Editing Anemometer (section)

====Acoustic resonance anemometers====
[[File:Acoustic Resonance Wind Sensor.jpg|thumb|left|Acoustic resonance anemometer]]
Acoustic resonance anemometers are a more recent variant of sonic anemometer. The technology was invented by Savvas Kapartis and patented in 1999.<ref>Kapartis, Savvas (1999) "Anemometer employing standing wave normal to fluid flow and travelling wave normal to standing wave" {{US Patent|5877416}}</ref> Whereas conventional sonic anemometers rely on time of flight measurement, acoustic resonance sensors use resonating acoustic (ultrasonic) waves within a small purpose-built cavity in order to perform their measurement.

[[File:Acoustic Resonance Anemometer.jpg|thumb|Acoustic resonance principle]]
Built into the cavity is an array of ultrasonic transducers, which are used to create the separate standing-wave patterns at ultrasonic frequencies. As wind passes through the cavity, a change in the wave's property occurs (phase shift). By measuring the amount of phase shift in the received signals by each transducer, and then by mathematically processing the data, the sensor is able to provide an accurate horizontal measurement of wind speed and direction.

Because acoustic resonance technology enables measurement within a small cavity, the sensors tend to be typically smaller in size than other ultrasonic sensors. The small size of acoustic resonance anemometers makes them physically strong and easy to heat, and therefore resistant to icing. This combination of features means that they achieve high levels of data availability and are well suited to wind turbine control and to other uses that require small robust sensors such as battlefield meteorology. One issue with this sensor type is measurement accuracy when compared to a calibrated mechanical sensor. For many end uses, this weakness is compensated for by the sensor's longevity and the fact that it does not require recalibration once installed.