Analog drive for ultrasonic probe with tunable phase angle

An apparatus to automatically tune the driving frequency of an ultrasonic probe comprising:

• means for sensing the phase angle between the current flowing through the ultrasonic probe caused by a driving signal characterized by a driving voltage having said driving frequency and the driving voltage and for generating a first control signal indicative of said phase angle;
• analog feedback means coupled to said probe and to said means for sensing, for generating said drive voltage at said driving frequency and for receiving said first control signal and for changing the frequency of the driving voltage until said phase angle changes to a predetermined value, said analog feedback means including integrator means for integrating said first control signal to generate a second control signal, said integrating for eliminating any offset errors or noise from said first control signal, said second control signal being coupled to and used by said analog feedback means for controlling said driving frequency of said driving voltage;
• programmable amplifier means coupled between said analog feedback means and said probe and having an input for receiving a gain control signal for amplifying said driving signal by an amount set by said gain control;
• and
• means including a tunable reactance coupled to said ultrasonic probe, for sensing said phase angle and for adjusting said tunable reactance so as to cause said phase angle to be substantially near zero to optimize power transfer to said ultrasonic probe.

An apparatus for driving an ultrasonic probe having an electrical input impedance comprising:

• a zero crossing detector for receiving a current phase sample signal indicative of the current flowing through said ultrasonic probe and for outputting a square wave alternating current waveform first signal;
• rectifier means coupled to receive said first signal and to convert said first signal to a direct current phase sample signal comprised of rectangular pulses all of the same polarity relative to some reference voltage;
• a frequency divider means for dividing the frequency of a first driving signal to a lower frequency second driving signal for said ultrasonic probe;
• a phase detector coupled to receive said direct current phase sample signal and said second driving signal, for generating therefrom a phase angle error signal in the form of a pulse width modulated pulse train where the pulse width is proportional to phase angle error;
• means for receiving said pulse width modulated phase angle error signal and for filtering out high frequency components and for converting the pulse width modulated pulse train to an analog phase angle error signal comprising a D.C. voltage proportional to the phase angle error;
• means for receiving said analog phase angle error signal and for integrating said phase angle error signal to generate a frequency correction signal having a magnitude and a polarity such that correction of the phase angle error toward a selectable, desired phase angle error is possible and for providing a means for selection of different phase angle error values;
• a voltage controlled oscillator means coupled to said frequency divider means for receiving said frequency correction signal and for generating said first driving signal for said ultrasonic probe, said driving signal having a frequency which is a function of said frequency correction signal;
• and
• means including a tunable inductor coupled to said ultrasonic probe for sensing the phase angle associated with said probe's input impedance and for tuning said tunable inductor to compensate for the reactive element of said input impedance of said ultrasonic probe so that the power factor is substantially near one.