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

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

An Implantable Peripheral Nerve Recording and Stimulation System for Experiments on Freely Moving Animal Subjects

A new study with rat sciatic nerve model for peripheral nerve interfacing is presented using a fully-implanted inductively-powered recording and stimulation system in a wirelessly-powered standard homecage that allows animal subjects move freely within the homecage. The Wireless Implantable Neural Recording and Stimulation (WINeRS) system offers 32-channel peripheral nerve recording and 4-channel current-controlled stimulation capabilities in a 3 × 1.5 × 0.5 cm3 package. A bi-directional data link is established by on-off keying pulse-position modulation (OOK-PPM) in near field for narrow-band downlink and 433 MHz OOK for wideband uplink. An external wideband receiver is designed by adopting a commercial software defined radio (SDR) for a robust wideband data acquisition on a PC. The WINeRS-8 prototypes in two forms of battery-powered headstage and wirelessly-powered implant are validated in vivo, and compared with a commercial system. In the animal study, evoked compound action potentials were recorded to verify the stimulation and recording capabilities of the WINeRS-8 system with 32-ch penetrating and 4-ch cuff electrodes on the sciatic nerve of awake freely-behaving rats. Compared to the conventional battery-powered system, WINeRS can be used in closed-loop recording and stimulation experiments over extended periods without adding the burden of carrying batteries on the animal subject or interrupting the experiment

Wireless tools for neuromodulation

Epilepsy is a spectrum of diseases characterized by recurrent seizures. It is estimated that 50 million individuals worldwide are affected and 30% of cases are medically refractory or drug resistant. Vagus nerve stimulation (VNS) and deep brain stimulation (DBS) are the only FDA approved device based therapies. Neither therapy offers complete seizure freedom in a majority of users. Novel methodologies are needed to better understand mechanisms and chronic nature of epilepsy. Most tools for neuromodulation in rodents are tethered. The few wireless devices use batteries or are inductively powered. The tether restricts movement, limits behavioral tests, and increases the risk of infection. Batteries are large and heavy with a limited lifetime. Inductive powering suffers from rapid efficiency drops due to alignment mismatches and increased distances. Miniature wireless tools that offer behavioral freedom, data acquisition, and stimulation are needed. This dissertation presents a platform of electrical, optical and radiofrequency (RF) technologies for device based neuromodulation. The platform can be configured with features including: two channels differential recording, one channel electrical stimulation, and one channel optical stimulation. Typical device operation consumes less than 4 mW. The analog front end has a bandwidth of 0.7 Hz - 1 kHz and a gain of 60 dB, and the constant current driver provides biphasic electrical stimulation. For use with optogenetics, the deep brain optical stimulation module provides 27 mW/mm2 of blue light (473 nm) with 21.01 mA. Pairing of stimulating and recording technologies allows closed-loop operation. A wireless powering cage is designed using the resonantly coupled filter energy transfer (RCFET) methodology. RF energy is coupled through magnetic resonance. The cage has a PTE ranging from 1.8-6.28% for a volume of 11 x 11 x 11 in3. This is sufficient to chronically house subjects. The technologies are validated through various in vivo preparations. The tools are designed to study epilepsy, SUDEP, and urinary incontinence but can be configured for other studies. The broad application of these technologies can enable the scientific community to better study chronic diseases and closed-loop therapies

Base station with wireless powering and communication for small rodents monitoring

