Wireless Power Delivery Research Articles

Enhancing Ultrasound Power Transfer: Efficiency, Acoustics, and Future Directions.

Implantable medical devices (IMDs), like pacemakers regulating heart rhythm or deep brain stimulators treating neurological disorders, revolutionize healthcare. However, limited battery life necessitates frequent surgeries for replacements. Ultrasound power transfer (UPT) emerges as a promising solution for sustainable IMD operation. Current research prioritizes implantable materials, with less emphasis on sound field analysis and maximizing energy transfer during wireless power delivery. This review addresses this gap. A comprehensive analysis of UPT technology, examining cutting-edge system designs, particularly in power supply and efficiency is provided. The review critically examines existing efficiency models, summarizing the key parameters influencing energy transmission in UPT systems. For the first time, an energy flow diagram of a general UPT system is proposed to offer insights into the overall functioning. Additionally, the review explores the development stages of UPT technology, showcasing representative designs and applications. The remaining challenges, future directions, and exciting opportunities associated with UPT are discussed. By highlighting the importance of sustainable IMDs with advanced functions like biosensing and closed-loop drug delivery, as well as UPT's potential, this review aims to inspire further research and advancements in this promising field.

Scalable Fabrication of Large-Scale, 3D, and Stretchable Circuits.

Stretchable electronics have demonstrated excellent potential in wearable healthcare and conformal integration. Achieving the scalable fabrication of stretchable devices with high functional density is the cornerstone to enable the practical applications of stretchable electronics. Here, a comprehensive methodology for realizing large-scale, 3D, and stretchable circuits (3D-LSC) is reported. The soft copper-clad laminate (S-CCL) based on the "cast and cure" process facilitates patterning the planar interconnects with the scale beyond 1 m. With the ability to form through, buried and blind VIAs in the multilayer stack of S-CCLs, high functional density can be achieved by further creating vertical interconnects in stacked S-CCLs. The application of temporary bonding substrate effectively minimizes the misalignments caused by residual strain and thermal strain. 3D-LSC enables the batch production of stretchable skin patches based on five-layer stretchablecircuits, which can serve as a miniaturized system for physiological signals monitoring with wireless power delivery. The fabrications of conformal antenna and stretchable light-emitting diode display further illustrate the potential of 3D-LSC in realizing large-scale stretchable devices.

Feasibility analysis of wireless power delivery to implanted sensors of XLIF patients

Abstract The paper aims to aid in developing a monitoring system for surgery patients who have undergone lumbar interbody fusion (LIF). The present body of work functions as a comprehensive analysis of relevant available literature along with our investigation regarding techniques for power delivery; both energy harvesting and wireless power transfer (WPT) alike. In addition, biological considerations are taken into account as they strongly influence the design and testing methodology of an implanted medical device (IMD). This study proposes using inductive coupling as a power delivery method. This was chosen due to the robust nature of the technology, with the IMD being deeply situated and encased in bone and tissue. Three types of receiver coil architectures were explored and designed around the geometry of a polyether ether ketone (PEEK) Extreme lateral interbody fusion (XLIF) Nuvasive Coroent XL interbody cage. With the use of off-the-shelf components, functionality was only attainable for the V3 coil design featured with 0.4 mm wire windings around horizontal and vertical beams present on the implant. The secondary coil was resonantly tuned and optimized for a 141 kHz working frequency. At a 100 mm coupling distance, it was demonstrated that a power delivery load (PDL) of 3.94 mA was able to be induced resulting in a power output of 7.21 mW. The recorded PDLs are capable of powering a high pressure P122 sensor, EFM8BB52 microcontroller, and Ultra-wideband (UWB) data telemetry link, and demonstrate the feasibility of this WPT technique for in vivo monitoring of bone fusion post XLIF surgery.

