Method for monitoring resonance frequency using reflected impedance measurement, and lc sensor system using the method

Abstract

An LC sensor system comprises an LC sensor composed of an LC resonant circuit, and a circuit that outputs an RF signal to obtain the frequency response of the wirelessly coupled LC sensor, and a transmitting module that determines the resonant frequency of the LC sensor from a reflection impedance reflecting the frequency response.

Description

Technology Field

[0001] The present disclosure relates to resonance frequency monitoring. Background Technology

[0002] A wireless pressure sensor is represented by an inductor-capacitor circuit (LC circuit) composed of a coil and a capacitor, and can measure pressure by utilizing the principle that capacitance and resonant frequency change as the gap between the capacitor plates changes according to pressure.

[0003] Conventional wireless pressure sensors are implemented as a combined model of a transmitter (TX) and a receiver (RX), and at the transmitter, input return loss (S 11 A method is used to measure the frequency at which ) is minimized. In this case, a Vector Network Analyzer (VNA) is used to measure S-parameters, but the application range of wireless pressure sensors is inevitably limited due to the expensive and complex VNA. The problem to be solved

[0004] The present disclosure relates to a resonant frequency monitoring method based on reflection impedance measurement and an LC sensor system utilizing the same. means of solving the problem

[0005] An LC sensor system according to one embodiment comprises an LC sensor composed of an LC resonant circuit, and a transmitting module comprising a circuit that outputs an RF signal to obtain the frequency response of the wirelessly coupled LC sensor, and a reflective impedance reflecting the frequency response to determine the resonant frequency of the LC sensor.

[0006] The above-described transmitting module can determine the frequency at which the imaginary part of the reflection impedance becomes zero as the resonance frequency.

[0007] The above-described transmitting module can determine the frequency corresponding to the midpoint of the imaginary part of the above-described reflection impedance as the above-described resonance frequency.

[0008] The transmitting module can measure the self-impedance with the LC sensor removed, measure the input impedance with the LC sensor combined, and then determine the difference between the input impedance and the self-impedance as the reflected impedance.

[0009] The above-described transmitting module can measure the change in impedance of the coil based on the voltage gain and phase difference across the ends of the coil wirelessly coupled with the LC sensor, and calculate the reflected impedance from the change in impedance.

[0010] The above-described transmitting module can output the measurement value of the LC sensor corresponding to the above-described resonant frequency.

[0011] The above LC sensor may be a wireless pressure sensor in which the resonant frequency of the LC resonant circuit changes according to pressure.

[0012] A method of operation of a receiving module and a wirelessly coupled transmitting module according to one embodiment includes the steps of: outputting an RF signal to obtain a reflection impedance reflecting the frequency response of the wirelessly coupled receiving module; and determining the resonance frequency of the receiving module from the reflection impedance.

[0013] The step of determining the above resonant frequency may determine the frequency at which the imaginary part of the reflection impedance becomes zero as the resonant frequency.

[0014] The step of determining the above resonant frequency may determine the frequency corresponding to the midpoint of the imaginary part of the above reflection impedance as the above resonant frequency.

[0015] The step of obtaining the reflection impedance may involve measuring the self-impedance with the receiving module removed, measuring the input impedance with the receiving module connected, and then determining the difference between the input impedance and the self-impedance as the reflection impedance.

[0016] The step of obtaining the reflection impedance may involve measuring the change in impedance of the coil based on the voltage gain and phase difference across the ends of the coil wirelessly coupled with the receiving module, and calculating the reflection impedance from the change in impedance.

[0017] The above operation method may further include a step of outputting a measurement value corresponding to the resonant frequency.

[0018] A transmitting module according to one embodiment includes an RF signal source that outputs an RF signal while sweeping a frequency, a coupling coil that wirelessly couples with a receiving module, a gain / phase detector that converts the voltage across the coupling coil into a voltage gain and / or phase difference, and a controller that measures a change in impedance of the coupling coil based on the output of the gain / phase detector, calculates a reflected impedance from the change in impedance, and determines a resonant frequency from the reflected impedance.

