Miniaturised Wireless Power Transfer Systems for Neurostimulation: A Review

In neurostimulation, wireless power transfer is an efficient technology to overcome several limitations affecting medical devices currently used in clinical practice. Several methods were developed over the years for wireless power transfer. In this review article, we report and discuss the three most relevant methodologies for extremely miniaturised implantable neurostimulator: ultrasound coupling, inductive coupling and capacitive coupling. For each powering method, the discussion starts describing the physical working principle. In particular, we focus on the challenges given by the miniaturisation of the implanted integrated circuits and the related ad-hoc solutions for wireless power transfer. Then, we present recent developments and progresses in wireless power transfer for biomedical applications. Last, we compare each technique based on key performance indicators to highlight the most relevant and innovative solutions suitable for neurostimulation, with the gaze turned towards miniaturisation

Implantable microdevice with integrated wireless power transfer for thermal neuromodulation applications

Medication resistant neurological and psychiatric disorders, RNPD, are devastating multicausal chronic diseases that cannot be adequately controlled using conventional pharmaco and/or psychotherapies, being epilepsy a well-known RNPD. Wireless biomedical device availability is growing at an impressive rate, and the systems' miniaturization, integration and complexity is also increasing, unveiling new therapies based on such new devices. This paper presents a new wireless implantable device as a solution for thermal neuromodulation of brain cells, which can be used to treat or study the brain's behavior when cooled down. The obtained results show that, despite these systems' potential to be power hungry, they may operate within acceptable electrical power values, while reaching the required neuromodulation temperatures.This work has been supported by FCT (Fundação para a Ciência e Tecnologia) in the scope of the project PTDC/EEITEL/5250/2014, project PTDC/CTM-NAN/5414/2014 and under grant SFRH/BD/100649/2014.info:eu-repo/semantics/publishedVersio

Miniaturized high gain flexible spiral antenna tested in human-like tissue

A miniaturized helical antenna is presented in this work. The antenna is flexible, it is 6100 μm long and it has a diameter of 352 μm. This antenna has such a small cross-section, that permits to be implanted in the human body with fine syringes and minimally invasive surgeries. The antenna can be used to receive power and/or send information in medical devices. The antenna is made of biocompatible materials: polytetrafluoroethylene (PFTE) and copper. The fundamental parameters of the antenna have been simulated and experimentally measured in animal human-like tissues, showing good agreement. The resonant frequency of the antenna is 4.7 GHz, with a reflection coefficient of −25.1 dB, and a gain of −4.7 dBi. As expected, the resonant frequency decreases inside biological tissues comparing to the free-space open-air measurement. Reducing the resonant frequency is an advantage because power signals can penetrate deeper into body tissues

Ultrasonically powered compact implantable dust for optogenetics

This paper presents an ultrasonically powered microsystem for deep tissue optogenetic stimulation. All the phases in developing the prototype starting from modelling the piezoelectric crystal used for energy harvesting, design, simulation and measurement of the chip, and finally testing the whole system in a mimicking setup are explained. The developed system is composed of a piezoelectric harvesting cube, a rectifier chip, and a micro-scale custom-designed light-emitting-diode (LED), and envisioned to be used for freely moving animal studies. The proposed rectifier chip with a silicon area of 300 μm × 300 μm is implemented in standard TSMC 0.18 μm CMOS technology, for interfacing the piezoelectric cube and the microLED. Experimental results show that the proposed microsystem produces an available electrical power of 2.2 mW while loaded by a microLED, out of an acoustic intensity of 7.2 mW/mm 2 using a (1 mm) 3 crystal as the receiver. The whole system including the tested rectifier chip, a piezoelectric cube with the dimensions of (500 μm) 3 , and a μLED of 300 μm × 130 μm have been integrated on a 3 mm × 1.5 mm glass substrate, encapsulated inside a bio-compatible PDMS layer and tested successfully for final prototyping. The total volume of the fully-packaged device is estimated around 2.85 mm 3

