This PDF file contains the front matter associated with SPIE Proceedings Volume 11722, including the Title Page, Copyright information and Table of Contents

Introduction to SPIE Defense and Commercial Sensing conference 11722: Energy Harvesting and Storage: Materials, Devices, and Applications XI

Thermophotovoltaics (TPV) is a versatile technology to generate high electrical power density utilizing multiple sources of heat, such as solar irradiation, radioisotope heaters, combustible materials, thermal storage systems, waste industrial heat etc., as input. TPV systems aim to surpass the efficiency beyond the Shockley-Queisser limit for photovoltaic conversion by tailoring the spectrum of the incident solar light to match the spectral response of a PV cell. Spectrally selective absorbers and emitters can greatly enhance the TPV conversion efficiency by maximizing the absorption of the incident sunlight and suppressing the emission of sub-bandgap and excessive energy photons. One approach of achieving spectral selectivity is through the use of micro and nanostructures to control light emission from surfaces. This presentation reviews optical modeling and characterization techniques of various types of novel nanostructures, including random textures, nanocones, nanoholes, and m ultilayer metal dielectric stack etc., for the design of high-performance selective surfaces needed for efficient TPV systems. In addition, the fabrication of a GaSb-based experimental TPV system comprising a multilayer metal-dielectric (Si₃N₄-W-Si₃N₄) coating-based selective emitter is also presented. The performance of the TPV system was evaluated using a high-power laser as a simulated input for concentrated solar power. The overall power conversion efficiency of 8.4% was measured at 1676 K.

State-of-the-art TPV converters use cells with high out-of-band reflectance to facilitate a photon recycle process, in which sub-bandgap photons are reflected by the cell and subsequently re-absorbed at the emitter. However, cells relying on metallic back surface reflectors, Bragg/plasma filters, and photonic crystals for spectral control suffer from undesired out-of-band absorptance and have yet to surpass 95% out-of-band reflectance. Here we describe the fabrication and characterization of a thin-film In0.53Ga0.47As thermophotovoltaic cell with an air-bridge architecture, in which the absorber material is suspended over an air gap, supported by Au grid lines. The average out-of-band reflectance of the cell exceeds 98% due to lossless Fresnel reflectance at the In0.53Ga0.47As-air interface and < 2% loss at the air-Au interface. The result is a record-high TPV conversion efficiency of 32%, characterized under illumination by a 1455K SiC globar.

The sensitized thermal cell (STC) is a battery that can convert heat directly into electric power at low environmental temperatures (100°C or lower). It can be buried in the ground and generate electricity directly from the Earth’s crust. This STC was originally suggested by the authors in 2017 (Mater. Horiz., 2017,4, 649-656), and media in different continents and countries, including Europa, the United States, Asia, Arab, and Africa, reported the STC as a sensational technique that can directly affect the oil price. The most valuable feature of the STC is, after the electricity generation was stop, the reaction could restart with a simple flip of an on/off switch in the external circuit after the electricity generation was stopped. These batteries could be, for example, buried in a geothermal spot and work as a power plant.

Control of thermal transport is of significant interest for a wide range of applications, such as buildings, vehicles and batteries, thermo-electric and solar-thermal energy conversion, bio/chemical sensing, etc. However, heat transfer processes are often difficult to actively control: heat conduction is usually diffusive in nature owing to the incoherence of heat carriers and thermal radiation is generally broadband or have wide energy distribution. In this talk, I will introduce a thermo-photonic engineering approach to manipulate nanoscale heat transport by using surface phonon polaritons (SPhP). I will mainly focus on how the SPhP can be utilized to tailor thermal radiation properties, especially to achieve a coherent, near-monochromatic far-field thermal emission, which is a big departure from the incandescent behaviour in the classic textbook as described by the Planck’s law.

