Patent Publication Number: US-2005116813-A1

Title: Radio and optical identification tags

Description:
RELATED APPLICATION  
      This Patent Application is a Continuation-in-Part of U.S. patent application Ser. No. 10/643,614 filed on Aug. 19, 2003. 
    
    
     FIELD OF THE INVENTION  
      This invention relates generally to identification tags, and more particularly to tags that can be selectively operated.  
     BACKGROUND OF THE INVENTION  
      Conventional radio-frequency identification (RFID) tags are used to identify objects, including people. RFID tags provide an alternative to bar codes for distinguishing and recording products for purchase. Using RFID tags can result in labor savings to manufacturers, distributors, and retailers. Annual estimated savings for a large retailer using RFID tags could amount to billions of dollars.  
      The typical prior art RFID tag includes a microchip and an antenna. The antenna can be in the form of a tuned induction coil. The operation is fundamentally simple. Typically, the microchip stores a unique identification code that can be detected when the antenna of the tag couples inductively with an antenna of the reader. This coupling changes the impedance, hence the load at the receiving antenna. The load can be modulated according to the stored identification code by switching the coil in and out.  
      Conventional RFID tags can be characterized according to the following basic attributes. An active RFID tag includes a power source to operate the microchip and to ‘broadcast’ the signal to the reader. Semi-passive tags use a battery to operate the microchip, but use an induced current to operate the transmitter. Because these types of tags are more costly to manufacture, they are typically used for high-cost objects that need to be identified at greater distances. For a passive tag, the reader induces a current in the tag by emitting electromagnetic radiation. These tags are relatively cheap, and are effective up to ranges of about 50 meters, depending on the power of the transmitted RF signal.  
      The tag can be read-only or read-and-write. In the latter type, information can be added to the tag over time using, e.g., an electrically erasable programmable read-only memory (EEPROM). For example, the tag can store when it was read, or how often it was read.  
      RFID tags can also be distinguished according to the frequency at which they operate. The operating frequencies need to be consistent with RF spectrum assignments made by regulatory agencies such as the FCC in the United States. Low frequency tags are generally cheaper to make than high frequency devices and use less power. Different applications may also prefer different frequencies. For example, low frequency tags are more suitable for applications with a high fluid content, e.g., items under water, humans, fruits, water based products. High frequency tags provide a higher data rate and range. Also, because high frequencies tend to be line-of-sight, they can be useful at fixed locations with a narrow field-of-view, for example, in assembly lines and doorways.  
      One problem encountered with RFID tags is collision.  
      Reader collision can happen when one reader interferes with the signal of another nearby reader. This can be a problem in warehousing where multiple users may want to identify stock at the same time. This can result in multiple readings of the same tag, which need to be resolved. In the prior art, time division multiplexing has been used to overcome this problem. However, this increases the complexity and cost of the system.  
      Tag collision also occurs when many tags are co-located. This can result in multiple simultaneous readings of different tags, which need to be resolved. A number of techniques have been proposed to mitigate such collisions. Most of these require complex protocols that slow down the process.  
      Therefore, there is a need for RFID tags that can be selectively operated.  
     SUMMARY OF THE INVENTION  
      An identification tag is formed with a single microcircuit. The microcircuit includes an optical transceiver in the form of a single photodiode or phototransistor. The diode can transmit and sense light depending on the direction current is driven through the diode.  
      The circuit also includes a radio transceiver. In its simplest form the transceiver is an induction coil. Both the optical and radio transceivers are connected to a memory storing an identification code.  
