Antenna sensing for wearable applications

As wearable technologies are growing fast, there is emerging trend to increase functionality of the devices. Antennas which are primarily component in communication systems can offer attractive route forward to minimize the number of components functioning as a sensing element for wearable and flexible electronics. Toward development of flexible antenna as sensing element, this thesis investigates the development of the flexible and printed sensing NFC RFID tag. In this approach, the sensor measurement is supported by the internal sensor and analog-to-digital convertor (ADC) of the NFC transponder. Design optimisation, fabrication and characterization of the printed antenna are described. Besides, the printed antenna, NFC transponder and two simple resistive sensors are integrated to form a fully flexible sensing RFID tag demonstrating applicability in food and health monitoring. This thesis also presents development of two antenna sensors by using functional materials: (i) An inductor-capacitor (LC) resonant tank based wireless pressure sensor on electrospun Poly-L-lactide (PLLA) nanofibers-based substrate. The screen-printed resonant tank (resonant frequency of ~13.56 MHz) consists of a planar inductor connected in parallel with an interdigitated capacitor. Since the substrates is piezoelectric, the capacitance of the interdigitated capacitor varies in response to the applied pressure. To demonstrate a potential application of developed pressure sensor, it was integrated on a compression bandage to monitor sub-bandage pressure. (ii) To investigate the realization of sensing antenna as temperature sensor simple loop antenna is designed and in this study unlike the first study that the sensing element was the substrate, the conductive body of the antenna itself is considered as a functional material. In this case, a small part of a loop antenna which originally was printed using silver paste is replaced by Poly(3,4-ethylenedioxythiophene): polystyrene (PEDOT: PSS). The sensing mechanism is based on the resonant frequency shift by varying temperature. While using functional materials is useful for realization of antenna sensor, another approach also is presented by developing stretchable textile-based microstrip antennas on deformable substrate which can measure joint angles of a human limb. The EM characteristics of the meshed patch antenna were compared with its metallic counterpart fabricated with lithography technique. Moreover, the concept of stretchable UHF RFID-based strain sensor is touched in the final part of this thesis

NFC based Polymer Strain Sensor for Smart Packaging

This paper presents a polymer strain sensor integrated with an NFC tag to detect strain semi-quantitatively. The strain sensor is fabricated using flexible and transparent polymer Polydimethylsiloxane (PDMS) microchannel having conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as an active material. The sensor was tested with different bending conditions and it was found that the resistance increases with higher bending. A maximum of 3 order change in resistance was observed for ~100 bending. The sensor was finally tested using a custom-developed passive NFC tag having an LED connected in series with the strain sensor and powered from the reader via the NFC antenna in the tag

Printed chipless antenna as flexible temperature sensor

The ever-increasing number of devices on wearable and portable systems comes with challenges such as integration complexity, higher power requirements, and less user comfort. In this regard, the development of multifunctional devices could help immensely as they will provide the same functionalities with lesser number of devices. Herein, we present a dual-function flexible loop antenna printed on Polyvinyl Chloride (PVC) substrate. With a PEDOT:PSS section as part of the printed structure, the presented antenna can also serve as a temperature sensor by means of change in resistance. The antenna resonates at 1.2 GHz and 5.8 GHz frequencies. The ohmic resistance of the temperature sensing part decreases by 70% when the temperature increases from 25.C to 90.C. The developed antenna was characterised using VNA in the same temperature range and the S11 magnitude was found to change by 3.5 dB. The induced current was also measured in the GSM frequency range and sensitivity of 1.2%/∘C was observed for the sensing antenna. The flexible antenna was also evaluated in lateral and cross bending conditions and the response was found to be stable for the cross bending. Due to these unique features, the presented antenna sensor could play a vital role in the drive toward ubiquitous sensing through wearables, smart labels, and the internet of things (IoT)

Flexible strain and temperature sensing NFC tag for smart food packaging applications

This paper presents a smart sensor patch with flexible strain sensor and a printed temperature sensor integrated with a Near Field Communication (NFC) tag to detect strain or temperature in a semi-quantitative way. The strain sensor is fabricated using conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in a polymer Polydimethylsiloxane microchannel. The temperature sensor is fabricated by printing silver electrodes and PEDOT:PSS on a flexible polyvinyl chloride (PVC) substrate. A customdeveloped battery-less NFC tag with an LED indicator is used to visually detect the strain or temperature by modulating the LED light intensity. The LED shows maximum brightness for relaxed or no strain condition, and also in the case of maximum temperature. In contrast, the LED is virtually off for the maximum strain condition and for room temperature. Both these could be related to food spoilage. Swollen food packages can be detected with the strain sensor, serving as beacons of microbial contamination. Temperature deviations can result in the growth or survival of food-spoilage bacteria. Based on this, the potential application of the sensor system for smart food packaging is presented

Smart bandage with wireless strain and temperature sensors and battery-less NFC tag

