NL8700463A - Personal alarm or monitoring bracelet - transmits HF signal via output circuit built into strap - Google Patents

Abstract

The signal to be transmitted is fed from the final output transistor (Q) to the primary winding of a transformer (T) via an LC filter. The secondary winding feeds a series resonator which acts as the transmitting aerial. The device resembles a wristwatch, the transmitter circuit, output filter and transformer being mounted in the 'watch' while the series inductance (1) is a copper track on a flexible substrate incorporated in the watch strap. The series capacitance (2) is a discrete component. The inductance, which is a multiturn rectangular track is enclosed by an insulator and separated from the wearer's wrist by a thin dielectric substrate. The wrist acts as a capacitive 'sink' for energy losses.

Description

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TRANSMISSION MOOR PER500NLI3KE ALARM AND TELEMETRY.

The invention relates to a miniature transmitter for personal alarm or telemetry. Usually, in such transmitters, the transmitter antenna is integrated into the strap with which these transmitters are worn on the wrist or on the body.

Due to the limited space in said tape, such an antenna will be very short with respect to the wavelength at which said transmitting devices operate.

10 In connection with this, a number of problems are known from radio technology.

An antenna which is very short with respect to the wavelength at which the transmitter operates will behave capacitively with respect to an antenna which is resonant at said wavelength. In order to resonate said very short antenna, an inductive reactance must be included in the antenna circuit. A consequence of this known from radio technology is that the Q factor of the antenna becomes larger, so that the bandwidth of the entire antenna system becomes smaller. The consequence of the latter is that a small change in the resonant frequency of said antenna relative to the frequency of the signal with which the antenna is supplied results in a relatively large decrease in the radiation efficiency.

The foregoing renders such an antenna less suitable for use on or near the human body, where the interaction between antenna and skin surface is variable. Think of individual differences in skin moisture and the like.

The object of the invention is the construction of an antenna which does not have, or to a lesser extent, said disadvantages.

For this purpose, use is made of a suitably designed electric series resonator, which layer impedance is coupled to the output of the relevant miniature transmitter.

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The orientation of the resonator according to the invention is based on the observation that if an electrical series circuit through which a high-frequency current passes is brought very close to the human skin, energy losses will occur with respect to this series circuit, which the skin as heat and high-frequency radiation are dissipated.

The embodiment of the resonator according to the invention will be described with reference to a number of drawings, serving only as an illustration.

Figure A shows how the electrical equivalent of the resonator, consisting of an amount of self-induction (I) and a capacitance (2) of low impedance, is connected to the output stage (3) of the transmitter by means of a suitable adaptation network or a transformer ( 4).

The resonator according to the invention consists of a self-induction in a flat plane combined with a series capacitance. This capacitance consists of a discrete component. Said inductance 55 consists of a strip-shaped conductor according to the pattern shown in B (I). and can be obtained by etching or punching from a copper foil sheet. Also, the inductance can be implemented as PCB (printed wiring), but this is not essential to the invention.

60 The complete resonator is mounted on a strip; dielectric material with suitable properties. Incidentally, some variation is possible in the pattern according to B (i). Figure C. shows how the resonator can be mounted in a wristband or in the housing of a body-mounted telemetry transmitter 65.

By proper electrical and geometrical dimensioning of the resonator in combination with the use of a dielectric of suitable thickness and dielectric properties, the ratio between the values of the inductive and capacitive components of the resonant is obtained; | in conjunction with the degree of capacitive coupling with. 'control the skin and the maximum expected variation herein .______ _________ H7 o λ / n% v / y V - »v. · λ. *

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The bandwidth of the resonator can now be determined in conjunction with the maximum expected amount of variation of the resonant frequency of the resonator. The advantage of this is that an antenna is obtained which, once the correct dimensioning has been determined, is reproducible and no longer requires individual adjustment, all the more since the construction of the self-induction can use the aforementioned, although then not flexible, PCB.

Another advantage over the conventional antennas is that the resonator according to the invention transmits energy to the skin, which in turn dissipates energy in the form of high-frequency radiation, so that the radiation efficiency of the resonator is greater than the radiation efficiency of usual antennas with the same dimensions.

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Claims (1)

Transmitting device according to claim 1, characterized in that the above-mentioned resonator is integrated in the housing of the transmitting device or in the fastening or bracelet connected to the housing, in such a way that the above dielectric forms part of that part 15 or that side of said housing or mounting band, which abuts the skin surface. ¢ 70040τ ....... "....." "~ ............... 6GS409LC