A Semi‐Passive Smart Contact Lens with on‐Lens Power Storage Element

This paper presents a semi‐passive smart contact lens platform for sensor and actuator applications. It focuses on design improvements made prior to human clinical trials involving basic considerations on comfort and safety, which are verified through animal studies. Observations of tissue temperature variation and post‐trial surgery examinations confirm that the 50 μW on‐lens wireless power delivery reduces the impact on tissue of previously reported SCL. Migration of wirelessly powered radio frequency identification (RFID)‐based passive SCL to semi‐passive systems is enabled with the proposed on‐lens power storage element. Furthermore, a switched capacitor converter extends the active time of the storage element and reduces electromagnetic influence. © 2024 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Maze-Based Scalable Wireless Power Transmission Experimental Arena for Freely Moving Small Animals Applications.

This paper presents an innovative T/Y-maze-based wireless power transmission (WPT) system designed to monitor spatial reference memory and learning behavior in freely moving rats. The system facilitates uninterrupted optical/electrical stimulation and neural recording experiments through the integration of wireless headstages or implants in T/Y maze setups. Utilizing an array of resonators covering the entire underneath of the mazes, the wireless platform ensures scalability with various configurations. The array is designed to ensure a natural localization mechanism to localize the Tx power toward the location of the Rx coil. The system is analyzed and modeled using ANSYS HFSS software to optimize design. The primary goal was to achieve uniform wireless power delivery throughout the mazes through a comparative study of different transmitter (Tx) array configurations, such as float, series, and parallel resonators. The calculated Specific Absorption Rate (SAR) in rat tissue model equals 1.7 W/kg at the power carrier frequency of 13.56 MHz. A prototype of the proposed maze-based WPT design, featuring 8 Tx resonators, a Tx coil and power amplifier, and a headstage power harvesting unit, is successfully implemented and its performance characterized for all three resonator configurations. The implemented T maze-based WPT system has a total length of 128 cm. In the overlapping Tx resonators configuration, a homogeneity of 94% is achieved for the measured power transfer efficiency at over 30%, while continuously delivering over 60 mW for series configuration.

A 40.68-MHz Active Rectifier With Cycle-Based On-/Off-Delay Compensation for High-Current Biomedical Implants

This article presents a 40.68-MHz active rectifier for high-current biomedical implants. Cycle-based timing control (CBTC) is proposed to significantly extend the duration for compensating both turn-on and turn-off delays of active diodes at 40.68 MHz, thereby improving both the power conversion efficiency (PCE) and the voltage conversion ratio (VCR) of the rectifier. The supply independent ramp, the delay-mimicking sample-and-hold (DMSH) circuit, and the low-voltage (LV)-stress startup scheme are also developed to maintain high PCE and VCR, and ensure rectifier reliability over a wide input range. Implemented in standard 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS, the proposed fully integrated rectifier delivers a maximum output power of 207 mW and operates at 40.68 MHz to enable the use of a small-diameter receiver coil of 4 mm. This rectifier is the first to achieve full turn-on and turn-off delay compensation at 40.68 MHz, so its maximum PCE and VCR obtain 86% and 96.3%, respectively. Compared with the prior art, this work not only provides more stable high PCE and VCR over a wider input range from 1.9 to 3.8 V at 40.68 MHz but also uses the smallest receiver coil for wireless power delivery.

Emerging Optoelectronic Devices Based on Microscale LEDs and Their Use as Implantable Biomedical Applications.

Thin-film microscale light-emitting diodes (LEDs) are efficient light sources and their integrated applications offer robust capabilities and potential strategies in biomedical science. By leveraging innovations in the design of optoelectronic semiconductor structures, advanced fabrication techniques, biocompatible encapsulation, remote control circuits, wireless power supply strategies, etc., these emerging applications provide implantable probes that differ from conventional tethering techniques such as optical fibers. This review introduces the recent advancements of thin-film microscale LEDs for biomedical applications, covering the device lift-off and transfer printing fabrication processes and the representative biomedical applications for light stimulation, therapy, and photometric biosensing. Wireless power delivery systems have been outlined and discussed to facilitate the operation of implantable probes. With such wireless, battery-free, and minimally invasive implantable light-source probes, these biomedical applications offer excellent opportunities and instruments for both biomedical sciences research and clinical diagnosis and therapy.

