A Study of Multi-Layer Spiral Inductors for Remote Powering of Implantable Sensors

An approach based on multi-layer spiral inductors to remotely power implantable sensors is investigated. As compared to single-layer inductors having the same area, multi-layer printed inductors enable a higher efficiency (up to 35% higher) and voltage gain (almost one order of magnitude higher). A system conceived to be embedded into a skin patch is designed to verify the performance. The system is able to transmit up to 15 mW over a distance of 6 mm and up to 1.17 mW where a 17 mm beef sirloin is placed between the inductors. Furthermore, the system performs downlink communication (up to 100 kbps) and uplink communication based on the backscattering technique (up to 66.6 kbps). Long-range communication is achieved by means of a bluetooth module

Design of Wireless Power Transfer and Data Telemetry System for Biomedical Applications

With the advancement of biomedical instrumentation technologies sensor based remote healthcare monitoring system is gaining more attention day by day. In this system wearable and implantable sensors are placed outside or inside of the human body. Certain sensors are needed to be placed inside the human body to acquire the information on the vital physiological phenomena such as glucose, lactate, pH, oxygen, etc. These implantable sensors have associated circuits for sensor signal processing and data transmission. Powering the circuit is always a crucial design issue. Batteries cannot be used in implantable sensors which can come in contact with the blood resulting in serious health risks. An alternate approach is to supply power wirelessly for tether-less and battery- less operation of the circuits.Inductive power transfer is the most common method of wireless power transfer to the implantable sensors. For good inductive coupling, the inductors should have high inductance and high quality factor. But the physical dimensions of the implanted inductors cannot be large due to a number of biomedical constraints. Therefore, there is a need for small sized and high inductance, high quality factor inductors for implantable sensor applications. In this work, design of a multi-spiral solenoidal printed circuit board (PCB) inductor for biomedical application is presented. The targeted frequency for power transfer is 13.56 MHz which is within the license-free industrial, scientific and medical (ISM) band. A figure of merit based optimization technique has been utilized to optimize the PCB inductors. Similar principal is applied to design on-chip inductor which could be a potential solution for further miniaturization of the implantable system. For layered human tissue the optimum frequency of power transfer is 1 GHz for smaller coil size. For this reason, design and optimization of multi-spiral solenoidal integrated inductors for 1 GHz frequency is proposed. Finally, it is demonstrated that the proposed inductors exhibit a better overall performance in comparison with the conventional inductors for biomedical applications

Remote Powering and Communication of Implantable Biosensors Through Inductive Link

Nowadays there is an increasing interest in the field of implantable biosensors. The possibility of real-time monitoring of the human body from inside paves the way to a large number of applications and offers wide opportunities for the future. Within this scenario, the i-IronIC project aims to develop an implantable, low cost, health-care device for real-time monitoring of human metabolites. The contribution of this research work to the i-IronIC project consists of the design and realization of a complete platform to provide power, data communication and remote control to the implantable biosensor. High wearability of the transmitting unit, low invasivity of the implanted electronics, integration of the power management module within the sensor, and a reliable communication protocol with portable devices are the key points of this platform. The power is transmitted to the implanted sensor by exploiting an inductive link. Simulations have been performed to check the effects of several variables on the link performance. These simulations have finally confirmed the possibility to operate in the low megahertz range, where tissue absorption is minimum, even if a miniaturized receiving inductor is used. A wearable patch has been designed to transmit power through the body tissues by driving an external inductor. The same inductive link is used to achieve bidirectional data communication with the implanted device. The patch, named IronIC, is powered by lithium-ion polymer batteries and can be remotely controlled by means of a dedicated Android application running on smartphones and tablets. Long-range communication between the patch and portable devices is performed by means of Bluetooth protocol. Different typologies of receiving inductors have been designed to minimize the size of the implantable device and reduce the discomfort of the patience. Multi-layer, printed spiral inductors and microfabricated spiral inductors have been designed, fabricated and tested. Both the approaches involve a sensibly smaller size, as compared to classic “pancake” inductors used for remote powering. Furthermore, the second solution enables the realization of the receiving inductor directly on the silicon substrate hosting the sensor, thus involving a further miniaturization of the implanted device. An integrated power module has been designed and fabricated in 0.18 μm CMOS technology to perform power management and data communication with the external patch. The circuit, to be merged with the sensor readout circuit, consists of an half-wave voltage rectifier, a low-dropout regulator, an amplitude demodulator and a load modulator. The module receives the power from the implanted inductor and provides a stable voltage to the sensor readout circuit. Finally, the amplitude demodulator and the load modulator enable short-range communication with the patch

Design and Optimization of Printed Circuit Board Inductors for Wireless Power Transfer System

