Ultrasonic Air Transducers Research Articles

Electrostatic solutions for a capacitive ultrasonic air transducer with a uniformly V-grooved backplate

Abstract Electrostatic solutions for a capacitive ultrasonic air transducer (CUT), consisting of a uniformly V-grooved backplate and a conductive membrane, are presented. The electric field and charge distribution of a membrane-V-groove element are modelled using two approximation methods. The distribution illuminates the background of non-linear effects in CUTs. The solutions also give the capacitance of the transducer. The calculated capacitance values compare well with the measured values.

Photoacoustic testing of ultrasonic air transducers

The use of sound from laser-induced, dielectric-breakdown-generated transient plasma as a signal for testing ultrasonic air transducer reception response was studied. The test signal takes the form of an acoustic impulse that is caused by the rapidly expanding plasma. The ultrasonic air transducer's receiving response and relative sensitivity can be quickly characterized using this method. The advantages that this method offers are speed and the fact that no calibrated wideband signal source is needed. Therefore it would be suited for fast, on-line mass testing of air ultrasonic transducers.

Micromachined 1–3 composites for ultrasonic air transducers

Airborne ultrasound has many applications, such as robotic sensing, NDE, and gas flow measurements. Coupling of ultrasound into air from plane piston piezoelectric transducers is inefficient because of the large impedance mismatch between the piezoelectric and air, and the lack of appropriate matching materials. Standard design practice requires the use of a matching layer material with an acoustic impedance of approximately 0.02 MRayls and a thickness of a quarter-wavelength. Such materials are not readily available. A method to manufacture low impedance materials using micromachining techniques for matching piezoelectrics into air are presented here. These materials are capped 1–3 composites of air and Kapton(R). The acoustic effect of the cap is significant and necessitates a modified design technique. This technique involves the use of two matching layers with inverted acoustic impedances. Using the new fabrication technology and the new design technique, an 860-kHz transducer was fabricated with a one-way insertion loss of 17 dB and a fractional 3 dB bandwidth of 6%. It is believed that, using this technology, a transducer with a one-way insertion loss of 10 dB and a fractional bandwidth of 10% is possible.

A Helmholtz resonator model for an electrostatic ultrasonic air transducer with a V-grooved backplate

Abstract A model for the resonance frequency of an electrostatic ultrasonic air transducer with a uniformly grooved backplate is described based on the Helmholtz resonator theory. The resonance frequency of the transducer can be determined from the shape and dimensions of the backplate's grooves and the membrane's characteristics. In the case of a V-grooved backplate, the depth of the groove and the mass per unit area of the membrane are the parameters that determinate the resonance frequency. Experimental results suggest that the tension of the membrane seems to have only a very weak influence on the resonance frequency.