JP2007020124A - Electric field communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric field communication system which is capable of performing communication even in a high-noise environment. <P>SOLUTION: An electric field communication system comprises a first communication apparatus including a transmission section which comprises: a modulation/output means for modulating and outputting information with an AC signal having a predetermined frequency; a transmission electrode which induces an electric field; impedance between a field transmission medium proximate to the transmission electrode and an earth ground; and a reactance means which incurs resonance with stray capacitance between a ground of the modulation/output means and the earth ground, and in which a circuit ground is floated from the earth ground, and a second communication apparatus including a reception section which comprises: an input amplification means for detecting an electric field, modulating it into an electric signal and amplifying it; a low impedance reactance means connected between an input of the input amplifying means and the earth ground, impedance of reactance being lower than input impedance of the input amplifying means; a receiving electrode for transmitting, to the input amplifying section, an electric field based on information induced by the field transmission medium; and a demodulation/waveform shaping means for demodulating and waveform-shaping a signal from the input amplifying means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric field communication system used in communication in which an electric field is induced in an electric field transmission medium, and the induced electric field is detected to transmit and receive information.

  Due to the miniaturization and high performance of portable terminals, wearable computers that can be attached to living bodies have been attracting attention. Conventionally, as information communication between such wearable computers, an electric field communication transceiver is connected and attached to a computer, and an electric field induced by the electric field communication transceiver is transmitted through a living body which is an electric field transmission medium, thereby There has been proposed a method for transmitting and receiving.

FIG. 13 shows a conventional electric field communication system. The transmitter 107 of the portable terminal 101 modulates information (data) to be transmitted output from the small computer 108 with a carrier wave having a predetermined frequency f and outputs the modulated information. The transmitter 107 is away from the ground, and a stray capacitance C _g 15 is generated between the circuit ground 109 and the ground. In addition, stray capacitance C _b 14 is generated between the living body 13 and the ground.

In the conventional technique, the reactance unit 110 is inserted between a transmission circuit such as the modulation / output unit 111 and a transmission / reception electrode including the insulator 113 and the transmission electrode 112, and a voltage applied to a living body due to stray capacitance and a resonance phenomenon. Electric field communication was realized by increasing the signal (see, for example, Patent Documents 1 and 2).
JP 2004-153708 A United States Patent Application Publication, Pub.No.:US2004/0092296A1 Pub.Date:May 13, 2004

  In an electric field communication system that performs communication by inducing an electric field in a human body that is an electric field transmission medium and detecting the electric field, an electric field signal radiated from another device that is not in contact with a living body is also detected. Therefore, in the electric field communication by the conventional system, even when the signal applied from the transmitter of the portable terminal is large, the intensity of the radiation signal from the radiation source detected by the receiver of the stationary apparatus is large. Communication with is interrupted.

  Further, in order to avoid interference with communication, it is necessary to separate other devices that are noise sources from the receiver.

  The present invention has been made in view of the above, and an object thereof is to provide an electric field communication system capable of communication even in a noisy environment.

  In order to achieve the above object, the present invention according to claim 1 induces an electric field based on information to be transmitted in an electric field transmission medium, and transmits information using the induced electric field, An electric field communication system which performs communication by receiving an electric field based on information to be received induced in an electric field transmission medium, and which modulates and outputs information to be transmitted with an AC signal having a predetermined frequency A transmission electrode for inducing an electric field based on the information to be transmitted, an impedance between the electric field transmission medium adjacent to the transmission electrode and the ground, and a stray capacitance between the ground of the modulation / output means and the ground Reacting means for inducing resonance between the first communication means having a transmitting section in which the circuit ground is floating from the ground, and the reception An input amplifying unit that detects an electric field based on power information, converts it into an electric signal and amplifies it, and a reactance having an impedance lower than the input impedance of the input amplifying unit, and is connected between the input of the input amplifying unit and the ground Low impedance reactance means, a receiving electrode for transmitting an electric field based on the information to be received induced in the electric field transmission medium to the input amplifier, and a signal output from the input amplifier for demodulating and shaping the waveform And a second communication unit having a receiving unit including a demodulation / waveform shaping unit.

