Digitally controlled power amplifier for underwater electro acoustic transducers

A digitally controlled sonar power amplifier for underwater transmitter is explained in this paper. It proposes a method of generating unipolar Sine Pulse Width Modulation (SPWM) signals for echo ranging sonar. This method can be effectively used in all kinds of inverters including high frequency inverters. A low cost digital signal controller was used to generate SPWM signals and used as gating pulses for a Controlled Full Bridge Circuit (CFBC). The power required, frequency, pulse-width and pulse repetition interval are given as the inputs to the digital controller and gating pulses for the CFBC are generated as output from the controller. A power transformer connected across CFBC boosts output voltage followed by power filter which removes unwanted harmonics present in the output. The output after the power filter is used to excite electro-acoustic transducer elements underwater. The voltage and current of the load were given as feedback to the same controller for voltage mode control loop implementation of the system. A prototype of 1kW Switch Mode Power Amplifier (SMPA) for echo ranging sonar has been designed and digital control has been implemented. Salient results are presented.

I. Introduction

ELECTRO acoustic transducers convert electrical energy into acoustic energy and vice versa. They find many application and very instrumental in underwater acoustic where it is used for the detection of objects under the sea. It is also used in seismic exploration, detection of depth of the sea and oil exploration industry. SOund Navigation And Ranging (SONAR) device is used for the above purpose and power amplifier is an integral part of SONAR system. A short duration of pulse is given to electro acoustic projectors and an echo returned from the object is used to find out the range of the object in sonar system. The signals most commonly used in echo-ranging systems are Continuous Wave (CW), Linear Frequency Modulation (LFM), and Pseudo Random Noise (PRN) etc. The signal(s) selected would depend upon the particular application, and the operational and hardware constraints [1].