Patent ID: 6990852

Claim:
A method of detecting particles in liquid samples, comprising the steps of: bringing a piezo-electric crystal, comprising at least one surface adapted to bind to said particles in said liquid, in contact with said liquid; said crystal being adapted to exhibit resonant mechanical vibrations; driving said crystal into mechanical vibration with a driving signal at a driving frequency; connecting said crystal to a first input of a balanced comparator circuit having a low input impedance; providing a cancellation signal at said driving frequency to a second input of said balanced comparator circuit; detecting an output signal near said driving frequency at an output of said balanced comparator circuit; adjusting said cancellation signal so that said output signal is substantially cancelled out; increasing the amplitudes of said driving signal and said cancellation signal proportional to each other; detecting transient signals at the output of said balanced circuitry; and determining that target particles are present in said liquid, based on said transient signals.