A calibration method for bone conduction transducers using electrical input impedance

The output energy transferred from bone conduction devices (BCDs) highly depends on the impedance match between the BCDs and their loads. However, current clinical calibration methods normally ignore individual impedance differences and therefore do not accurately assess the output force of the BCDs at the subject’s stimulation position. To address this issue, this study proposes a non-invasive BCD calibration method integrating electromechanical modeling and electrical input impedance measurement. The lumped-parameter model subtly fuses the models of demagnetized electrical impedance and mechanical impedance, leading to a better description of BCD’s physical properties. Once these model parameters are determined, measurements of the electrical input impedance can be used to determine the mechanical load impedance, and further the BCD’s output force. Experiments on the Radio Ear B71 showed that this new calibration method can accurately estimate the mechanical load impedance and the output force of B71 in the frequency range of 300–2000 Hz with an average error of 0.7 and 1.0 dB, respectively. It was also found that the B71 wearing status can be monitored by measuring the electrical input impedance. In conclusion, the proposed BC calibration method provides a promising way to calibrate the output and monitor the status of the BCDs non-invasively.