### Recent Submissions

• #### Additively Manufactured Triple-Band Fractal Antenna-on-Package for Ambient RF Energy Harvesting

(Institute of Electrical and Electronics Engineers (IEEE), 2019) [Conference Paper]
Billions of wireless sensing devices must be powered for Internet of Things (IoT) applications. Collecting energy from ambient RF spectrum to power sensor nodes is one of the possible solutions. In this work, we present an antenna for RF energy harvesting applications which operates at multiple bands and has been realized through additive manufacturing (combination of 3D and screen printing) on a package, thus optimizing the space and cost requirements. The antenna design utilizes the cantor fractal approach which enables it to operate at three frequencies (GSM900, GSM1800 and 3G at 2100MHz) simultaneously. Decent gain, triple-band performance, lower cost and compact size makes this antenna a promising candidate for ambient RF energy harvesting applications.
• #### Silver Nanowires Based Transparent, Broadband FSS Microwave Absorber

(Institute of Electrical and Electronics Engineers (IEEE), 2019) [Conference Paper]
An optically transparent microwave absorber with broadband absorption based on frequency selective surface (FSS) have been proposed and fabricated using a simple, cost-effective, and controllable inkjet printing assisted patterning technique. The FSS and ground layers are made of silver nanowires (AgNWs) conductive networks with desired patterns. This new device exhibits broadband absorption performance with an optimized 90% absorption bandwidth over the frequency range of 9.1 to 12.2 GHz in X-band. Besides, due to the patterning of AgNWs FSS and ground layers, the optical transmittance of the fabricated absorber exceeds 83% at 550 nm wavelength, which is the highest among the transparent absorbers in literature. Based on the easy-processing, high performance, and excellent transparency, the proposed absorber shows great promise for various applications relating to transparent absorbers, such as photonic detectors, antennas and solar cells.
• #### Flexible, Stretchable and Washable Filter Printed Directly on Textile

(2018 48th European Microwave Conference (EuMC), Institute of Electrical and Electronics Engineers (IEEE), 2018-12-07) [Conference Paper]
With the emergence of wearable and textile electronics, there is a need to study the effects of flexibility, stretchability and washing on the performance of such electronic components and systems. In this work, we demonstrate an RF filter which has been directly printed on textile (a sports T-shirt in this case). With the help of a stretchable dielectric ink and a stretchable metallic ink, the printed filter on textile can provide decent performance (with little degradation in performance) in stretched conditions (up to 25% stretching), as compared to a non-stretchable metallic ink which develops permanent cracks and cannot be used during or after stretching cycles. The filter is back to its normal performance, once it is released back to its unstretched position. It is also shown that the filter can withstand many washing cycles and can maintain its performance.
• #### SIW Cavity Filters with Embedded Planar Resonators in LTCC Package for 5G Applications

(2018 48th European Microwave Conference (EuMC), Institute of Electrical and Electronics Engineers (IEEE), 2018-12-07) [Conference Paper]
Two three dimensional (3D) integrated System on Package (SoP) Low Temperature Co-fired Ceramic (LTCC) two-stage SIW single cavity filters with embedded planar resonators are designed, fabricated and tested. The embedded resonators create a two-stage effect in a single cavity filter. The design with a stripline ring around the center post of the cavity provides a 13% fractional bandwidth with a center frequency of 28.21 GHz, and with an insertion loss of -0.82 dB. The design that feeds at the middle of a stripline resonator provides a 15% fractional bandwidth at a center frequency of 28.12 GHz, and with an insertion loss of -0.53 dB.
• #### A Reconfigurable Inkjet-Printed Antenna on Paper Substrate for Wireless Applications

