JP2012244516A - Electric field communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a decline in communication quality even in a noisy environment.SOLUTION: An electric field communication system for performing electric communication between a mobile terminal 1 carried by a user 2 and an installation-type terminal 5, 6 includes: a floor electrode 3 disposed on a floor 17; and an anti-resonant circuit 4 for connecting an inductor between the floor electrode 3 and the conductive member of the floor 17 using parasitic capacitance formed between the floor electrode 3 and the conductive member of the floor 17.

Description

  The present invention relates to an electric field communication system that induces an electric field based on information to be transmitted in an electric field transmission medium, and detects the induced electric field to transmit and receive information.

  Although wearable computers are attracting attention due to the miniaturization and high performance of portable terminals, FIG. 9 shows an example in which such wearable computers are used while being worn by humans. As shown in the figure, the wearable computer 7 is mounted on a person's arm, shoulder, torso, etc. via a transceiver 9 to transmit / receive data to / from each other, and is further provided on the wall or floor so that it can be touched by the tip of a limb. Communication is performed with a computer 8 provided outside via the transceivers 9a and 9b and cables.

  Here, the transceiver 9 used for data communication between the wearable computer 7 and between the wearable computer 7 and the computer 8 induces an electric field based on information to be transmitted to a living body that is an electric field transmission medium. Information is transmitted and received using an induced electric field. The transceiver 9 is described in Patent Document 1 and Patent Document 2.

JP 2001-352298 A JP 2006-081111 A

  In addition to piping, electric power and communication cables may be embedded in floors of offices, laboratories, factories, and the like. Also, the floor is often made of iron for the reasons of strength, and it is easy to pick up induction noise due to radiation and electrostatic noise from the buried cable.

  When the user stands on the floor where such noise is easily picked up and performs electric field communication using the user's human body as the communication medium between the portable terminal carried by the user and the installed transceiver installed on the wall There is a problem that the S / N ratio deteriorates (N increases) and the communication quality deteriorates due to the influence of noise mixed into the human body from the floor.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric field communication system that prevents deterioration in communication quality even in a noisy environment.

  In order to achieve the above object, the present invention provides an electric field communication system that performs electric field communication between a portable terminal carried by a user and an installation terminal, the floor electrode installed on the floor, and the conductivity of the floor electrode and the floor And an anti-resonance circuit in which an inductor is connected between the floor electrode and the conductive member of the floor using a parasitic capacitance formed between the member and the member.

  Moreover, this invention is an electric field communication system which performs electric field communication with the portable terminal and installation terminal which a user carries, Comprising: A pair of 1st floor electrodes installed on the floor and provided with a 2nd floor electrode A floor electrode, and an anti-resonance circuit in which an inductor is connected between the first floor electrode and the second floor electrode using a parasitic capacitance formed between the pair of floor electrodes. .

  According to the present invention, it is possible to provide an electric field communication system that prevents deterioration of communication quality even in a noisy environment.

1 is an overall configuration diagram of an electric field communication system according to an embodiment of the present invention. It is an equivalent circuit of the electric field communication system shown in FIG. It is a graph which shows that a noise voltage reduces with a resonant frequency. It is a figure which shows the modification of a floor electrode. It is a structural example of a transceiver. It is a block diagram which shows the structure of a portable terminal. It is a whole block diagram of the electric field communication system of a comparative example. It is an equivalent circuit of the electric field communication system of the comparative example shown in FIG. It is a figure which shows the example in the case of mounting | wearing and using a wearable computer for a person via a transceiver.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram of an electric field communication system according to an embodiment of the present invention. The illustrated electric field communication system includes a mobile terminal 1 carried by a user 2, a floor electrode 3, an anti-resonance circuit 4, an installation terminal (a wall electrode 5 and a transceiver 6 connected to the wall electrode 5), and a computer 7. And have. The portable terminal 1 and the transceiver 6 of the installation terminal can perform electric field communication via the human body of the user 2 and the wall electrode 5. The transceiver 6 and the computer 7 are connected by a network such as a LAN, for example.