      At least one of the transceivers operates in receive mode, and at least one of the transceivers operates in transmit mode. The identification code is transmitted by the transceiver operating in the transmit mode in response to receiving a predetermined signal by the transceiver operating in the receive mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of an identification tag according to the invention;  
       FIG. 2  is a top view of the tag of  FIG. 1  to scale;  
       FIG. 3  is a block diagram of an RFID system including an identification tag and reader according to the invention;  
       FIG. 4  is a detailed block diagram of the identification tag according to the invention;  
       FIG. 5  is a detailed block diagram of a reader according to the invention;  
       FIG. 6 a  flow diagram of the RFID system operation;  
       FIG. 7 a  flow diagram of the initialization steps;  
       FIG. 8  is a flow diagram of a read ID command;  
       FIG. 9  is a block diagram of an alternative embodiment of the RFID tag according to the invention;  
       FIG. 10  is a block diagram of an alternative embodiment of the reader according to the invention;  
       FIG. 11  is a block diagram of an alternative embodiment of a reader;  
       FIG. 12  is a block diagram of an alternative embodiment of a RFID tag;  
       FIG. 13  is a block diagram of an alternative embodiment of a tag reader; and  
       FIGS. 14-18  are flow diagrams of operations of the RFID tag and reader according to the invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIGS. 1 and 2  show an identification tag  100  according to the invention. The tag is formed on a single integrated microcircuit a few millimeters in length on each side. The tag is comparable to RFID tags as known in the art. The primary purpose of the tag is to provide identification to users. In addition, the tag according to the invention also provides for visual identification.  
      The tag  100  includes an optical-frequency (OF) transceiver  201  and a radio-frequency (RF) transceiver  202 . The OF transceiver uses a single frequency band (optical channel) to receive and transmit signals. The RF transceiver uses another single frequency band (RF channel) to transmit and receive signals.  
      The OF transceiver  201  includes a photodiode or phototransistor  101  that is capable of receiving light  160  and transmitting light  161  in a specific frequency band. U.S. patent application Ser. No. 10/126,761, “Communication Using Bi-Directional LEDs,” filed by Dietz et al. on Apr. 19, 2002 and incorporated herein by reference in its entirety, describes such a photo transceiver. Alternatively, the OF transceiver can be a phototransistor. The OF transceiver can be used to acquire synchronization information to support communications with tag readers. The OF transceiver can be configured to be narrow beam or omni-directional.  
      The RF transceiver  202  includes an antenna  102  that can receive radio signals  170  and transmit radio signals  171 . By ‘transmitting,’ it is meant that the RF antenna  102  can selectively couple to another antenna by a radio frequency signal. That is, the antenna is in the form of an induction coil. The current induced in the coil can also be used to power the OF and RF transceivers parasitically. The current can be stored in a capacitor.  
      Both transceivers  201 - 202  have access to a memory  103  storing an identification (ID) code. The code can include other information, such as a manufacturing date or an expiration date. The ID code can be unique or belong to a class of codes.  
      During operation, at least one of the transceivers operates in a receive mode and at least one transceiver operates in a transmit mode. The receiving and transmitting transceivers can be the same or different. The ‘receiving’ transceiver, upon detecting a received signal on its associated channel, e.g., either the optical signal  160  or the RF signal  170 , causes the ‘transmitting’ transceiver to respond with a transmitted signal, e.g., either the RF signal  171  or the optical signal  161 . The transmitted signal is modulated according to the ID code  103 , or some other stored information. It should be understood that the tag can also have both the transceivers operate in both modes concurrently. For example, if the ID code corresponds to a particular product class, and multiple products of that class are within range, only products with an expired date can respond.  
      Modes of Operation  
      Light-In/RF-Out  
      A user shines a narrow beam of predetermined signal light  160  at the tag  100 . The tag, in response to receiving the predetermined signal, transmits the ID in the RF signal  171 . This allows the user to select a specific tag for identification. For example, the user can identify a box at a hard to reach location. The RF transceiver is said to be transmitting when the RF antenna is selectively coupled to a sensing device to convey, e.g., the ID code  103 .  
      RF-In/Light-Out  
      A user transmits a query in the form of the predetermined radio signal  170  to an area including one or more tags. The tag then emits light  161  if the received signal matches the ID  103 . This allows the user to visually identify a specific tag. This is useful to pick out a specific box mingled among other identical boxes. The light can be steady or modulated according to the code  103 .  
