| Cochlear implant, an auditory prostheic which could stimulate auditory nerve cell is currently the only solution to the patients with total deafness and is an electronic device with higher technology in the bionics.Weak electric current pulse in electrode that cochlear converts from acoustic mechanical vibration energy stimulate the auditory nerve fibers. The process spreads auditory nerve pulse to the brain and forms a hearing through simulating auditory function. Currently, medical institutions in the countries take cochlear implant as a conventional treatment for severe hearing loss or severe deafness, and the number of patients with cochlear around the world has amounted to more than10million.For people with normal hearing, the vibration of the sound waves are collected with the auricle through the external auditory canal to the tympanic membrane then to the inner ear perilymph with the leverage of ossicles, cause the vibration of the basilar membrane at last. Cilia swing on basilar membrane’s hair cell produce the membrane potential change which release thereby the neurotransmitter. The neurotransmitter causes a potential change on auditory nerve endings at the base of the hair fiber. Such potential changes transmitted by the central spiral ganglion cells resulting in hearing. Sensorineural hearing loss patients have varying degrees of hair cell lesions or reduced. However there still retains a certain number of auditory nerve fibers and spiral ganglion cells. So it could be restored by electrical stimulation.Cochlear implant, also known as the "bionic ear", is a prosthetic device developed on an in-depth understanding of the human hearing system. To imitate the physiological function of the peripheral auditory system such as a normal outer ear, middle ear, inner ear by a special mean, cochlear implant directly stimulate the residual auditory nerve fibers instead of the function of the inner ear cells which pathological change take place. Then people regain hearing.Cochlear implant consists of two parts:the speech processor in vitro and implant in the body.They are wirelessly linked to electromagnetic coupling and no direct wire connection between in vitro and in vivo. Speech processing apparatus comprises:a microphone for voice collecting, the analog-digital conversion circuit, an encoding circuit, a radio frequency transmitter circuit, and a power transmission circuit. The implant includes a radio frequency receiver, a energy receiver, a decoder and the stimulating electrodes. The speech signal is encoded and modulated at speech processing apparatus first according to ear coding principle, then transmitting to the implant through RF. After receiving the speech signal, the decoder analysis it and then encodes the n-channel electrodes for stimulating the auditory nerve fibers.Cochlear implant is the most successful application of modern technology in the field of medical science. With the maturity and stability of cochlear implant technology, deafness patients are more and more favour of cochlear implant which helps deafness patients of all ages re-establish hearing and improve the quality of life. Different groups benefit from the high technology about cochlear implant.Mainstream cochlear companies in the world come from abroad. Such as Advanced Bionics Corporation in America, Its representative product is HiRes90K; MED-EL in Austria, Its representative product is PulsarCI100; and Cochlear in Australia, Its representative product is CI24RE. The biggest problem of these three products in our clinical application of Chinese is low recognition rate and expensive.Cochlear research started relatively late in our country, in recent years, some domestic researchers have set out to build artificial cochlear hardware development platform. The main research focus on three aspects:First, set up to provide speech algorithm processing acquisition and processing of cochlear speech acquisition platform; Second, design a kind of ability of transcutaneous energy transmission power source; Third, Circuit design of the implanted stimulation.In2006, Cao Yuzhen proposed a design of inductive charging, using the electromagnetic induction principle for transcutaneous energy transmission.In2008, Meng Li.etc designs an electronic cochlear speech processor in vitro based on general DSP. The processor can effectively deal with speech signal, but the efficiency is very low.In2009, Wang designed an electric current pulse exciting way of cochlear implants stimulate circuit in the body, which dedicated to16channels. The chip can stimulate a bipolar current of16channels, electrode will be short circuited through the switch when without current stimulation, which can discharge the imbalance of charge on the electrode, so improving the security of the stimulus. NiuShuai of Shanghai JiaoTong University in his master’s degree thesis, puts forward a kind of wireless micro-current nerve stimulation system suitable for neural interface based on SimpliciTI. A special micro electric current nerve stimulator used in his design. Yingdeng Li’s articles published in the international journal of biomedical engineering design an electrical stimulator of bipolar output and the protection circuit, which realizes bipolar output by combine DAC of one-way control with op-amp circuit, has a good simulation effect. In2011, Tian Liangyang in Shanghai jiaotong university, in his doctoral dissertation on transcutaneous energy transmission system closed-loop control method has carried on the system research, through the simulation and experiment show that the design of class E amplifier can make the transcutaneous energy transmission under the condition of certain parameters change secondary output voltage constant, but the efficiency is low, vulnerable to interference.In2013, Zhang Shuwei and others designs a kind of cochlear speech processor based on DSP, which adopts double microphone accept voice input adaptive denoising technology, can be better to eliminate the noise in the speech signal.The literature suggests that, in recent years, the domestic hearing science researchers began to bold attempt at the beginning of the cochlear hardware platforms. Based on summarizing the existing technology, the paper launches a series of research for the artificial cochlear hardware platform design:In this paper, Firstly, simulate the coding strategy of CIS with MATLAB, which is international mainstream for cochlear implants. The preprocessed voice through the8bandpass filter, and then obtain the amplitude envelope extraction (A1,A2,..., A8). Finally, by envelope nonlinear compression to stimulus frequency mapping of auditory nerve cells. CIS strategy using pulse phase modulation, at the same time only one channel stimulation is selected, it can avoid the mutual interference of different channel between the electrodes. In general, stimulation rate selection scheme ofCIS900Hz.Secondly, the analog front end audio acquisition acquisition circuit and wireless communication circuit is designed, the experimental results show that the circuit anti-interference ability, low power consumption.Once again, especially the problem of cochlear energy supply, on the transcutaneous energy transmission simple modeling, and gets the part parameters coupling coil transcutaneous energy transmission design, summarizes the design methods to improve the efficiency of the energy transmission. Based on the design of a wireless energy transmission circuit, measured by the experiment, the circuit can output5V voltage and small fluctuation stability in the range of primary, secondary coillcm.Finally, cochlear hardware platform transplant from the MATLAB platform, CIS algorithm to build, through debugging results can be seen, cochlear processing result is consistent with the simulation results.In this paper, based on the design of transcutaneous energy transmission of cochlear, can satisfy the voice pick-up, the basic algorithm processing, wireless communication and decoding stimulation function. In the design of a body worn artificial cochlea, an audio acquisition module, voice processing module, wireless transceiver module, every module of transcutaneous energy transmission and implant module. Each module circuit chip select the relatively high-end commercial chip project implementation, and the whole design process will be low power consumption as the basic criterion system design. In the design of BTE cochlear implants, to ensure the minimum volume, the lowest quality principles, to meet the premise of speech signal processing system is normal, the design of a worn on the ear hanging micro cochlear, and real-time processing results of speech algorithm. |
PDF Full Text Request