Fiber-based structures are highly desirable for wearable electronics that are expected to be light-weight, long-lasting, flexible, and conformable Many fibrous structures have been manufactured by well-established lost-effective textile processing technologies, normally at ambient conditions The advancement of nanotechnology has made it feasible to build electronic devices directly on the surface or inside of single fibers, which have typical thickness of several to tens microns However, imparting electronic functions to porous, highly deformable and three-dimensional fiber assemblies and maintaining them during wear represent great challenges from both views of fundamental understanding and practical implementation This article attempts to critically review the current state-of-arts with respect to materials, fabrication techniques, and structural design of devices as well as applications of the fiber-based wearable electronic products In addition, this review elaborates the performance requirements of the fiber-based wearable electronic products, especially regarding the correlation among materials, fiber/textile structures and electronic as well as mechanical functionalities of fiber-based electronic devices Finally, discussions will be presented regarding to limitations of current materials, fabrication techniques, devices concerning manufacturability and performance as well as scientific understanding that must be improved prior to their wide adoption

Fiber‐Based Wearable Electronics: A Review of Materials, Fabrication, Devices, and Applications

WITH the ever-widening scope of modern mathematical analysis and its many ramifications, it is quite impossible to include, in a single volume of reasonable size, an adequate and exhaustive discussion of the calculus in its more advanced stages. It therefore becomes necessary, in planning a thoroughly sound course in the subject, to consider several important aspects of the vast field confronting a modern writer. The limitation of space renders the selection of subject-matter fundamentally dependent upon the aim of the course, which may or may not be related to the content of specific examination syllabuses. Logical development, too, may lead to the inclusion of many topics which, at present, may only be of academic interest, while others, of greater practical value, may have to be omitted. The experience and training of the writer may also have, more or less, a bearing on both these considerations.Advanced CalculusBy Dr. C. A. Stewart. Pp. xviii + 523. (London: Methuen and Co., Ltd., 1940.) 25s.

Advanced Calculus I

Radio-frequency identification technology, based on the reader/tag paradigm, is quickly permeating several aspects of everyday life. The electromagnetic research mainly concerns the design of tag antennas having high efficiency and small size, and suited to complex impedance matching to the embedded electronics. Starting from the available but fragmented open literature, this paper presents a homogeneous survey of relevant methodologies for the design of UHF passive tag antennas. Particular care is taken to illustrate, within a common framework, the basic concepts of the most-used design layouts. The design techniques are illustrated by means of many noncommercial examples.

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The art of UHF RFID antenna design: impedance-matching and size-reduction techniques

Antenna Theory And Design

RFID research: An academic literature review (1995–2005) and future research directions

In this letter, we establish a new type of passive ultrahigh-frequency (UHF) radio frequency identification (RFID) technology-based sensor with a referenced readout for moisture. We introduce the sensor system, which consists of a sensor tag and a reference tag. In a highly moist environment, the sensor tag, which is fabricated by embroidery and three-dimensional (3-D) printing, permanently changes its shape from flat to curved, which then influences its wireless performance. By recording the backscattered powers of the sensor tag and the unaffected reference tag, the presence of moisture could be detected. Based on our preliminary results, when the mean value of ΔP% was higher than 0.8, the sensor system indicated exposure to a high-moisture environment. Our moisture sensing system can provide cost-effective zero-energy monitoring of moisture exposure for versatile application fields.

Textile-Based Batteryless Moisture Sensor

Strain measurements could be utilized in monitoring human bodily functions and movements. Cost effective and low maintenance wearable sensors are needed in this field. The goal of this paper was to produce wearable strain sensors based on UHF RFID technology and the behavior of the materials which were utilized in prototypes. Two tag geometries were compared. Polymer thick film silver ink was used as the conductive medium. The tags were fabricated by screen printing the ink on stretchable PVC and on fabric substrates. Performance of the tags and the effect of mechanical straining on tag functioning was examined. The prototypes tolerated large strain levels. The results showed that the behavior of the UHF RFID tag strain sensor is dependent on the material behavior under strain as well as the tag antenna geometry. These offer various possibilities in strain measuring.

Printed passive UHF RFID tags as wearable strain sensors

Reliability of washable wearable screen printed UHF RFID tags

We present a wearable passive UHF RFID tag based on a slotted patch antenna comprising only textile materials (e-textile, textile substrate, and conductive yearn). As a novel manufacturing approach, we realize the patch-to-ground and antenna-to-IC interfaces using only conductive thread and a sewing machine. We outline the electromagnetic optimization of the antenna for body-worn operation through simulations and present a performance comparison between the e-textile tag and a tag produced using regular electronics materials and methods. The measured results show that the textile tag achieves the electrical performance required in practical applications and that the slotted patch type antenna provides stable electromagnetic performance in different body-worn configurations.

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Wearable passive E-textile UHF RFID tag based on a slotted patch antenna with sewn ground and microchip interconnections

This paper provides a full analysis of powering mm-size cortical implants wirelessly. An effective approach for wireless power and data transfer in neurorecording microsystems is the backscattering-based RFID-inspired communication. In this mechanism, an external interrogator powers the implant unit by microwave radiation power, and the implant IC superimposes the neurosignal on top of the signal backscattered to the interrogator. This paper characterizes wireless RF link between an external transmit antenna and an implantable antenna using the two-port model. It presents the design of a novel 1-mm3 implantable loop antenna and four different external loop antennas with various features to analyze aspects and factors limiting the wireless power transfer.

Leena Ukkonen

Papers

Textile-Based Batteryless Moisture Sensor

Printed passive UHF RFID tags as wearable strain sensors

Reliability of washable wearable screen printed UHF RFID tags

Wearable passive E-textile UHF RFID tag based on a slotted patch antenna with sewn ground and microchip interconnections

Analysis of wireless powering of mm-size neural recording tags in RFID-inspired wireless brain-machine interface systems