      Light-In/Light and RF-Out  
      A user shines a narrow beam of predetermined signal light  160  at the tag  100 . The tag responds the ID in the RF signal  171  if the predetermined signal  160  is sensed. In addition, the tag transmits light  161  if the RF query signal matches the ID  103 . This allows the user to select a specific tag for identification and to visually locate the tag.  
      RF-In/Light and RF-Out  
      A user transmits a query in the form of the predetermined radio signal  170  to an area including one or more tags. The tag then emits light  161  if the query matches the ID  103 . In addition, the tag emits the RF signal  171  if the query matches the ID  103 . This allows the user to visually identify a specific tag, and obtain its identification.  
      Light and RF-In//Light and RF-Out  
      In this case, the tag will respond with a light and an RF signal only if both a light and a RF signal are received.  
      The mode of operation can be predetermined, can be encoded in the tag, or can be selected dynamically by modulating the received signal appropriately.  
      The tag according to the invention solves the collision problem as described above. In addition, the tag allows for visual identification in applications where a large number of tags are co-located.  
      It should be understood that the tag can be enhanced to include means for storing power to increase the range of the transceivers. The transceivers can be operated parasitically from power obtained from the RF signal.  
      The tag can perform additional processing to store received data and to operate in accordance with the stored data.  
      RFID System  
       FIG. 3  shows a RFID system including a tag  10  and a RFID reader  20 . The tag transmits information from the tag  10 , e.g., an ID, to the reader  20  as a response signal (RS)  9  when detecting a predetermined signal, e.g., a command light (CL)  8  emitted by the reader  20  and directed onto the tag  10 . Hence, the reader  20  obtains the ID of the tag, and other information as described above.  
      The reader  20  is usually operated by the user and the tag  10  is usually attached to a product, pallet, case, or other packing materials. The emitted light can be passed through a lens to control a range and shape of the light beam. Alternatively, the light beam can be shaped by a pixel-based digital projector. Thus, the command light can be directed at a single tag or a predetermined number of adjacent tags. The light beam indicates that the tag is being read so that other users do not accidentally also attempt to read the tag at the same time.  
      TAG Structure  
       FIG. 4  shows the details of the identification tag  10 . The ID tag  10  is passive. Electric power is supplied by electromagnetic waves radiated from the reader  20 . The ID tag  10  includes an optical frequency receiver (OFR)  11 , a radio frequency transceiver (RFT)  12 , a controller  13 , a memory  14  storing an ID and other information, a power unit  15 , and an antenna  16 . The OFR  11 , RFT  12 , memory  14  and power unit  15  are implemented in a single integrated circuit (IC). The OFR  11 , RFT  12 , memory  14  and power unit  15  are connected electrically to the control unit  13 .  
      The OFR  11  includes a light receiving portion  11   a . The light receiving portion  11   a  includes a light sensitive element such as a photodiode or a phototransistor. The OFR  11  supplies a signal demodulated from the command light CL when the command light CL is received by the light receiving portion  11   a . The command light CL is a light with specific frequency and modulation, which are predetermined. The frequency can be visible light or infrared in order to configure the light receiving portion inexpensively. The modulation can be amplitude modulation (AM) or others such as frequency modulation (FM).  
      The input light can be thresholded to enable stable optical communication. Before the optical communication, the luminance threshold is initialized. Thus, stable optical communication is possible even when the ambient light or the command light varies in intensity.  
      The controller portion  13  includes a determining portion  13   a  for a determination process, a memory access portion  13   b  for a memory access process, an ID transmitting portion  13   c  for an ID transmission process and a register  13   d.    
      The determining portion  13   a  compares the luminance signal from the OFR  11  with the luminance threshold value stored in the register  13   a . When the luminance is in a one state, that is, the ID tag  10  is illuminated by the reader  20 , the determining portion  13   a  causes the memory access portion  13   b  to read the ID in response to an ID read command from the RFT  12 . Then, the memory access portion  13   b  supplies an ID read signal to the memory  14 . In other words, the controller  13  asserts the ID read signal only when it is verified that the receiving light corresponds to the command light CL.  
