Recent Advances on Implantable Wireless Sensor Networks

Implantable electronic devices are undergoing a miniaturization age, becoming more efficient and yet more powerful as well. Biomedical sensors are used to monitor a multitude of physiological parameters, such as glucose levels, blood pressure and neural activity. A group of sensors working together in the human body is the main component of a body area network, which is a wireless sensor network applied to the human body. In this chapter, applications of wireless biomedical sensors are presented, along with state-of-the-art communication and powering mechanisms of these devices. Furthermore, recent integration methods that allow the sensors to become smaller and more suitable for implantation are summarized. For individual sensors to become a body area network (BAN), they must form a network and work together. Issues that must be addressed when developing these networks are detailed and, finally, mobility methods for implanted sensors are presented

Design and Implementation of a Passive Neurostimulator with Wireless Resonance-Coupled Power Delivery and Demonstration on Frog Sciatic Nerve and Gastrocnemius Muscle

The thesis presented has four goals: to perform a comprehensive literature review on current neurostimulator technology; to outline the current issues with the state-of-the-art; to provide a neurostimulator design that solves these issues, and to characterize the design and demonstrate its neurostimulation features. The literature review describes the physiology of a neuron, and then proceeds to outline neural interfaces and neurostimulators. The neurostimulator design process is then outlined and current requirements in the field are described. The novel neurostimulator circuit that implements a solution that has wireless capability, passive control, and small size is outlined and characterized. The circuit is demonstrated to operate wirelessly with a resonance-coupled multi-channel implementation, and is shown powering LEDs. The circuit was then fabricated in a miniature implementation which utilized a 10 x 20 x 3 mm&179 antenna, and occupied a volume approximating 1 cm&179. This miniature circuit is used to stimulate frog sciatic nerve and gastrocnemius muscle in vitro. These demonstrations and characterization show the device is capable of neurostimulation, can operate wirelessly, is controlled passively, and can be implemented in a small size, thus solving the aforementioned neurostimulator requirements. Further work in this area is focused on developing an extensive characterization of the device and the wireless power delivery system, optimizing the circuit design, and performing in vivo experiments with restoration of motor control in injured animals. This device shows promise to provide a comprehensive solution to many application-specific problems in neurostimulation, and be a modular addition to larger neural interface systems

Modulaarinen kehitysalusta langattomille lääketieteellisille anturi-implanteille

Implanting medical sensor devices under skin improves the quality of the acquired measurement results, and can greatly increase the comfort for the patient in prolonged measurement. Design of such complex devices and related systems benefits from using a dedicated development platform that represents the functionalities and associated challenges. This work presents the design, implementation and verified performance of a modular platform that can be used in demonstration, development and testing of various functionalities of wireless medical sensor implants. The system is constructed using discrete components and consists of five inter connectable modules, each representing a specific function of the sensor implant system: bio potential measurement front-end module, wireless communication front-end module, clock and power management module, control logic module and external reader module. The implemented system has measurement front-end with an ENOB of 9 bits and configurable structure for the needs of various bio potentials. Wireless data transfer operates at 840-960 MHz with supported data rate up to 640 kbps. The system demonstrates dual carrier operation for separating the power and data transfers. Power can be harvested and clock extracted from 6.75 MHz or 865 MHz radio signals, both radio signals can be generated by the external reader. Control logic is provided with a high-end FPGA evaluation board. The completed platform can be used for developing and testing aspects for novel implanted devices, such as different radio communication schemes, radio antenna options, or controls and algorithms in digital logic.Lääketieteellisten anturien asettaminen ihon alle parantaa biopotentiaalimittauksien tulosten laatua ja pitkäaikaisten mittauksien mukavuutta potilaalle. Näiden monimutkaisten laitteiden suunnittelua voidaan tehostaa käyttämällä apuna sovelluskohtaista kehitysalustaa. Tässä työssä suunnitellaan ja toteutetaan modulaarinen, korkean suorituskyvyn kehitysalusta biopotentiaalia mittaavien langattomien anturi-implanttijärjestelmien eri toiminnallisuuksien esittelyyn, kehitykseen ja testaukseen. Diskreeteillä komponenteilla toteutettu järjestelmä koostuu viidestä moduulista: biopotentiaalien mittausmoduuli, langattoman tiedonvälityksen radiomoduuli, tehon ja kellosignaalin keräysmoduuli, ohjauslogiikkamoduuli, ja kehon ulkopuolinen lukijamoduuli. Kehitysalusta on muokattavissa eri biopotentiaalien mittauksien tarpeisiin. Mittausetupään tehollinen bittimäärä on 9 bittiä. Langatonta tiedonsiirtoa tuetaan 840 - 960 MHz taajuuskaistalla 640 kbps siirtonopeuksiin asti. Järjestelmällä voidaan demonstroida kahden kantoaallon yhtäaikaista käyttämistä, jolloin tehon- ja tiedonsiirto voidaan tarvittaessa erottaa toisistaan. Tehoa voidaan kerätä ja kellosignaaleja muodostaa 6,75 MHz ja 865 MHz taajuuksien radiosignaaleilta, jotka molemmat voidaan luoda hallitusti lukijamoduulilla. Ohjauslogiikka on toteutettu käyttäen ohjelmoitavaa porttimatriisipiiriä. Kehitysalustaa voidaan käyttää uusien implanttijärjestelmien suunnittelussa, esimerkiksi eri tiedonsiirtotapojen, antennirakenteiden, ohjauslogiikan ja digitaalisten algoritmien arvioinnissa

