Mahmoud Wagih - Academia.edu (original) (raw)

Papers by Mahmoud Wagih

While research in passive flexible circuits for Wireless Power Transfer (WPT) such as coils and r... more While research in passive flexible circuits for Wireless Power Transfer (WPT) such as coils and resonators continues to advance, limitations in their power handling and low efficiency have hindered the realization of efficient all-printed high-power wearable WPT receivers. Here, we propose a screen-printed textile-based 6.78 MHz resonant inductive WPT system using planar inductors with concealed metal-insulator-metal (MIM) tuning capacitors. A printed voltage doubler rectifier based on Silicon Carbide (SiC) diodes is designed and integrated with the coils, showing a power conversion efficiency of 80-90% for inputs between 2 and 40 W. Compared to prior wearable WPT receivers, it offers an order of magnitude improvement in power handling along with higher efficiency (approaching 60%), while using all-printed passives and a compact rectifier. The coils exhibit a simulated Specific Absorption Rate (SAR) under 0.4 W/kg for 25 W received power, and under 21◦C increase in the coils’ temper...

2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (AP-S/URSI)

2022 Wireless Power Week (WPW)

While far-field wireless power transfer (WPT) promises a long range of operation, it falls short ... more While far-field wireless power transfer (WPT) promises a long range of operation, it falls short on the DC power which can be provided. On the other hand, resonant near-field WPT suffers from a short wireless range. In this work, a dualmode high/low-power near/far-field rectenna is demonstrated for the first time based on a flexible rectifier and a textile antenna. Based on a high-efficiency single-series rectifier, the far-field rectenna achieves a peak efficiency of 42.7% from an ultralow power density of 0.43 µW/cm 2 , with a 1 V DC output from 4 µW/cm 2. A high-power 6.78 MHz bridge rectifier is designed and implemented on a flexible textile-based substrate with a 10 dB return loss for inputs above 15 dBm. As a near-field receiver, the antenna could receive 3.75 W DC power at 5 cm from the transmitting coil, with an end-to-end efficiency of 30% inclusive of rectifier, coils, and power amplifier losses. Based on the proposed dual-mode antenna, textile-based wearables could be wirelessly powered dynamically using resonant near-field and radiative near-field WPT.

Sensors

Radio frequency identification (RFID) represents an emerging platform for passive RF-powered wire... more Radio frequency identification (RFID) represents an emerging platform for passive RF-powered wireless sensing. Differential Multi-port RFID systems are widely used to enable multiple independent measurands to be gathered, or to overcome channel variations. This paper presents a dual-port/dual-integrated circuit (IC) RFID sensing tag based on a shared aperture dual-polarized microstrip antenna. The tag can be loaded with different sensors where the received signal strength indicator (RSSI) of one IC is modulated using a sensor, and the other acts as a measurand-insensitive reference, for differential sensing. The 868 MHz tag maintains a minimum unloaded read range of 14 m insensitive to deployment on metals or lossy objects, which represents the longest reported range of a multi-port RFID sensing tag. The tag is loaded with a light-dependent resistor (LDR) to demonstrate its functionality as a battery-less wireless RFID light sensor. Following detailed RF characterization of the LDR,...

2022 16th European Conference on Antennas and Propagation (EuCAP)

Anticipated by 2035, a trillion wirelessly connected Internet of Everything (IoE) devices will be... more Anticipated by 2035, a trillion wirelessly connected Internet of Everything (IoE) devices will be deployed in various pervasive applications. Therefore, sustainable and low-cost antennas are crucial for enabling an environmentally-friendly IoE. Furthermore, advances in carbon-based energy storage and harvesting devices motivates research in carbon-based antennas for wireless power transmission (WPT) applications. In this paper, we present the first non-metallic carbon-based microstrip patch antenna implemented on textiles for wearable applications. The antenna is fabricated on a standard felt/woven-polyester fabric substrate using stencil casting and demonstrated for Sband applications. The antenna maintains a wide 10% fractional bandwidth from 3.16 to 3.49 GHz, in agreement with the simulated bandwidth. The achieves at least 30% radiation efficiency, 10.4 dBi measured directivity, and 6.1 dBi measured gain. Based on the measured radiation properties of the patch, it is concluded that non-metallic carbon-based antennas are suitable for future wearable IoE applications.

IEEE Open Journal of Antennas and Propagation

Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna... more Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna-based "RFID" sensing can detect various measurands, antenna-based sensors are not currently designed based on a systematic methodology, and in most cases may have a low sensitivity requiring specialist hardware or broadband interrogation signals, incompatible with spectrum regulations. Here, we develop a systematic methodology for designing an antenna-based sensor, applicable to measurands inducing a dielectric change in the near-field of the antenna. The proposed methodology is applied to designing printable antennas as highly-sensitive sensors for detecting and measuring the thickness of ice, demonstrating best-in-class sensory response compared to more complex antenna designs. Antenna design is investigated systematically for wireless interrogation in the 2.4 GHz band, where it is found that a loop antenna outperforms a dipole owing to its more distributed capacitance. The antenna's realized gain was identified as the optimum parameter-under-test, with "positive" sensing proposed as a method of improving linearity and immunity to interference. The developed loop antenna sensor exhibits resilience to interference and applicability to different real-world deployment environments, demonstrated through over 80% average ice thickness measurement accuracy and at least 5 dB real-time sensitivity to ice deposition.