  According to a second aspect of the present invention, in the first aspect, the receiving unit of the second communication unit includes a reactance component having a low input impedance, and detects an electric field based on the information to be received. An input amplifying means for converting and amplifying the electric signal; a receiving electrode for transmitting an electric field based on the information to be received induced in the electric field transmission medium to the input amplifying section; and a signal output from the input amplifying means. Demodulation and waveform shaping means for demodulating and shaping the waveform.

  According to a third aspect of the present invention, in the first aspect, the receiving unit of the second communication unit detects a gradient of an electric field based on the information to be received, converts the electric field into an electric signal, and amplifies the difference. Dynamic input amplifying means, a first receiving electrode for transmitting an electric field based on the information to be received induced in the electric field transmission medium to the input amplifying unit, and an electric field based on the information to be received on the input amplifying unit A second receiving electrode transmitted to the first amplifying means, and a reactance having an impedance lower than an input impedance of the input amplifying means, the first low impedance reactance means connected between the first receiving electrode and the ground, A reactance having an impedance lower than an input impedance of the input amplifying means, the second low impedance connected between the second receiving electrode and the ground. Comprising a copy dance reactance means, and a demodulation and waveform shaping means for wave-shaping demodulates the signal output from the input amplifier means.

  According to a fourth aspect of the present invention, in the first aspect, the receiving unit of the second communication unit is configured with a reactance component having a low input impedance, and detects an electric field gradient based on the information to be received. Differential input amplifying means for converting and amplifying the electric signal, a first receiving electrode for transmitting an electric field based on the information to be received induced in the electric field transmission medium to the input amplifying unit, and the receiving A second receiving electrode that transmits an electric field based on power information to the input amplifying unit; and a demodulating / waveform shaping unit that demodulates and shapes a signal output from the input amplifying unit.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the reactance means provided in the transmission unit of the first communication means is a variable reactance means capable of changing a reactance value. And a first communication unit having a transmission unit including a reactance control unit that varies a reactance value of the variable reactance unit to maximize a signal applied to the electric field transmission medium.

  According to a sixth aspect of the present invention, in the fifth aspect, the reactance control means provided in the transmission unit of the first communication means is configured such that the reactance of the variable reactance means is output for each output of the transmission signal for the communication. Reactance control means for executing control for sequentially changing the value.

  According to a seventh aspect of the present invention, in any one of the first to fourth aspects, the reactance means provided in the transmission unit of the first communication means resonates with a transmission signal for the communication. Obtained by rectifying the transmission signal input to the resonance circuit with the variable capacitance diode, and a resonance circuit having a variable capacitance diode whose capacitance changes according to the applied voltage. Self-tuning variable reactance means having a resistor for applying a potential difference corresponding to a direct current between an anode and a cathode of the variable capacitance diode.

  According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the low impedance reactance means is configured with a capacitance larger than 100 pF.

Further, the present invention according to claim 9 is the invention according to any one of claims 1 to 7, wherein the low impedance reactance means is constituted by reactance, and the susceptance B _in is B _in = −1 / ωL _in . _{there, - (ωC b + -1 /} ωL in)> 2ωC b
L _in <1 / (3ω ² C _b )
It is determined by the relational expression.

  ADVANTAGE OF THE INVENTION According to this invention, the electric field communication system which can communicate also in a noisy environment can be provided.

<First Embodiment>
FIG. 1 shows a configuration diagram of a first embodiment of an electric field communication system. The transmitter 10 is carried by a human body 13 that is an electric field transmission medium, and transmits data to the receiver 4 via the human body 13. The human body 13 is floating from the ground, and stray capacitances C _b 14 and C _g 15 exist between the human body 13 and the ground and between the circuit ground 9 and the ground. A low impedance reactance unit 1 is connected to the input stage of the receiver 4 in order to reduce the input impedance.

Data from a terminal (not shown) is modulated and output by a modulation / output unit 8 in the transmitter 10 with a carrier wave having a predetermined frequency. The output signal is efficiently transmitted to the receiver 4 by series resonance between the reactance unit 7, the stray capacitances C _b 14 and C _g 15, and the low impedance reactance unit 1 of the receiver 4. The receiver 4 amplifies / filters / demodulates / waveforms the transmitted signal by the input amplifier 2 and demodulation / waveform shaping unit 3 to reproduce the original data, and outputs it to a computer (not shown).

