Devices used in healthcare applications frequently require powering. With the rapid development of implantable devices for disease treatment, as well as smart digital devices dedicated for healthcare operations, wireless charging of these systems is critical. The majority of wireless powering currently uses electromagnetic fields. This work describes the in vivo demonstration of Ultrasound Power Delivery (UPD) for charging Li-ion batteries, adequate for a gastro-esophageal junction (GEJ) neurostimulator device, while fulfilling the charging module's space budget of 1.2 cc. Using the same 1 - 3 MHz UPD approach, this work describes the feasibility of charging batteries for smart devices intended for dedicated applications in a healthcare environment, with similar specifications as the wireless Qi-standard version 1.0.
The design of a rectenna system for practical use is outlined in detail. The system is physically small ($24 \times 20 \times 3 mm^{3}$) and is shielded by a ground plane from electronics behind. First experimental results are shown, using Direct Antenna Modulation, for combining power and data transfer using an information bandwidth that is wider than the antenna bandwidth.
In wireless power transfer system, a leakage electromagnetic field (EMF) that can affect a human body or peripheral devices is one of the most important problems along with system efficiency. Since ferrite and aluminum which are basically used to reduce the EMF have a high weight and cost, various studies to cancel the EMF using reverse magnetic field by additional coil are being conducted. In this paper, a reactive shield coil that can be applied to a wireless charger with multiple transmitter coils is proposed. The EMF is reduced by applying the proposed coil up to 85%.
The measurement of a microwave beam focus location was performed to validate theoretical results obtained previously using the quasioptical framework. The system in question is a preliminary set-up of a double reflector system designed for wireless power transfer studies. A very approximate value was achieved but the slight differences verified must be taken into account for the complete system experiment.
This work presents the theoretical and numerical design of a novel radiative near-field wireless power transfer (WPT) system at millimeter waves (mm-waves), based on one TX and one RX resonant Bessel-beam launcher, with the aim of providing superior performance in terms of energy focusing capabilities. To evaluate the achievable rectified power, for several TX-RX distances, the wireless link is accurately and efficiently accounted for, by combining the EM analysis of the launchers with EM theory. A single-diode rectifier is designed to operate at 37.5 GHz: for a received power of 0 dBm the expected rectifier efficiency exceeds 30%. Radiative near-field wireless power transfer (WPT) promises several benefits over both nonradiative near-field and radiative far-field wireless links. The compact size of the proposed system makes it particularly attractive for future mm-wave wearable WPT systems.
This paper presents a novel wireless power transfer design to seamlessly power a smart health tracking ring using a smartphone. The reverse wireless charging feature of smartphones allows them to transmit sufficient energy to charge the smart ring when users hold the smartphones in their hands without impacting the user. The tested system includes a transmitter generating 170.07 kHz signals from a 5 V DC supply and a receiver circuit that captures the magnetic signal and converts it into a DC output to charge a 3.7 V battery and power a heart rate sensing monitor. The experimental results demonstrate that the smart ring can receive a maximum power of 102.4 mW from a 5 V DC smartphone power supply. The maximum measured efficiency of the wireless power transfer system from the transmitting power amplifier input to the DC output of a full-bridge rectifier is 13.39%. If the smartphone is held at least 1.52 hours a day, the ring will receive sufficient power to continuously track the user's heart rate in a 24-hour period.
This paper reports 400-W 85-kHz band inductive charging system prototype for UAV or drone to be employed for overhead power transmission line patrol. For patrol of the long overhead power transmission line network, the consecutive charging opportunities which will be provided by multiple rapid wireless charging ports are desired. The rapid inductive charging system with frustum-shape wireless charging port and lightweight on-board power receive equipment is prototyped to serve such opportunity charging. The successful test of sequential operation of landing on the wireless charging port, 400-W or more wireless charging of lithium ion battery, taking off, and photo-shooting of overhead power transmission lines between actual high-rise steel towers by high-precision camera, show a great potential of the proposed inductive charging system for opportunity charging of long range patrol.