Dissertação de mestrado integrado em Engenharia Biomédica (área de especialização em Eletrónica Médica)Dealing with medical complications such as arrhythmia, diabetes, deafness, and neurological diseases is a challenging task that is generally tackled resorting to drugs. Nevertheless, some diseases are resistant to drug-based treatments, which leads to a demand for alternative solutions. One of these can be the use of implantable devices, which play a fundamental role in monitoring and treating diseases in modern medicine. However, prior to their use in humans, extensive and rigorous tests in animal models must be performed to assess their safety and efficacy. In a first stage, these tests are performed in lab animals, usually rodents. For an implantable medical device to be tested in rats, it must be as small and lightweight as possible and not have wired connections to the exterior. This is desirable to minimize its impact in the rodent’s normal behavior, which can influence the experimental data. As such, it is necessary to implement wireless communication and power transfer modules in the implant. This avoids problems related with the device’s size, shape, weight and biocompatibility. Additionally, wirelessly recharging the battery maximizes the implant’s lifetime and eliminates the need to perform surgical procedures to change batteries, thus reducing shock and infection risk for the animal. An implantable device for the treatment of epilepsy, developed in the scope of an ongoing research project, must be implanted and tested in rats. As such, a base station that allows to compensate the aforementioned issues was required. Due to the inexistence of communication and wireless powering systems that are suitable to the problem at hand, these were proposed, developed and tested during this dissertation’s work. The developed communication system allows sending and receiving data with OOK modulation at a 1 GHz frequency, with a communication distance of up to 1.5 meters which can be extended with the use of amplifiers. This system is regulated by a microcontroller and it is composed of several blocks, which facilitates its modification to tackle problems with diverse specifications. The wireless power transfer system is based in a two-element antenna array which allows for the maximum power to be focused at the implant through a tracking mechanism, thus maximizing the power transfer. The tracking system resorts to a feedback mechanism that receives information from the implant concerning the amount of power it is receiving at any given moment. With this information, an algorithm controls the phase difference of the excitation signals of the antenna array to ensure that maximum power is transferred to the implant. The system resorts to this information at a rate of 1 kHz, and wireless power transfer occurs at a 2 GHz frequency with a theoretical maximum tracking speed of 3.41 m/s. Since it is also necessary to supply power and recharge the batteries of implants placed at a considerable depth inside the human body, it is useful to study the power distribution inside biological tissues. In order to do this, a system capable of mapping power distributions inside liquid phantoms was developed. Knowing that biological tissues interact with and absorb electromagnetic radiation, it was necessary to study its dosage. To achieve this, a specific absorption rate (SAR) mapping system for biological tissue liquid phantoms was developed, allowing to conclude if the RF exposure safety limits are respected or not. This system was then validated resorting to electromagnetic simulation tools.O tratamento de complicações médicas, tais como a arritmia, diabetes, surdez e doenças neurológicas, é um desafio árduo que é, tipicamente, resolvido recorrendo a medicamentos. No entanto, algumas doenças são resistentes a este tipo de tratamento, o que leva a uma procura por soluções alternativas. Umas destas reside na utilização de dispositivos implantáveis, que são parte fundamental da monitorização e tratamento de doenças na medicina moderna. Contudo, previamente à sua aplicação em humanos, extensos e rigorosos testes em modelos animais devem sem realizados por forma a avaliar a segurança e eficácia do dispositivo. Numa primeira fase, estes testes são feitos em animais de laboratório, normalmente roedores. Para que seja possível testar um dispositivo médico implantável neste tipo de animais, este deve ser o mais pequeno e leve possível e não ter ligações para o exterior. Isto é desejável para minimizar o seu impacto no comportamento natural do roedor, o que pode influenciar os resultados obtidos nas experiências. Para tal, é necessária a utilização de módulos de comunicação e carregamento sem fios no implante. Isto permite evitar problemas relacionados com o seu tamanho, forma, peso e biocompatibilidade. Adicionalmente, o carregamento sem fios da bateria permite maximizar o tempo de vida do implante e elimina a necessidade de procedimentos cirúrgicos para trocar baterias, reduzindo assim o choque para o animal e o risco de infeções. Um dispositivo implantável para o tratamento da epilepsia, desenvolvido no âmbito de um projeto de investigação, necessita ser implantado em roedores para ser testado. Para tal, é necessário utilizar uma estação base que permita solucionar os problemas previamente mencionados. Devido à inexistência de sistemas de comunicação e carregamento sem fios adequados ao problema em mãos, estes foram propostos, desenvolvidos e testados no âmbito da presente dissertação. O sistema de comunicação desenvolvido permite o envio e receção de dados com modulação OOK a uma frequência de 1 GHz, permitindo uma distância de comunicação de até 1.5 m, que pode ser aumentada recorrendo a amplificadores. Este sistema é regulado por um microcontrolador e composto por diversos blocos, o que facilita a sua adaptabilidade para as mais diversas aplicações. O sistema de transferência de energia sem fios baseia-se num array de antenas com dois elementos que permite focar o máximo da potência no implante através de um mecanismo de seguimento, maximizando assim a transferência de energia. Este sistema de seguimento recorre a um mecanismo de feedback que recebe informação do implante sobre a quantidade de potência que este está a receber num dado instante. Com esta informação, um algoritmo controla a diferença de fase dos sinais de excitação do array de antenas e faz com que o máximo de potência seja transmitida para o implante. O sistema adquire esta informação a uma taxa de 1 kHz, sendo que a transferência de potência sem fios ocorre a uma frequência de 2 GHz e com uma velocidade teórica máxima de seguimento de 3.41 m/s. Uma vez que também é necessário fornecer energia e recarregar baterias de implantes colocados a uma certa profundidade, torna-se necessário estudar a distribuição de potência no interior de tecidos biológicos. Para tal, foi desenvolvido um sistema que permite fazer o mapeamento de níveis de potência no interior de um fantoma líquido. Sabendo-se que os tecidos biológicos interagem com a radiação eletromagnética e absorvem-na, foi necessário o estudo da sua dosagem. Consequentemente, foi desenvolvido um sistema que permite avaliar os níveis de SAR em fantomas líquidos de tecido biológico, permitindo concluir se os limites de segurança destes níveis são ultrapassados. Este sistema foi posteriormente validado com recursos a ferramentas de simulação eletromagnética.Projeto de investigação PTDC/EEI-TEL/5250/2014, suportado por fundos FEDER POCI-01-145-FEDER-16695

