WO1992009906A1

WO1992009906A1 - Electronic detection system

Info

Publication number: WO1992009906A1
Application number: PCT/SE1991/000785
Authority: WO
Inventors: Hans Löfberg; Jan Eriksson
Original assignee: Loefberg Hans; Jan Eriksson
Priority date: 1990-11-21
Filing date: 1991-11-20
Publication date: 1992-06-11
Also published as: SE9003698L; AU9029391A; SE9003698D0; SE467640B

Abstract

A system for discovering objects of different kinds, for finding victims of avalanches, ship wreckage etc., for warning of risky actions etc., consisting of a transmitter and a transponder. A signal emitted from the transmitter is reflected by the transponder in the form of an overtone of the emitted signal. The transponder, which can be double-sided with a reflector inbetween, consists of an antenna with one or several semiconductors, a reflector and an intervening dielectricum dimensioned to give the reflected output signal maximum strength. The dielectricum can be an integral part of an article of clothing or an object. It can also be arranged to be introduced between antenna and reflector at for example inflation of a life-jacket, whereby life-jackets not in use may be inactive and not interfer with the search for floating persons. In order to ease the handling the transmitter can also be divided up so that only a smaller part with the antennas has to be kept in the hand while batteries and the remaining construction for example can be carried on the back. The weight of the movable part thus can be brought down to a fifth of the total weight (about 1 kg), which is a substantial relief during hours of searching.

Description

Electronic detection system

The invention relates to systems for locating and relocating obstacles, objects etc. of different kinds, consisting of trans- itter, receiver and reflector.

In order to locate and identify different objects, many different systems and means are known and used, such as radar, which is used on practically every ship for locating obstacles of different kinds. Other systems with a widely spread use are different means for opening doors, register passing people, reveal thefts in stores, emit burglar alarm and further applica¬ tions.

Common of all these systems is that a signal is emitted and reflected and that the reflected signal is captured and is used in different ways, in order to start an alarm, open a door, show the distance to an object etc. The signal used might be of different kinds, a light beam, visible or invisible, ultrasound, radiowaves, etc. The systems can principally be divided into such giving response for optional objects, such as radar for ships, the outline of land, etc., detectors giving response if a signal, such as a light beam, is broken in some way and so on, and systems giving response for a certain reflector.

The invention refers to systems of the latter type, and uses for locating avalanche victims, informing aircraft crews of the presence of power lines, ease the rescuing of survivors from ships wreckage, and so on.

Technical background

In US-A-4 566 478 a means is disclosed including a trans- mitter sending electromagnetic waves on one frequency, a trans¬ ponder reflecting the waves with an harmonic frequency and a receiver to catch the reflected waves and emit a apprehendable signal.

In US-A-4 331 957 a similar means is disclosed including a transponder also consisting of an antenna with a diode for the reflection of waves with an altered frequency. These means are both intended for retrieving avalanche victims. The object of the invention

The object of the invention is to accomplish a system accor¬ ding to the prior art with an improved sensitivity, range and identification ability.

Another object of the invention is to accomplish a system with a broad applicability for, besides retrieving avalanche victims, locating survivors from accidents at sea, warning low flying air crafts, esp. helicopters, of power lines and other obstacles.

Technical description of the invention

The transponder according to the invention is principally in accordance with the prior art transponders, such as those dis¬ closed in the above mentioned patent publications. It consists like those of an antenna optimized for the two frequencys used, the incoming one coming from the transmitter and the outgoing harmonic overtone. An incoming frequency of e.g. 1000 MHz and an outgoing frequency of 2000 MHz have proven themselves to be suitable and an optimal effect can be obtained by tuning the components. In the patent publications mentioned a system with matching components is disclosed.

The position of the transponder on the object to be located or preferably the human body is of great importance. The sum of the field inciding upon the human body and the ield reflected by the human body is a standing wave having a nodal point situa¬ ted in the nearest environment of the reflecting background, which in case of humans is the skin surface. A transponder with the antenna directly against the skin will be located in a nodal point and therefore does not give any field and thus no signal which makes possible the localisation of the transponder. If the antenna part instead is placed at a distance from the skin the effect increases and at a certain distance it will give a maxi¬ mum signal. With a dielectric material between the reflecting skin and the antenna part this necessary distance is reduced. In the earlier constructions the transponder is arranged behind any suitable dielectricum in order to give a space between the antenna and the skin under any circumstances. When placed in a pocket or in a ski boot the thickness and the dielectric con¬ stant of the intervening fabric or leather will act in an unpre- dictable way, and that is why the sensitivity and the range, i.e. the strength of the signal, never or only in extremly exceptional cases, can be expected to be the best possible. According to the invention this drawback is eliminated by always maintaining the optimum dielectric distance between the reflector and the antenna. One way would be to place the trans¬ ponder on the skin with intervening distance means, but accor¬ ding to the invention instead a special dielectricum is arranged on the back of the antenna and on top of this a special reflec- tor mounted on the back of the dielectricum. The localisation in an inner pocket or outer pocket or directly onto the skin there¬ fore lacks importance, and the transponder will always show maxium sensitivity. Maximum sensitivity in two directions can also be achieved by making the transponder double-sided by placing two transponders with the reflectors against each other or having a common reflector for two assembled transponders.

