Department of Electrical Engineering

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In this paper, an artificial noise (AN) injection technique is incorporated in a free-space optical (FSO) communication system with the aim of enhancing the secrecy performance of the system. An intensity modulated direct detection (IM/DD) FSO link which is subjected to Malaga ($\mathcal {M}$) distributed turbulence with pointing errors is considered in this paper. The performance of FSO systems is evaluated by deriving novel closed-form expressions for the secrecy outage probability (SOP), strictly positive secrecy capacity (SPSC), and throughput of the system. By formulating a constrained optimization problem, we discuss an optimal power allocation strategy for throughput maximization in the considered system. It is shown through the results that the proposed technique is very effective in improving the secrecy performance of FSO systems. © 2009-2012 IEEE.

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IEEE Photonics Journal

Artificial Noise Injection-Based Secrecy Improvement for FSO Systems

The single-stage DC–AC converters are capable of boosting the DC voltage and conversion to AC by incorporating the shoot-through state between the dead time intervals of traditional inverters. However, these suffer from second-order voltage and current reflections at the DC input side. The paper proposes a sliding mode control (SMC) based control of single-stage inverters. The proposed control is used to reduce second-order ripples currents (SRCs) by inductor impedance shaping which significantly reduces SRC propagation to the source. This improves the life span of source and converter components without any external ripple reduction circuitry. The proposed methodology is applied to two topologies-Quasi-ZSI, and Embedded Switched Boost Inverter. The proposed method is verified by simulation and experimentation. © 2021, Springer Nature Singapore Pte Ltd.

Studies in Systems, Decision and Control

Control of Single Stage Inverters and Second-Order Ripple Regulation Using Sliding Mode Control

Wearable dosimeters form an essential part of the personnel protection scheme in work spaces such as defence, nuclear establishments, and medical fields with radiation hazard. In the current scenario where use of high energy ionizing radiation sources (nuclear sources) is indispensable, the need of radiation detectors is mandatory for measuring the dose received by the person exposed in his work space and also measure the dose for patients where nuclear radiation is used for treatment. Wearable dosimeters need to have some special requirements apart from being accurate, precise, and robust. These need to be light in weight and should cause no harm to the human body while it is touching the body or apparels. This paper comprises an introduction to dosimeters, key characteristics, important techniques used for detection of neutrons and X-rays and also mentions about a few potential companies involved in developing wearable dosimeters in these application areas. The techniques have been collated, described, compared and the need to detect neutrons and X-rays has been expressed keeping in mind the demand from the defence and medical disciplines. This review also contains artificial intelligence and internet of things which form the basis of trending and upcoming wearable dosimeters. © 2021 Wiley-VCH GmbH

Advanced Materials Technologies

Wearable Dosimeters for Medical and Defence Applications: A State of the Art Review

This communication presents substrate integrated coaxial resonator (SICR) based triple-mode bandpass filters designed for K{u} -band. A self-shielded SICR based third-order filter is realized using two planar coaxial resonators (SICR) embedded in a substrate integrated waveguide cavity (SIW). Merging the TEM based mode of two SICR's with TE101 mode of SIW significantly enhances the bandwidth in a compact size. A novel topology realized using short circuited metallic via connecting to the top conducting plane through a metal strip demonstrates high degree of flexibility in positioning the transmission zeros to improve the selectivity as well as extend the out-of-band rejection of proposed filter. The three experimental prototypes devised for K{u} -band with fractional bandwidth more than 23% demonstrate multiple transmission zeros for good selectivity and out-of-band rejection with low insertion loss in a compact form factor. © 2004-2012 IEEE.

IEEE Transactions on Circuits and Systems II: Express Briefs

Triple-Mode Substrate Integrated Coaxial Resonator Based Bandpass Filter Featuring Flexible Transmission Zeros and Adjustable Bandwidth

Quality assessment of audiovisual (AV) signals is important from the perspective of system design, optimization, and management of a modern multimedia communication system. However, automatic prediction of AV quality via the use of computational models remains challenging. In this context, machine learning (ML) appears to be an attractive alternative to the traditional approaches. This is especially when such assessment needs to be made in no-reference (i.e., the original signal is unavailable) fashion. While development of ML-based quality predictors is desirable, we argue that proper assessment and validation of such predictors is also crucial before they can be deployed in practice. To this end, we raise some fundamental questions about the current approach of ML-based model development for AV quality assessment and signal processing for multimedia communication in general. We also identify specific limitations associated with the current validation strategy which have implications on analysis and comparison of ML-based quality predictors. These include a lack of consideration of: (a) data uncertainty, (b) domain knowledge, (c) explicit learning ability of the trained model, and (d) interpretability of the resultant model. Therefore, the primary goal of this article is to shed some light into mentioned factors. Our analysis and proposed recommendations are of particular importance in the light of significant interests in ML methods for multimedia signal processing (specifically in cases where human-labeled data is used), and a lack of discussion of mentioned issues in existing literature. © 2021 ACM.

