Query: Wireless power transfer to deep-tissue microimplants

Candidate papers:

abstract: Significance Advances in miniaturization paved the way for tiny medical devices that circumvent conventional surgical implantation, but no suitable method for powering them deep in the body has been demonstrated. Existing methods for energy storage, harvesting, or transfer require large components that do not scale to millimeter dimensions. We report a wireless powering method that overcomes this challenge by inducing spatially focused and adaptive electromagnetic energy transport via propagating modes in tissue. We use the method to realize a tiny electrostimulator that is orders of magnitude smaller than conventional pacemakers. The demonstrated performance characteristics far exceed requirements for advanced electronic function and should enable new generations of miniaturized electronic implants. The ability to implant electronic systems in the human body has led to many medical advances. Progress in semiconductor technology paved the way for devices at the scale of a millimeter or less "microimplants" but the miniaturization of the power source remains challenging. Although wireless powering has been demonstrated, energy transfer beyond superficial depths in tissue has so far been limited by large coils (at least a centimeter in diameter) unsuitable for a microimplant. Here, we show that this limitation can be overcome by a method, termed midfield powering, to create a high energy density region deep in tissue inside of which the power harvesting structure can be made extremely small. Unlike conventional near field (inductively coupled) coils, for which coupling is limited by exponential field decay, a patterned metal plate is used to induce spatially confined and adaptive energy transport through propagating modes in tissue. We use this method to power a microimplant (2 mm, 70 mg) capable of closed chest wireless control of the heart that is orders of magnitude smaller than conventional pacemakers. With exposure levels below human safety thresholds, milliwatt levels of power can be transferred to a deep tissue >5 cm) microimplant for both complex electronic function and physiological stimulation. The approach developed here should enable new generations of implantable systems that can be integrated into the body at minimal cost and risk.
author_names: John S Ho

Alexander J Yeh

Evgenios A Neofytou

Sanghoek Kim

Yuji Tanabe

Bhagat Patlolla

Ramin E Beygui

Ada S Y Poon
title: Wireless power transfer to deep tissue microimplants
venue: Proceedings of the National Academy of Sciences
year: 2014

abstract: Wireless power transfer (WPT) plays critical roles in powering deep tissue implants, which also contributes to several emerging advances for biomedical engineering. To enable a high power density region in implants, this article presents a method, termed the self phasing technology, to focus electromagnetic fields from various paths at a deep tissue spot. By performing the phase conjugated operation on the incident signal and then retransfer back to the source, coherent RF power can be achieved without learning the precise or even dynamic locations of sources and concerning inhomogeneous medium perturbations. An external slot antenna array placed above skin surface 4 mm is considered as a transmitter and an implanted rectenna consisting of a magnetic resonant coil and an RF to dc rectifier circuit is treated as a receiver. The conversion efficiency of the rectifier circuit is optimized within the received power range and the measured efficiency of 50% can be achieved at 0 dBm. To visualize the transceiver effects of the integrated system under safety thresholds, a light emitting diode (LED) is soldered at the terminal of the rectenna and measurements show that smooth drive can be achieved. Certain brightness of LED can demonstrate that the self phasing technology can support WPT for biomedical applications.
author_names: Kecheng Zhang

Changrong Liu

Zhi Hao Jiang

Yudi Zhang

Xue-guan Liu

Huiping Guo

Xinmi Yang
title: Near Field Wireless Power Transfer to Deep Tissue Implants for Biomedical Applications
venue: IEEE Transactions on Antennas and Propagation
year: 2020

abstract: In future wireless implants, tiny sensor nodes may be used for detection and treatment of various diseases and for monitoring therapeutic activities. This requires ultralow power tiny sensors implantable inside different body organs. This letter presents a biomedical RFID system meant for wireless interrogation of deep tissue millimeter size implant sensors. The communication system is based on using a repeater device that amplifies the attenuated downlink power and thus extends sensor read distance. This system enables monitoring of different body organs by placing miniature sensor implants inside them. This letter studies wireless power transmission in this system through fabrication of the antennas and conducting two port wireless link measurements.
author_names: Elham Moradi

Lauri Sydanheimo

George Steven Bova

Leena Ukkonen
title: Measurement of Wireless Power Transfer to Deep Tissue RFID Based Implants Using Wireless Repeater Node
venue: IEEE Antennas and Wireless Propagation Letters
year: 2017

abstract: This paper proposes a biomedical RFID system meant for wireless interrogation of deep tissue mm size implant sensors. The communication system is based on using a repeater device that amplifies the attenuated downlink power and thus extends sensor read distance. This system enables monitoring of different body organs by placing miniature sensor implants inside them. The repeater device should also be implanted in the wireless power path from external reader to the sensor implant in a safe place not disturbing any body functions.
author_names: Elham Moradi

Lauri Sydanheimo

Leena Ukkonen

George Steven Bova
title: Wireless power transfer to deep tissue mm size implants using wireless repeater node
venue: 2016 Loughborough Antennas Propagation Conference (LAPC)
year: 2016

abstract: Midfield wireless power transfer has proved its advantages in power delivery to miniature implantable medical devices located deeply in the human body; however, the delivered power level is still low. Besides, design proposals for a compact source structure concentrating the transmitter field on a miniature implant remain challenges. This letter presents a novel compact transmitting structure (TX) at the midfield band and shows the capability of focusing the magnetic field inside the human tissue. Source performance has been verified by implantable planar inverted F antenna (PIFA) with a total size of 9 x 13 mm$^2} (RX) that positioned in the heart tissue layer at a 55 mm separated distance of TX and RX. In addition, the power transfer efficiency has been demonstrated by a measurement setup using pork muscle, which obtained a good match of the transmission coefficient between the simulation and experiment results. Consequently, for 1 W of output power from the midfield transmitter, the received energy could be achieved more than 5.6 mW via the implantable antenna at a subwavelength distance.
author_names: Ngan Nguyen

