Sensormatic Electronics Corporation

Raymond L Barrett, Jr

Thomas A Gross

Henry F Pfister

A coil assembly that is essentially isotropic in a plane normal to the plane of the coil includes two flat coils stacked one next to the other. One coil is connected in series with a resistor in a closed loop and has a strip of high permeability material woven through it. The other coil is tuned by a parallel capacitor across its coil terminals, such terminals being connected to electronic circuitry. The coil is separated from the printed circuit board that contains the electronic circuitry by a sheet of high permeability material. The assembly is self-contained and powered by a flat battery on which the circuit board is placed. Another embodiment is disclosed that contains only one coil, the terminals of which are connected to a suitable electronic circuit, not shown. Strips of high permeability material are disposed on both sides of the coil and an assembly is produced with a printed circuit board and a flat battery.

Coil assembly for substantially isotropic flux linkage in a given plane

A coil assembly that is essentially isotropic in a plane normal to the plane of the coil includes two flat coils stacked one next to the other. One coil is connected in series with a resistor in a closed loop and has a strip of high permeability material woven through it. The other coil is tuned by a parallel capacitor across its coil terminals, such terminals being connected to electronic circuity. The coil is separated from the printed circuit board that contains the electronic circuitry by a sheet of high permeability material. The assembly is self-contained and powered by a flat battery on which the circuit board is placed. Another embodiment is disclosed that contains only one coil, the terminals of which are connected to a suitable electronic circuit, not shown. Strips of high permeability material are disposed on both sides of the coil and an assembly is produced with a printed circuit board and a flat battery.

A duplexer is provided in which a transmit input signal is fed in parallel through two autotransformers to a pair of portal loops for establishing an interrogation field. Significantly lower voltage response signals returning via the autotransformers are applied in push-push relationship to the primary of one transformer for producing a difference signal output, and in parallel to a second transformer primary for producing a sum signal output. Back-to-back diodes across the secondary windings of the sum and difference output transformers limit the volt drop across the respective primaries for the relatively higher voltage transmit input signal. The response signal, however, is below the threshold of the diodes and, consequently, the diodes do not attenuate such signal.

Duplexer with sum and difference signal outputs

Communication between portal units and identification tags is accomplished by continually radiating an interrogation signal consisting of a code pattern from each portal unit followed by a listening interval. Tags within range of such interrogation signal test the incoming signals for frequency, bit duration, bit rate, a preamble code and a facility identifying code. If the tag receives a valid signal to which it has been preprogramed, such signal synchronizes and initiates a plurality of tag responses within a given overall response interval and with each response transmitted during randomly selected time slot. Each tag is provided with its own pseudorandom binary sequence generator and reply counter with the pseudorandom generator sequenced by a signal derived from the carrier signal radiated by the tag. The portal units also test incoming signals for frequency bit rate and bit duration as well as for a preamble code generically indicative of a tag. If the test is passed, the remaining tag response consisting of an identifier and an error correcting code is accepted and passed on to a CPU.

Growing community of inventors

Oakland Park, FL, United States of America

Raymond L Barrett, Jr