Output characteristics modeling and experimental verification of secondary-uncompensated inductive power delivery link operating without feedback

Series-none compensated induction wireless power delivery link (SN-IPDL) was recently shown to be capable of achieving minimal complexity receiver with reduced losses in case of strong coupling, typical for applications such as power delivery into enclosed compartments such as industrial glove boxes and close-range inductive heating. Common practical applications often feature power delivery to varying loads which require a stable operational voltage. Operation at LIVO frequency allows establishing potentially feedback-free wireless power delivery with constant output voltage for varying loads. The paper reveals that due to nonzero equivalent series resistances and invalidity of the first-harmonic-approximation (FHA) based equivalent circuit, the output voltage remains affected by the load despite operation at LIVO frequency, residing within a certain range of values, lower and upper bounds of which correspond to rated and zero loading, respectively. This must be considered during SN-IPDL system design in order to assure that output voltage stays within allowed bounds for relevant loading conditions. This paper derives analytical expressions for output voltage bounds of a power-loaded series-to SN-IPDL, functioning at load-independent-voltage-output (LIVO) frequency. Time domain differential equations (DE)-based analysis is applied to derive the two bounds and allows (as a by-product) establishing an alternative FHA-based equivalent circuit of SN-IPDL operating in continuous conduction mode. Simulations and experiments based on 380V, 1.2 kW-rated prototype demonstrate excellent matching with analytical outcomes, validating the proposed analysis.

Wireless Electrical Power Delivery Using Light through Soft Skin Tissues under Misalignment and Deformation

AbstractProviding sustainable electrical power to medical electronic implants is key to enabling the diverse functions of implants and to avoiding repetitive replacement surgeries of depleted batteries. Subcutaneous photovoltaic energy harvesting with an external light source patch can be a reliable approach that provides sufficient power using light. However, from a practical perspective, aligning the external light source patch over opaque skin by patients may affect the amount of delivered electrical power. The amount of delivered power may also be affected by the deformation of the light source and receiver patches in accordance with thin skin layers. In this paper, an experimental and analytical study on the performance of a power implant under an animal skin depending on the implantation depth, lateral misalignment with the external light patch, and bending radius and direction is presented. The experimental results indicate that the transferred power by the patches in misalignment (about 20% of the transmitter length) or in bending (≈30 mm radius) is maintained at least 90% power of the aligned and flat ones. The results provide important characteristic data that are required in designing reliable wireless power transfer systems for various types of implantable medical devices.

Charging of devices for healthcare applications, using ultrasound wireless power

Current wireless powering is frequently accomplished through inductive fields. An alternative for wireless powering systems is via ultrasound. Potential advantages are deeper penetration, delivery through metals, no electronic interference, and beam steerability to correct for misalignment. These characteristics enable ultrasound-based recharging of batteries located within a hermetically sealed enclosure, e.g., an implantable pulse generator (IPG). Another growth area for wireless power delivery is to support healthcare operations, when digital devices used for healthcare delivery need regular charging. Ultrasound Wireless Powering (UWP) is convenient, avoids cable clutter, and is safe. Planar ultrasound transducers operating between 1 and 3 MHz provide a practical compromise between useful directivity and effective propagation range. This talk will describe the development and evaluation of a UWP recharging system operating at 1 MHz transferring up to 100 mA at nominally 4 V, to charge a Li-Ion battery 10–20 mm through tissue. For potential neurostimulator applications, the receiver module was packaged within 1.2 cc inside a 17-cc titanium-IPG. For digital device charging with UWP, benchtop experiments will demonstrate characteristics to power smartphones comparable to the Qi-standard, version 1.0, which is an industry standard for characterizing charging with inductive fields. [Work partially supported by the NIH/NIBIB R43EB019225.]

A 0.5-mm2 Solar Cell-Powered Biofuel Cell-Input Biosensing System With LED Driving for Stand-Alone RF-Less Continuous Glucose Monitoring Contact Lens

This letter presents the first solar cell (SC)-powered biofuel cell (BFC)-input biosensing system with pulse interval modulation (PIM) and pulse density modulation (PDM) LED driving capability for continuous glucose monitoring (CGM) contact lenses featuring stand-alone RF-less operation. Power supply from on-lens SCs can eliminate the necessity of wireless power delivery, and LED implementation can eliminate the necessity of wireless communication. By employing the BFC-input approach instead of using a power-hungry potentiostat, powering and sensing components are separated, which reduces the power budget from SCs. The measured power of 28/144 nW at the PIM/PDM mode with a 0.31/0.39-V supply voltage can be managed by the on-lens SCs, enabling a fully stand-alone on-lens operation under office-room ambient light whose typical illumination intensity is 800–1600 lx.

