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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]

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]

Next generation implantable neural interfaces are targeting devices with mm-scale form factors that are freely floating and completely wireless. Scalability to more recording (or stimulation) channels will be achieved through distributing multiple devices, instead of the current approach that uses a single centralized implant wired to individual electrodes or arrays. In this way, challenges associated with tethers, micromotion, and reliability of wiring is mitigated. This concept is now being applied to both central and peripheral nervous system interfaces. One key requirement, however, is to maximize specific absorption rate (SAR) constrained achievable wireless power transfer efficiency (PTE) of these inductive links with mm-sized receivers. Chip-scale coil structures for microsystem integration that can provide efficient near-field coupling are investigated. We develop near-optimal geometries for three specific coil structures: in-CMOS, above-CMOS (planar coil post-fabricated on a substrate), and around-CMOS (helical wirewound coil around substrate). We develop analytical and simulation models that have been validated in air and biological tissues by fabrications and experimental measurements. Specifically, we prototype structures that are constrained to a 4 mm $ \times$ 4 mm silicon substrate, i.e., the planar in-/above-CMOS coils have outer diameters $<$ 4 mm, whereas the around-CMOS coil has an inner diameter of 4 mm. The in-CMOS and above-CMOS coils have metal film thicknesses of 3- $\mu$ m aluminium and 25- $\mu$ m gold, respectively, whereas the around-CMOS coil is fabricated by winding a 25- $\mu$ m gold bonding wire around the substrate. The measured quality factors (Q) of the mm-scale Rx coils are 10.5 @450.3 MHz (in-CMOS), 24.61 @85 MHz (above-CMOS), and 26.23 @283 MHz (around-CMOS). Also, PTE of 2-coil links based on three types of chip-scale coils is measured in air and tissue environment to demonstrate tissue loss for bio-implants. The SAR-constrained maximum PTE measured (together with resonant frequencies, in tissue) are 1.64% @355.8 MHz (in-CMOS), 2.09% @82.9 MHz (above-CMOS), and 3.05% @318.8 MHz (around-CMOS). [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]

Abstract: Improving the efficiency of the inductive wireless power transfer (WPT) is an effective way to increase the power transfer distance, reduce the power exposure, and popularize the WPT application. If the geometrical sizes of the transmitting and receiving coils and the distance between them have been determined, an operating frequency exists to maximize the power transfer efficiency. In this work, a method to find this optimal frequency is introduced by virtue of analytical models of self‐ and mutual‐inductances and parasitic resistances and capacitances of the coils, and verified via simulations and measurements. [ABSTRACT FROM AUTHOR]

The new trend towards minimally invasive millimeter-sized and free-floating distributed implants promises to enable emerging applications, such as chronic neural recording with minimal damage to the surrounding tissue. However, wireless power transmission (WPT) to these medical devices is quite challenging. The magnetic field produced by external transmitter (Tx) coils at the position of small implants can be considered homogeneous to separate the optimization of Tx and receiver (Rx) coils for efficient WPT. This paper focuses on the optimization of the solenoid-type Rx coils, which are suitable for this application. We have developed an analytical model of solenoid coils that includes the impact of tissue and coating around the coils, verified through simulations and measurements. Using the proposed model, under a given size restriction and a specific load, we find the optimal operating frequency and coil geometry to maximize a figure of merit (FoM) for the Rx that includes the loaded quality factor and its internal efficiency as well as a factor related to the coupling coefficient. For a millimeter-sized coil, the optimal operating frequency for the Rx and the number of turns are found to be 500 MHz and six, respectively, if the coil is closely wound using AWG36 copper wires. If the pitch is also optimized, then 700 MHz and four turns provide the best FoM for the solenoid Rx. [ABSTRACT FROM PUBLISHER]

The mutual inductance between two coils is a key parameter in the inductively coupled wireless power transmission. The spiral rectangular coils are easier to implement than the circular ones, but the study of the mutual inductance of the spiral rectangular coils is not enough. In this paper, a new analytical calculation of the coaxial spiral rectangular coils is presented, which is simpler than the greenhouse method. The impact of the track thickness and width is also analyzed. The calculation results are verified by the existing methods and the experimental results. Based on these results, some guidelines for optimizing the coupling coefficient are given, when the received coil's size is limited by space constraints. [ABSTRACT FROM AUTHOR]

Optimizing deployment of charging base stations in wireless rechargeable sensor networks can considerably reduce the cost. Previously, the charging base stations are simply installed at some fixed special points (e.g., the grid points) after partitioning the area distributed by sensor nodes. In this paper, a new algorithm of planning the charging base stations is proposed based on the greedy algorithm and the location relationship of the sensor nodes. The proposed algorithm exploits the local search ability and avoids falling into an exponential increase of the number of the charging base stations (i.e., combinatorial explosion). The simulated results show that the proposed algorithm can result in less number and flexible deployed locations of the charging base stations. In addition, this algorithm provides a novel solution for the point coverage problems. [ABSTRACT FROM AUTHOR]