Bone Conduction Characteristics Of Ultrasonic Acoustic Analysis And System Design

People has began to study characteristics of the Bone-Conducted Ultrasound (BCU) with human hearing tests since it was found that people can perceive the ultrasound through the bone conduction. The BCU has several medical applications, among which the Bone Conducted Ultrasonic Hearing Aid (BCUHA) is the most important one. The BCUHA can help those hearing impaired persons with sensorineural hearing loss and some profound hearing loss who can not restore their hearing with the traditional hearing aid. However, the performance of this new hearing aid is not quite favorable. Meanwhile, as the underlying perception mechanism of the BCU is unknown yet, it is difficult to improve the hearing aid directly and effectively from its principle.This dissertation is aimed at improving the performance of the BCUHA by studying characteristics of the BCU. The study can be divided into three aspects: the computer modeling, the hardware design and the human psychoacoustical test. In the computer modeling, the Finite Difference Time Domain (FDTD) method is used to calculate the acoustic field in the human head model to simulate the transmission of the ultrasound. By comparing with the bone conducted audible sound, new characteristics of the BCU are obtained. Then, guided by the principle of the BCUHA, a BCUHA device based on the Digital Signal Processor (DSP) system is developed. With this device, a few sets of psychoacoustical tests are conducted to study more about characteristics of the BCU. Several methods have been proposed to improve the performance of the BCUHA.Simulation results show that the bilateral BCU hearing doesn't have the space perception ability as the common binaural hearing, while the unilateral BCU stimulus can stimulate both cochleae. The study indicates that the unilateral BCUHA may perform better than the bilateral one. Meanwhile, results in psychoacoustical tests show that most subjects can perceive the high-frequency pitch of the ultrasound and part of subjects can discriminate different audible signals modulated onto the ultrasonic carrier. In addition, this dissertation also estimates the demodulation type of the BCU and the best choice for the ultrasonic carrier frequency. It is hoped that these results can help to further improve the performance of the BCUHA.