KR100833884B1 - Sensing apparatus and sensing method using surface acoustic wave - Google Patents

Abstract

A sensing apparatus and a sensing method using SAW(Surface Acoustic Wave) are provided to reduce a production cost of a powerless/wireless SAW sensor by optimizing the function of a SAW transponder by installing a digital sensor. In a sensing apparatus using SAW, a sensed signal input unit receives an encoded signal. An interrogation signal input unit receives and converts an electric wave of an encoded interrogation signal into SAW. A response signal generating unit(160) generates a response signal by overlapping the SAW to increase the amplitude of the SAW, if codes of the interrogation signal and the sensed signal correspond to each other. A response signal output unit converts the response signal into an electric wave and outputs the converted electric wave.

Description

Sensing apparatus and sensing method using surface acoustic wave

1 is a view showing a state of use of a non-powered wireless sensor system using a conventional SAW.

FIG. 2 is a schematic block diagram showing the configuration of the SAW powerless wireless sensor system of FIG.

3 is a screen output of a response measurement result of the wireless power sensor system of FIG.

4 is a graph showing the maximum sensing distance of the unpowered wireless SAW sensor system of FIG.

5 and 6 are schematic block diagrams of one embodiment of a sensing device according to the invention.

7 shows the sensing device of FIG. 5 in more detail.

8 and 9 are tables illustrating a process of generating a response signal in the sensing device of FIG. 7.

10 and 11 show the response signals generated by FIGS. 8 and 9, respectively.

12 to 14 are diagrams showing a structure for controlling the magnitude of the reflected wave through a change in the external impedance.

15 and 16 show a phase controlled IDT structure different from that shown in FIG.

17 is a graph showing the maximum sensing distance of the sensing device of FIG.

18 is a diagram illustrating an algorithm for finding code values of digital sensors.

The present invention relates to a sensor device, and more particularly to a wireless sensor device capable of remote sensing.

The sensing device refers to a device having a function of detecting, detecting, determining, and measuring various physical quantities such as temperature, pressure, and humidity. Various types of sensing devices have been developed for measuring various physical quantities. .

Recently, a wireless sensing device capable of remote sensing even in a location where human beings are difficult to measure directly has been developed. In particular, a wireless sensing device that can operate without a power source has been of interest.

A representative example of such a sensing device may be a wireless sensing device using surface acoustic wave (SAW), and currently, a non-powered sensor device using a conventional surface acoustic wave has a structure in which a surface acoustic wave device is connected to a variable impedance sensor. Have

1 is a view illustrating a state of use of a non-powered wireless sensor system using a conventional SAW. 1 shows an external reader system 20 and a SAW transponder 10, but no sensor.

The external reader system 20 not only transmits a call signal to the SAW system 10 so that the SAW system 10 responds, but also receives and interprets an echo signal returned from the SAW system 10 to detect a sensor located at an actual remote location. It calculates the physical quantity (temperature, pressure, humidity, acceleration, strain, etc.) of the (not shown) and performs the role of recognizing the user.

FIG. 2 is a schematic block diagram illustrating a configuration of the non-powered wireless sensor system of FIG. 1.

When an RF interrogation signal incident to the SAW non-powered wireless sensor system 10 from the outside enters the antenna 12 of the SAW non-powered wireless sensor system 10, the transceiver IDT (Inter Digital Transducer) 14 The RF signal is reverse piezoelectric converted into surface acoustic waves.

In this case, the reverse piezoelectric converted surface acoustic wave 'A' propagates while mechanically vibrating the substrate surface by the reflected wave IDT 16 to which the sensor is connected. After the surface acoustic wave 'A' propagates to the reflected wave IDT, the reflected wave IDT 16 generates the (reflected) surface acoustic wave 'B' in the direction opposite to the (progressive) surface acoustic wave 'A'.

At this time, the magnitude of the reflected surface acoustic wave 'B' is influenced by the impedance 30 of the variable impedance sensor connected to the outside, and when the degree of influence is expressed by the equation, it is expressed as Equation (1), Equation (2) And formula (3) are parameter components constituting formula (1).

식 (1)

식 (2)

식 (3)

Formula (1)

Formula (2)

Formula (3)

이고,here,

ego,

이다.

to be.

Surface acoustic wave 'B' is a vibration propagation toward the Transceiver IDT 14, when the surface acoustic wave is propagated to the Transceiver IDT 14, the surface acoustic wave is converted into an RF signal by the piezoelectric effect. In this case, the converted RF signal is propagated into the air as a sensor response signal, and an external reader may receive the signal and calculate a sensor value.