(IEEE Antennas and Wireless Propagation Letters, Institute of Electrical and Electronics Engineers (IEEE), 2018-07-31) [Article]
An inkjet-printed reconfigurable multiband antenna printed on a low-cost commercial photo paper substrate using two p-i-n diodes is proposed for the first time. A main radiator is designed to operate at 3.4 GHz band, whereas L-shaped and U-shaped radiating elements are designed to operate at 1.9 and 2.4 GHz, respectively. The antenna has a size of 30 × 40 × 0.44 mm and can cover most of the mobile and wireless bands between 1.5 and 4 GHz. A prototype of the proposed antenna is fabricated and measured. Measured and simulated results of S, radiation pattern, gain, and efficiency are in good agreement. Measured results show that the antenna has a gain and efficiency of 2 dBi and 50%, respectively. A parametric study is proposed as a guidance to design the antenna for operating in other bands between 1.5 and 4 GHz.
• #### Massive MIMO antenna system for 5G base stations with directive ports and switched beamsteering capabilities

(IET Microwaves, Antennas & Propagation, Institution of Engineering and Technology (IET), 2018-04-17) [Article]
A 72-port (288 antennas) triangular-shaped massive multiple-input-multiple-output (mMIMO) antenna system is presented for fifth generation (5G) base stations. Each side of the antenna system consists of three layers with a total size of 44.4 × 29.6 × 0.1524 cm, and contains 24 ports. Each port (subarray) consists of 2 × 2 patches on the top layer, their feeding network with pre-calculated phases is on the bottom layer and the ground plane is in the middle one. Each port is fed in a way to tilt its beam direction with respect to others to achieve uncorrelated individual patterns. The antenna system is the first to support two operating modes: simultaneous individual port operation (i.e. 72-port MIMO) and mMIMO array operation (i.e. with beam switching). The measured bandwidth is 100 MHz that covers the band from 3.45 to 3.55 GHz. The measured gain of a single port equals to 9.41 dBi. The envelop correlation coefficient does not exceed 0.1198. A beamsteering method to steer the beam of each 24-port side to different locations in the space is presented and applied based on the non-uniform port patterns (unlike most conventional methods). Thirteen switched beams are obtained with centre angle coverage up to 34° in elevation with maximum gain of 19.5 dBi.
• #### Iron Oxide Nanoparticle-Based Magnetic Ink Development for Fully Printed Tunable Radio-Frequency Devices

(Advanced Materials Technologies, Wiley, 2018-01-30) [Article]
The field of printed electronics is still in its infancy and most of the reported work is based on commercially available nanoparticle-based metallic inks. Although fully printed devices that employ dielectric/semiconductor inks have recently been reported, there is a dearth of functional inks that can demonstrate controllable devices. The lack of availability of functional inks is a barrier to the widespread use of fully printed devices. For radio-frequency electronics, magnetic materials have many uses in reconfigurable components but rely on expensive and rigid ferrite materials. A suitable magnetic ink can facilitate the realization of fully printed, magnetically controlled, tunable devices. This report presents the development of an iron oxide nanoparticle-based magnetic ink. First, a tunable inductor is fully printed using iron oxide nanoparticle-based magnetic ink. Furthermore, iron oxide nanoparticles are functionalized with oleic acid to make them compatible with a UV-curable SU8 solution. Functionalized iron oxide nanoparticles are successfully embedded in the SU8 matrix to make a magnetic substrate. The as-fabricated substrate is characterized for its magnetostatic and microwave properties. A frequency tunable printed patch antenna is demonstrated using the magnetic and in-house silver-organo-complex inks. This is a step toward low-cost, fully printed, controllable electronic components.
• #### Live demonstration: Screen printed, microwave based level sensor for automated drug delivery

(2017 IEEE SENSORS, Institute of Electrical and Electronics Engineers (IEEE), 2018-01-02) [Conference Paper]
Level sensors find numerous applications in many industries to automate the processes involving chemicals. Recently, some commercial ultrasound based level sensors are also being used to automate the drug delivery process [1]. Some of the most desirable features of level sensors to be used for medical use are their non-intrusiveness, low cost and consistent performance. In this demo, we will present a completely new method of sensing the liquid level using microwaves. It is a common stereotype to consider microwaves sensing mechanism as being expensive. Unlike usual expensive, intrusive and bulky microwave methods of level sensing using guided radars, we will present an extremely low cost printed, non-intrusive microwave sensor to reliably sense the liquid level.
• #### A wearable 3D motion sensing system integrated with a Bluetooth smart phone application: A system level overview

