WIRELESS COMMUNICATION SYSTEM, METHOD FOR WIRELESS COMMUNICATION, AND WIRELESS DEVICE

A wireless communication system includes a first wireless device configured to be introduced inside a living body and including an antenna; and a second wireless device configured to communicate with the first wireless device via the antenna. The wireless communication system carries out communication between the first wireless device and the second wireless device via the antenna at a first frequency when the first wireless device is outside the living body and carries out the communication at a second frequency lower than the first frequency when the first wireless device is inside the living body.

FIELD

The embodiments discussed herein are related to a wireless communication system, a method for wireless communication, and a wireless device.

BACKGROUND

A wireless system is known that includes a first wireless device and a second wireless device configured to communicate with the first wireless device via an antenna of the first wireless device, where the first wireless device can be introduced to the inside of a living body (for example, refer to Patent Document 1).

LIST OF RELATED ART DOCUMENT

Patent Document 1: Japanese National Publication of International Patent Application No. 2014-525780

In such a wireless communication system, the communication between the first wireless device and the second wireless device is carried out when the first wireless device is not only inside a living body but also outside the living body.

The antenna of the first wireless device inside the living body is often in contact with biological fluids, for example, digestive fluid, inside the living body. In contrast, the antenna of the first wireless device outside the living body is often in contact with air. The permittivity of the biological fluid inside the living body differs from the permittivity of air.

Thus, the resonance frequency of the antenna of the first wireless device inside the living body often differs from the resonance frequency of the antenna of the first wireless device outside the living body. This may preclude communication between the first wireless device and the second wireless device regardless of whether the first wireless device is inside or outside the living body.

According to an aspect, a wireless communication system includes a first wireless device configured to be introduced inside a living body, the first wireless device comprising an antenna; and a second wireless device configured to communicate with the first wireless device via the antenna. The wireless communication system carries out communication between the first wireless device and the second wireless device via the antenna at a first frequency when the first wireless device is outside the living body and carries out the communication at a second frequency lower than the first frequency when the first wireless device is inside the living body.

According to another aspect, a method for wireless communication is carried out by a wireless communication system including a first wireless device including an antenna and configured to be introduced inside a living body and a second wireless device configured to communicate with the first wireless device via the antenna.

The method includes carrying out communication between the first wireless device and the second wireless device via the antenna at a first frequency when the first wireless device is outside the living body; and carrying out the communication at a second frequency lower than the first frequency when the first wireless device is inside the living body.

According to another aspect, a wireless device is configured to be introduced inside a living body and include an antenna. The wireless device includes a detector configured to detect whether the wireless device is inside the living body; a transmitter configured to transmit a signal via the antenna; and a controller configured to control the frequency of the signal to a first frequency when the wireless device is detected to be outside the living body, and control the frequency of the signal to a second frequency lower than the first frequency when the wireless device is detected to be inside the living body.

According to another aspect, a wireless device functions as a second wireless device configured to communicate with a first wireless device via an antenna of the first wireless device, the first wireless device being configured to be introduced inside a living body.

The wireless device includes a transmitter that transmits a signal; and a controller configured to control the frequency of the signal to a first frequency when the first wireless device is outside the living body, and control the frequency of the signal to a second frequency that is lower than the first frequency when the first wireless device is inside the living body.

DESCRIPTION OF EMBODIMENTS

A wireless communication system, a method for wireless communication, and a wireless device according to embodiments of the present invention will now be described with reference toFIGS. 1 to 22.

First Embodiment

With reference toFIG. 1, a wireless communication system1according to a first embodiment includes a reader10and a tag device20. In this embodiment, the wireless communication system1is a Radio Frequency IDentifier (RFID) system.

Besides the RFID system, the wireless communication system1may be any wireless communication system. For example, the wireless communication system1may carry out communication in accordance with a specific wireless communication scheme. Examples of the wireless communication scheme include Bluetooth Low Energy (BLE), ANT, ANT+, and ZigBee schemes. Bluetooth, ANT+, and ZigBee are trademarks. BLE may also be known as Bluetooth 4.0, Bluetooth Smart, or Bluetooth Smart Ready.

The tag device20may also be referred to as the RFID, RFID tag, wireless tag, or Integrated Circuit (IC) tag.

In this embodiment, the tag device20corresponds to a first wireless device. In this embodiment, the reader10corresponds to a second wireless device.

The tag device20can be introduced inside a living body (a human body, in this embodiment). In this embodiment, the tag device20can be introduced inside the living body through oral administration. For example, the tag device20may be attached to an artificial tooth. The tag device20may constitute at least a portion of the artificial tooth. In this embodiment, the artificial tooth is a partial denture. Alternatively, the artificial tooth may be a complete denture. Alternatively, the tag device20may be attached to a sensor that detects a physical quantity or otherwise constitute at least part of the sensor. Alternatively, the tag device20may be attached to a pharmaceutical formulation, such as a capsule or a tablet, or otherwise constitute at least a portion of the pharmaceutical formulation.

With reference toFIG. 2, the reader10includes a control circuit110, a first transmission circuit121, a second transmission circuit122, a first transmission antenna131, a second transmission antenna132, a first reception antenna141, a second reception antenna142, a first reception circuit151, and a second reception circuit152.

In this embodiment, the first transmission circuit121and the second transmission circuit122correspond to transmitters. In this embodiment, the first reception circuit151and the second reception circuit152correspond to receivers. In this embodiment, the control circuit110corresponds to a controller.

In this embodiment, at least part of the reader10is composed of a Large Scale Integration (LSI) circuit. The at least part of the reader10may be composed of a programmable logic circuit (for example, a Programmable Logic Device (PLD) or a Field-Programmable Gate Array (FPGA)).

The reader10includes a processor and a storage unit. At least some of the functions of the reader10may be provided through execution of programs stored in the storage unit by the processor. For example, the processor may include a Central Processing Unit (CPU), a Micro-Processing Unit (MPU), or a Digital Signal Processor (DSP). The storage unit may include a Random Access Memory (RAM), a semiconductor memory, or an organic memory.

The reader10may constitute at least part of a mobile phone, a smart phone, or a personal computer, for example. The reader10may be in connection with a mobile phone, a smart phone, or a personal computer, for example.

The first transmission circuit121transmits a request signal having a carrier wave having a first frequency (in other words, first request signal) via the first transmission antenna131. In this embodiment, the first frequency is included in a first frequency band among multiple frequency bands collectively referred to as an Industrial-Scientific-Medical (ISM) band. In this embodiment, the first frequency is in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example). In this embodiment, the request signal requests the tag device20to transmit information. In this embodiment, the request signal includes a first signal component, a second signal component, and a third signal component, which are continuous along a time axis.

The first signal component and the third signal component are unmodulated waves (in other words, carrier waves). The second signal component is a modulated wave (in other words, radio wave obtained by modulating a carrier wave). For example, the second signal component represents identification information. The identification information identifies the information requested to be transmitted from the tag device20.

In this embodiment, the first signal component, the second signal component, and the third signal component have predetermined durations of a first length, a second length, and a third length, respectively.

The second transmission circuit122transmits a request signal having a carrier wave having a second frequency (in other words, second request signal) via the second transmission antenna132. The second frequency is lower than the first frequency. In this embodiment, the second frequency is lower than the half of the first frequency. In this embodiment, the second frequency is included in a second frequency band lower than the first frequency band among multiple frequency bands collectively referred to as an ISM band. In this embodiment, the second frequency is included in the 2.45 GHz band (from 2.4 to 2.5 GHz, for example).

The first reception circuit151receives a response signal having a carrier wave having the first frequency (in other words, first response signal) via the first reception antenna141. In this embodiment, the response signal represents information specified by the identification information (in other words, response information). The response information includes at least one of the information stored in the tag device20and the information generated by the tag device20, as described below. In this embodiment, the response signal is generated through modulation of at least a portion of the third signal component of the request signal as a result of being reflected at the tag device20, as described below.

The second reception circuit152receives a response signal having a carrier wave having the second frequency (in other words, second response signal) via the second reception antenna142.

The control circuit110controls the first transmission circuit121to start the transmission of the request signal. The control circuit110also controls the first transmission circuit121to end the transmission of the request signal. The control circuit110controls the second transmission circuit122in a similar manner to the first transmission circuit121.

The control circuit110controls the first reception circuit151to start the stand-by for reception of the response signal. The control circuit110also controls the first reception circuit151to end the stand-by for reception of the response signal. The control circuit110controls the second reception circuit152in a similar manner to the first reception circuit151.

In this embodiment, the control circuit110simultaneously instructs the first transmission circuit121and the second transmission circuit122to start transmission of request signals and simultaneously instructs the first reception circuit151and the second reception circuit152to start the stand-by for reception of the response signals. In this embodiment, the control circuit110controls the first reception circuit151and the second reception circuit152such that the stand-by for reception of the response signals starts substantially simultaneously with the start of the transmission of the request signals. The stand-by for the reception of the response signals may start after a predetermined delay time from the start of the transmission of the request signals.

The control circuit110may control the first transmission circuit121and the second transmission circuit122so as to alternately carry out the transmission of the request signal by the first transmission circuit121and the transmission of the request signal by the second transmission circuit122.

In such a case, the control circuit110controls the first reception circuit151such that the first reception circuit151enters the stand-by for reception of the response signal for at least a portion of the period during which the request signal is transmitted by the first transmission circuit121. Also in such a case, the control circuit110controls the second reception circuit152such that the second reception circuit152enters the stand-by for reception of the response signal for at least a portion of the period during which the request signal is transmitted by the second transmission circuit122.

In this embodiment, the control circuit110obtains the response information on the basis of only the signal having the larger intensity among the first response signal received by the first reception circuit151and the second response signal received by the second reception circuit152. For example, the intensity of the signal is a parameter that increases as the electrical energy and/or the amplitude of the signal increases.

