The effect of bending on laser-cut electro-textile inductors and capacitors attached on denim as wearable structures

In this paper we present the design, fabrication and characterization of electro-textile inductor and capacitor patterns on denim fabric as a basis for the development of wearable e-textiles. Planar coil inductors have been harnessed as antenna structures for the development of Near Field Communication (NFC) tags with temperature sensing capability, while interdigitated electrode (IDE) capacitors have been used as humidity sensors for wearable applications. The effect of bending in the electrical performance of such structures was evaluated, showing variations below 5% in both inductance and capacitance values for bending angles in the range of interest, i.e. those fitting to human limbs. In the case of the fabricated NFC tags, a shift in the resonance frequency below 1.7% was found, meaning that the e-textile tag would still be readable by an NFC- enabled smartphone. In respect of the capacitive humidity sensor, we obtained a minimum capacitance variation of 40% for a relative humidity range from 10% to 90%. Measured thermal shift was below 5% in the range from 10 to 40oC. When compared to the 4% variation due to bending, it can be concluded that this capacitive structure can be harnessed as humidity sensor even under bending strain conditions and moderate temperature variations. The development and characterization of such structures on denim fabrics, which is one of the most popular fabrics for everyday clothing, combined with the additional advantage of affordable and easy fabrication methodologies, means a further step towards the next generation of smart e-textile products

Delay line based passive radio frequency identification tags

This work describes the concept, design, fabrication, and characterization of delay-based radio frequency identification (RFID) tags and RFID-based sensor tags, representing a novel RFID technology. The presented delay-based RFID concept is based on the LC-delay-line and transmission-delay-line based approaches. The proposed concept allows the realization of RFIDs and RFID-based sensor tags at any allowed radio frequency, with the limitation of realizing delay elements capable of producing required delays. The RFID configurations presented in this work are for operation at 915 MHz. Simulations are used to design and optimize components and devices that constitute the tags, and to integrate them to realize tags of different configuration. A set of fabrication processes has been developed for the realization of the tag. Characterization and field testing of these tags show that delay-based RFID approach can be used to make passive tags at ultra high frequency (UHF) and other allowed frequencies. Delay-based tags have the advantages of time domain operation, and the feasibility of complying with FCC regulations. However, size, need of isolators and circulator, and design constraints in producing higher number of bits are some of the concerns that need to be further addressed. In summary, this dissertation work presents a viable alternative RFID approach based on the delay line concept. The results obtained show great promise for further development and optimization of this approach for a wide range of commercial applications

Modern Microelectronic Technologies in Fabrication of RFID Tags

This paper presents fabrication of RFID tags, especially antennas for HF band (13.56 MHz), on cheap flexible substrates. The physicochemical, geometrical, DC and AC electrical properties as well as long-term stability (under thermal, moisture-thermal and mechanical exposures) have been characterized for several low-temperature polymer thick-film conductive films made on various paper or foil substrates. Resistance measurement during curing has been used for investigation of polymerization velocity, which is very important for increase of process capacity

Paper-based Screen-printed Passive Electronic Components

This thesis investigates paper-based electronics in terms of various substrates, fabrication methods and example devices, including touch sensors and microwave resonators. The term ‘paper’ is very broad and covers a wide range of substrates. A decision matrix has been created to determine the optimum paper for an application, based on a range of properties. Thermal evaporation and screen printing are compared for their use as fabrication methods for paper-based electronics and a second decision matrix has been compiled. Based on these decision matrices, screen printing onto a thicker matt paper was determined to be optimal. The printing process was further optimised to achieve the best results from the in-house process. Using this well-developed screen-printing method, passive components (including inductors and interdigitated capacitive touch sensors) were fabricated and found to be comparable with state-of-the- art results reported in the literature. Measurements from the touch pads were compared to modelling, with little variation between the two, and were confirmed to work under a wide range of conditions, showing that they are compatible with any user. The microwave characteristics, up to 3GHz, of both the chosen substrate and silver-flake ink were investigated through production of screen-printed transmission lines. These characteristics were then used to create microwave resonators. The frequency range is important for applications as the industrial, scientific and medical radio band (ISM band) lies between 2.45 and 2.55 GHz which includes Wi-Fi and Bluetooth. Initially, stub resonators were considered to determine the cause of differences between theoretical and measured results. Then spiral defected ground structures were made, with multiple resonances, and sensitivity to touch and humidity demonstrated. As paper is hygroscopic, the effect of humidity on paper-based electronics is of key importance. This has been considered for all the devices fabricated in this work and it has been determined that the change in permittivity of the substrate, as a result of absorbed water within paper, is the most dominant factor

Electrical and Physical Property Characterization of Single Walled Carbon Nanotube Ink for Flexible Printed Electronics

This research presents a method of characterizing single-walled carbon nanotube (SWCNT) ink. This research also examines the results of our characterization efforts. First, the process of ink jet printing SWCNT ink onto organic and inorganic substrates is discussed. Next, the tests for measuring sheet resistance, conductance, inductance, adherence, thickness, roll-off, and S-parameters of the ink are described. Results and findings of the research are presented. The SWCNT ink created by Brewer Science © is shown to be an effective material for additive manufacturing using an aerosol jet printer, but not an inkjet printer. The ink is shown to have a sheet resistance on the order of 5 kiloohm per square. The thickness is shown to be between 50 and 800 nm. An inductor is printed and shown to have an inductance on the order of 1 microhenry. Future research directions are discussed, including the additional characterization of SWCNT ink

Design and Optimization of Printed Antennas for Wireless Powering

The aim of present research was design and optimization of printed spiral inductor coils as the antennas for wireless powering. Power transfer was limited to some milliwatts over several centimeters with mega Hertz range frequency for low power consumer products like desktop accessories or packaging. Generally, the efficiency of power transferring through printed antennas is less than conventional coils because of some characteristics of conductive inks and printing processes. In this thesis, design and optimization of printed antennas based on printing limits was considering. Geometrical parameters of spiral antennas and the effect of them on inductive powering were reviewed. Three layouts for screen printing of the antennas were represented: Preliminary layout for practical tests on fine line printing and dimensional characteristics of antennas; Comparative layout for comparison between electromagnetic characteristics of antennas; and a Final layout for using in wireless powering. Two types of mesh screens and three types of conductive silver inks were applied for printing the samples on PET substrates. Characterization of printed samples was done by application of a network analyzer based on reflection method in frequency range of 100 Hz to 40 MHz. The magnitude and phase angle of impedance spectrum were plotted and the inductance, resistance, and parasitic capacitance were calculated based on equivalent RLC model. The first resonance frequency of most of antennas was included in the frequency range of measurement. The phase angle did not exceed 90° in all of the samples. The resonance frequency improved extremely by increasing the track width and decreasing the number of turns. Application of different inks could significantly change the impedance value. The measurements showed that the proximity effect losses could be more effective than skin effect in printed samples. Also, by increasing the track length or turn numbers, the parasitic capacitance and inductance could be increased. The results represented that the quality factor could be a problematic factor for comparison between different geometries. Figure-of-merit was applied for comparison between different antennas based on overall area of the antennas. The overall area was substituted with ink area to represent the ratio of efficiency to ink consumption. The FOM of printed antennas in present research was relatively less than PCB antennas that could be caused by high resistive losses of conductive inks. Finally, the functionality of printed antennas was represented by a demonstrator. Also, a concept for software workflow for the design of printed antennas was represented