equation (12a) is the natural frequency of the LC resonator.

[0072] After decoupling formula (12), the system capacitance C, resistance R and coupling coefficient k can be obtained.

[0073]

[0074]

[0075] simulation:

[0076] To verify that the resonant frequency of the system can be used to measure multiple sensitive parameters, the PT symmetrical LC sensing system was simulated using Agilent software ADS. The circuit connections are as follows: Figure 2b As shown. The sensor inductor coil Ls = 5μH is connected in series with the variable capacitor Cs and the variable resistor Rs to simulate the changes of sensitive capacitance and resistance in the experiment. To maintain PT symmetry, the inductor Lr is 5μH, and the variable capacitor Cr and the variable resistor Rr in the readout circuit change with the change of the sensor. In addition, the coupling coefficient k is fixed to 0.1, and the scanning range is 0MHz to 30MHz.

[0077] Dual resonant frequency:

[0078] First, keep the resistance Rs = 10Ω, change the sensor capacitance Cs from 10pF to 50pF in 10pF intervals, and read the circuit capacitance Cr to keep changing synchronously. 11 The changes of the two resonance peaks in the curve are as follows Figure 3a The curves of different colors represent S under different capacitance values. 11 Amplitude-frequency curve, f1 and f2 correspond to the low frequency and high frequency at the minimum value of the curve respectively. Figure 3a Extract the resonant frequency from the simulated reflection spectrum, Figure 3b The resonant frequency w is shown 1,2 As the capacitance value increases, both frequencies decrease at the same time. The simulation results (symbols) are similar to Figure 3b The theoretical results (lines) are consistent with those in .

[0079] Then, keeping the capacitance Cs = Cr = 10pF, the resistance Rs changes from 10Ω to 50Ω in 10Ω intervals, and the resistance in the readout circuit also changes accordingly to maintain PT symmetry. The frequency response function of the resistance Rs is as follows Figure 3c As shown. The blue and orange symbols represent f1 and f2 under different resistance values, respectively. f1 and f2 correspond to the low resonant frequency and high resonant frequency at the minimum value of the simulation curve, respectively. Figure 3cIt can be seen that as the resistance increases, the low frequency f1 increases and the high frequency f2 decreases. The two peaks gradually approach each other, indicating that the splitting of f1 and f2 decreases. This phenomenon is due to the increase of the gain / loss parameter γ as the resistance increases. When γ increases to γ EP When the characteristic frequency f 1,2 The simulation results (symbols) are consistent with the theoretical analysis (lines).

[0080] Figure 3d-3e The dual-frequency motion phenomenon of capacitance and resistance changing simultaneously is shown. During the entire change process, the resistance and capacitance values ​​change from 10 to 30 with an interval of 5, the low frequency f1 changes from 21.47MHz to 12.59MHz, and the high frequency f2 changes from 23.71MHz to 13.48MHz. The simulation results (symbols) are consistent with the theoretical analysis (surfaces). Figure 3d The simulation results verify the dual resonant frequency f of the system. 1,2 It can be used to measure dual sensitive parameters Rs and Cs. Substituting the known inductance value L = 5H, coupling coefficient k = 0.1, simulation results f1 = w1 / 2π = 21.471MHz, f2 = w2 / 2π = 23.713MHz into equations (5) and (6), the capacitance value Cs = 10.000pF, the resistance value Rs = 10.050Ω, and the maximum relative error is 0.5%. The error mainly comes from the extracted resonant frequency f 1,2 The accuracy is related to the frequency sweep step of the instrument. The smaller the step, the smaller the error.

[0081] Multiple resonant frequencies

[0082] The simulation of the PT symmetric LC sensing system verifies the use of the reflection coefficient S 11 The phase-frequency characteristic curve can obtain three resonant frequencies f 0,1,2 , and used to measure three sensitive parameters Rs, Cs and k. The inductance value is set to 5μH, the capacitance range is 10pF~50pF, and the resistance range is 5Ω~45Ω.

[0083] In order to ensure that the entire variation range is within the system PT symmetric precision area, it is necessary to satisfy the requirement that γ<γ EP ,Right now

[0084]

[0085] Therefore, k should be The range of k is set from 0.15 to 0.35 with an interval of 0.1. The coupling coefficient k is not set very large to avoid w 1,2 There is an obvious frequency division between the two frequencies to minimize the scanning frequency range and improve measurement accuracy.

