JP2008204234A - RFID tag built-in SAW sensor and measurement system - Google Patents

Abstract

An RFID tag built-in type SAW sensor capable of extending a communication distance with a reader and a measurement system with a simplified system construction using the same.
An RFID tag built-in type SAW sensor receives an RFID tag communication command signal transmitted from a reader, and obtains an operation control of the SAW sensor corresponding to the content of the command signal and the control. A sensor signal analysis and recording process, an RFID tag with a sensor input terminal for controlling transmission of measurement data obtained by the process, and a SAW sensor drive signal transmitted from the reader are received, and the drive signal The RFID tag includes a SAW sensor that detects a phase difference between a reference wave obtained directly and a delayed wave reflected by a reflector on the SAW chip, converts the phase difference into an analog signal, and outputs the signal as sensor data. Sensor signal processing is performed in the built-in SAW sensor, and measurement data is transmitted to the reader by RFID tag communication.
[Selection] Figure 1

Description

  The present invention relates to a SAW (Surface Acoustic Wave) sensor and a system for measuring an external temperature, pressure, stress, etc. using the SAW sensor, and in particular, extends a communication distance with a reader by using an RFID tag with a sensor input terminal. The present invention relates to a SAW sensor with a built-in RFID tag and a measurement system.

  Conventionally, there are a thermistor, a resistance temperature detector, a thermocouple, an IC temperature sensor, etc. as a sensor, for example, a temperature sensor for measuring temperature, all of which convert a signal obtained from the temperature sensor into temperature data. Required peripheral circuits and a power supply. For this reason, in the use which installs many said temperature sensors, installation of a power wire, a signal wire, etc. was complicated. However, if a SAW sensor is used as the temperature sensor, it is not necessary to install the power supply line, the signal line, etc., and a system suitable for the application can be constructed. For example, as described in “SAW sensor, individual identification device using SAW sensor, and method of manufacturing SAW sensor” in Japanese Patent Application Laid-Open No. 2004-129185, the SAW sensor is formed on a piezoelectric substrate using comb-shaped electrodes. The SAW element and the antenna are arranged, the drive signal is transmitted from the SAW element drive signal generation unit, and the temperature change of the measurement object is received as the change of the surface acoustic wave speed, the delay time, etc. Is to be calculated.

  As in the above publication example, in the method of measuring the temperature by changing the speed of the reflected signal due to the surface acoustic wave, the delay time, etc., the delay time in the SAW element unit is in nanosecond units, so it is necessary to perform the arithmetic processing at high speed. There is a disadvantage that the arithmetic circuit becomes complicated and expensive.

  In order to solve the above-mentioned drawbacks, in the “Room temperature management and fire alarm system using SAW thermometer” disclosed in Japanese Patent Application Laid-Open No. 2006-170864 by the applicant of the present application, the SAW element for room temperature measurement and the SAW element for high temperature measurement are formed on each piezoelectric substrate. An IDT (Interdigital Transducers), which is a comb-shaped electrode, and a temperature measurement reflector are arranged, and an ID (Identification) detection reflector is arranged on one of the piezoelectric substrates, and the reference transmitted by the reader during temperature measurement A large number of the SAW sensors were installed by converting the phase difference between the signal and the reflected signal reflected from each SAW element into a voltage signal by a phase detector and further converting it into temperature data by an A / D converter. We proposed a SAW thermometer and fire alarm system that can easily and inexpensively measure a wide range of temperatures.

JP 2004-129185 A JP 2006-170864 A

  However, since the reflected signal propagation from the SAW sensor to the reader is directly propagated in the air, the attenuation of the reflected signal is large in the example described in the above publication. For this reason, the transmission distance of the reflected signal is shortened, causing a problem that the system cannot function sufficiently. Although the problem of attenuation of the reflected signal is solved by raising the radio wave transmission level from the reader, it is actually difficult because there is a limitation in the radio wave law depending on the carrier frequency.