Coupled resonator based wireless power transfer for bioelectronics

Implantable and wearable bioelectronics provide the ability to monitor and modulate physiological processes. They represent a promising set of technologies that can provide new treatment for patients or new tools for scientific discovery, such as in long-term studies involving small animals. As these technologies advance, two trends are clear, miniaturization and increased sophistication i.e. multiple channels, wireless bi-directional communication, and responsiveness (closed-loop devices). One primary challenge in realizing miniaturized and sophisticated bioelectronics is powering. Integration and development of wireless power transfer (WPT) technology, however, can overcome this challenge. In this dissertation, I propose the use of coupled resonator WPT for bioelectronics and present a new generalized analysis and optimization methodology, derived from complex microwave bandpass filter synthesis, for maximizing and controlling coupled resonator based WPT performance. This newly developed set of analysis and optimization methods enables system miniaturization while simultaneously achieving the necessary performance to safely power sophisticated bioelectronics. As an application example, a novel coil to coil based coupled resonator arrangement to wirelessly operate eight surface electromyography sensing devices wrapped circumferentially around an able-bodied arm is developed and demonstrated. In addition to standard coil to coil based systems, this dissertation also presents a new form of coupled resonator WPT system built of a large hollow metallic cavity resonator. By leveraging the analysis and optimization methods developed here, I present a new cavity resonator WPT system for long-term experiments involving small rodents for the first time. The cavity resonator based WPT arena exhibits a volume of 60.96 x 60.96 x 30.0 cm3. In comparison to prior state of the art, this cavity resonator system enables nearly continuous wireless operation of a miniature sophisticated device implanted in a freely behaving rodent within the largest space. Finally, I present preliminary work, providing the foundation for future studies, to demonstrate the feasibility of treating segments of the human body as a dielectric waveguide resonator. This creates another form of a coupled resonator system. Preliminary experiments demonstrated optimized coupled resonator wireless energy transfer into human tissue. The WPT performance achieved to an ultra-miniature sized receive coil (2 mm diameter) is presented. Indeed, optimized coupled resonator systems, broadened to include cavity resonator structures and human formed dielectric resonators, can enable the effective use of coupled resonator based WPT technology to power miniaturized and sophisticated bioelectronics

Self-folding 3D micro antennas for implantable medical devices

Tese de Doutoramento em Engenharia Biomédica.Recent advances in device miniaturization have been enabling smart and small implantable medical devices. These are often powered by bulky batteries whose dimensions represent one of the major bottlenecks on further device miniaturization. However, alternative powering methods, such as electromagnetic waves, do not rely on stored energy and are capable of providing high energy densities per unit of area, thus increasing the potential for device miniaturization. Hence, we envision an implanted medical device with an integrated miniaturized antenna, capable of receiving a radiofrequency signal from an exterior source, and converting it to a DC signal, thus enabling remote powering. This thesis addresses the analysis, design, fabrication and characterization of novel 3D micro antennas that can be integrated on 500 × 500 × 500 μm3 cubic devices, and used for wireless power transfer purposes. The analysis is built upon the theory of electrically small antennas in lossy media, and the antenna design takes into consideration miniaturization techniques which are compatible with the antenna fabrication process. For the antenna fabrication, a methodology that combines conventional planar photolithography techniques and self-folding was used. While photolithography allows the easy patterning of virtually every desired planar antenna configuration with reproducible feature precision, and the flexibility to easily and precisely change the antenna geometry and size, self-folding allows assembly of the fabricated planar patterns into a 3D structure in a highly parallel and scalable manner. After fabrication, we characterized the fabricated antennas by measuring their S-parameters and radiation patterns, demonstrating their efficacy at 2 GHz when immersed in dispersive media such as water. This step required the development and test of multiple characterization setups based on connectors, RF probes and transmission lines and the use of an anechoic chamber. Moreover, we successfully show that the antennas can wireless transfer energy to power an LED, highlighting a proof of concept for practical applications. Our findings suggest that self-folding micro antennas could provide a viable solution for powering tiny micro devices.Os recentes avanços das tecnologias de miniaturização têm permitido o desenvolvimento de dispositivos médicos implantáveis inteligentes e mais pequenos. Estes são muitas vezes alimentados por baterias volumosas cujas dimensões limitam o nível de miniaturização alcançável por um micro dispositivo. No entanto, existem formas alternativas de alimentar estes dispositivos que não dependem de energia armazenada, tais como ondas eletromagnéticas, que são capazes de providenciar uma elevada densidade de energia por unidade de área, aumentando assim o potencial de miniaturização dos dispositivos. Desta forma, visionamos um dispositivo médico implantado, com uma antena miniaturizada e integrada, capaz de receber um sinal de rádio frequência a partir de uma fonte externa, e convertê-lo num sinal DC, permitindo assim a alimentação remota do aparelho. Esta tese apresenta a análise, desenho, fabrico e caracterização de micro antenas 3D, passíveis de serem integradas em micro dispositivos cúbicos (500 × 500 × 500 μm3), e utilizadas para fins de transferência de energia sem fios. A análise assenta na teoria das antenas eletricamente pequenas em meios com perdas, e o design da antena considera técnicas de miniaturização de antenas. Para o fabrico da antena foi utilizada uma metodologia que combina técnicas de fotolitografia planar e auto-dodragem (self-folding). Enquanto a fotolitografia permite a padronização de virtualmente todos os tipos de configurações planares de forma precisa, reprodutível, e com a flexibilidade para se mudar rapidamente a geometria e o tamanho da antena, o self-folding permite a assemblagem dos painéis planares fabricados numa estrutura 3D. Depois do fabrico, as antenas foram caracterizadas medindo os seus parâmetros S e diagramas de radiação, demonstrando a sua eficácia a 2 GHz quando imersas num meio dispersivo, tal como água. Esta etapa exigiu o desenvolvimento e teste de várias setups de caracterização com base em conectores, sondas de RF e linhas de transmissão, e ainda o uso de uma câmara anecóica. Além disso, mostramos com sucesso que as micro antenas podem receber e transferir o energia para um LED acendendo-o, destacando assim esta prova de conceito para aplicações práticas. Os nossos resultados sugerem que estas micro antenas auto-dobráveis podem fornecer uma solução viável para alimentar micro dispositivos implantáveis muito pequenos.Fundação para a Ciência e a Tecnologia (FCT) bolsa SFRH/BD/63737/2009