2021 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (APS/URSI)

RFID tags can operate in a wide variety of environments enabling battery-free pervasive sensing. ... more RFID tags can operate in a wide variety of environments enabling battery-free pervasive sensing. In this paper, timevarying impedance measurements are presented to evaluate the sensitivity of inductive-matched dipole antennas as ice thawing monitors. Relative Signal Strength (RSS) measurements of an encapsulated RFID tags based on a commercial IC are presented showing that the tags can be read for up to 45 minutes inside 9 mm-thick thawing ice. Furthermore, the relationship between the ice thickness and the RSS of the ice-loaded RFID tags. The experimental results show that inductive-fed dipole antennas are highly suited for RFID-based monitoring of ice formation and thawing for smart city and remote sensing applications.

Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna... more Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna-based “RFID” sensing can detect various measurands, antenna-based sensors are not currently designed based on a systematic methodology, and in most cases may have a low sensitivity requiring specialist hardware or broadband interrogation signals, incompatible with spectrum regulations. Here, we develop a systematic methodology for designing an antenna-based sensor, applicable to measurands inducing a dielectric change in the near-field of the antenna. The proposed methodology is applied to designing printable antennas as highly-sensitive sensors for detecting and measuring the thickness of ice, demonstrating best-in-class sensory response compared to more complex antenna designs. Antenna design is investigated systematically for wireless interrogation in the 2.4 GHz band, where it is found that a loop antenna outperforms a dipole owing to its more distributed capacitance. The antenna’s ...

E-Textiles 2021, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

E-Textiles 2021, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

International Conference on the Challenges, Opportunities, Innovations and Applications in Electronic Textiles, 2021

Radio frequency energy harvesting (RFEH) and wireless power transfer (WPT) are increasingly seen ... more Radio frequency energy harvesting (RFEH) and wireless power transfer (WPT) are increasingly seen as a method of enabling sustainable computing, as opposed to mechanical or solar EH WPT does not require special materials or resonators and can be implemented using low-cost conductors and standard semiconductor devices. This work revisits the simplest antenna design, the wire monopole to demonstrate the lowest-footprint, lowest-cost rectifying antenna (rectenna) based on a single Schottky diode. The antenna is fabricated using a single Litz-wire silk-coated thread, embroidered into a standard textile substrate. The rectifier is fabricated on a compact lowcost flexible printed circuit board (PCB) using ultra-thin polyimide copper laminates to accommodate low-footprint surface mount components. The antenna maintains its bandwidth across the 868/915 MHz license-free band on-and off-body with only −4.7 dB degradation in total efficiency in human proximity. The rectenna achieves up to 55% RF to DC efficiency with 1.8 V DC output, at 1 mW of RF power, demonstrating its suitability as a power-supply unit for ultra-low power e-textile nodes.

2020 14th European Conference on Antennas and Propagation (EuCAP), 2020

Electronic textiles and seamlessly integrated flexible wearable electronics are an emerging platf... more Electronic textiles and seamlessly integrated flexible wearable electronics are an emerging platform for sensing and computing. Batteries and energy harvesters relying on specific materials and transducers are not fully compatible with e-textiles fabrication and large-scale manufacturing. This work proposes a radio frequency energy harvesting rectenna, operating in the sub-1 GHz license-free band, packaged in the form a of rectenna yarn which can be concealed in standard textile weaves. The rectenna yarn is fabricated using thin polyimide copper laminates using photolithography. The rectenna is composed of a 50Ω meanderline coplanar waveguide monopole antenna and a voltage doubler rectifier, with a lumped matching network. The rectenna achieves 65.8% RF-DC efficiency and a 8.0-V DC output at 6 and 11 dBm input power, respectively. This is the highest voltage output of a textile wearable rectenna, while maintaining high efficiency down to −20 dBm and a −7 dBm 1-V sensitivity.

