Miniature Directional Microphone for Handheld Automatic Speech Recognition in Military Environments

The Phraselator, a handheld automatic translation device, currently uses a cardioic microphone as an input for automatic speech recognition (ASR). This microphone is highly vulnerable to performance degradation in typical noisy military environments and,thus, there is a need for an improved transducer for this application. We propose to develop a new directional microphone that is immune to extraneous sound inputs that are outside the microphone's forward detection lobe, i.e., there is a zero backsideresponse. The microphone is comprised of a small parabolic reflector (20-40 mm diameter) that focuses the incoming sound onto a small (1-3 mm diameter) spherical receiver. Preliminary calculations indicate that such a parabolic reflector-baseddirectional microphone will have an excellent directional response characteristic (forward detection response of 21 degrees FWHM) and will have an estimated sensitivity of about 2 x 10-3 Pa (20 db on the acoustic scale). Experimental measurements will bemade to verify these calculations and various designs will be evaluated in order to realize optimum performance of the new miniaturized directional microphone. Various methods of encapsulation for ruggedizing the device for military applications will bestudied. The miniature directional acoustic sensor has numerous military and industrial applications. Military uses include surveillance, location of vehicles, water craft, or sniper fire, command and control, and nondestructive evaluation. Commercialapplications include sensitive hearing aids and inspection of processing equipment and machinery. The extreme sensitivity and directionality of the new microphone brings great benefits to each of these applications.