Abstract:

The PANEL (Piezoelectric Acoustic Noise ELiminator) transducer was developed for air acoustic noise cancellation in the frequency range of 200--1000 Hz. It has a thin panel structure, occupies less volume, and is lighter than an equivalent electromagnetic transducer. This device consists of a U-shaped configuration of piezoelectric bimorph and unimorph actuators bridged by a triangular amplifying diaphragm, which acts as an effective source of the sound radiation into air. The role of the diaphragm is twofold: it amplifies by a factor of 5--20 the tip displacement of the piezoelectric actuators and it also increases the sound emitting area. Amplitude of the vibrations and usable frequency range of the transducer depend on the dimensions and material of the actuators and diaphragm. The overall dimensions of the device fabricated were 52x50x24 mm. Soft PZT ceramics were used. The diaphragm was made of a carbon fiber reinforced composite. The diaphragm vibrations reach 500 (mu)m rms well below the fundamental resonant frequency of bending vibrations which lies between 200 and 500 Hz. Above resonance, the amplitude of vibrations gradually decreases to 25 (mu)m rms at 1000 Hz. The experimental results indicate that the transducer developed is promising as a sound transmitter for acoustic noise canceling devices.