  The computer 7 receives signals (information and data) transmitted from the mobile terminal 1 via the transceiver 6 and performs predetermined control. For example, the computer 7 performs user authentication using a signal from the portable terminal 1 and opens / closes a security door (not shown) or opens / closes a gate of a ticket gate or the like according to the authentication result. To do.

  The transceiver 6 induces an electric field based on information to be transmitted in a human body as an electric field transmission medium, and transmits / receives information using the induced electric field.

  The wall electrode 5 connected to the transceiver 6 is installed on a wall in the vicinity of a control target (for example, a door, a gate, etc.) of the computer 7 in order to perform electric field communication with the portable terminal 1. The wall electrode 5 has a surface covered with an insulating sheet. In the illustrated electric field communication system, the electrode connected to the transceiver 6 is the wall electrode 6 installed on the wall. However, the electrode is not limited to the wall electrode 6. The electrode connected to the transceiver 6 may be disposed at a place other than the wall (for example, a ticket gate).

The floor of this embodiment has a double floor structure, and a double floor 17 is disposed on a reinforced concrete floor 18. Between the double floor 17 and the concrete floor 18, an embedded cable 19 such as a power cable and a communication cable is disposed. Since a conductive material such as iron is used for the double floor 17, the double floor 17 picks up floor noise such as electrostatic noise from the embedded cable 19 and induction noise due to radiation. In FIG. 1, such floor noise is indicated by a noise voltage V _N 16.

  The floor electrode 3 of the present embodiment is installed floating (separated) from the double floor 17 and is installed at an appropriate position for the user 2 to contact (touch) the wall electrode 5. The surface of the floor electrode 3 is covered with an insulating sheet.

The anti-resonance circuit (parallel resonance circuit) 4 uses a parasitic capacitance C ₀ formed between the floor electrode 3 and the double floor 17 and uses an inductor L ₀ between the floor electrode 3 and the double floor 17. Connected. In the present embodiment, by using this anti-resonance circuit 4, a situation equivalent to separating the user's human body from the floor surface of the double floor 17 is created, and the floor noise is generated through the user's human body. Mixing into the transceiver 6 is prevented. That is, the conductive floor electrode 3 (tread board) is insulated from the double floor 17 to prevent noise due to capacitive coupling with the double floor 17 from being mixed into the user's human body.

  FIG. 2 shows an equivalent circuit of the electric field communication system shown in FIG.

Z ₁ is an impedance due to capacitive coupling between the floor electrode 3 and the human body 2 and is relatively small. Z ₂ is an impedance due to capacitive coupling between the wall electrode 5 and the human body 2 and is relatively small. Z ₃ is an impedance due to capacitive coupling between the portable terminal 1 and the wall (conductive), and is relatively large. Z ₄ is the input impedance of the receiving circuit of the transceiver 6 and is, for example, about 1 kΩ. Z ₀ is the impedance due to the anti-resonance circuit 4.

Here, by approximating Z ₁ and Z ₂ to zero and applying the relationship of (Z ₃ >> Z ₄ ), the noise voltage V ₄ induced in Z ₄ can be approximated as follows.

Thereby, the noise voltage V ₄ induced in Z ₄ can be reduced by increasing the impedance Z ₀ of the anti-resonance circuit 4.

Therefore, using the anti-resonance circuit 4, in the carrier frequency f ₀ which is used in the electric field communication, Z ₀ is set the inductor L ₀ so that the maximum (design).

That is, the carrier frequency of the electric field communication used in the transceiver 6 is set to the resonance frequency F ₀ of the anti-resonance circuit 4, and an inductor L ₀ that satisfies the following equation is calculated and set.

The parasitic capacitance C ₀ formed between the floor electrode 3 and the double floor 17 is a value determined by a physical structure. The carrier frequency f _{0 of} electric field communication is also a predetermined frequency (in the case of communication using a human body as a transmission path, for example, several tens of MHz or less). Therefore, it is possible to calculate the inductor L ₀ according to the above equation.