      The memory  14  stores the ID related information. The ID related information includes tag specific identification; other attributes as described above; and control information, for example, a bit to command the tag to ‘sleep’, an error detection code such as CRC, and general information defined by the user. The controller  13  transfers the ID information to the RFT  12 .  
      The RFT  12  includes an RF demodulation portion  12   a  and an RF modulation portion  12   b . The RF demodulation portion  12   a  demodulates the ID read command transmitted from the reader  20  using radio waves of a predetermined frequency. The demodulated command is sent to the controller  13 . The ID transmitting portion  13   c  of the controller  13  receives the ID related information from the memory and transfers the ID related information to the RFT  12 . Based on the ID related information, the RF modulation portion  12   b  transmits the response signal via the antenna  16 .  
      Usually, RFID uses frequency bands such as 125 kHz (low-frequency), 13.56 MHz (high-frequency), 860-960 MHz (ultra-high-frequency), 2.45 GHz (microwave) and so on.  
      The antenna  16  includes an induction coil, for example, at relatively low frequencies such as LF and HF, and the RF communication and power transmission is done by inductive coupling with the antenna of the reader  20 .  
      In another instance using relatively high frequency, such as UHF and microwave, the antenna  16  includes a dipole antenna or a patch antenna to transmit and receive radio waves.  
      The power portion  15  includes a rectifier, a capacitor, and a reset controller. The rectifier rectifies power received by the antenna  16 . The rectified power is stored in the capacitor and supplied to the tag  10 . Thus, the tag  10  can operate without battery. The reset controller monitors the electric power stored in the capacitor and enables operation of the ID tag  10  only when sufficient power is stored.  
      As described above, the tag  10  transmits the response signal RS including the ID related information in response to receiving the command light CL.  
      Reader  
       FIG. 5  show the reader  20  including an optical communication portion  21 , an RF communication portion  22 , a controller  23  and an external interface  24 . The reader  20  causes the optical communication portion  21  to emit the command light CL based on a command received from the external interface  24 , and causes the RF communication portion  22  to transmit the radio waves for the power supply of the reader and the ID read command. In response, the reader  20  receives the response signal RS transmitted from the ID tag  10  in the RF communication portion  22 .  
      The optical communication portion  21  includes a light emission portion  21   a . The light emission portion  21   a  includes a photo emitter, such as an LED, electric bulb, digital projector, and the like. The optical communication portion  21  emits the command light CL having a predetermined shape from the light emission portion  21   a  at a predetermined range and frequency. Therefore, the number of tags illuminated can be strictly controlled.  
      In response to receiving a start command from the controller  23 , the RF communication portion  22  transmits the RF signal for the power supply of the tag. The RF communication portion  22  also receives the transmitted response signal RS, extracts the ID related information by demodulating the response signal RS, and then supplies the demodulated signal to the controller  23 .  
      The controller  23  controls the optical communication portion  21  and the RF communication portion  22 . More detailed, the controller  23  controls the RF communication portion  22  in response to receiving the read start signal from the external interface  24  and makes the RF communication portion  22  radiate the power supply electromagnetic wave and the read command. The controller  23  controls the optical communication portion  21  in response to receiving the read start signal from the external interface  24  and makes the light emission portion  21   a  emit the command light CL.  
      The external interface  24  is used for operations including sending commands to the reader  20  and outputting the result. As stationary RFID readers are usually configured, the external interface  24  can include communication portions such as Ethernet, wireless LAN, RS-232C and USB, and a communication processing portion such as a microprocessor to implement communication protocols for exchanging commands and data. The read start command signal is provided by the external interface  24  to the controller  23 . The external interface can be connected to another computer or a user interface with control buttons. The external interface can also include a display unit.  
      RFID Operation  
       FIG. 6  shows the operation of the RFID system. A reading operation of the ID related information is started by a read start command given to the reader  20  through the external interface  24 .  
      First, the luminance threshold of the OFR  11  is initialized  601 . Next, one or more read operation  602  are performed.  
