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Kaijie Wu, Xinyu Chai, Qiushi Ren, Yun Gu, Xuping Lei; A Self-adaptive Wireless Transmission System Based on Visual Image Information For Visual Prostheses. Invest. Ophthalmol. Vis. Sci. 2012;53(14):291.
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The tread for enhancing the resolution of visual prostheses is to increasing the channels of neural stimulator. However, the power dissipation due to the electrode impedance of numerous channels will be also increasing inevitably. In fact, the power dissipation varies greatly with the complex of visual image. A novel self-adaptive RF system was designed to calculate the power requirement of neural stimulators based on the analyses of visual image information, and then transmit optimal power to internal micro-stimulator of visual prostheses.
We developed a demonstration system combining image processing circuits, a Class E power amplifier and power-controlling circuits. Visual images were captured by a micro camera and processed into ones with low resolution and low gray level in a DSP using information-minimizing strategies. Then the processed images were encoded into data about amplitude and frequency of pulse current on each channel. Based on these data information and impedances of electrodes, power dissipation of a neural stimulator could be evaluated. According to evaluated power dissipation, power-controlling circuits adjusted the power supplier of the Class E power amplifier to change transmission power.
This wireless transmission system controlled its adjustable power supplier from 5V to 10V, providing a maximum power of 500mW. Based on analyses of visual image encoding, output power of the wireless transmission system changed obviously, timely and effectively. Overall transmission efficiency of the system, defined as rate of received micro-stimulator power to emission system power, remained steady.
This self-adaptive system provided a novel method to adjust transmission power for micro-stimulator in visual prosthesis. Results showed that the RF system timely switched transmission power and thus maintained high transmission efficiency, which promoted usage duration in portable applications. This system was especially applicable to visual prostheses with large-scale micro-electrode array.
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