JP2010204927A - Active rfid tag using thermoelectric conversion element as power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active RFID (Radio Frequency Identification) tag permanently operating by use of faint electromotive force of a thermoelectric conversion element. <P>SOLUTION: This active RFID tag includes a redundant circuit including first and second circuit blocks as a power supply mechanism thereof. The first and second circuit blocks are alternately and exclusively connected to the thermoelectric conversion element and a booster circuit. A plurality of electric double layer capacitors included in each circuit block are connected to the thermoelectric conversion element in parallel and are connected to the booster circuit in series, so that drive voltage of the RFID tag can be generated even from the faint electromotive force of the thermoelectric conversion element in a short time, and it can be permanently supplied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an active RFID tag, and more particularly to an active RFID tag that operates continuously using a weak electromotive force of a thermoelectric conversion element.

  In recent years, individual identification technology using RFID (Radio Frequency Identification) tags has been applied to various solutions. Here, RFID tags are classified into an active type that has a built-in power supply and can oscillate and drive radio waves spontaneously, and a passive type that oscillates and drives in response to external radio wave energy. . In general, the active RFID has the advantage that the communication distance is much longer and the application is wider than the passive type. However, the battery must be built in as a driving power source. Maintenance costs are incurred.

  In this regard, Japanese Patent Application Laid-Open No. 2007-280368 (Patent Document 1) discloses an active RFID including a thermoelectric element as a drive power supply in order to eliminate the cost associated with such a power supply. However, Patent Document 1 does not disclose any specific configuration of the power supply mechanism including the thermoelectric element, and the content is merely a mere idea.

JP 2007-280368 A

The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to provide an active RFID tag that operates permanently using the weak electromotive force of a thermoelectric conversion element. .

  As a result of intensive studies on an active RFID tag that can operate permanently using the weak electromotive force of the thermoelectric conversion element, the present inventor has obtained two circuits including a plurality of electric double layer capacitors as a power supply mechanism. The idea was to form it as a redundant circuit. Further, in addition to alternately and exclusively connecting the two redundant circuits to the thermoelectric conversion element side and the RFID main body side, a plurality of electric double layer capacitors included in each redundant circuit are converted to thermoelectric conversion. By connecting in parallel to the device and in series to the booster circuit, the drive voltage of the RFID tag can be generated in a short time from the weak electromotive force of the thermoelectric conversion device and supplied permanently. As a result, the present inventors have found out that they can do this, and have reached the present invention.

  That is, according to the present invention, there is provided an active RFID tag including a thermoelectric conversion element, a booster circuit connected to an RFID main body, and a redundant circuit exclusively connected to the thermoelectric conversion element and the booster circuit. The redundant circuit includes first and second circuit blocks each including a plurality of electric double layer capacitors, and the plurality of electric double layer capacitors of the first circuit block are connected in parallel with the thermoelectric conversion element. A first state in which the plurality of electric double layer capacitors of the second circuit block are connected in series to the booster circuit; and the plurality of electric double layer capacitors of the second circuit block are the thermoelectric conversion elements. A second state in which the plurality of electric double layer capacitors of the first circuit block are connected in parallel and alternately connected in series to the booster circuit is alternately repeated. Active RFID tags to be controlled is provided.

  In the present invention, the redundant circuit is controlled so that, in the first state, the first circuit block is disconnected from the booster circuit, and the second circuit block is disconnected from the thermoelectric conversion element. In the second state, the second circuit block can be controlled to be disconnected from the booster circuit, and the first circuit block can be controlled to be disconnected from the thermoelectric conversion element. In the present invention, the redundant circuit can be controlled to transition between the states in response to the input voltage of the booster circuit reaching the threshold voltage, and the threshold voltage is The minimum input voltage of the booster circuit can be set.

As described above, according to the present invention, an active RFID tag that can operate permanently using the weak electromotive force of the thermoelectric conversion element is provided.

The conceptual diagram of the electric power supply mechanism of the active RFID tag of this invention. The conceptual diagram of the electric power supply circuit of the active RFID tag of this embodiment. The operation | movement flowchart of the active RFID tag of this embodiment.

  Hereinafter, the present invention will be described with reference to embodiments shown in the drawings, but the present invention is not limited to the embodiments shown in the drawings. In the drawings referred to below, the same reference numerals are used for common elements, and the description thereof is omitted as appropriate.