[0019] The controller may determine the frequency at which the imaginary part of the reflection impedance becomes zero as the resonant frequency, or determine the frequency corresponding to the midpoint of the imaginary part of the reflection impedance as the resonant frequency. Effects of the invention

[0020] According to the present disclosure, the resonant frequency of a receiving module including an LC sensor that changes with pressure can be measured by measuring the reflection impedance instead of the S-parameter.

[0021] According to the present disclosure, the complexity and cost of an LC sensor system can be reduced, and in particular, the transmitting module can be made lighter and smaller.

[0022] According to the present disclosure, even if an offset occurs due to changes in the coil characteristics of the transmitting module caused by interference from the surrounding environment during impedance measurement, the influence of the external environment can be corrected by utilizing the symmetry of the imaginary part of the reflected impedance, and as a result, measurement accuracy can be increased and the detection distance can be increased. Brief explanation of the drawing

[0023] Figure 1 is a diagram illustrating a general LC sensor measurement method. FIG. 2 is a diagram illustrating an LC sensor system and an equivalent circuit thereof according to one embodiment. FIG. 3 is a diagram illustrating the relationship between reflection impedance and resonance frequency according to one embodiment. FIG. 4 is a diagram illustrating a reflection impedance distortion correction method according to one embodiment. FIG. 5 is a configuration diagram of a transmission module according to another embodiment. FIG. 6 is a method of operation of a transmission module according to one embodiment. Specific details for implementing the invention

[0024] Embodiments of the present disclosure are described below with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present disclosure in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification are denoted by similar reference numerals.

[0025] In the description, drawing symbols and names are provided for convenience of explanation and are not limited to drawing symbols or names.

[0026] In the description, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, terms such as "…part," "…unit," and "module" as used in the specification refer to a unit that processes at least one function or operation, and this may be implemented in hardware, software, or a combination of hardware and software.

[0027] In the description, expressions written in the singular may be interpreted as singular or plural unless explicit expressions such as "one" or "singular" are used. Terms containing ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by these terms. These terms may be used for the purpose of distinguishing one component from another.

[0028] Figure 1 is a diagram illustrating a general LC sensor measurement method.

[0029] Referring to Fig. 1, a typical LC sensor system consists of a transmitting module (TX module) and a receiving module, which is an LC sensor. Here, the LC sensor generally consists of a sensing capacitor C RX and the inductor L connected thereto RX It is represented as an inductor-capacitor resonant circuit (LC circuit) composed of. The transmitting module is a readout coil L coupled with the LC sensor. TX Through this, the input return loss (S 11 By monitoring ) the resonance frequency f of the LC sensor RX It can detect.

[0030] Referring to (a), in the case of a conventional LC sensor system composed of a transmitting module and an LC sensor, the input reflection loss S is obtained through the Vector Network Analyzer (VNA) of the transmitting module. 11 Measure and S 11 The frequency at which this becomes minimum is output as the resonance frequency.

[0031] Referring to (b), the read coil L of the transmitting module TX variable capacitor C TX By adding, the transmitting module is configured as a resonant circuit, and the resonant frequency f of the transmitting moduleTX and the resonance frequency f of the LC sensor RX It can be matched. Even in this case, S measured through the VNA 11 The frequency at which this becomes the minimum can be output as the resonant frequency.

[0032] However, input reflection loss S 11 Since an expensive and complex VNA is used to measure it, the application range of the LC sensor is inevitably limited. In the case of the LC sensor system of (a), the measurement method is simple, but the read coil L of the transmitting module TX Since only the transmission module is used, it has the disadvantage of low power transfer efficiency and a short detection distance. In the case of the LC sensor system of (b), it has the advantage of improving transmission efficiency and increasing the detection distance by utilizing the resonance of the transmission module. However, due to changes in coil parasitic resistance according to frequency, S-parameter distortion of the VNA occurs, which reduces measurement accuracy. Also, if the resonance frequencies of the transmission module and the LC sensor do not exactly match, the minimum point of the S-parameters changes, which may reduce measurement accuracy.

