Abstract: A sensor (2) is provided, having an acoustic resonator (18) for containing a fluid such as air and at least one transducer (22, 24) arranged to emit an acoustic signal into the acoustic resonator (18) in response to an excitation signal provided to the transducer (22, 24) by an electronic unit (4). The electronic unit (4) receives a response signal from at least one transducer (22, 24), and processes the excitation signal and the response signal to derive the acoustic signal response of the acoustic resonator. The pressure and/or temperature of the fluid may be derived from the acoustic signal response. More specifically, the electronic unit (4) may derive the temperature of fluid inside the acoustic resonator (18) by obtaining the resonant frequencies of the acoustic signal inside the acoustic resonator (18), or may derive the barometric pressure from the acoustic signal response in the vicinity of the fundamental frequency and its harmonics.

Abstract: A sensor (2) is provided, having an acoustic resonator (18) for containing a fluid such as air and at least one transducer (22, 24) arranged to emit an acoustic signal into the acoustic resonator (18) in response to an excitation signal provided to the transducer (22, 24) by an electronic unit (4). The electronic unit (4) receives a response signal from at least one transducer (22, 24), and processes the excitation signal and the response signal to derive the acoustic signal response of the acoustic resonator. The pressure and/or temperature of the fluid may be derived from the acoustic signal response. More specifically, the electronic unit (4) may derive the temperature of fluid inside the acoustic resonator (18) by obtaining the resonant frequencies of the acoustic signal inside the acoustic resonator (18), or may derive the barometric pressure from the acoustic signal response in the vicinity of the fundamental frequency and its harmonics.

Abstract: An anemometer comprises an acoustic resonant cavity 1 between two plates 2 and 3 and open in the direction of flow of a fluid, the cavity having at least one pair of electro acoustic transducers 5 which are energised at an Eigenfrequency to produce a standing wave perpendicular to the direction of flow of the fluid and a travelling wave perpendicular to the standing wave. By using the time delays or phase shifts between the signal energising a transducer and the signal generated by the response of the other transducer the velocity of flow of the fluid can be calculated. Compensation is provided for changes in the Eigenfrequency caused by changes in the environment.