Aerial coupling device

Abstract

 An aerial coupling device enables an electronic circuit, such as a radio receiver or transmitter to be coupled to a body which then acts as an aerial. The aerial coupling device comprises one or more inductive elements (3) which may be part of respective resonating circuits (2), supported by a bracelet or wrist strap (1). Each inductive element (3) includes one or more loops or coils, which may be wound on a ferrite core (6), the loops or coils extending in the direction of the arm, i.e. being transverse to the longitudinal axis of the bracelet or wrist strap. A case, such as a watch case (9), attached to the bracelet or wrist strap (1) houses receiver or transmitter circuitry (7) and optionally a timing circuit and a time display (10). The aerial coupling device may also be incorporated in other means, such as belt.

Description

[0001] This invention relates to an aerial coupling device which enables an electronic circuit, such as a radio receiver or transmitter, to be coupled to a body, particularly a part of a human body. One application of the invention is to a radio receiver, particularly a radio paging device, that can be worn on the person, for example, like a wristwatch. In such an application the human body acts as an aerial and the invention is employed to couple radio frequency current, flowing in the body to the receiver circuitry.

[0002] Known radio paging devices of the pocket or chest type are normally carried in a pocket and/or attached to clothing by means of a clip. A drawback of such devices is that the human body, being a moderate conductor, introduces a damping or loss factor which leads to a loss in signal strength. In such known devices, the proximity of the body is, therefore, a disadvantage.

[0003] The present invention overcomes such a problem by making use of a body as an aerial and, in effect, turning the above disadvantage into an advantage.

[0004] More particularly, the present invention provides an aerial coupling device comprising means adapted to be worn on a body and including at least one inductive element which is located in said means so as to enable radio frequency current to be coupled either from said body to said inductive element, or from said inductive element to said body.

[0005] The inductive element or elements can be either provided with terminals for connection, or connected to electronic circuitry which either responds to the induced radio frequency current received from the body (in a receiver mode), or which provides radio frequency current to the body (in a transmitter mode).

[0006] Since the proximity of the body does not have any disadvantageous effect, devices employing the invention may be worn close to the body without causing any loss in signal strength. This enables the invention to be advantageously embodied in various forms, for example, in a bracelet or wrist strap, belt, necklace, clothing, or spectacles, which are far less obtrusive and/or inconvenient to carry than, for example, in radio paging devices of the known pocket or chest type. Moreover, since the body is used as an aerial, it is not necessary to provide an aerial in a device which includes or is connected to a coupling device according to the invention.

[0007] The aerial coupling device may provide either a broad, or a narrow transmission band for the radio frequency current. For example, a bracelet , wrist strap, or belt may support one or more inductive elements which pick up a wide band of radio frequencies (such as 20-50 Megaherz). The electronic circuitry used in such a case (such as a radio receiver or transmitter) could then be provided with appropriate tuning circuits. However, it can be advantageous to provide a narrow band (particularly for low frequencies,but possibly for frequencies in the range of from a few Megaherz to about 100 Megaherz), by using one or more electrical resonating circuits. For example, a distributed resonance arrangement comprising a plurality of parallel connected resonating circuits each having a similar inductance and capacitance will advantageously provide improved signal strength for radio receivers at the respective resonant frequency. The latter arrangement is particularly useful in the receiver mode, for example, where the invention is applied to a radio paging device. The use of resonance arrangements is, however, optional, since it may be possible to pick up an open circuit voltage across tne inductive element or elements.

[0008] According to one embodiment of the invention, an aerial coupling device comprises a bracelet or wrist strap, one or more inductive elements supported by the bracelet or wrist strap, each of said inductive elements including at least one loop or coil which is transverse to the longitudinal axis of the bracelet or wrist strap. Preferably, each inductive loop or coil is wound on a core made of ferrite in order to improve the signal coupling.

[0009] The latter embodiment of the invention may include a case attached to the bracelet or wrist strap, the case containing, for example, a radio receiver such as an FM broadcast receiver or a radio paging device. The receiver or paging device may be advantageously contained in a watch case which includes timing circuitry and a time display.

[0010] An embodiment of the invention will now be described with reference to the accompanying drawings in which:-

Fig. 1 schematically illustrates an example in which a radio paging device includes an aerial coupling device according to one embodiment of the invention.

Fig. 2 is a schematic block diagram of circuitry used in the device of Fig. I.

Fig. 3 schematically illustrates a further embodiment of the invention.

[0011] The paging device shown in Figs. 1 and 2 comprises a bracelet or wrist strap 1 which supports a plurality of resonating circuits 2 each including an inductive element 3 connected to a capacitor 4. Instead of using a discrete component as capacitor 4, the required capacitance may be provided by an inherent capacitance between adjacent end portions 5a, 5b of one or more open inductive loops or coils 5, as shown in Fig. 3. In either case, each inductive element preferably includes, either a single turn or multiple turns wound on a core or cores 6 made of ferrite or iron dust, for example. However, in some cases, core or cores 6 may not be necessary (e.g. when using air-cored loops or coils).

[0012] The resonating circuits 2 are connected in parallel and the parallel network is either provided with terminals (not shown), or connected to radio receiver circuitry 7 of a paging device, as shown in Fig. 2.

