US-20260128521-A1 - COMMUNICATION APPARATUS AND CONTROL METHOD OF COMMUNICATION APPARATUS

US20260128521A1US 20260128521 A1US20260128521 A1US 20260128521A1US-20260128521-A1

Abstract

A communication apparatus configured to communicate with a wireless tag, includes: a plurality of loop antennas, each of the antennas being configured to output a magnetic field corresponding to a transmission signal relating to the communication with the wireless tag to independently communicate with the wireless tag; a communication control unit configured to output the transmission signal to a communication-target loop antenna among the plurality of loop antennas; and a control unit configured to control a non-target loop antenna different from the communication-target loop antenna to generate a magnetic field for negating a magnetic field leaking from the communication-target loop antenna.

Inventors

Shigeru Arisawa

Assignees

Yoshikawakogyo RF Semicon Co., Ltd.

Dates

Publication Date: 20260507
Application Date: 20251028
Priority Date: 20241105

Claims (10)

1 . A communication apparatus configured to communicate with a wireless tag, comprising: a plurality of loop antennas, each of the loop antennas being configured to output a magnetic field corresponding to a transmission signal relating to the communication with the wireless tag to independently communicate with the wireless tag; a communication control unit configured to output the transmission signal to a communication-target loop antenna among the plurality of loop antennas; and a control unit configured to control a non-target loop antenna different from the communication-target loop antenna to generate a magnetic field for negating a magnetic field leaking from the communication-target loop antenna.
2 . The communication apparatus of claim 1 , wherein the control unit is configured to control the non-target loop antenna to generate a magnetic field in a direction opposite to a magnetic field outside the communication-target loop antenna.
3 . The communication apparatus of claim 1 , wherein the control unit includes a capacitance configured to be connected to the non-target loop antenna, and the control unit is configured to tune a resonance frequency of a circuit including the loop antenna and the capacitance that are connected to each other to a frequency different from a carrier frequency of the transmission signal.
4 . The communication apparatus of claim 3 , wherein the control unit is configured to tune the resonance frequency of a circuit including the loop antenna and the capacitance that are connected each other to a frequency lower than the carrier frequency of the transmission signal.
5 . The communication apparatus of claim 3 , wherein the control unit includes a switch configured to connect the communication control unit to the communication-target loop antenna and connect the capacitance to the non-target loop antenna.
6 . The communication apparatus of claim 1 , wherein the control unit is configured to output, to the non-target loop antenna, a signal of a same phase as a phase of the transmission signal output to the communication-target loop antenna.
7 . The communication apparatus of claim 6 , wherein the control unit is configured to output, to the non-target loop antenna, the transmission signal having a level adjusted depending on an intensity of the magnetic field from the communication-target loop antenna.
8 . The communication apparatus of claim 6 , wherein the control unit is configured to output, to the non-target loop antenna, the transmission signal having a current level attenuated depending on an intensity of the magnetic field from the communication-target loop antenna.
9 . The communication apparatus of claim 6 , wherein the control unit is configured to output, to the non-target loop antenna, a carrier wave of the transmission signal having a level adjusted depending on an intensity of the magnetic field from the communication-target loop antenna.
10 . A control method of a communication apparatus including a plurality of loop antennas, each of the loop antennas being configured to output a magnetic field corresponding to a transmission signal relating to communication with a wireless tag to independently communicate with the wireless tag, the control method comprising: outputting the transmission signal to a communication-target loop antenna among the plurality of loop antennas; and controlling a non-target loop antenna different from the communication-target loop antenna to generate a magnetic field for negating a magnetic field leaking from the communication-target loop antenna.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2024-193775, filed on Nov. 5, 2024, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a communication apparatus configured to communicate with a wireless tag and a control method thereof. Description of the Related Art A reader and reader/writer conforming to the ISO 15693 standard uses a frequency band such as the high frequency (HF) band, and reads and writes data to a wireless tag such as a radio frequency identification (RFID) tag or an RFID card. Hereinafter, such a reader and a reader/writer are collectively referred to as a reader/writer without distinction. The reader/writer is configured to read and/or write data to the wireless tag in a non-contact manner by coupling a loop antenna provided in the reader/writer and a loop antenna provided in the wireless tag. For example, the reader/writer puts information, such as a read command of the wireless tag, onto a high-frequency carrier signal (carrier wave) by using a predetermined modulation method and outputs it as a magnetic field from the loop antenna. The wireless tag uses the electromagnetic induction of its mounted loop antenna to capture the magnetic field generated by the reader/writer as an electrical signal for its operating power. The wireless tag also decodes the read command contained in the captured electrical signal, and according to the decoding result, returns data stored in an internal memory to the reader/writer with a load switch or other means. The reader/writer then receives the returned signal from the wireless tag via the loop antenna and decodes the signal to read the data. As illustrated in FIG. 11A, a reader/writer is proposed that includes a plurality of loop antennas and reads and/or writes data from/to a wireless tag through the respective loop antennas. The reader/writer with a plurality of loop antennas includes a control unit 1110 for communication-related control, an antenna unit 1120 including the loop antennas 1121 and matching circuits 1122, and a switching circuit provided between the control unit 1110 and the antenna unit 1120. The switching circuit is configured to select a loop antenna 1121 as communication target, and the reading/writing of data is performed for a wireless tag 1123 arranged for the target loop antenna 1121. For such a reader/writer with a plurality of loop antennas, the spacing between antennas needs to be narrowed to reduce the overall area occupied by the loop antennas. However, the narrowed spacing between loop antennas may result in unintended writing or reading of data to/from a wireless tag arranged for a loop antenna that is adjacent to the target loop antenna, which may make it impossible to independent reading or writing of a wireless tag arranged for each loop antenna. This is because, as illustrated in FIG. 11B, a magnetic field 1142 generated by the target loop antenna 1141 may leak outside from the loop antenna 1141 and may cause reading or writing of data to the wireless tag arranged for the adjacent loop antenna 1143. As one solution to such a situation, Patent Document 1 proposes a technique to prevent unintended reading of an RF tag that is close to an RF tag on a specimen container adjacent to a reading target. Patent Document 2 proposes a technique to appropriately control a reading antenna configured to read an RFID tag and a read-restriction antenna configured to restrict an RFID tag from being read by another adjacent reading antenna to prevent unintended reading of the RFID tag arranged for the adjacent antenna. However, the technique proposed by Patent Document 1 only includes one reading antenna in the system and is not applicable to a reader/writer with a plurality of antennas. Additionally, providing the read-restriction antenna for read restriction as described in Patent Document 2 is not preferable because it results in a more complicated antenna structure. Other solutions may include installing a shield plate between the target loop antenna and the adjacent loop antenna, or generating an interference signal from the adjacent loop antenna. To reduce the leakage field with the shield plate between the loop antennas, it is necessary to place the shield plate as close as possible to the loop antennas, and to ensure an appropriate length of the shield plate. However, these requirements may result in the loss of the intensity of the magnetic field that is inherently involved in reading and writing, and therefore the shield plate cannot be an appropriate solution. Alternatively, to reduce the leakage field by generating an interference signal from the adjacent loop antenna, it is necessary to generate an interference signal of sufficient level. However, such an interference signal may unintentionally reach the target loop an