[0086] First, keep the resistance Rs = 5Ω and the coupling coefficient k = 0.15 unchanged, and change the sensor capacitance Cs from 10pF to 50pF in 20pF increments, and the capacitance Cr of the reading circuit changes accordingly. 11 Phase changes with frequency as Figure 4a As shown in the figure, each color curve corresponds to a fixed capacitance. The zero-phase horizontal gray dashed line has three intersections with each curve, indicating that there are three resonant frequencies corresponding to zero phase. As the capacitance increases, the curve shifts to the left, and the three resonant frequencies f 0,1,2 The change of capacitance Cs affects the three frequencies at the same time, which is consistent with the theoretical analysis of formula (12).

[0087] Then, keeping the capacitance fixed at Cs = 10pF and the coupling coefficient k = 0.15, the sensor resistance Rs changes from 5Ω to 45Ω in 20Ω intervals, and the read-out resistance Rr changes accordingly at 50-Rs, satisfying PT symmetry. 0,1,2 Changes such as Figure 4b As shown in the figure, it can be seen that the different symbol curves represent the simulation results under different resistances. As the resistance increases, the middle resonant frequency f0 remains unchanged, while the other two resonant frequencies f1 and f2 are close to each other, indicating that the resistance Rs has no effect on f0, but only reduces f 1,2 This result is also consistent with formula (12) and Figure 2c When the resistance continues to increase and inequality (16) becomes an equation, the frequencies f1 and f2 gather together in the middle, indicating that the system is in EP.

[0088] Then, keeping the capacitance Cs=10pF and the resistance Rs=5Ω unchanged, the coupling coefficient k was changed from 0.15 to 0.35 at intervals of 0.1. Figure 4c The variation of three resonant frequencies with the coupling coefficient k is given. Different style curves represent the simulation results under different coupling coefficients. It can be observed that as the coupling coefficient increases, the middle resonant frequency f0 remains fixed, while the other two resonant frequencies f 1,2 far away from each other, indicating that the coupling coefficient k does not affect f0, but only increases f 1,2 Splitting. The larger the k value, the farther the two resonant frequencies f1 and f2 are apart.

[0089] at last, Figure 4dThe functional relationship between frequency response and sensitive capacitance, resistance and coupling coefficient is given. Substituting the known inductance value L = 5μH, the simulation results corresponding to the orange curve are f1 = w1 / 2π = 14.54MHz, f0 = w0 / 2π = 15.92MHz, f2 = w2 / 2π = 17.79MHz. (13-15), the calculated capacitance value Cs = 19.989pF, the resistance value Rs = 9.384Ω, and the coupling coefficient k = 0.2. Compared with the theoretical value Cs = 20pF, Rs = 10Ω, k = 0.2, the maximum relative error of this resistor is 6.16%, mainly due to the limited accuracy of the extracted resonant frequency f 1,2。 The measurement accuracy is related to the simulation scanning step size. The smaller the step size, the more scanning points there are in the same scanning frequency range, and the smaller the error. The simulation results verify the three resonant frequencies f 0,1,2 It can be used to measure three sensitive parameters: Rs, Cs and k.

[0090] Experimental results:

[0091] To demonstrate the results of this application, a board-mounted circuit was constructed using Figure 2b The experimental setup is shown in Figure 5a As shown, it includes a humidity chamber (OMEGA205), a light source (LED bulb), an illuminance meter (PM6612), a vector network analyzer (AgilentN5224APNA), a DC voltage source, etc. In the experiment, humidity-sensitive capacitors and photoresistors made with MEMS technology are used to detect ambient humidity, light intensity, and inductive coupling distance (sensor position). Figure 5b The actual experimental circuit is shown in Figure 2. The sensor inductor L2 is a PCB planar spiral inductor with a substrate thickness of 1.5 mm. It contains 6 coils with an outer diameter of 10 mm, a line width of 150 μm, and a line spacing of 100 μm. The humidity-sensitive capacitor C uses MEMS technology to achieve a sandwich structure, and the humidity-sensitive medium is graphene oxide. The capacitance C2 value changes with humidity as shown in Figure 2. Figure 6a As shown. The photoresistor is a commercial product, model 5537. The resistance value of the photoresistor varies with the light intensity in the range of 20kΩ to 50kΩ. In order to reduce the resistance value, three photoresistors are connected in parallel with two low resistors as sensitive resistor R2. The resistance R2 value changes with the light intensity as shown in Figure 6b As shown in Figure 1. Inductor L2, sensitive capacitor C2 and sensitive resistor R2 are connected in series to form an LCR resonant circuit as an LC sensor. It is worth noting that since the small resistor in the LCR circuit is connected in parallel with the sensitive resistor, a large change in light intensity will cause a relatively small change in resistance, such as Figure 6b As shown, this results in a smaller frequency change. Therefore, in practical application scenarios, a sensitive resistor with a reasonable variation range should be selected.