(2017 IEEE SENSORS, Institute of Electrical and Electronics Engineers (IEEE), 2018-01-02) [Conference Paper]
An era of ubiquitous motion sensing has just begun. All electronic gadgets ranging from game consoles to mobile phones have some sort of motion sensors in them. In contrast to rigid motion sensing systems, this paper presents a system level description of a wearable 3D motion sensor. The sensing mechanism is based upon well-established magnetic and inertial measurement unit (MIMU), which integrates accelerometer, gyroscope and magnetometer data. Two sensor boards have been integrated within a wearable arm sleeve to capture 3D orientation of the human arm. The sensors have been interfaced with a Bluetooth transceiver chip, which transmits data to a mobile phone app using standard Bluetooth protocol. An android mobile phone app has been developed to display the human arm motion in real time.
• #### 24GHz paper based inkjet printed quasi Yagi-Uda antenna with new bowtie director

(Institution of Engineering and Technology (IET), 2018) [Conference Paper]
This paper presents a 24 GHz quasi Yagi-Uda antenna with a new bowtie director. The new bowtie director shape is introduced to improve the bandwidth of a typical Yagi-Uda antenna using a straight director by 240%. In addition to the enhanced impedance bandwidth, it makes its gain-bandwidth three times that of a standard Yagi-Uda antenna and demonstrates a measured 4 dBi gain. The presented inkjet printed paper based antenna operates at 24GHz which is one of the highest reported operating frequencies for an inkjet printed antenna on this lossy substrate. The paper substrate has been characterized for these frequencies. The measurement results indicate that the proposed design is highly suitable for low cost, environmentally friendly and flexible wireless applications.
• #### 3D printed System-on-Package (SoP) for environmental sensing and localization applications

(2017 International Symposium on Antennas and Propagation (ISAP), Institute of Electrical and Electronics Engineers (IEEE), 2017-12-22) [Conference Paper]
This paper presents for the first time an innovative 3D printed SoP sensor node with temperature, pressure and humidity sensing capabilities. It has an integrated wireless readout through a near isotropic (900MHz) GSM antenna-on-package. This sensor node is connected to the internet for remote monitoring and has the capability of localization. The paper presents the design of antenna-on-package as well as details of the communication and localization system. Fabrication challenges unique to 3D printing and integration of electronics on 3D printed circuit board are also discussed. Finally, the paper presents measurement results of antenna radiation pattern, return loss, localization accuracy and accuracy of sensing parameters.
• #### Physically Connected Stacked Patch Antenna Design with 100% Bandwidth

(IEEE Antennas and Wireless Propagation Letters, Institute of Electrical and Electronics Engineers (IEEE), 2017-11-01) [Article]
Typically, stacked patch antennas are parasitically coupled and provide larger bandwidth than a single patch antenna. Here, we show a stacked patch antenna design where square patches with semi-circular cutouts are physically connected to each other. This arrangement provides 100% bandwidth from 23.9–72.2 GHz with consistent high gain (5 dBi or more) across the entire bandwidth. In another variation, a single patch loaded with a superstrate provides 83.5% bandwidth from 25.6–62.3 GHz. The mechanism of bandwidth enhancement is explained through electromagnetic simulations. Measured reflection coefficient, radiation patterns and gain results confirm the extremely wideband performance of the design.
• #### A 3D printed dual GSM band near isotropic on-package antenna