2019 IEEE Wireless Power Transfer Conference (WPTC), 2019

Millimeter-Wave (mmWave) bands will be a key part of future 5G networks, with the 26 and 28 GHz b... more Millimeter-Wave (mmWave) bands will be a key part of future 5G networks, with the 26 and 28 GHz bands being introduced first. The wide bandwidth aims to solve traffic-related issues. The projected high base-station density, highly directive transmitters, and the wide bandwidth make it a very promising RF energy harvesting (RFEH) source. Broadband antennas are necessary to harvest power efficiently from the full spectrum. This work presents the first antenna on textile for wearable ambient RFEH in the 26 GHz and 28 GHz bands. The antenna has an impedance bandwidth from 20 to 30 GHz, and exhibits a peak on-body gain of 7 dB with an omnidirectional radiation pattern for capturing ambient RF energy. The radiation efficiency on-and off-body was observed to be at least 40% and 60% respectively, between 24 and 30 GHz. A two-line microstrip dielectric characterization of the textile substrate in the mmWave band has been performed. The antenna has been fabricated on a 310 μm woven polyester substrate using etched ultra-thin Polyimide copper laminates with a minimum feature size of 150μm. A high robustness against human proximity has been demonstrated with a stable bandwidth and improved gain.

2021 IEEE 20th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS), 2021

Wearable Radio Frequency (RF) rectennas do not require expensive or hazardous materials and can b... more Wearable Radio Frequency (RF) rectennas do not require expensive or hazardous materials and can be easily integrated with conventional e-textiles. In this paper, we investigate the use of ultra-miniaturized wire-type monopole antennas for energy harvesting (EH) applications, as a method maximizing the effective collection area of a rectenna relative to its physical size, while not reducing the net DC output. The rectenna, operating in the 915 MHz band, is integrated with a simple carbon-based e-textile supercapacitor for direct energy conversion and storage. The integrated module is then demonstrated, for the first time, wirelessly-charging a Bluetooth Low Energy sensor node at over 1 m distance from a license-free Powercast transmitter. The 14.1 mF supercapacitor is charged using the e-textile rectenna filament in 83 s up to 4.14 V, from an incident power density of 23.9 µW/cm 2 and a timeaveraged efficiency over 40%, enabling the sensor node to sustain operation for 108 s after the wireless RF source is stopped. Compared to state-of-the-art RF energy harvesters, the proposed module achieves over five fold improvement in the RF to DC power harvesting efficiency normalized to the harvester's area.

2021 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP), 2021

Wearable radio frequency (RF) energy harvesting is highly dependent on the distance from the sour... more Wearable radio frequency (RF) energy harvesting is highly dependent on the distance from the source and human-caused RF shadowing. Therefore, energy storage devices integrated with rectennas are of paramount importance to overcome this intermittency. In this paper, the use of carbonbased e-textile supercapacitors for storing the RF-DC converted power for powering body area networks nodes is investigated. A voltage doubler sub-1 GHz flexible rectifier, whose peak power conversion efficiency (PCE) approaches 80% is coupled to a two-cell 15.5 mF textile-based supercapacitor operating up to 4 V DC. Owing to the rectifier's low optimum load resistance and high DC Voltage output, the average charging PCE of the rectifier-supercapacitor module reaches 31% for a 9.5 dBm input. Time-varying s-parameter measurements are performed to compare the time-averaged matching as opposed to instantaneous measurements using a resistive load, where the textile supercapacitor exhibits a similar response to a commercial supercapacitor. Finally, the RF-charged textile supercapacitor is demonstrated, for the first time, powering a microcontroller and Bluetooth transmitter with an average power consumption of 350 µW for up to 102 s, following 40 s of charging at 9.5 dBm, demonstrating its suitability for RF-powered body area networks applications.

2019 19th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS), 2019

Coupled wireless power transfer (WPT) has been widely used for near-field high-efficiency WPT app... more Coupled wireless power transfer (WPT) has been widely used for near-field high-efficiency WPT applications. However, the efficiency of the WPT link is highly sensitive to separation and alignment, and is prone to over-coupling, making it unsuitable for mobile systems with unknown or loose coupling such as wearables. While ultra-high frequency (UHF) and microwave radiative WPT (0.3-3 GHz) enables meters-long separation between the transmitter and the receiver, free space propagation losses, and rectification inefficiencies, adversely limit the end-to-end efficiency of the WPT link. This work proposes radiative WPT, in the 6.78 MHz license-free band, based on resonant electrically small antennas fabricated using embroidered textile coils, tuned using L-matching networks. The proposed WPT system achieves a stable forward transmission of S21>-17 dB and S21>-28 dB, independent of coil, separation on the XZ and XY planes respectively, in a 27 m 3 volume space. The presented approach demonstrates the highest WPT-link efficiency, and promises higher end-to-end efficiency, compared to UHF WPT.

Microwave microfluidic sensors are typically designed with a channel in vicinity of a resonator&#... more Microwave microfluidic sensors are typically designed with a channel in vicinity of a resonator's fringing electric (E)-fields, to characterize the material properties of a single fluid. This paper leverages hybrid 3D and dispenser printing to realize a scalable microfluidic sensor utilizing the parallel-plate capacitance of an open-ended microstrip stub, enabling, for the first time, a tunable sensitivity. A stub-loaded microstrip line is then proposed for characterizing multiple microfluidic samples simultaneously using a simple two-port multi-band resonator. The physical constrains which limit the scalability of the proposed sensors have been analyzed analytically and numerically, prior to implementing a three-channel triple-band sensor. The microfluidic channels have been fabricated using stereolithography 3D printing with the microstrip line directly dispenser printed on a conformable polyimide substrate. To accommodate varying channel thicknesses, a tapered microstrip line...