The control circuit110may detect that the tag device20has been introduced from the outside to the inside of a living body on the basis of the intensity of the first response signal received by the first reception circuit151and the intensity of the second response signal received by the second reception circuit152. In such a case, the control circuit110may detect that the tag device20has been introduced from the outside to the inside of the living body through a variation in the intensity of the first response signal from being larger than the intensity of the second response signal to being smaller than the intensity of the second response signal.

The control circuit110may detect that the tag device20has been moved from the inside to the outside of the living body on the basis of the intensity of the first response signal received by the first reception circuit151and the intensity of the second response signal received by the second reception circuit152. In such a case, the control circuit110may detect that the tag device20has been moved from the inside to the outside of the living body through a variation in the intensity of the second response signal from being larger than the intensity of the first response signal to being smaller than the intensity of the first response signal.

(Configuration of Tag Device)

With reference toFIG. 3, the tag device20includes an antenna210and an IC unit220. In this embodiment, the IC unit220corresponds to a transmitter.

In this embodiment, at least part of the tag device20is composed of an LSI circuit. The at least part of the tag device20may be composed of a programmable logic circuit. The tag device20includes a processor and a storage unit. At least some of the functions of the tag device20may be provided through execution of programs stored in the storage unit by the processor.

The antenna210includes a first antenna component211and a second antenna component212. In this embodiment, the first antenna component211and the second antenna component212constitute a dipole antenna. In this embodiment, the first antenna component211and the second antenna component212have a meandering shape. The first antenna component211and the second antenna component212may have any shape (for example, a linear shape) besides a meandering shape.

In this embodiment, the resonance frequency of the antenna210is substantially identical to the first frequency during contact of the antenna210with air. In this embodiment, the resonance frequency of the antenna210is substantially identical to the second frequency during contact of the antenna210and a fluid inside the living body (for example, a digestive fluid, such as saliva, in this embodiment).

The antenna210may be of any type (such as a loop antenna, a plate antenna, or a flat antenna) besides a dipole antenna.

The IC unit220is in connection with the first antenna component211and the second antenna component212. The IC unit220includes a switching device221and a modulation circuit222.

In this embodiment, the tag device20is of a passive type. The IC unit220is activated by a potential difference generated between the first antenna component211and the second antenna component212when the antenna210receives signals.

In this embodiment, the IC unit220includes a rectifier and a capacitor (not illustrated). The current generated between the first antenna component211and the second antenna component212is rectified at the rectifier and stored in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The IC unit220demodulates the second signal component for at least a portion of the period during which the second signal component of the request signal is received using the electrical energy stored in the capacitor. The IC unit220obtains identification information on the basis of the demodulated signal.

The switching device221switches between a short-circuited state in which the first antenna component211and the second antenna component212are short-circuited (in other words, connected) and a disconnected state in which the first antenna component211and the second antenna component212are cutoff (in other words, disconnected).

In this embodiment, the reflection intensity in a short-circuited state of the switching device221is larger than the reflection intensity in the cutoff state of the switching device221. The reflection intensity refers to the intensity of a signal reflected at the tag device20among the signals received by the antenna210(in other words, signal transmitted by the tag device20).

In other words, the electrical energy absorbed by the IC unit220from a signal received by the antenna210in the disconnected state of the switching device221is larger than that in the short-circuited state of the switching device221.

The modulation circuit222controls the state of the switching device221on the basis of the information specified by the identification information (in other words, response information) using the electrical energy stored in the capacitor for at least a portion of the period during which the third signal component of the request signal is received. In this embodiment, the modulation circuit222controls the state of the switching device221such that the state of the switching device221corresponds to at least one bit representing response information.

In this embodiment, the short-circuited state corresponds to a bit value “1,” whereas the cutoff state corresponds to a bit value “0.” Alternatively, the short-circuited state may correspond to a bit value “0,” whereas the cutoff state may correspond to a bit value “1.”

In this embodiment, the response information contains information stored in the IC unit220in advance. For example, the response information may contain an identifier for identifying the tag device20. If the tag device20includes a sensor for detecting a physical quantity, the response information may contain information representing the physical quantity detected by the sensor in addition to the information stored in the IC unit220in advance or instead of the information stored in the IC unit220in advance. The physical quantity is temperature, humidity, illuminance, pH, acceleration, angular velocity, pressure, or concentration of a subject, for example. Examples of the subject include a digestive fluid (e.g., saliva, gastric juice, intestinal juice, or pancreatic juice), blood, normal microbial flora, and infectious material (for example, bacteria or viruses).

In other words, in this embodiment, the IC unit220modulates the request signal received by the antenna210in accordance with an Amplitude Modulation (AM) scheme and transmits the modulated request signal as a response signal. In other words, in this embodiment, the tag device20transmits a response signal representing response information in accordance with a backscattering scheme.

The IC unit220may perform modulation in accordance with a modulation scheme other than the AM scheme. For example, the modulation scheme may be a Frequency Modulation (FM) or a Phase Modulation (PM) scheme. Alternatively, the modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

The operation of the wireless communication system1according to the first embodiment will now be explained with reference toFIGS. 4 and 5.

A case of the tag device20outside the living body will now be explained. In this case, the antenna210of the tag device20is in contact with air.

The reader10starts transmission of a request signal having a carrier wave having the first frequency (in other words, first request signal) and a request signal having a carrier wave having the second frequency (in other words, second request signal) and starts the stand-by for reception of a response signal having a carrier wave having the first frequency (in other words, first response signal) and a response signal having a carrier wave having the second frequency (in other words, second response signal) (Step S101in FIG.4).

The tag device20receives the first request signal and the second request signal. Since the antenna210is in contact with air, the resonance frequency of the antenna210is substantially identical to the first frequency. Thus, the intensity of the first request signal received by the antenna210is larger than the intensity of the second request signal received by the antenna210.

The tag device20rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20demodulates the second signal component of the request signal for at least a portion of the period during which the second signal component is received, and obtains identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

For at least a portion of the period during which the third signal component of the request signal is received, the tag device20modulates the request signal received by the antenna210on the basis of the response information and transmits the modulated request signal as a response signal, using the electrical energy stored in the capacitor (S102inFIG. 4). In this embodiment, the tag device20transmits a response signal representing response information in accordance with a backscattering scheme.

In this embodiment, the response signal transmitted by the antenna210contains a first response signal component having a carrier wave having the first frequency (in other words, first component) and a second response signal component having a carrier wave having the second frequency (in other words, second component). Since the resonance frequency of the antenna210is substantially identical to the first frequency, the intensity of the first response signal component is larger than the intensity of the second response signal component.

The reader10receives the response signal transmitted by the tag device20. The reader10obtains the response information on the basis of only the response signal component having the larger intensity among the first response signal component and the second response signal component of the received response signal. Thus, the reader10obtains the response information on the basis of only the first response signal component among the first response signal component and the second response signal component of the received response signal.

A case of the tag device20inside the living body will now be described. In this case, the antenna210of the tag device20is in contact with a fluid inside the living body (saliva, in this embodiment).

Similar to the operation explained above, the reader10starts transmission of the first request signal and transmission of the second request signal and starts the stand-by for reception of the first request signal and the stand-by for reception of the second request signal (S101inFIG. 5).

The tag device20receives the first request signal and the second request signal. Since the antenna210is in contact with the fluid inside the living body, the resonance frequency of the antenna210is substantially identical to the second frequency. Thus, the intensity of the second request signal received by the antenna210is larger than the intensity of the first request signal received by the antenna210.

The tag device20rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20demodulates the second signal component for at least a portion of the period during which the second signal component of the request signal is received, and obtains the identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

For at least a portion of the period during which the third signal component of the request signal is received, the tag device20modulates the request signal received by the antenna210on the basis of the response information and transmits the modulated request signal as a response signal, using the electrical energy stored in the capacitor (Step S102inFIG. 5). In this embodiment, the tag device20transmits a response signal representing response information in accordance with a backscattering scheme.

In this embodiment, the response signal transmitted by the antenna210contains a first response signal component having a carrier wave having the first frequency (in other words, first component) and the second response signal component having a carrier wave having the second frequency (in other words, second component). Since the resonance frequency of the antenna210is substantially identical to the second frequency, the intensity of the second response signal component is larger than the intensity of the first response signal component.

The reader10receives the response signal transmitted by the tag device20. The reader10obtains the response information on the basis of only the response signal component having the larger intensity among the first response signal component and the second response signal component of the received response signal. Thus, the reader10obtains the response information on the basis of only the second response signal component among the first response signal component and the second response signal component of the received response signal.

As described above, the wireless communication system1according to the first embodiment carries out communication between the tag device20and the reader10via the antenna210at the first frequency when the tag device20is outside the living body. The wireless communication system1carries out communication between the tag device20and the reader10via the antenna210at the second frequency, which is lower than the first frequency, when the tag device20is inside the living body.

Thus, the reader10can communicate with the tag device20via the antenna210of the tag device20regardless of whether the tag device20is inside or outside the living body.

The reader10according to the first embodiment receives a signal having the first frequency and a signal having the second frequency.

Thus, the reader10can receive a signal having the first frequency when the tag device20is outside the living body. The reader10can receive a signal having the second frequency when the tag device20is inside the living body. Thus, the reader10can communicate with the tag device20via the antenna210of the tag device20regardless of whether the tag device20is inside or outside the living body.

The reader10according to the first embodiment transmits a signal having the first frequency and a signal having the second frequency.

Thus, the tag device20can receive the signal having the first frequency when the tag device20is outside the living body. The tag device20can receive the signal having the second frequency when the tag device20is inside the living body. Thus, the tag device20can communicate with the reader10via the antenna210of the tag device20regardless of whether the tag device20is inside or outside the living body.