)는 외부에 연결된 가변 임피던스 센서의 임피던스에 영향을 받으므로 결과적으로,

의 크기는 외부에 연결된 센서의 물리적인 정보를 내포하고 있다. 외부 수신기에서는 이 신호(센서 응답 Echo)를 수신하여 RF 신호를 복조함으로써 센서 값을 연산함으로써 무전원 무선 센서 시스템을 구성한다. That is, the size of the (reflective) surface acoustic wave (

) Is affected by the impedance of the variable impedance sensor connected externally,

The size of contains the physical information of the sensor connected to the outside. The external receiver receives this signal (sensor response echo) and demodulates the RF signal to calculate the sensor value to form a no-power wireless sensor system.

3 is a view illustrating a response measurement result of the sensing device of FIG. 2.

However, in terms of the maximum sensing distance, which is one of the biggest performance indices of the wireless sensor, the maximum sensing distance of the conventional SAW powerless wireless sensor is quite limited. The sensing distance of SAW wireless / wireless sensors can be calculated using the commonly accepted RADAR formula. The RADAR formula is as shown in equation (4).

식 (4)

Formula (4)

Among the many factors that determine the sensing distance in Eq. (4), important factors are antenna gain, system SNR, and SAW loss.

However, the SAW non-powered wireless sensor using the conventional technology has a structure of a reflective delay line that includes a round trip loss of the SAW, so that the loss of the reflected wave reaches -20 dB to -30 dB, thereby limiting the detection distance.

)는 1/20 ~ 1/10 정도인데, 이것은 종래 방식의 SAW 무전원 무선 센서 장치의 경우

이 보통 -20dB ~ -30dB 사이의 값을 나타냄에 기인한다. Magnitude ratio between the sensor interrogation signal and the sensor response echo

) Is about 1/20 to 1/10, which is the case for the conventional SAW powerless wireless sensor device.

This is usually due to a value between -20dB and -30dB.

은

의 절반 정도인 -10dB ~ -15dB정도를 나타낸다. SAW에서 이러한 손실이 일어나는 것은 SAW 소자가 RF 신호를 표면 탄성파로 전환하거나 표면 탄성파를 RF 신호로 변환하는데 따른 변환 손실에 기인하는데, 이 손실은 재료의 물성값 및 전극의 형상으로 인해 발생한다. 통상 SAW 소자의 경우 압전 효율(Piezoelectric conversion efficiency)은 10% 미만이다.In addition, of the conventional SAW powerless wireless sensor device

silver

It is about -10dB to -15dB which is about half of. This loss in SAW is due to the conversion loss caused by the SAW device converting the RF signal into a surface acoustic wave or converting the surface acoustic wave into an RF signal, which is caused by the material properties and the shape of the electrode. Piezoelectric conversion efficiency is typically less than 10% for SAW devices.

However, the conventional SAW non-powered wireless sensor system is a form in which the SAW reflected wave ('B' of FIG. 2) is converted into an RF signal to the outside through an antenna of the SAW non-powered wireless sensor, thereby causing a double conversion loss. Therefore, since the SAW loss of Equation (4) is large, the sensing distance is limited.

4 is a graph illustrating a maximum sensing distance of the powerless wireless SAW sensor system of FIG. 1.

In FIG. 4, when the center frequency, reader and sensor antenna gain, SAW loss, system bandwidth, system SNR, noise figure, and transmit power are 433 MHz, 2.15 dBi, 2.15 dBi, 30 dB, 10 MHz, 20 dB, 3 dB, and 10 dBm (10 mW), respectively. The maximum sensing distance is theoretically 2.83m.

Therefore, a new method different from the configuration of a conventional non-powered wireless SAW sensor device is required for transmission power prescribed by the radio wave law (domestic and national) and long distance detection of 10 m or more at the center frequency.

In addition, in the prior art, when detecting a moving object, the fluctuation of the signal value corresponding to the sensor value (physical amount: pressure, strain, etc.) of the SAW echo signal is severely changed according to the antenna angle between the receiver and the SAW sensor. This results in poor measurement stability, one of the most important parameters of sensor performance.

 Such signal instability is a problem that occurs in a general electronic communication system (Multi-path problem). Inconvenience and limitations of use due to such a problem exist in a general communication system.

Moreover, since the conventional non-powered sensor device using SAW does not use a power source, it cannot be equipped with a special circuit or algorithm for compensating signal instability like a general electronic communication system. Because of the complexity, the price becomes relatively expensive to construct a stable sensor measurement reader.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a wireless power supply device using a SAW element that can be measured at a low cost while long distance measurement and digital signal processing in the sensor itself.

