Acoustic source used for Active Noise Control at low frequency (80 - 250 Hz) is designed and developed by using a piezoelectric ceramic actuator and a flextensional panel diaphragm. In order to reach the vibration magnitude and radiation area needed for high and flat sound pressure level in the low frequency range. Pseudo-Shear Universal (PSU) actuator has been used as the driving part which is a new type of multilayer piezoelectric actuator originated from MRL offering the advantages of large displacement and high blocking force; on the other hand, Carbon Fiber Reinforced Composite has been used as the diaphragm material which provides a more rigid structure than conventional loudspeaker paper. A prototype device was fabricated which has the following characterizations: 40 layers PSU actuator with a compact dimension: 38 mm X 50 mm X 23.6 mm. Two of them are needed for a device. Diaphragm area is 126 mm X 152 mm. At quasistatic condition (5 Hz) and at the 0.84 kV/cm electric field, 344 micrometers displacement could be achieved at the apex of the diaphragm resulted from the flextensional amplifying mechanism with an amplification factor more than 11. The sound passive level in the frequency range 100 - 250 Hz shows better flat behavior than the acoustic sources studied earlier such as Double Amplifier and PANEL air transducers which exhibit a significant reduction of sound pressure level in the low frequency range. By a slight modification, it is likely to make this device in a total thickness of 10 - 15 mm range. High and stable sound pressure level as well as thin flat structure make it much more competitive in the whole area of applications for low frequency active noise control.
Piezoelectric actuators have significant potential for use in smart systems like vibration suppression and acoustic noise canceling devices. In this work, a novel piezoelectric bending actuator CRESCENT was developed. CRESCENT is a stress-biased ceramic-metal composite actuator. The technology involves the use of the difference in thermal contraction between the ceramic and the metal plates bonded together at a high temperature by a polymeric agent to produce a stress-biased curved structure. An extensive experimental investigation of this device in the cantilever configuration was carried out. The tip displacement, blocking force and electrical admittance and were chosen to characterize the performance of the actuator under quasistatic conditions. The device fabricated at optimum temperature exhibits large tip displacement and blocking force and possesses superior electromechanical characteristics to conventional unimorph actuators.
During the last several years novel piezoelectric bending actuators have been developed: RAINBOW, CERAMBOW, CRESCENT, d<SUB>33</SUB> bimorph and THUNDER. A comparative experimental investigation of electromechanical characteristics of these devices along with conventional d<SUB>31</SUB> bimorph and unimorph actuators was conducted in this work. All transducers were fabricated from soft piezoelectric ceramics. The experimental results show the d<SUB>33</SUB> bimorph and unimorph elements have superior quasistatic characteristics as compared to other type of bending-mode actuators. All these piezoelectric devices demonstrate a significant dependence of electromechanical performance on the magnitude of the driving electric field. It was found that the decrease in the mechanical quality factor and resonant frequency of bending vibrations in d<SUB>31</SUB> unimorph, RAINBOW, CRESCENT (CERAMBOW) and THUNDER with increasing electric field is much smaller than that in bimorph and d<SUB>33</SUB> unimorph actuators. The dependence of the behavior of these devices on the operating conditions governs the selection of a particular device for a specific application.
A new type of piezoelectric air transducer has been developed for active noise control and other air acoustics applications. The transducer is based on the composite panel structure of a bimorph-based double amplifier, that is, two parallel bimorphs or bimorph arrays with a curved cover plate as an active face attached to the top of the bimorphs. The electro- mechanical and electro-acoustic properties of the double amplifier structure and the transducer are investigated in this paper. The displacement of the cover plate of the double amplifier structure can reach millimeter scale with a relatively low driving voltage, which is more than ten times larger than the tip displacement of bimorphs. The sound pressure level (SPL) of the transducer can be larger than 90 dB (near field) in the frequency range from 50 to 1000 Hz and be larger than 80 dB (far field) from 200 Hz to 1000 Hz, with the largest value more than 130 dB (near field). Because of its light weight and panel structure, it has the potential to be used in active noise control.