Biointegrated and wirelessly powered implantable brain devices: a review

Implantable neural interfacing devices have added significantly to neural engineering by introducing the low-frequency oscillations of small populations of neurons known as local field potential as well as high-frequency action potentials of individual neurons. Regardless of the astounding progression as of late, conventional neural modulating system is still incapable to achieve the desired chronic in vivo implantation. The real constraint emerges from mechanical and physical diffierences between implants and brain tissue that initiates an inflammatory reaction and glial scar formation that reduces the recording and stimulation quality. Furthermore, traditional strategies consisting of rigid and tethered neural devices cause substantial tissue damage and impede the natural behaviour of an animal, thus hindering chronic in vivo measurements. Therefore, enabling fully implantable neural devices, requires biocompatibility, wireless power/data capability, biointegration using thin and flexible electronics, and chronic recording properties. This paper reviews biocompatibility and design approaches for developing biointegrated and wirelessly powered implantable neural devices in animals aimed at long-term neural interfacing and outlines current challenges toward developing the next generation of implantable neural devices

Millimeter-Scale Encapsulation of Wireless Resonators for Environmental and Biomedical Sensing Applications

Wireless magnetoelastic resonators are useful for remote mapping and sensing in environments that are harsh or otherwise difficult to access. Compared to other wireless resonators, magnetoelastic devices are attractive because of their inherently wireless nature, and their ability to operate passively without a power source, integrated circuitry, or antenna. An open challenge for using miniaturized magnetoelastic resonators is application-tailored encapsulation and packaging. General packaging considerations for magnetoelastic resonators include not only the mechanical design but also electromagnetic transparency, adaptability of form factor with appropriate feature size, and chemical inertness and/or biocompatibility. In this thesis, the packaging of magnetoelastic resonators is investigated in two contexts: environmental sensing and biomedical sensing. The first context is for tagging and mapping applications in a high temperature (≥ 150°C), high pressure (≥ 10 MPa), corrosive environment, such as a hydraulic fracture branching from a wellbore. This work utilizes for the first time a micro molding process to thermoform liquid crystal polymer (LCP) packages for protecting magnetoelastic resonators. The package is < 10 mm3 and includes micron-scale features to support the resonator and allow it to vibrate with low loss. It has an average shear strength of 60 N, and can endure pressure up to 2000 psi (≈13.8 MPa). The second context is for implantable magnetoelastic resonators, which are used for sensing biological parameters. These packages must: protect the sensors during deployment through an endoscope, be biocompatible and chemically inert, be able to pass through a complex delivery path, and fit within a limited size. Protecting the resonator during delivery while still allowing interaction with biological fluids is achieved with polymeric packages incorporating features such as a perforated housing and tapered and smoothed edges. This approach also includes features to aid in assembling with plastic stents via polyethylene tethers. The packaged resonator must pass through a complex delivery path without damage due to bending, so the compromise between two architectures – one mechanically flexible (Type F) and one mechanically stiff (Type S) – is evaluated. The primary advantage of the Type F package is the flexibility of the package during the delivery process while that of the Type S package is to maintain a strong signal even when the stent is in a curved bile duct. The length, width, and maximum thickness of the Type F package are 26.40 mm, 2.30 mm and 0.53 mm, respectively. The Type S package has an outer diameter of 2.54 mm, a length of 15 mm, and a maximum thickness of 0.74 mm. The two package types are tested in benchtop flexibility tests, and in vivo and in situ in porcine specimens. The animal tests demonstrate partial functionality of both types of packages, while also indicating that smaller and more elastic package designs are needed. Remaining in the implantable sensor context, an improved and miniaturized resonator design is explored. Miniaturizing the resonator accordingly allows miniaturization of the packaging, reducing the impact on the overall functionality of the medical device. The fabricated sensor is 8.25 mm long, 1 mm wide with the largest thickness of 218 μm. The resonant frequency of the resonator is around 173 kHz which is similar to that of a 12.5 mm long ribbon sensor. This resonator design is self-biased, simplifying the packaging and assembly compared to previous designs.PHDElectrical & Computer Eng PhDUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146089/1/jqjiang_1.pd