(2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, Institute of Electrical and Electronics Engineers (IEEE), 2017-10-25) [Conference Paper]
In this paper, we propose an on-package dual band monopole antenna with near-isotropic radiation pattern for GSM mobile applications. The proposed antenna is well matched for both GSM 900 and 1800 bands and provides decent gain for both the bands (1.67 and 3.27 dBi at 900 MHz and 1800 MHz respectively). The antenna is printed with silver ink on a 3D printed polymer based package. The package houses the GSM electronics and the battery. By optimizing the antenna arms width and length, a near-isotropic radiation pattern is achieved. Unlike the published isotropic antennas which are either single band or large in size, the proposed antenna covers both GSM bands with required bandwidth and is only half wavelength long. The design is low cost and highly suitable for various GSM applications such as localization, in additional to conventional communication applications.
• #### Back radiation suppression through a semi-transparent round ground plane for a mm-Wave monopole antenna

(2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, Institute of Electrical and Electronics Engineers (IEEE), 2017-10-25) [Conference Paper]
Omnidirectional radiation pattern with minimum backward radiation is highly desirable for millimeter-wave telecommunication antennas. In this work, we propose a round, semitransparent ground plane of radius 0.8λ with uniform impedance distribution that can reduce the back radiation of a monopole antenna by 8.8 dB as compared with a similar sized metallic ground plane. The value of uniform impedance is obtained through analytical optimization by using asymptotic expressions in the Kirchhoff approximation of the radiation pattern of a toroidal wave scattered by a round semitransparent ground plane. The semitransparent ground plane has been realized using a low-cost carbon paste on a Kapton film. Experimental results match closely with those of simulations and validate the overall concept.
• #### 5G antenna array with wide-angle beam steering and dual linear polarizations

(2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, Institute of Electrical and Electronics Engineers (IEEE), 2017-10-25) [Conference Paper]
In this paper, we present the design of a switched-beam antenna array at millimeter-wave frequencies for future 5G applications. The proposed antenna array is based on wideband patch antenna elements and a Butler matrix feed network. The patch antenna has a broad radiation pattern for wide-angle beam steering and allows the simultaneous operation with two orthogonal linear polarizations. A combination of two separated Butler matrices provides independent beam steering for both polarizations in the wide operating band. The antenna array has a simple multilayer construction, and it is made on a low-cost Rogers laminate.
• #### A low-cost, orientation-insensitive microwave water-cut sensor printed on a pipe surface

(2017 IEEE MTT-S International Microwave Symposium (IMS), Institute of Electrical and Electronics Engineers (IEEE), 2017-10-24) [Conference Paper]
This paper presents a novel and contactless water fraction (also known as water cut) measurement technique, which is independent of geometric distribution of oil and water inside the pipe. The sensor is based upon a modified dual helical stub resonators implemented directly on the pipe's outer surface and whose resonance frequency decreases by increasing the water content in oil. The E-fields have been made to rotate and distribute well inside the pipe, despite having narrow and curved ground plane. It makes the sensor's reading dependent only on the water fraction and not on the mixture distribution inside the pipe. That is why, the presented design does not require any flow conditioner to homogenize the oil/water mixture unlike many commercial WC sensors. The presented sensor has been realized by using extremely low cost methods of screen-printing and reusable 3D printed mask. Complete characterization of the proposed WC sensor, both in horizontal and vertical orientations, has been carried out in an industrial flow loop. Excellent repeatability of the sensor's response has been observed under different flow conditions. The measured performance results of the sensor show full range accuracy of ±2-3% while tested under random orientations and wide range of flow rates.
• #### A low cost, printed microwave based level sensor with integrated oscillator readout circuitry

(2017 IEEE MTT-S International Microwave Symposium (IMS), Institute of Electrical and Electronics Engineers (IEEE), 2017-10-24) [Conference Paper]
This paper presents an extremely low cost, tube conformable, printed T-resonator based microwave level sensor, whose resonance frequency shifts by changing the level of fluids inside the tube. Printed T-resonator forms the frequency selective element of the tunable oscillator. Unlike typical band-pass resonators, T-resonator has a band-notch characteristics because of which it has been integrated with an unstable amplifying unit having negative resistance in the desired frequency range. Magnitude and phase of input reflection coefficient of the transistor has been optimized over the desired frequency range. Phase flattening technique has been introduced to maximize the frequency shift of the oscillator. With the help of this technique, we were able to enhance the percentage tuning of the oscillator manifolds which resulted into a level sensor with higher sensitivity. The interface level of fluids (oil and water in our case) causes a relative change in oscillation frequency by more than 50% compared to maximum frequency shift of 8% reported earlier with dielectric tunable oscillators.
• #### Design and Dynamic Characterization of an Orientation Insensitive Microwave Water-Cut Sensor

