Showing papers by "Raheel M. Hashmi published in 2018"

Compact High-Gain Antenna With Simple All-Dielectric Partially Reflecting Surface

Abstract: This communication presents a simplified approach to design compact, wideband resonant-cavity antennas (RCAs) with partially reflecting surfaces (PRSs) made out of only a single dielectric material. Gain enhancement over a large bandwidth is obtained by using a high-permittivity dielectric PRS, which is flat at the bottom and has a stair-case profile on the top. The resulting RCA demonstrates a measured directivity-bandwidth product (DBP) of 5990 and a DBP per unit area of 1222. To the best of our knowledge, these figures are comparable to the figures for RCAs with transverse permittivity gradient PRSs, which require multiple dielectric materials. The measured radiation patterns of this RCA demonstrate low sidelobe levels (<−15 dB in the E-plane and −20 dB in the H-plane, with a peak directivity of 20.3 dBi), which are consistent across the half-power directivity bandwidth.

Polydimethylsiloxane-Embedded Conductive Fabric: Characterization and Application for Realization of Robust Passive and Active Flexible Wearable Antennas

Abstract: We present our study on polydimethylsiloxane (PDMS)-embedded conductive fabric, which we propose as a simple yet effective solution to the challenging issue of poor PDMS-metal adhesion, allowing for a relatively easy realization of robust flexible antennas for wearable applications. The method combines the use of conductive fabric as a radiator with PDMS, which acts as the substrate and a protective encapsulation simultaneously. For the first time, a holistic study on the mechanical and electrical properties of the proposed combination of materials is presented thoroughly using a number of fabricated samples. As concept demonstrations, a microstrip patch and a reconfigurable patch antenna are fabricated using the proposed technique to validate the idea. The inclusion of a PDMS-ceramic composite as part of the antenna’s substrate, which leads to over 50% reduction in the size compared with a pure PDMS, is also demonstrated to showcase further the versatility of the proposed technique. The fabricated antennas are tested in several wearable scenarios and consistent performance including reconfigurability is obtained even after the antennas are exposed to harsh environments, i.e., extreme bending and machine-washing.

A Transparent Strain Sensor Based on PDMS-Embedded Conductive Fabric for Wearable Sensing Applications

Abstract: In this paper, we present a new approach to realize flexible transparent strain sensors. It combines the use of transparent conductive fabric with polydimethylsiloxane (PDMS) through a simple and straightforward layer-by-layer assembly process. The conductive fabric is used to realize the transparent electrodes while the PDMS is utilized as both the substrate and encapsulation layers. As a concept demonstration, an interdigital capacitive sensor is designed and fabricated using the proposed approach. The fabricated sensor is then characterized in terms of its transparency and electro-mechanical nature. This is followed by the application of the sensor in several physiological sensing scenarios, including the sensing of various body-part movements and tactile sensing. Apart from a high optical transparency (~70%), the sensor shows promising sensing results which validate the applicability of the proposed approach for realization of flexible and transparent strain sensors for wearable sensing applications.

Design and Characterization of a Flexible Wideband Antenna Using Polydimethylsiloxane Composite Substrate

Abstract: The design and characterization of a simple, flexible wideband antenna using polydimethylsiloxane (PDMS) composite are presented. Conductive fibers are used to construct the metallic parts on a PDMS composite. To characterize the performance, two identical antennas are designed, one using the PDMS composite while the other on conventional dielectric materials. It was observed that both antennas behave well in terms of the matched bandwidth; however, the radiation towards the broadside direction is reduced when using the PDMS composite as substrate, particularly at higher frequencies. The antenna exhibits a matched bandwidth of 59.9%, ranging from 3.43 to 11.1 GHz. Moreover, the bending analysis carried out for different scenarios show that the wideband behavior of the antenna is well preserved and the variation reaches a maximum of 1% variation.