  The present invention has been made in order to solve the above-described problems, eliminates the attenuation problem associated with the propagation of reflected signals from the SAW sensor in the air, and is a sufficiently large radio wave that can be used under the Radio Law. Provided are an RFID tag built-in type SAW sensor that can stably extend a communication distance with a reader by using a transmission level, and a measurement system that simplifies system construction using the RFID tag built-in type SAW sensor. For the purpose.

  In order to solve the above problems, the RFID tag built-in type SAW sensor of the present invention receives a command signal for RFID tag communication transmitted from a reader, and controls the operation of the SAW sensor corresponding to the content of the command signal. And an RFID tag with a sensor input terminal that performs analysis and recording processing of sensor data obtained by the control and transmission control of measurement data obtained by the processing, and a driving signal for the SAW sensor transmitted from the reader To the SAW sensor that detects the phase difference between the reference wave directly obtained from the drive signal and the delayed wave reflected by the reflector on the SAW chip, converts it to an analog signal, and outputs it as sensor data. Configured to perform sensor signal processing within the RFID tag built-in SAW sensor, and transmit measurement data to the reader via RFID tag communication. It is characterized in.

  The RFID tag with sensor input terminal supplies an antenna and an RFID chip for receiving a command signal for RFID tag communication transmitted from a reader, and a driving power source for controlling the SAW sensor in accordance with the content of the command signal. Power supply circuit, and an A / D converter for analyzing sensor data obtained by controlling the SAW sensor.

  The SAW sensor includes an antenna and a SAW chip for receiving a drive signal for a SAW sensor transmitted from a reader, a switch control circuit that operates using a drive power supply from the RFID tag with the sensor input terminal as a trigger, A switch driven by the switch control circuit so that a signal directly obtained from the drive signal is a reference wave and a signal reflected between the IDT on the SAW chip and the reflector is a delay wave, and the order of the reference wave and the delay wave It comprises a phase difference detector for detecting a phase difference and converting it into an analog signal, and a sample and hold circuit for temporarily holding sensor data from the phase difference detector.

  In addition, in the measurement system using the RFID tag built-in type SAW sensor of the present invention, one or a plurality of RFID tag built-in type SAW sensors capable of transmitting measurement data by performing wireless communication with the reader. One unit or a plurality of units are connected to the network according to the scale of the system.

  The reader includes an RFID communication unit for performing wireless communication between the RFID tags with sensor input terminals in the RFID tag built-in type SAW sensor and driving the SAW sensor, a network communication unit for communicating with an external network, It comprises a CPU for controlling each communication unit, a memory, a clock, and a power supply unit.

  Carriers used for wireless communication between the reader and the RFID tag with a sensor input terminal in the RFID tag built-in SAW sensor and for driving the SAW sensor in the RFID tag built-in SAW sensor are defined by the Radio Law for RFID communication. Use the same frequency and radio wave transmission level.

  According to the SAW sensor with built-in RFID tag and the measurement system of the present invention, it is not necessary to directly propagate the reflected signal to the reader in the air with respect to the driving signal for measurement transmitted from the reader. Since the sensor signal processing is performed and the measurement data is transmitted to the reader by RFID tag communication, the problem of attenuation of the reflected signal is eliminated, and there is an effect that a long communication distance can be obtained. In addition, since the carrier frequency used for the wireless communication between the reader and the RFID tag with a sensor input terminal in the SAW sensor with a built-in RFID tag and the driving of the SAW sensor is unified with the frequency defined by the Radio Law for RFID communication, the reader's There is also an effect that the system construction can be simplified by reducing the number of installations.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic circuit block diagram showing the SAW sensor with a built-in RFID tag according to the present invention. The SAW sensor 3 with a built-in RFID tag receives a command signal for RFID tag communication transmitted from a reader, and the command signal RFID tag 4 with a sensor input terminal for performing operation control of SAW sensor 6 corresponding to the contents of the above, analysis and recording processing of sensor data obtained by the control, and transmission control of measurement data obtained by the processing, A driving signal for the SAW sensor transmitted from the reader is received, and the phase difference between the reference wave directly obtained from the driving signal and the delayed wave reflected by the reflector 16 on the SAW chip 14 is detected and analogized. It is composed of a SAW sensor 6 that converts it into a signal and outputs it as sensor data, and performs sensor signal processing within the RFID tag built-in type SAW sensor 3. There, it transmits the measured data at the RFID tag communicating to the reader.

