Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

The 2016 terahertz science and technology roadmap

Robust Adaptive Beamforming Based on Steering Vector Estimation and Covariance Matrix Reconstruction.

Digital Signal Processing System Analysis and Design: Preface

Near-field imaging with terahertz (THz) waves is emerging as a powerful technique for fundamental research in photonics and across physical and life sciences. Spatial resolution beyond the diffraction limit can be achieved by collecting THz waves from an object through a small aperture placed in the near-field. However, light transmission through a sub-wavelength size aperture is fundamentally limited by the wave nature of light. Here, we conceive a novel architecture that exploits inherently strong evanescent THz field arising within the aperture to mitigate the problem of vanishing transmission. The sub-wavelength aperture is originally coupled to asymmetric electrodes, which activate the thermo-electric THz detection mechanism in a transistor channel made of flakes of black-phosphorus or InAs nanowires. The proposed novel THz near-field probes enable room-temperature sub-wavelength resolution coherent imaging with a 3.4 THz quantum cascade laser, paving the way to compact and versatile THz imaging systems and promising to bridge the gap in spatial resolution from the nanoscale to the diffraction limit.

Near-field terahertz probes with room-temperature nanodetectors for subwavelength resolution imaging

The eco-friendly vegetable liquid is increasingly used because of the growing demand for environmentally friendly dielectric liquid. A vegetable liquid/fullerene nanofluid was fabricated via ultrasonic processing with good dispersion of the fullerene nanoparticles. It was observed that a small amount of fullerene (~100 mg/L) can significantly improve the electrical properties of vegetable insulating liquid (dissipation factor decreased by 20.1%, volume resistivity increased by 23.3%, and Alternating Current (AC) dielectric breakdown strength increased by 8.6%). Meanwhile, the trace amount of fullerene is also able to improve the electrical performances (i.e., dissipation factor and electrical resistivity) of the vegetable nanofluid under harsh conditions of long-term thermal aging compared with the blank contrast. The reduced acid values (25%) and dissolved decomposition gases (58.2% for hydrogen) in the aged vegetable nanofluid indicate the inhibition of molecule decomposition of vegetable liquid with fullerene. The improved electrical performances and thermal resistance of the vegetable nanofluid contribute to the electron affinity of fullerene proved by calculation of electron density distribution on the surface. The thermogravimetric analysis of the nanofluid under different atmospheres interprets that the oxygen absorbed inevitably in the fullerene contributes to the performance deterioration of the nanofluids during the initial aging. This work provides a potential method towards eco-friendly dielectric liquid with great electrical performances for harsh environments.

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Significantly Enhanced Electrical Performances of Eco-Friendly Dielectric Liquids for Harsh Conditions with Fullerene.

The performance of a Concentric Circular Antenna Array (CCAA) is presented in this paper with variable loading technique. A CCAA geometry is chosen because of its symmetrical configuration which enables the phased array antenna to scan azimuthally with minimal changes in its beam width and side-lobe levels. The performance of CCAA system is degraded, if any disparity occurs between the original signal direction and the steering direction of the beamformer. This performance degradation problem due to look direction disparity can be improved by using robust techniques. This paper proposes a technique, named variable diagonal loading (VDL) technique for CCAA system and compares the performance of the proposed robust CCAA processor with existing CCAA processors. The proposed robust CCAA beamformer enhances the output power 28.9 dB, 9.34 dB and 1.63 dB at 1◦ disparity angle in comparison to the CCAA standard capon beamformer (SCB), robust SCB and existing novel loading technique. Numerical examples are presented to analyze the performance of the proposed robust beamformer in different scenarios.

Robust Concentric Circular Antenna Array with Variable Loading Technique in the Presence of Look Direction Disparity

The concentric circular array with robust algorithm is addressed in this paper. A uniform concentric circular array antenna (CCAA) geometry is targeted due to its symmetrical configuration which enables the phased array antenna to scan azimuthally with minimal changes in its beam width and sidelobe levels. This paper first compares the performances of CCAA configuration with existing uniform circular arrays (UCA) to validate the suitability of the presented beamformer. Then the performance of CCAA based optimal beamformer is compared with delay-and-sum beamformer in the presence of interfering signals. The performance of optimal CCAA processor is reduced if signal of interest is deviate from the look direction. This paper also presents a diagonal loading technique to make the system robust for resolving the degradation problem and compare the performance with existing beamforming technique. MATLAB software is used to analyze the performance of proposed CCAA processor.

Robust uniform concentric circular array beamforming in the existence of look direction disparity

This paper presents the performance of a Concentric Circular Antenna Array (CCAA) with robust optimal diagonal loading (ODL) technique. Because of the symmetrical configuration of a CCAA geometry, it enables the antenna array to scan azimuthally with minimal changes in its beam width and side-lobe levels. The performance of CCAA system is degraded in the presence of disparity between the original signal direction and the steering direction of the beamformer. This performance degradation problem due to look direction disparity can be improved by using robust techniques. This paper proposes the ODL technique for CCAA system and compare the performance of proposed robust CCAA processor with the existing CCAA processors. The proposed robust CCAA beamformer enhances the output power 28.12 dB and 8.624 dB at 2° disparity angle compared to the existing CCAA processor (Hossain et al., 2016) and robust CCAA beamformer (Reza et al., 2016) respectively. Numerical examples are presented to analyze the performance of proposed robust beamformer in different scenarios.

Performance investigation of robust concentric circular antenna array beamformer in the presence of look direction disparity

This paper presents centered element concentric circular antenna array (CECCAA) using variable diagonal loading (VDL) technique and different filtering windows. The different filtering windows are modified to apply in the CECCAA system. The modified novel technique not only is able to reduce the side lobe level (SLL) but also has the ability to detect and highly attenuate the directional interferences. However, the performance of CECCAA system is degraded in the presence of array imperfections. This performance degradation problem due to array imperfections can be improved by using robust techniques. The proposed technique is also robust against array imperfections and improves the performance. Moreover, the performance of the proposed structure is better than a concentric circular antenna array (CCAA). Several examples are presented to analyze the performance of proposed beamformer by using different tapering windows.

https://downloads.hindawi.com/journals/ijap/2017/1408183.pdf

Robust Centered Element Concentric Circular Antenna Array with Low Side Lobe Using Variable Loading and Tapering Windows in the Presence of Array Imperfections

The broadband concentric circular antenna array beamformer with convolution constraints and efficient realization techniques are addressed in this paper. The concentric circular array processor is competent to scan a beam azimuthally through 360 degree and inherently cover up the entire breathing space. The behavior of the time domain element space array processor is appraised by comparing its recital, sensitivity to the stare direction and computational effectiveness. The simulation effect shows that the proposed processor has superior performance than the existing circular processor. It has capability to steer the main beam at any random direction without using presteering delays and has aptitude to cancel directional interferences as well.

Md. Farhamdur Reza

Papers

Robust Concentric Circular Antenna Array with Variable Loading Technique in the Presence of Look Direction Disparity

Robust uniform concentric circular array beamforming in the existence of look direction disparity

Performance investigation of robust concentric circular antenna array beamformer in the presence of look direction disparity

Robust Centered Element Concentric Circular Antenna Array with Low Side Lobe Using Variable Loading and Tapering Windows in the Presence of Array Imperfections

Performance analysis of broadband concentric circular antenna array processor