The tag device20according to the first embodiment modulates the signal transmitted by the reader10and transmits the modulated signal.

Thus, the reader10can receive the signal having the first frequency when the tag device20is outside the living body. The reader10can receive the signal having the second frequency when the tag device20is inside the living body. Thus, the reader10can communicate with the tag device20via the antenna210of the tag device20regardless of whether the tag device20is inside or outside the living body.

The wireless communication system1may use a frequency included in the 2.45 GHz band (from 2.4 to 2.5 GHz, for example) as the first frequency and use a frequency included in the 900 MHz band (from 915 to 955 MHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the first frequency and use a frequency included in the 900 MHz band (from 915 to 955 MHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 60 GHz band (from 57 to 66 GHz, for example) as the first frequency and use a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 24 GHz band (from 24 to 24.25 GHz, for example) as the first frequency and use a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the second frequency.

The tag device20may include a modifier that modifies the resonance frequency of the antenna210. For example, the modifier may include a first antenna extension, a second antenna extension, a first switching device, and a second switching device.

The first antenna extension is in connection with the first antenna component211via the first switching device. The first switching device switches between a state in which the first antenna component211and the first antenna extension are connected and a state in which the first antenna component211and the first antenna extension are disconnected.

The second antenna extension is in connection with the second antenna component212via the second switching device. The second switching device switches between a state in which the second antenna component212and the second antenna extension are connected and a state in which the second antenna component212and the second antenna extension are disconnected.

This can modify the ratio of the first frequency to the second frequency to a value different from the ratio of the permittivity of air to the permittivity of a fluid inside the living body. Thus, the frequency used for communication between the reader10and the tag device20can be selected from a wider range.

With reference toFIG. 6, the reader10may end the transmission of the first request signal and the stand-by for reception of the first response signal component of the response signal if the reader10receives the response signal and if the intensity of the first response signal component of the response signal is smaller than the intensity of the second response signal component of the response signal (S103A inFIG. 6). The reader10may end the transmission of the second request signal and the stand-by for reception of the second response signal component of the response signal if the reader10receives the response signal and if the intensity of the second response signal component of the received response signal is smaller than the intensity of the first response signal component of the received response signal.

This can reduce the electrical power consumption at the reader10during transmission of a request signal and the stand-by for reception of a response signal by the reader10.

<First Modification to First Embodiment>

A wireless communication system according to a first modification to the first embodiment will now be described. The wireless communication system according to the first modification to the first embodiment differs from the wireless communication system according to the first embodiment in that the tag device detects whether it is inside a living body, the detected result is sent to the reader, and the reader controls the frequency to be used for communication on the basis of the detected result. The wireless communication system will now be described with focus on these differences. In the first modification to the first embodiment, components that are identical or very similar to those according to the first embodiment are indicated by the same reference signs.

With reference toFIG. 7, a reader10B according to the first modification to the first embodiment includes a control circuit110B, a first transmission circuit121, a second transmission circuit122, a first transmission antenna131, a second transmission antenna132, a first reception antenna141, a second reception antenna142, a first reception circuit151, and a second reception circuit152.

In this modification, the first transmission circuit121and the second transmission circuit122correspond to transmitters. In this modification, the first reception circuit151and the second reception circuit152correspond to receivers. In this modification, the control circuit110B corresponds to a controller.

The first transmission circuit121and the second transmission circuit122have the same configurations as those of the first transmission circuit121and the second transmission circuit122according to the first embodiment.

The first reception circuit151and the second reception circuit152operate in a similar manner as the first reception circuit151and the second reception circuit152according to the first embodiment and receive detection signals representing detection information. The detection information represents results detected by a sensor223B of the tag device20B, as described below.

The first reception circuit151receives a detection signal having a carrier wave having a first frequency (in other words, first detection signal) via the first reception antenna141.

The second reception circuit152receives a detection signal having a carrier wave having a second frequency (in other words, second detection signal) via the second reception antenna142.

The control circuit110B controls the first transmission circuit121to start transmission of a request signal. The control circuit110B controls the first transmission circuit121to end the transmission of the request signal. The control circuit110B controls the second transmission circuit122in a similar manner to the first transmission circuit121.

The control circuit110B controls the first reception circuit151to start the stand-by for reception of a detection signal and a response signal. The control circuit110B controls the first reception circuit151to end the stand-by for reception of the detection signal and the response signal. The control circuit110B controls the second reception circuit152in a similar manner to the first reception circuit151.

In this embodiment, the control circuit110B simultaneously instructs the first transmission circuit121and the second transmission circuit122to start the transmission of request signals and simultaneously instructs the first reception circuit151and the second reception circuit152to start the stand-by for reception of detection signals and response signals. In this embodiment, the control circuit110B controls the first reception circuit151and the second reception circuit152such that the stand-by for reception of the detection signals and the response signals starts substantially simultaneously with the start of the transmission of the request signals. The stand-by for reception of the detection signals and the response signals may start after a predetermined delay time from the start of the transmission of the request signals.

The control circuit110B may control the first transmission circuit121and the second transmission circuit122so as to alternately carry out the transmission of the request signal by the first transmission circuit121and the transmission of the request signal by the second transmission circuit122.

In such a case, the control circuit110B controls the first reception circuit151such that the first reception circuit151enters the stand-by for reception of the detection signal and the response signal for at least a portion of the period during which the request signal is transmitted by the first transmission circuit121. Also in such a case, the control circuit110B controls the second reception circuit152such that the second reception circuit152enters the stand-by for reception of the detection signal and the response signal for at least a portion of the period during which the request signal is transmitted by the second transmission circuit122.

The control circuit110B obtains detection information on the basis of the detection signal having the larger intensity among the detection signal having a carrier wave having the first frequency (in other words, first detection signal) received by the first reception circuit151and the detection signal having a carrier wave having the second frequency (in other words, second detection signal) received by the second reception circuit152. The control circuit110B may obtain the detection information on the basis of both the first detection signal received by the first reception circuit151and the second detection signal received by the second reception circuit152.

The control circuit110B ends either the stand-by for reception and the transmission of the signal having a carrier wave having the first frequency or the stand-by for reception and the transmission of the signal having a carrier wave having the second frequency, on the basis of the detected result indicated by the obtained detection information.

In this modification, the control circuit110B ends the transmission of the second request signal and the stand-by for reception of the response signal having a carrier wave having the second frequency (in other words, second response signal) and the second detection signal when the obtained detection information indicates that the tag device20B is outside the living body. In this modification, the control circuit110B ends the transmission of the first request signal and the stand-by for reception of a response signal having a carrier wave having the first frequency (in other words, first response signal) and the first detection signal when the obtained detection information indicates that the tag device20B is inside the living body.

The control circuit110B obtains response information on the basis of the response signal received by the first reception circuit151or the second reception circuit152.

(Configuration of Tag Device)

With reference toFIG. 8, the tag device20B according to the first modification to the first embodiment includes an IC unit220B in place of the IC unit220of the tag device20according to the first embodiment. The IC unit220B includes a switching device221, a modulation circuit222B, and a sensor223B. In this modification, the sensor223B corresponds to a detector. In this modification, the IC unit220B corresponds to a notifier.

The switching device221has the same configuration as that of the switching device221according to the first embodiment.

The sensor223B detects whether the tag device20B is inside a living body. In this modification, the sensor223B detects temperature. The sensor223B detects that the tag device20B is inside the living body when the detected temperature is higher than or equal to a predetermined threshold (307K, for example) and detects that the tag device20B is outside the living body when the detected temperature is lower than the threshold.

In addition to or instead of detecting temperature, the sensor223B may detect whether the tag device20B is inside the living body on the basis of a physical quality other than temperature. The physical quantity may be illuminance, pH, or concentration of a subject, for example. Examples of the subject include a digestive fluid (e.g., saliva, gastric juice, intestinal juice, or pancreatic juice), blood, and normal microbial flora.

In this modification, the sensor223B operates by the electrical energy stored in the capacitor. The sensor223B may include a battery, which provides electrical energy to the sensor223B for operation.

The modulation circuit222B operates in the same manner as the modulation circuit222for a period during which the first signal component and the second signal component of the request signal are received and operates in a different manner as the modulation circuit222for a period during which the third signal component of the request signal is received.

The modulation circuit222B controls the state of the switching device221on the basis of information indicating the result detected by the sensor223B (in other words, detection information) during a first sub-period, which is a portion of the period during which the third signal component of the request signal is received, using the electrical energy stored in the capacitor. In this modification, the modulation circuit222B controls the state of the switching device221such that the state of the switching device221corresponds to at least one bit representing detection information.

In other words, in this modification, the tag device20B transmits a detection signal representing detection information in accordance with a backscattering scheme. In this modification, the transmission of a detection signal corresponds to notification to the reader10B of the result detected by the sensor223B.

The IC unit220B may perform modulation on the basis of the detection information in accordance with a modulation scheme other than the AM scheme.

The modulation circuit222B controls the state of the switching device221on the basis of the response information for a second sub-period following the first sub-period in the period during which the third signal component of the request signal is received, using the electrical energy stored in the capacitor. In this embodiment, the modulation circuit222B controls the state of the switching device221such that the state of the switching device221corresponds to at least one bit representing the response information.

In other words, in this modification, the tag device20B transmits a response signal representing response information in accordance with a backscattering scheme. The IC unit220B may perform modulation on the basis of the response information in accordance with a modulation scheme other than the AM scheme.

The operation of the wireless communication system1according to the first modification to the first embodiment will now be explained with reference toFIGS. 9 and 10.

A case of the tag device20B outside the living body will now be explained. In this case, the antenna210of the tag device20B is in contact with air.