IEEE Journal of Microwaves, 2021

In this paper, a novel multi-layered microstrip line with built-in parallel-plate capacitors is p... more In this paper, a novel multi-layered microstrip line with built-in parallel-plate capacitors is proposed for DC-blocking applications, with its transmission characteristics measured up to 50 GHz. The microstrip lines are fabricated via screen printing directly onto polyurethane films laminated on standard textile substrates which would otherwise be unsuitable for printing. Compared to a standard microstrip line on the same substrate, the proposed 10 cm-long line on felt (with an embedded 44 pF capacitance) suffers from less than 0.1 dB higher insertion loss up to 4 GHz. Furthermore, varying the overlapping length of the lines and hence the capacitance enables the realization of DC blocking and −3 dB high-pass filtering with pass-bands starting between 88 MHz and 1.2 GHz. This is achieved without altering the cutoff frequency of the microstrip line's mode-free propagation, measured up to 50 GHz, exhibiting a low attenuation of 0.32 dB/mm at 50 GHz on a felt fabric substrate. Compared to a lumped capacitor, the proposed microstripembedded printed capacitor demonstrates a significant improvement in mechanical reliability, withstanding over 10,000 bending cycles, and RF power handling with under 6 • C temperature rise at 1 W. The lines are fabricated on two textile substrates and their transmission characteristics were measured up to 50 GHz, which represents the highest frequency characterization of textile-based lines to date, demonstrating a stable group delay and insertion losses. Based on the proposed multi-layered integration method, low-cost screen-printed microstrip-embedded capacitors on textiles can be used for microwave applications up to mmWave bands. INDEX TERMS Additive manufacturing, capacitors, DC block, high-pass filter, microstrip lines, printed capacitors, radio frequency (RF), textile capacitors, transmission lines. I. INTRODUCTION Flexible, printable, and conformable microwave and millimeter-wave (mmWave) components have attracted significant research interest for a variety of Internet of Things (IoT) and 5G+/6G applications [1], [2]. Wireless communication antennas [3], energy harvesting rectennas [4], mmWave imaging arrays [5], and RFIC packaging [6] are among the applications tackled through additive manufacturing of microwave and mmWave distributed components. Furthermore, the realization of individual components such as RF capacitors using inkjet [7] and 3D printing [8] has been demonstrated. In low-cost, large-area, printed electronics, and wearable applications, it is desirable to minimize the lumped components count in the system and utilize printed components to maximize flexibility [9]. Shortly after the early development of planar microstrip transmission lines, DC-blocking microstrip lines attracted significant interest [10]-[12], [12], [13]. In planar microstrip technology, DC-blocks are typically realized using coupled lines [13]. As a result, they are often integrated within filters

2021 IEEE International Conference on RFID Technology and Applications (RFID-TA), 2021

Radio Frequency (RF) power transfer is an enabling technology of RFID systems. CMOS RF rectifiers... more Radio Frequency (RF) power transfer is an enabling technology of RFID systems. CMOS RF rectifiers enable miniaturization and improved integration with full systems. For certain applications, rectifiers may need to be deployed in high or low temperature environments, which can affect their power conversion efficiency (PCE). This work presents the design of a high efficiency 915 MHz CMOS Dickson charge-pump in a 2S nm FDSOI process, and investigates antenna-based impedance matching as a method of maximizing the PCE for different temperatures and CMOS process variations. With a co-designed antenna, the proposed rectifier achieves $ 5.4\times $ higher PCE compared to simple inductive-matching at -20dBm. The PCE is then analyzed for CMOS process and temperature variations. It is shown that the rectifier can maintain 94% of its peak PCE at -15dBm at -10°C through input-impedance matching. The proposed rectifier and matching technique achieves the highest PCE compared to state-of-the-art Dickson multipliers, while having the smallest die area.

Wireless power transfer (WPT) and Radio Frequency (RF) energy harvesting (EH) are increasingly se... more Wireless power transfer (WPT) and Radio Frequency (RF) energy harvesting (EH) are increasingly seen as an enabling technology for power-autonomous Internet of Things (IoT) [1, 2]. RFEH and WPT are a particularly attractive power source for flexible, printed, and e-textile systems due to their compatibility with standard fabrication processes, abolishing the need for specific materials and transducers. This work provides an overview on flexible WPT at multiple frequencies (6.78 MHz to 26 GHz) and techniques from near-field WPT to Millimetre-wave WPT and RFEH.

