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Acoustic Resonance Airflow Sensing
What is Acoustic Resonance airflow sensing?Acoustic Resonance airflow Our sensors use this unique operating principle to achieve an unrivalled specification - wide air velocity range, long maintenance-free life, small lightweight construction, and exceptional sensitivity and accuracy. Having no exposed parts, our sensors are environmentally shielded, robust and operate under extreme weather conditions. Acoustic Resonance also provides built-in compensation against environmental factors known to affect other technologies.
What are the features and benefits of Acoustic Resonance airflow sensing?Key Technology Features
Key Product Benefits
How does it work?The following simplified diagram shows the basic Acoustic Resonance airflow sensing arrangement.
In the horizontal plane, the structure is unbounded and air flows freely between the plates. Acoustic (ultrasonic) waves are generated and received by means of three vibrating diaphragms coupled to an equal number of piezo-electric elements. The diaphragms are arranged in a triangular formation. One diaphragm is electrically excited at any one time. Ultrasound is emitted from its surface and travels outwards until it hits the opposite reflector where it undergoes a near total reflection. The resulting wavefront travels back and hits the opposite reflector and is reflected again. Ultrasound continues to bounce between the pair of reflectors and over a narrow frequency band the individual reflections combine in phase to produce a dramatic increase in signal strength. The net wave distribution behaves like a vertical standing wave, and a horizontal two-dimensional radial travelling wave. This dual character of the acoustic field is exploited in the following manner:- Airflow Measurement is based on the Travelling Wave behaviour
The net phase between any diaphragm pair is indicative of the airflow along the axis of the pair. With all three diaphragm pairs measured, the component vectors of the airflow along the sides of the triangle (formed by the diaphragms) are determined. These vectors are combined to give the overall speed and direction. Automatic Compensation is based on the Standing Wave behaviour It is known that the speed of sound in air varies as a function of temperature, and to a lesser extent, humidity and Operation at resonance drastically reduces the undesirable influence of acoustic reflections from nearby objects, aerodynamic effects, e.g. turbulence, and flow non-uniformity. The close proximity of the vibrating diaphragms permits operation at high air speed, and the monolithic construction results in improved accuracy. The selective response at resonance provides a “front-end tuned filter”, dramatically improving the signal to noise ratio. Signal power is kept extremely low, (typically tenths of microwatts) and the operating signature is negligible. As long as resonance is maintained, the relationship between air speed and measured phase is linear.
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sensing is a patented method for measuring wind speed and wind direction. As the name implies, the technique uses an acoustic (ultrasonic) wave which is resonated inside a small
cavity.
pressure. The instrument is capable of providing automatic compensation for this undesirable effect without the need for additional sensors. In operation
the acoustic frequency is automatically adjusted to maximise the received
signal and maintain resonance. Under these conditions the indication of the instrument is made independently of the speed of sound.