The reflector in this case is metallic such as a plate, optionally perforated, a metal screen, a foil, an electro-depo¬ sit, a metallized fabric, etc., but may also consist of another reflecting material, e.g. conductive plastic material, and the transponder is produced in the form of a laminate of protective layer, antenna, dielectricum and reflector. The reflector is somewhat bigger than the antenna in order to prevent the in¬ fluence of the background material. An existing metal surface might also be used as reflector, such as a power line pole, whereby the antenna with the dielec¬ tricum is mounted tight against the pole.

At the manufacture of the transponder the dielectrical con¬ stant and the thickness of the dielectricum are tuned so that the sensitivity of the laminate is at maximum. Practical tests have shown that with the transponder according to the invention the reflecting effect is increased so that the discovery distan¬ ce becomes at least twice as big as compared to previously known constructions using the same transmitter. If thus the output effect is tuned so that a desired reading is obtained at a distance of 40 m to a prior art transponder, a reflected signal strength with a reading at 80 m is obtained with the transponder according to the invention.

The transponder may be incorporated as an integral part in different articles for every day use or in articles of clothing, at the manufacture thereof. For example, on a ski boot the re¬ flector may sit on the inside and the antenna on the outside of the leg with the space inbetween filled with the material in the boot leg, i.e. leather or plastic. The antenna and the reflector are then tuned to the characteristics and thickness of the material so that the sensitivity becomes optimal in the same way as when the transponder is a separate unit.

The transponder according to the invention is also well suited for rescuing survivors in accidents at sea, when mounted on a life-jacket it makes it possible to quickly find people in the water. In this case the transponder might be put into the life-jackets during their manufacture and then be made in such a way that the antenna is lying directly against the reflector, and thus is passive, and to be activated only when the life- jacket is inflated. The activation may be achieved in that only upon inflation a dielectrical layer is introduced between the antenna and the reflector or a loose metal plate or foil is removed from between the dielectricum and the antenna. Further, the transponders may be made in two halves with dielectricum and reflector in one half and antenna in the other, which for the activation are displaced or asembled to form the transponder according to the invention.

Irrespective of if the transponder is integrated or loosely fitted the sensitivity of the system of course will be dependent of the screening of the transponder from the transmitter and the angel in relation to the direction of the incoming signal. By placing at least two transponders on a person on different places the risk of both being screened or being turned in the wrong direction will be very small, especially when using double sided transponders.

The transmitter emits a high frequency signal to the passive transponder which returns an harmonic overtone to the receiver. For different cases the first, the second or the third overtone may be the most suitable, for example in order to distinguish different types of re lectors or in order to be able to use a lower frequency on the transmitter and thereby enhance the penetration. Otherwise, as high frequencies as possible are elected in order to make the apparatus light, but at the same time the choice is limited by the fact that the damping of the signal may not become to big. For example, in snow high frequen¬ cies are strongly dampened, which puts a limit on the frequen¬ cies that may be used. A relatively good balance between the equipment, weight and sensitivity has been found with an output signal of about 1000 MHz.

The transmitter and the reciever with the accompanying antennas may as in prior constructions be assembled into one unit which is kept in the hand and is directed manually in order to sweep a search area. According to a preferred embodiment of the invention, however, the batteries and parts of the construc¬ tion are made as a separate unit, which is carried on the back and is connected to the finder through a cable, in order to make the use of the equipment less tiresome during the fairly long time needed to search through an avalanche or a water area. The weight of the part which has to be held in the hand thereby can be brought down to about a fifth of the total weight, i.e. be reduced from about 5 kg to about 1 kg. Of course, the equipment can also be made for fixed installation, e.g. for searching an area from an helicopter.

Claims

1. An electronic search system consisting of a transmitter and a receiver for localizing a transponder, wherein a high frequency signal emitted from the transmitter is transformed into an harmonic overtone by the transponder and is reflected to the reciever and is transformed into a detectable signal there¬ in, characterized in that the transponder consists of an antenna part with one or several semiconductors for tranformation of the input signal, a dielectrical layer and a reflector assembled into a unit, whereby the incoming signal received by the antenna part passing through the dielectrical layer is reflected back to the antenna part, and in that the dielectrical layer is dimen¬ sioned to give an anti-node in the wave form of the reflected signal in the antenna part.

2. An electronic search system according to claim 1, charac¬ terized in that the transponder is double-sided having an an¬ tenna part and a dielectrical layer on each side of a reflector, assembled into an integral unit.

3. An electronic search system according to claim 1, charac- terized in that the antenna part, the dielectrical layer and the reflector is assembled with e.g. a ski boot into an integral unit, whereby the dielectrical layer at least partly is compri¬ sed of the material of the ski boot.

4. An electronic search system according to claim 1 or claim 2, characterized in that the transponder is inactive in e.g. a non-inflated life-jacket and is activated at inflation when antenna, dielectricum and reflector are brought into the correct position in relation to each other.

5. Use of the search system according to any of the precee- ding claims, to warn of power lines or other obstacles.