Particle Velocity Sensors

The Microflown sensor, a MEMS-based transducer, has the capability to measure acoustic particle velocity directly. Crafted on silicon wafers using clean room technology, these sensors are incredibly compact transducers. The sensor's core consists of two ultra-thin platinum wires, each 400 thinner than a human hair strand. These wires serve as temperature sensors, with electrical current inducing heat within them. As a result, any local temperature fluctuations influence the wires' resistance. As sound propagates across the wires, it disrupts the temperature distribution around the resistors asymmetrically. This disturbance creates a resistance differential, which generates a broadband signal (ranging from 20 Hz up to 14 kHz) with a figure-of-eight directivity. This signal is proportional to the acoustic particle velocity, providing a precise measurement of this unique acoustic quantity.

The figure-of-eight directivity pattern allows the sensor to selectively measure the particle velocity in a specific direction while mitigating 1/3 of the total sound field. This is particularly useful in situations where there is a high level of background noise or multiple sound sources present.

The vector nature of particle velocity results in different phase information depending on the sound direction of arrival. Sound waves coming towards the front or the back of the sensor are captured with the opposite phase. Unlike with regular microphones, the particle velocity level measured close to a rigid boundary becomes smaller as the sensor approaches the surface, effectively reducing the background noise induced by the target environment.