We propose herein a metamaterial (MM) dual-band THz sensor for various biomedical sensing applications. An MM is a material engineered to have a particular property that is rarely observed in naturally occurring materials with an aperiodic subwavelength arrangement. MM properties across a wide range of frequencies, like high sensitivity and quality factors, remain challenging to obtain. MM-based sensors are useful for the in vitro, non-destructive testing (NDT) of samples. The challenge lies in designing a narrow band resonator such that higher sensitivities can be achieved, which in turn allow for the sensing of ultra-low quantities. We propose a compact structure, consisting of a basic single-square split ring resonator (SRR) with an integrated inverted Z-shaped unit cell. The projected structure provides dual-band frequencies resonating at 0.75 THz and 1.01 THz with unity absorption at resonant peaks. The proposed structure exhibits a narrow bandwidth of 0.022 THz and 0.036 THz at resonances. The resonant frequency exhibits a shift in response to variations in the refractive index of the surrounding medium. This enables the detection of various biomolecules, including cancer cells, glucose, HIV-1, and M13 viruses. The refractive index varies between 1.35 and 1.40. Furthermore, the sensor is characterized by its performance, with an average sensitivity of 2.075 THz and a quality factor of 24.35, making it suitable for various biomedical sensing applications

Tera Hertz photoconductive antennas (THz PCAs) have significantly advanced the THz research by offering room-temperature operation, broad bandwidth and relatively low cost as both emitters and detectors. However, the primary limitation has been their low power output due to inefficient conversion. This article demonstrates a substantial improvement in efficiency (?200%) by incorporating sub-micron photonic structures on the surface. These photonic structures enhance pump beam coupling, leading to increased photocarrier generation. They also facilitate efficient carrier recombination after THz emission, thereby suppressing carrier screening. Experimental and numerical studies confirm the enhanced photocarrier generation and controlled transport through defect-free paths, further reducing screening effects. The integration of photonic structures into large area emitters (LAEs) holds the potential to develop emitters and detectors suitable for real-world THz systems, overcoming the limitations of the current commercial LAEs that rely on plasmonic structures or antireflection coatings. This innovation has the potential to revolutionise THz technology, enabling the development of more powerful and efficient THz sources and detectors. This can lead to advancements in various fields, including wireless communication, imaging and sensing and spectroscopy. © Indian Academy of Sciences 2025

This paper introduces a compact, rhombus-shaped antenna based on a Half-Mode Substrate Integrated Waveguide (HMSIW) with a cavity-backed design, tailored to operate at 5.8 GHz within Industrial, Scientific, and Medical (ISM) band. The HMSIW cavity is designed to maintain the half-dominant TE110 mode while reducing the cavity size by 50%. Initially, the antenna's bandwidth is insufficient for the entire ISM band. To address this, a rectangular slot is etched into the center of the cavity, which divides the dominant mode into TE110-odd and TE110-even modes resonating at 5.74 GHz and 5.8 GHz, respectively. This modification results in around 63% increase in bandwidth. For a Multiple Input Multiple Output (MIMO) application, the design extends from a single element to a four-element configuration, arranged orthogonally to achieve a high isolation level of approximately -23 dB in a compact footprint. The antenna has been prototyped and experimentally validated. The measured -10 dB impedance bandwidth spans 240 MHz (from 5.63-5.87 GHz), covering the full ISM band. The peak gain of the antenna is measured at 6.2 dBi, compared to the simulated value of 5.95 dBi, with an efficiency exceeding 90% across the operating frequency range. The MIMO diversity metrics parameters have been evaluated which are found in satisfactory limit.

Dipole antennae are commonly used radio frequency devices. They gained good prominence as a result of their efficiency, consistent performance and flexibility. Different optimization strategies such as particle swarm optimization, differential evolution and Machine Learning algorithms have been utilized in the past to design dipole antennae. This helps in creating a complete device profile and increases its efficacy. Due to the complexity of modern antennas in terms of topology and performance requirements, standard antenna design approaches are tedious and cannot be guaranteed to produce effective results. Out of the strategies that are widely being utilized, Machine Learning (ML) algorithms evolved rapidly due to their capabilities in extrapolating the dimensional and material profiles of the device. Antenna design optimization still faces several difficulties, even though machine learning-based design optimization complements traditional antenna design methodologies. The effectiveness and optimization capabilities of available ML approaches to address a wide range of antenna design problems, considering the increasingly strict specifications of current antennas, are the fundamental difficulties in antenna design optimization which need to be focused on. In our current work, the capability of ML algorithms in elucidating minor trends in device profiles is tested. A bootstrap aggregation model is proposed, concatenating Linear Regression, Support Vector Regression and Decision Tree Regression algorithms. The concatenated model was used to optimize the parameters of reflection coefficient, directivity, efficiency and operating frequency, depending on the feed length, dipole radius and dipole length of the antenna.