This paper presents a smart bandage with wireless strain and temperature sensors and a battery-less Near Field Communication tag. Both sensors are based on conductive poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymer. The highly sensitive strain sensor consists of a microfluidic channel filled with PEDOT:PSS in Polydimethylsiloxane (PDMS) substrate. The strain sensor shows 3 order ( 1250) increase in the resistance for 10% strain and considerably high gauge factor of 12500. The sensor was tested for 30% strain, which is more than typical stretching of human skin or body parts such as chest expansion during respiration. The strain sensor was also tested for different bending and the electrical resolution was 150% per degree of free bending and 12k% per percentage of stretching. The resistive temperature sensor, fabricated on a Polyvinyl Chloride (PVC) substrate, showed a 60% decrease in resistance when the temperature changed from 25.C to 85.C and a sensitivity of 1% per.C. As a proof of concept, the sensors and NFC tag were integrated on wound dressing to obtain wearable systems with smart bandage form-factor. The sensors can be operated and read from distance of 25 mm with a user-friendly smartphone application developed for powering the system as well as real-time acquisition of sensors data. Finally, we demonstrate the potential use of smart bandage in healthcare applications such as assessment of wound status or respiratory diseases such as asthma and COVID-19, where monitoring via wearable strain (e.g., respiratory volume) and temperature sensors is critical

Printed Flexible Temperature Sensor with NFC Interface

Integration of sensors with antennas is becoming popular for compact high-performance wireless sensing systems. In this direction, here we present a silver electrodes and Poly(3,4-ethylenedioxythiophene:polystyrene (PEDOT:PSS) based printed temperature sensor on a flexible PVC substrate. The temperature sensor was characterised using a digital multimeter for a temperature range from 25¤C to 90□C. The sensor showed a 70% change in resistance for the tested temperature range. Further, the sensing part was integrated with a Near Field Communication (NFC) tag with the data obtained semi-quantitatively by means of the intensity of an Light Emittign Diode (LED) connected with the antenna system. In this case, the antenna works as an energy harvester to power an LED indicator connected in series to the resistive temperature sensor. The intensity of the LED, which varies with the increase of temperature, was measured using a lux-meter mobile application. The intensity at 70□C was ~42 lux whereas it decreased down to ~14 lux at room temperature (~25□C). The presented system showed potential use as a smart label in applications requiring temperature monitoring

Flexible Strain Sensor with NFC Tag for Food Packaging

In this work we present a polymer-based flexible strain sensor integrated with an NFC tag to detect strain by means of a visual LED indicator. The sensor was fabricated using conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as an active material inside a flexible and transparent polymer Polydimethylsiloxane (PDMS) microchannel. The strain sensor changes its resistance at different bending conditions, showing up to three order increase in resistance for ∼100 bending. A custom-developed passive NFC tag with an LED connected in series to the strain sensor is powered from an NFC reader to detect strain in a semi-quantitative way. The light intensity of the LED indicator is modulated according to the strain level, showing maximum brightness (∼67 lux) for relaxed or no strain condition, and being almost OFF (∼8 lux) for the maximum strain condition. The potential application of the NFC-based strain sensor system in food package for spoilage detection is also presented

Wireless microwave signal transmission for cryogenic applications

Microwave wireless signal propagation in cryogenic environments has applications in radio astronomy and quantum computing. This paper demonstrates for the first time a cryogenic wireless setup and investigates the antenna-to-antenna signal transmission in Liquid Nitrogen (LN) and inside the dilution refrigerator at room temperature (296 K). The antenna under investigation consists of a wideband antenna operating in from 8-12 GHz. The antenna was modelled and designed in CST MWS and fabricated on the Rogers RT/duroid 5880 substrate. The measured transmission coefficient (S21) results demonstrate that there was reasonable signal transmission between the antenna pairs when tested in LN (77 K) and inside the dilution refrigerator (tested at 296 K). The results indicate that the proposed Over- The-Air (OTA) system is suitable for cryogenic applications down to 77K

Characterization of a compact wideband microwave metasurface lens for cryogenic applications

In this paper, we present characterization of a compact flat microwave lens operating between 6 GHz and 14 GHz using a near field scanning system. An X-band horn antenna and open-end rectangular waveguide were used as an illumination source and probe, respectively. |S21| is measured as the probe antenna moves on a plane orthogonal to the optical axis vertically and horizontally. The lens is made of a metasurface layer that is sandwiched by two layers of cross-oriented gratings. The overall dimension of the lens is 10 cm in diameter and 0.57 cm in thickness. The measurement results show that the lens's focal length is 8 cm, and the beamwidth (full width at half maximum (FWHM)) is 3.5 cm, A transmission efficiency of over 90% and a cross-polarization gain of 25 dB were achieved over the entire bandwidth. The measurement results at room temperature are in good agreement with numerical simulations. The proposed lens will be used in a cryogenic environment e.g. dilution refrigerators for quantum computing systems. More results at cryogenic temperature e.g, below 30 K will be shown at the conference

Hybrid integration of screen-printed RFID tags and rigid microchip on paper

Hybrid or heterogenous integration of silicon technologies and printed electronics is a promising approach for high-performance flexible electronics. It is essentially the integration of rigid microchips with the printed circuit on a flexible substrate. However, microchips with no-lead and mm size pitch introduce practical challenges in terms of precise electrical bonding onto the printed pattern. The differences in mechanical and thermal requirements also make it challenging to use conventional bonding and interconnect technology to robustly connect the microchips on flexible substrates. The focus of this work is to present these challenges with respect to different substrate-adhesive combinations and to provide a facile technique for integrating NFC microchips on different flexible substrates. Following the successful integration, the smart tags were characterised to demonstrate reliable performance in the NFC reading range. Whilst presenting a hybrid integration for the smart tag, this work also shows a potential solution for several other applications of flexible electronics where high-performance cannot be achieved by printed electronics alone