       FIG. 7  shows the steps of initializing. First, the reader  20  transmits  701  the power supply electromagnetic waves from the RF communication portion  22 , and the ID tag  10  stores power in the capacitor of the power portion  15  and supplies the power to each component of the tag  10 . At the same time, the reader  20  emits  702  the light from the optical communication portion  21 .  
      Then, the reader  20  transmits  703  the “initialize  1 ” command from the RF communication portion  22 , and the tag  10  saves the luminance value when receiving the “initialize  1 ” command. After that, the reader  20 : stops  704  emitting the light from the optical communication portion  21 , radiates  705  the power supply electromagnetic waves, and sends  706  the “initialize  0 ” command. The ID tag  10  saves the luminance value when receiving the “initialize  0 ” command, stores  707  an intermediate value between the luminance values of “initialize  1 ” and “initialize  0 ” to the register  13   d  as the luminance threshold.  
       FIG. 8  shows the operation of the “read ID” command of  FIG. 6 . First, the reader  20  radiates the power supply electromagnetic waves from the RF communication portion  22 . Then the ID tag  10  stores power at the capacitor of the power portion  15  and supplies  801  the power to each component of the ID tag  10 . Then the reader  20  emits the command light CL at the predetermined range, and synchronously, radiates  802  the “read ID” command from the RF communication portion  22 . After verifying  803  that the command light CL has been received, the ID tag  10  transmits  804  the response signal including the ID related information to the reader  20 .  
      Specifically, the tag  10  determines whether or not the received light is the command light CL by comparing the intensity of the received light in the OFR  11  with the luminance threshold value stored in the register  13   d . When it is verified that the received light is the command light CL, then the controller  13  supplies the ID read signal to the memory  14  and reads out the ID related information from the memory  14 . The ID related information, which is read out, is transmitted  804  from RFT  12  as the response signal.  
      The reader  20  extracts the ID related information from the response signal received at the RF communication portion  22 . The extracted ID related information can be stored to the memory of the reader  20 . The information can also be displayed and transmitted to another computer.  
       FIG. 9  shows an alternative embodiment  30  of the tag  10 . The tag has an optical frequency receiver (OFR)  31  including a light receiving portion  31   a ; a radio frequency receiver (RFT)  32  with a RF demodulation portion  32   a  and a RF modulated portion  32   b ; a controller  33  having a determining portion  33   a , a memory access portion  33   b , an ID transmitting portion  33   c  and a register  33   d ; a memory  34 , an antenna  36 , and a battery  35 . The battery  35  supplies electric power to each portion in ID tag  30 .  
      The battery can extend the transmission range of the tag and the reader does not need to supply power.  
      Another embodiment  40  of the reader is shown in  FIG. 10 . The tag has an optical frequency receiver (OFR)  41  including a light receiving portion  41   a ; a radio frequency receiver (RFT)  42  with a RF demodulation portion  42   a  and a RF modulated portion  42   b ; a controller  43  having a determining portion  43   a , a memory access portion  43   b , an ID transmitting portion  43   c , a register  43   d , and a comparing portion  43   e ; a memory  44 , an antenna  46 , and a power portion  45 . The power portion  45  supplies electric power to each portion in ID tag  40 .  
      The ID tag  40  determines whether or not the command light CL is received according to a modulated pattern of received light. In other words, the command light CL has multiple ‘bits’. The modulation pattern can use the well known Gray code. More specifically, a determining portion  43   a  includes a register  43   d  and a comparing portion  43   e . The register  43   d  stores predetermined binary code in predetermined number of bits. The register  43   d  can also be implemented as a electronically rewritable memory such as EEPROM. The comparing portion  43   e  compares the demodulated signal output from a light receiving portion  41   a  in a OFR  41  with the code stored in the register  43   d . If the two are identical, then the ID read signal is supplied to a memory access portion  43   b.    
      As a result, the memory access portion  43   b  reads the ID related information from a memory  44 , and a ID transmitting portion  43   c  supplies the information to a RFT  42 . The RFT  42  generates the response signal including the ID related information to the RF modulation portion  42   b  and transmits the response signal via the antenna  46 .  