In order to achieve the above object, the sensing device using the surface acoustic wave includes a sensing signal input unit, a call signal input unit, a response signal generator, and a response signal output unit.

The sensing signal input unit receives an encoded sensing signal, and the call signal input unit receives a radio wave of the encoded calling signal and converts the surface acoustic wave. When the sign of the call signal has a predetermined correspondence with the sign of the detection signal, the response signal generator generates a response signal by overlapping the amplitude of the surface acoustic wave, and the response signal output unit converts the response signal into a radio wave and outputs the response signal.

Since a sense signal and a call signal are encoded and a response signal is generated by overlapping the amplitude of the surface acoustic wave to increase, a stable and high output sense response can be obtained even without a power supply.

The response signal generation unit may generate a response signal by superimposing the converted surface acoustic wave converted into surface acoustic waves and then converting the surface acoustic wave into surface acoustic waves and the delayed surface acoustic wave that has propagated the surface acoustic waves into the surface acoustic wave state.

The propagation speed is fast and has the same phase in the device, but since the surface acoustic wave has a different phase according to its position in the device, it is possible to amplify the amplitude of the surface acoustic wave by using it.

The response signal generator may include a plurality of converters spaced apart from each other by a predetermined distance and capable of converting between radio waves and surface acoustic waves.

In consideration of the traveling speed of the surface acoustic wave, the amplitude of the surface acoustic wave can be adjusted for each of the transform units by using a plurality of transform units spaced apart by a predetermined distance.

Each converter may activate a selected polarity according to the sign of the sensing signal among different polarities, and the response signal generator may include a selector for selecting the polarity of the converter according to the sign of the sensing signal.

By selecting the polarity of the converter according to the sensing signal input and activating only the selected polarity, it is possible to selectively control the call signal input according to the sensing signal input to generate a desired response signal.

The converter may include a split finger IDT or a SPUDT IDT. Adoption of such IDT structures enables more efficient suppression of reflected waves than in the case of employing a single IDT.

In addition, an invention embodying the apparatus in the form of a method is disclosed.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

5 and 6 are schematic block diagrams of one embodiment of a sensing device according to the present invention.

In FIG. 5, the sensing device includes a SAW transponder 100, a digital sensor 300, and a matching circuit (not shown) designed to enable digital signal processing.

FIG. 5 illustrates an operation and response signal of the sensing device 100 in the case where there is a correlation between the digital sensor 300 and the external reader call sign, and FIG. 6 between the digital sensor 300 and the external reader call sign. The operation and output signal of the sensing device 100 when there is no correlation is shown.

In more detail, in FIG. 5, both the detection signal input input from the sensor 300 and the call signal input input from an external reader (not shown) are encoded digital signals '1011', whereas the call signal input is shown in FIG. 6. Although it is '1011', it can be seen that the sensing signal input is '1001'.

On the other hand, it can be seen that the output of the response signal is much larger than that of FIG. This is because, in FIG. 5, the response signal generator generates and outputs a superposed response signal to increase the call signal when the predetermined detection signal input and the call signal input have a predetermined correspondence.

의 값이 작도록 반사형이 아닌 진행형의 표면 탄성파를 이용하고, 자기 상관관계(Auto correlation)가 성립할 경우에만 감지 장치인 SAW 무전원 무선 센서 장치(100)의 응답 신호가 나올 수 있는 구조를 가진다. As can be seen in Figure 5, in the present invention

Using a non-reflective type surface acoustic wave so that the value of is small, and only when auto correlation is established, the response signal of the SAW powerless wireless sensor device 100, which is a sensing device, may be output. .

In addition, the SAW itself adopts a new method in which a non-powered digital signal processor is embedded in the SAW itself, rather than an analog method of extracting the ratio of the response echo of the SAW sensor device 100.

Therefore, the present invention can significantly extend the short sensing distance, which is a limitation of the conventional non-powered wireless sensor.

The SAW transponder 100, which is a sensing device, is used as a main transmission medium for enabling use as a non-powered wireless sensor device. The SAW transponder 100 includes an IDT (Inter Digital Transducer) (not shown) connected to the digital sensor 300 and capable of digital signal processing. When the IDT and the sensor are connected, the pulse combination of the surface acoustic wave varies depending on the value of the sensor, so it can be used as a sensor.

In particular, the IDT electrode array capable of digital signal processing in the SAW transponder 100 performs phase demodulation (PSK) on the input signal unlike the AM and FM processing schemes of the IDT array of a typical SAW device. .

