Study Of Core Fixing And Rectangle Cantilever Structure Piezoelectric Bone Conduction Hearing Aid Devices

In recent years, with the development of the new materials, piezoelectric materials have being used in more and more fields, the advantages of piezoelectric materials have presented in some aspects, so people begin to pay more attention to the application of the piezoelectric materials. Based on the program of the Ji Lin province technology development plan of"study of the piezoelectric bone conduction hearing aid devices `principle and key technology",this article combine converse piezoelectric effect with bone conduction theory to develop a sort of piezoelectric bone conduction hearing aid. The article has analyzed and researched the construction of the earphone and piezoelectric oscillator which is the most important part of the earphone, and the amplifying circuit is also designed elaborately. The main content of this article is as follows:1. The application and research condition of the bone conductionThe technology of bone conduction mainly applies in the fields of bone conduction earphone,bone conduction mobile etc, and most of them are driven by the electromagnetic force, the force will make vibration ,so the information can be conducted through the bone. At present, the current study abroad on bone conduction is much earlier, and some products have been sold in the market, but the research of piezoelectric bone conduction devices is little. The study domestic on bone conduction just at the starting stage, but people have paid more and more attention to the bone conduction, and the future of the bone conduction is though to be amazing.2. The theoretical research of the piezoelectric bone conduction hearing aidThe principle of the bone conduction hearing aid is: a mike gets the sound signal from outside, and translates it into an electrical signal, then the signal is amplified by the amplifying circuit, the amplified signal makes the piezoelectric oscillator to vibrate, then the vibration conducted to the hearing system through the skull. This article first described the construction of inner ear,tympana,auricle and process of the hearing. Then researched the conduction of the sound wave and auditory threshold of people. Piezoelectric oscillator is the most important part of the bone conduction hearing aid devices, this article has analyzed the piezoelectric effect,piezoelectric ceramic,parameters of the piezoelectric ceramic,vibration modal and resonance characteristics of the piezoelectric oscillator ,and deduced the theoretical mode of the cantilever beam piezoelectric oscillator, the equation of cantilever beam piezoelectric oscillator`s resonance frequency gives directly. It also researched the working process and performance index of the hearing aid at last. 3. The finite element analysis and experimental research about piezoelectric oscillator of the piezoelectric bone conduction hearing aid devicesModeling piezoelectric oscillator in the software of ANSYS, then analyze the statics and mode of the piezoelectric oscillator in different fixing ways, including rectangle cantilever fixing,rectangle two sides fixing,circular periphery fixing,circular core fixing and circular freely-supported fixing ways. Comparing these fixing ways, choosing rectangle cantilever fixing and circular core fixing as the final fixing ways of the piezoelectric bone conduction hearing aid device. Changing the voltage which add to the piezoelectric,the diameters/lengths and depths of the piezoelectric ceramic and copper plate, noting the displacement of piezoelectric oscillator at every condition. Next, changing the diameter/length and depths of the piezoelectric ceramics and copper plate, testing the response of frequency at different condition. Doing experiments about the displacement distribution of the piezoelectric oscillator which fixed in the rectangle cantilever and circular core ways. For the piezoelectric oscillator of circular core fixing, add some block of different mass on it, observing the tendency of the first resonance frequency which will be changed, and the results indicate that the block can reduce the first resonance frequency of piezoelectric oscillator, the heavier the block is, the lower the first resonance frequency is.4. The construction design and experimental research on the piezoelectric bone conduction earphoneWith the purpose of function and beauty, in this article , the upper cover,upper supporter,epivalve,hypotheca,fulcrum bearing,contact film and conduction pillar of the two piezoelectric bone conduction earphones have been designed. As to test the performance of the piezoelectric bone conduction earphone, this article fist test the impedance of common earphone,electromagnetic bone conduction earphone,rectangle cantilever piezoelectric bone conduction earphone,circular core fixing piezoelectric bone conduction earphone , the results indicate the two piezoelectric bone conduction earphone have large impedances, so the power consumption of piezoelectric bone conduction earphone is very small. Then choose the signal at different frequency and the signal of human`s sound to make this four earphones produce sound, and then test the value of the sound pressure of them, the results indicate that both the two piezoelectric bone conduction earphone can satisfy the requirement of human hearing at normal frequency .5. The design and experimental research of the amplifying circuit of the piezoelectric bone conduction hearing aidThe signal from the mike is very weak, and it is not strong enough to make the earphone vibration, so the signal need to be amplified. Compared with the separation circuit, integrated circuit has some advantages, such as smaller volume, smaller power consumption, longer utility time, higher reliability etc, so this circuit chooses the integrated circuit TDA2822 as the main part of the amplifying circuit, then choose other discrete elements make up the whole amplifying circuit. Simulating the amplifying circuit in the software of the Multisim, and then doing experiments to test the performance of the amplifying circuit, which including the magnification times and whether there is a distortion about the output waves, the result is satisfactory.