WO2015104783A1

WO2015104783A1 - Communication device for human body transmission

Info

Publication number: WO2015104783A1
Application number: PCT/JP2014/006463
Authority: WO
Inventors: Takafumi Ohishi; Kazuhiro Inoue
Original assignee: Kabushiki Kaisha Toshiba
Priority date: 2014-01-08
Filing date: 2014-12-25
Publication date: 2015-07-16
Also published as: JP2015130607A

Abstract

A communication device includes a substrate, a line, a communication circuit, and a variable capacitance. The substrate includes a ground section and a dielectric section stacked on the ground section. The substrate has a first surface and a second surface on an opposite side of the first surface. The first surface includes the ground section. And the second surface includes the dielectric section. The line is provided on the second surface side and has an inductive reactance. The communication circuit is provided on the second surface and connected to one end of the line and the ground section. The variable capacitance element includes a conductor connected to the other end of the line and is capable of varying a capacitance between the conductor and the ground section when a human body contacts with or comes close to the conductor.

Description

[Title established by the ISA under Rule 37.2] COMMUNICATION DEVICE FOR HUMAN BODY TRANSMISSION

Field

Embodiments of the invention relates to a communication device.

Background

The human body can be used as part of a signal transmission path. For instance, there is known an intra-body communication device in which an electromagnetic field generated between a signal electrode and a ground propagates through the human body surface.

However, if the spacing between the signal electrode and the ground is narrow, the signal electrode has a high capacitance. This increases the reflection loss. Thus, it is difficult to efficiently generate an electromagnetic field at the human body surface.

The transmission efficiency is improved if the ground is brought into contact with the human body to establish impedance matching. However, if the signal electrode and the ground are simultaneously brought into contact with the human body, the potential difference decreases. Thus, the reception sensitivity may be decreased. This may be solved in a structure in which the signal electrode and the ground of the reception side are not simultaneously brought into contact with the human body. However, in this case, the reception side and the transmission side are different in configuration. This complicates the communication device.

JP-A H10-229357

FIG. 1 is a schematic perspective view of a communication device according to a first embodiment.
FIG. 2 is a configuration view of a communication system using the communication device of the first embodiment.
FIG. 3 is an equivalent circuit diagram of the communication device of the first embodiment.
FIG. 4 is a schematic view showing a variation of the attachment site of the communication device.
FIG. 5 is a schematic perspective view of a communication device according to a comparative example.
FIG. 6 is a configuration view of a communication system of the comparative example.
FIG. 7 is an equivalent circuit diagram of the communication device of the comparative example.
FIG. 8 is a graph showing the dependence of voltage standing wave ratio on frequency.
FIG. 9A is a schematic perspective view of a communication device according to a second embodiment and FIGS. 9B and 9C are schematic views of an inductive reactance line used in a variation thereof.
FIG. 10A is a schematic perspective view of a communication device according to a third embodiment, and FIG. 10B is an equivalent circuit diagram.
FIG. 11A is a schematic perspective view of a communication device according to a fourth embodiment. FIG. 11B is an equivalent circuit diagram.
FIG. 12 is a schematic perspective view of a communication device according to a fifth embodiment.
FIG. 13 is a schematic perspective view of a communication device according to a sixth embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a communication device includes a substrate, a line, a communication circuit, and a variable capacitance. The substrate includes a ground section and a dielectric section stacked on the ground section. The substrate has a first surface and a second surface on an opposite side of the first surface. The first surface includes the ground section. And the second surface includes the dielectric section. The line is provided on the second surface side and has an inductive reactance. The communication circuit is provided on the second surface and connected to one end of the line and the ground section. The variable capacitance element includes a conductor connected to the other end of the line and is capable of varying a capacitance between the conductor and the ground section when a human body contacts with or comes close to the conductor.

Embodiments of the invention will now be described with reference to the drawings.

The drawings are schematic or conceptual. The size ratio between the portions, for instance, is not necessarily identical to those in reality. The same portion may be shown with different dimensions or ratios depending on the figures.

In the present description and the drawings, components similar to those described previously with reference to earlier figures are labeled with like reference numerals, and the detailed description thereof is omitted appropriately.

(First embodiment)
FIG. 1 is a schematic perspective view of a communication device according to a first embodiment.

The communication device 100 includes a substrate 103, a communication circuit 104, an inductor section 107, and a variable capacitance element 109.