The reader10B starts the transmission of a request signal having a carrier wave having the first frequency (in other words, first request signal) and a request signal having a carrier wave having the second frequency (in other words, second request signal) and starts the stand-by for reception of signals having carrier waves having the first frequency (in other words, first detection signal and first response signal) and signals having carrier waves having the second frequency (in other words, second detection signal and second response signal) (Step S201inFIG. 9).

The tag device20B receives the first request signal and the second request signal. Since the antenna210is in contact with air, the resonance frequency of the antenna210is substantially identical to the first frequency. Thus, the intensity of the first request signal received by the antenna210is larger than the intensity of the second request signal received by the antenna210.

The tag device20B rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20B demodulates the second signal component of the request signal for at least a portion of the period during which the second signal component is received, and obtains identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

The tag device20B detects whether the tag device20B is inside the living body with the sensor223B. In this case, the tag device20B detects that the tag device20B is not inside the living body (in other words, being outside the living body) (Step S2021inFIG. 9).

For the first sub-period of the period during which the third signal component of the request signal is received, the tag device20B modulates the request signal received by the antenna210using the electrical energy stored in the capacitor, on the basis of the detection information and transmits the modulated request signal as a detection signal (Step S203inFIG. 9). In this modification, the tag device20B transmits a detection signal representing detection information in accordance with a backscattering scheme.

In this modification, the detection signal transmitted by the antenna210includes a first detection signal component having a carrier wave having the first frequency (in other words, first component) and a second detection signal component having a carrier wave having the second frequency (in other words, second component). Since the resonance frequency of the antenna210is substantially identical to the first frequency, the intensity of the first detection signal component is larger than the intensity of the second detection signal component.

The reader10B receives the detection signal transmitted by the tag device20B. The reader10B obtains detection information on the basis of only the detection signal component having the larger intensity among the first detection signal component and the second detection signal component of the received detection signal. Thus, the reader10B obtains the detection information on the basis of only the first detection signal component among the first detection signal component and the second detection signal component of the received detection signal.

The reader10B then ends either the stand-by for reception and the transmission of the signal having a carrier wave having the first frequency or the stand-by for reception and the transmission of the signal having a carrier wave having the second frequency, on the basis of the detected result indicated by the obtained detection information. Since the detected result indicates that the tag device20B is outside the living body, the reader10B ends the transmission of the second request signal and the stand-by for reception of the second detection signal and the second request signal (Step S2041inFIG. 9).

For the second sub-period of the period during which the third signal component of the request signal is received, the tag device20B modulates the request signal received by the antenna210using the electrical energy stored in the capacitor, on the basis of the response information and transmits the modulated request signal as a response signal (Step S205inFIG. 9). In this modification, the tag device20B transmits a response signal representing response information in accordance with a backscattering scheme.

In this case, the carrier wave of the response signal transmitted by the antenna210has the first frequency. In other words, the response signal does not contain a component whose carrier wave has the second frequency.

The reader10B receives the response signal transmitted by the tag device20B. In this case, the reader10B obtains the response information on the basis of the first response signal received by the first reception circuit151.

A case of the tag device20B inside the living body will now be described. In this case, the antenna210of the tag device20B is in contact with a fluid inside the living body (saliva, in this modification).

The reader10B starts the transmission of the first request signal and the second request signal, and starts the stand-by for reception of the first detection signal and the first response signal and the stand-by for reception of the second detection signal and the second response signal (S201inFIG. 10).

The tag device20B receives the first request signal and the second request signal. Since the antenna210is in contact with the fluid inside the living body, the resonance frequency of the antenna210is substantially identical to the second frequency. Thus, the intensity of the second request signal received by the antenna210is larger than the intensity of the first request signal received by the antenna210.

The tag device20B rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20B demodulates the second signal component of the request signal for at least a portion of the period during which the second signal component is received, and obtains the identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

The tag device20B detects whether the tag device20B is inside the living body with the sensor223B. In this case, the tag device20B detects that the tag device20B is inside the living body (Step S2022inFIG. 10).

For the first sub-period of the period during which the third signal component of the request signal is received, the tag device20B modulates the request signal received by the antenna210using the electrical energy stored in the capacitor, on the basis of the detection information and transmits the modulated request signal as a detection signal (Step S203inFIG. 10). In this modification, the tag device20B transmits a detection signal representing detection information in accordance with a backscattering scheme.

In this modification, the detection signal transmitted by the antenna210includes a first detection signal component having a carrier wave having the first frequency (in other words, first component) and a second detection signal component having a carrier wave having the second frequency (in other words, second component). Since the resonance frequency of the antenna210is substantially identical to the second frequency, the intensity of the second detection signal component is larger than the intensity of the first detection signal component.

The reader10B receives the detection signal transmitted by the tag device20B. The reader10B obtains detection information on the basis of only the detection signal component having the larger intensity among the first detection signal component and the second detection signal component of the received detection signal. Thus, the reader10B obtains the detection information on the basis of only the second detection signal component among the first detection signal component and second detection signal component of the received detection signal.

The reader10B then ends either the stand-by for reception and the transmission of the signal having a carrier wave having the first frequency or the stand-by for reception and the transmission of the signal having a carrier wave having the second frequency, on the basis of the detected result indicated by the obtained detection information. Since the detected results indicates that the tag device20B is inside the living body, the reader10B ends the transmission of the first request signal and the stand-by for reception of the first detection signal and the first response signal (Step S2042inFIG. 10).

For the second sub-period of the period during which the third signal component of the request signal is received, the tag device20B modulates the request signal received by the antenna210using the electrical energy stored in the capacitor, on the basis of the response information and transmits the modulated request signal as a response signal (Step S205inFIG. 10). In this modification, the tag device20B transmits a response signal representing response information in accordance with a backscattering scheme.

In this case, the carrier wave of the response signal transmitted by the antenna210has the second frequency. In other words, the response signal does not contain a component whose carrier wave has the first frequency.

The reader10B receives the response signal transmitted by the tag device20B. In this case, the reader10B obtains the response information on the basis of the second response signal received by the second reception circuit152.

As described above, the wireless communication system1according to the first modification to the first embodiment operates in the same manner and achieves the same advantages as those of the wireless communication system1according to the first embodiment.

The reader10B of the wireless communication system1according to the first modification to the first embodiment controls the frequency of the carrier wave of the signal transmitted by the reader10B to the first frequency when the tag device20B is outside the living body and controls the frequency of the carrier wave of the signal transmitted by the reader10B to the second frequency when the tag device20B is inside the living body.

Such control can prevent the transmission of the signal having a carrier wave having the first frequency by the reader10B while the tag device20B is being inside the living body. The control can also prevent the transmission of the signal having a carrier wave having the second frequency by the reader10B while the tag device20B is being outside the living body. Thus, for example, the electrical power consumption of the reader10B can be reduced compared to that of the reader10B for the transmission of both the signal having a carrier wave having the first frequency and the signal having a carrier wave having the second frequency.

When the stand-by for reception of and the transmission of either the signal having a carrier wave having the first frequency or the signal having a carrier wave having the second frequency continue for a threshold time or longer, the reader10B may resume the stand-by and the transmission of the other one of the signal having a carrier wave having the first frequency and the signal having a carrier wave having the second frequency.

Thus, the reader10B can communicate with the tag device20B via the antenna210of the tag device20B regardless of whether the tag device20B is move to the inside or outside of the living body.

Second Embodiment

A wireless communication system according to a second embodiment will now be described. The wireless communication system according to the second embodiment differs from the wireless communication system according to the first embodiment in that the tag device is of an active type. The wireless communication system will now be described with focus on the difference. In the second embodiment, components that are identical or very similar to those according to the first embodiment are indicated by the same reference signs.

With reference toFIG. 11, a reader10C according to the second embodiment includes a control circuit110C, a first reception antenna141, a second reception antenna142, a first reception circuit151, and a second reception circuit152.

In this embodiment, the first reception circuit151and the second reception circuit152correspond to receivers. In this embodiment, the control circuit110C corresponds to a controller.

The first reception circuit151receives an broadcast (in other words, advertisement or announcement) signal having a carrier wave having a first frequency (in other words, first broadcast signal) via the first reception antenna141. In this embodiment, the broadcast signal represents broadcast information. The broadcast information contains at least one of the information stored in the tag device20C and the information generated by the tag device20C. In this embodiment, the first frequency is included in a first frequency band among multiple frequency bands collectively referred to as an ISM band. In this embodiment, the first frequency is included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example).

The second reception circuit152receives an broadcast signal having a carrier wave having a second frequency (in other words, second broadcast signal) via the second reception antenna142. The second frequency is lower than the first frequency. In this embodiment, the second frequency is lower than half the first frequency. In this embodiment, the second frequency is included in a second frequency band, which is lower than the first frequency band, among multiple frequency bands collectively referred to as an ISM band. In this embodiment, the second frequency band is included in the 2.45 GHz band (from 2.4 to 2.5 GHz, for example).

The control circuit110C controls the first reception circuit151to start the stand-by for reception of the broadcast signal. The control circuit110C also controls the first reception circuit151to end the stand-by for reception of the broadcast signal. The control circuit110C controls the second reception circuit152in a similar manner to the first reception circuit151.

In this embodiment, the control circuit110C instructs the first reception circuit151and the second reception circuit152to simultaneously start the stand-by for reception of the broadcast signal.

The control circuit110C may control the first reception circuit151and the second reception circuit152so as to alternately enter the stand-by for reception of the broadcast signal by the first reception circuit151and the stand-by for reception of the broadcast signal by the second reception circuit152.

In this embodiment, the control circuit110C obtains broadcast information on the basis of only the signal having the larger intensity among the first broadcast signal received by the first reception circuit151and the second broadcast signal received by the second reception circuit152.

