Wireless Power Transfer Receiver Research Articles

Wireless Frequency‐Multiplexed Acoustic Array‐Based Acoustofluidics

AbstractAcoustofluidics has shown great potential in enabling on‐chip technologies for driving liquid flows and manipulating particles and cells for engineering, chemical, and biomedical applications. To introduce on‐demand liquid sample processing and micro/nano‐object manipulation functions to wearable and embeddable electronics, wireless acoustofluidic chips are highly desired. This paper presents wireless acoustofluidic chips to generate acoustic waves carrying sufficient energy and achieve key acoustofluidic functions, including arranging particles and cells, generating fluid streaming, and enriching in‐droplet particles. To enable these functions, the wireless acoustofluidic chips leverage mechanisms, including inductive coupling‐based wireless power transfer (WPT), frequency multiplexing‐based control of multiple acoustic waves, and the resultant acoustic radiation and drag forces. For validation, the wirelessly generated acoustic waves are measured using laser vibrometry when different materials (e.g., bone, tissue, and hand) are inserted between the WPT transmitter and receiver. Moreover, the wireless acoustofluidic chips successfully arrange nanoparticles into different patterns, align cells into parallel pearl chains, generate streaming, and enrich in‐droplet microparticles. This research is anticipated to facilitate the development of embeddable wireless on‐chip flow generators, wearable sensors with liquid sample processing functions, and implantable devices with flow generation and acoustic stimulation abilities for engineering, veterinary, and biomedical applications.

A Wearable All-Printed Textile-Based 6.78 MHz 15 W-Output Wireless Power Transfer System and Its Screen-Printed Joule Heater Application

While research in passive flexible circuits for Wireless Power Transfer (WPT) such as coils and resonators continues to advance, limitations in their power handling and low efficiency have hindered the realization of efficient all-printed high-power wearable WPT receivers. Here, we propose a screen-printed textile-based 6.78 MHz resonant inductive WPT system using planar inductors with concealed metal-insulator-metal (MIM) tuning capacitors. A printed voltage doubler rectifier based on Silicon Carbide (SiC) diodes is designed and integrated with the coils, showing a power conversion efficiency of 80-90% for 2-40 W inputs over a wide load range. Compared to prior wearable WPT receivers, it offers an order of magnitude improvement in power handling along with higher efficiency (approaching 60%), while using all-printed passives and a compact rectifier. The coils exhibit a simulated Specific Absorption Rate (SAR) under 0.4 W/kg for 25 W received power, and under 21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C increase in the coils' temperature for a 15 W DC output. Additional fabric shielding is investigated, reducing harmonics emissions by up to 17 dB. We finally demonstrate a wirelessly-powered textile-based carbon-silver Joule heater, capable of reaching up to 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C at 2 cm separation from the transmitter, as a wearable application which can only be wireless-powered using the proposed system.

Linear-in-dB Logarithmic Signal Strength Sensor Circuit for Wireless Power Transfer Receivers

Tracking systems for wireless power transfer are becoming a necessity. The received target signals are sometimes weak, which is why it is critical to have a dedicated received–signal–strength indicator (RSSI) for signal detection. It can also be used for transmitter localization and automatic gain control (AGC) to ensure continuous coverage. In this paper, a logarithmic detector coupled with a high-speed full-wave rectifier is designed for an RSSI system. The aim is to place the RSSI on the receiver side of unmanned aerial vehicles used, for example, as agricultural drones. This system is intended to operate in a scenario where multiple drones in a smart farm are charged wirelessly whilst airborne. An RSSI is placed in the receiver to detect and track wireless signals and to ensure the drone is charged while in motion. The RSSI system operates at 5.8 GHz, reported for the first time, and is capable of detecting signal strengths from −60 dBm to 0 dBm with a sensitivity level of 17 mV/dBm. A logarithmic error of 0.4 dB with a dynamic range of 34 dB was achieved. The proposed RSSI system was designed using 65 nm TSMC CMOS technology, and it exhibits high sensitivity, better efficiency, and lower power consumption than those in other reported works.

