MODELING AND OPTIMISATION OF AN ULTRASONIC GENERATOR

The aim of our project is to develop an optimised generator for ultrasonic transducer within a range of frequency from 1 to 10 MHz. In this paper the design and first results on the automatic optimisation of the transducer central frequency is introduced. The generator delivers burst sine wave signals and its output impedance equals to 50 W. The sine waves are produced by a Cordic algorithm. We choose to exploit the characteristics of the transducer impedance in order to search the optimal excitation frequency. A control unit through a feedback research the parallel resonance frequency for which the impedance of the transducer is maximum. The impedance module is obtained from the envelope of the signal at the input of the transducer. We chose to use as criterion for our application a numerical detector of envelope and particularly the detection of the maximum value in established mode. The detection of optimal frequency is based on the iterative algorithm of the gradient. We have tested our method and present the first results to find the optimal excitation frequency. The transducer is made of PZT and is a 50 mm diameter planar transducer at a resonant frequency of about 2 MHz