  The present invention includes a mechanism for operating an active RFID tag by an electromotive force of a thermoelectric conversion element. That is, in the present invention, the electromotive force of the thermoelectric conversion element is temporarily stored in the electric double layer capacitor, and the RFID tag is operated using this stored power. However, the electromotive force of the thermoelectric conversion element is generally small, especially in applications where the body temperature of a human or a constant temperature animal is used as the heat source, the temperature difference between the heat source and the outside air is as small as about a dozen degrees C. The amount of power generation is extremely small, and it takes a long time for the terminal voltage of the electric double layer capacitor to reach the driving voltage of the RFID tag. Furthermore, since the electric power cannot be supplied to the RFID main body until the electric double layer capacitor is discharged and stored again, the RFID tag cannot oscillate during that time. In this regard, the present invention discloses a power supply mechanism for permanently operating an active RFID tag with only a weak electromotive force of a thermoelectric conversion element.

  FIG. 1 is a conceptual diagram for explaining a power supply mechanism of an active RFID tag (hereinafter referred to as an active RFID tag) operating with an electromotive force of a thermoelectric conversion element of the present invention. Hereinafter, the power supply mechanism of the active RFID tag according to the present invention will be described separately for a power storage mode and a supply mode.

FIG. 1A is a conceptual diagram of the power storage mode 100. The storage mode 100 is a circuit block A that includes the thermoelectric conversion element 10, two electric double layer capacitors 12 and 12, and a circuit block that also includes two electric double layer capacitors 12 and 12 and has the same circuit configuration as the circuit block A. B. In the power storage mode 100, each of the circuit blocks A and B includes two electric double layer capacitors 12 and 12 connected in parallel to the thermoelectric conversion element 10, and the circuit block A Alternatively, either one of B is configured to be exclusively connected to the thermoelectric conversion element 10. In addition, the thermoelectric conversion element 10 in the present invention is a Seebeck element formed by joining two different metals or semiconductors, and may be an element that generates an electromotive force when a temperature difference is generated between both ends.

  As shown in FIG. 1A, the thermoelectric conversion element 10 is connected to the circuit block A. In this state, the electromotive force of the thermoelectric conversion element 10 is the electric power of the circuit block A connected in parallel. Electricity is stored in the multilayer capacitors 12 and 12. On the other hand, the thermoelectric conversion element 10 is configured to be connected to the circuit block B as indicated by a broken arrow, and in this case, the electromotive force of the thermoelectric conversion element 10 is the same as that of the circuit block B connected in parallel. The electric double layer capacitors 12 and 12 are charged. In FIG. 1A, it is assumed that the terminal voltage of the electric double layer capacitor 12 is 0.6 V due to the electromotive force of the thermoelectric conversion element 10.

  The capacitance of the electric double layer capacitor 12 in each circuit block is an appropriate value based on the power consumption per hour of the RFID, the amount of power generation per hour of the thermoelectric conversion element 10 in the assumed usage mode, and the like. It is desirable to select one. This point will be described in detail later.

  On the other hand, FIG. 1B is a conceptual diagram of the supply mode 200. The supply mode 200 includes the circuit block A or B described above and the DC-DC converter 14 for boosting the DC voltage. Here, the following description will be made assuming that the minimum input voltage for operating the DC-DC converter 14 is 0.8 V, and the driving voltage of the RFID main body 16 that is the final power supply destination is 3.0 V.

  In supply mode 200, one of circuit blocks A and B including two stored electric double layer capacitors 12, 12 is exclusively connected to DC-DC converter 14. A solid line arrow in FIG. 1B illustrates a case where the circuit block B is connected to the DC-DC converter 14. Here, in the power storage mode 100 described above, the two electric double layer capacitors 12 and 12 in the circuit block B are stored, and as a result, the terminal voltage is 0.6V. However, this value does not reach the minimum input voltage of 0.8 V of the DC-DC converter 14.

  Therefore, in the supply mode 200, first, the connection of the two electric double layer capacitors 12 and 12 in the circuit block B is switched so as to be in series with the DC-DC converter 14. As a result, the input voltage to the DC-DC converter 14 is 0.6 × 2 = 1.2 V, and can exceed 0.8 V, which is the lowest input voltage of the DC-DC converter 14. That is, the electric power stored in the electric double layer capacitors 12 and 12 of the circuit block B is input to the DC-DC converter 14 at 1.2 V, boosted to 3.0 V, and then supplied to the RFID main body 16. The In parallel with this, in the electricity storage mode 100, electricity is stored from the thermoelectric conversion element 10 to the two electric double layer capacitors 12, 12 of the circuit block A.