Thermophotovoltaic power conversion relies on a highly reflective mirror to reduce parasitic power consumption and increase power conversion efficiency. Here, we show the designs of broadband thermophotovoltaic mirrors, that can achieve >99% reflectivity, over 3-octaves of bandwidth.

The development of transparent flexible organic photovoltaic solar cells, using an optically transparent substrate material and new organic semiconductor materials, has been widely utilized by the electronic industry when producing new technological products. The transparent flexible organic photovoltaic solar cell are the base Poly (3,4- ethylenedioxythiophene), PEDOT:PSS, Poly(3-hexyl thiophene, P3HT, Phenyl-C61-butyric acid methyl ester, PCBM and Polyaniline, PANI, were deposited in Indium Tin Oxide, ITO, and characterized by Electrical Measurements and Scanning Electron Microscopy (SEM). In addition, the thin film obtained by the deposition of PANI, prepared in perchloric acid solution, was identified through PANI-X1. The result obtained by electrical Measurements has demonstrated that the PET/ITO/PEDOT:PSS/P3HT:PCBM Blend/ PANI-X1/ITO/PET layer presents the characteristic curve of standard solar cell after spin-coating and electrodeposition. The Thin film obtained by electrodeposition of PANI-X1 on P3HT/PCBM Blend was prepared in perchloric acid solution. These transparent flexible organic photovoltaic solar cells presented power conversion efficiency of 12%. The inclusion of the PANI-X1 layer reduced the effects of degradation these organic photovoltaic panels induced for solar irradiation. In Scanning Electron Microscopy (SEM) these studies reveal that the surface of PANI-X1 layers is strongly conditioned by the surface morphology of the dielectric.

This presentation was recorded for the SPIE Defense and Commercial Sensing 2021 conference

Li, Na, K, and Mg metal anodes have the highest capacities of anodes of their respective rechargeable metal-ion battery systems but suffer from several issues that have precluded their practical deployment. While the electrochemistry of these systems has received extensive study, at the heart of many issues lies a mechanics of materials problem: damage or unstable deformation occurs during cycling. A deeper understanding of mechanics in these systems is thus required to mitigate these issues. To this end, through nanoindentation, microhardness, and bulk testing, this talk will present experimental studies of the mechanical properties of metallic Li, Na, K, and Mg anodes. These properties will be connected to implications in battery performance, as to provide insight into guiding the design of battery materials, architectures, and electrochemical conditions that mitigate unstable growth of metal anodes during electrochemical cycling.

The talk will discuss possible high capacity negative electrode materials for potassium-ion batteries. This new type of high voltage batteries currently attracts significant attention as an alternative to lithium-ion batteries due to the abundance of potassium in nature and its relatively homogeneous distribution globally. Identification of possible electrode materials for these new batteries is therefore a key task. Selected negative electrode materials operating via alloying, conversion and conversion-alloying mechanisms and capable of significantly exceeding the capacity of graphite will be discussed in this talk.

Among the potential cathode materials for the upcoming Na-ion battery system, O3-type Na-TM-oxides are promising due to their inherently high initial Na-content; but suffer from instabilities caused due to multiple phase transformations during Na-removal/insertion and sensitivity to air/moisture. Against this backdrop, we have tuned the composition and structural features to suppress the phase transitions and also improve the air/water-stability; so much so that long-term cyclic stability has been achieved with health/environment friendly aqueous processed electrodes. At the anode front, development of carefully tuned bi-phase Na-titanate based electrodes have been able to address the cyclic instability of single-phase Na-titanate (viz., otherwise a ‘safe’ anode), leading to long-term cyclic stability even at high current densities (up to 50C!). These are important steps towards the development of health/environment friendly, cost-effective, safe and high-performance Na-ion batteries.