While research in passive flexible circuits for Wireless Power Transfer (WPT) such as coils and r... more While research in passive flexible circuits for Wireless Power Transfer (WPT) such as coils and resonators continues to advance, limitations in their power handling and low efficiency have hindered the realization of efficient all-printed high-power wearable WPT receivers. Here, we propose a screen-printed textile-based 6.78 MHz resonant inductive WPT system using planar inductors with concealed metal-insulator-metal (MIM) tuning capacitors. A printed voltage doubler rectifier based on Silicon Carbide (SiC) diodes is designed and integrated with the coils, showing a power conversion efficiency of 80-90% for inputs between 2 and 40 W. Compared to prior wearable WPT receivers, it offers an order of magnitude improvement in power handling along with higher efficiency (approaching 60%), while using all-printed passives and a compact rectifier. The coils exhibit a simulated Specific Absorption Rate (SAR) under 0.4 W/kg for 25 W received power, and under 21◦C increase in the coils’ temper...

2022 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (AP-S/URSI)

2022 Wireless Power Week (WPW)

While far-field wireless power transfer (WPT) promises a long range of operation, it falls short ... more While far-field wireless power transfer (WPT) promises a long range of operation, it falls short on the DC power which can be provided. On the other hand, resonant near-field WPT suffers from a short wireless range. In this work, a dualmode high/low-power near/far-field rectenna is demonstrated for the first time based on a flexible rectifier and a textile antenna. Based on a high-efficiency single-series rectifier, the far-field rectenna achieves a peak efficiency of 42.7% from an ultralow power density of 0.43 µW/cm 2 , with a 1 V DC output from 4 µW/cm 2. A high-power 6.78 MHz bridge rectifier is designed and implemented on a flexible textile-based substrate with a 10 dB return loss for inputs above 15 dBm. As a near-field receiver, the antenna could receive 3.75 W DC power at 5 cm from the transmitting coil, with an end-to-end efficiency of 30% inclusive of rectifier, coils, and power amplifier losses. Based on the proposed dual-mode antenna, textile-based wearables could be wirelessly powered dynamically using resonant near-field and radiative near-field WPT.

Sensors

Radio frequency identification (RFID) represents an emerging platform for passive RF-powered wire... more Radio frequency identification (RFID) represents an emerging platform for passive RF-powered wireless sensing. Differential Multi-port RFID systems are widely used to enable multiple independent measurands to be gathered, or to overcome channel variations. This paper presents a dual-port/dual-integrated circuit (IC) RFID sensing tag based on a shared aperture dual-polarized microstrip antenna. The tag can be loaded with different sensors where the received signal strength indicator (RSSI) of one IC is modulated using a sensor, and the other acts as a measurand-insensitive reference, for differential sensing. The 868 MHz tag maintains a minimum unloaded read range of 14 m insensitive to deployment on metals or lossy objects, which represents the longest reported range of a multi-port RFID sensing tag. The tag is loaded with a light-dependent resistor (LDR) to demonstrate its functionality as a battery-less wireless RFID light sensor. Following detailed RF characterization of the LDR,...

2022 16th European Conference on Antennas and Propagation (EuCAP)

Anticipated by 2035, a trillion wirelessly connected Internet of Everything (IoE) devices will be... more Anticipated by 2035, a trillion wirelessly connected Internet of Everything (IoE) devices will be deployed in various pervasive applications. Therefore, sustainable and low-cost antennas are crucial for enabling an environmentally-friendly IoE. Furthermore, advances in carbon-based energy storage and harvesting devices motivates research in carbon-based antennas for wireless power transmission (WPT) applications. In this paper, we present the first non-metallic carbon-based microstrip patch antenna implemented on textiles for wearable applications. The antenna is fabricated on a standard felt/woven-polyester fabric substrate using stencil casting and demonstrated for Sband applications. The antenna maintains a wide 10% fractional bandwidth from 3.16 to 3.49 GHz, in agreement with the simulated bandwidth. The achieves at least 30% radiation efficiency, 10.4 dBi measured directivity, and 6.1 dBi measured gain. Based on the measured radiation properties of the patch, it is concluded that non-metallic carbon-based antennas are suitable for future wearable IoE applications.

IEEE Open Journal of Antennas and Propagation

Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna... more Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna-based "RFID" sensing can detect various measurands, antenna-based sensors are not currently designed based on a systematic methodology, and in most cases may have a low sensitivity requiring specialist hardware or broadband interrogation signals, incompatible with spectrum regulations. Here, we develop a systematic methodology for designing an antenna-based sensor, applicable to measurands inducing a dielectric change in the near-field of the antenna. The proposed methodology is applied to designing printable antennas as highly-sensitive sensors for detecting and measuring the thickness of ice, demonstrating best-in-class sensory response compared to more complex antenna designs. Antenna design is investigated systematically for wireless interrogation in the 2.4 GHz band, where it is found that a loop antenna outperforms a dipole owing to its more distributed capacitance. The antenna's realized gain was identified as the optimum parameter-under-test, with "positive" sensing proposed as a method of improving linearity and immunity to interference. The developed loop antenna sensor exhibits resilience to interference and applicability to different real-world deployment environments, demonstrated through over 80% average ice thickness measurement accuracy and at least 5 dB real-time sensitivity to ice deposition.