      As described above, the code is extracted from the received signal by the light receiving portion  41   a  of the OFR  41 , and the ID related information is transmitted only when the extracted code corresponds to the stored contents in register  43   d . Consequently, the accuracy of the ID verification is improved.  
       FIG. 11  shows an alternative embodiment  60  of a reader  20 . In this embodiment, the emission range of the command light CL can be varied by the reader  60 .  
      The optical communication portion  61  in the reader  60  has an emission range setting portion  61   b  in addition to a light emission portion  61   a . The emission range setting portion  61   b  changes the emission range according to a control signal generated by the controller  63 . The controller  63  controls the emission range setting portion  61   b  based on an instruction signal from the external interface  64 . More detailed, the external interface  64  provides the command to start reading and a command to set the emission range. The controller  63  controls the emission range setting portion  61   b  so that the light is emitted at a range corresponding to the command to set the emission range. The function of the RF communication portion  62  is as described above.  
       FIG. 12  shows an alternative embodiment  70  of a ID tag  10 . The ID tag  70  includes an optical frequency transceiver (OFT)  71  having a light emission portion  71   b  in addition to a light receiving portion  71   a . The ID tag  70  can set a transmit and a receive mode for both the OFT  71  and the RFT  72 , and transmits the responding signal from the transceiver being operated in the transmit mode in response to receiving a predetermined signal at the transceiver being operated in the receive mode. This ID tag  70  is an example of an active tag.  
      In more detail, the ID tag  70  includes the OFT  71 , the RFT  72  having an RF demodulation portion  72   a  and an RF modulation portion  72   b , a controller  73 , a memory  74 , a battery  75  and an antenna  76 .  
      The OFT  71  includes a light receiving portion  71   a  and a light emission portion  71   b  and can receive and emit light at predetermined frequencies. The light receiving portion  71   a  includes a photodiode or phototransistor for example, and the light emission portion  71   b  includes an LED, for example. Both the light receiving portion  71   a  and the light emission portion  71   b  can be implemented with a single LED as described in U.S. Patent Application Ser. No. 10/126,761, “Communication Using Bi-Directional LEDs,” filed by Dietz et al. on Apr. 19, 2002 incorporated herein by reference in its entirety.  
      The OFT  71 , the RFT  72 , the controller  73  and the memory  74  can be implemented in a single integrated circuit (IC) to reduce cost, but this is not necessary for implementation.  
      The controller  73  in the ID tag  70  includes a mode setting portion  73   g  and a mode communication controller  73   h  in addition to a determining portion  73   a , a memory access portion  73   b  and an ID transmitting portion  73   c . The mode setting portion  73   g  sets up one of a transmitting and receiving mode to one of two transceivers and the other mode to the other transceiver. The mode setting portion  73   g  sets up a transmitting/receiving mode to one of two transceivers and transmitting or receiving mode to the other transceiver. This mode setting process is conducted in response to the mode setting signal transmitted from the reader  80  and is implemented as switching or software in controller  73 .  
      The possible setting pattern is as follows: (a) receiving mode to OFT and transmitting mode to RFT, transmitting mode to OFT and receiving mode to RFT, (c) transmitting/receiving mode to OFT and transmitting mode to RFT, 
          (d) transmitting mode to OFT and transmitting/receiving mode to RFT, and (e) transmitting/receiving mode to OFT and transmitting/receiving mode to RFT.        

      The mode communication controller  73   h  controls the transceiver being operated in the transmitting mode so as to transmit the ID related information as the response signal, in response to receiving the command signal at the transceiver being operated in the receiving mode. The mode communication controller  73   h  controls the OFT  71  so as to emit light in a case where the mode (c) or (e) is used.  
       FIG. 13  is a block diagram of an alternative reader  80 . The reader  80  includes an optical communication portion  81 , an RF communication portion  82 , a controller  83  and an external interface  84 . The external interface  84  can be implemented as described above, and can also include a mode change portion  84   a . The mode change portion  84   a  is for changing the transmitting/receiving mode, as controlled by an external communication protocol or a mode change key in an interactive interface.  
