Piezoelectric acoustic transducers for electronic telephone sets
Juro Ohga · The Journal of the Acoustical Society of America · 1988
The development of piezoelectric ceramic transducers for the transmitter, receiver, and tone-ringer sounder of recent electronic telephone sets is reviewed. As the first development stage, the working attenuation (WA) was studied as a measure to compare efficiencies of various types of electroacoustic transducers. The conclusions were that WA for electroacoustic transducers, which was defined in a similar way to WA for electrical circuits, could be estimated easily from the specific response for a microphone, and that WA was almost independent from transducer size. Then, it was shown by comparison of WAs that the efficiency of the simplest piezoelectric ceramic transducer using a unimorph diaphragm was as high as that of ordinary electromagnetic or electrodynamic ones. Moreover, a piezoelectric transmitter and receiver needed the same resonant frequency of the diaphragm, because both diaphragms should work in the stiffness-controlled region. Fortunately, their optimum resonant frequency was close to that of the tone-ringer sounder. Therefore, the main problem of the second development stage was how to design acoustical circuits for the piezoelectric transmitter, receiver, and tone-ringer sounder using the same diaphragms. This was solved by introducing a circuit with four degrees of freedom. As a related problem, simplification of transducer structure was also studied.