[0013] The circuitry includes a sound transducer 8 which provides a "bleep" or some other suitable audio signal to attract the user's attention when a predetermined radio signal is received. Such circuitry is well known in the art, so no detailed description will be given. The circuitry 7 . is housed in a watch case 9 together with known timing circuitry for driving a display 10. The watch circuitry is suitably of the type which includes an alarm function whereby the audio alarm transducer may be connected to the radio paging receiver circuitry. Means may be employed for providing different tones in order to enable the user to distinguish between time alarms and radio paging sounds. Alternatively or additionally, the radio paging alarm may be given by means of a flashing light.

[0014] Instead of using a bracelet or wrist strap (as shown in Fig. 1), the aerial coupling device (including the resonating circuits 2) and the radio receiver circuitry (7) may be incorporated into a waist belt (not shown). This provides the advantage of using the body as a dipole aerial.

[0015] The radio frequency may be in the range of 20 Megaherz to 1 Gigaherz and preferably about 100 Megaherz and the circuits 2 are resonant at the selected frequency. The specific construction of circuits 2 and the number used will depend on the selected frequency. For example, fewer resonating circuits 2 each having one loop or coil may be used at higher frequencies, whereas more resonating circuits possibly having . more than one loop or coil wound on ferrite cores will be required at lower frequencies. Separate ferrite cores may be provided for each respective resonating circuit or the loops or coils of each resonating circuit may be wound in a common ferrite core.

[0016] Fig. 2 schematically shows how the resonating circuits are connected in parallel, the parallel network being connected to a signal input lla, llb, of receiver circuitry 7. Since the body is a moderate conductor and has currents flowing in it caused by EM fields in the vicinity, the radio frequency current flowing in the wrist inducesa secondary current in the loops or coils of the inductive elements 2 in the resonating circuits 2 which are close to the wrist. That is the wrist, arm and body act as an aerial and the aerial coupling device acts as a transformer for coupling the currents in the aerial. Efficient coupling to the wrist current is achieved by using many small loops or coils running in the direction of the arm (i.e. transverse to the longitudinal axis of the bracelet 1) with low loss ferrite cores. The loops or coils of the inductive elements 3 are all coupled together as shown in Fig. 2 to form the composite signal available at the receiver input. To minimize resistive and mis-match loss each inductive element 3 is parallel resonated before coupling to the next.

[0017] It is to be noted that the inductive elements 3 are symbolically represented in Fig. 2, since each may have one or more loops or coils which may be wound on a core (e.g. made of ferrite). In Fig. 1, for ease of illustration and in each resonating circuit 2, the inductive elements 3 are represented by only one loop or coil, and the capacitance by the standard symbol.

[0018] Although the above embodiments have been described with reference to a radio paging device, the aerial coupling circuit may be used with other electronic circuitry. For example, an FM broadcast receiver may be coupled to the body to receive broadcast transmissions, or a low power transmitter may be coupled to the body in order to radiate a radio signal. The latter device may be used for telecommunication or position monitoring and, in this case, the body may be that of an animal (e.g. which is free to roam on open pasture land).

[0019] The resonating circuits 2 are preferably evenly spaced around the bracelet or wrist strap 1 and they may, for example, be incorporated in each link of an expanding watch bracelet.

[0020] If the bracelet or wrist strap (or other support means incorporates only the inductive element or elements, the capacitance(2) required for the resonating circuits may be built into, or be part of a receiver or transmitter which is housed, for example, in the watch case 9.

[0021] It is of course an important feature of the invention for efficient coupling to the current that the inductive element(s) e.g. the loop(s) or coil(s) extend generally parallel to the main current flow in the body member in which it (they) is/are wom. This means that in a strap worn round a body or body member, they would be located transverse to the longitudinal direction of the strap.

Claims

1. An aerial coupling device comprising means (1) adapted to be worn on a body and including at least one inductive element' (3) which is located in said means (1) so as to enable radio frequency current to be coupled either from said body to said inductive element (3) or from said inductive element (3) to said body.

2. A device according to claim 1, wherein the or each inductive element (3) is part of a resonating circuit (2) including a respective capacitance (4).

3. A device according to claim 1 or 2 wherein said means (1) adapted to be worn on a body comprises a bracelet, wrist strap or belt.

4. A device according to claim 3 wherein the or each inductive element (3) includes one or more loops or coils arranged transversely of a longitudinal axis of said bracelet or wrist strap, or of said belt (1).

5. A device according to claim 4 wherein the or each loop or coil is wound on a respective core (6).

6. An aerial coupling device comprising a bracelet, wrist strap or belt (1), one or more inductive elements (3) supported by said bracelet, wrist strap or belt (1) each of said inductive elements (3) including at least one loop or coil which is transverse to the longitudinal axis of said bracelet, wrist strap or belt (1).

7. A device according to claim 6, wherein each of said inductive elements (3) is part of a resonating circuit (2) including a respective capacitance (4).

8. A device according to any one of the preceding claims in which the inductive elements (3) are either provided with terminals for connection, or connected to electronic circuitry (7).

₉. A device according to any one of the preceding claims 6-8 including a case (9) attached to the bracelet, wrist strap or belt (1), the case (9) containing a radio receiver or transmitter.

₁0. A device according to claim 9 in which said case (9) is a watch case which also includes timing circuitry and the time display (10).

Drawing