[0092] Correspondingly, the design of inductor L1 is the same as that of sensor inductor L2, and a variable capacitance diode of model BB910 is connected in the readout circuit as a variable capacitor. The DC voltage source connected in parallel at both ends of the variable capacitance diode controls the capacitance value. Capacitors C3 and C4 are decoupling capacitors with a capacitance of 1μF, which are used to isolate the influence of DC voltage on the circuit. Resistor RV equal to 1MΩ is used to prevent the RF signal of the readout circuit from entering the DC voltage source. C3 and C4 are decoupling capacitors with a capacity of 1μF, which are used to isolate the influence of DC voltage on the circuit. When the resistor RV is equal to 1MΩ, it is used to prevent the RF signal in the readout circuit from entering the DC voltage source. The variable resistor R1 connected to the other end of the diode can be adjusted to match the sensor resistor R2. The readout circuit port is connected to a vector network analyzer with an output power of 20dBm, and scanned from 13MHz to 17MHz at 6KHz steps. The sensor and readout circuit are fixed on two movable brackets. In the experiment, the coupling coefficient of the system is changed by manually adjusting the coupling distance between the two inductors, and the relationship is as follows Figure 6c shown.

[0093] During measurement, the sensor is placed in a humidity chamber, and the humidity of the humidity chamber environment can be manually set. A wirelessly adjustable brightness LED bulb is placed in the humidity chamber as a light source to change the light intensity in the environment. At the same time, an illuminance meter is used to calibrate the illumination in the humidity chamber. VNA is used to measure the frequency of the LC sensor.

[0094] First, the humidity was increased from 40%RH to 70%RH at intervals of 10%RH, the illumination was set to 0lux, and the coupling distance was kept at 1.15cm. The S 11 Phase-frequency characteristic curve Figure 7a As shown in the figure, the curves of different colors represent the measurement results under different relative humidity. Each curve intersects with the zero phase line (gray dotted line) at three points. The resonant frequencies of the left, middle and right intersections correspond to f1, f0 and f2 in the above analysis. When the humidity changes and the capacitance changes, it can be seen that the three resonant frequencies have changed, which is consistent with the simulation results. Figure 4a The trends shown are consistent.

[0095] Then, the LED bulb lighting intensity was varied from 0lux to 1625lux, the humidity was maintained at 50%RH, and the coupling distance was maintained at 1.15cm. 11 Phase frequency characteristic curve is as follows Figure 7b As shown. Curves with different symbols represent the measurement results under different light intensities. It can be observed that the resonant frequencies f1 and f2 change with the light intensity, while f0 remains unchanged. This is because the change in resistance R2 caused by light intensity has nothing to do with 0. This is consistent with Figure 2c and Figure 4b The theoretical and simulation results are consistent.

[0096] Then, the coupling distance between the two induction coils was manually adjusted from 0.9 cm to 1.3 cm, with a spacing of 0.2 cm, while the room humidity was maintained at 18% RH and the illumination was maintained at 0 lux. The experimental results show that S 11 Phase-frequency characteristics such as Figure 7c As shown in the figure, the different style curves represent the measurement results at different coupling distances. As the distance changes, the resonant frequencies f1 and f2 change significantly, while the middle f0 remains basically unchanged, which is consistent with Figure 4c This error is caused by parasitic effects.

[0097] at last, Figure 7d The two curves shown are the measurement results under different light intensities, relative humidity and coupling distances. It can be seen that when the three parameters change at the same time, the three resonant frequencies are shifted, which is consistent with Figure 4d The theoretical and simulation results are qualitatively consistent.

[0098] In summary, this application has conducted theoretical analysis and simulation on the PT symmetric circuit, and the results show that the system has two real resonant frequencies related to the circuit parameters in the PT symmetric precise phase. 11 The frequencies corresponding to the two minimum values ​​of the parameter amplitude-frequency characteristic curve are the two resonant frequencies of the system. The two frequency equations can be decoupled to obtain the two unknown circuit element parameter values ​​of the system. Therefore, it can be applied to the dual parameter measurement of LC passive wireless sensors, and the changes in the measured system dual resonant frequencies are used to respond to the changes in the parameters of the two system sensitive components caused by the environment. On this basis, it is further found that the measured S 11 The zero phase of the phase-frequency characteristic curve corresponds to three resonant frequencies, so the three frequency equations can be solved to obtain three system parameters such as capacitance, resistance, and coupling coefficient. The three parameters can be measured simultaneously. Finally, the sensitivity of humidity, illumination, and distance parameters was experimentally verified using the PT symmetrical LC passive wireless sensing system.

