Wireless power transfer (WPT) systems have become increasingly suitable solutions for the electrical powering of advanced multifunctional micro-electronic devices such as those found in current biomedical implants The design and implementation of high power transfer efficiency WPT systems are, however, challenging The size of the WPT system, the separation distance between the outside environment and location of the implanted medical device inside the body, the operating frequency and tissue safety due to power dissipation are key parameters to consider in the design of WPT systems This article provides a systematic review of the wide range of WPT systems that have been investigated over the last two decades to improve overall system performance The various strategies implemented to transfer wireless power in implantable medical devices (IMDs) were reviewed, which includes capacitive coupling, inductive coupling, magnetic resonance coupling and, more recently, acoustic and optical powering methods The strengths and limitations of all these techniques are benchmarked against each other and particular emphasis is placed on comparing the implanted receiver size, the WPT distance, power transfer efficiency and tissue safety presented by the resulting systems Necessary improvements and trends of each WPT techniques are also indicated per specific IMD

Wireless Power Transfer Techniques for Implantable Medical Devices: A Review.

Magnetically coupled resonance wireless power transfer systems (MCR WPT) have been developed in recent years. There are several key benefits of such systems, including dispensing with power cords, being able to charge multiple devices simultaneously, and having a wide power range. Hence, WPT systems have been used to supply the power for many applications, such as electric vehicles (EVs), implantable medical devices (IMDs), consumer electronics, etc. The literature has reported numerous topologies, many structures with misalignment effects, and various standards related to WPT systems; they are usually confusing and difficult to follow. To provide a clearer picture, this paper aims to provide comprehensive classifications for the recent contributions to the current state of MCR WPT. This paper sets a benchmark in order to provide a deep comparison between different WPT systems according to different criteria: (1) compensation topologies; (2) resonator structures with misalignment effects; and, (3) electromagnetic field (EMF) diagnostics and electromagnetic field interference (EMI), including the WPT-related standards and EMI and EMF reduction methods. Finally, WPT systems are arranged according to the application type. In addition, a WPT case study is proposed, an algorithm design is given, and experiments are conducted to validate the results obtained by simulations.

Magnetically Coupled Resonance WPT: Review of Compensation Topologies, Resonator Structures with Misalignment, and EMI Diagnostics

In this article, we demonstrate flexible and lightweight textile-integrated rectenna arrays for powering wearable electronic devices. We propose a method to exploit large clothing-areas to integrate arrays consisting of $2\times2$ and $2\times3$ rectenna elements. Each element comprises a patch antenna and a rectifier which are fabricated using embroidery of conductive thread on the textile substrates. The rectifier used single-diode circuit configuration and showed a radio frequency (RF)-to-dc conversion efficiency of 70% for an applied input RF-power of 8 dBm at its input port. We also present several tests to demonstrate the applicability of the rectenna array. Specifically, in boosted-Wi-Fi modality, a dc power of $600~\mu \text{W}$ was collected at 10 cm from the source and $80~\mu \text{W}$ was collected at 60 cm from the source. These demonstrations show the proposed system’s applicability for charging and powering low-power wearable electronic devices.

Textile-Based Large Area RF-Power Harvesting System for Wearable Applications

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In this paper, we present the design, fabrication, and measurement of an ultra-wideband phased array antenna, with continuous coverage of all six allocated fifth generation and industrial, scientific, medical bands in the millimeter-wave spectrum. Of importance is that the complete array is co-fabricated as a single printed circuit board using commercial processes, implying a significant reduction in cost over previous microfabrication-based designs. The design is demonstrated in simulation to operate across 24–72 GHz with VSWR $3\times 3$ array prototype, which shows close agreement to the simulated values.

Ultra-Wideband Phased Array for Millimeter-Wave ISM and 5G Bands, Realized in PCB

This paper presents a novel technique for high efficiency and compact size wireless power transfer (WPT) systems. These systems are based on coupled defected ground structure (DGS) resonators. Two types of DGSs (H-shape and semi-H-shape) are proposed. The semi-H-shaped DGS realizes larger inductance value, and this results in higherWPT efficiency. Instead of using an inductive-fed resonant coupling, we propose capacitive-fed resonant coupling, which reduces the design complexity and enhances the efficiency further. The DGS resonator of both the systems is loaded by chip capacitors for miniaturization. An equivalent circuit using approximate quasi-static modeling is extracted. An analytical design procedure is developed to calculate the optimum design parameters for the proposed WPT systems. The optimized structures are fabricated and measured. The simulation and measurement results are in good agreement. The proposed semi-H-shaped DGS WPT system has a peak efficiency of 73% at a transmission distance of 25 mm. In turn, the figure of merit becomes the highest among the WPT systems proposed so far.

