HIM electronic and conventional sensors and devices for determining wind speed using the ultrasonic method
A recent development in the field of ultrasonic wind measurement is based on acoustic resonance . While conventional ultrasonic anemometers are based on measuring the time of flight, wind sensors with acoustic resonance reflect an ultrasonic wave in a small cavity.
Measuring principle of acoustic resonance (ultrasonic anemometer)
In the cavity there are several oscillating membranes which generate and receive acoustic ultrasonic waves. The repeated reflection between the reflectors generates a quasi-standing wave perpendicular to the wind direction and a transverse wave parallel to the wind direction. If air flows along the axis between the reflectors, this affects the propagation speed of the wave and creates a phase shift, which is measured. To compensate for changes in the speed of sound, for example due to temperature changes, the ultrasonic frequency is continuously adjusted so that the cavity is operated in resonance. This makes the measurement of the air velocity independent of the variable sound velocity.
From successive measurements of different pairs of membranes, the vector components of the air flow can be determined and thus the wind speed and direction can be mathematically calculated.