A Wireless Power and Data Transfer IC for Neural Prostheses Using a Single Inductive Link With Frequency-Splitting Characteristic.

This paper presents a frequency-splitting-based wireless power and data transfer IC that simultaneously delivers power and forward data over a single inductive link. For data transmission, frequency-shift keying (FSK) is utilized because the FSK modulation scheme supports continuous wireless power transmission without disruption of the carrier amplitude. Moreover, the link that manifests the frequency-splitting characteristic due to a close distance between coupled coils provides wide bandwidth for data delivery without degrading the quality factors of the coils. It results in large power delivery, high data rate, and high power transfer efficiency. The presented IC fabricated in a 180-nm BCD process simultaneously achieves up-to-115-mW wireless power delivery to the load and 2.5-Mb/s downlink data rate over the single inductive link. The measured overall power efficiency from the DC power supply at the transmitter module to the load at the receiver module reaches 56.7 % at its maximum, and the bit error rate is lower than 10 -6 at 2.5 Mb/s. As a result, the figure of merit (FoM) for data transmission is enhanced by 2 times, and the FoM for power delivery is improved by 38.7 times compared to prior state-of-the-arts using a single inductive link.

Recent advances in power supply strategies for untethered neural implants

Recent advances in neural implantable systems have paved the way for neuroscience and neurosurgery research and clinical practice. Conventional tethered neural implants use physical wires for power supply and signal transmission, which impose many restrictions on the subjects. Untethered, wireless power solution has been one of the widely recognized engineering goals for neural implants. The past decade has witnessed significant technical advancement on how to achieve wireless neural implants and how to solve the wireless power delivery challenge. This paper briefly reviews and discusses the recent advances in wireless neural implantable systems based on existing power supply techniques, including batteries, electromagnetic power transfer, photovoltaic device, ultrasound power transfer, and self-powered energy harvester. Finally, future opportunities and challenges of wireless neural implantable systems are discussed.

An Integrated 2D Ultrasound Phased Array Transmitter in CMOS With Pixel Pitch-Matched Beamforming.

Emerging non-imaging ultrasound applications, such as ultrasonic wireless power delivery to implantable devices and ultrasound neuromodulation, require wearable form factors, millisecond-range pulse durations and focal spot diameters approaching 100 μm with electronic control of its three-dimensional location. None of these are compatible with typical handheld linear array ultrasound imaging probes. In this work, we present a 4 mm × 5 mm 2D ultrasound phased array transmitter with integrated piezoelectric ultrasound transducers on complementary metal-oxide-semiconductor (CMOS) integrated circuits, featuring pixel-level pitch-matched transmit beamforming circuits which support arbitrary pulse duration. Our direct integration method enabled up to 10 MHz ultrasound arrays in a patch form-factor, leading to focal spot diameter of ∼200 μm, while pixel pitch-matched beamforming allowed for precise three-dimensional positioning of the ultrasound focal spot. Our device has the potential to provide a high-spatial resolution and wearable interface to both powering of highly-miniaturized implantable devices and ultrasound neuromodulation.

Wireless, battery-free, subdermally implantable platforms for transcranial and long-range optogenetics in freely moving animals

Wireless, battery-free, and fully subdermally implantable optogenetic tools are poised to transform neurobiological research in freely moving animals. Current-generation wireless devices are sufficiently small, thin, and light for subdermal implantation, offering some advantages over tethered methods for naturalistic behavior. Yet current devices using wireless power delivery require invasive stimulus delivery, penetrating the skull and disrupting the blood-brain barrier. This can cause tissue displacement, neuronal damage, and scarring. Power delivery constraints also sharply curtail operational arena size. Here, we implement highly miniaturized, capacitive power storage on the platform of wireless subdermal implants. With approaches to digitally manage power delivery to optoelectronic components, we enable two classes of applications: transcranial optogenetic activation millimeters into the brain (validated using motor cortex stimulation to induce turning behaviors) and wireless optogenetics in arenas of more than 1 m2 in size. This methodology allows for previously impossible behavioral experiments leveraging the modern optogenetic toolkit.