The substrate 103 includes a ground section 102 and a dielectric section 101 stacked on the ground section 102. The ground section 102 is formed from a conductor having a reference potential, such as a metal layer of e.g. copper or gold. The dielectric section 101 can be made of e.g. glass epoxy resin. The substrate 103 has a first surface 103a and a second surface 103b. The first surface 103a includes the ground section 102. The second surface 103b is provided on the opposite side of the first surface 103a and includes the dielectric section 101.

The communication circuit 104 is connected to one end of the inductor section 107 through e.g. a signal line 105 and a terminal 106 placed on the second surface 103b. The communication circuit 104 is also connected to the ground section 102. Alternatively, a through hole (not shown) may be provided so as to extend from the surface of the dielectric section 101 to the ground section 102. Furthermore, a conductor (not shown) may be provided to allow connection with the ground section 102 by the through hole. Thus, the communication circuit 104 may be connected with the ground section 102.

The terminal 106 includes an external conductor part connected to the ground section 102 and an internal conductor part connected to the signal line 105. The external conductor part and the internal conductor part are electrically insulated from each other.

The inductor section 107 includes a wire 107a and a core 107b. The wire 107a has e.g. a helical structure. The core 107b is made of e.g. a magnetic body and surrounded with the helical structure. That is, in the first embodiment, the line having an inductive reactance is the inductor section 107 including the helical structure. One end of the wire 107a is connected to the terminal 106. The other end is connected to a conductor 108. The wire 107a is made of a material such as copper.

The conductor 108 is placed inside the ground section 102 as viewed from above. In FIG. 1, the conductor 108 is placed on the second surface 103b side. The conductor 108 is formed from e.g. an electrode used in medical equipment, a conductive sheet such as copper foil, or a conductive material such as conductive ink and transparent conductive material. In a configuration using conductive ink, the conductor 108 can be easily formed inside or outside a casing irrespective of the structure of the casing. In the case of using a transparent conductive material, the display content can be recognized even if the transparent conductive material is superposed on the display or the manipulation section.

FIG. 2 is a configuration view of a communication system using the communication device of the first embodiment.

The communication device 100 and the communication device 200 communicate with each other using part of a human body (living body) 20 as a signal transmission path. One hand of the human body 20 is in contact with the conductor 108 of the communication device 100. The other hand is in contact with the conductor 208 of the communication device 200. Alternatively, the hand may be made close to the conductor without contact. For instance, the hand may be held over the conductor.

Here, the state of being close means that the human body 20 can be coupled with the

conductor

108, 208 by an electromagnetic field via e.g. a thin sheet, without direct contact with the

conductor

108, 208. A small current, for instance, flows between one region of the human body 20 coupled with the conductor 108 and the other region of the human body 20 coupled with the conductor 208. This constitutes a first transmission line TL1. The ground section 102 and the ground section 202 are coupled with each other by an electromagnetic field via the atmosphere without passing through the earth. This constitutes a second transmission line TL2. It is assumed that the communication device 100 is a transmission side, and the communication device 200 is a reception side. It is understood that the communication device may be a device that can perform transmission and reception.

FIG. 3 is an equivalent circuit diagram of the communication device of the first embodiment.
A signal is transmitted from the communication circuit 104 through the terminal 106 and the inductor section 107 to the conductor 108. The inductor section 107 is represented as a parallel connection circuit of an inductance and a capacitance occurring between the lines of the helical structure. The conductor 108 forms a capacitor with the ground section 102.

In this figure, the communication circuit 104 can include one of a transmitter and a receiver. The communication circuit 204 can include one of a receiver and a transmitter.

In the first embodiment, the conductor 108 is connected to the other end of the inductor section 107. The inductor section 107 includes a capacitance in the helical structure. The capacitor occurring between the conductor 108 and the ground section 102 is series connected with the inductive reactance of the inductor section 107.

The capacitor represented by the equivalent circuit is a variable capacitance element 109. The capacitance (C1) of the variable capacitance element 109 varies with the coupling state between the conductor 108 and the human body 20. In the first embodiment, the inductive reactance of the inductor section 107 is determined so as to establish impedance matching with the capacitance C1 of the state coupled with the human body 20. This enables efficient communication in the case where the human body 20 is in contact with the communication device. This is fundamental to intra-body communication.