A compact dual-band, 2-elements antenna-diplexer is investigated and extended to a 2×2 multi-input and multi-output (MIMO) antenna. The proposed design employs half-mode Substrate Integrated Waveguide (HMSIW) technology, which reduces the antenna footprint by 50%. To enhance the bandwidth, a rectangular slot is engraved at the center of each HMSIW cavity. The slot splits the dominant mode of the HM cavity into two odd-and even-half TE110 modes in a proximity, which leads to enhancement in the bandwidth by 50%. The antenna resonates around 3.4 GHz with a fractional bandwidth of 5% and around 4.3 GHz with a bandwidth of 4.7%, when corresponding ports are excited, respectively. Both the lower and upper frequency bands can be tuned individually, by simply altering the dimensions of each HMSIW cavity. This can be achieved in a common antenna, without employing filters, which satisfies the antenna-diplexer function. The isolation levels between any two radiating elements are obtained below-23 dB for the proposed MIMO antenna, and it occupies overall size of 1.0?g × 0.8?g. The peak gain of the antenna is obtained 5.35 dBi in the lower frequency band and 6.75 dBi in the upper frequency band while radiation efficiency is better than 80% in both frequency bands. The MIMO antenna properties have been evaluated and all found satisfactory. The envelope correlation coefficient (ECC) is obtained less than 0.13, DG around 9.9 dBi, and mean effective gain (MEG) around-3.05 dB. The 2×2 MIMO antenna is prototyped and experimentally verified. The measured results are closely following the simulation counterparts. The proposed 2×2 MIMO antenna is an appropriate alternative for LTE frequency bands in 5G wireless communication.

A novel, compact, dual-band 4-elements multi-input and multi-output (MIMO) antenna diplexer is investigated, prototyped, and tested. The proposed design is based on a planar half-mode Substrate Integrated Waveguide (HMSIW) technology, that diminishes size by 50% than of full-mode Substrate Integrated waveguide (FMSIW) cavity. Later, to enhance the bandwidth around 50%, a rectangular slot is introduced at the center of each cavity. The slot splits the dominant mode half-TE110 into an odd- and even-modes. The proposed antenna resonates at 3.3 GHz and 3.4 GHz when either Port-1 or Port-3 is fed, and Port-2 or Port-4 are terminated with matched loads. Similarly, the antenna operates at 4.2 GHz and 4.3 GHz, either Port-2 or Port-4 is fed, and the rest are matched terminated. The intrinsic isolation between any two ports is achieved below -23 dB with an antenna footprint of 1.0?1 × 0.8 ?1. The average gain in the lower and upper frequency bands are around 5.15 dBi and 6.1dBi, respectively while radiation efficiency is more than 80% in both frequency bands. The envelope correlation coefficient (ECC) of the MIMO antenna has been achieved < 0.13, directive gain (DG) around 9.9 dBi, and mean effective gain (MEG) around -3.05 dB in both frequency bands.

A new periodic Leaky-Wave Antenna (LWA) based on Substrate Integrated waveguide (SIW) technology is proposed and investigated. To scan the beam in backward as well as forward plane, a periodic leaky LWA has been employed in this work. Periodic LWA also offers the advantage of larger bandwidth with higher gain. This LWA is realized using a sensibly developed SIW technology to achieve the proposed geometry in a planar form. In this antenna, multiple square-shaped slots are etched into the top plane for radiation. An investigative study on stop-band minimization and thereby increasing scan range, scan resolution has been performed by varying the periodic range between the slots. The antenna shows a scanning from -78° to 73° in the frequency range of 7.5 to 14.8 GHz with a peak gain of 11.8 dBi. It is observed from simulation studies that the period 20 mm is the best choice with respect to the stopband, scan resolution, and gain.