(IEEE Transactions on Microwave Theory and Techniques, Institute of Electrical and Electronics Engineers (IEEE), 2017-06-12) [Article]
Modern reservoir management in oil and gas industry relies on accurate water fraction measurement which is produced as a by-product with oil. This paper presents a novel and contactless water fraction (also known as water-cut) measurement technique which is independent of geometric distribution of oil and water inside the pipe. The sensor is based on a modified T-resonator implemented directly on the pipe's outer surface and whose resonance frequency decreases by increasing the water content in oil. The E-fields have been made to rotate and distribute well inside the pipe, despite having narrow and curved ground plane. It makes the sensor's reading dependent only on the water fraction and not on the mixture distribution inside the pipe. That is why, the presented design does not require any flow conditioner to homogenize the oil/water mixture unlike many commercial water-cut (WC) sensors. The presented sensor has been realized by using extremely low-cost methods of screen printing and reusable 3-D printed mask. Complete characterization of the proposed WC sensor, both in horizontal and vertical orientations, has been carried out in an industrial flow loop. Excellent repeatability of the sensor's response has been observed in 'dispersed bubble' as well as in 'stratified wavy' flow regimes. The performance test of the sensor confirms that the water fraction measurement is independent of the flow pattern, flow rate or orientation. The measured performance results of the sensor show full range accuracy of $±$2%-3% while tested under random orientations and wide range of flow rates.
• #### Design methodology of single-feed compact near-isotropic antenna design

(2017 11th European Conference on Antennas and Propagation (EUCAP), Institute of Electrical and Electronics Engineers (IEEE), 2017-06-07) [Conference Paper]
The abundance of mobile wireless devices is giving rise to a new paradigm known as Internet of Things. In this paradigm, wireless devices will be everywhere and communicating with each other. Since they will be oriented randomly in the environment, they should be able to communicate equally in all directions in order to have stable communication link. Hence, compact near isotropic antennas are required, which can enable orientation insensitive communication. In this paper, we propose a simple design methodology to design a compact near-isotropic wire antenna based on equal vector potentials. As a proof of concept, a quarter wavelength monopole antennas has been designed that is wrapped on a 3D-printed box keeping the vector potentials in three orthogonal different directions equal. By optimizing the dimension of the antenna arms, a nearly isotropic radiation pattern is thus achieved. The results show that the antenna has a maximum gain of 2.2dBi at 900 MHz with gain derivation of 9.4dB.
• #### A wearable tracking device inkjet-printed on textile

(Microelectronics Journal, Elsevier BV, 2017-05-20) [Article]
Despite the abundance of localization applications, the tracking devices have never been truly realized in E-textiles. Standard printed circuit board (PCB)-based devices are obtrusive and rigid and hence not suitable for textile based implementations. An attractive option would be direct printing of circuit layout on the textile itself, negating the use of rigid PCB materials. However, high surface roughness and porosity of textiles prevents efficient and reliable printing of electronics on textile. In this work, by printing an interface layer on the textile first, a complete localization circuit integrated with an antenna has been inkjet-printed on the textile for the first time. Printed conductive traces were optimized in terms of conductivity and resolution by controlling the number of over-printed layers. The tracking device determines the wearer's position using WiFi and this information can be displayed on any internet-enabled device, such as smart phone. The device is compact (55mm×45mm) and lightweight (22g with 500mAh battery) for people to comfortably wear it and can be easily concealed in case discretion is required. The device operates at 2.4GHz communicated up to a distance of 55m, with localization accuracy of up to 8m.