2021 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (APS/URSI)

RFID tags can operate in a wide variety of environments enabling battery-free pervasive sensing. ... more RFID tags can operate in a wide variety of environments enabling battery-free pervasive sensing. In this paper, timevarying impedance measurements are presented to evaluate the sensitivity of inductive-matched dipole antennas as ice thawing monitors. Relative Signal Strength (RSS) measurements of an encapsulated RFID tags based on a commercial IC are presented showing that the tags can be read for up to 45 minutes inside 9 mm-thick thawing ice. Furthermore, the relationship between the ice thickness and the RSS of the ice-loaded RFID tags. The experimental results show that inductive-fed dipole antennas are highly suited for RFID-based monitoring of ice formation and thawing for smart city and remote sensing applications.

Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna... more Remote ice detection has emerged as an application of Radio Frequency (RF) sensors. While antenna-based “RFID” sensing can detect various measurands, antenna-based sensors are not currently designed based on a systematic methodology, and in most cases may have a low sensitivity requiring specialist hardware or broadband interrogation signals, incompatible with spectrum regulations. Here, we develop a systematic methodology for designing an antenna-based sensor, applicable to measurands inducing a dielectric change in the near-field of the antenna. The proposed methodology is applied to designing printable antennas as highly-sensitive sensors for detecting and measuring the thickness of ice, demonstrating best-in-class sensory response compared to more complex antenna designs. Antenna design is investigated systematically for wireless interrogation in the 2.4 GHz band, where it is found that a loop antenna outperforms a dipole owing to its more distributed capacitance. The antenna’s ...

E-Textiles 2021, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

E-Textiles 2021, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

International Conference on the Challenges, Opportunities, Innovations and Applications in Electronic Textiles, 2021

Radio frequency energy harvesting (RFEH) and wireless power transfer (WPT) are increasingly seen ... more Radio frequency energy harvesting (RFEH) and wireless power transfer (WPT) are increasingly seen as a method of enabling sustainable computing, as opposed to mechanical or solar EH WPT does not require special materials or resonators and can be implemented using low-cost conductors and standard semiconductor devices. This work revisits the simplest antenna design, the wire monopole to demonstrate the lowest-footprint, lowest-cost rectifying antenna (rectenna) based on a single Schottky diode. The antenna is fabricated using a single Litz-wire silk-coated thread, embroidered into a standard textile substrate. The rectifier is fabricated on a compact lowcost flexible printed circuit board (PCB) using ultra-thin polyimide copper laminates to accommodate low-footprint surface mount components. The antenna maintains its bandwidth across the 868/915 MHz license-free band on-and off-body with only −4.7 dB degradation in total efficiency in human proximity. The rectenna achieves up to 55% RF to DC efficiency with 1.8 V DC output, at 1 mW of RF power, demonstrating its suitability as a power-supply unit for ultra-low power e-textile nodes.

2020 14th European Conference on Antennas and Propagation (EuCAP), 2020

Electronic textiles and seamlessly integrated flexible wearable electronics are an emerging platf... more Electronic textiles and seamlessly integrated flexible wearable electronics are an emerging platform for sensing and computing. Batteries and energy harvesters relying on specific materials and transducers are not fully compatible with e-textiles fabrication and large-scale manufacturing. This work proposes a radio frequency energy harvesting rectenna, operating in the sub-1 GHz license-free band, packaged in the form a of rectenna yarn which can be concealed in standard textile weaves. The rectenna yarn is fabricated using thin polyimide copper laminates using photolithography. The rectenna is composed of a 50Ω meanderline coplanar waveguide monopole antenna and a voltage doubler rectifier, with a lumped matching network. The rectenna achieves 65.8% RF-DC efficiency and a 8.0-V DC output at 6 and 11 dBm input power, respectively. This is the highest voltage output of a textile wearable rectenna, while maintaining high efficiency down to −20 dBm and a −7 dBm 1-V sensitivity.