A Three – tier bio-implantable sensor monitoring and communications platform

One major hindrance to the advent of novel bio-implantable sensor technologies is the need for a reliable power source and data communications platform capable of continuously, remotely, and wirelessly monitoring deeply implantable biomedical devices. This research proposes the feasibility and potential of combining well established, ‘human-friendly' inductive and ultrasonic technologies to produce a proof-of-concept, generic, multi-tier power transfer and data communication platform suitable for low-power, periodically-activated implantable analogue bio-sensors. In the inductive sub-system presented, 5 W of power is transferred across a 10 mm gap between a single pair of 39 mm (primary) and 33 mm (secondary) circular printed spiral coils (PSCs). These are printed using an 8000 dpi resolution photoplotter and fabricated on PCB by wet-etching, to the maximum permissible density. Our ultrasonic sub-system, consisting of a single pair of Pz21 (transmitter) and Pz26 (receiver) piezoelectric PZT ceramic discs driven by low-frequency, radial/planar excitation (-31 mode), without acoustic matching layers, is also reported here for the first time. The discs are characterised by propagation tank test and directly driven by the inductively coupled power to deliver 29 μW to a receiver (implant) employing a low voltage start-up IC positioned 70 mm deep within a homogeneous liquid phantom. No batteries are used. The deep implant is thus intermittently powered every 800 ms to charge a capacitor which enables its microcontroller, operating with a 500 kHz clock, to transmit a single nibble (4 bits) of digitized sensed data over a period of ~18 ms from deep within the phantom, to the outside world. A power transfer efficiency of 83% using our prototype CMOS logic-gate IC driver is reported for the inductively coupled part of the system. Overall prototype system power consumption is 2.3 W with a total power transfer efficiency of 1% achieved across the tiers

The Development of a Capacitance-Based Biotelemetry System for Implantable Applications

Most modern biomedical implants implement some form of communications link between the implant and the outside world. This biotelemetry link has many requirements such as data bandwidth and power consumption. Designing an appropriate link that meets these requirements is one of the most significant engineering challenges associated with these implants. Communications methods that are currently used for this link include standard Radio Frequency (RF) approaches, inductively coupled approaches, and load modulation approaches. This thesis describes the development of a unique capacitance-based biotelemetry system for implantable applications. This system consists of two distinct parts: the implanted transmitter and the external body-mounted receiver. The prototype transmitter is based on a custom Application Specific Integrated Circuit (ASIC) fabricated using the AMI 1.5µ process. This ASIC encodes and transmits predetermined data packets by driving two electrodes in a slew-controlled manner, all contained within a biocompatible material. The receiver consists of charge-sensitive amplifier front end using a discriminator to distinguish individual bits. A Field Programmable Gate Array (FPGA) decodes the transmitted data and relays it to a PC- based LabVIEW interface. Test results using a saline-based human tissue model are presented

Inductively Coupled CMOS Power Receiver For Embedded Microsensors

Inductively coupled power transfer can extend the lifetime of embedded microsensors that save costs, energy, and lives. To expand the microsensors' functionality, the transferred power needs to be maximized. Plus, the power receiver needs to handle wide coupling variations in real applications. Therefore, the objective of this research is to design a power receiver that outputs the highest power for the widest coupling range. This research proposes a switched resonant half-bridge power stage that adjusts both energy transfer frequency and duration so the output power is maximally high. A maximum power point (MPP) theory is also developed to predict the optimal settings of the power stage with 98.6% accuracy. Finally, this research addresses the system integration challenges such as synchronization and over-voltage protection. The fabricated self-synchronized prototype outputs up to 89% of the available power across 0.067%~7.9% coupling range. The output power (in percentage of available power) and coupling range are 1.3× and 13× higher than the comparable state of the arts.Ph.D