      The controller  83  includes a mode controller  83   a . The mode controller  83   a  controls the optical communication portion  81  and the RF communication portion  82  so as to be operated in the mode instructed by the mode change portion  84   a  in the external interface  84 . The controller  83  also generates a mode setting signal so as to make the ID tag  70  operate in the same mode as that instructed by the mode change portion  84   a  and transmits the mode setting signal from the RF communication portion  82  to the ID tag  70 . As described above, the ID tag  70  sets up a mode instructed by the mode setting signal.  
      The optical communication portion  81  in the reader  80  includes a light emission portion  81   a  and a light receiving portion  81   b . The light receiving portion  81   b  receives the light emitted from the ID tag  70  as a response signal including the ID related information.  
       FIG. 14  shows the operation of the reader of the above embodiment. For example, the reader  80  transmits  1401  the mode setting signal instructing the mode pattern (a) to the ID tag  70 . The ID tag  70  sets up  1402  the receiving mode to the OFT  71  and the transmitting mode to the RFT  72 . More detailed, the RFT  72  in the ID tag  70  supplies the mode setting signal to the controller  73  when receiving the mode setting signal. The mode setting portion  73   g  in the controller  73  sets up the receiving mode to the OFT  71  and the transmitting mode to the RFT  72  based on the instruction of the mode setting signal.  
      When the reader  80  receives the command to start reading through the external interface  84 , the reader executes  1403  the “initialize threshold” process. Then, the reader  80  modulates the light based on the predetermined code and emits  1404  the modulated light toward the predetermined range as a command light CL.  
      When the ID tag  70  within the emission range verifies  1405  that the received light is the command light CL, the tag transmits  1406  the response signal RS including the ID related information. More detailed, because the transmitting mode is set up to the RFT  72 , the controller  73  reads out the ID related information from the memory  74  in response to receiving the command light at the OFT  71  and supplies the information to the RFT  72 . The RFT  72  generates the response signal having the ID related information and transmits the information by radio frequency. The RF communication portion  82  in the reader  80  extracts the ID related information from the received response signal.  
       FIG. 15  shows the operation of the RFID of the above embodiment for an alternative mode set up. The controller  83  in the reader  80  sets up the mode pattern (b) based on the instruction from the external interface  84 . The controller  83  makes the RF communication portion  82  transmit  1501  the mode setting signal instructing to set up the mode pattern (b) to the ID tag  70 . As a result, the ID tag  70  sets up  1502  the transmitting mode to the OFT  71  and the receiving mode to the RFT  72 .  
      When the reader  80  receives the command to start reading through the external interface  84 , the reader executes  1503  the “initialize threshold” process. In this case, the ID tag  70  emits light and the reader  80  receives light, and therefore, the threshold initialization is done in the reader  80 . Then, the reader  80  generates the command RF signal having the predetermined command and transmits  1504  the command via the RF communication portion  82 .  
      When the command RF signal is received at RFT  72 , the controller  73  in the ID tag  70 , verifies  1505  that the receive signal is the command RF signal and transmits  1506  the response signal having the ID related information to the reader  80 . More detailed, because the transmitting mode is set up for the OFT  71 , the controller  73  generates a light signal having the ID related information read out from the memory  74  as the response signal and makes the OFT  71  transmit the response signal. When the response signal is received at the optical communication portion  81  in the reader  80 , the controller  83  extracts the ID related information from the response signal.  
       FIG. 16  is a flowchart showing an operation of the RFID for setting up mode pattern (c). The controller  83  in the reader  80  sets up the mode pattern (c) based on the instruction from the external interface  84 . The controller  83  makes the RF communication portion  82  transmit  1601  the mode setting signal instructing the set up mode pattern (c) in the ID tag  70 . The ID tag  70  sets up  1602  the transmitting/receiving mode for the OFT  71  and the transmitting mode for the RFT  72 .  
      When the reader  80  receives the command to start reading through the external interface  84 , the reader executes  1603  the “initialize threshold” process. The reader  80  generates the command light CL and emits  1604  the CL toward the RFID at the predetermined range.  