The control circuit110C may detect that the tag device20C has been introduced from the outside to the inside of the living body on the basis of the intensity of the first broadcast signal received by the first reception circuit151and the second broadcast signal received by the second reception circuit152. In such a case, the control circuit110C may detect that the tag device20C has been introduced from the outside to the inside of the living body through a variation in the intensity of the first broadcast signal from being larger than the intensity of the second broadcast signal to being smaller than the intensity of the second broadcast signal.

The control circuit110C may detect that the tag device20C has been moved from the inside to the outside of the living body on the basis of the intensity of the first broadcast signal received by the first reception circuit151and the intensity of the second broadcast signal received by the second reception circuit152. In such a case, the control circuit110C may detect that the tag device20C has been moved from the inside to the outside of the living body through a variation in the intensity of the second broadcast signal from being larger than the intensity of the first broadcast signal to being smaller than the intensity of the first broadcast signal.

(Configuration of Tag Device)

With reference toFIG. 12, the tag device20C according to the second embodiment includes an antenna210and an IC unit220C. In this embodiment, the IC unit220C corresponds to a transmitter.

The antenna210has a configuration that is the same as that of the antenna210according to the first embodiment.

The IC unit220C is in connection with the first antenna component211and the second antenna component212. The IC unit220C includes a first transmission circuit224C, a second transmission circuit225C, and a battery226C. In this embodiment, the tag device20C is of an active type.

The first transmission circuit224C transmits an broadcast signal having a carrier wave having the first frequency (in other words, first broadcast signal) via the antenna210, using the electrical energy stored in the battery226C. The first transmission circuit224C transmits the first broadcast signal modulated in accordance with a preselected first modulation scheme. The first modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the first modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

The second transmission circuit225C transmits an broadcast signal having a carrier wave having a second frequency (in other words, second broadcast signal) via the antenna210, using the electrical energy stored in the battery226C. The second transmission circuit225C transmits the second broadcast signal modulated in accordance with a preselected second modulation scheme. The second modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the second modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

In this embodiment, the broadcast information contains information stored in the IC unit220C in advance. For example, the broadcast information may contain an identifier for identifying the tag device20C. If the tag device20C includes a sensor for detecting a physical quantity, the broadcast information may contain information representing the physical quantity detected by the sensor in addition to or instead of the information stored in the IC unit220C in advance. The physical quantity is temperature, humidity, illuminance, pH, acceleration, angular velocity, pressure, or concentration of a subject, for example. Examples of the subject include a digestive fluid (e.g., saliva, gastric juice, intestinal juice, or pancreatic juice), blood, normal microbial flora, and infectious material (for example, bacteria or viruses).

The tag device20C may include a first battery in connection with the first transmission circuit224C and a second battery in connection with the second transmission circuit225C, in addition to or in place of the battery226C.

The operation of the wireless communication system1will now be explained with reference toFIG. 13.

A case of the tag device20C outside the living body will now be explained. In this case, the antenna210of the tag device20C is in contact with air.

The reader10C starts the stand-by for reception of an broadcast signal having a carrier wave having the first frequency (in other words, first broadcast signal) and the stand-by for reception of an broadcast signal having a carrier wave having the second frequency (in other words, second broadcast signal) (Step S301inFIG. 13).

The tag device20C starts the transmission of the first broadcast signal and the second broadcast signal (Step S302inFIG. 13).

The broadcast signal transmitted by the antenna210contains a first broadcast signal component having a carrier wave having the first frequency (in other words, first component) and a second broadcast signal component having a carrier wave having the second frequency (in other words, second component). Since the antenna210is in contact with air, the resonance frequency of the antenna210is substantially identical to the first frequency. Thus, the intensity of the first broadcast signal component transmitted by the antenna210is larger than the intensity of the second broadcast signal component transmitted by the antenna210.

The reader10C receives the broadcast signal transmitted by the tag device20C. The reader10C obtains broadcast information on the basis of only the broadcast signal component having the larger intensity among the first broadcast signal component and the second broadcast signal component of the received broadcast signal. Thus, the reader10C obtains the broadcast information on the basis of only the first broadcast signal component among the first broadcast signal component and the second broadcast signal component of the received broadcast signal.

A case of the tag device20C inside the living body will now be described. In this case, the antenna210of the tag device20C is in contact with a fluid inside the living body (saliva, in this embodiment).

Similar to the operation explained above, the reader10C starts the stand-by for reception of a first broadcast signal component and a second broadcast signal component.

The tag device20C starts the transmission of the first broadcast signal component and the second broadcast signal component.

The broadcast signal transmitted by the antenna210contains a first broadcast signal component having a carrier wave having the first frequency (in other words, first component) and a second broadcast signal component having a carrier wave having the second frequency (in other words, second component). Since the antenna210is in contact with the fluid inside the living body, the resonance frequency of the antenna210is substantially identical to the second frequency. Thus, the intensity of the second broadcast signal component transmitted by the antenna210is larger than the intensity of the first broadcast signal component transmitted by the antenna210.

The reader10C receives the broadcast signal transmitted by the tag device20C. The reader10C obtains the broadcast information on the basis of only the broadcast signal component having the larger intensity among the first broadcast signal component and the second broadcast signal component of the received broadcast signal. Thus, the reader10C obtains the broadcast information on the basis of only the second broadcast signal component among the first broadcast signal component and the second broadcast signal component of the received broadcast signal.

As described above, the wireless communication system1according to the second embodiment carries out communication between the tag device20C and the reader10C via the antenna210at the first frequency when the tag device20C is outside the living body. The wireless communication system1also carries out communication between the tag device20C and the reader10C via the antenna210at the second frequency, which is lower than the first frequency, when the tag device20C is inside the living body.

Thus, the reader10C can communicates with the tag device20C via the antenna210of the tag device20C regardless of whether the tag device20C is inside or outside the living body.

The reader10C according to the second embodiment receives a signal having the first frequency and a signal having the second frequency.

Thus, the reader10C can receive a signal having the first frequency when the tag device20C is outside the living body. The reader10C can receive a signal having the second frequency when the tag device20C is inside the living body. Thus, the reader10C can communicate with the tag device20C via the antenna210of the tag device20C regardless of whether the tag device20C is inside or outside the living body.

The tag device20C according to the second embodiment transmits the signal having the first frequency and the signal having the second frequency via the antenna210.

Thus, the reader10C can receive the signal having the first frequency when the tag device20C is outside the living body. The reader10C can receive the signal having the second frequency when the tag device20C is inside the living body. Thus, the reader10C can communicate with the tag device20C via the antenna210of the tag device20C regardless of whether the tag device20C is inside or outside the living body.

The wireless communication system1may use a frequency included in the 2.45 GHz band (from 2.4 to 2.5 GHz, for example) as the first frequency and a frequency included in the 900 MHz band (from 915 to 955 MHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the first frequency and a frequency included in the 900 MHz band (from 915 to 955 MHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 60 GHz band (from 57 to 66 GHz, for example) as the first frequency and a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 24 GHz band (from 24 to 24.25 GHz, for example) as the first frequency and a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the second frequency.

The tag device20C may include a modifier that modifies the resonance frequency of the antenna210. For example, the modifier may include a first antenna extension, a second antenna extension, a first switching device, and a second switching device.

The first antenna extension is in connection with the first antenna component211via the first switching device. The first switching device switches between a state in which the first antenna component211and the first antenna extension are connected and a state in which the first antenna component211and the first antenna extension are disconnected.

The second antenna extension is in connection with the second antenna component212via the second switching device. The second switching device switches between a state in which the second antenna component212and the second antenna extension are connected and a state in which the second antenna component212and the second antenna extension are disconnected.

This can modify the ratio of the first frequency to the second frequency to a value different from the ratio of the permittivity of air to the permittivity of a fluid inside the living body. Thus, the frequency used for communication between the reader10C and the tag device20C can be selected from a wider range.

The reader10C may end the stand-by for reception of the first broadcast signal component of the broadcast signal if the reader10C receives the broadcast signal and if the intensity of the first broadcast signal component is smaller than the intensity of the second broadcast signal component of the broadcast signal. The reader10C may end the stand-by for reception of the second broadcast signal component of the broadcast signal if the reader10C receives the broadcast signal and if the intensity of the second broadcast signal component is smaller than the intensity of the first broadcast signal component of the broadcast signal.

This can reduce the electrical power consumption at the reader10C during the stand-by for reception of an broadcast signal by the reader10C.

In the wireless communication system1, the tag device20C may start the transmission of the signal having the first frequency and the signal having the second frequency before the reader10C starts the stand-by for reception of the signal having the first frequency and the signal having the second frequency.

<First Modification to Second Embodiment>

A wireless communication system according to a first modification to the second embodiment will now be described. The wireless communication system according to the first modification to the second embodiment differs from the wireless communication system according to the second embodiment in that the tag device detects whether it is inside a living body and the frequency to be used for communication is controlled on the basis of the detected result. The wireless communication system will now be described with focus on these differences. In the first modification to the second embodiment, components that are identical or very similar to those according to the second embodiment are indicated by the same reference signs.

(Configuration of Tag Device)

With reference toFIG. 14, a tag device20D according to the first modification to the second embodiment includes an IC unit220D in place of the IC unit220C of the tag device20C according to the second embodiment. The IC unit220D includes a first transmission circuit224D, a second transmission circuit225D, a battery226D, a switching device227D, and a sensor228D. In this modification, the sensor228D corresponds to a detector. In this modification, the IC unit220D corresponds to a transmitter.

