Anhui Bureau of Technical Supervision, Hefei, Anhui 230001, People's Republic of China
Although most conventional transducers are usually regarded as reciprocal at nominal signal level, it is still necessary to ascertain that the presumed reciprocal transducer is indeed reciprocal or possesses sufficient reciprocity in reciprocity calibration practice. A conventional reciprocity check involves a system comprised of the two transducers and the gaseous, liquid, or solid medium and its boundaries. This paper tries to give an absolute method for reciprocity assessment without the need of any other auxiliary transducer. The principle is that if the imaginary part of the electrical impedance of a transducer (i.e., the capacitance for piezoelectric-type or the inductance for electrodynamic-type transducers) varies linearly with its mass load impedance, the transducer is reciprocal. So, the linear correlation coefficient could be considered as a reciprocity index. The theory is applied to evaluate the reciprocity of a piezoelectric and an electrodynamic vibration generator. The coefficients are determined as 0.9915 (at 10 kHz) and 0.9773 (at 1 kHz), respectively. With the data processed by a complex least-square-fitting code [L.-F. Ge, J. Acoust. Soc. Am. 91, 2326 (1992)], the relevant coefficients are adjusted to 0.9987 and 0.9724. Thereupon, the transducers can be regarded as reciprocal at their respective working frequencies. The assessment has been verified by the accurate calibration results.