Nam Ha-Van

Chulhun Seo
title: Midfield Wireless Power Transfer for Deep Tissue Biomedical Implants
venue: IEEE Antennas and Wireless Propagation Letters
year: 2020

abstract: Passive operation and battery charging of deep body implants can be insured through wireless power transfer (WPT) technologies. However, the power transfer efficiency (PTE) is constrained by device miniaturization and implantation depth. This study proposes a complete WPT system consisting of a patterned WPT transmitter (Tx) an efficient rectifier, and an antenna integrated with the system. The WPT Tx had a size of 6 cm <inline formula> <tex math notation="LaTeX"\times$ /tex math>/inline formula> 6 cm and was optimized to focus the power on the deep tissue implants at 1470 MHz. The voltage doubler was optimized at 1470 MHz, had a small size of 5 mm <inline formula> <tex math notation="LaTeX"\times$ /tex math>/inline formula> 10 mm, and exhibited a high radio frequency (RF) to direct current (dc) conversion efficiency of 90% at 2 dBm RF input power. Moreover, the implantable antenna occupies a small volume of 8.43 mm<sup>3</sup> and supports quad band operations: telemetry at 403 and 915 MHz, WPT at the midfield band of 1470 MHz, and control signaling at 2.4 GHz. First, the fabricated prototypes were measured individually in minced pork, in the American Society for Testing and Materials (ASTM) model, and in the saline filled 3 D head phantom. While operating collectively as an integrated system, the PTE of the system was measured. Additionally, to enhance the PTE of the WPT system, a high dielectric matching layer <inline formula> <tex math notation="LaTeX"\varepsilon _{r} 78$ /tex math>/inline formula> was used between the WPT Tx and the phantom. Furthermore, to demonstrate the PTE of the WPT system, the voltage doubler was integrated with the implantable antenna, encapsulated in a 3 D printed capsule endoscope, and its PTE was measured in a saline solution and minced pork. Finally, the compliance of the WPT system with the human safety standards was analyzed and found that the system solely satisfied the safety limits. It is evident from the experimental results that the system can transfer 6.7 mW power to millimeter sized implants located 5 cm deep in tissues.
author_names: Abdul Basir

Hyoungsuk Yoo
title: Efficient Wireless Power Transfer System With a Miniaturized Quad Band Implantable Antenna for Deep Body Multitasking Implants
venue: IEEE Transactions on Microwave Theory and Techniques
year: 2020

abstract: In this study, we introduce a triple band flexible implantable antenna that is tuned by using a ground slot in three specific bands, namely Medical Implanted Communication Service (MICS: 402 405 MHz) for telemetry, the midfield band (lower gigahertz: 1.45 1.6 GHz) for Wireless Power Transfer (WPT) and the Industrial, Scientific and Medical band (ISM: 2.4 2.45 GHz) for power conservation. The telemetry performance of the proposed antenna was simulated and measured by using a porcine heart. To check the feasibility of WPT, a midfield transmitter antenna was introduced. In addition, to reduce the unwanted power leakage due to WPT, a Near Field Plate (NFP) was also used. Finally, power conservation can be realized by triggering the antennas sleep mode in the ISM band.
author_names: Rupam Das

Hyoungsuk Yoo
title: A triple band deep tissue implantable antenna incorporating biotelemetry and unidirectional wireless power transfer system
venue: 2017 IEEE International Symposium on Antennas and Propagation USNC/URSI National Radio Science Meeting
year: 2017

abstract: In this study, we introduce a triple band flexible implantable antenna that is tuned by using a ground slot in three specific bands, namely Medical Implanted Communication Service (MICS: 402~405 MHz) for telemetry, the midfield band (lower gigahertz: 1.45~1.6 GHz) for Wireless Power Transfer (WPT) and the Industrial, Scientific and Medical band (ISM: 2.4~2.45 GHz) for power conservation. The telemetry performance of the proposed antenna was simulated and measured by using a porcine heart. To check the feasibility of WPT, a midfield transmitter antenna was introduced. In addition, to reduce the unwanted power leakage due to WPT, a Near Field Plate (NFP) was also used. Finally, power conservation can be realized by triggering the antenna's `sleep mode' in the ISM band.
author_names: Rupam Das

Youngdae Cho

Hyoungsuk Yoo
title: High efficiency unidirectional wireless power transfer by a triple band deep tissue implantable antenna
venue: 2016 IEEE MTT S International Microwave Symposium (IMS)
year: 2016

author_names: Tracy A Hampton
title: Wireless System Transfers Power to Deep Tissue Microimplants
year: 2014

abstract: Mid field wireless power transfer (MF WPT) is a scheme developed for transcutaneous power transfer to microimplants kept deep inside the body in GHz frequency.With deep seated implants, the possible locations available for application increases to almost the entire body. But, this advantage of applicability is severely limited as the power delivered to the micro implants by MF WPT is very low in the range of few 100W. Yet, the mid field operations have higher efficiency in miniaturized weakly coupled coil implants compared to traditional near field system. So, with improvement in certain aspects, MF WPT is expected to play a vital role in biomedical field. For the same reason this paper focuses on analyses of literature available in various aspects of MF WPT, its challenges, drawbacks and future scope of the scheme in medical field.
author_names: K Keerthi

K Ilango

G N Manjula
title: Study of Midfield Wireless Power Transfer for Implantable Medical Devices
venue: 2018 2nd International Conference on Biomedical Engineering (IBIOMED)
year: 2018