  Thereafter, the terminal voltage of the electric double layer capacitors 12 and 12 of the circuit block B connected in series to the DC-DC converter 14 decreases with time from the initial 1.2 V with the power consumption of the RFID main body 16. I will do it. Here, if this falls below 0.8 V, which is the minimum input voltage of the DC-DC converter 14, the DC-DC converter 14 cannot be boosted and power supply to the RFID main body 16 is stopped. Therefore, in the present invention, before such a situation occurs, the connection destination of the DC-DC converter 14 is switched from the circuit block B to the circuit block A as indicated by a broken line arrow in FIG. By repeating the control described above, power is permanently supplied to the RFID main body 16.

  That is, the circuit block A and the circuit block B connect a plurality of electric double layer capacitors in parallel to the thermoelectric conversion element in the storage mode 100, and a plurality of stored electric double layer capacitors in the supply mode 200. Are connected in series and then connected to the booster circuit, whereby the RFID driving voltage can be generated in a short time from the weak electromotive force of the thermoelectric conversion element 10.

  Furthermore, through the storage mode 100 and the supply mode 200, the circuit block A and the circuit block B are alternately connected to the power generation side and the other is connected to the power consumption side, thereby alternately repeating the circuit. Blocks A and B function as two redundant circuits, which enables permanent power supply to the RFID main body 16. The outline of the power supply mechanism of the active RFID tag of the present invention has been described above. Next, the operation of the power supply mechanism will be specifically described with reference to FIGS.

  FIG. 2 conceptually shows a power supply circuit of an active RFID tag 20 (hereinafter referred to as the active RFID tag 20) that operates with an electromotive force of a thermoelectric conversion element according to an embodiment of the present invention. The active RFID tag 20 of the present embodiment includes a thermoelectric conversion element 10, a redundant circuit 22, a DC-DC converter 14, and an RFID main body 16, and the redundant circuit 22 includes the thermoelectric conversion element 10. And the DC-DC converter 14 are formed so as to be freely connectable. The redundant circuit 22 in the present embodiment includes a circuit block A and a circuit block B, and both blocks are configured as equivalent circuits including two electric double layer capacitors 12 and 12. .

  The circuit blocks A and B in the redundant circuit 22 are configured to include a plurality of switches SW. When these switches are ON / OFF controlled, the redundant circuit 22 has a first configuration shown in FIG. The state transits to the second state shown in FIG. FIG. 2 conceptually shows the power supply circuit of the active RFID tag 20, and does not show an actual circuit. In an actual power supply circuit, the switch SW for controlling the transition from the first state to the second state can be configured by a diode switch, for example.

  In the first state, as indicated by a thick line in FIG. 2 (a), the electric double layer capacitors 12 and 12 included in the circuit block A are connected in parallel to the thermoelectric conversion element 10, and a DC-DC converter. 14 is disconnected. In the first state, the electric double layer capacitors 12 and 12 included in the circuit block B are connected in series to the DC-DC converter 14 and are disconnected from the thermoelectric conversion element 10.

  On the other hand, in the second state, as indicated by the thick line in FIG. 2B, the electric double layer capacitors 12 and 12 included in the circuit block A are connected in series to the DC-DC converter 14 and are connected to the thermoelectric circuit. It is separated from the conversion element 10. In the second state, the electric double layer capacitors 12 and 12 included in the circuit block B are connected in parallel to the thermoelectric conversion element 10 and are disconnected from the DC-DC converter 14. The redundant circuit 22 efficiently boosts the weak electromotive force generated from the thermoelectric conversion element 10 to the drive voltage of the DC-DC converter 14 by alternately repeating the first state and the second state described above, This makes it possible to supply continuously.

  FIG. 3 shows an operation flowchart of the active RFID tag 20 of the present embodiment. Hereinafter, the power supply operation in the active RFID tag 20 of this embodiment will be described more specifically with reference to the operation flowchart of FIG. 3 and the circuit conceptual diagram of FIG. 2 alternately.

The active RFID tag 20 of the present embodiment will be described assuming that the first state shown in FIG. First, in step 101, the voltage (V _PA ) between terminals of the electric double layer capacitors 12 and 12 of the circuit block A connected in parallel to the thermoelectric conversion element 10 is monitored. This voltage monitoring is repeated until (V _PA ) reaches the threshold voltage (V ₁ ) (No in step 101). Here, the threshold voltage (V ₁ ) in the present embodiment can be set to an appropriate value according to the following criteria.

First, the threshold voltage (V ₁ ) is larger than the value obtained by dividing the minimum input voltage (V _DC-DC ) of the DC-DC converter 14 by the number of electric double layer capacitors 12 included in the circuit block A, and the minimum input voltage It is preferable to set an appropriate value smaller than the voltage. Here, if the minimum input voltage is “0.8 V” and the number of electric double layer capacitors 12 is “2”, the threshold voltage (V ₁ ) is {0.4 (= 0.8 / 2). ) can be defined as _<V 1 <0.8}.

