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

Antenna Theory And Design

A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Post-transition elements, together with zinc-group metals and their alloys belong to an emerging class of materials with fascinating characteristics originating from their simultaneous metallic and liquid natures. These metals and alloys are characterised by having low melting points (i.e. between room temperature and 300 °C), making their liquid state accessible to practical applications in various fields of physical chemistry and synthesis. These materials can offer extraordinary capabilities in the synthesis of new materials, catalysis and can also enable novel applications including microfluidics, flexible electronics and drug delivery. However, surprisingly liquid metals have been somewhat neglected by the wider research community. In this review, we provide a comprehensive overview of the fundamentals underlying liquid metal research, including liquid metal synthesis, surface functionalisation and liquid metal enabled chemistry. Furthermore, we discuss phenomena that warrant further investigations in relevant fields and outline how liquid metals can contribute to exciting future applications.

Liquid metals: fundamentals and applications in chemistry

The current evolution of the traditional medical model toward the participatory medicine can be boosted by the Internet of Things (IoT) paradigm involving sensors (environmental, wearable, and implanted) spread inside domestic environments with the purpose to monitor the user’s health and activate remote assistance. RF identification (RFID) technology is now mature to provide part of the IoT physical layer for the personal healthcare in smart environments through low-cost, energy-autonomous, and disposable sensors. It is here presented a survey on the state-of-the-art of RFID for application to bodycentric systems and for gathering information (temperature, humidity, and other gases) about the user’s living environment. Many available options are described up to the application level with some examples of RFID systems able to collect and process multichannel data about the human behavior in compliance with the power exposure and sanitary regulations. Open challenges and possible new research trends are finally discussed.

RFID Technology for IoT-Based Personal Healthcare in Smart Spaces

Concurrently with the continuously developing radio frequency identification (RFID) technology, new types of tag antenna materials and structures are emerging to fulfill the requirements encountered within the new application areas. In this work, a radiation efficiency measurement method is developed and verified for passive ultra-high frequency (UHF) RFID dipole tag antennas. In addition, the measurement method is applied to measure the radiation efficiency of sewed dipole tag antennas for wearable body-centric wireless communication applications. The acquired information from measurements can be used to characterize tag antenna material structures losses and to further both improve and optimize tag antenna performance and reliability.

Radiation Efficiency Measurement Method for Passive UHF RFID Dipole Tag Antennas

We study the impact of recurrent stretching on the performance of passive ultra-high frequency radio-frequency identification tag based on a textile antenna patterned from stretchable silver coated fabric. We also outline the simulation-based design of the antenna composed of this unconventional conductor and report the measured performance of the tag when attached to a shirt and worn in the upper arm.

Impact of recurrent stretching on the performance of electro-textile UHF RFID tags

3D printing, the latest additive manufacturing technique, has the advantage of printing complex 3D structures using layer-by-layer deposition of versatile materials. The electrical and mechanical properties of these 3D printed materials can be customized depending on the printing specifications, like infill percentage, in-fill pattern, and thickness. Especially flexible 3D printed material, NinjaFlex, is a highly potential substrate material for wearable passive ultra-high frequency (UHF) radio-frequency identification (RFID) tags. This paper presents the fabrication and wireless evaluation of embroidered passive UHF RFID tags on a 3D printed (NinjaFlex) substrate. The paper outlines the details of the 3D printing of the substrate, the characterization of the substrate material at the UHF band, the embroidery process using conductive yarn, and the wireless measurement results of the fabricated tags. Measurement results show that the manufactured tags achieve peak read ranges of 6 meters. To the best of our knowledge, this is the first demonstration of embroidery on 3D printed flexible substrate. The stability of the results show that this hybrid fabrication methodology offers an easy, quick, and cost-effective approach for manufacturing RFID tags for future wearable identification and sensing applications.

Embroidered passive UHF RFID tag on flexible 3D printed substrate

We compare the performance of equal-sized dipole and folded dipole wearable passive UHF RFID tags using three different body models for the torso of an adult male: cuboid and anatomical models with and without internal structures. The results show that all models estimate the antenna impedance matching appropriately, but only the anatomical models predict the full spatial coverage of the tags properly. We present a novel metrics for analysing the coverage in simulations and compare the simulated and measured tag read ranges to validate our modelling results.

Comparison of Three Body Models of Different Complexities in Modelling of Equal-Sized Dipole and Folded Dipole Wearable Passive UHF RFID Tags

Body-centric wireless systems demand wearable sensor and tag antennas that have robust impedance matching and provide enough gain for a reliable wireless communication link. In this paper, we discuss a novel and practical technique for the modeling of the human body in UHF RFID body-centric wireless systems. What makes this technique different is that we base the human model on measured far-field response from a reference tag attached to the human body. Hereby, the human body model accounts for the encountered human body effects on the tag performance. The on-body measurements are fast, which allows establishing a catalog of human body models for different tag locations and human subjects. Such catalog would provide a ready simulation model for a wide range of wireless body-centric applications in order to initiate a functional design. Our results demonstrate that the suggested modeling technique can be used in the design and optimization of wearable antennas for different real-case body-centric scenarios.

https://downloads.hindawi.com/journals/ijap/2014/368090.pdf

Toni Bjorninen

Papers

Radiation Efficiency Measurement Method for Passive UHF RFID Dipole Tag Antennas

Impact of recurrent stretching on the performance of electro-textile UHF RFID tags

Embroidered passive UHF RFID tag on flexible 3D printed substrate

Comparison of Three Body Models of Different Complexities in Modelling of Equal-Sized Dipole and Folded Dipole Wearable Passive UHF RFID Tags

A New Approach and Analysis of Modeling the Human Body in RFID-Enabled Body-Centric Wireless Systems