A self-biased magnetoelectric wireless power transfer receiver targeting biomedical implants

A self-biased magnetoelectric wireless power transfer receiver targeting biomedical implants

C2DD—An omnidirectional receiver based on single‐coil transmitter

AbstractIn this paper, the omnidirectional receiver (Rx) of wireless power transfer (WPT) system is proposed, making any transmitter (Tx) into omnidirectional Tx. The omnidirectional Rx is composed of the quadrature double‐D (DD) coils and circular coil in series (C2DD). The C2DD Rx can utilize the toroidal magnetic field (TMF) and the linear magnetic field (LMF). The paper presents the circuit diagram model of WPT system. Based on the analysis of circuit model, the smooth mutual inductance of system is responsible for stable transmission performance during C2DD Rx movement. The result of numerical calculation and magnetic field simulation verifies the omnidirectional capability of the C2DD Rx with circular Tx as an example. Experiment shows that the C2DD Rx receives power in any direction. The C2DD Rx can receive maximum transmission power of 7.1 W with maximum transmission efficiency of 59%.

On Performance of a SWIPT Enabled FD CRN With HIs and Imperfect SIC Over α–μ Fading Channel

This paper investigates the performance of overlay full-duplex cooperative cognitive radio network in the presence of imperfect self interference cancellation over generalized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\mu $ </tex-math></inline-formula> fading channels effected by nonlinearity of the propagation medium. In practice, physical transceivers create distortion which degrades the performance, hence, the impact of transceiver hardware impairments (HIs) is considered. To overcome the energy constraint problem, a hybrid simultaneous wireless information and power transfer receiver is adopted that includes both the time switching and the power splitting protocols. To improve reliability of the communication link, we employ a hybrid relaying protocol that combines both the decode-and-forward and amplify-and-forward relaying protocols. The closed-form expressions of outage probability and asymptotic outage probability are derived for both the primary and the secondary networks over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\mu $ </tex-math></inline-formula> fading channels. The diversity order, throughput, and energy efficiency of the considered network are derived. Optimal values of time switching factor is obtained for which the considered network exhibits optimum outage probability, maximum throughput and energy efficiency. Further, optimal value of power splitting factor is obtained for which the considered network shows maximum throughput and energy efficiency. Finally, the Monte-Carlo simulations validate correctness of the derived closed-form expressions.

2.4 GHz 대역 무선전력전송 고효율 수신부 IC 설계

A high-efficiency wireless power transfer-receiver IC that can operate at 2.4 GHz has been proposed. The IC consists of a matching network, rectifier, and DC-DC converter. The rectifier based on the Dickson charge pump topology is designed to have high efficiency by optimizing the number of stages and matching networks. In the proposed IC, a high-efficiency CMOS step-up/step-down DC-DC converter that can operate over a wide input range is involved. The converter provides quadruple conversion ratios of 1/3, 1/2, 2/3, and 2/1, which are determined by the mode selector by sensing the input voltage level. The IC was implemented in a standard 28-nm CMOS process, and post-layout simulation results for the IC demonstrated that the rectifier operates at −8 dBm to 20 dBm and shows a maximum efficiency of 66 % for an input power from −4 to 20 dBm. The DC-DC converter outputs a voltage of 1.6∼2.2 V for a wide input voltage range of 1.2∼5 V and shows a power conversion efficiency of up to 80 %. For the entire IC, the maximum efficiency is 50.8 % at an input power of 12 dBm.

A miniaturized low frequency direct-current magnetic-bias-integrated magnetoelectric wireless power transfer system with enhanced energy conversion efficiency

Wireless power transfer (WPT), which transfers energy without a physical link, has recently received significant research interest. Due to the advantages of small dimension, low operation frequency, and low transmission loss, magnetoelectric WPT (ME-WPT) has been shown to be a promising technology for internet of things (IoT) and implantable medical device (IMD) applications. However, ME-WPT requires a direct-current (DC) magnetic bias for optimal performance and prior arts have implemented large electromagnets, Helmholtz coils, or externally positioned magnet bias systems, which increase the system dimension. Furthermore, the highest energy conversion efficiency (ECE) reported by prior ME-WPT studies is 0.62%, which needs to be improved. In this paper, we present an ME-WPT system with a novel miniaturized ME-WPT receiver and a spiral coil based transmitter. Four DC magnets are integrated onto the ME-WPT receiver to significantly reduce its dimension while providing a DC magnetic bias of 190 Oe for optimal performance. Electrochemical polarization characterizations are introduced to analyze the performance of the WPT receiver, which reveal that a maximum output power of 4.096 mW is obtained. A record ECE of 2.64% is reported, the highest among all ME-WPTs to date. The output power is improved by at least 49.3 times compared with the ME-WPT without integrated DC magnets. The influence of the input voltage and the distance between transmitter/receiver on the performance of the ME-WPT system is studied, which shows that the output power increases as the distance decreases and the input voltage increases. The proposed ME-WPT system with integrated DC magnets has potential applications in IoT and IMDs.