FIG. 2 shows a configuration diagram when this system is exposed to a radiation signal from another device (radiation source). Here, the modulation / output unit 8 of the transmitter 10 is replaced with a signal source of an output resistance R _s 18 and an output voltage V _s 19. There is a stray capacitance between the radiation source 20 and the receiving electrode (consisting of the insulator 5 and the receiving electrode 6), which is represented by _Cr 21 in the drawing. When the radiation source 20 approaches the receiver 4, the stray capacitance C _r 21 increases and the impedance of the stray capacitance (1 / ωCr: ω is each frequency of the radiated signal) decreases, so that the radiated signal (noise) is transmitted to the receiver 4. It becomes easy to input.

A signal and a radiation signal input to the receiver 4 from the transmitter 10 in a resonance state are obtained using an equivalent circuit of the system considering the radiation source 20 shown in FIG. It is assumed that a signal having the same frequency as the carrier wave of the transmitter 4 is output from the radiation source 20. The potential difference V _in the receiver 4, received from the earth ground electrode is input as a signal. Here, if the signal input from the transmitter 10 is V _{in, s} and the signal input from the radiation source 20 is V _{in, r} , V _in is expressed by the following equation from the principle of superposition.

V _in = V _{in, s} + V _{in, r} (1)
First, in order to consider the signal input from the transmitter 10, the radiation source V _r 20 is ignored. From this equivalent circuit, V _{in, s} is

It is expressed. Here, B _in is the susceptance of the low impedance reactance unit 1 (the imaginary part of the reciprocal of the impedance). The reactance X _v 17 of the reactance part of the transmitter 10 is

When it is, it will be in a resonance state and Vin _{, s} will become the maximum. At this time, the signal input from the transmitter 10 to the receiver 4 is

It becomes. Further, when the impedance Z (Z shown in FIG. 3) of the electric field communication system viewed from the stray capacitance C _r 21 in the resonance state is obtained.

It becomes.

Next, the signal V _{in, r} input from the radiation source 20 to the receiver 4 ignoring the signal of the transmitter 10 will be considered. From the impedance Z expressed by the equation (5), V _{in, r} is expressed by the following equation.

Substituting equation (5) into equation (6) and expanding

It becomes.

The ratio of V _{in, s} and V _{in, r} obtained above is a signal-to-noise ratio (S / N ratio). If this ratio is increased, communication is possible even if exposed to a radiation signal. Equation (4) and (7) from _{V in, s / V in,} r is expressed by the following equation.

Here by increasing the B _in reducing the first term of the denominator in the parentheses of formula (8), by reducing the resistance R _s 18, may be V _{in, s} / V _in, the _r to increase . Therefore, as shown in FIG. 1, by using a receiver 4 to which a reactance having a low impedance (a large susceptance B _in ) is connected, a series resonance occurs in the transmitter 10, so that the noise source 20 is close to the noise. It is possible to provide an electric field communication system capable of communication even in a large environment.

  In the embodiment of FIG. 1, the low impedance reactance unit 1 is connected to the input amplification unit 2, but the input amplification unit using an electric field sensor or amplifier having a low reactance component as the input impedance is used as the input amplification unit 2 and the low impedance. The reactance unit 1 may be used instead. Further, in order to realize a low impedance reactance, the area of the receiving electrode 27 may be increased as shown in FIG. Further, as shown in FIG. 4, a conductor connected to the ground or connected with a low impedance or a high dielectric constant object 28 may be installed near the human body 13.

Furthermore, since the impedance of the low impedance reactance unit 1 is expected to provide more effective if lower than C _b. For example, according to the document “Personal Area Networks: Near-field intrabody communication” Thomas Zimmerman. Vol. 35, No. 3 & 4, 1996-MIT Media Lab, the stray capacitance C _b between the human body 13 and the ground is about 100 pF. Therefore, when the low-impedance reactance unit 1 has a capacitance C _in , B _in = ωC _in. Therefore, if the capacitance value is larger than 100 pF, a great effect can be expected. Further, the low impedance reactance unit 1 may be an inductive component, and in this case, B _in = −1 / ωL _in ,
_{- (ωC b + -1 / ωL} in)> 2ωC b
L _in <1 / (3ω ² C _b )
It becomes. Therefore, when the signal frequency is 5 MHz, a great effect can be expected if the inductance is lower than 3.4 μH.