The existing contactless energy transfer of rotary ultrasonic machining equipment involves a small transmission distance (0.1-1 mm). In this research, magnetically coupled resonant wireless power transfer was used in rotary ultrasonic machining process. A series of theoretical models were established to explore the transmission characteristics of the system, and experiments were carried out to verify transmission characteristics.
This paper presents a tunable multistage matching network (TMMN) for compensating variations in large air-gap capacitive wireless power transfer (WPT). The proposed multistage matching network is employed with a variable capacitor, whose capacitance value is suitably modified to compensate for misalignments and distance variations between couplers. This capacitor is connected at an intermediate port of the multistage matching network, allowing it to be realized using devices rated for a much lower voltage than the coupler voltage, which is rated at kilo-volt level for large air gap capacitive WPT system. A systematic methodology to design the proposed TMMN which maximizes its compensation range while maintaining low losses is also introduced. A 27.12-MHz prototype is designed, built and tested to validate the concept and design methodology.
This paper proposes a three-layers stack metasurface first, and then employed it to a compact double-band wireless power transfer (WPT) system. For the proposed dual-band WPT system, the metasurface exhibits the wide-band characteristic of the negative-near-zero permeability from 222 MHz to 889 MHz, where the transmission efficiency improves significantly at longer WPT distance at the lower band. Only a unit cell is stacked in three layers so that the size of the proposed metasurface has significantly reduced compared to a conventional metasurface where several unit cells are arranged in 1-D topology. The size of the proposed WPT system and the metasurface is 15 x15 mm and 20 x20 mm, respectively. Also, capacitors with the value of 0.1pF are etched on the gaps of the metasurface. The measured efficiencies’ improvement ratios are 1.13 at 390 MHz in the air, where the WPT distance is significantly improved from 19 mm to 23 mm.
Using ultrasound to power deeply implanted biomedical devices is a promising technique due to its low attenuation in body tissue and its short wavelength that allows precise focusing of the energy. Ultrasound energy harvesting conventionally has been done using lead zirconate titanate (PZT) ultrasound transducers, which uses the piezoelectric effect to convert mechanical vibration to an electrical voltage. However, PZT is typically bulky, and is not bio-compatible, and cannot be monolithically integrated with application-specific integrated circuits (ASIC). In this work, a pre-charged collapse-mode capacitive micromachined ultrasonic transducer (CMUT) was fabricated to harvest ultrasound energy. The pre-charged CMUT has a high power transfer efficiency over a wide bandwidth at optimal loading conditions; 43 % at 2.15 MHz and 47 % at 5.85 MHz. For the last 1.4 years, the device has been in collapse-mode, and it is still functional without any additional charging. This device will enable the development of smaller implantable biomedical devices in the future.
Digital Low Drop-Out regulators, in contrast to analog counterparts, provide an architecture of sub-1 V regulation with low power consumption, high power efficiency, and system integration. Towards an optimized integration in the ultra-low-power System-On-Chip Internet of Things architecture that is operated through Radio Frequency energy harvesting scheme, the D-LDO regulator should constitute the main regulator that powers the master-clock and rest loads of the SoC. In this context, this work presents a self-clocked D-LDO design dedicated for wireless power transfer and harvesting applications such as RFID with nano-power consumption and 0.5 V operational voltage, fabricated at a 55-nm Global Foundries CMOS process. With the purpose to validate the self-start-up capability of the presented D-LDO in the presence of ultra-low input power, a test-bench with a RF rectifier is implemented that provides the RF to DC operation and feeds the D-LDO. Power efficiency and load regulation curves of the D-LDO are presented as extracted from the RF to DC operation. It presents 386 nA minimum quiescent current, 83.6 % power efficiency during the RF to DC operation with 3.65 mu A load current and regulator referred input power of -27 dB(m).