Analysis of a Dual-Transduction Receiver for Electrodynamic Wireless Power Transfer

In this article, we present the characterization and an experimentally validated electromechanical model of a dual-transduction receiver for electrodynamic wireless power transfer (EWPT) system. This dual-transduction EWPT receiver contains two unimorph-type, series-connected piezoelectric transducers and an electrodynamic transducer within a compact footprint and low-profile design. The receiver makes simultaneous use of both piezoelectric and electrodynamic transducers to generate electrical power while operating at its torsion mode mechanical resonance at ∼744 Hz. The electromechanical system behavior and output performance under low-frequency, magnetic near-fields are analyzed by establishing an equivalent lumped-element equivalent electrical circuit model. A prototype device is fabricated, assembled, characterized, and the experimental results are compared with the model predictions under various excitation and loading conditions. A maximum of 49 μW average power is generated by the prototype under 120 μT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> , which corresponds to 0.54 mW·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–3</sup> power density and 37 mW·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–3</sup> ·mT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–2</sup> normalized power density. This chip-sized (0.09 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) design offers an innovative and volume-efficient architecture for application in wirelessly charging wearable and implantable medical devices.

Acoustic vibrations for versatile wireless power transfer

We present an overview of prior/recent work done at the US Army Combat Capabilities Command—Army Research Laboratory on using acoustic waves for wireless power transfer (WPT). In the past we have demonstrated through-air ultrasonic phased array power beaming, through-metal longer distance transfer using Lamb waves, and power/data transfer to embedded sensor nodes. Acoustic WPT has the advantage of not being shielded by metal, and can achieve higher efficiencies than inductive WPT at larger distances. Part of our recent work is on developing a through-metal acoustic WPT based wireless UAV recharging platform. For the first time, we have demonstrated a self-detachable acoustic WPT receiver, using the switchable magnetic force from electro-permanent-magnets to attach a receiver transducer onto a steel platform to receive power (a transmitter is bonded on the other side of the platform), without the need of any liquid couplant. The magnetic force enhances the mechanical mode coupling, while allowing the receiver to attach/detach freely from the platform. AC-AC power efficiency up to 63% was achieved, and with the appropriate power electronics and matching network, an overall DC-DC efficiency of 44% was achieved when charging a 3-cell LiPo UAV battery with 4.6 W, with higher power levels achievable.

Air‐Pressure‐Assisted Pen‐Nib Printing for 3D Printed Electronics

Abstract3D printed electronics employing direct‐ink‐writing methods are promising alternative manufacturing technologies for realizing structural electronics. The emerging demand for accessible, cost‐effective, and rapid writing calls for novel approaches to print functional components onto nonflat and 3D architectures. This study presents a novel air‐pressure‐assisted pen‐nib printing approach producing electrical and functional components with various material inks on flat and 3D surfaces. Based on the inks’ rheological properties, the ejected ink's quantity through the nib is manipulated via air pressure; thus, the printed line width is controlled. This strategy also achieves the viscosity range extension of printable inks by enabling printing inks that cannot be used in general pen‐based printing. Three functional inks with different rheological properties—Ag catalyst ink for Cu electroless deposition, Ag‐PEDOT:PSS ink, and thermochromic pigment inks are designed. Several electrical and functional components, such as highly conductive Cu interconnects, Cu spiral coils for wireless power transfer receivers, flexible heaters, and matrix data codes based on temperature‐responsive color transitions are demonstrated. Furthermore, parallel printing with a multi‐nib print‐head is demonstrated for improving the printing speed and manufacturing scalability. The authors believe that this novel approach is promising as a manufacturing technique for realizing 3D printed electronics.