<Second Embodiment>
FIG. 5 shows a configuration diagram of the second embodiment of the electric field communication system. In this system, a receiver that detects the gradient of an electric signal input using two receiving electrodes is used. The two receiving electrodes used are the receiving electrode <1> composed of the insulator 5 and the receiving electrode 6 and the receiving electrode <2> 30.

  The gradient of the radiated electrical signal decreases with distance from the radiation source. Since the human body 13 that performs communication is close to the receiver 4, in the system of FIG. 5, communication can be performed relatively unaffected by the radiation signal from the radiation source at a remote location. Moreover, the above-mentioned effect can be expected by connecting a low impedance to the receiver and causing series resonance in the transmitter. The low impedance reactance part <1> 33 is connected to the reception electrode <1> as a low impedance, and the low impedance reactance part <2> 34 is connected to the reception electrode <2> 30.

  With the above effects, it is possible to provide an electric field communication system capable of communication even in a noisy environment where a noise source is in the vicinity.

<Third Embodiment>
FIG. 6 shows a configuration diagram of the third embodiment of the electric field communication system. The transmitter 10 includes a reactance control unit 36 that adjusts the reactance value of the variable reactance unit 35 while monitoring the voltage so that the voltage applied to the human body 13 is maximized. Even if the stray capacitances C _b 14 and C _g 15 change depending on the surrounding environment or the like, the resonance state can be maintained in the present embodiment.

  When the data to be transmitted is fixed data such as an ID, the reactance may not be adjusted while monitoring, but may be transmitted while sequentially changing the reactance value. The operation of this method will be described with reference to the timing chart shown in FIG.

  In this method, data is transmitted by changing the reactance value as shown in the timing chart of FIG. Here, the reactance value is divided into five stages (1) to (5), and fixed data is transmitted five times.

Like the reactance value dependency of the voltage V _b between the human body 13 and the ground shown in FIG. 8, the amplitude of V _b becomes maximum at a certain reactance value due to resonance. Therefore, when the variable reactance of the transmitter reaches a certain reactance value ((3) in FIG. 7), the signal applied to the human body 13 is maximized.

  The reactance value at which resonance occurs varies depending on the ground of the circuit and the stray capacitance between the human body 13 and the ground, but if this change is within the set range, a large signal can be applied at any set value of reactance. For applications such as transmitters that only need to receive fixed data once, not only is the method of adjusting reactance values reliably and sequentially transmitting them, but it is also possible to change the reactance values to several preset values before changing the fixed data. Communication is possible even if is transmitted.

<Fourth embodiment>
FIG. 9 shows a configuration diagram of a fourth embodiment of the electric field communication system. In this embodiment, a self-adjusting variable reactance unit is used, and a configuration example of this self-adjusting variable reactance unit is shown in FIG.

The part of the self-adjusting variable reactance unit 40 that causes resonance is composed of an inductor 41 and a variable capacitance diode 42. Capacitance <1> 45 and capacitance <2> 43 are for cutting off the DC component, and can be regarded as a short circuit for the AC signal. The AC component of the potential difference between the human body 13 and the ground is defined as V _b, and the AC component of the potential difference of the self-adjusting variable reactance unit 40 is defined as V _AC . Further, the DC component of the voltage applied to the variable capacitance diode 42 and the flowing current is V _DC and I _D , respectively. The voltage of the variable capacitance diode 42 is positive in the reverse bias direction. The change of each voltage / current signal when the self-adjusting variable reactance unit 40 of the present embodiment changes with respect to the stray capacitance and converges to a value close to the optimum will be described with reference to the graph of FIG.

FIG. 11A shows the relationship of the DC component I _D of the current generated when an AC voltage having an amplitude | V _AC | is applied to the variable capacitance diode 42. When the reverse bias voltage V _DC is generated at both ends of the variable capacitance diode 42, the period during which the variable capacitance diode 42 is short-circuited is shortened, so that _ID becomes small with respect to the same V _AC .

