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In the inductive wireless power transmission (WPT) designs of consumer electronics and implantable devices, the printed planar coil in standard manufacture is commonly used. Layout optimization of the coils is one of the important ways to make the power transmission system more efficient. Varying the trace width and turn-to-turn spacing together for the coils is proposed to optimize the maximum achievable power transfer efficiency (max). An accurate analytical model for the printed square coils is also established as well to speed up the design process. By virtue of this model, an optimal scaling factor of the trace width and the optimal frequency can be quickly estimated. The proposed model is validated by both the simulations (ANSYS HFSS) and experiments. A WPT link of two planar coils with size of 50 mm × 50 mm × 1 mm, operating at 23 MHz, is optimized by using this methodology. After optimization, the measured max of the WPT system is increased from 22.60% to 32.74% at a 100-mm transmission distance. [ABSTRACT FROM AUTHOR]

Recent progress on human brain science requires developing advanced neural recording system to capture the activity of large neural populations accurately, across a large area of the brain, and over extended periods. Recently proposed distributed neural recording systems with numerous implanted devices require reliably energizing them wirelessly. Random distribution of these mm-sized implants and brain motion place them at different positions and orientations with respect to the power transmitter. Therefore, traditional wireless power transfer techniques fall short of reaching sufficient power for all implants simultaneously, rendering some implants nonfunctional. In this paper, a three-layer power transmitting array with three-phase coil excitation current is introduced, which is capable of producing omnidirectional and homogeneous magnetic field across the volume where the Rx coils are located. The individual coil dimensions in the array is optimized to improve the worst-case scenario in terms of homogeneity, which is further verified by the measurements using a scaled-up prototype system. The measurement results show that the minimum received voltages is improved from 0.34 V for 10-mm side-length hexagonal transmitting coil array to 0.83 V for the optimal case, i.e., 35 mm side-length hexagonal transmitting coil array. [ABSTRACT FROM AUTHOR]

L-type impedance matching circuits (IMCs) can maximize the power transfer efficiency (PTE) by converting the load to the optimum one in the wireless power transfer system. However, their effectiveness is inadequately studied. In this work, the applicability of the L-type IMCs is carefully examined under the restriction of capacitance realization. The sensitivities with respect to the deviation of the capacitance in mass production as well as the variations of the load and the mutual inductance are analyzed in detail and validated by experiments. By comparison with the basic-type IMCs, the L-type IMCs have higher, nearly equal and lower sensitivities with respect to the deviation of the capacitance, the variation of the load, and the variation of the mutual inductance, respectively. [ABSTRACT FROM AUTHOR]

Inserting metamaterials into the path of wireless power transfer (WPT) is an effective way to improve the power transfer efficiency (PTE) or extend the power transfer distance. The resonant frequency f0 of the metamaterial is a critical parameter to distinguish the positive or negative permeability regions, which should be determined accurately. A new method to measure f0 is developed and validated in theory and simulation. The paramagnetic region (where the effective permeability is positive) is a frequency band below f0, and is used as the operating region of WPT with insertion of the metamaterial. According to experiments, the PTE is improved by comparison to the case without metamaterial. More interestingly, the PTE improvement effects at different operating regions are compared. It is shown that the region, where the forced-resonant frequency fRS is close to f0, has better effect than the other regions where fRS is lower or higher than f0. [ABSTRACT FROM AUTHOR]

The mutual inductance between the transmitted and received coils is an important parameter in the inductively coupled wireless power transmission system. The relative position between the linked coils may be arbitrary according to the applications. In this paper the analytical calculation of the mutual inductance between two arbitrarily positioned rectangular filaments is proposed based on a more general expression of mutual inductance calculation of two arbitrarily positioned straight filaments than Grover's. The calculation results are validated by using the finite element simulation tools. The previous published approximation methods for square coils in the coaxial, lateral misalignment or angular misalignment situations are verified that they are accurate when the two coils' relative distances are large. [ABSTRACT FROM AUTHOR]