Wireless Powered Dielectric Elastomer Actuator

The need for cable connection with soft robotic systems suppresses the benefits granted by their softness and flexibility. Such systems can be untethered by equipping batteries or by relying on non-electrical actuation mechanisms. However, these approaches cannot simultaneously support long-term and intelligent operations. This research examines a proposed wireless soft actuator based on wireless power transfer (WPT) and dielectric elastomer actuator (DEA) technology, thereby realizing soft robomore diversified application and long-term locomotion. A compact conical DEA fabrication process is presented with 6 mm periodic linear output and design of a lightweight WPT receiver that weighs only 13 g integrated with a driver circuit. Evaluation results show that this system remotely powers the DEA and the intelligent peripheral circuits for system control. Furthermore, our design seamlessly bridges the WPT system, power-efficient in low-voltage output conditions, and the DEA, which requires high-voltage input (kV) for deformation, by leveraging high-voltage boost-converters. Experimentally obtained results demonstrate untethered DEA operation at 170 mm from the transmitter. Also, we demonstrated applying this DEA as a wireless pump.

A 6.78 MHz Single-Stage Wireless Power Transmitter Using a 3-Mode Zero-Voltage Switching Class-D PA

A 6.78 MHz single-stage transmitter (TX) using a reconfigurable regulating class-D power amplifier (PA) for wireless power transfer (WPT) applications is presented. Based on a 3-mode modulation scheme, the TX achieves power regulation and transmission with only one power stage. A discontinuous-conduction-mode (DCM) zero-voltage switching (ZVS) scheme is adopted to reduce switching loss. A control loop is set to regulate the output voltage of the WPT receiver (RX) by automatically adjusting the transmitting power. With dual-loop control and a proportional-integral (PI) compensation scheme, the loop achieves tight regulation and fast response. The controller is implemented digitally to benefit from the AirFuel <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> embedded Bluetooth communication link. The PA was fabricated with a high-voltage 0.35 μm CMOS process, and the digital controller with a standard 0.35 μm CMOS process, respectively. Measurement results show that the output voltage of the RX was correctly regulated to 11.7 V under a load change of 50mA to 500mA, and the WPT system could deliver a maximum power of 7.3 W to the RX over a distance of 4.0 cm, and achieved TX to RX peak efficiency of 57.3%.

Wireless power transfer system rigid to tissue characteristics using metamaterial inspired geometry for biomedical implant applications

Conventional resonant inductive coupling wireless power transfer (WPT) systems encounter performance degradation while energizing biomedical implants. This degradation results from the dielectric and conductive characteristics of the tissue, which cause increased radiation and conduction losses, respectively. Moreover, the proximity of a resonator to the high permittivity tissue causes a change in its operating frequency if misalignment occurs. In this report, we propose a metamaterial inspired geometry with near-zero permeability property to overcome these mentioned problems. This metamaterial inspired geometry is stacked split ring resonator metamaterial fed by a driving inductive loop and acts as a WPT transmitter for an in-tissue implanted WPT receiver. The presented demonstrations have confirmed that the proposed metamaterial inspired WPT system outperforms the conventional one. Also, the resonance frequency of the proposed metamaterial inspired TX is negligibly affected by the tissue characteristics, which is of great interest from the design and operation prospects. Furthermore, the proposed WPT system can be used with more than twice the input power of the conventional one while complying with the safety regulations of electromagnetic waves exposure.

Overshoot Damping and Dynamics Improvement in Wireless Power Transfer Systems via Receiver-Side Controller Design

Buck converters have been extensively used for output regulation in the receiver of series–series compensated wireless power transfer (WPT) systems. Nonetheless, there are two major challenges in the controller design of this class of WPT systems. First, due to the current-source nature and finite dc-link capacitance, a right-half-plane (RHP) zero exists in the WPT receiver, reducing its stability margin and causing limited system dynamics. Second, this RHP zero can cause an overshoot issue in the WPT system. Without proper treatment, this overshoot may largely increase the voltage/current stress of the system and even cause catastrophic failure. However, existing solutions to the above two issues suffer from long communication delays or significantly compromised output regulation, degrading system performance. In this article, the slow dynamics and the overshoot issue of the WPT system are elaborated in theory and a solution is proposed by adding a feedforward path of the dc-link voltage in the receiver's controller. No communication is involved in the proposed control method, and only trivial computation is added to the controller. The proposed method is examined on a WPT prototype. The experimental results show that the two issues of the WPT system can be simultaneously solved by the proposed method while the output regulation of the system is not compromised.