Graph of the potential difference (V _DC equivalent) caused by flowing the I _D resistance <1> 44 in FIG. 11 (b), the voltage V _DC of the capacitance C _v of the variable capacitance diode 42 in FIG. (C) Indicates dependency. Further, FIG. 11 (d) is the amplitude of V _b | a C _v dependence of | V _b. The points in the graph indicate changes in each current voltage since the start of input of an AC signal to the self-adjusting variable reactance unit 40. The initial value of the capacity C _v is a value C ₁ when V _DC = 0. | V _AC | is proportional to | V _b |.

When an AC signal is input, it is rectified by the variable capacitance diode 42 to generate a DC current _ID (point (1) in FIG. 11A). When this flows through the resistor <1> 44, a DC voltage V _DC is generated, and the same potential difference is applied to the variable capacitance diode 42. As a result, the capacitance C _v decreases (point (1) in FIG. 11C), approaches the capacitance value causing resonance, and | V _b | increases. | V _AC | is | proportional to, | | V _b V _AC | but increases, since the V _DC also increases | V _AC | and the point in relation FIG 11 (a) of the I _D (2 )

After this, C _v similarly decreases and | V _AC | increases, but V _DC also increases, so that the amount of change in _ID gradually decreases and converges to zero. When the amount of change in _ID becomes zero, | V _AC | becomes constant, and is closer to resonance amplification than the initial value. By utilizing the above phenomenon, the reactance value can be brought close to the resonance state, although the resonance state is not completely achieved.

  In the above electric field communication system, unidirectional communication is performed. FIG. 12 shows a configuration diagram of a transceiver used for bidirectional communication. An electric field communication system is constructed by attaching this transceiver to a stationary device.

  This transceiver is provided with a switch 52 for switching between transmission and reception in addition to a modulation / output unit 51 for transmission, a variable reactance unit 53, and a reactance control unit 54. At the time of transmission, a1 and b1 of the switch 52 are connected, and the output signal of the modulation / output unit 51 is output to the transmission / reception electrode composed of the insulator 59 and the electrode 60 through the variable reactance unit 53.

  In addition, the reactance control unit 54 adjusts the reactance value of the variable reactance unit 53 so that the output signal is maximized. At the time of reception, a1 and c1 of the switch 52 are connected, and a signal received by the transmission / reception electrode is transmitted to the input amplification unit 56 to which the low impedance reactance unit 57 is connected. At this time, the reactance value of the variable reactance unit 53 is set to the minimum. If the above transceiver is used, bidirectional communication is also possible.

It is explanatory drawing which shows the basic composition of 1st Embodiment of an electric field communication system. It is a block diagram of the electric field communication system which considered the radiation source (noise source). It is the equivalent circuit of the electric field communication system which considered the radiation source (noise source). It is a figure which shows the modification of the electric field communication system of 1st Embodiment. It is a block diagram which shows 2nd Embodiment of an electric field communication system. It is a block diagram which shows 3rd Embodiment of an electric field communication system. It is a timing chart which shows the operation | movement of the modification of 3rd Embodiment of an electric field communication system. It is a graph which shows the reactance dependence of voltage signal | _Vb | in the modification of 3rd Embodiment of an electric field communication system. It is a block diagram which shows 4th Embodiment of an electric field communication system. It is a block diagram of the self-adjustment variable reactance part used in 4th Embodiment of an electric field communication system. Graphs for explaining the operation of the self-adjusting variable reactance unit used in the fourth embodiment of the electric field communication system are shown in (a) to (d). It is a block diagram of the transceiver for performing two-way communication in an electric field communication system. It is a block diagram explaining the electric field communication system by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Low impedance reactance part 2 Input amplification part 3 Demodulation and waveform shaping part 4 Receiver 5, 12 Insulator 6 Reception electrode 7 Reactance part 8 Demodulation and output part 9 Circuit ground 10 Transmitter 11 Transmission electrode 13 Human body (electric field transmission medium)
14 Cb14
15 C _g
16 X _in
17 X _v
18 R _s
19 V _s
20 V _r
21 _Cr

Claims (9)