Further, the threshold voltage (V ₁ ) is the rate of decrease (ΔV / t) of the series terminal voltage of the electric double layer capacitors 12 and 12 per time associated with the power consumption of the RFID, and the operation of the RFID per one charge. An appropriate value can be determined according to time (t). Here, the operation time (t) of RFID per power storage is an arbitrary design item and can be determined as appropriate.

Specifically, first, the circuit blocks A and B determine the initial voltage (V _i ) when connected to the DC-DC converter 14 according to the operation time (t). Here, assuming that the operation time (t) is “10 minutes” and the rate of decrease (ΔV / t) is “0.04 V / min”, the operation time of “10 minutes” is realized with one power storage. For this purpose, “1.2V” is obtained by adding “0.04 (V / min) × 10 (min) = 0.4 V” to the value “0.8 V” of the minimum input voltage (V _DC-DC ). It is necessary to set the initial voltage (V _i ). If the initial voltage (V _i ) is determined in this way, the threshold voltage (V ₁ ) is derived by dividing this by the number of electric double layer capacitors 12. In the example described above, the threshold voltage (V ₁ ) is 1.2V ÷ 2 = 0.6V.

When the voltage (V _PA ) between the terminals of the electric double layer capacitors 12 and 12 of the circuit block A reaches the threshold voltage (V ₁ ) set in the above procedure (step 101, Yes), the process proceeds to step 102, and the circuit Switching processing is executed. In step 102, the redundant circuit 22 switches from the first state shown in FIG. 2A to the second state shown in FIG. Specifically, the electric double layer capacitors 12 and 12 of the circuit block A are disconnected from the thermoelectric conversion element 10 and connected in series to the DC-DC converter 14 which is a booster circuit. Double-layer capacitors 12 and 12 are disconnected from DC-DC converter 14 and connected in parallel to thermoelectric conversion element 10.

In step 102, when the circuit switching process is performed, the input voltage (V _PA × 2) from the electric double layer capacitors 12 and 12 of the circuit block A is boosted by the DC-DC converter 14 to the drive voltage of the RFID main body 16. After that, power is supplied to the RFID main body 16 (step 103). In parallel with this, the electric double layer capacitors 12 and 12 of the circuit block B are connected and stored in parallel with the thermoelectric conversion element 10 (step 104).

During this time, in step 105, it is monitored input voltage of the DC-DC converter 14 _{(V DC-DC)} is, to below the threshold voltage _{(V 2)} (step 105, No), the steps 103 and 104 are executed. Here, the threshold voltage (V ₂ ) can be set to a value of the minimum input voltage of the DC-DC converter 14 or a value obtained by adding an appropriate margin thereto.

When the input voltage of the DC-DC converter 14 _{(V DC-DC)} is below the threshold value voltage _{(V 2)} (step 105, Yes), in step 106, the switching processing circuits is performed, redundant circuit 22, FIG. 2 A transition is made from the second state shown in FIG. 2B to the first state shown in FIG. Specifically, the electric double layer capacitors 12 and 12 of the circuit block A are disconnected from the DC-DC converter 14 and connected in parallel to the thermoelectric conversion element 10, and at the same time, the electric double layer capacitor 12 of the circuit block B. , 12 are disconnected from the thermoelectric conversion element 10 and connected in series to the DC-DC converter 14.

When the circuit switching process is performed in step 106, in step 107, the input voltage (V _PB × 2) from the electric double layer capacitors 12 and 12 of the circuit block B is converted by the DC-DC converter 14 into the RFID main body 16. After the voltage is raised to the drive voltage, power is supplied to the RFID main body 16. In parallel with this, in step 108, the electric double layer capacitors 12 and 12 of the circuit block A or the thermoelectric conversion element 10 are connected in parallel to store electricity (step 108).

During this time, in step 109, it is monitored input voltage of the DC-DC converter 14 _{(V DC-DC)} is, until the above-mentioned threshold voltage _{(V 2)} (step 109, No), the steps 107 and 108 are executed The

When the input voltage (V _DC-DC ) of the DC-DC converter 14 falls below the threshold voltage (V ₂ ) (step 109, Yes), the operation returns to step 102, and a power generation of a predetermined amount or more is generated from the thermoelectric conversion element 10. As long as there is, the operation after step 102 is repeated.

In the embodiment described above, the voltage between the terminals of the circuit block in the power storage mode is not monitored, but only the input voltage (V _DC-DC ) of the DC-DC converter 14 is monitored, and the circuit switching timing is determined. The structure to decide is adopted. The reason for this will be described below.

