Damped sinusoidal current pulse generator and method

Claim 1

An electrical circuit for producing a damped sinusoidal electromagnetic field in an interrogation zone for activating a responder passing through the zone, comprising a resonant circuit adapted to receive electrical energy and including an inductive component and a capacitive component connected in parallel, the inductive component comprising a conductor for producing an electromagnetic field; means for intermittently coupling a source of electrical energy to the resonant circuit to transfer a predetermined amount of electrical energy to the resonant circuit, the dissipation of residual transferred energy in the resonant circuit upon decoupling of the energy source and resonant circuit producing in the interrogation zone a damped sinusoidal electromagnetic field of sufficient intensity to activate a responder; and an inductor connected in series with the resonant circuit and the coupling means, wherein the inductance of the inductive component is at least 4.7 times the inductance of the inductor; and which coupling means comprises a trigger circuit and an SCR having an anode lead, a cathode lead and a gate lead, the SCR being connected in series between the energy source and the inductor by the anode and cathode leads, and the trigger circuit being coupled to the SCR gate lead to forward bias the SCR in response to a turn-on control signal to transfer electrical energy through the inductor to the resonant circuit until current flow in the inductor essentially stops, whereupon the SCR ceases to conduct to decouple the energy source and resonant circuit.