The sensor228D detects whether the tag device20D is inside a living body. In this modification, the sensor228D detects temperature. The sensor228D detects that the tag device20D is inside the living body when the detected temperature is higher than or equal to a predetermined threshold (307K, for example) and detects that the tag device20D is outside the living body when the detected temperature is lower than the threshold.

In addition to or instead of detecting temperature, the sensor228D may detect whether the tag device20D is inside the living body on the basis of a physical quality other than temperature. The physical quantity may be illuminance, pH, or concentration of a subject, for example. Examples of the subject include a digestive fluid (e.g., saliva, gastric juice, intestinal juice, or pancreatic juice), blood, and normal microbial flora.

In this modification, the sensor228D operates by the electrical energy stored in the battery226D.

The switching device227D switches between a first connection state and a second connection state on the basis of the detected result by the sensor228D. In the first connection state, the switching device227D connects the first transmission circuit224D and the battery226D and cuts off or disconnects the second transmission circuit225D and the battery226D. In the second connection state, the switching device227D disconnects the first transmission circuit224D and the battery226D and connects the second transmission circuit225D and the battery226D.

The switching device227D switches to the first connection state when the detected result by the sensor228D indicates that the tag device20D is outside the living body. The switching device227D switches to the second connection state when the detected result by the sensor228D indicates that the tag device20D is inside the living body.

In this modification, the switching device227D operates by the electrical energy stored in the battery226D.

When the switching device227D is in the first connection state, the first transmission circuit224D transmits an broadcast signal having a carrier wave having a first frequency (in other words, first broadcast signal) via the antenna210, using the electrical energy stored in the battery226D. The first transmission circuit224D transmits the first broadcast signal modulated in accordance with a preselected first modulation scheme. The first modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the first modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

When the switching device227D is in the second connection state, the second transmission circuit225D transmits an broadcast signal having a carrier wave having a second frequency (in other words, second broadcast signal) via the antenna210, using the electrical energy stored in the battery226D. The second transmission circuit225D transmits the second broadcast signal modulated in accordance with a preselected second modulation scheme. The second modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the second modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

The operation of the wireless communication system1according to the first modification to the second embodiment will now be explained with reference toFIGS. 15 and 16.

A case of the tag device20D outside the living body will now be explained. In this case, the antenna210of the tag device20D is in contact with air.

The reader10C starts the stand-by for reception of an broadcast signal having a carrier wave having a first frequency (in other words, first broadcast signal) and the stand-by for reception of an broadcast signal having a carrier wave having a second frequency (in other words, second broadcast signal) (Step S401inFIG. 15).

The tag device20D detects whether the tag device20D is inside the living body with the sensor228D. In this case, the tag device20D detects that the tag device20D is not inside the living body (in other words, being outside the living body) (Step S4021inFIG. 15).

Thus, the switching device227D switches to the first connection state. This starts the transmission of the first broadcast signal by the tag device20D (Step S4031inFIG. 15).

Thus, the carrier wave of the broadcast signal transmitted by the antenna210has the first frequency. In other words, the broadcast signal does not contain a component whose carrier wave has the second frequency.

The reader10C receives the broadcast signal transmitted by the tag device20D. In this case, the reader10C obtains broadcast information on the basis of the first broadcast signal received by the first reception circuit151.

A case of the tag device20D inside the living body will now be explained. In this case, the antenna210of the tag device20D is in contact with a fluid inside the living body (saliva, in this modification).

The reader10C starts the stand-by for reception of the first broadcast signal and the stand-by for reception of the second broadcast signal (S401inFIG. 16).

The tag device20D detects whether the tag device20D is inside the living body with the sensor228D. In this case, the tag device20D detects that the tag device20D is inside the living body (Step S4022inFIG. 16).

Thus, the switching device227D switches to the second connection state. This starts the transmission of the second broadcast signal by the tag device20D (Step S4032inFIG. 16).

Thus, the carrier wave of the broadcast signal transmitted by the antenna210has the second frequency. In other words, the broadcast signal does not contain a component whose carrier wave has the first frequency.

The reader10C receives the broadcast signal transmitted by the tag device20D. In this case, the reader10C obtains the broadcast information on the basis of the second broadcast signal received by the second reception circuit152.

As explained above, the wireless communication system1according to the first modification to the second embodiment operates in the same manner and achieves the same advantages as those of the wireless communication system1according to the second embodiment.

The tag device20D of the wireless communication system1according to the first modification to the second embodiment controls the frequency of the carrier wave of the signal transmitted by the tag device20D to the first frequency if the tag device20D is detected to be outside the living body and controls the frequency of the carrier wave of the signal transmitted by the tag device20D to the second frequency if the tag device20D is detected to be inside the living body.

Such control can prevent the transmission of the signal having the first frequency by the tag device20D while the tag device20D is being inside the living body. The control can also prevent the transmission of the signal having the second frequency by the tag device20D while the tag device20D is being outside the living body. Thus, the electrical power consumption of the tag device20D can be reduced compared to that of the tag device20D for transmission of both the signal having the first frequency and the signal having the second frequency.

When the transmission of either the signal having a carrier wave having the first frequency or the signal having a carrier wave having the second frequency continues for a threshold time or longer, the tag device20D may repeat the detection for whether the tag device20D is inside the living body and the frequency control on the basis of the detected result.

Thus, the reader10C can communicate with the tag device20D via the antenna210of the tag device20D regardless of whether the tag device20D is move to the inside or outside of the living body.

In the wireless communication system1, the tag device20D may start the detection of whether the tag device20D is inside the living body and the transmission of the signal having the first frequency or the signal having the second frequency before the reader10C starts the stand-by for reception of the signal having the first frequency and the signal having the second frequency.

Third Embodiment

A wireless communication system according to a third embodiment will now be described. The wireless communication system according to the third embodiment differs from the wireless communication system according to the first embodiment in that the tag device is of a semi-active type. The wireless communication system will now be described with focus on this difference. In the third embodiment, components that are identical or very similar to those according to the first embodiment are indicated by the same reference signs.

With reference toFIG. 17, a reader10E according to the third embodiment includes a control circuit110E, a first transmission circuit121, a second transmission circuit122, a first transmission antenna131, a second transmission antenna132, a first reception antenna141, a second reception antenna142, a first reception circuit151, and a second reception circuit152.

In this embodiment, the first transmission circuit121and the second transmission circuit122correspond to transmitters. In this embodiment, the first reception circuit151and the second reception circuit152correspond to receivers. In this embodiment, the control circuit110E corresponds to a controller.

The first transmission circuit121transmits a request signal having a carrier wave having a first frequency (in other words, first request signal) via the first transmission antenna131. In this embodiment, the first frequency is included in a first frequency band among multiple frequency bands collectively referred to as an ISM band. In this embodiment, the first frequency is included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example). In this embodiment, a request signal requests a tag device20E, which is described below, to transmit information. In this embodiment, the request signal includes a first signal component and a second signal component, which are continuous along a time axis.

The first signal component is an unmodulated wave (in other words, carrier wave). The second signal component is a modulated wave (in other words, radio wave obtained by modulating a carrier wave). For example, the second signal component represents identification information. The identification information identifies the information requested to be transmitted from the tag device20E.

In this embodiment, the first signal component and the second signal component have predetermined durations of a first length and a second length, respectively.

The second transmission circuit122transmits a request signal having a carrier wave having a second frequency (in other words, second request signal) via the second transmission antenna132. The second frequency is lower than the first frequency. In this embodiment, the second frequency is lower than half the first frequency. In this embodiment, the second frequency is included in a second frequency band, which is lower than the first frequency band, among multiple frequency bands collectively referred to as an ISM band. In this embodiment, the second frequency band is included in the 2.45 GHz band (from 2.4 to 2.5 GHz, for example).

The first reception circuit151receives a response signal having a carrier wave having the first frequency (in other words, first response signal) via the first reception antenna141. In this embodiment, the response signal represents response information. The response information includes at least one of the information stored in the tag device20E and the information generated by the tag device20E, as described below.

The second reception circuit152receives a response signal having a carrier wave having the second frequency (in other words, second response signal) via the second reception antenna142.

The control circuit110E controls the first transmission circuit121to start the transmission of the request signal. The control circuit110E also controls the first transmission circuit121to end the transmission of the request signal. The control circuit110E controls the second transmission circuit122in a similar manner to the first transmission circuit121.

The control circuit110E controls the first reception circuit151to start the stand-by for reception of the response signal. The control circuit110E also controls the first reception circuit151to end the stand-by for reception of the response signal. The control circuit110E controls the second reception circuit152in a similar manner to the first reception circuit151.

In this embodiment, the control circuit110E instructs the first transmission circuit121and the second transmission circuit122to simultaneously start the transmission of request signals. The control circuit110E then instructs the first transmission circuit121and the second transmission circuit122to simultaneously end the transmission of the request signals. The control circuit110E instructs the first reception circuit151and the second reception circuit152to simultaneously start the stand-by for reception of the request signals. The control circuit110E may control the first reception circuit151and the second reception circuit152to start the stand-by for reception of the request signals substantially simultaneously with the end of the transmission of the request signals.

The control circuit110E may control the first transmission circuit121and the second transmission circuit122so as to alternately carry out the transmission of the request signal by the first transmission circuit121and the transmission of the request signal by the second transmission circuit122.

The control circuit110E may control the first reception circuit151and the second reception circuit152so as to alternately carry out the stand-by for reception of the response signal by the first reception circuit151and the stand-by for reception of the response signal by the second reception circuit152.

In this embodiment, the control circuit110E obtains response information on the basis of only the signal having the larger intensity among the first response signal received by the first reception circuit151and the second response signal received by the second reception circuit152.