Claims

1. A method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system, characterized in that The steps include: A readout circuit (2) is constructed which is PT-symmetrical with the LC sensor (1); the LC sensor (1) and the readout circuit (2) constitute a PT-symmetrical LC passive wireless sensing system; Obtain the reflection coefficient S of the passive wireless sensor system measured by the single port of the readout circuit (2) 11 The two minimum values ​​of the amplitude-frequency characteristic curve, the frequencies corresponding to the two minimum values ​​are the two resonant frequencies of the measurement system, and the two frequency equations are decoupled to obtain the capacitance and resistance values ​​of the sensor system; The reflection coefficient S 11 The zero phase of the phase-frequency characteristic curve corresponds to three resonant frequencies, and the three frequency equations are solved to obtain the capacitance, resistance and coupling coefficient values ​​of the sensing system.

2. The method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system as claimed in claim 1, characterized in that: The LC sensor (1) is a passive device with a positive resistor Rs. In the LC sensor, an inductor Ls is connected in series with a sensitive variable capacitor Cs and a sensitive variable resistor Rs. In the readout circuit (2), an inductor Lr is connected in series with a sensitive variable capacitor Cr and a sensitive variable negative resistor -Rr. The relationship between the inductance value, the capacitance value and the resistance value in the two circuits is: Lr=Ls=L, Cr=Cs=C, Rr=Rs=R.

3. The method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system as claimed in claim 2, characterized in that: M is the mutual inductance between the two inductors, Where k is the inductive coupling coefficient, a coefficient with a value between 0 and 1. When k is 0, there is no coupling, and when k is 1, there is maximum coupling.

4. The method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system as claimed in claim 2, characterized in that: Applying Kirchhoff's laws in two series circuits, Among them, I r and I s are the currents of the reading circuit loop and the sensor loop, respectively; w is the system frequency; the natural frequency of the LC resonator is, Formula (1a)-(1b) can be rewritten as From the above equation, we can see that the system satisfies PT symmetry, that is, equation (2) remains unchanged after exchanging the subscripts r and s and changing the polarity of the imaginary unit i; this linear system has four characteristic frequencies: Define the dimensionless number of non-Hermitian parameters or the gain / loss parameter system in the above system, when When the system is in the PT symmetric precise region, w 1,2 are two unequal real eigensolutions; when When 1,2 Convergence at the singular point (EP); when When the system is in the PT symmetry breaking region, w 1,2 is a pair of conjugate complex numbers; By decoupling formula (4), we can get the capacitance and resistance values, 5. The method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system as claimed in claim 4, characterized in that: By connecting a vector network analyzer (VNA) to the readout circuit, the reflection coefficient S of the sensing system is monitored. 11 , and obtain the characteristic frequency w to be measured 1,2 The vector network analyzer VNA with characteristic impedance Z0 of 50Ω is simulated as negative resistance -Z0. At the same time, in order to meet the PT symmetry of the system, a variable resistor R is added to the readout circuit. r =Z0-R s , so that the total equivalent series resistance is -R s , to match the variable resistor R in the sensor circuit s =R; In addition, Lr = Ls = L, Cr = Cs = C; Input impedance Z at the readout circuit port in for: Single port reflection coefficient S 11 As a function of input impedance Zin, it is expressed as: Its amplitude varies with frequency, The reflection coefficient S 11 The amplitude is differentiated with respect to the frequency w, that is Get S 11 The resonant frequency at the amplitude minimum, 6. The method for realizing dual and triple parameter measurement using a PT symmetrical LC sensing system as claimed in claim 5, characterized in that: According to the reflection coefficient S given by formula (8) 11 The functional relationship between the phase and the frequency is as follows: By solving the equation Φ=0, we can get 11 The resonant frequency corresponding to zero phase is: In formula (12b), S 11 The frequency of zero contact w 1,2 It is the system resonant frequency w in equation (3) 1,2 , and the additional frequency w0 in equation (12a) is the natural frequency of the LC resonator; after decoupling equations (12a)-(12b), the system capacitance C, resistance R and coupling coefficient k are obtained:

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