GB1605288A - Recognition devices - Google Patents

Description

N (54) IMPROVEMENTS IN OR RELATING TO RECOGNITION DEVICES (71) We, EMI LIMITED, a British Company, of Blyth Road, Hayes, Middlesex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to recognition devices, and it relates especially, though not exclusively to such devices as may be employed for military purposes, for recognising friendly vehicles or persons. A military system incorporating such a recognition device is commonly referred to as an "interrogate friend or foe" or briefly I.F.F. system.

Since a military I.F.F. system requires similar recognition devices to be carried by many vehicles and/or persons, it is desirable that the said devices be efficient yet economical to produce.

According to the invention there is provided a recognition device responsive to incident energy, including first means capable of reflecting said incident energy, second means arranged to selectively admit or not admit said incident energy to said first means, control means arranged to control the operation of said second means and receiving means adapted to receive said incident energy, the arrangement being such that said control means is responsive to the receipt by said receiving means, of a coded message, superimposed on said incident energy, to render said second means operative.

In order that the invention may be clearly understood and readily carried into effect, one embodiment thereof will now be described, by way of example only with reference to the drawing filed with the Provision Specification which shows, in block diagrammatic form, an I.F.F. system incorporating a recognition device in accordance with the invention.

Referring now to the drawing, the I.F.F.

system includes, as the active element, a laser interrogating device 1. This device may, for example, be of a kind which can also be used for range finding. In its interrogating mode, the laser device 1 is adapted to emit a short burst of pulses which are, for example, position coded or binary coded in accordance with a selected interrogating code for the day.

All friendly vehicles, and possibly also certain persons, carry transponding means, as shown within the dotted rectangle 2. The transponding means includes an omnidirectional sensing device 3 which has a frequency response adapted to embrace substantially only the spectral band of friendly interrogating laser devices such as I. The sensor 3 is coupled to a code discriminating circuit 4, which comprises a logic circuit adapted to recognise the interrogating code for the day. The transponder unit also includes reflecting means, comprising an omnidirectional cluster of corner reflectors 5, the open faces of which are covered by shutters 6.

These shutters may be mechanically operated in response to electrical signals, or they may be purely electrically operable devices such as Kerr cells. The shutters 6 are ganged so as to operate synchronously, and are controlled by electrical signals from shutter control circuits 7, the opening and shutting thereof being in accordance with a transponding code selected and imposed by shutter code circuits 8, which are, in turn, controlled by the output of code discrimination circuit 4.

In operation, when the sensor 3 has received an interrogation signal which is recognised by the code discriminating circuit 4 as being coded in accordance with the interrogating code of the day. the circuit 4 is arranged to produce a signal which causes circuits 8 to apply a set of signals, coded in accordance with the transponding code for the day, to the shutter control circuits 7. By this means, circuits 7 are arranged to produce electrical signals which cause the opening and closing of shutters 6 in accordance with the said transponding code for the day. The timing of the transponding code is standardised, and preferably also phased to the interrogation code.Thus the energy from laser device 1 is reflected back towards it in accordance with the transponding code, since the interrogating laser device is arranged to continue sending pulses, in one example, at constant rate, during the time in which the shutters 6 are operating, so as to detect the coded opening and shutting sequence of the shutters. The total number of pulses or pulse positions in the interrogating code emitted by the laser device may be for example 10, and the laser device may be arranged to emit a further 10 pulses during the time of shutter operation of the transponder.

Alternative arrangements are possible, particularly with regard to the shutters 6. The reflectors may comprise means connected into an electro-magnetic circuit, so that the reflectors are physically moved when a current flows in the circuit, somewhat as in a galvonometer arrangement.

WHAT WE CLAIM IS:- 1. A recognition device resposive to incident energy, including first means capable of reflecting said incident energy, second means arranged to selectively admit or not admit said incident energy to said first means control means arranged to control the operation of said second means and receiving means adapted to receive said incident energy, the arrangement being such that said control means is responsive to the receipt by said receiving means, of a coded message, superimposed on said incident energy to render said second means operative.

2. A device according to Claim 1 in which said first means comprises an omnidirectional cluster of corner reflectors and said second means comprises a plurality of shutters, each associated with one of said reflectors, which can be opened or closed in response to signals derived from said control means.

3. A device according to Claim 1 in which said first means comprises on omnidirectional cluster of corner reflectors and said second means comprises a plurality of kerr cells which can be rendered transmissive to said incident energy by means of signals derived from said control means.

4. A device according to any of the preceding claims in which said receiving means in arranged to receive light from a laser source and said coded message is in the form of a burst of pulses of said light.

5. A device according to Claim 4 in which said burst of pulses is position coded or binary coded in accordance with a currently prevailing code.

6. A recognition device substantially as herein described with reference to the drawing filed with the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. total number of pulses or pulse positions in the interrogating code emitted by the laser device may be for example 10, and the laser device may be arranged to emit a further 10 pulses during the time of shutter operation of the transponder. Alternative arrangements are possible, particularly with regard to the shutters 6. The reflectors may comprise means connected into an electro-magnetic circuit, so that the reflectors are physically moved when a current flows in the circuit, somewhat as in a galvonometer arrangement. WHAT WE CLAIM IS:-

1. A recognition device resposive to incident energy, including first means capable of reflecting said incident energy, second means arranged to selectively admit or not admit said incident energy to said first means control means arranged to control the operation of said second means and receiving means adapted to receive said incident energy, the arrangement being such that said control means is responsive to the receipt by said receiving means, of a coded message, superimposed on said incident energy to render said second means operative.

2. A device according to Claim 1 in which said first means comprises an omnidirectional cluster of corner reflectors and said second means comprises a plurality of shutters, each associated with one of said reflectors, which can be opened or closed in response to signals derived from said control means.

3. A device according to Claim 1 in which said first means comprises on omnidirectional cluster of corner reflectors and said second means comprises a plurality of kerr cells which can be rendered transmissive to said incident energy by means of signals derived from said control means.

4. A device according to any of the preceding claims in which said receiving means in arranged to receive light from a laser source and said coded message is in the form of a burst of pulses of said light.

5. A device according to Claim 4 in which said burst of pulses is position coded or binary coded in accordance with a currently prevailing code.

6. A recognition device substantially as herein described with reference to the drawing filed with the Provisional Specification.