Energy-Efficient Integrated Circuit Solutions Toward Miniaturized Closed-Loop Neural Interface Systems.

Miniaturized implantable devices play a crucial role in neural interfaces by monitoring and modulating neural activities on the peripheral and central nervous systems. Research efforts toward a compact wireless closed-loop system stimulating the nerve automatically according to the user's condition have been maintained. These systems have several advantages over open-loop stimulation systems such as reduction in both power consumption and side effects of continuous stimulation. Furthermore, a compact and wireless device consuming low energy alleviates foreign body reactions and risk of frequent surgical operations. Unfortunately, however, the miniaturized closed-loop neural interface system induces several hardware design challenges such as neural activity recording with severe stimulation artifact, real-time stimulation artifact removal, and energy-efficient wireless power delivery. Here, we will review recent approaches toward the miniaturized closed-loop neural interface system with integrated circuit (IC) techniques.

Stable Power Delivery Efficiency in Misaligned Wireless Power Transfer Systems Using Triffid Antennas

Stable power delivery efficiency is difficult in wireless power transfer systems without using power control. Misalignment between power transmitter and receivers makes this difficult since power is delivered axially. This paper reports on a new method for providing stable wireless power delivery efficiency in misaligned systems. By employing triffid antennas arranged in a cube stability is obtained at wide angles and all over the cubical structure.

Wireless power transfer through asymmetric topological edge states in diatomic chains of coupled meta-atoms

We present a different perspective on wireless power transfer by uniting topological edge states, which are robust states on the edge of a material enforced by topological invariants, with magnetoinductive waves on a 1D diatomic chain of magnetically coupled meta-atoms with intracell coupling exceeding intercell coupling. We show that robust edge states that exist in the stop band of the magnetoinductive waves can, in fact, be used for efficient wireless power delivery by relying on coupling via evanescent modes. Advantages in comparison to wireless power delivery via travelling magnetoinductive waves include lower electromagnetic pollution of the space around the wireless power delivery channel due to the evanescent nature of the modes and robustness against perturbations in the system. This study may change the approach to wireless power systems and near-field sensors based on arrays of coupled meta-atoms.

Magnetoelectric Materials for Miniature, Wireless Neural Stimulation at Therapeutic Frequencies

A major challenge for miniature bioelectronics is wireless power delivery deep inside the body. Electromagnetic or ultrasound waves suffer from absorption and impedance mismatches at biological interfaces. On the other hand, magnetic fields do not suffer these losses, which has led to magnetically powered bioelectronic implants based on induction or magnetothermal effects. However, these approaches have yet to produce a miniature stimulator that operates at clinically relevant high frequencies. Here, we show that an alternative wireless power method based on magnetoelectric (ME) materials enables miniature magnetically powered neural stimulators that operate up to clinically relevant frequencies in excess of 100Hz. We demonstrate that wireless ME stimulators provide therapeutic deep brain stimulation in a freely moving rodent model for Parkinson's disease and that these devices can be miniaturized to millimeter-scale and fully implanted. These results suggest that ME materials are an excellent candidate to enable miniature bioelectronics for clinical and research applications.

Miniature power and data transceiver based on multimodal operation of a single photovoltaic device

Wireless bi-directional data telemetry and power delivery are demonstrated using a single photovoltaic (PV) cell. The same cell functions as a light-emitting diode (LED), a power transducer, and a reverse-biased photodiode. This is achieved through the use of a simple inductor-capacitor resonator, with the cell’s junction providing the circuit’s capacitive element. We show that pulsed illumination at the circuit’s resonance frequency results in active switching of the PV cell between the three operating modes. Using this approach we demonstrate backward data transmission in the form of optical pulses generated by the PV cell, as well as enhanced forward data transmission and power generation. This work demonstrates the principle of using a single PV cell as an optical data transceiver while simultaneously generating energy using only two circuit elements; an inductor and a PV cell. This approach benefits miniature wireless devices, such as medical implants, which operate within significant size, weight, and energy constraints.