Wireless power transfer via inductive link is becoming a popular choice as an alternate powering scheme for biomedical sensor electronics. Spiral printed circuit board (PCB) inductors are gaining attractions for wireless power transfer applications due to their various advantages over conventional inductors such as low-cost, batch fabrication, durability, manufacturability on flexible substrates, etc. In this work, design of a multi-spiral stacked solenoidal inductor for biomedical application in 13.56 MHz band is presented. Proposed stacking method enhances the inductance density of the inductor for a given area. This paper reports an optimization technique for design and implementation of the PCB inductors. The proposed scheme shows higher inductance and better figure-of-merit values compared to PCB inductors reported in literature, which are desirable for wireless power transfer system. DOI: 10.4236/cs.2013.4203

A Novel Power-Efficient Wireless Multi-channel Recording System for the Telemonitoring of Electroencephalography (EEG)

This research introduces the development of a novel EEG recording system that is modular, batteryless, and wireless (untethered) with the supporting theoretical foundation in wireless communications and related design elements and circuitry. Its modular construct overcomes the EEG scaling problem and makes it easier for reconfiguring the hardware design in terms of the number and placement of electrodes and type of standard EEG system contemplated for use. In this development, portability, lightweight, and applicability to other clinical applications that rely on EEG data are sought. Due to printer tolerance, the 3D printed cap consists of 61 electrode placements. This recording capacity can however extend from 21 (as in the international 10-20 systems) up to 61 EEG channels at sample rates ranging from 250 to 1000 Hz and the transfer of the raw EEG signal using a standard allocated frequency as a data carrier. The main objectives of this dissertation are to (1) eliminate the need for heavy mounted batteries, (2) overcome the requirement for bulky power systems, and (3) avoid the use of data cables to untether the EEG system from the subject for a more practical and less restrictive setting. Unpredictability and temporal variations of the EEG input make developing a battery-free and cable-free EEG reading device challenging. Professional high-quality and high-resolution analog front ends are required to capture non-stationary EEG signals at microvolt levels. The primary components of the proposed setup are the wireless power transmission unit, which consists of a power amplifier, highly efficient resonant-inductive link, rectification, regulation, and power management units, as well as the analog front end, which consists of an analog to digital converter, pre-amplification unit, filtering unit, host microprocessor, and the wireless communication unit. These must all be compatible with the rest of the system and must use the least amount of power possible while minimizing the presence of noise and the attenuation of the recorded signal A highly efficient resonant-inductive coupling link is developed to decrease power transmission dissipation. Magnetized materials were utilized to steer electromagnetic flux and decrease route and medium loss while transmitting the required energy with low dissipation. Signal pre-amplification is handled by the front-end active electrodes. Standard bio-amplifier design approaches are combined to accomplish this purpose, and a thorough investigation of the optimum ADC, microcontroller, and transceiver units has been carried out. We can minimize overall system weight and power consumption by employing battery-less and cable-free EEG readout system designs, consequently giving patients more comfort and freedom of movement. Similarly, the solutions are designed to match the performance of medical-grade equipment. The captured electrical impulses using the proposed setup can be stored for various uses, including classification, prediction, 3D source localization, and for monitoring and diagnosing different brain disorders. All the proposed designs and supporting mathematical derivations were validated through empirical and software-simulated experiments. Many of the proposed designs, including the 3D head cap, the wireless power transmission unit, and the pre-amplification unit, are already fabricated, and the schematic circuits and simulation results were based on Spice, Altium, and high-frequency structure simulator (HFSS) software. The fully integrated head cap to be fabricated would require embedding the active electrodes into the 3D headset and applying current technological advances to miniaturize some of the design elements developed in this dissertation

Skin-Integrated wearable systems and implantable biosensors: a comprehensive review

Biosensors devices have attracted the attention of many researchers across the world. They have the capability to solve a large number of analytical problems and challenges. They are future ubiquitous devices for disease diagnosis, monitoring, treatment and health management. This review presents an overview of the biosensors field, highlighting the current research and development of bio-integrated and implanted biosensors. These devices are micro- and nano-fabricated, according to numerous techniques that are adapted in order to offer a suitable mechanical match of the biosensor to the surrounding tissue, and therefore decrease the body’s biological response. For this, most of the skin-integrated and implanted biosensors use a polymer layer as a versatile and flexible structural support, combined with a functional/active material, to generate, transmit and process the obtained signal. A few challenging issues of implantable biosensor devices, as well as strategies to overcome them, are also discussed in this review, including biological response, power supply, and data communication.This research was funded by FCT- FUNDAÇÃO PARA A CIÊNCIA E TECNOLOGIA, grant numbers: PTDC/EMD-EMD/31590/2017 and PTDC/BTM-ORG/28168/2017

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

Electronic Implants: Power Delivery and Management

A power delivery system for implantable biosensors is presented. The system, embedded into a skin patch and located directly over the implantation area, is able to transfer up to 15 mW wirelessly through the body tissues by means of an inductive link. The inductive link is also used to achieve bidirectional data communication with the implanted device. Downlink communication (ASK) is performed at 100 kbps; uplink communication (LSK) is performed at 66.6 kbps. The received power is managed by an integrated system including a voltage rectifier, an amplitude demodulator and a load modulator. The power management system is presented and evaluated by means of simulations

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