2019 IEEE Wireless Power Transfer Conference (WPTC), 2019

Millimeter-Wave (mmWave) bands will be a key part of future 5G networks, with the 26 and 28 GHz b... more Millimeter-Wave (mmWave) bands will be a key part of future 5G networks, with the 26 and 28 GHz bands being introduced first. The wide bandwidth aims to solve traffic-related issues. The projected high base-station density, highly directive transmitters, and the wide bandwidth make it a very promising RF energy harvesting (RFEH) source. Broadband antennas are necessary to harvest power efficiently from the full spectrum. This work presents the first antenna on textile for wearable ambient RFEH in the 26 GHz and 28 GHz bands. The antenna has an impedance bandwidth from 20 to 30 GHz, and exhibits a peak on-body gain of 7 dB with an omnidirectional radiation pattern for capturing ambient RF energy. The radiation efficiency on-and off-body was observed to be at least 40% and 60% respectively, between 24 and 30 GHz. A two-line microstrip dielectric characterization of the textile substrate in the mmWave band has been performed. The antenna has been fabricated on a 310 μm woven polyester substrate using etched ultra-thin Polyimide copper laminates with a minimum feature size of 150μm. A high robustness against human proximity has been demonstrated with a stable bandwidth and improved gain.

2021 IEEE 20th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS), 2021

Wearable Radio Frequency (RF) rectennas do not require expensive or hazardous materials and can b... more Wearable Radio Frequency (RF) rectennas do not require expensive or hazardous materials and can be easily integrated with conventional e-textiles. In this paper, we investigate the use of ultra-miniaturized wire-type monopole antennas for energy harvesting (EH) applications, as a method maximizing the effective collection area of a rectenna relative to its physical size, while not reducing the net DC output. The rectenna, operating in the 915 MHz band, is integrated with a simple carbon-based e-textile supercapacitor for direct energy conversion and storage. The integrated module is then demonstrated, for the first time, wirelessly-charging a Bluetooth Low Energy sensor node at over 1 m distance from a license-free Powercast transmitter. The 14.1 mF supercapacitor is charged using the e-textile rectenna filament in 83 s up to 4.14 V, from an incident power density of 23.9 µW/cm 2 and a timeaveraged efficiency over 40%, enabling the sensor node to sustain operation for 108 s after the wireless RF source is stopped. Compared to state-of-the-art RF energy harvesters, the proposed module achieves over five fold improvement in the RF to DC power harvesting efficiency normalized to the harvester's area.

2021 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP), 2021

Wearable radio frequency (RF) energy harvesting is highly dependent on the distance from the sour... more Wearable radio frequency (RF) energy harvesting is highly dependent on the distance from the source and human-caused RF shadowing. Therefore, energy storage devices integrated with rectennas are of paramount importance to overcome this intermittency. In this paper, the use of carbonbased e-textile supercapacitors for storing the RF-DC converted power for powering body area networks nodes is investigated. A voltage doubler sub-1 GHz flexible rectifier, whose peak power conversion efficiency (PCE) approaches 80% is coupled to a two-cell 15.5 mF textile-based supercapacitor operating up to 4 V DC. Owing to the rectifier's low optimum load resistance and high DC Voltage output, the average charging PCE of the rectifier-supercapacitor module reaches 31% for a 9.5 dBm input. Time-varying s-parameter measurements are performed to compare the time-averaged matching as opposed to instantaneous measurements using a resistive load, where the textile supercapacitor exhibits a similar response to a commercial supercapacitor. Finally, the RF-charged textile supercapacitor is demonstrated, for the first time, powering a microcontroller and Bluetooth transmitter with an average power consumption of 350 µW for up to 102 s, following 40 s of charging at 9.5 dBm, demonstrating its suitability for RF-powered body area networks applications.

2019 19th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS), 2019

Coupled wireless power transfer (WPT) has been widely used for near-field high-efficiency WPT app... more Coupled wireless power transfer (WPT) has been widely used for near-field high-efficiency WPT applications. However, the efficiency of the WPT link is highly sensitive to separation and alignment, and is prone to over-coupling, making it unsuitable for mobile systems with unknown or loose coupling such as wearables. While ultra-high frequency (UHF) and microwave radiative WPT (0.3-3 GHz) enables meters-long separation between the transmitter and the receiver, free space propagation losses, and rectification inefficiencies, adversely limit the end-to-end efficiency of the WPT link. This work proposes radiative WPT, in the 6.78 MHz license-free band, based on resonant electrically small antennas fabricated using embroidered textile coils, tuned using L-matching networks. The proposed WPT system achieves a stable forward transmission of S21>-17 dB and S21>-28 dB, independent of coil, separation on the XZ and XY planes respectively, in a 27 m 3 volume space. The presented approach demonstrates the highest WPT-link efficiency, and promises higher end-to-end efficiency, compared to UHF WPT.

Microwave microfluidic sensors are typically designed with a channel in vicinity of a resonator&#... more Microwave microfluidic sensors are typically designed with a channel in vicinity of a resonator's fringing electric (E)-fields, to characterize the material properties of a single fluid. This paper leverages hybrid 3D and dispenser printing to realize a scalable microfluidic sensor utilizing the parallel-plate capacitance of an open-ended microstrip stub, enabling, for the first time, a tunable sensitivity. A stub-loaded microstrip line is then proposed for characterizing multiple microfluidic samples simultaneously using a simple two-port multi-band resonator. The physical constrains which limit the scalability of the proposed sensors have been analyzed analytically and numerically, prior to implementing a three-channel triple-band sensor. The microfluidic channels have been fabricated using stereolithography 3D printing with the microstrip line directly dispenser printed on a conformable polyimide substrate. To accommodate varying channel thicknesses, a tapered microstrip line...