  The RFID tag 4 with the sensor input terminal controls the antenna 5 and the RFID chip 8 for receiving the RFID tag communication command signal transmitted from the reader, and the SAW sensor 6 corresponding to the content of the command signal. A power supply circuit for supplying the drive power supply 10 and an A / D converter 9 for analyzing the sensor data obtained by the control of the SAW sensor 6 are configured. The A / D converter 9 may be integrated in the RFID chip 8.

  The SAW sensor 6 is a switch control that operates using the antenna 7 and the SAW chip 14 for receiving the driving signal for the SAW sensor transmitted from the reader and the driving power supply from the RFID tag 4 with the sensor input terminal as a trigger. Switches 17 and 18 driven by the switch control circuit 11 so that a signal directly obtained from the circuit 11 and the drive signal is a reference wave and a signal reflected between the IDT 15 on the SAW chip 14 and the reflector 16 is a delayed wave. A phase difference detector 19 for detecting a phase difference between the reference wave and the delayed wave and converting it to an analog signal, and a switch 12 and a capacitor 13 for temporarily holding sensor data from the phase difference detector 19 The sample and hold circuit is configured. The switches 17, 18 and 12 are not mechanical switches such as relays but semiconductor switches capable of high-speed switching.

  Next, FIG. 2 is a schematic configuration diagram of a measurement system using the SAW sensor with a built-in RFID tag of the present invention. The measurement system can transmit measurement data by performing wireless communication with the reader 1 and the reader 1. One unit is constituted by one or a plurality of RFID tag built-in type SAW sensors 3, and one unit or a plurality of units are connected to a network depending on the scale of the measurement system. The network is generally the Internet or an intranet, but is not particularly limited. If it is small, it may be a stand-alone. The RFID tag built-in SAW sensor 3 is configured to be directly installed at a location where temperature, pressure, stress, and the like are measured. Therefore, the RFID tag 4 with a sensor input terminal in the RFID tag built-in type SAW sensor 3 is preferably a batteryless type that performs passive operation.

  Next, FIG. 3 is a schematic circuit block diagram of a reader used in the measurement system using the SAW sensor with a built-in RFID tag of the present invention. The reader 1 is an RFID tag with a sensor input terminal in the SAW sensor 3 with a built-in RFID tag. An antenna 2 and an RFID communication unit 20 for performing wireless communication with each other and driving the SAW sensor 6, a network communication unit 22 for communicating with a network, and a CPU 21 for controlling each of the communication units , A memory 23, a clock 24, and a power supply unit 25.

  The carrier used for wireless communication between the reader 1 and the RFID tag 4 with the sensor input terminal in the RFID tag built-in type SAW sensor 3 and for driving the SAW sensor 6 in the RFID tag built-in type SAW sensor 3 is used for RFID communication. The frequency and radio wave transmission level defined by the Radio Law are used, and for example, the 953 MHz band is suitable. The 953 MHz band is a frequency used for remote RFID tag communication, and the communication distance is about 3 to 5 m even in passive operation, so the communication distance is greatly extended compared to the reflected signal propagation of the conventional SAW sensor. can do.

  FIG. 4 is an operation principle diagram of the phase difference detector in FIG. 1. When a reference wave is input to one input terminal of the phase difference detector 19 and a reflected wave is input to the other input terminal, the built-in log amplifier After the signal level is adjusted appropriately, the phase difference between both signals is calculated and output as an analog signal (voltage signal). As this type of IC, for example, there is AD8302 of Analog Devices, Inc., and the phase difference measurement range is -180 to + 180 °, and it is common not to distinguish the difference of ± 90 °. The range is 0 to + 180 ° centered on 0 to −180 ° or + 90 °. The output voltage is 0 to 1.8 V in the range of −180 to 0 °, 1.8 V to 0 V in the range of 0 to + 180 °, and one of the phase ranges is used. Thus, the phase difference detector 18 uses the IC or an IC having an equivalent function.

