MEMS Acoustic Sensor for High SPL Measurement and Launch Vehicle Applications

Acoustic Sensors is a device, which can monitor physical, biological, and chemical stimulus by producing an electrical signal. The miniature acoustic sensor developed so far have focused primarily on hearing aid applications and therefore, most of the researchers concentrated on acoustic detection only in a limited audio range.

Moreover, the measurement of high sound pressure level is an important requirement for aerospace applications because sound pressure produced by launch vehicle and large booster rocket can cause fatigue of metal panels and structures. CSIR-CEERI has developed a MEMS-based acoustic sensor for high sound pressure level (SPL) generated during Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV) launching. The developed MEMS acoustic sensor chips have been delivered to Vikram Sarabhai Space Centre (VSSC), Indian Space Research Organization (ISRO) Thiruvananthapuram for their PSLV/GSLV missions. The sensor is used for monitoring the acoustic levels generated during the launch of a satellite launch vehicle. It is the first indigenously developed MEMS technology based sensor flight-tested in an Indian Launch Vehicle and has operational heritage of 12 successive PSLV flights.

The structure consists with a piezoelectric zinc oxide layer, sandwiched between two aluminum electrodes on a thin silicon diaphragm. The pressure compensation in the developed acoustic sensor is achieved by using a micro-tunnel development in the structure. The measured sensor outputs such as sensitivity, sound pressure level range and bandwidth were found to be 380 mV/Pa, 120 dB to 180 dB and 30 Hz to 8 kHz respectively. The developed acoustic sensor is a substitute of imported sensor for high SPL measurement and can also be used as a microphone. It is an emerging need of high volume consumer communication device manufactures that are looking for acoustic sensing with the unique combination of high performance and low manufacturing cost. The markets and applications for this sensor include aero-space, defense and societal impact such hearing aids and medical applications etc.