[0033] In the following, a resonant frequency monitoring method based on reflection impedance measurement that solves the problems of such conventional LC sensor systems, and an LC sensor system utilizing this method are described in detail.

[0034] FIG. 2 is a diagram illustrating an LC sensor system and its equivalent circuit according to one embodiment, and FIG. 3 is a diagram illustrating the relationship between reflection impedance and resonance frequency according to one embodiment.

[0035] Referring to FIG. 2, the LC sensor system (10) may be composed of an LC sensor (100) and a transmitting module (TX module) (200). The transmitting module (200) is wirelessly coupled with the LC sensor (100) and includes a receiving circuit (TX circuit) (210) that obtains the frequency response of the LC sensor (100), and the resonance frequency f of the LC sensor (100) obtained from the frequency response obtained from the receiving circuit (210). RX It may further include a measurement unit (220) for calculating the monitored reflection impedance Z. Here, the measurement unit (220) calculates the monitored reflection impedance Z Ref Based on , the resonant frequency f of the LC sensor (100) RX Calculate. The measurement unit (220) may be included in the transmission module (200), configured separately from the transmission module (200), or configured so that some functions are built into the transmission module (200) and some functions are built into an external device of the transmission module (200). The measurement unit (220) may include a processor selected from various types of processors and memory, and may further include a communication module as needed.

[0036] The LC sensor (100) is a sensing capacitor C RX , inductor L RX , and resistance R RX It can be represented as an LC resonant circuit composed of. For example, the LC sensor (100) may be a wireless pressure sensor that measures pressure by utilizing the principle that the capacitance and resonant frequency change as the gap of the capacitor plates changes according to pressure. In addition, the receiving module of the LC sensor system (10) may be a receiving module of a wireless power transmission system, and the operation and configuration of the present disclosure may also be applied to a wireless power transmission system, but in the description, the LC sensor (100) is used as an example.

[0037] The transmitting module (200) is an inductor L combined with the LC sensor (100). TX , and resistance RTX Input impedance Z viewed from the LC sensor (100), including TX&RX is Z TX Wow Z Ref It can be expressed as the sum of. In addition, the transmitting module (200) includes an RF signal source that outputs an RF signal, and a reflected impedance Z that reflects the frequency response of the LC sensor (100). Ref It may include additional circuit components for measuring, but a detailed explanation is omitted.

[0038] When coupling occurs between the transmitting module (200) and the receiving module, which is an LC sensor (100), the impedance viewed from the transmitting module (200) is resistance R TX , inductor L TX In addition, an additional impedance is added due to the LC sensor (100), which is the reflected impedance Z. Ref It is said that

[0039] Referring to Fig. 3, the reflected impedance Z Ref is the input impedance Z TX&RX The self-impedance Z of the transmission module (200) TX It can be obtained by removing.

[0040] Reflection impedance Z Ref includes a complex component due to the frequency of the LC sensor (100), and the shape of the imaginary part of the reflection impedance Im(Z Ref ) is the resonant frequency f RX It exhibits symmetry around . In this case, the frequency where the imaginary part is zero is the resonance frequency f RX am.

[0041] Reflection impedance Z Ref is expressed as in Equation 1, and the reflected impedance Z Ref The imaginary part of Im(Z Ref) It can be expanded as in Equation 2, and the frequency where the imaginary part is zero is the resonance frequency f RX am.