A 65nm CMOS Process Li-Ion Battery Charging Cascode SIDO Boost Converter with 89% Maximum Efficiency for RF Wireless Power Transfer Receiver

This paper proposes a 65nm CMOS process cascode single-inductor-dual-output (SIDO) boost converter for RF wireless power transfer (WPT) receiver. In order to withstand 4.2V Li-ion battery output, cascode 2.5V I/O PFETs are used at the power stage while 2.5V cascode NFETs are used for 1V output to supply low voltage control circuit. By using NFETs, 1V output with 5V tolerance can be achieved. Measurement results show conversion efficiency of 89% at P IN =7.9mW and V BAT =3.4V.

A Sub-THz Wireless Power Transfer for Non-Contact Wafer-Level Testing

In this paper, a sub-THz wireless power transfer (WPT) interface for non-contact wafer-level testing is proposed. The on-chip sub-THz couplers, which have been designed and analyzed with 3-D EM simulations, could be integrated into the WPT to transfer power through an air media. By using the sub-THz coils, the WPT occupies an extremely small chip size, which is suitable for future wafer-testing applications. In the best power transfer efficiency (PTE) condition of the WPT, the maximum power delivery is limited to 2.5 mW per channel. However, multi-channel sub-THz WPT could be a good solution to provide enough power for testing purposes while remaining high PTE. Simulated on a standard 28-nm CMOS technology, the proposed eight-channel WPT could provide 20 mW power with the PTE of 16%. The layouts of the eight-channel WPT transmitter and receiver occupy only 0.12 mm2, 0.098 mm2, respectively.

Multiuser Full-Duplex IoT Networks With Wireless-Powered Relaying: Performance Analysis and Energy Efficiency Optimization

This paper considers an Internet-of-Things (IoT) network where a multi-antenna access point (AP) and several single-antenna IoT devices (IoDs), operating under the full-duplex (FD) mode, communicate with each other bidirectionally through the help of a wireless-powered FD relay. In particular, the power splitting (PS) protocol is adopted at the amplify-and-forward (AF) relay to implement a simultaneous wireless information and power transfer (SWIPT) receiver. For such a multiuser FD-IoT network assisted by a wireless-powered two-way relay, we derive exact overall outage probability (OOP) expressions and tight closed-form expressions for the ergodic sum rate (ESR) under generalized Nakagami-m fading channels. Furthermore, aiming to maximize the energy efficiency (EE), we obtain optimal power allocation (OPA) under the total power and rate threshold constraints. Finally, extensive numerical and simulation results are presented to corroborate our analytical findings.

Power Allocation for SWIPT in Full-Duplex AF Relay Interference Channels Using Game Theory

A full-duplex, amplify-and-forward multiple relay system employing simultaneous wireless information and power transfer receivers operating in interference channels is studied. Since all links want to maximize their own achievable rate, a power allocation problem under transmit power and energy harvesting constraints is developed. Through alternative optimization, a distributed iterative water-filling algorithm based on game theory with provable convergence is devised. The existence and uniqueness of a Nash equilibrium point are both guaranteed and the convergence of the proposed algorithm is examined using a diagonally strict concavity condition. Numerical results show that the proposed algorithm is convergent and can achieve a higher sum rate than previous schemes.

Transmitter-Side Wireless Information- and Power-Transfer in Massive MIMO Systems

Both time-switching (TS) and power splitting has been used at the receiver for wireless information and power transfer in the downlink of massive multiple-input-multiple-output systems. By contrast, this correspondence adopts the transmit-TS approach, where the energy and information are transferred over different fractions of a time slot. Our goal is to jointly optimize the transmit-TS factor and power allocation coefficients during energy and information transfer for maximizing the users' minimum throughput subject to transmit power and minimum harvested energy constraints. This nonconvex problem is solved by our path following algorithm. Our simulation results demonstrate the benefits of the proposed transmit-TS algorithm, which easily doubles the throughput compared to that of the existing techniques.