A Low-Profile Phase Correcting Solution to Improve Directivity of Horn Antenna

Abstract: In this paper, we present a phase-corrected horn antenna with improved directivity. An increase in the horn aperture size results in a significantly non-uniform phase distribution contributing to the poor radiation characteristics. A low-profile phase correction surface (PCS) is therefore designed to address this problem. Significant improvement has been achieved in the horn antenna performance by placing the proposed PCS right at the mouth of the horn. The near-field transformation method is applied to demonstrate an improvement of 10 dBi in the peak directivity at the operating frequency of 11 GHz. This feature can be extended to manipulate the far-field pattern of horn and even for beam steering applications.

Sidelobe Suppression in Resonant Cavity Antennas through Near-field Analysis

Abstract: This paper describes an effective approach to reduce the high sidelobe levels (SLLs) in resonant cavity antennas (RCAs) with small footprints. The objective is to first understand the reason behind the high SLL in compact RCAs and than improve its radiation characteristics. For this, a near-field to far-field transformation routine is implemented in MATLAB, which allows to understand the individual effects of near-field amplitude and phase distributions on the SLL in the far-field patterns. This approach resulted in an optimal electric-field distribution, which is realized by a dielectric partially reflecting superstructure (PRS) exhibiting a broadside directivity of 19.5 dBi with significantly low sidelobe levels of -30dB in both the principle planes. It is important to note that the proposed approach can be linked easily with global optimization techniques to fit the radiation patterns within specific pattern masks.

Transverse Permittivity Gradient (TPG) Superstrates or Lens: A Critical Perspective

Abstract: This paper presents a quantitative comparison of superstrates with transverse permittivity gradient (STPG) when used in RCAs, as compared to stand-alone lens configurations. RCAs with TPG superstrates are often compared with lens antennas, considering the apparent structural similarity between the two. However, these two classes of antennas present inherent differences in terms of characteristics as well as principle of operation. Detailed comparisons are carried out using full-wave simulations. It was found that nearly 50% reduction in 3dB bandwidth was observed when a TPG superstrate was used as a lens antenna, as opposed to in an RCA.

A Linearly Polarised Radial Line Slot Array Antenna with Reflection Cancelling Slots

Abstract: In this paper, a linearly polarised radial line slot array antenna (LP-RLSA) is presented for satellite communication. The antenna makes use of reflection cancelling slots to improve impedance matching. The antenna has highly directive radiation with a peak directivity of 37 dBi at 12.3 GHz. At this directivity, the antenna has demonstrated a very lower side lobe level (SLL) of −23.1 dB and radiation efficiency greater than 96%. The designed LP-RLSA antenna has successfully overcame the limitation of poor return loss through reflection cancelling slots.

Feasibility of a Single Port Flexible Antenna Array for Energy Harvesting from Ambient Sources

Abstract: In this paper the performance of a single port antenna array is analysed for energy harvesting. Two types of feeds used to feed a flexible patch antenna array are compared. The array consists of 4 rectangular patch antennas made from conductive fabric and Polydimethylsiloxane (PDMS), which are flexible. The proposed array is for energy harvesting for wearable systems. Energy harvesting from ambient energy sources needs an antenna array for collecting a sufficient power level and for wearable applications the array materials must be flexible. For this reason, conductive fabric and PDMS are chosen for conductive and non-conductive parts of the array. However, the array can be fed from a single port signal or individual elements can be fed from simultaneous individual port signals. If the array with a single port has good electromagnetic performance then it is more useful for energy harvesting because it requires single rectifier, which will reduce microwave to DC conversion loss. In this paper these two types of feeding methods are compared with respect to array matching, peak gain and radiation performance. From this comparison we can observe the performance of single port array system for energy harvesting in wearable applications.

A Wideband Antenna Based on Composite Flexible Substrate for Wearable Application

Abstract: TPID5180187. Conductive fibers are used to construct the metallic parts on a PDMS composite. To characterize the performance, two identical antennas are designed, one using the PDMS composite while the other on conventional dielectric materials. The antenna exhibits a matched bandwidth of 59.9%, ranging from 3.43 to 11.1 GHz. With excellent performance and high flexibility, this antenna is well-suited for body area networks and other wearable applications.