In this regard, step 105 will be described as an example. As described above, in step 101, the circuit block A is charged until it reaches the threshold voltage (V ₁ ), and the discharge time (that is, the operation) The time (t)) is uniquely determined. Here, in the present embodiment, the storage time of the circuit block B (that is, the time required for the voltage between the terminals of the electric double layer capacitor of the circuit block B to reach the threshold voltage (V ₁ )) The capacitance of the electric double layer capacitor 12 is designed so as to be shorter than the discharge time.

Therefore, in step 105, when the input voltage (V _DC-DC ) of the DC-DC converter 14 is lower than the threshold voltage (V ₂ ), naturally, between the terminals of the electric double layer capacitor of the circuit block B on the power storage side. Since the voltage has reached the threshold voltage (V ₁ ), the determination is omitted. The same applies to step 109 as well. In the present invention, both the voltage between the terminals of the circuit block on the power storage side and the input voltage (V _DC-DC ) of the DC-DC converter 14 are compared with a predetermined threshold value, and both conditions are satisfied. Only the circuit can be switched.

  As described above, the active RFID tag of the present invention has been described with the embodiment shown in FIGS. 2 and 3. However, the active RFID tag of the present invention is not limited to the above-described embodiment, and each circuit block described above. May be provided with three or more electric double layer capacitors, and the redundant circuit described above may be constituted by three or more circuit blocks.

  Furthermore, it should be noted that the active RFID tag of the present invention can be applied as a temperature sensor. At that time, the RFID operation time (t) corresponding to the amount of electricity stored once in the circuit block is the time resolution of the temperature sensor. In other words, the power supply to the RFID tag is cut off at most (t) hours after the heat source stops generating heat, and the RFID tag stops oscillating, so the temperature drop is detected when the oscillation signal cannot be received. can do.

  As described above, the active RFID tag of the present invention can be used permanently in a battery-free manner where there is a heat source, so the maintenance cost of the existing system using the active RFID tag is greatly increased. Reduced to

  Further, since the active RFID tag of the present invention can operate permanently even with a very small heat source, it is conceivable to use body temperature as the heat source. For example, by attaching the active RFID tag of the present invention to the body of a constant temperature animal represented by livestock such as cattle and pigs and pets such as dogs and cats, various solutions using these individual authentication information can be obtained. Can be deployed. Furthermore, by mounting the active RFID tag of the present invention on the human body, for example, it is possible to develop a solution relating to security management of hospitalized patients and confirmation of the safety of elderly people living alone.

  Further, attention should be paid to the application development as a temperature sensor of the active RFID tag of the present invention. For example, when the active RFID tag of the present invention is attached to a person or a constant temperature animal, the oscillation from the RFID tag means that there is a life function there. Such a temperature sensor function of the active RFID tag of the present invention may be used for searching for a victim and confirming safety during a large-scale earthquake disaster.

DESCRIPTION OF SYMBOLS 10 ... Thermoelectric conversion element, 12 ... Electric double layer capacitor, 14 ... DC-DC converter, 16 ... RFID main-body part, 20 ... Active RFID tag, 22 ... Redundant circuit, 100 ... Power storage mode, 200 ... Supply mode

Claims (4)

An active RFID tag including a thermoelectric conversion element, a booster circuit connected to the RFID main body, and a redundant circuit exclusively connected to the thermoelectric conversion element and the booster circuit,
The redundant circuit includes first and second circuit blocks including a plurality of electric double layer capacitors,
The plurality of electric double layer capacitors of the first circuit block are connected in parallel to the thermoelectric conversion element, and the plurality of electric double layer capacitors of the second circuit block are connected in series to the booster circuit. And the plurality of electric double layer capacitors of the second circuit block are connected in parallel to the thermoelectric conversion element, and the plurality of electric double layer capacitors of the first circuit block are connected in series to the booster circuit Controlled to alternately repeat the second state to be performed,
Active RFID tag.   The redundant circuit is controlled such that, in the first state, the first circuit block is separated from the booster circuit, and the second circuit block is separated from the thermoelectric conversion element, 2. The active RFID tag according to claim 1, wherein, in a state, the second circuit block is controlled to be disconnected from the booster circuit, and the first circuit block is controlled to be disconnected from the thermoelectric conversion element.   The active RFID tag according to claim 1, wherein the redundant circuit is controlled to transition between the states in response to the input voltage of the booster circuit reaching a threshold voltage.   The active RFID tag according to claim 1, wherein the threshold voltage is a minimum input voltage of the booster circuit.

Images