Design Of Multiple Frequency Tympanometry On Ear System Based On FPGA

Tympanometry is an objective method to test the function of middle ear.It has been generally acknowledged as a critical tool in clinical otology and audiology diagnosis to improve the diagnostic accuracy of ear diseases.At present,the probe tone for a clinic tympanometry is a pure tone of three different frequency,such as 226 Hz,678Hz or 1000Hz.However,the acoustic immittance can only partly reflect middle ear diseases using single probe tone,because 226 Hz low probe frequency will mainly affect the acoustic stiffness,while probing tone of 678 Hz or 1000 Hz is mainly sensitive to the massive factor in the acoustic immittance.Recent research indicates that if the frequency of probing tone close to the middle ear resonant frequency,the middle ear disease can be fully described,which advocates a new method for the tympanometry with sweep-frequency probing tone to test middle ear function.This paper introduced a design of a multiple frequency tympanometry with the functionality of tympanometry and middle ear resonant frequency detection.The system contains a salve FPGA-based computer and a host computer running a computer program developed by Visual C#.The working process is as follow:1)the slave computer was controlled by the host to change its function pattern,frequency and intensity of probing tone and the air pressure in ear cannel;.2)the data collected by sensors were sent back to the host through serial port in the slave.3)the host computer presents the result and storage the data via a series of analyzing and processing procedures.The whole system contains both hardware and software designs.The rules of hardware design are highly integrated and low noise.According to the different function of circuit,hardware can be divided into probing tone generating part,air pressure controlling part,sound pressure collecting part,FPGA part,power supply part and the host computer.The software of the system contains FPGA program design and host computer program based on Visual C#.Adopting from top to bottom modular design method,FPGA program contains top modular,control modular,PLL modular,AD transfer modular,serial port modular,driver control modular,probing tone generating modular.According to different functions,the program of host computer includes serial communication modular,testing pattern modular,data analyzing modular and data administrating modular and so on.The testing results for this system justifies the feasibility,stability and repeatability of the design by experiments which are the frequency test of probing tone,tympanometry and middle ear resonant test.The consisting and stable results are in line with the theoretical analysis indicating the correctness and reliability of the designed system.