[0042]

[0043]

[0044] Accordingly, the measuring unit (220) has a reflection impedance Z Ref Based on the frequency characteristics of the LC sensor (100), the resonant frequency f RX It can measure the reflection impedance Z obtained from the transmission module (200). That is, the measuring unit (220) can measure the reflection impedance Z obtained from the transmission module (200). Ref From the frequency characteristic graph of, find the frequency where the imaginary part is zero, and this is the resonance frequency f RX It can be output as.

[0045] Meanwhile, the reflection impedance Z Ref is the self-impedance Z of the transmission module (200) TX Because it exists as a minute component compared to, a process of separating it is necessary. The self-impedance Z of the transmitting module (200) TX It is represented as a complex circuit due to parasitic components of the coil and capacitor, and distortion caused by coupling with the LC sensor (100) must also be taken into account. Therefore, the measurement unit (220) measures the self-impedance Z of the transmitting module (200) with the LC sensor (100) removed. TX Measures the input impedance Z of the transmitting module (200) with the LC sensor (100) combined. TX&RX After measuring, the difference between the two impedances (Z TX&RX -Z TX ) reflection impedance Z Ref It can be determined as such. And, the measuring unit (220) has a reflection impedance Z Ref Find the frequency where the imaginary part of is zero, and this is the resonance frequency f RX It can be measured as follows. The measuring unit (220) has a resonant frequency f RX It can output a measurement value corresponding to . If the LC sensor (100) is a wireless pressure sensor, the measuring unit (220) can output the resonant frequency f based on the resonant frequency-pressure relationship. RX The converted pressure value can be output.

[0046] Thus, the LC sensor system (10) of the present disclosure has a reflection impedance Z Ref The resonance frequency of the LC sensor (100) can be measured by directly calculating it.

[0047] Meanwhile, in the case of conventional LC sensor systems, the reflected impedance can be measured by converting the S-parameters measured by the VNA into impedance (Z-parameters). However, it is difficult to detect minute changes in reflected impedance using S-parameters, so there is a limit to the detection distance.

[0048] FIG. 4 is a diagram illustrating a reflection impedance distortion correction method according to one embodiment.

[0049] Referring to FIG. 4, when measuring the reflection impedance in the transmitting module (200), the coil characteristics of the transmitting module (200) may change due to interference from the surrounding environment, and an offset may occur.

[0050] For example, in an ideal environment such as a laboratory, the reflection impedance Z as in (a) Ref The imaginary part of Im(Z Ref) A frequency in which the imaginary part is symmetric and the imaginary part is 0 can be determined as the resonant frequency. However, in a real environment, as in (b), the imaginary part value may be offset, so the frequency in which the imaginary part is 0 may not be the actual resonant frequency. Therefore, the measurement unit (220) can utilize the symmetry of the imaginary part of the reflected impedance to determine the intermediate value of the imaginary part and determine its frequency as the resonant frequency. There are various ways to determine the intermediate value of the imaginary part; for example, the average of the maximum and minimum values ​​of the imaginary part can be defined as the intermediate value.

[0051] Thus, even if the reflection impedance is affected by the external environment, the LC sensor system (10) can correct distortion caused by offset or noise by utilizing the symmetry of the imaginary part of the reflection impedance, thereby increasing measurement accuracy and increasing detection distance.

[0052] FIG. 5 is a configuration diagram of a transmission module according to another embodiment.

[0053] Referring to FIG. 5, the transmitting module (200) of the LC sensor system (10) can be configured in various ways, for example, it can be configured as a transmitting module (200A) including an RF signal source (201), an impedance matching and low pass filter (202), a coupling coil (203), a matching capacitor (204), a gain / phase detector (205), and a controller (206).

[0054] The RF signal source (201) can output an RF signal while sweeping the frequency to obtain frequency-specific resonance characteristics in the receiving module.

[0055] The impedance matching and low-pass filter (202) can maximize RF signal transmission and remove unnecessary harmonic and noise components.

[0056] The transmitting module and the receiving module are wirelessly coupled by the coupling coil (203), and the matching capacitor (204) can match the resonant frequencies of the transmitting module and the receiving module to detect the response of the receiving module or to transmit wireless power.