The control circuit110E may detect that the tag device20E has been introduced from the outside to the inside of a living body on the basis of the intensity of the first response signal received by the first reception circuit151and the intensity of the second response signal received by the second reception circuit152. In such a case, the control circuit110E may detect that the tag device20E has been introduced from the outside to the inside of the living body through a variation in the intensity of the first response signal from being larger than the intensity of the second response signal to being smaller than the intensity of the second response signal.

The control circuit110E may detect that the tag device20E has been moved from the inside to the outside of the living body on the basis of the intensity of the first response signal received by the first reception circuit151and the intensity of the second response signal received by the second reception circuit152. In such a case, the control circuit110E may detect that the tag device20E has been moved from the inside to the outside of the living body through a variation in the intensity of the second response signal from being larger than the intensity of the first response signal to being smaller than the intensity of the first response signal.

(Configuration of Tag Device)

With reference toFIG. 18, the tag device20E according to the third embodiment includes an antenna210and an IC unit220E. In this embodiment, the IC unit220E corresponds to a transmitter.

The antenna210has a configuration that is the same as that of the antenna210according to the first embodiment.

The IC unit220E is in connection with the first antenna component211and the second antenna component212. The IC unit220E includes a first transmission circuit224E, a second transmission circuit225E, and a battery226E. In this embodiment, the tag device20E is of a semi-active type.

In this embodiment, the IC unit220E includes a rectifier and a capacitor (not illustrated). The current generated between the first antenna component211and the second antenna component212is rectified at the rectifier and stored in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The IC unit220E demodulates the second signal component for at least a portion of the period during which the second signal component of the request signal is received, using the electrical energy stored in the capacitor. The IC unit220E obtains identification information on the basis of the demodulated signal.

Alternatively, without using the rectifier and the capacitor (not illustrated), the IC unit220E may demodulate the second signal component for at least a portion of the period during which the second signal component of the request signal is received, using the electrical energy stored in the battery226E. In such a case, the request signal does not always include the first signal component.

The first transmission circuit224E transmits a response signal having a carrier wave having a first frequency (in other words, first response signal) via the antenna210, using the electrical energy stored in the battery226E. The first transmission circuit224E transmits the first response signal modulated in accordance with a preselected first modulation scheme. The first modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the first modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

The second transmission circuit225E transmits a response signal having a carrier wave having the second frequency (in other words, second response signal) via the antenna210, using the electrical energy stored in the battery226E. The second transmission circuit225E transmits the second response signal modulated in accordance with a preselected second modulation scheme. The second modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the second modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

In this embodiment, the response information contains information stored in the IC unit220E in advance. For example, the response information may contain an identifier for identifying the tag device20E. If the tag device20E includes a sensor for detecting a physical quantity, the response information may contain information representing the physical quantity detected by the sensor in addition to or instead of the information stored in the IC unit220E in advance. The physical quantity is temperature, humidity, illuminance, pH, acceleration, angular velocity, pressure, or concentration of a subject, for example. Examples of the subject include a digestive fluid (e.g., saliva, gastric juice, intestinal juice, or pancreatic juice), blood, normal microbial flora, and infectious material (for example, bacteria or viruses).

The tag device20E may include a first battery in connection with the first transmission circuit224E and a second battery in connection with the second transmission circuit225E, in addition to or in place of the battery226E.

The operation of the wireless communication system1according to the third embodiment will now be explained with reference toFIG. 19.

A case of the tag device20E outside the living body will now be explained. In this case, the antenna210of the tag device20E is in contact with air.

The reader10E starts the transmission of a request signal having a carrier wave having the first frequency (in other words, first request signal) and the transmission of a request signal having a carrier wave having the second frequency (in other words, second request signal) (Step S501inFIG. 19).

The tag device20E receives the first request signal and the second request signal. Since the antenna210is in contact with air, the resonance frequency of the antenna210is substantially identical to the first frequency. Thus, the intensity of the first request signal received by the antenna210is larger than the intensity of the second request signal received by the antenna210.

The tag device20E rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20E demodulates the second signal component of the request signal for at least a portion of the period during which the second signal component is received, and obtains the identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

The reader10E ends the transmission of the first request signal and the transmission of the second request signal (Step S502inFIG. 19).

The reader10E then starts the stand-by for reception of a response signal having a carrier wave having the first frequency (in other words, first response signal) and the stand-by for reception of a response signal having a carrier wave having the second frequency (in other words, second response signal) (Step S503inFIG. 19).

The tag device20E starts the transmission of the first response signal and the transmission of the second response signal (Step S504inFIG. 19).

The response signal transmitted by the antenna210includes a first response signal component having a carrier wave having the first frequency (in other words, first component) and a second response signal component having a carrier wave having the second frequency (in other words, second component). Since the antenna210is in contact with air, the resonance frequency of the antenna210is substantially identical to the first frequency. Thus, the intensity of the first response signal component transmitted by the antenna210is larger than the intensity of the second response signal component transmitted by the antenna210.

The reader10E receives the response signal transmitted by the tag device20E. The reader10E obtains the response information on the basis of only the response signal component having the larger intensity among the first response signal component and the second response signal component of the received response signal. Thus, the reader10E obtains the response information on the basis of only the first response signal component among the first response signal component and the second response signal component of the received response signal.

A case of the tag device20E inside the living body will now be described. In this case, the antenna210of the tag device20E is in contact with a fluid inside the living body (saliva, in this embodiment).

Similar to the operation explained above, the reader10E starts the transmission of the first request signal and the transmission of the second request signal.

The tag device20E receives the first request signal and the second request signal. Since the antenna210is in contact with the fluid inside the living body, the resonance frequency of the antenna210is substantially identical to the second frequency. Thus, the intensity of the second request signal received by the antenna210is larger than the intensity of the first request signal received by the antenna210.

The tag device20E rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20E demodulates the second signal component of the request signal for at least a portion of the period during which the second signal component is received, and obtains the identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

The reader10E ends the transmission of the first request signal and the transmission of the second request signal. The reader10E then starts the stand-by for reception of the first response signal and the stand-by for reception of the second response signal.

The tag device20E starts the transmission of the first response signal and the transmission of the second response signal.

The response signal transmitted by the antenna210includes a first response signal component having a carrier wave having the first frequency (in other words, first component) and the second response signal component having a carrier wave having the second frequency (in other words, second component). Since the antenna210is in contact with the fluid inside the living body, the resonance frequency of the antenna210is substantially identical to the second frequency. Thus, the intensity of the second response signal component transmitted by the antenna210is larger than the intensity of the first response signal component transmitted by the antenna210.

The reader10E receives the response signal transmitted by the tag device20E. The reader10E obtains the response information on the basis of only the response signal component having the larger intensity among the first response signal component and the second response signal component of the received response signal. Thus, the reader10E obtains the response information on the basis of only the second response signal component among the first response signal component and the second response signal component of the received response signal.

As described above, the wireless communication system1according to the third embodiment carries out communication between the tag device20E and the reader10E via the antenna210at the first frequency when the tag device20E is outside the living body. The wireless communication system1carries out communication between the tag device20E and the reader10E via the antenna210at the second frequency, which is lower than the first frequency, when the tag device20E is inside the living body.

Thus, the reader10E can communicate with the tag device20E via the antenna210of the tag device20E regardless of whether the tag device20E is inside or outside the living body.

The reader10E according to the third embodiment receives a signal having the first frequency and a signal having the second frequency.

Thus, the reader10E can receive the signal having the first frequency when the tag device20E is outside the living body. The reader10E can receive the signal having the second frequency when the tag device20E is inside the living body. Thus, the reader10E can communicate with the tag device20E via the antenna210of the tag device20E regardless of whether the tag device20E is inside or outside the living body.

The tag device20E according to the third embodiment transmits the signal having the first frequency via the antenna210and transmits the signal having the second frequency via the antenna210.

Thus, the reader10E can receive the signal having the first frequency when the tag device20E is outside the living body. The reader10E can receive the signal having the second frequency when the tag device20E is inside the living body. Thus, the reader10E can communicate with the tag device20E via the antenna210of the tag device20E regardless of whether the tag device20E is inside or outside the living body.

The reader10E according to the third embodiment transmits the signal having the first frequency and the signal having the second frequency.

Thus, the tag device20E can receive the signal having the first frequency when the tag device20E is outside the living body. The tag device20E can receive the signal having the second frequency when the tag device20E is inside the living body. Thus, the tag device20E can communicate with the reader10E via the antenna210of the tag device20E regardless of whether the tag device20E is inside or outside the living body.

The wireless communication system1may use a frequency included in the 2.45 GHz band (from 2.4 to 2.5 GHz, for example) as the first frequency and a frequency included in the 900 MHz band (from 915 to 955 MHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the first frequency and a frequency included in the 900 MHz band (from 915 to 955 MHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 60 GHz band (from 57 to 66 GHz, for example) as the first frequency and a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the second frequency.

Alternatively, the wireless communication system1may use a frequency included in the 24 GHz band (from 24 to 24.25 GHz, for example) as the first frequency and a frequency included in the 5.8 GHz band (from 5.725 to 5.875 GHz, for example) as the second frequency.

The tag device20E may include a modifier that modifies the resonance frequency of the antenna210. For example, the modifier may include a first antenna extension, a second antenna extension, a first switching device, and a second switching device.

The first antenna extension is in connection with the first antenna component211via the first switching device. The first switching device switches between a state in which the first antenna component211and the first antenna extension are connected and a state in which the first antenna component211and the first antenna extension are disconnected.

The second antenna extension is in connection with the second antenna component212via the second switching device. The second switching device switches between a state in which the second antenna component212and the second antenna extension are connected and a state in which the second antenna component212and the second antenna extension are disconnected.

This can modify the ratio of the first frequency to the second frequency to a value different from the ratio of the permittivity of air to the permittivity of a fluid inside the living body. Thus, the frequency used for communication between the reader10E and the tag device20E can be selected from a wider range.

