Patent ID: 7089794

Claim:
A method of tracking resonant frequencies of first and second electrically resonant structures having a nominal difference frequency comprising the steps of: generating a first reference signal having a variable frequency encompassing the possible resonant frequency of the first resonant structure; generating a second reference signal having a variable frequency encompassing the possible resonant frequency of the second resonant structure; summing the first and second reference signals; exciting said first and second resonant structures with said summed signal; mixing a composite response signal received from said first and second resonant structures with the first reference signal; filtering the mixed composite response and first reference signals and using the resulting filtered signal within a controlled loop to track the resonant frequency of the first structure; mixing the composite response signal of said first and second resonant structures with said second reference signal; and filtering the mixed composite response and second reference signals and using the resulting filtered signal within a controlled loop to track the resonant frequency of the second resonant structure.