By adopting the IDT structure of the SAW transponder 100 with frequency spreading and auto-correlation through PSK modulation and demodulation, the distance limitation problem, which is a disadvantage of the conventional SAW powerless wireless sensor device, is drastically improved. can do. In addition, since the sensing distance is greatly extended, the range of application can be broadly widened as compared with the conventional SAW powerless wireless sensor device.

The digital sensor 300 senses an external continuous analog physical quantity and digitizes an analog signal for each sensor resolution. In addition, the sensor 300 may measure pressure, temperature, strain, acceleration, and the like, and is used in connection with the SAW transponder 100.

The sensing device of the present invention has a structure such that the value of the sensor digitally affects the surface acoustic wave generation using the non-powered digital sensor 300.

Unlike an analog sensor of a general continuous signal, the digital sensor 300 implements a desired resolution / precision by dividing a full span of a sensor into a predetermined section (n-step), and the present invention provides a surface acoustic wave device. It uses properties that can affect the surface acoustic waves occurring inside.

For example, a switch-on / off state in the form of a general conductor is typical. If the switch-on state can change the magnitude, direction, vibration frequency, or phase of the surface acoustic wave, this may affect the surface acoustic wave. do. In addition, the structure that can change the impedance (R, L, C) of the SAW IDT may be one of the properties suitable for digital sensors.

If such a switch is to implement a certain resolution for the full span of the sensor, at least n or digitize sensor arrays are required.

The digital sensor array is connected to the internal IDTs of the SAW transponder to convert the surface acoustic waves that can be generated by the IDT. As a result, multiple array sensors are used, resulting in a digital sensor with n-step resolution. .

However, in this embodiment, the electrode arrangement of the unit sensor, which may cause a phase change of the surface acoustic wave, should have a complementary shape. That is, the sensor must be located in any one of the two electrodes in accordance with the external state change. An example is a 2x1 SPDT <Single Pole Double Throw> switch without a neutral state.

The IDT (not shown) is connected to the digital sensor by its structure and can change the property of the surface acoustic wave according to the state of the sensor. The present invention overcomes the sensing distance limitation due to the signal strength of weak output signal which is severely reduced from 1/50 to 1/10 compared to the input signal, which is a disadvantage of the general reflective delay line SAW powerless wireless sensor. At the same time, it features an IDT structure designed to ensure that the output signal is present only when it exactly matches the value of a digital sensor that senses an external physical change.

FIG. 7 illustrates the sensing device of FIG. 5 in more detail. 8 and 9 are tables illustrating a process of generating a response signal in the sensing apparatus of FIG. 7, and FIGS. 10 and 11 are diagrams illustrating response signals generated by FIGS. 8 and 9, respectively.

In FIG. 7, the response signal generator 160 of FIG. 5 includes four converters 162 to 168 and a selector 180 for selecting one of different polarities of the converters 162 to 168. . The selector 180 selects the polarities of the four converters 162 to 168 according to the sensing input signal '1011'.

As shown in FIG. 7, the sensing signal input is '1011', and as shown in FIGS. 8 and 9, respectively, the signal input of FIG. 8 is '1011' and the call signal input of FIG. 9 is '1001'.

8 and 10, when the sensing signal input and the call signal input coincide, it can be seen that the response signal output at t ₅ is amplified. However, in FIGS. 9 and 11, when the sensing signal input and the call signal input do not coincide, it can be seen that the response signal output at t ₅ is an unamplified signal.

 The IDT 160 structure, which is a conversion unit illustrated in FIG. 7, is an IDT structure in which a phase change of a signal generated by the IDT 160 is applied by surface acoustic waves and incident surface acoustic waves, and a structure capable of changing the properties of surface acoustic waves is In addition to the structure shown in Figure 7 there are several forms.

12 to 14 are diagrams illustrating a structure for controlling the magnitude of the reflected wave through a change in external impedance. FIG. 12 illustrates a typical single IDT impedance transformed structure, and FIGS. 13 and 14 illustrate a split finger IDT or a double IDT structure.

13 and 14 are diagrams for controlling the surface acoustic wave reflected wave to be generated or not generated according to the off or on state of an external switch, respectively.

15 and 16 illustrate a phase controlled IDT structure different from that of FIG. 7. 15 and 16 have an improved efficiency compared to FIG. In FIG. 15, the external switch uses a switch capable of complementary operation.

That is, the switch of FIGS. 15 and 16 refers to a form in which only the operation of 'A' or 'B' is shown in the figure. FIG. 16 is a structure for suppressing reflected waves by improving the Single IDT structure of FIG. 15 to Split Finger IDT.