  FIG. 5 is a circuit block diagram of the first embodiment of the RFID tag with sensor input terminal in the SAW sensor with built-in RFID tag of the present invention. The RFID tag 4 with sensor input terminal receives sensor data from the SAW sensor 6 as A / An RFID chip 8 having a function of inputting serial data obtained by conversion into measurement data by the D converter 9 and transmitting it to the reader 1 by a read command, and an antenna 5 connected to the RFID chip 8 Constitute.

  Since the antenna 5 performs radio communication with the reader 1 by electromagnetic waves, the antenna 5 is connected to a tuning circuit 26 composed of a tuning capacitor (not shown) in the RFID chip 8 or partly outside the RFID chip 8, so that the carrier frequency such as 953 MHz band is obtained. A resonance circuit is formed by tuning.

  At the subsequent stage of the tuning circuit 26, the voltage waveform of the induced electromotive force generated when the electromagnetic wave output from the antenna 2 of the reader 1 passes through the antenna 5 of the RFID tag 4 with the sensor input terminal is detected. A rectifier circuit 27 is connected to extract the DC voltage by rectifying the electromotive force by half wave or full wave.

  Next, after the rectifier circuit 27, a clock generation circuit 28 for dividing the detected carrier to generate a system clock, and a demodulation operation for extracting a signal from the carrier at the time of signal reception are performed. A modulation / demodulation circuit 29 for performing a modulation operation by a switching element (not shown) during transmission, stabilizes the DC voltage, supplies circuit power to the RFID chip 8 and peripheral circuits, and charges the charging capacitor 31. A power supply circuit 30 for supplying voltage is connected. The power supply circuit 30 is also used to supply a drive power supply 10 that controls the SAW sensor 6.

  Next, after the modulation / demodulation circuit 29, control of the modulation / demodulation circuit 29 and ID data, measurement data, etc. of the RFID chip 8 with respect to FRAM (Ferroelectric RAM: a registered trademark of Ramtron USA) 33 which is a nonvolatile memory are provided. A logic circuit 32 for performing writing or reading control is connected. The logic circuit 32 is provided with terminals for a clock signal (CLK) and a serial input signal (SI) for inputting serial data obtained by the external A / D converter 9.

  The FRAM 33 is a ferroelectric nonvolatile memory, and the ID data and measurement data of the RFID chip 8 are not lost even when the circuit power is turned off. In addition, since the data write voltage does not need to be boosted to a high voltage unlike an EEPROM or a flash memory, the booster circuit is simplified. Further, the writing or reading speed is equivalent to that of DRAM, and is characterized by being much faster than EEPROM and flash memory. Thus, although FRAM33 is suitable as a non-volatile memory, you may use another memory.

  FIG. 6 is a circuit block diagram of a second embodiment of the RFID tag with sensor input terminal in the SAW sensor with a built-in RFID tag of the present invention, which is basically the same as the first embodiment, The only difference is that the A / D converter 9 is incorporated as an A / D conversion circuit 34. In this case, the A / D conversion circuit 34 is provided with a terminal for an analog input signal (Ai) for inputting sensor data obtained by the SAW sensor 6. In any embodiment, the sensor data held by the sample hold circuit is scaled to an appropriate level by a scaler amplifier (not shown) built in the A / D converter 9 or the A / D conversion circuit 34, Measurement data is obtained by performing A / D conversion.

  Next, an outline of the operation of the measurement system will be described using a flowchart.

  FIG. 7 is a flowchart at the start of measurement of the measurement system using the RFID tag built-in type SAW sensor of the present invention. In the operation, first, a measurement start command is transmitted from the RFID communication unit 20 in the reader 1 to the RFID tag built-in type SAW sensor 3. (Step S1-1) The command signal is a modulated wave in which a Manchester code is superimposed on a carrier.