Stepper microactuators driven by ultrasonic power transfer

Advances in miniature devices for biomedical applications are creating ever-increasing requirements for their continuous, long lasting, and reliable energy supply, particularly for implanted devices. As an alternative to bulky and cost inefficient batteries that require occasional recharging and replacement, energy harvesting and wireless power delivery are receiving increased attention. While the former is generally only suited for low-power diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding therapeutic actuation such as drug release, implant mechanical adjustment or microsurgery. This thesis presents a novel approach to delivering wireless power to remote medical microdevices with the aim of satisfying higher energy budgets required for therapeutic functions. The method is based on ultrasonic power delivery, the novelty being that actuation is powered by ultrasound directly rather than via piezoelectric conversion. The thesis describes a coupled mechanical system remotely excited by ultrasound and providing conversion of acoustic energy into motion of a MEMS mechanism using a receiving membrane coupled to a discrete oscillator. This motion is then converted into useful stepwise actuation through oblique mechanical impact. The problem of acoustic and mechanical impedance mismatch is addressed. Several analytical and numerical models of ultrasonic power delivery into the human body are developed. Major design challenges that have to be solved in order to obtain acceptable performance under specified operating conditions and with minimum wave reflections are discussed. A novel microfabrication process is described, and the resulting proof-of-concept devices are successfully characterized.Open Acces

Implantable Wireless Systems: A Review of Potentials and Challenges

With the current advancement in micro-and nano-fabrication processes and the newly developed approaches, wireless implantable devices are now able to meet the demand for compact, self-powered, wireless, and long-lasting implantable devices for medical and health-care applications. The demonstrated fabrication advancement enabled the wireless implantable devices to overcome the previous limitations of electromagnetic-based wireless devices such as the high volume due to large antenna size and to overcome the tissue and bone losses related to the ultrasound implantable devices. Recent state-of-the-are wireless implantable devices can efficiently harvest electromagnetic energy and detect RF signals with minimum losses. Most of the current implanted devices are powered by batteries, which is not an ideal solution as these batteries need periodic charging and replacement. On the other hand, the implantable devices that are powered by energy harvesters are operating continuously, patient-friendly, and are easy to use. Future wireless implantable devices face a strong demand to be linked with IoT-based applications and devices with data visualization on mobile devices. This type of application requires additional units, which means more power consumption. Thus, the challenge here is to reduce the overall power consumption and increase the wireless power transfer efficiency. This chapter presents the state-of-the-art wireless power transfer techniques and approaches that are used to drive implantable devices. These techniques include inductive coupling, radiofrequency, ultrasonic, photovoltaic, and heat. The advantages and disadvantages of these approaches and techniques along with the challenges and limitations of each technique will be discussed. Furthermore, the performance parameters such as operating distance, energy harvesting efficiency, and size will be discussed and analyzed to introduce a comprehensive comparison. Finally, the recent advances in materials development and wireless communication strategies, are also discussed

Modeling induction and routing to monitor hospitalized patients in multi-hop mobility-aware body area sensor networks

In wireless body area sensor networks (WBASNs), energy efficiency is an area of extreme significance. At first, we present a mathematical model for a non-invasive inductive link which is used to recharge the battery of an implanted biomedical device (pacemaker). Afterwards, we propose a distance-aware relaying energy-efficient (DARE) and mutual information-based DARE (MI-DARE) routing protocols for multihop mobility-aware body area sensor networks (MM-BASNs). Both the routing protocols and the non-invasive inductive link model are tested with the consideration of eight patients in a hospital unit under different topologies, where the vital signs of each patient are monitored through seven on-body sensors and an implanted pacemaker. To reduce energy consumption of the network, the sensors communicate with a sink via an on-body relay which is fixed on the chest of each patient. The behavior (static/mobile) and position of the sink are changed in each topology, and the impact of mobility due to postural changes of the patient(s) arms, legs, and head is also investigated. The MI-DARE protocol further prolongs the network lifetime by minimizing the number of transmissions. Simulation results show that the proposed techniques outperform contemporary schemes in terms of the selected performance metrics. © 2016, Javaid et al