Acoustic Vector Sensing

Undergraduate Research by Ian Beil and Evan Nixon

Top: AVS

 

Bottom: Magnified view of heated platinum strips

(both from microflown.com)

Acoustic Vector Sensors

The sensors we are using in our experiment are called Ultimate Sound Probes and are manufactured by Microflown Technologies (microflown.com). One sensor integrates one pressure microphone with three orthogonally placed particle velocity sensors. This enables three dimensional measurements of a sound field. The sensors are responsive to particles under a very broad bandwidth (2 Hz – 20 kHz).

 

The sensors used in the USP work by measuring the velocity of air across two very thin strips of platinum that are heated to 200°C. The sensors thus do not measure fluctuating pressure but instead measure air particle velocity. The strips work by measuring their temperatures. When air passes by the first strip it cools it and heats the air that passes it. This air then cools the second strip (it will still be less than 200°C), but by a lesser degree. This produces a temperature difference and changes the electrical resistivity of each wire. This creates a voltage difference that is proportional to particle velocity.

 

Each sensor does not respond equally to varying frequencies, so each has been calibrated by the manufacturers using a response model. This

mathematical model is applied in a data conditioner unit and gives the sensor equal response over a wide range of frequencies.