ACM Transactions on Multimedia Computing, Communications and Applications

Assessment of Machine Learning-Based AudiovisualQuality Predictors:Why Uncertainty Matters

In this work, a wideband DC isolated substrate integrated coaxial line (SICL) transition for thick substrates is presented. The planar transition is devised utilizing a substrate truncated microstrip line as a transition to SICL section. Tapered slots etched on the top ground plane aid in improving the transition characteristics over a wide bandwidth. The DC isolation in the proposed transition is achieved by embedding a compact interdigital capacitor in a microstrip line connected to the SICL section. Performance of the transition with an embedded interdigital capacitor is analyzed. The proposed transition exhibits a fractional bandwidth of 22.37% with a measured mean insertion loss less than 1.2 dB in 9.09 GHz to 11.38 GHz band. The loss group delay characteristics of the wideband transition are studied in this work. Development of DC isolated transition for the self-packaged electromagnetically shielded SICL simplifies integration of active components for superior performance of the communication system. © 2021 EuMA.

2020 50th European Microwave Conference, EuMC 2020

A Wideband DC Isolated Substrate Integrated Coaxial Line Transition for System Integration

Interceptors operate at wide range of operating conditions in terms of Mach number, altitude and angle of attack. The aerodynamic design caters for such wide operating envelope by appropriate sizing of lifting and control surfaces for meeting the normal acceleration capability requirements. The wide range of operating conditions leads to an inevitable spread in center of pressure location and hence spread in static stability. The performance of control design is a strong function of the aerodynamic static stability. The total operating envelope can be bifurcated into statically stable and unstable zones and the aerodynamic lifting surface location can be used as a control parameter to identify the neutral stability point. During the homing phase lesser static stability is desirable for good speed of response, hence the lifting surface location needs to be chosen based on the capability of control to handle instability. This paper analyses the limitations of autopilot design for the control of an unstable interceptor and brings out a method to identify the optimum aerodynamic lifting surface location for efficiently managing static margin while satisfying the control limitations and homing phase performance. This provides an input on the most appropriate lifting surface location to the aerodynamic designer during the initial CFD based aerodynamic characterisation stage itself, before commencing the rigorous wind tunnel based characterisation. © 2021, DESIDOC

Defence Science Journal

Choice of interceptor aerodynamic lifting surface location based on autopilot design considerations

This chapter presents an event-triggering approach to the design of sliding mode control (SMC) for an uncertain linear dynamical system. In the event-triggering mechanism, only discrete measurements are used to verify the event condition for generating a sequence of triggering instants. Such a triggering mechanism is known as the periodic triggering mechanism. Due to the periodic evaluation, the event condition in the triggering mechanism can only be detected at a time instant, which is a multiple of sampling period, although it may hold before this instant. The design of SMC in the periodic event-triggering framework becomes even more complicated because of the dependency of switching gain on the triggering parameter. This chapter presents a novel method of designing the periodic triggering mechanism-based SMC that can control the plant under external perturbations. In our approach, we decouple the design of event condition and the switching gain of SMC by choosing appropriately the sampling period for the periodic evaluation. Therefore, one may design the switching gain first to obtain a suitable sampling period so that the desired bound for the state trajectories can be achieved by the event-triggered controller. Finally, the simulation results are presented to demonstrate the performance of the proposed triggering mechanism. © 2021, Springer Nature Singapore Pte Ltd.

Design of Periodic Event-Triggered Sliding Mode Control

The recent advances in the field of 2D hexagonal boron nitride (hBN) for realizing electronic and optoelectronic devices, including wearable and portable devices, have aroused scientific interest in this ultrathin material for a wide range of applications. Its exceptionally high thermal conductivity and temperature stability make it one of the most promising materials for next-generation high-performance gas sensors. Although a number of review articles on hBN have already been published focusing on its synthesis, properties, and functionalities, however, none of them has made a significant contribution to the field of gas sensing. Hence, in this review, we have analytically summarized the state-of-art advances in hBN based devices with a particular emphasis on gas sensors. Moreover, we have also explained the comprehensive physics of hBN based gas sensors. The recent technological advancements to overcome the inherent properties such as poor surface reactivity and low conductivity have also been thoroughly compiled. Finally, we have discussed some of the prominent challenges faced by hBN technology for developing practical gas sensors. © The Royal Society of Chemistry 2021.

Journal of Materials Chemistry C

Recent advances in ultrathin 2D hexagonal boron nitride based gas sensors

We present comprehensive temperature dependent Raman measurements for chemical vapor deposition grown horizontally aligned layered MoS2 in a temperature range of 4–330 K under a resonance condition. Our analysis of temperature dependent phonon frequency shift and linewidth suggests a finite role of three and four phonon anharmonic effect. We observe Davydov splitting of the out-of-plane (A1g) and in-plane (E21g) modes for both three layer (3L) and few layer (FL) systems. The number of Davydov splitting components are found more in FL compared to 3L MoS2, which suggests that it increases with an increasing number of layers. Further, Davydov splitting is analyzed as a function of temperature. Temperature evaluation of the Raman spectra shows that the Davydov splitting, especially for A1g mode, is very strong and well resolved at low temperature. We observe that A1g mode shows the splitting at low temperature, while E21g mode is split even at room temperature, which suggests a prominent role of A1g mode in the interlayer interaction at low temperature. Further, an almost 60-fold increase in the intensity of the phonon modes at low temperature clearly shows the temperature dependent tuning of the resonance effect. © 2021 IOP Publishing Ltd.