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Show 163 THE UNIVERSITY OF UTAH RESEARCH POSTERS ON THE HILL 2012 METAMATERIAL MINIATURIZATION FOR BIOMEDICAL DEVICES Katie Furse (Gianluca Lazzi) Department of Electrical and Computer Engineering University of Utah In this project, we investigate metamaterials to improve the efficiency of a wireless power transmission coil used in a retinal prosthesis that restores eyesight to people blinded by degenerative eye disorders. Metamaterial Miniaturization for Biomedical Devices Katie Furse, Dr. Gianluca Lazzi, and Dr. Ajit Rajagopalan Department of Electrical Engineering In a healthy eye, electrical impulses help us see. Electrical impulses are created by the retina and interpreted by the brain to form an image. Degenerative eye disorders may prevent the retina from producing electrical impulses, though the brain can still interpret the impulses. The anatomy of the eye is shown in Fig. 1. Katie Furse Dr. Gianluca Lazzi In a retinal prosthesis, a camera picks up the image, and wireless electronics transmit information from the image to electronics implanted at the back of the eye, where they can stimulate the brain with the missing electrical impulses based on this image as shown in Fig. 2. Fig. 2. Epiretinal prosthesis setup (from [2]) A metamaterial is a material with a negative refractive index that can be used to focus the power from the coil. This improves coupling and thus efficiency [4]. The metamaterial is placed between the coils as shown in Fig. 3. Fig. 3.Power transfer system with metamaterial We need a metamaterial that is small and works at 10 MHz. This low frequency usually requires larger devices, so the largest challenge is miniaturizing the metamaterial. Addition of capacitors: -Frequency reduced to around 15-20 MHz Combination/rotatio n: -Frequency reduced to 12MHz - lowest found so far Parameter extraction is an equation that checks the metamaterial properties at different frequencies. Because we want a metamaterial, this means = -1, as shown in Fig. 3. Want = -1 If is not -1 at the desired frequency, the metamaterial will not increase coupling or efficiency. Conclusion Metamaterials can improve efficiency of wireless power coupling for implantable medical devices. Further testing of our design will be done in Spring 2012. Fig. 3. Paramater extraction Spiral resonator vs. split ring resonator: -Split ring resonator -Spiral resonator Increasing outer turn lengths: -Not a significant decrease in size/frequency [1] S. DeMarco, G. Lazzi, W. Liu, J. Weiland, M. Humayun, -Computed SAR and thermal elevation in a 0.25-mm 2-D Model of the human eye and head in response to an implanted retinal stimulator- part I: models and methods‖, IEEE Transactions on Antennas and Propagation, Sep. 2003 [2] E. Strickland, -The birth of the eye‖, IEEE Spectrum, Jan. 2012 [3] B. Wang, T. Nishino, K. Teo, -Wireless power transmission efficiency enhancement with metamaterials,‖ Mitsubishi research report, Sep 2010 [4] J. B. Pendry, -Negative refraction makes a perfect lens," Phys. Rev. Lett. 85, 3966 (2000) Dr. Ajit Rajagopalan Abstract The Eye's Electrical Functions Retinal Prosthesis Metamaterials for Higher Efficiency Metamaterial Designs Parameter Extraction Conclusion References Device Efficiency Efficiency of power transfer in the wireless system is a concern with implantable electronics. Higher efficiency would increase the battery life of these devices. The current two-coil wireless transfer system has an efficiency of 20-30% [3]. An additional 70-80% of the power is lost into tissue. It has been shown that metamaterials (a man-made Fig. 1. Epiretinal prosthesis and the eye (from [1]) material with a negative refractive index) improve coupling in a two-coil system. Metamaterials are a fairly new phenomenon. Little is known about the materials at lower frequencies required by biomedical devices. This research investigated the use of metamaterials to improve an already-developed retinal implant system that restores sight to patients blinded by degenerative eye disorders. An increase in coupling means higher e ciency of the system, and thus more signals are transmitted to the coil on the implanted device and the battery powering the signal is drained less, making the implant more accurate with a longer battery life. The metamaterial is placed directly outside the head in order to set it between the two coils, so it is important that the metamaterial be a small enough that the patient will not be bothered by it. This research investigates not only the behavior of the metamaterial but miniaturizing the material for biomedical applications. The metamaterial is miniaturized by adding length, investigating di erent kinds of metamaterials, adding capacitance, and by di erent dimensions of metamaterial cells. This research has found that increasing the outer lengths of the metamaterial produces minimal e ects for miniaturizing the material, but that a spiral resonator with added capacitances makes a critical di erence in the size of meta-material. Multi-dimensional simulations haven't been completed yet, but it is expected that the material will be miniaturized even more with a 2-dimensional, rather than 1-dimensional, material. Later in the project the material will be fabricated and tested in a two-coil system for accuracy of experimental results versus simulated results and to verify that the metamaterial is working properly. Researching metamaterials for bioapplications not only investigates a fairly unknown material, but also may improve already cutting edge technology for restoring sight to the blind. |