As in the present invention, when selecting a reverse phase shift instead of a reflective delay line structure adopted in a conventional SAW powerless wireless sensor, the reflective surface acoustic wave should be suppressed as much as possible. In general, a single phase unit directional transducer (SPUDT) structure may be adopted to suppress reflected waves to the maximum.

 The reflected wave not only disturbs the traveling wave signal, but also involves energy loss for generating the reflected wave. Therefore, when adopting the progressive structure, it is advantageous to select the SPUDT IDT.

The present invention can obtain the response of the SAW non-powered wireless sensor device to the variable code (Variable Code or Digit) through the combination of the digital sensor and the phase change IDT structure.

17 is a graph showing the maximum sensing distance of the sensing device of FIG. 5. In FIG. 17, it can be seen that the sensing device of the present invention has increased the maximum sensing distance by five times than the conventional sensing device.

In addition, since the wireless sensor device using the conventional battery technology is a sensor that requires most power, real-time measurement is impossible, but the sensing device according to the present invention can operate even without power.

In addition, since the present invention system is a non-powered system, the resistance to discharge or external environment is strong, so that the number of components can be reduced when designing a system, and thus, the economical advantage is increased because low-cost production is possible than the conventional SAW non-powered wireless sensor device.

18 is a diagram illustrating an algorithm for finding code values of digital sensors.

As can be seen from the SAW operation part of FIG. 18, the sensing device of the present invention outputs an amplified response signal only when a detection signal input from a digital sensor and a call signal input from a reader are correlated, so that a user calls various calls. After inputting the signal to the sensing device, if there is a desired response signal from the sensing device, the sign of the digital sensor may be known.

According to the present invention, real-time measurement is possible without using a battery, and the IDT structure of the SAW transponder is designed to perform autocorrelation function and frequency despreading function, thereby significantly increasing the sensing distance of the sensing device. .

In addition, by mounting the digital sensor to optimize the function of the SAW transponder can significantly reduce the mass production cost of the wireless power SAW sensor.

In addition, due to the finiteness of the battery life of the conventional battery-type wireless sensor it is possible to overcome the point that it is impossible to detect in real time.

Although the present invention has been described in terms of some preferred embodiments, the scope of the present invention should not be limited thereby, but should be construed as modifications or improvements of the embodiments supported by the claims.

Claims (12)

A detection signal input unit configured to receive an encoded detection signal; A call signal input unit configured to receive a radio wave of an encoded call signal and convert it into a surface acoustic wave; A response signal generator for generating a response signal by overlapping the amplitude of the surface acoustic wave when the sign of the call signal has a predetermined correspondence with the sign of the detection signal; And And a response signal output unit converting the response signal into a radio wave and outputting the response signal. The method of claim 1, The response signal generator, Using a surface acoustic wave, a response signal is generated by superimposing the converted surface acoustic wave converted into surface acoustic waves and then the delayed surface acoustic wave propagating the surface acoustic wave into a surface acoustic wave state. Sensing device. The method of claim 2, The response signal generator, A sensing device using a surface acoustic wave, characterized in that it comprises a plurality of converters spaced apart from each other by a predetermined distance and capable of converting between radio waves and surface acoustic waves. The method of claim 3, wherein Wherein each of the converters activates a polarity selected according to a sign of the sensing signal among different polarities. The method of claim 4, wherein And the response signal generator includes a selector configured to select the polarity of the converter based on a sign of the sensed signal. The method of claim 4, wherein And the converting unit comprises a split finger IDT. The method of claim 4, wherein The conversion unit is a sensing device using a surface acoustic wave, characterized in that it comprises a SPUDT IDT. A sensing signal input step of receiving an encoded sensing signal; A call signal input step of receiving a radio wave of an encoded call signal and converting the signal to a surface acoustic wave; A response signal generating step of generating a response signal by overlapping the amplitude of the surface acoustic wave to increase when a sign of the call signal corresponds to a sign of the detection signal; And And a response signal output step of converting the response signal into a radio wave and outputting the response signal. The method of claim 8, The response signal generation step, Using a surface acoustic wave, a response signal is generated by superimposing the converted surface acoustic wave converted into surface acoustic waves and then the delayed surface acoustic wave propagating the surface acoustic wave into a surface acoustic wave state. Detection method. The method of claim 9, The response signal generation step, A sensing method using a surface acoustic wave, which is spaced apart from each other by a predetermined distance and is performed by a plurality of converters capable of converting between radio waves and surface acoustic waves. The method of claim 10, And each of the converters activates a polarity selected according to a sign of the sensing signal among different polarities. The method of claim 11, The generating of the response signal includes selecting a polarity of the conversion device according to a sign of the detection signal.

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