FIG. 3 is a graph showing the relationship between the noise voltage V ₄ and the frequency f, and shows that the noise voltage V ₄ decreases at the carrier frequency (resonance frequency) f ₀ .

By providing the anti-resonance circuit 4 in which such an inductor L ₀ is set, the anti-resonance circuit 4 has an infinite impedance, so that floor noise from the double floor 17 is cut off. That is, since the floor electrode 3 installed so as to float from the double floor 17 is electrically disconnected from the double floor 17 at the resonance frequency f ₀ , floor noise can be blocked.

  Next, a modified example of the floor electrode will be described.

FIG. 4 shows a modification of the floor electrode. Bed electrode 3 shown in Figure 1, installed float from double floor 17, with anti-resonant circuit 4 connected to the bed electrode 3 and the double bed 17 in the inductor L _0. On the other hand, the floor electrode of FIG. 4 is a pair of floor electrodes including a first floor electrode 3A and a second floor electrode 3B, and the anti-resonant circuit 4A includes the first floor electrode 3A and the second floor electrode 3B. utilizing the parasitic capacitance C ₀ is formed between the bed electrode 3B, connecting the inductor L ₀ between the first bed electrode 3A and the second bed electrode 3B.

  By using the floor electrode shown in FIG. 4, construction on the double floor 17 becomes unnecessary, and the floor electrode can be easily installed at an arbitrary place. Also, in the floor electrode shown in FIG. 4, the floor noise can be blocked because the floor electrode is electrically disconnected from the double floor 17 as in FIG.

  FIG. 5 is a configuration example of the transceiver 6 shown in FIG. The transceiver 6 uses an electric field signal detection technique, induces an electric field based on information to be transmitted in an electric field transmission medium, and transmits and receives information using the induced electric field. Specifically, when transmission data from the computer 7 is received via the input / output (I / O) circuit 901, the transmission data is supplied to the wall electrodes (S +, S−) 5 via the transmission circuit 902, An electric field is induced in the electric field transmission medium via the electrode, and this electric field is transmitted to other parts of the electric field transmission medium. The transceiver 6 detects the electric field induced and transmitted by the electric field transmission medium by the wall electrodes (S +, S−) 5 and couples the electric field to the electric field detection unit 905 to convert it into an electric signal. This electric signal is subjected to signal processing such as amplification and noise removal by the signal processing circuit 906, further subjected to waveform shaping by the waveform shaping circuit 907, and output to the computer 7 via the input / output circuit 901. ing.

  FIG. 6 is a block diagram illustrating a configuration of the mobile terminal 1. As shown in FIG. 6, the portable terminal 1 includes a pair of electric field communication electrodes (S +) 101A and an electrode (S−) 101B, a battery 104 as a power source, a transceiver 102 for electric field communication, and a computer (microcomputer). 103). The pair of electrodes 101A and 101B is connected to the transceiver 102. Similar to the transceiver 6 shown in FIG. 5, the transceiver 102 of the portable terminal 1 performs electric field communication via an electric field transmission medium. Further, for example, the computer 103 stores an ID in a storage unit such as a memory, and uses the transceiver 102 to transmit an ID signal including the ID.

  Next, an electric field communication system which is a comparative example of the present invention will be described.

  FIG. 7 is a diagram illustrating an electric field communication system of a comparative example. FIG. 8 is an equivalent circuit of the electric field communication system shown in FIG.

  In the electric field communication system of the comparative example, the floor electrode and the anti-resonance circuit are not provided. Since the user 2 stands directly on (contacts with) the double floor 17, electrostatic noise from an embedded cable between the double floor 17 and the concrete floor 18, induction noise due to radiation, etc. Are transmitted to the wall electrode 5 and the transceiver 6 through the human body of the user 2. Thereby, floor noise is mixed in the signal transmitted from the mobile terminal 1, the S / N ratio is deteriorated, and the communication quality is deteriorated.

