Resonance-based wireless power delivery is an efficient technique to transfer power over a relatively long distance. This technique typically uses four coils as opposed to two coils used in conventional inductive links. In the four-coil system, the adverse effects of a low coupling coefficient between primary and secondary coils are compensated by using high-quality (Q) factor coils, and the efficiency of the system is improved. Unlike its two-coil counterpart, the efficiency profile of the power transfer is not a monotonically decreasing function of the operating distance and is less sensitive to changes in the distance between the primary and secondary coils. A four-coil energy transfer system can be optimized to provide maximum efficiency at a given operating distance. We have analyzed the four-coil energy transfer systems and outlined the effect of design parameters on power-transfer efficiency. Design steps to obtain the efficient power-transfer system are presented and a design example is provided. A proof-of-concept prototype system is implemented and confirms the validity of the proposed analysis and design techniques. In the prototype system, for a power-link frequency of 700 kHz and a coil distance range of 10 to 20 mm, using a 22-mm diameter implantable coil resonance-based system shows a power-transfer efficiency of more than 80% with an enhanced operating range compared to ~40% efficiency achieved by a conventional two-coil system.

Design and Optimization of Resonance-Based Efficient Wireless Power Delivery Systems for Biomedical Implants

Smart wearable systems: Current status and future challenges

This paper provides a review of recent developments in the rapidly changing and advancing field of smart fabric sensor and electronic textile technologies. It summarizes the basic principles and approaches employed when building fabric sensors as well as the most commonly used materials and techniques used in electronic textiles. This paper shows that sensing functionality can be created by intrinsic and extrinsic modifications to textile substrates depending on the level of integration into the fabric platform. The current work demonstrates that fabric sensors can be tailored to measure force, pressure, chemicals, humidity and temperature variations. Materials, connectors, fabric circuits, interconnects, encapsulation and fabrication methods associated with fabric technologies prove to be customizable and versatile but less robust than their conventional electronics counterparts. The findings of this survey suggest that a complete smart fabric system is possible through the integration of the different types of textile based functional elements. This work intends to be a starting point for standardization of smart fabric sensing techniques and e-textile fabrication methods.

https://iopscience.iop.org/article/10.1088/0964-1726/23/5/053001/pdf

Smart fabric sensors and e-textile technologies: a review

Accelerometry: a technique for quantifying movement patterns during walking.

This article reviews recent advances and developments in the field of wearable sensors with emphasis on a subclass of these devices that are able to perform highly-sensitive electrochemical analysis Recent insights into novel fabrication methodologies and electrochemical techniques have resulted in the demonstration of chemical sensors able to augment conventional physical measurements (ie heart rate, EEG, ECG, etc), thereby providing added dimensions of rich, analytical information to the wearer in a timely manner Wearable electrochemical sensors have been integrated onto both textile materials and directly on the epidermis for various monitoring applications owing to their unique ability to process chemical analytes in a non-invasive and non-obtrusive fashion In this manner, multi-analyte detection can easily be performed, in real time, in order to ascertain the overall physiological health of the wearer or to identify potential offenders in their environment Of profound importance is the development of an understanding of the impact of mechanical strain on textile- and epidermal (tattoo)-based sensors and their failure mechanisms as well as the compatibility of the substrate employed in the fabrication process We conclude this review with a retrospective outlook of the field and identify potential implications of this new sensing paradigm in the healthcare, fitness, security, and environmental monitoring domains With continued innovation and detailed attention to core challenges, it is expected that wearable electrochemical sensors will play a pivotal role in the emergent body sensor networks arena

Wearable Electrochemical Sensors and Biosensors: A Review

In this paper, we present textile sensors for the equipment of a wireless monitoring suit. The suit is intended for the monitoring of electrocardiogram (ECG) and respiration rate of children in a hospital environment. Special attention is given to the dedicated sensor interface circuits. The sensors, which are entirely fabricated out of textile, are integrated in a prototype belt of the monitoring suit. The complete suit will not contain only the sensors, but also the interface, data handling, storage and transmission electronics. Therefore, distributed, miniaturized circuitry, textile interconnections, a textile antenna and hermetic packaging are developed.

Towards the integration of textile sensors in a wireless monitoring suit

An inductive powering system is presented, capable of remotely powering implantable monitoring and stimulating devices. The system is capable of delivering at least 50 mW, with an efficiency of 36% over a distance of 3 cm. The power transfer frequency is 700 kHz. Optimisation of the power transfer efficiency and the misalignment tolerance was obtained using a self-developed design tool. Bi-directional data-transmission is integrated in the system: amplitude modulation is applied for the downlink transmission, absorption modulation for the uplink transmission. Our new system is capable of transmitting data at a maximal bit rate of 60,000 bits/s.

An inductive power system with integrated bi-directional data-transmission

This paper proposes a system for the detection of hip prosthesis loosening by means of a vibration analysis technique. Although this technique has been adapted before, the novelty presented here lies in the fact that the monitoring is done inside the prosthesis itself, offering better measurement results. Thus, an implantable monitoring system is required, involving low power consumption and miniaturization. Monitoring is done by a miniature, capacitive accelerometer. The monitoring system is equipped with a telemetric link, to provide data transmission from the implant to a PC, where the data are analyzed. The system is powered inductively, since it is intended for long-term implantation.

A telemetry system for the detection of hip prosthesis loosening by vibration analysis

A readout circuit for a passive telemetric intra-ocular pressure (IOP) sensor is being developed. The intra-ocular sensor consists of a capacitive pressure sensor in parallel with a planar coil. This inductor–capacitor (LC) resonant circuit transduces the pressure into a shift of resonance frequency. A voltage controlled oscillator (VCO) is used to excite the sensor over a large frequency range (20–40 MHz), hereby detecting resonance of the internal sensor, and thus enabling the measurement of the intra-ocular pressure. This low power circuit is extremely compact, making it suitable for long-term ambulant patient monitoring. The circuit allows wireless readout of the smallest pressure transducers. Tests show promising results at mutual coil distances up to 7.5 mm.

A readout circuit for an intra-ocular pressure sensor

In this paper, we present fabric sensors for the recording of electrocardiogram (ECG) and respiration rate. Special attention is given to the dedicated sensor interface circuits. The sensors are integrated in a prototype belt for an intelligent suit. The suit will contain not only the sensors, but also the interface, data handling, storage and transmission circuitry. The suit is intended for the monitoring of children in a hospital environment.

Michael Catrysse

Papers

Towards the integration of textile sensors in a wireless monitoring suit

An inductive power system with integrated bi-directional data-transmission

A telemetry system for the detection of hip prosthesis loosening by vibration analysis

A readout circuit for an intra-ocular pressure sensor

Fabric sensors for the measurement of physiological parameters