IEEE Journal of Microwaves, 2021

In this paper, a novel multi-layered microstrip line with built-in parallel-plate capacitors is p... more In this paper, a novel multi-layered microstrip line with built-in parallel-plate capacitors is proposed for DC-blocking applications, with its transmission characteristics measured up to 50 GHz. The microstrip lines are fabricated via screen printing directly onto polyurethane films laminated on standard textile substrates which would otherwise be unsuitable for printing. Compared to a standard microstrip line on the same substrate, the proposed 10 cm-long line on felt (with an embedded 44 pF capacitance) suffers from less than 0.1 dB higher insertion loss up to 4 GHz. Furthermore, varying the overlapping length of the lines and hence the capacitance enables the realization of DC blocking and −3 dB high-pass filtering with pass-bands starting between 88 MHz and 1.2 GHz. This is achieved without altering the cutoff frequency of the microstrip line's mode-free propagation, measured up to 50 GHz, exhibiting a low attenuation of 0.32 dB/mm at 50 GHz on a felt fabric substrate. Compared to a lumped capacitor, the proposed microstripembedded printed capacitor demonstrates a significant improvement in mechanical reliability, withstanding over 10,000 bending cycles, and RF power handling with under 6 • C temperature rise at 1 W. The lines are fabricated on two textile substrates and their transmission characteristics were measured up to 50 GHz, which represents the highest frequency characterization of textile-based lines to date, demonstrating a stable group delay and insertion losses. Based on the proposed multi-layered integration method, low-cost screen-printed microstrip-embedded capacitors on textiles can be used for microwave applications up to mmWave bands. INDEX TERMS Additive manufacturing, capacitors, DC block, high-pass filter, microstrip lines, printed capacitors, radio frequency (RF), textile capacitors, transmission lines. I. INTRODUCTION Flexible, printable, and conformable microwave and millimeter-wave (mmWave) components have attracted significant research interest for a variety of Internet of Things (IoT) and 5G+/6G applications [1], [2]. Wireless communication antennas [3], energy harvesting rectennas [4], mmWave imaging arrays [5], and RFIC packaging [6] are among the applications tackled through additive manufacturing of microwave and mmWave distributed components. Furthermore, the realization of individual components such as RF capacitors using inkjet [7] and 3D printing [8] has been demonstrated. In low-cost, large-area, printed electronics, and wearable applications, it is desirable to minimize the lumped components count in the system and utilize printed components to maximize flexibility [9]. Shortly after the early development of planar microstrip transmission lines, DC-blocking microstrip lines attracted significant interest [10]-[12], [12], [13]. In planar microstrip technology, DC-blocks are typically realized using coupled lines [13]. As a result, they are often integrated within filters

2021 IEEE International Conference on RFID Technology and Applications (RFID-TA), 2021

Radio Frequency (RF) power transfer is an enabling technology of RFID systems. CMOS RF rectifiers... more Radio Frequency (RF) power transfer is an enabling technology of RFID systems. CMOS RF rectifiers enable miniaturization and improved integration with full systems. For certain applications, rectifiers may need to be deployed in high or low temperature environments, which can affect their power conversion efficiency (PCE). This work presents the design of a high efficiency 915 MHz CMOS Dickson charge-pump in a 2S nm FDSOI process, and investigates antenna-based impedance matching as a method of maximizing the PCE for different temperatures and CMOS process variations. With a co-designed antenna, the proposed rectifier achieves $ 5.4\times $ higher PCE compared to simple inductive-matching at -20dBm. The PCE is then analyzed for CMOS process and temperature variations. It is shown that the rectifier can maintain 94% of its peak PCE at -15dBm at -10°C through input-impedance matching. The proposed rectifier and matching technique achieves the highest PCE compared to state-of-the-art Dickson multipliers, while having the smallest die area.

Wireless power transfer (WPT) and Radio Frequency (RF) energy harvesting (EH) are increasingly se... more Wireless power transfer (WPT) and Radio Frequency (RF) energy harvesting (EH) are increasingly seen as an enabling technology for power-autonomous Internet of Things (IoT) [1, 2]. RFEH and WPT are a particularly attractive power source for flexible, printed, and e-textile systems due to their compatibility with standard fabrication processes, abolishing the need for specific materials and transducers. This work provides an overview on flexible WPT at multiple frequencies (6.78 MHz to 26 GHz) and techniques from near-field WPT to Millimetre-wave WPT and RFEH.