Patent ID: 7276910

Claim:
An electrical resonator having a primary resonant frequency value f R , the resonator comprising: a conductor having an inductance value L; a plurality of capacitors coupled to the conductor having a net capacitance value C disposed to provide a primary resonant frequency value f R <500 kHz, wherein the capacitance value of at least one of the capacitors varies as a function of the voltage drop across it; and a controller coupled to the at least one of the capacitors, including first circuit means for generating a control voltage V C corresponding to the difference between a first predetermined resonant frequency value f R1 and the primary resonant frequency value f R <500 kHz, and second circuit means for applying the control voltage V C to the at least one of the capacitors, thereby obtaining the capacitance value C necessary to produce a primary resonant frequency value f R =f R1 .