  Next, the command signal is received by the antenna 5 of the RFID tag 4 with a sensor input terminal in the RFID tag built-in type SAW sensor 3. (Step S1-2) At this time, the modulation signal resonates in the tuning circuit 26 in the antenna 5 and the RFID chip 8, and an induced electromotive force is generated. Therefore, the induced electromotive force is charged into the charging capacitor 31 from the power supply circuit 30 in the RFID chip 8, and the drive power supply 10 that controls the RFID chip 8, the peripheral circuit power supply, and the SAW sensor 6 is used. (Step S1-3)

  Next, a drive signal is transmitted from the RFID communication unit 20 in the reader 1 to the RFID tag built-in type SAW sensor 3. (Step S1-4) The drive signal is a carrier signal that is continuously transmitted after the command signal is transmitted.

  Next, the drive signal is also received by the antenna 7 of the SAW sensor 6 in the RFID tag built-in type SAW sensor 3. (Step S1-5) At this time, the switch 17 and the switch 18 in the SAW sensor 6 are switched by the control of the switch control circuit 11 in the SAW sensor 6, and the reference wave obtained directly from the drive signal and the IDT 15 on the SAW chip 14 are switched. The delayed wave reflected between the reflector 16 and the reflector 16 is input to the phase difference detector 19. (Step S1-6) Note that the states of the switches 17 and 18 in the drawing indicate the state in which the drive signal is supplied to the IDT 15, and the case where the delayed wave from the reflector 16 is received from the IDT 15 is illustrated. Control is performed by the switch control circuit 11 so that the connection is reversed.

  Next, the sensor data obtained by the phase difference detector 18 is input to the capacitor 13 constituting the sample hold circuit under the control of the switch control circuit 11 in the SAW sensor 6 and temporarily held. (Step S1-7)

  Next, the hold voltage is input to the A / D converter 9 in the RFID tag 4 with a sensor input terminal or the A / D conversion circuit 34 built in the RFID chip 8 and converted into digital data as measurement data. (Step S1-8) Thereafter, the measurement data is written into the FRAM 33 under the control of the logic circuit 32 in the RFID chip 8. (Step S1-9) As described above, external temperature, pressure, stress, and the like are measured by the RFID tag built-in type SAW sensor 3.

  FIG. 8 is a flowchart at the time of reading measurement data of the measurement system using the RFID tag built-in type SAW sensor of the present invention. In the operation, first, a data read command is transmitted from the RFID communication unit 20 in the reader 1 to the RFID tag built-in type SAW sensor 3. (Step S2-1)

  Next, the command signal is received by the antenna 5 of the RFID tag 4 in the RFID tag built-in type SAW sensor 3. (Step S2-2)

  Next, the measurement data is read from the FRAM 33 under the control of the logic circuit 32 in the RFID chip 8. (Step S2-3)

  Next, data is read by modulating the carrier signal with the measurement data and responding to the reader 1. (Step S2-4)

  As described above, there is obtained the RFID tag built-in type SAW sensor 3 that can stably extend the communication distance with the reader 1 without the problem of attenuation caused by the propagation of the reflected signal from the SAW sensor 6 in the air. Since the RFID tag 4 with a sensor input terminal and the SAW sensor 6 in the RFID tag built-in type SAW sensor 3 can wirelessly communicate with the same reader 1, a measurement system with a simplified system construction can be obtained.