By inducing an electric field based on information to be transmitted in the electric field transmission medium and transmitting information using the induced electric field, while receiving an electric field based on the information to be received induced in the electric field transmission medium. An electric field communication system for performing communication,
Modulation / output means for modulating and outputting information to be transmitted with an AC signal having a predetermined frequency;
A transmission electrode for inducing an electric field based on the information to be transmitted;
Reactance means for inducing resonance between the impedance between the electric field transmission medium adjacent to the transmission electrode and the ground, and the stray capacitance between the ground of the modulation / output means and the ground, and A first communication means having a transmitter in which the circuit ground is floating from the ground;
An input amplifying means for detecting an electric field based on the information to be received, converting it to an electric signal and amplifying it;
A low-impedance reactance means connected between an input of the input amplification means and a ground, comprising a reactance having an impedance lower than an input impedance of the input amplification means;
A receiving electrode for transmitting an electric field based on the information to be received, induced in the electric field transmission medium, to the input amplification unit;
Demodulation and waveform shaping means for demodulating and shaping the signal output from the input amplification means, second communication means having a receiving unit;
An electric field communication system comprising: The receiving unit of the second communication means is
An input amplifying means comprising a reactance component having a low input impedance, detecting an electric field based on the information to be received, converting it to an electric signal, and amplifying;
A receiving electrode for transmitting an electric field based on the information to be received, induced in the electric field transmission medium, to the input amplification unit;
Demodulation / waveform shaping means for demodulating and shaping the signal output from the input amplification means;
The electric field communication system according to claim 1, comprising: The receiving unit of the second communication means is
Differential input amplifying means for detecting a gradient of an electric field based on the information to be received, converting the electric field into an electric signal, and amplifying the electric signal;
A first receiving electrode for transmitting an electric field based on the information to be received induced in the electric field transmission medium to the input amplification unit;
A second receiving electrode for transmitting an electric field based on the information to be received to the input amplifier;
Reactance having an impedance lower than the input impedance of the input amplification means, the first low impedance reactance means connected between the first receiving electrode and the ground,
Reactance having an impedance lower than the input impedance of the input amplification means, the second low impedance reactance means connected between the second receiving electrode and the ground,
Demodulation / waveform shaping means for demodulating and shaping the signal output from the input amplification means;
The electric field communication system according to claim 1, comprising: The receiving unit of the second communication means is
A differential input amplifying unit configured by reactance components having low input impedance, detecting a gradient of an electric field based on the information to be received, converting the detected electric field into an electric signal, and amplifying the electric signal;
A first receiving electrode for transmitting an electric field based on the information to be received induced in the electric field transmission medium to the input amplification unit;
A second receiving electrode for transmitting an electric field based on the information to be received to the input amplifier;
Demodulation / waveform shaping means for demodulating and shaping the signal output from the input amplification means;
The electric field communication system according to claim 1, comprising: The reactance means included in the transmission unit of the first communication means is
First communication having variable reactance means capable of changing a reactance value, the transmitter having a reactance control means for changing a reactance value of the variable reactance means to maximize a signal applied to the electric field transmission medium. The electric field communication system according to any one of claims 1 to 4, further comprising: means. Reactance control means provided in the transmission unit of the first communication means,
Reactance control means for executing control for sequentially changing the reactance value of the variable reactance means for each output of the transmission signal for the communication,
The electric field communication system according to claim 5. The reactance means included in the transmission unit of the first communication means is
A resonance circuit comprising: an inductor for resonating with a transmission signal for communication; and a variable capacitance diode whose capacitance changes according to an applied voltage;
A resistor for applying a potential difference according to a direct current obtained by rectifying the transmission signal input to the resonance circuit with the variable capacitance diode between an anode and a cathode of the variable capacitance diode;
5. The electric field communication system according to claim 1, wherein the electric field communication system is a self-adjusting variable reactance unit. The low impedance reactance means includes
The electric field communication system according to claim 1, wherein the electric field communication system is configured with a capacitance larger than 100 pF. The low impedance reactance means includes
It is composed of reactance, and its susceptance B _in is B _in = −1 / ωL _in ,
_{- (ωC b + -1 / ωL} in)> 2ωC b
L _in <1 / (3ω ² C _b )
The electric field communication system according to claim 1, wherein the electric field communication system is determined by the relational expression:

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