A wideband hybrid dielectric resonator antenna (DRA) consisting of a rectangular slot patch and a perforated stacked cylindrical dielectric resonator (DR) is proposed. A rectangular slot was etched on the grounding side of a microwave laminate (ϵs =3.38) to excite the hybrid resonator at a high frequency. The stacked DR used consists of three different layers of permittivity, in which air-cavity was introduced internally to form a perforated structure. With a proper stacking arrangement of the perforated DRs on top of the rectangular slot, their operating frequencies were merged together to produce a wideband hybrid DRA. It was found that the combination of the stacked DR with perforated structure in the hybrid element had yielded an impedance bandwidth of as wide as 75.8% (12.2 GHz - 27.1 GHz). Huge improvement in bandwidth was successfully achieved in this study in comparison to that without a perforated structure of only 48.9%. Simulation of the antenna was performed in time domain using Computer Simulation Technology (CST) and was subsequently verified with the measurement results. The average simulated and measured directivity of the antenna were recorded to be 6.05 dBi and 5.65 dBi, respectively, with a stable broadside radiation throughout the operating range of frequency. The radiation characteristics were seen to be broadside in both the E-plane and H-plane.

High electron mobility transistor (HEMT) biosensors hold great potential for realizing label-free, real-time, and direct detection. Owing to their unique properties of two-dimensional electron gas (2DEG), HEMT biosensors have the ability to amplify current changes pertinent to potential changes with the introduction of any biomolecules, making them highly surface charge sensitive. This review discusses the recent advances in the use of AlGaN/GaN and AlGaAs/GaAs HEMT as biosensors in the context of different gate architectures. We describe the fundamental mechanisms underlying their operational functions, giving insight into crucial experiments as well as the necessary analysis and validation of data. Surface functionalization and biorecognition integrated into the HEMT gate structures, including self-assembly strategies, are also presented in this review, with relevant and promising applications discussed for ultra-sensitive biosensors. Obstacles and opportunities for possible optimization are also surveyed. Conclusively, future prospects for further development and applications are discussed. This review is instructive for researchers who are new to this field as well as being informative for those who work in related fields.

This letter presents a dual-element multiple-input–multiple-output antenna for applications in the very high frequency band. A compact geometry of microstrip line-fed radiators engaging 0.04 $ \times $ 0.04 ${{\boldsymbol{\lambda }}}^2$ footprint at 150 MHz was fabricated on an FR-4 substrate and tested in the anechoic chamber. Good circularly polarized radiation patterns were generated by employing two corner-fed meander lines and integrating slots at strategic locations of the ground. A dielectric strip was stacked above the substrate and between the two meandered elements to enable $ -$ 10 dB impedance bandwidth of 24%. In the operating frequency band from 133 to 169 MHz, the proposed antenna offered axial ratio of -25 dB, gain of $\sim $ 3 dBi, efficiency ( ${\boldsymbol{\eta }}$ ) of $\sim $ 80%, envelope correlation coefficient of $ < $ 0.5 and diversity gain of $\sim $ 10 dB.

In this present work, we aim to improve the hydrophobicity of a polydimethylsiloxane (PDMS) surface. Various heights of 3D PDMS micropillars were fabricated via grayscale photolithography, and improved wettability was investigated. Two approaches of PDMS replication were demonstrated, both using a single master mold to obtain the micropillar arrays. The different heights of fabricated PDMS micropillars were characterized by scanning electron microscopy (SEM) and a surface profiler. The surface hydrophobicity was characterized by measuring the water contact angles. The fabrication of PDMS micropillar arrays was shown to be effective in modifying the contact angles of pure water droplets with the highest 157.3-degree water contact angle achieved by implementing a single mask grayscale lithography technique.

Conventional pseudomorphic high electron mobility transistor (pHEMTs) with lattice-matched InGaAs/InAlAs/InP structures exhibit high mobility and saturation velocity and are hence attractive for the fabrication of three-terminal low-noise and high-frequency devices, which operate at room temperature. The major drawbacks of conventional pHEMT devices are the very low breakdown voltage (<2 V) and the very high gate leakage current (∼1 mA/mm), which degrade device and performance especially in monolithic microwave integrated circuits low-noise amplifiers (MMIC LNAs). These drawbacks are caused by the impact ionization in the low band gap, i.e., the In${}_x$Ga${}_{(1-x)}$As (x = 0.53 or 0.7) channel material plus the contribution of other parts of the epitaxial structure. The capability to achieve higher frequency operation is also hindered in conventional InGaAs/InAlAs/InP pHEMTs, due to the standard 1 $\mathsf{\mu }$m flat gate length technology used. A key challenge in solving these issues is the optimization of the InGaAs/InAlAs epilayer structure through band gap engineering. A related challenge is the fabrication of submicron gate length devices using I-line optical lithography, which is more cost-effective, compared to the use of e-Beam lithography. The main goal for this research involves a radical departure from the conventional InGaAs/InAlAs/InP pHEMT structures by designing new and advanced epilayer structures, which significantly improves the performance of conventional low-noise pHEMT devices and at the same time preserves the radio frequency (RF) characteristics. The optimization of the submicron T-gate length process is performed by introducing a new technique to further scale down the bottom gate opening. The outstanding achievements of the new design approach are 90% less gate current leakage and 70% improvement in breakdown voltage, compared with the conventional design. Furthermore, the submicron T-gate length process also shows an increase of about 58% and 33% in f${}_T$ and f${}_{max}$, respectively, compared to the conventional 1 $\mathsf{\mu }$m gate length process. Consequently, the remarkable performance of this new design structure, together with a submicron gate length facilitatesthe implementation of excellent low-noise applications.

The increasing applications for nomadic computing have experienced enormous development over the preceding period. This has eventually prejudiced to the lack of bandwidth. Accordingly, to fulfil the consumers’ necessity, economical radiating elements needs to be constructed for the next generation wireless network. As a result, this paper presents a quasi-lumped element (LE) resonator antenna printed on an air-substrate. Copper (Cu) was employed to construct the quasi-LE model. The impacts of antenna’s and substrate’s thickness on bandwidth or resonant frequency have been studied. The finalized arrangement occupied 1219 mm ² extent and operated at 28 GHz with approximately 2 GHz bandwidth. The system displayed efficiency and peak gain values of 94% and 9.26 dBi, respectively. The primary objective of this article is to describe an antenna featuring cost-effective and simple design together with premium results for mmWave frequency band.