Finite Difference Time Domain Simulation of Active Cancellation of Radar Echoes

AbstractRadar evasion or Stealth is a technology most desirable among all the military research areas currently pursued. Research organisations have focused their attention on electronic stealth technology or cancellation of waves since it is feasible now due to the improvement of high end processing and fast electronic systems. In an attempt to increase our understanding of this field, we have analysed the phenomenon through computer aided simulation. In this paper, we have created an electromagnetic wave simulation platform and using finite difference time domain method, analysed a method of active cancellation. We have found results showing complete effectiveness of this method assured by the accuracy of FDTD method

Influence of leg geometry on the performance of bismuth telluride-based thermoelectric generator

Thermoelectric generators have been widely used to transform heat into electrical energy. Over the last few decades, researchers have studied the impact of thermoelement height and cross-section area on the efficiency of thermoelectric generators. This paper investigates and analyzes the effect of various thermoelement leg geometries, including rectangular, trapezoidal, cylindrical and cone, for a bismuth telluride-based thermoelectric generator using finite element analysis. The influence of thermoelement leg height on achieving an optimized temperature gradient, producing open-circuit voltage, and achieving maximum output power is studied. Based on the analysis, the thermoelectric generator with the cone shaped leg provided optimal temperature gradient, the open-circuit voltage of 87.8 mV and a maximum power of ~270 mW at a leg height of 5 mm

Hybrid power for energy harvesting design and applied to quadcopter system

Quadcopter cannot fly for longer time even though the battery capacity is bigger. The suggested solution to this problem is to harvest energy from the surroundings and the system. This project is to study and designed a power system that uses surrounding energy to charge the battery of the quad-copter. The system requires a stable input charging to the battery from the harvester; a power controller is used to steady the input charging power. There are some limitations to the system where different harvester had different output power, which in turn difficult to choose a harvester to power the system. Thus, a hybrid power system is considered as a solution to generate a certain power from the harvester to the required system

Non‑traditional machining techniques for silicon wafers

Silicon (Si) micromachining techniques have recently witnessed significant advancement, attributable to the high surge in demand for microelectromechanical and microelectronic devices. Micromachining techniques are widely used to cut or pattern Si, in order to obtain high-quality surface finishes for the fabrication of devices. Micromachining techniques are used for the fabrication of three-dimensional (3D) microstructures for microelectromechanical devices. In this work, the capabilities and competencies of non-traditional Si micromachining techniques, including ultrasonic, ion beam milling, laser machining, and electrical discharge machining, are discussed and compared accordingly. The working principles, advantages, limitations, and Si microstructures that have been fabricated before are discussed in detail. Additionally, this work covers the performance reported by multiple researchers on these micromachining methods, spanning the temporal range of 1990 to 2020. The key outcomes of this study are explored and summarized

Finite element analysis of silicon nanowire array based SAW gas sensor

This work presents the design and finite element analysis of a surface acoustic wave (SAW)-based sensor for the detection of volatile organic compound (VOC) gases. The effect of silicon nanowire array (SiNWA) on a 128º YX-lithium niobate (LiNbO3) substrate for sensing the VOC gases was simulated using COMSOL Multiphysics. The frequency response was investigated in relation to changes in the SiNWA sensitive layer and VOC gas concentration. The resonant frequency of the SAW device was also evaluated, and simulation results were obtained after being exposed to 100ppm concentration of VOC gas. It was determined that the frequency increased, after the sensor was exposed to VOC gases. In general, extending the length of the SiNWA enhances the sensor's sensitivity

Thermoelectric generator: Materials and applications in wearable health monitoring sensors and internet of things devices

Wearable sensors and biomedical devices have attracted a great deal of attention among users. Despite technological advancements in this field, a mixture of both progress and setbacks has been witnessed. The limited battery life of these devices for long-term operation remains a major challenge. In this context, thermoelectric generators have emerged as potential candidates for harvesting energy from temperature gradients to power wearable sensors and devices. This review focuses on the working mechanism of a thermoelectric generator, as well as the current progress of a variety of promising and widely used inorganic and organic thermoelectric materials. Encouragingly, the highest ZT values of 2.27, 2.5, 2.8, 2.3, and 1.85 are obtained for bismuth telluride, lead telluride, tin selenide, copper selenide, and magnesium antimonide, respectively, at various temperature ranges. Meanwhile, organic materials such as poly (3,4-ethylenedioxythiophene) polystyrene sulfonate, polyaniline composite, and graphdiyne showed the highest ZT values of 0.75, 0.74, and 4.8, respectively, at near-room temperature. Furthermore, numerous novel thermoelectric generator-powered wearable health monitoring sensors and Internet of Things devices are also presented. Finally, the current challenges and perspectives on the future development of thermoelectric generator, in particular for efficient materials and self-powered devices, are also discussed