Improving the mechanistic study of neuromuscular diseases through the development of a fully wireless and implantable recording device

Neuromuscular diseases manifest by a handful of known phenotypes affecting the peripheral nerves, skeletal muscle fibers, and neuromuscular junction. Common signs of these diseases include demyelination, myasthenia, atrophy, and aberrant muscle activity—all of which may be tracked over time using one or more electrophysiological markers. Mice, which are the predominant mammalian model for most human diseases, have been used to study congenital neuromuscular diseases for decades. However, our understanding of the mechanisms underlying these pathologies is still incomplete. This is in part due to the lack of instrumentation available to easily collect longitudinal, in vivo electrophysiological activity from mice. There remains a need for a fully wireless, batteryless, and implantable recording system that can be adapted for a variety of electrophysiological measurements and also enable long-term, continuous data collection in very small animals. To meet this need a miniature, chronically implantable device has been developed that is capable of wirelessly coupling energy from electromagnetic fields while implanted within a body. This device can both record and trigger bioelectric events and may be chronically implanted in rodents as small as mice. This grants investigators the ability to continuously observe electrophysiological changes corresponding to disease progression in a single, freely behaving, untethered animal. The fully wireless closed-loop system is an adaptable solution for a range of long-term mechanistic and diagnostic studies in rodent disease models. Its high level of functionality, adjustable parameters, accessible building blocks, reprogrammable firmware, and modular electrode interface offer flexibility that is distinctive among fully implantable recording or stimulating devices. The key significance of this work is that it has generated novel instrumentation in the form of a fully implantable bioelectric recording device having a much higher level of functionality than any other fully wireless system available for mouse work. This has incidentally led to contributions in the areas of wireless power transfer and neural interfaces for upper-limb prosthesis control. Herein the solution space for wireless power transfer is examined including a close inspection of far-field power transfer to implanted bioelectric sensors. Methods of design and characterization for the iterative development of the device are detailed. Furthermore, its performance and utility in remote bioelectric sensing applications is demonstrated with humans, rats, healthy mice, and mouse models for degenerative neuromuscular and motoneuron diseases

Design of an Integrated CMOS Transceiver with Wireless Power and Data Telemetry with Application to Implantable Flexible Neural Probes

Recent developments in implantable medical devices (IMDs) have created a need for communication systems integrated directly into the implant with feedback data for various sensing systems. The need for modern communication techniques, power delivery systems, and usable interfaces for smart implants present an interesting challenge for engineers trying to provide doctors and medical professionals with the best resources available for medical research. This dissertation will cover the design of an integrated CMOS transceiver and near-field inductive link used for an IMD and the accompanying CMOS front end for the application space of neural recording in the brain of lab mice. The design process of the CMOS IC, along with thinning techniques, the nearfield inductive link, and the design of an external reading system will be discussed in detail. The various wireless power and data telemetry techniques applicable for IMDs and their strengths and weaknesses will also be described. Software techniques and implementation for real-time analysis of a high data rate communication system from the designed IMD will be covered. Finally, transceiver verification will be given for both power and data telemetry under various scenarios, with front end verification performed via controlled lab bench experiments using input sinusoidal wave forms