Thus, the impedance Z_L seen toward the variable capacitance element 109 (in the state coupled with the human body 20) from one end of the line can be matched with the impedance of the communication circuit 104 within the band.

The signal electrode generates and receives an electric field perpendicular to the surface of the human body 20 by the conductor 108. Furthermore, the signal electrode also generates and receives a magnetic field perpendicular to the surface of the human body 20 by the inductor section 107 of the helical structure. This can reduce the transmission power.

FIG. 4 is a schematic view showing a variation of the attachment site of the communication device.

For instance, the communication circuit 104 including a transmitter can be provided on the chest. The communication circuit 204 including a receiver can be provided on the abdomen. This facilitates configuring a wearable biological sensor. Furthermore, the communication device of the first embodiment can transmit e.g. ID information (identification information) and voice signals.

FIG. 5 is a schematic perspective view of a communication device according to a comparative example.

FIG. 6 is a configuration view of a communication system of the comparative example.

FIG. 7 is an equivalent circuit diagram of the communication device of the comparative example.

In the comparative example, communication is performed by a signal electrode consisting only of a conductor 408. Thus, in the equivalent circuit diagram shown in FIG. 7, the conductor 408 is represented only by a capacitance 601 occurring with the ground section 402. The capacitance 601 is in inverse proportion to the spacing between the conductor 408 and the ground section 402. Thus, if the spacing is narrow, the capacitivity of the signal electrode increases. As a result, the signal inputted from the terminal 406 to the conductor 408 is reflected and not transmitted to the communication device 500, causing loss.

FIG. 8 is a graph showing the dependence of voltage standing wave ratio on frequency.

The vertical axis represents voltage standing wave ratio. The horizontal axis represents frequency (MHz).

In FIG. 8, the voltage standing wave ratio was measured in the state of the human body 20 being in contact with the conductor 108. In the comparative example, the voltage standing wave ratio was as high as 8 or more in the band of use.

The voltage standing wave ratio VSWR is given by Equation (1) using a voltage reflection coefficient.

(1)

The reflection loss L_REF (dB) is given by Equation (2) using the voltage reflection coefficient.

(2)

In the comparative example, the voltage standing wave ratio is 8 or more. Thus, the reflection loss L_REF is as high as 4 dB or more. In contrast, in the first embodiment, the voltage standing wave ratio was successfully made close to 1 at frequency f. Thus, the reflection loss L_REF was reduced to the vicinity of zero.

The transmission power of the first embodiment was 9.7 dB higher than the transmission power of the comparative example. The reception power of the first embodiment was 1.6 dB higher than the reception power of the comparative example.

(Second embodiment)
FIG. 9A is a schematic perspective view of a communication device according to a second embodiment. FIGS. 9B and 9C are schematic views of an inductive reactance line used in a variation thereof.

As shown in FIG. 9A, in the communication device 800 according to the second embodiment, the inductor section 807 includes a wire 807a and a magnetic body 807b of e.g. ferrite. The wire 807a has a reciprocating meander structure and is provided on the magnetic body 807b. That is, the line having an inductive reactance is the inductor section 807 including the meander structure. One end of the wire 807a is connected to the terminal 106. The other end of the wire 807a is connected to the conductor 108.

Thus, a planar shape can be realized by providing a meander shape part on the magnetic body 807b. Furthermore, the magnetic body 807b may be a foldable magnetic sheet. Then, the magnetic body 807b can be affixed to e.g. the inner side surface of a casing. This facilitates implementation.

In the variation of FIGS. 9B and 9C, a zigzag line pattern 822 is provided on a magnetic body 820 of e.g. ferrite to realize a line having an inductive reactance. FIG. 9B is a schematic plan view. FIG. 9C is a schematic sectional view taken along line A-A.

(Third embodiment)
FIG. 10A is a schematic perspective view of a communication device according to a third embodiment. FIG. 10B is an equivalent circuit diagram.

In the communication device 900, the line having an inductive reactance further includes a chip inductor section 901. The chip inductor section 901 is series connected between the inductor section 107 and the terminal 106. The chip inductor section 901 thus provided can downsize the shape of the inductor section 107 for obtaining a desired inductive reactance.

(Fourth embodiment)
FIG. 11A is a schematic perspective view of a communication device according to a fourth embodiment. FIG. 11B is an equivalent circuit diagram.