The efficiency of an on-body wireless power transfer system for implant powering is defined by how the electromagnetic energy interacts with the lossy, heterogeneous, and dispersive body tissues. The objective of this study is to discuss the methodology and evaluate the theoretical bounds for the frequency-dependent electromagnetic energy transfer efficiency. We propose a simplified model that uses a finite tissue-equivalent phantom enclosing an implantable receiver surrounded by a medium that represents a transmitter matched to the wave impedance of the body. This model is used to study different cases and evaluate the wireless power transfer efficiency as a function of the operating frequency and implantation depth. The obtained results can be used as a guideline to choose the design parameters and constraints of the on-body power source and gauge its performance against the predicted maximum achievable efficiency.
This paper presents a nonlinear capacitive WPT system that automatically compensate for the coupling variation between the transmitter and receiver in a capacitive wireless power transfer (WPT) system with no active circuitry. The system is capable of minimizing the output power variation at a fixed operating frequency of 13 MHz as the coupling distance varies. A constant output power is achieved over a wide range of coupling capacitance variation in comparison to the conventional capacitive wireless power transmission circuits. Such an approach is attractive for biomedical implants employing a capacitive WPT system.
This paper introduces a new method for optimizing the efficiency of two planar coils for a wireless power transfer system, assuring a specific pre-defined efficiency over the entire given charging surface. The referred efficiency is calculated from the transmitter's source to the receiver's load. This study is based on rectangular shaped coils. The electrical parameters, coupling and efficiency of the system are calculated and optimized as function of their physical dimensions. Thus, taking those parameters into account a useful design tool is proposed here. One of many possible designs is presented as example, which proves by theoretical and simulation results that the receiver might be free-positioned over the surface of charging without losing efficiency. Results for a 13.56 MHz system show that more than 82 % of efficiency (load to transmitter coil) can be achieved for a 4 cm x4 cm receiver moving over a 12 cm x8 cm surface.
In this paper, several retro-reflective beamforming schemes for wireless power transmission to multiple targets (with "targets" standing for "wireless power receivers" in this paper) are analyzed with the aid of numerical simulations. Various practical complications are identified if the pilot signals of multiple targets are not differentiated from each other properly. A retro-reflective beamforming scheme based on frequency division, in which multiple targets transmit continuous-wave pilot signals at respective frequencies, is demonstrated capable of generating multiple wireless power beams aiming at the targets respectively with power transmission performance in excellent agreement with the theoretical values.
This paper describes a method to reduce magnetic field leakage from a Wireless Power Transfer (WPT) systems. By using frequency split phenomena, the reactive shield can reduce the magnetic field of the target frequency band with increasing power transfer efficiency. The simulation results of the suggested reactive shielding coil structure are verified with a 50W-WPT system.
RF wireless power transfer (WPT) is an essential building block for simultaneous wireless information and power transfer (SWIPT) and wireless powered communication (WPC) systems. It has been shown that the efficiency of RF-DC conversion of a rectifier is dependent on both input power and the load resistance. In this paper, we present a novel analytical solution for the optimal load resistance in terms of DC power on the resistive load for two harvester topologies, namely the series-diode half-wave rectifier and Greinacher voltage doubler. Additionally, closed-form solutions are presented for low input power to obtain intuitive insights. The proposed method models the diode with the equivalent Schottky diode model, taking the parasitic and packaging effects into consideration. The validity of the method is verified by simulations with both continuous sinewave (CW) and multi-sinewave input.
This paper describes the 2.4GHz band SOI-CMOS high power bridge rectifier IC with the cross coupled CMOS pair (CCP). At first of all, topologies of the rectifier diodes are investigated for improvement of rectifier efficiency and handling power. It is clarified that the CCP has advantages on low threshold and breakdown voltages compared with the gated anode diode (GAD). The developed bridge rectifier IC achieves rectification efficiency of 51 % at input power of 25 dBm. This is top efficiency in sub-W class CMOS rectifier ICs.
In recent, microwave power transfer (MPT) for IoT devices has been studied. The distributed MPT can supply power efficiently by cooperate multiple transmit antenna arranged distributed in a relatively wide area. In this paper, we propose a method for distributed beam control by closed-loop with a backscatter signal from the receiver. The effectiveness of the proposed method will be demonstrated by lay-trace simulation and experiment.
