Yuriko Kaneko

Novel air-borne ultrasonic sensor using nanofoam and a laser Doppler vibrometer

We propose a novel airborne ultrasonic sensor, using nanofoam and a laser Doppler vibrometer that can operate over a wide frequency range and provide high sensitivity. Nanofoam is a porous material made by sol-gel process and has low density, low elasticity, and extremely low acoustic impedance. These properties enable nanofoam to take in acoustic energy from ultrasonic waves. In addition, nanofoam has a good optical transmittance. Because optical detection can be much faster than detection period in the sound frequency range, it has been considered that a wideband ultrasonic sensor can be realized by the combination of nanofoam and laser measurement. In this report, we describe fabrication of the proposed sensor and determine its basic properties.

Palm sized airborne ultrasonic sensor with nanofoam acoustic lens and homodyne interferometer

We propose an optoacoustic airborne ultrasonic sensor consisting of a 633-nm He-Ne laser, an Si PIN photodetector, and a sensor head. The device has a sensitivity of 92.7 dB SPL (Sound Pressure Level) for acoustic signal inputs of single 40-kHz pulses, and it exhibits wideband receiving properties because of excluding mechanical moving elements such as diaphragms or voice coils from the sensor. The sensor head, which incorporates an acoustic lens, is made of nanoporous silica in which the sound speed is 50 m/s. Also, it has tapered aperture fields designed to improve its focusing properties and achieve high sound pressure at its focal point, and an integrated Mach-Zehnder homodyne interferometer that translates the pressure into the intensity of optical interference light. The entire device occupies a volume of 65×70×70 mm3. In addition, we discuss the design methods and derive the equations for the acoustic lens. Finally, a strategy to achieve more stable and highly sensitive optoacoustic sensors is also discussed.