A chip capacitor 1101 is provided in parallel to the variable capacitance element 109. That is, one end of the chip capacitor 1101 is connected to the wire 107a of the inductor section 107 through a terminal 1102. The other end is connected to a through hole 1103 connected to the ground section 102. Thus, a desired capacitive reactance can be obtained even if the size of the conductor 108 is restricted by the requirement of implementation.

(Fifth embodiment)
FIG. 12 is a schematic perspective view of a communication device according to a fifth embodiment.

The inductor section 107 includes two helical structures that are series connected and orthogonal to each other. Thus, a diversity effect can be obtained for the magnetic field. This can improve the transmission/reception gain.

(Sixth embodiment)
FIG. 13 is a schematic perspective view of a communication device according to a sixth embodiment.

The conductor can be provided on at least one of the first surface 103a side and the second surface 103b side of the substrate 103. In the sixth embodiment, a conductor 1409 is provided also on the opposite side (first surface side) of the substrate 103 from the conductor 108. In the equivalent circuit, two variable capacitance elements are parallel connected to the end of the inductor section 107. Thus, a desired capacitance can be obtained between the conductor and the ground section 102 when the human body 20 is brought into contact with or made close to any of the upper surface side and the lower surface side of the communication device 1400.

According to the first to sixth embodiments, the line having an inductive reactance and the conductor are series connected. The variable capacitance element 109 and the line having an inductive reactance are series connected. The capacitance C1 of the variable capacitance element varies when the human body 20 is brought into contact with or made close to the conductor. By varying the capacitance C1 of the variable capacitance element 109, the impedance of the communication circuit can be matched with the impedance of the variable capacitance element 109 as viewed from one end of the line. This can reduce the transmission power.

Also in the communication device of the reception side, a line having an inductive reactance and a variable capacitance element can be similarly provided. Thus, impedance matching can be established also on the reception side. This can further reduce the transmission power in the overall communication system.

Such a communication device can be used for e.g. a biological sensor, a contact sensor, a tablet PC, and an NFC-enabled (near field communication-enabled) IC card.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.

Claims

A communication device comprising:
a substrate including a ground section and a dielectric section stacked on the ground section, the substrate having a first surface and a second surface on an opposite side of
the first surface, the first surface including the ground section, and the second surface including the dielectric section;
a line provided on the second surface side and having an inductive reactance;
a communication circuit provided on the second surface and connected to one end of the line and the ground section; and
a variable capacitance element including a conductor connected to the other end of the line and being capable of varying a capacitance between the conductor and the ground section when a human body contacts with or comes close to the conductor.
The device according to claim 1, wherein impedance seen toward the variable capacitance element from the one end of the line can be matched with impedance of the communication circuit within a band of the communication circuit by varying the capacitance.
The device according to claim 1, wherein the line includes two regions crossing each other and connected in series.
The device according to claim 3, wherein the line is placed outside the ground section as viewed from above.
The device according to claim 3, wherein the two regions of the line are orthogonal to each other.
The device according to claim 5, wherein the line is placed outside the ground section as viewed from above.
The device according to claim 1, wherein the line is placed outside the ground section as viewed from above.
The device according to claim 1, wherein the line has a helical structure.
The device according to claim 8, wherein the conductor can be brought into contact with or made close to the human body so that a center axis of the helical structure is parallel to a surface of the human body.
The device according to claim 8, wherein the line includes a magnetic body inside the helical structure, the magnetic body extending along a center axis of the helical structure.
The device according to claim 10 wherein the conductor can be brought into contact with or made close to the human body so that the center axis of the helical structure is parallel to a surface of the human body.
The device according to claim 1, wherein the line has a meander structure.
The device according to claim 12, wherein the meander structure is formed on a magnetic body.
The device according to claim 1, wherein the conductor is provided on at least one of the first surface side and the second surface side.
The device according to claim 14, wherein impedance seen toward the variable capacitance element from the one end of the line can be matched with impedance of the communication circuit within a band of the communication circuit by varying the capacitance.
The device according to claim 14, wherein the line includes two regions crossing each other and connected in series.
The device according to claim 16, wherein the line is placed outside the ground section as viewed from above.
The device according to claim 16, wherein the two regions of the line are orthogonal to each other.
The device according to claim 18, wherein the line is placed outside the ground section as viewed from above.
The device according to claim 14, wherein the variable capacitance element is placed inside the ground section as viewed from above.