      When it is verified  1605  that the received light is the command light CL, the ID tag  70  transmits  1606  the response signal having the ID related information to the reader  80 . More detailed, because the transmitting mode is set up to the RFT  72 , the controller  73  generates the RF signal having the ID related information read out from the memory  74  as the response signal and makes the RFT  72  transmit the signal. When the response signal is received at the RF communication portion  82  in the reader  80 , the controller  83  extracts the ID related information from the response signal.  
      The ID tag  70  also sets up the transmitting mode to the OFT  71 . When it is verified  1605  the received light is the command light CL, the controller  73  in ID tag  70  makes the emission portion  71   b  in the OFT  71  emit  1607  light. Therefore, user can see the light emitted from the ID tag  70  and thus can recognize the location of the ID tag  70 .  
       FIG. 17  shows the operation of the RFID for mode pattern (d) set up. The reader  80  sets up each component for the mode pattern (d) based on the instruction from the external interface  84 . The reader  80  makes the RF communication portion  82  transmit  1701  the mode setting signal instructing the tag to set up the mode pattern (d) in the ID tag  70 . As a result, the ID tag  70  sets up  1702  the transmitting mode to the OFT  71  and the transmitting/receiving mode to the RFT  72  based on the mode setting signal.  
      When the reader  80  receives the command to start reading through the external interface  84 , the reader generates the command RF signal and makes the RF communication portion  82  transmit  1703  the signal.  
      When it is verified  1704  that the received RF signal is the command RF signal, the ID tag  70  transmits  1705  the response signal having the ID related information to the reader  80 . More detailed, because the transmitting mode is set up to the RFT  72 , the controller  73  generates the RF signal having the ID related information read out from the memory  74  as the response signal and makes the RFT  72  transmit the signal. When the response signal is received at the RF communication portion  82  in the reader  80 , the controller  83  extracts the ID related information from the response signal.  
      In addition, the ID tag  70  also sets up the transmitting mode to the OFT  71 . When it is verified that the received RF signal is the command RF signal, the controller  73  in ID tag  70  makes the light emission portion  71   b  in the OFT  71  emit  1706  light. Therefore, the user can see the light emitted from the ID tag  70  and thus can recognize the location of the ID tag  70 .  
       FIG. 18  shows the operation of the RFID for mode pattern (e) set up. The reader  80  sets up each component so as to activate the mode pattern (e) based on the instruction from the external interface  84 . The reader  80  makes the RF communication portion  82  transmit  1801  the mode setting signal instructing the set up of the mode pattern (e) to the ID tag  70 . As a result, the ID tag  70  sets up  1802  the transmitting/receiving mode to both the OFT  71  and RFT  72  based on the mode setting signal.  
      When the reader  80  receives the command to start reading through the external interface  84 , the reader executes  1803  the “initialize threshold” process. Then, the reader  80  generates both the command light CL and command RF signal and makes the optical communication portion  81  and the RF communication portion  82  transmit them, respectively steps  1804  and  1805 .  
      When the tag verifies  1806  that the received light and RF signal are the command light and the command RF signal, the ID tag  70  transmits  1807  the response signal having the ID related information to the reader  80 .  
      More detailed, when the luminance of the received light is equal or more than the luminance threshold value and the predetermined command is included in the received radio wave, the controller  73  generates the RF signal having the ID related information read out from the memory  74  and makes the RFT  72  transmit the information. When the response signal is received at the RF communication portion  82  in the reader  80 , the controller  83  extracts the ID related information from the response signal.  
      In addition, the ID tag  70  also sets up the transmitting mode to the OFT  71 . When the command light and the command RF signal is verified, the controller  73  in ID tag  70  makes the light emission portion  71   b  in the OFT  71  emit  1808  light. Therefore, the user can see the light emitted from the ID tag  70  and thus can recognize the position of the ID tag  70 .  
      Although the invention has been described by way of examples of preferred embodiments, it is to be understood that various other adaptations and modifications may be made within the spirit and scope of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.