Index of content:
Volume 130, Issue 2, August 2011
- TRANSDUCTION 
130(2011); http://dx.doi.org/10.1121/1.3605561View Description Hide Description
A semicylindrical acoustic transducer was constructed using a dielectricelastomerfilm with compliant electrodes that is an electroactive polymer composed of a polyurethane elastomer base and polyethylene dioxythiophene/polystyrene sulfonate electrodes. The use of this dielectricelastomer is advantageous because polyurethane is a common material that keeps its shape without any rigid frame. Because the dielectricelastomerfilms are essentially incompressible, electric-field-induced thickness changes are usually translated into much larger changes of the film area and side length. Here it is proposed that this change in side length can be utilized for sound generation when the film is bent into a semicylindrical shape. Accordingly, a semicylindrical acoustic transducer was fabricated using a film of thickness of 300 and its acoustic characteristics were investigated. The transducer can be operated at low applied voltages by reducing the film thickness, as long as the film is thick enough to generate sufficient force to overcome sound radiation impedance. The second harmonic distortion of the transducer was also investigated as a function of the ratio of the direct current bias voltage to the alternating current audio signal amplitude.
130(2011); http://dx.doi.org/10.1121/1.3593364View Description Hide Description
The current study considers piezoelectric ceramic electromechanical transducers utilizing axisymmetric vibrations of complete and incomplete spherical shells. Analysis is focused on generating the modes of vibration that can be employed in the design of multimode unidirectional electroacoustic transducers for underwater applications and on determining the electrode configurations that achieve optimal electromechanical coupling for the different modes of vibration considered. Analytical expressions are presented for the modal and intermodal equivalent parameters characterizing the energy state of the shell vibration. Results of calculation and experimental verification of the resonance frequencies and effective coupling coefficients for different modes of vibration of the complete and incomplete spherical shells are in good agreement.