The reader10E may end the stand-by for reception of the first response signal component of the response signal if the reader10E receives the response signal and if the intensity of the first response signal component is smaller than the intensity of the second response signal component of the response signal. The reader10E may end the stand-by for reception of the second response signal component of the response signal if the reader10E receives the response signal and if the intensity of the second response signal component is smaller than the intensity of the first response signal component of the response signal.

This can reduce the electrical power consumption at the reader10E during the stand-by for reception of a response signal by the reader10E.

In the wireless communication system1, the tag device20E may start the transmission of the signal having the first frequency and the signal having the second frequency before the reader10E starts the stand-by for reception of the signal having the first frequency and the signal having the second frequency.

<First Modification to Third Embodiment>

A wireless communication system according to a first modification to the third embodiment will now be described. The wireless communication system according to the first modification to the third embodiment differs from the wireless communication system according to the third embodiment in that the tag device detects whether it is inside a living body and the frequency to be used for communication is controlled on the basis of the detected result. The wireless communication system will now be described with focus on these differences. In the first modification to the third embodiment, components that are identical or very similar to those according to the third embodiment are indicated by the same reference signs.

(Configuration of Tag Device)

With reference toFIG. 20, a tag device20F according to the first modification to the third embodiment includes an IC unit220F in place of the IC unit220E of the tag device20E according to the third embodiment. The IC unit220F includes a first transmission circuit224F, a second transmission circuit225F, a battery226F, a switching device227F, and a sensor228F. In this modification, the sensor228F corresponds to a detector. In this modification, the IC unit220F corresponds to a transmitter.

In this modification, the IC unit220F includes a rectifier and a capacitor (not illustrated). The current generated between the first antenna component211and the second antenna component212is rectified at the rectifier and stored in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The IC unit220F demodulates the second signal component for at least a portion of the period during which the second signal component of the request signal is received, using the electrical energy stored in the capacitor. The IC unit220F obtains identification information on the basis of the demodulated signal.

Alternatively, without using the rectifier and the capacitor (not illustrated), the IC unit220F may demodulate the second signal component for at least a portion of the period during which the second signal component of the request signal is received, using the electrical energy stored in the battery226F. In such a case, the request signal does not always include the first signal component.

The sensor228F detects whether the tag device20F is inside the living body. In this modification, the sensor228F detects temperature. The sensor228F detects that the tag device20F is inside the living body when the detected temperature is higher than or equal to a predetermined threshold (307K, for example) and detects that the tag device20F is outside the living body when the detected temperature is lower than the threshold.

In addition to or instead of detecting temperature, the sensor228F may detect whether the tag device20F is inside the living body on the basis of a physical quality other than temperature. The physical quantity may be illuminance, pH, or concentration of a subject, for example. Examples of the subject include a digestive fluid (e.g., saliva, gastric juice, intestinal juice, or pancreatic juice), blood, and normal microbial flora.

In this modification, the sensor228F operates by the electrical energy stored in the capacitor. Alternatively, the sensor228F may operate by the electrical energy stored in the battery226F.

The switching device227F switches between a first connection state and a second connection state on the basis of the detected result by the sensor228F. In the first connection state, the switching device227F connects the first transmission circuit224F and the battery226F and cuts off or disconnects the second transmission circuit225F and the battery226F. In the second connection state, the switching device227F disconnects the first transmission circuit224F and the battery226F and connects the second transmission circuit225F and the battery226F.

The switching device227F switches to the first connection state when the detected result by the sensor228F indicates that the tag device20F is outside the living body. The switching device227F switches to the second connection state when the detected result by the sensor228F indicates that the tag device20F is inside the living body.

In this modification, the switching device227F operates by the electrical energy stored in the capacitor. Alternatively, the switching device227F may operate by the electrical energy stored in the battery226F.

The first transmission circuit224F transmits a response signal having a carrier wave having a first frequency (in other words, first response signal) via the antenna210when the switching device227F is in the first connection state, using the electrical energy stored in the battery226F. The first transmission circuit224F transmits the first response signal modulated in accordance with a preselected first modulation scheme. The first modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the first modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

The second transmission circuit225F transmits a response signal having a carrier wave having a second frequency (in other words, second response signal) via the antenna210when the switching device227F is in the second connection state, using the electrical energy stored in the battery226F. The second transmission circuit225F transmits the second response signal modulated in accordance with a preselected second modulation scheme. The second modulation scheme may be an AM, FM, or PM scheme, for example. Alternatively, the second modulation scheme may be a combination of at least two of the AM, FM, and PM schemes, for example.

The operation of the wireless communication system1according to the first modification to the third embodiment will now be explained with reference toFIGS. 21 and 22.

A case of the tag device20F outside the living body will now be explained. In this case, the antenna210of the tag device20F is in contact with air.

The reader10E starts the transmission of a request signal having a carrier wave having the first frequency (in other words, first request signal) and the transmission of a request signal having a carrier wave having the second frequency (in other words, second request signal) (Step S601inFIG. 21).

The tag device20F receives the first request signal and the second request signal. Since the antenna210is in contact with air, the resonance frequency of the antenna210is substantially identical to the first frequency. Thus, the intensity of the first request signal received by the antenna210is larger than the intensity of the second request signal received by the antenna210.

The tag device20F rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20F demodulates the second signal component of the request signal for at least a portion of the period during which the second signal component is received, and obtains the identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

The reader10E ends the transmission of the first request signal and the transmission of the second request signal (Step S602inFIG. 21).

The reader10E then starts the stand-by for reception of a response signal having a carrier wave having the first frequency (in other words, first response signal) and the stand-by for reception of a response signal having a carrier wave having the second frequency (in other words, second response signal) (Step S603inFIG. 21).

The tag device20F detects whether the tag device20F is inside the living body with the sensor228F. In this case, the tag device20F detects that the tag device20F is not inside the living body (in other words, outside the living body) (Step S6041inFIG. 21).

Thus, the switching device227F switches to the first connection state. This starts the transmission of the first response signal by the tag device20F (Step S6051inFIG. 21).

Thus, the carrier wave of the response signal transmitted by the antenna210has the first frequency. In other words, the response signal does not contain a component whose carrier wave has the second frequency.

The reader10E receives the response signal transmitted by the tag device20F. In this case, the reader10E obtains the response information on the basis of the first response signal received by the first reception circuit151.

A case of the tag device20F inside the living body will now be described. In this case, the antenna210of the tag device20F is in contact with a fluid inside the living body (saliva, in this embodiment).

Similar to the operation explained above, the reader10E starts the transmission of the first request signal and the transmission of the second request signal (Step S601inFIG. 22).

The tag device20F receives the first request signal and the second request signal. Since the antenna210is in contact with the fluid inside the living body, the resonance frequency of the antenna210is substantially identical to the second frequency. Thus, the intensity of the second request signal received by the antenna210is larger than the intensity of the first request signal received by the antenna210.

The tag device20F rectifies the current generated between the first antenna component211and the second antenna component212at the rectifier and stores a charge in the capacitor for at least a portion of the period during which the first signal component of the request signal is received.

The tag device20F demodulates the second signal component of the request signal for at least a portion of the period during which the second signal component is received, and obtains the identification information on the basis of the demodulated signal, using the electrical energy stored in the capacitor.

The reader10E ends the transmission of the first request signal and the transmission of the second request signal (Step S602inFIG. 22). The reader10E then starts the stand-by for reception of the first response signal and the stand-by for reception of the second response signal (Step S603inFIG. 22).

The tag device20F detects whether the tag device20F is inside the living body with the sensor228F. In this case, the tag device20F detects that the tag device20F is inside the living body (Step S6042inFIG. 22).

Thus, the switching device227F switches to the second connection state. This starts the transmission of the second response signal by the tag device20F (Step S6052inFIG. 22).

Thus, the carrier wave of the response signal transmitted by the antenna210has the second frequency. In other words, the response signal does not contain a component whose carrier wave has the first frequency.

The reader10E receives the response signal transmitted by the tag device20F. In this case, the reader10E obtains the response information on the basis of the second response signal received by the second reception circuit152.

As described above, the wireless communication system1according to the first modification to the third embodiment operates in the same manner and achieves the same advantages as those of the wireless communication system1according to the third embodiment.

The tag device20F of the wireless communication system1according to the first modification to the third embodiment controls the frequency of the carrier wave of the signal transmitted by the tag device20F to the first frequency if the tag device20F is detected to be outside the living body and controls the frequency of the carrier wave of the signal transmitted by the tag device20F to the second frequency if the tag device20F is detected to be inside the living body.

Such control can prevent the transmission of the signal having the first frequency by the tag device20F while the tag device20F is being inside the living body. The control can also prevent the transmission of the signal having the second frequency by the tag device20F while the tag device20F is being outside the living body. Thus, the electrical power consumption of the tag device20F can be reduced compared to that of the tag device20F for transmission of both the signal having the first frequency and the signal having the second frequency.

When the transmission of either the signal having a carrier wave having the first frequency or the signal having a carrier wave having the second frequency continues for a threshold time or longer, the tag device20F may repeat the detection for whether the tag device20F is inside the living body and the frequency control on the basis of the detected result.

Thus, the reader10E can communicate with the tag device20F via the antenna210of the tag device20F regardless of whether the tag device20F is moved to the inside or outside of the living body.

In the wireless communication system1, the tag device20F may start the detection of whether the tag device20F is inside the living body and the transmission of the signal having the first frequency or the signal having the second frequency before the reader10E starts the stand-by for reception of the signal having the first frequency and the signal having the second frequency.

According to the above-described technologies, it is possible to carry out communication regardless of whether a wireless device is inside or outside a living body.