[0057] The gain / phase detector (205) is the voltage (V) across the coupling coil (203). x , V Y) can be converted into voltage gain and phase difference. The controller (206) can control the RF signal source (201) and the matching capacitor (204). And, the controller (206) can obtain the voltage gain and phase difference from the gain and phase detector (205). The controller (206) can measure the change in impedance of the coupling coil (203) based on the voltage gain and phase difference across the coupling coil (203), calculate the reflected impedance from the change in impedance, and then determine the resonance frequency from the reflected impedance. Alternatively, the controller (206) can transmit the voltage gain and phase difference of the coupling coil (203) to an external computing device. Then, the external computing device can measure the change in impedance of the coupling coil (203) based on the voltage gain and phase difference, calculate the reflected impedance from the change in impedance, and then determine the resonance frequency from the reflected impedance. Since the reflected impedance generated when the coupling coil (203) is coupled with the LC sensor induces a change in the impedance of the coupling coil (203), the reflected impedance can be derived by measuring the change in the impedance of the coupling coil (203). Impedance of the coupling coil (203) As shown in Equation 3, the voltage gain (V x , V Y ) and phase difference( It can be calculated based on ). In mathematical formula 3, is the impedance of the matching capacitor (204).

[0058]

[0059] At this time, the controller (206) or the external computing device may determine the frequency at which the imaginary part of the reflection impedance becomes zero as the resonant frequency, or determine the frequency at which the midpoint of the imaginary part of the reflection impedance becomes the resonant frequency.

[0060] As such, the transmitting module (200A) can measure reflected impedance without using a VNA, allowing for integration to a portable level, and can be manufactured as a flexible PCB (flexible Printed Circuit Board) to improve weight reduction and portability. In addition, real-time wireless monitoring is possible through the transmitting module (200A), and by improving the sampling rate, information such as pressure can be accurately measured even when the resonant frequency changes rapidly.

[0061] FIG. 6 is a method of operation of a transmission module according to one embodiment.

[0062] Referring to FIG. 6, the transmitting module (200 / 200A) of the LC sensor system (10) outputs an RF signal, and the reflected impedance Z reflecting the frequency response of the wirelessly coupled receiving module Ref The transmitting module (200) obtains its own impedance Z with the receiving module removed (S110). TX Measure , and input impedance Z with the receiving module coupled TX&RX After measuring, the difference between the two impedances (Z TX&RX -Z TX ) reflection impedance Z Ref It can be determined as such. Alternatively, the transmitting module (200A) can measure the change in impedance of the coupling coil based on the voltage gain / phase difference between the ends of the coil wirelessly coupled with the receiving module, and calculate the reflected impedance from the change in impedance.

[0063] The transmitting module (200 / 200A) has a frequency corresponding to the frequency at which the imaginary part of the reflected impedance becomes zero or the intermediate value of the imaginary part, and a resonant frequency f RX Determined as (S120). Reflection impedance Z Ref includes a complex component due to the frequency of the LC sensor (100), and the shape of the imaginary part of the reflection impedance Im(Z Ref ) is the resonant frequency f RXIt exhibits symmetry centered on [something]. Since an offset or noise may appear in the imaginary part of the reflection impedance due to interference from the surrounding environment, the transmitting module (200 / 200A) can utilize the symmetry of the imaginary part of the reflection impedance to determine the intermediate value of the imaginary part and determine its frequency as the resonance frequency.

[0064] The transmitting module (200 / 200A) has a resonant frequency f RX It outputs a measurement value corresponding to (S130). If the LC sensor (100) is a wireless pressure sensor, the transmitting module (200 / 200A) outputs the resonant frequency f based on the resonant frequency-pressure relationship. RX The converted pressure value can be output.

