Research Of The Multichannel Wireless Telemetry Technology For Visual Cortex Prosthesis

Blindness has become a major disease which seriously endangers the life quality of all mankind, and there are about 500 million legal blind people in China causing great loss of hundreds of billions every year. Neurological blindness inducing eye diseases have the common characters of retina and optic neuropathy and are eventually showed as information conduction disturbances at all levels of neurons of retina, thereby affecting the final output of visual information, and senior visual centre could not receive the normal visual signal, thereby leading to vision loss of patients. Therefore, the development of an implantable prosthesis capable of completing visual repair has practical significance and potential applications in the engineering technology and clinical applications. Currently, restoration of visual function based on nerve electrical stimulation can be divided into three types: retinal repair, optic nerve repair, and visual cortex repair. Wherein visual cortex repair is an external electrical stimulation nerve prosthesis which is developed through MEMS technology and processes through retina and optic nerve whose bypass already has lesions, the method achieves the purpose of visual rehabilitation through utilizing micro-electrode array stimulation visual cortex arranged outside endocranium or skull.The working principles of visual cortex false body are as the follows: Firstly, the in vitro image sensor captures image information, sends the information to a signal processor for processing and coding into electrical signals, the signals are transferred to an in vivo implanted device through an energy and signal transmitting device to enable the micro-electrode array to produce electrical pulses to stimulate the visual cortex to produce vision. As an important part of visual cortex false body, the signal transmitting device can effectively finish in vivo and in vitro data exchange tasks and adopts cable transmission and radio frequency wireless transmission, and the transmission signals can be single-channel signals and can also be multi-path signals. However, since the infection risk of cable transmission is considerable, wireless minimally invasive technique becomes the focus of the study in recent years, at the same time, a mature false body needs to form stimulation on multi-point positions of visual cortex, and thereby multi-path signal transmission also has become necessary. This paper presents a design scheme of a multi-path wireless signal transmission system based on visual cortical false body. The multi-path wireless signal transmission system is divided into an in vivo part and an in vitro part, a frequency division multiplexing technique is utilized to finish wireless transmission of multi-path signals on a single channel (ie, a set of coils) (with signals of two paths as example). The circuits of two paths of signals are basically the same, thereby greatly reducing the complexity of the system; the paper innovatively adopts in vivo passive design in order to prevent bringing damages to the in vivo implanted part, thereby greatly reducing the damages of implanted body on human bodies.Main contents of the research program include the following: Firstly, the design of in vitro transmission circuits of the multi-channel wireless signal transmission system; the design of this part aims at demodulating signals processed through encoding onto carrier waves of different frequencies and transmitting into bodies wirelessly, and the part is composed of four parts of a carrier frequency signal generator, a modulator, a combiner and a high-frequency power amplifier. Wherein the carrier frequency signal generator uses a crystal oscillator circuit to generate high frequency electromagnetic waves, modulation circuit uses MC1496 for amplitude modulation (AM), while the combiner aims at combining two paths of modulated signals into a path of signals through utilizing a summing amplifier, the signals are amplified through the high-frequency power amplifier and are transmitted into bodies through transmitting coils. Secondly, the design of the in vivo receiving circuit of the multi-path wireless signal transmission system adopts passive design. The role of circuits in this part is to sense signals sent in vitro through receiving coil coupling, and then two paths of primary signals are demodulated to be transmitted to a stimulation electrode. The circuits of the part are composed of a splitter and a demodulator. Wherein the splitter uses a passive LC bandpass filter, it can divide signals coupled by the receiving coil into two. Compared with in vitro AM modulation modes, the demodulator adopts the diode peak envelope detector for demodulation. Thirdly, circuits of each part can accept simulation experiments through multisim 10.The paper has the innovation points that: firstly, frequency division multiplexing technique is used to finish transmission of two paths of signals on a single channel and to expand two paths of signals into parallel transmission of multi-path signals. Secondly, in vivo passive design is innovatively used, thereby greatly reducing the damages of the in vivo implanted device on the human body.It is proved that the multi-channel wireless signal transmission system can conveniently obtain two paths of demanded signals with less distortion and feasibility through simulation experiments. The in vivo circuit has simple design and can be extended and applied on the signal transmission parts of all visual prostheses.