Determination of the sensitivity behavior of an acoustic, thermal flow sensor by electronic characterization

The microflown is an acoustic, thermal flow sensor that measures sound particle velocity instead of sound pressure. It is a specific example of a wide range of two- and three-wire thermal flow sensors. For most applications the microflown should be calibrated, which is usually performed acoustically in a standing-wave-tube. Here, it is shown that the sensor’s sensitivity and frequency behavior can be determined electronically as well, and an electronic method for determination of the device output response, which is more convenient, is therefore presented. The method is not only less complicated, but also makes it possible to cover easily the entire acoustic frequency spectral range. The method is shown to be geometry-independent, and it can be applied for a wide range of thermal flow sensors, even for those consisting of more than two wires. The method is based on a general relation following from the heat transfer theory. This relation does not depend on the precise geometry of the sensor. The theory has been experimentally verified for various thermal flow sensors of different geometries, up to approximately 10 kHz, and a good correspondence between measurements and theory was found.