In the equivalent circuit shown in FIG. 8, Z ₁ is an impedance due to capacitive coupling between the double floor 17 and the human body 2 and is relatively small. Z ₂ is an impedance due to capacitive coupling between the wall electrode 5 and the human body 2 and is relatively small. Z ₃ is an impedance due to capacitive coupling between the portable terminal 1 and the wall (conductive), and is relatively large. Z ₄ is the input impedance of the receiving circuit of the transceiver 6 and is, for example, about 1 kΩ.

Here, by approximating the _{Z 1} and _{Z 2} is zero, and when _{Z 3} and _{Z 4} is to note that in parallel with respect to noise source _{V N,} the noise voltage _{V 4} induced in _{Z 4} are, V ₄ = V _N is approximated, and floor noise is transmitted to the receiving circuit of the transceiver 6 without being attenuated.

  On the other hand, in the electric field communication system according to the present embodiment shown in FIG. 1, the floor electrode 3 that is placed floating from the double floor 17 and the parasitic capacitance formed between the floor electrode 3 and the double floor 17 are reduced. The anti-resonance circuit 4 having an inductor connected between the floor electrode 3 and the double floor 17 is provided. Thereby, in this embodiment, the floor electrode 3 is electrically disconnected from the double floor 17, and mixing of the floor noise to the user can be blocked. Specifically, it is possible to prevent floor noise from being transmitted to the wall electrode 5 and the transceiver 6 through the user's human body and mixed with a signal transmitted from the mobile terminal 1 to deteriorate communication quality. it can.

  Further, in the electric field communication system of the modification example of the floor electrode shown in FIG. 4, a parasitic capacitance formed between the pair of floor electrodes 3A and 3B installed on the double floor 17 and the pair of floor electrodes 3A and 3B is used. And an anti-resonance circuit 4A in which an inductor is connected between the pair of floor electrodes 3A and 3B. Thereby, a pair of floor electrodes 3A and 3B are electrically disconnected from the double floor 17, and can prevent mixing of floor noise to the user. Specifically, it is possible to prevent floor noise from being transmitted to the wall electrode 5 and the transceiver 6 through the user's human body and mixed with a signal transmitted from the mobile terminal 1 to deteriorate communication quality. it can. In addition, this invention is not limited to the said embodiment, Many deformation | transformation are possible within the range of the summary. For example, the transceiver 6 according to the present embodiment inputs signals from a pair of electrodes (S +) and electrodes (S−), and removes common-mode noise using a differential amplifier. However, the transceiver 6 uses a signal electrode and a ground electrode. It may be.

  Moreover, although the transceiver of this embodiment is described as a transceiver that can transmit and receive, it may be a transceiver that does not have a transmission circuit and performs only a reception operation. The transceiver of the mobile terminal 1 of the present embodiment is also described as a transceiver that can transmit and receive, but may be a transceiver that does not have a receiving circuit and performs only a transmission operation.

DESCRIPTION OF SYMBOLS 1 Mobile terminal 2 User 3 Floor electrode 3A A pair of floor electrodes 4, 4A Anti-resonance circuit 5 Wall electrode 6 Transceiver 7 Computer 17 Double floor 18 Concrete floor

Claims (2)

An electric field communication system for performing electric field communication between a portable terminal carried by a user and an installation terminal,
A floor electrode installed on the floor;
An anti-resonance circuit in which an inductor is connected between the floor electrode and the floor conductive member by utilizing a parasitic capacitance formed between the floor electrode and the floor conductive member. An electric field communication system. An electric field communication system for performing electric field communication between a portable terminal carried by a user and an installation terminal,
A pair of floor electrodes, provided on the floor, comprising a first floor electrode and a second floor electrode;
An anti-resonance circuit in which an inductor is connected between the first floor electrode and the second floor electrode by utilizing a parasitic capacitance formed between the pair of floor electrodes. Electric field communication system.

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