[0065] The embodiments of the present disclosure described above are not implemented only through devices and methods, but may also be implemented through a program that realizes a function corresponding to the configuration of the embodiments of the present disclosure or a recording medium on which such program is recorded.

[0066] Although embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts of the present disclosure as defined in the following claims also fall within the scope of the present disclosure.

Claims

Claim 1 An LC sensor system comprising an LC sensor composed of an LC resonant circuit and a circuit that outputs a frequency sweeping RF signal to obtain the frequency response of the wirelessly coupled LC sensor, and a transmitting module that determines the resonant frequency of the LC sensor from a reflected impedance reflecting the frequency response, wherein the transmitting module measures the self-impedance with the LC sensor removed, calculates the input impedance based on the voltage gain and phase difference between the ends of the wirelessly coupled coil and the LC sensor measured during the frequency sweep with the LC sensor coupled, and determines the difference between the input impedance and the self-impedance as the reflected impedance. Claim 2 An LC sensor system according to claim 1, wherein the transmitting module determines the frequency at which the imaginary part of the reflection impedance becomes zero as the resonance frequency. Claim 3 An LC sensor system according to claim 1, wherein the transmitting module determines the frequency corresponding to the midpoint of the imaginary part of the reflection impedance as the resonance frequency. Claim 4 delete Claim 5 delete Claim 6 In claim 1, the transmitting module outputs a measurement value of the LC sensor corresponding to the resonant frequency, an LC sensor system. Claim 7 In claim 1, the LC sensor system is a wireless pressure sensor in which the resonant frequency of the LC resonant circuit changes according to pressure. Claim 8 A method of operation for a receiving module and a wirelessly coupled transmitting module, comprising the steps of: outputting a frequency sweeping RF signal to obtain a reflected impedance that reflects the frequency response of the wirelessly coupled receiving module; and determining the resonant frequency of the receiving module from the reflected impedance, wherein the step of obtaining the reflected impedance involves measuring the self-impedance with the receiving module removed, calculating the input impedance based on the voltage gain and phase difference between the ends of the wirelessly coupled coil and the receiving module measured during the frequency sweep with the receiving module coupled, and determining the difference between the input impedance and the self-impedance as the reflected impedance. Claim 9 In claim 8, the step of determining the resonant frequency is a method of operation in which the frequency at which the imaginary part of the reflection impedance becomes zero is determined as the resonant frequency. Claim 10 In claim 8, the step of determining the resonant frequency is to determine the frequency corresponding to the midpoint of the imaginary part of the reflection impedance as the resonant frequency. Claim 11 In claim 8, the step of obtaining the reflection impedance involves measuring the self-impedance with the receiving module removed, measuring the input impedance with the receiving module coupled, and then determining the difference between the input impedance and the self-impedance as the reflection impedance. Claim 12 In claim 8, the step of obtaining the reflection impedance is a method of operation in which the change in impedance of the coil is measured based on the voltage gain and phase difference between the ends of the coil wirelessly coupled with the receiving module, and the reflection impedance is calculated from the change in impedance. Claim 13 A method of operation according to claim 8, further comprising the step of outputting a measurement value corresponding to the resonant frequency. Claim 14 A transmitting module comprising: an RF signal source that outputs an RF signal while sweeping a frequency; a coupling coil that wirelessly couples with a receiving module; a gain / phase detector that converts the voltage across the coupling coil into a voltage gain and / or phase difference; and a controller that measures self-impedance with the receiving module removed, calculates an input impedance based on the output of the gain / phase detector measured during the frequency sweep with the receiving module coupled, calculates a reflection impedance based on the difference between the input impedance and the self-impedance, and then determines a resonant frequency from the reflection impedance. Claim 15 In claim 14, the controller determines the frequency at which the imaginary part of the reflection impedance becomes zero as the resonant frequency, or determines the frequency corresponding to the median value of the imaginary part of the reflection impedance as the resonant frequency, a transmitting module.

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