Abstract
This work focuses on the optimization of coupling coefficient (k) of the inductive link for the wireless power transfer (WPT) system to be used in implantable medical devices (IMDs) of centimeter size. The analytic expression of k is presented. Simulations are conducted by using the high-frequency structure simulator (HFSS). Analytic results are verified with simulations. The receiving (Rx) coil is implanted in the body and set as a circular coil with a radius of 5 millimeters for reducing the risk of tissue inflammation. The inductive link under misalignment scenarios is optimized to improve k. When the distance between the transmitting (Tx) and Rx coils is fixed at 20 mm, it is found that, to maximize k, the Tx coil in a planar spiral configuration with an average radius of 20 mm is preferred, and the Rx coil in a solenoid configuration with a wire pitch of 0.7 mm is recommended. Based on these optimization results, an inductive link WPT system is proposed; the coupling coefficient k, the power transfer efficiency (PTE), and the maximum power delivered to the load (MPDL) of the system are obtained with both simulation and experiment. Different media of air, muscle, and bone separating the Tx and Rx coils are tested. For the muscle (bone) medium, PTE is 44.14% (43.07%) and MPDL is 145.38 mW (128.13 mW), respectively.
Highlights
Implantable medical devices (IMDs) have been widely used in the clinical society, such as cardiac pacemakers, cochlear implants, left vagus nerve stimulators, spinal cord stimulators, retinal implants, and deep brain stimulators [1,2,3,4,5,6,7,8,9]
As a key parameter of the WPT s y s tem, k can be obtained with the relationship k M/ L1L2, where L1 and L2 are the self-inductances of the Tx and Rx coils, respectively, and M is the mutual inductance, which typically depends on the geometries of the two coils, their distance, and the material separating them
For the cmsized IMDs, the operating frequency of a few tens of MHz is good for both power transfer efficiency (PTE) and specific absorption rate (SAR)-constrained PDL
Summary
Implantable medical devices (IMDs) have been widely used in the clinical society, such as cardiac pacemakers, cochlear implants, left vagus nerve stimulators, spinal cord stimulators, retinal implants, and deep brain stimulators [1,2,3,4,5,6,7,8,9]. Ere are several techniques to realize WPT, such as ultrasound, optical, microwave radiation, electric field coupling, and inductive coupling [10,11,12,13,14,15,16,17,18]. Among these methods, inductive coupling is the most preferred for IMDs, where power is transmitted from one coil and received by the other (usually integrated with the IMD inside a human body) through electromagnetic induction. As a key parameter of the WPT s y s tem, k can be obtained with the relationship k M/ L1L2, where L1 and L2 are the self-inductances of the Tx and Rx coils, respectively, and M is the mutual inductance, which typically depends on the geometries of the two coils, their distance, and the material separating them
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