Bionode5.0: A miniature, wireless, closed-loop biological implant for neuromodulation

The needs for electrotherapy, using electrical devices, are significantly increasing, due to limitations that pharmaceutical therapies may have, such as unignorable side effects and meager side effects on a multitude of cardiovascular and neurological diseases. To research on electrotherapy using an implantable electronic module, a miniature, wireless, and closed-loop implantable device, called Bionode , has been developed at Center for Implantable Device, directed by Dr. Pedro Irazoqui. Bionode4.1, the most recent version of the Bionode, is a device that consists of three different printed circuit boards(PCB), including a wireless communication system, an inductive power receiving system, and a two-channel recording system with a stimulator that has an ability to output a biphasic constant current stimulation. However, a few issues were brought to the surface during the fabrication process and in-vivo animal tests: 1) Unwanted data loss due to the failure of communication between the device and the Base Station, 2) stimulator\u27s imbalanced output with glitches and noise, 3) structural complexity that made debugging and constructing the device difficult, 4) device configuration, which could not be customized for the specific applications. These limitations found in Bionode 4.1 led to the development of the new version of Bionode, Bionode 5.0 . In order to increase the fidelity of the data transmission, a meandered inverted F trace antenna, which can cover the 2.4 GHz industrial, scientific, and medical (ISM) radio band, was designed and implemented in the wireless communication system of the Bionode 5.0. In order to resolve the stimulation issue, the old stimulator built in Bionode 4.1 was replaced with an upgraded stimulation circuitry that consists of the additional feedback system and the switches for suppressing the imbalanced pulses and controlling the unwanted glitches on the output. Re-optimizing the overall floor plan of the device and utilizing a new type of board-to-board connector solved the issues related to the structure and customizability. As a result, Bionode 5.0 with the smaller volume and the larger utilizable surface area resolved the issues that Binode4.1 had and would potentially allow the users to widely utilize the new version in various applications for the medical research

A Low-Power Wireless Multichannel Microsystem for Reliable Neural Recording.

This thesis reports on the development of a reliable, single-chip, multichannel wireless biotelemetry microsystem intended for extracellular neural recording from awake, mobile, and small animal models. The inherently conflicting requirements of low power and reliability are addressed in the proposed microsystem at architectural and circuit levels. Through employing the preliminary microsystems in various in-vivo experiments, the system requirements for reliable neural recording are identified and addressed at architectural level through the analytical tool: signal path co-optimization. The 2.85mm×3.84mm, mixed-signal ASIC integrates a low-noise front-end, programmable digital controller, an RF modulator, and an RF power amplifier (PA) at the ISM band of 433MHz on a single-chip; and is fabricated using a 0.5µm double-poly triple-metal n-well standard CMOS process. The proposed microsystem, incorporating the ASIC, is a 9-channel (8-neural, 1-audio) user programmable reliable wireless neural telemetry microsystem with a weight of 2.2g (including two 1.5V batteries) and size of 2.2×1.1×0.5cm3. The electrical characteristics of this microsystem are extensively characterized via benchtop tests. The transmitter consumes 5mW and has a measured total input referred voltage noise of 4.74µVrms, 6.47µVrms, and 8.27µVrms at transmission distances of 3m, 10m, and 20m, respectively. The measured inter-channel crosstalk is less than 3.5% and battery life is about an hour. To compare the wireless neural telemetry systems, a figure of merit (FoM) is defined as the reciprocal of the power spent on broadcasting one channel over one meter distance. The proposed microsystem’s FoM is an order of magnitude larger compared to all other research and commercial systems. The proposed biotelemetry system has been successfully used in two in-vivo neural recording experiments: i) from a freely roaming South-American cockroach, and ii) from an awake and mobile rat.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91542/1/aborna_1.pd