A Novel Technique for Compact Size Wireless Power Transfer Applications Using Defected Ground Structures

This brief proposes a design methodology based on the admittance ( ${J}$ -) inverters for a dual-band wireless power transfer (WPT) system that employs two cascaded circulars defected ground structure (DGS) resonators with different capacitive loading to guarantee distinct resonances. A single microstrip line excites the two DGSs, and when two DGS resonators are coupled back to back, it transforms to a dual band pass filter leading to WPT at both bands. Each of the DGS resonators has independent coupling. Thus, the realized ${J}$ -Inverters are designed independently. Also, we employ a single stub for the matching. This stub appears with a different length according to the operating frequency; hence, an independent external coupling is achieved at both frequencies. A compact size of 30 mm ${\times } \,\, 15$ mm is fabricated achieving a WPT efficiency of more than 71% at a power transfer distance of 16 mm for both bands (0.3 and 0.7 GHz).

Dual-Band Defected Ground Structures Wireless Power Transfer System With Independent External and Inter-Resonator Coupling

In this letter, we propose a compact size, small insertion loss 60 GHz on-chip H-shaped resonator bandpass filter (BPF) using 0.18 $\mu\text{m}$ standard CMOS technology. The BPF Size is miniaturized by loading the H-shaped resonator with metal-insulator-metal capacitors at its ends. Besides, two defected ground structure cells are etched under the coupled lines to improve the filter insertion loss. Furthermore, selectivity is enhanced by loading the center of the H-shaped resonator with two unsymmetrical meander line stubs generating two transmission zeroes at 50 and 70 GHz. The fabricated BPF chip size is $240 \times 650\ \mu\text{m}^{2}$ . The measured insertion loss and fractional bandwidth are 2.5 dB at 60 GHz and 21%, respectively.

Compact Size On-Chip 60 GHz H-Shaped Resonator BPF

This letter presents a 60-GHz ultracompact on-chip bandpass filter (BPF). The designed filter is based on a unique structure, which consists of two overlapped broadside-coupled open-loop resonators, achieving a high level of miniaturization. Moreover, each resonator is loaded by a metal–insulator–metal capacitor to get further miniaturization. Defected ground structure pattern is constructed under the filter structure to enhance the insertion loss (IL). This BPF is designed and fabricated using a standard 0.18- $\mu \text{m}$ complementary metal–oxide–semiconductor technology for millimeter-wave applications. The fabricated BPF chip size is $240 \times 225~\mu \text{m}^{2}$ including pads. The measured results agree well with the simulation ones and show that the BPF has an IL of 3.3 dB at 59.5-GHz center frequency, and a bandwidth of 12.9 GHz.

Ultracompact 60-GHz CMOS BPF Employing Broadside-Coupled Open-Loop Resonators

This paper methodizes efficiency improvement during lateral misalignment for the wireless power transfer (WPT) system using two coupled semielliptic defected ground structure (DGS) resonators. We design the WPT system using a scaled value of the available mutual coupling between the resonators at perfect alignment. This scaled mutual coupling value enforces over-coupling regime, and the WPT efficiency is lower than the peak one. Then, during lateral misalignment, WPT efficiency improves until it peaks at critical coupling. Next, with further misalignment, the efficiency drops as the system enters loose coupling regime. The proposed method consists of two steps. First, we derive an analytical approach to determine the scaled mutual coupling value for efficiency design during lateral misalignment, and second, we improve the maximum obtainable efficiency by careful designing of the DGS structures’ profile. We verify the proposed method by implementing the WPT system at 300 MHz, which shows a peak efficiency of 80% for a size $D_{o} \times D_{o} = 40 \times 40$ mm2 with a transfer distance $d = D_{o}$ . During misalignment, the efficiency is higher than 50% for a lateral shift up to ±0.75 $D_{o}$ .

Adel Barakat

Papers

A Novel Technique for Compact Size Wireless Power Transfer Applications Using Defected Ground Structures

Dual-Band Defected Ground Structures Wireless Power Transfer System With Independent External and Inter-Resonator Coupling

Compact Size On-Chip 60 GHz H-Shaped Resonator BPF

Ultracompact 60-GHz CMOS BPF Employing Broadside-Coupled Open-Loop Resonators

Design Approach for Efficient Wireless Power Transfer Systems During Lateral Misalignment