It is a schematic circuit block diagram which comprises the RFID tag built-in type SAW sensor of this invention. It is a schematic block diagram of the measurement system using the RFID tag built-in type SAW sensor of this invention. 1 is a schematic circuit block diagram of a reader used in a measurement system using a SAW sensor with a built-in RFID tag of the present invention. FIG. 2 is an operation principle diagram of the phase difference detector in FIG. 1. 1 is a circuit block diagram of a first embodiment of an RFID tag with a sensor input terminal in a SAW sensor with a built-in RFID tag of the present invention. It is a circuit block diagram of the 2nd Example of the RFID tag with a sensor input terminal in the RFID tag built-in type SAW sensor of this invention. It is a flowchart at the time of the measurement start of the measurement system using the RFID tag built-in type SAW sensor of the present invention. It is a flowchart at the time of measurement data reading of the measurement system using the RFID tag built-in type SAW sensor of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reader 2 Antenna 3 SAW sensor with built-in RFID tag 4 RFID tag with sensor input terminal 5 Antenna 6 SAW sensor 7 Antenna 8 RFID chip 9 A / D converter 10 Driving power supply 11 Switch control circuit 12 Switch 13 Capacitor 14 SAW chip 15 IDT
16 Reflector 17 Switch 18 Switch 19 Phase Difference Detector 20 RFID Communication Unit 21 CPU
DESCRIPTION OF SYMBOLS 22 Network communication part 23 Memory 24 Clock 25 Power supply part 26 Tuning circuit 27 Rectifier circuit 28 Clock generation circuit 29 Modulation / demodulation circuit 30 Power supply circuit 31 Charging capacitor 32 Logic circuit 33 FRAM
34 A / D conversion circuit

Claims (7)

  In the RFID tag built-in type SAW sensor, the command signal for RFID tag communication transmitted from the reader is received, the operation control of the SAW sensor corresponding to the content of the command signal, and the sensor data obtained by the control The RFID tag with a sensor input terminal for performing the analysis and recording processing of the data and the transmission control of the measurement data obtained by the processing, and the SAW sensor driving signal transmitted from the reader are received and directly obtained from the driving signal. And a SAW sensor that detects the phase difference between the generated reference wave and the delayed wave reflected by the reflector on the SAW chip, converts it to an analog signal, and outputs it as sensor data. An RFID tag that performs sensor signal processing in a sensor and transmits measurement data to the reader by RFID tag communication Built-type SAW sensors and measurement systems.   The RFID tag with sensor input terminal supplies an antenna and an RFID chip for receiving a command signal for RFID tag communication transmitted from a reader, and a driving power source for controlling the SAW sensor in accordance with the content of the command signal. 2. The RFID tag according to claim 1, comprising: a power supply circuit for performing the processing and an A / D converter for performing an analysis process of sensor data obtained by controlling the SAW sensor. Built-in SAW sensor and measurement system.   The SAW sensor includes an antenna and a SAW chip for receiving a drive signal for a SAW sensor transmitted from a reader, a switch control circuit that operates using a drive power supply from the RFID tag with the sensor input terminal as a trigger, A switch driven by the switch control circuit so that a signal directly obtained from the drive signal is a reference wave and a signal reflected between the IDT on the SAW chip and the reflector is a delay wave, and the order of the reference wave and the delay wave The phase difference detector for detecting a phase difference and converting it into an analog signal, and a sample and hold circuit for temporarily holding sensor data from the phase difference detector are provided. RFID tag built-in type SAW sensor and measurement system.   In a measurement system using an RFID tag built-in type SAW sensor, a measurement system including one or more RFID tag built-in type SAW sensors capable of transmitting measurement data by wireless communication with the reader. 4. The RFID tag built-in type SAW sensor and measurement system according to claim 1, wherein one unit or a plurality of units are connected to a network depending on the scale of the system.   The reader includes an RFID communication unit for performing wireless communication between the RFID tags with sensor input terminals in the RFID tag built-in type SAW sensor and driving the SAW sensor, a network communication unit for communicating with an external network, 5. The RFID tag built-in type SAW sensor and measurement system according to claim 1, comprising a CPU for controlling each of the communication units, a memory, a clock, and a power supply unit. .   The carrier used for wireless communication between the reader and the RFID tag with a sensor input terminal in the RFID tag built-in type SAW sensor and for driving the SAW sensor in the RFID tag built-in type SAW sensor is a frequency determined by the Radio Law for RFID communication. The RFID tag built-in type SAW sensor and measurement system according to any one of claims 1 to 5, wherein a radio wave transmission level is used.   7. The RFID tag built-in type SAW sensor and measurement system according to claim 1, wherein the RFID tag with a sensor input terminal is a battery-less type.

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