State-of-the-art reviews and analyses of emerging research findings and achievements of thermoelectric materials over the past years

This review is focused on state-of-the-art thermoelectric materials (or thermoelements), from which the thermoelements with the highest figures of merit (z) along with the those having the greatest research interest and findings were surveyed and analyzed. These were in addition to the statistical analyses made in this review for categorizing z achievement ranges for all types of thermoelements. Almost 56% of positive thermoelements and 39.6% of negative thermoelements were discovered from 1950 to 2017, and a total of 62.2% of thermoelement research findings were reported in 2010–2017. Furthermore, nearly 47.65% of the discovered thermoelements preserved z in the range of 1–4.99 × 10−3 K−1, and only about 2.52% possessed less than 9.9 × 10−6 K−1. Chalcogenide was the major type of thermoelement studied to date, with overall representation of 37.2%. Nearly 68.9% of chalcogenide thermoelements were capable of reach 1–4.99 × 10−3 K−1, while 53% of metal oxide thermoelements ranged within 0.1–0.499 × 10−3 K−1. Nanostructure thermoelements achieved the highest z of 47 × 10−3 K−1 and 17 × 10−3 K−1 at 300 K, for Bi2Te3 quantum wires and Bi2Te3 quantum wells, respectively. Correspondingly, hybrid and conducting polymer thermoelements also reached z as high as 16 × 10−3 K−1 at 300 K for positive thermoelement: nano-Ag/regioregular poly(3-octylthiophene-2,5-diyl) and negative thermoelement: graphdiyne

Methodological reviews and analyses on the emerging research trends and progresses of thermoelectric generators

Thermoelectric generator is among the earliest initiated electricity-harvesting methods. It is a very potential power harvester that can convert wasteful thermal energy into electricity. However, it often suffers from low energy conversion rate due to its inconsistent heat source, inefficient thermoelectric material (or thermoelement) performance, and incompetent structural issues. Progressively for the first time, detailed methodological surveys and analyses are made for bulk, thick, and thin films in this review. This is in order to accommodate better insights and comprehensions on the emerging trends and progresses of thermoelectric generators from 1989 to 2017. The research interests in thermoelectric generators have started back in 1989, and have continuously experienced emerging progresses in the number of studies over the last years. The methodological reviews and analyses of thermoelectric generator showed that almost 46.6% of bulk and 46.1% of thick and thin film research works, respectively, are actively progressed in 2014 to 2017. Nearly 86.2% of bulk and 44.1% of thick and thin film thermoelectric generators are realizing in between 0.001 and 4 μW cm−2 K−2, while 43.1% of thick and thin films are earning among 10−6 to 0.001 μW cm−2 K−2. The highest achievement made until now is 2.5 W cm−2 at a temperature difference of 140 K and thermoelectric efficiency factor of 127.55 μW cm−2 K−2. This achievement remarked positive elevation for the field and interest in thermoelectric power generation. Consecutively, the research trends of fundamental devices' structure, thermoelement, fabrication, substrate, and heat source characteristics are analyzed too, along with the desired improvement highlights for the applications of thermoelectric generators

MEMS actuators for biomedical applications: a review

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Energy harvesters for wearable electronics and biomedical devices

Energy harvesters (EHs) are widely used to transform ambient energy sources into electrical energy, and have tremendous potential to power wearables electronics and biomedical devices by eliminating, or at least increasing, the battery life. Nevertheless, the use of EHs for a specific application depends on various aspects including the form of energy source, the structural configuration of the device, and the properties of materials. This paper presents a comprehensive review of the classification of EHs, notably thermoelectric generators (TEGs), triboelectric nanogenerators (TENGs), and piezoelectric generators (PEGs) that allows a wide variety of devices to be operated. The EHs are discussed in terms of their operating principles, optimization factors, state-of-the-art materials, and device structure, that directly influence their operational efficiency. Besides, the breakthrough performance of each of the EHs listed above is highlighted. From the review and analysis, the maximum output power density of 9.2 mW cm-2, 50 mW cm-2, and 64.9 µW cm-2, respectively, are obtained from the TEG, TENG, and PEG, respectively. Furthermore, recent applications relevant to a specific EH and their output performance, are also enlightened. Eventually, the essential outcomes and future direction from this review are discussed and encapsulated