Engineers find it of importance to have a quantitative understanding of the charge-depletion characteristics of the battery-bank that powers a mobile unmanned ground vehicle (UGV) so as to have mission-duration, cost-of-transport, range, and other useful estimates. Data analysis to determine the energy use of a ‘large’ wheeled robot – the Clearpath™ Warthog – with Gross Vehicle Weight (GVW) 590 Kg. -- are here discussed. The analysis is based on gravel-surface, straight-path level trials. The results of this analysis inform how far the UGV can travel over the specified surface. We give basic methods for obtaining expected energy usage: tables with estimates for cost of transport and for mission range. Included in the analysis is a nonparametric method for identifying and dealing with the small number of ‘outlier,’ readings that often occur in field trials.

The prompt and accurate detection of laser strikes is increasingly important to the survivability of military assets in modern warfare as offensive and defensive laser weapon systems have become more widely implemented. Current laser detection systems on military assets can compromise an asset’s low observability features. This paper presents an addressed detection system based on an array of thermoelectric generators (TEGs) that can be integrated into the skin of an asset. An irradiated TEG harvests the incident energy of a high energy laser (HEL) strike to power a sensor node that transmits an address, via a wireless medium, to a reader in order to indicate which TEG within the array is being irradiated. The wireless sensor node consists of an ultralow voltage step-up converter and microcontroller and a low power RF link.

Individual 2-dimensional materials exhibit remarkable properties, but neither of them can show all the required attributes. Stacking different 2-dimensional materials in hetero-layered architecture unlock the combined ad- vantages of the individual building blocks. In recent experiments 2-dimensional vertical heterostructures of graphene/hBN/W_xMo_(1-x)S₂ have been successfully grown. Herein, using the first-principles method, we have analyzed the stability, electronic band structures, and electronic transport coefficients of such vertical heterostructure at 300 K. The calculated bandgap of the pristine monolayer of graphene, hBN, MoS₂, and WS₂ is 0 eV, 3.1 eV, 1.6 eV, and 1.8 eV, respectively. Furthermore, we have observed the atomic level phenomena of bandgap opening in graphene upon changing the interlayer distance. Electrical conductivity (σ/τ) and thermoelectric power factor (PF/τ) are calculated as a function of Fermi energy (E_F). At the studied E_F range, for the graphene/hBN/W_xMo_(1-x)S₂ 2D vertical heterostructure, the achieved electrical conductivity and thermoelectric power factor are 0.7x10²⁰Ω^-1m^-1s^-1 and 0.75x10¹¹ Wm^-1K^-2s^-1, respectively. Our findings provide solid outlines for TMDs alloyed based thin-layer 2D heterostructures that could play a crucial role in revolutionizing energy storage devices and expanding all limits of current technologies in super-capacitors and next-generation reliable batteries due to its slit-shaped diffusion channel and high surface to mass ratio, which could enable the fast movements of ions approaching the excellent electrochemical properties.

The pandemic has accelerated the shift toward wearable technologies and remote monitoring techniques for healthcare. To facilitate autonomous or self-powered devices, development of mechanical energy harvesting devices that are compliant to curvilinear surfaces or wearable on human body or skin are attractive for cyber physical applications. This presentation underlines our efforts in developing compliant mechanical energy harvesters to power interactive electronic and tactile sensing devices. We design mechanical interlocked stretchable nanofibers that were fabricated using electrospinning for breathable and wearable TENG for tactile interactive sensing and energy harvesting. 3D printable thermoplastic elastomer has also been synthesized to function as a triboelectric active layer which can be simultaneously used as the matrix for stretchable current collector.

Electronic skin (e-skin) is expected to play a crucial role in the next generation of robotics and medical devices. However, existing e-skin-based sensing platforms primarily focus on monitoring physical parameters and rely on the power from the batteries or near field communication, which significantly hinders their broad use and sustainability toward continuous wireless sensing. Here I will introduce our recent works on flexible self-powered integrated electronic skin for multiplexed metabolic sensing in situ. These battery-free wearable sensors contain biosensors as well as highly efficient energy harvesters (such as biofuel cells and triboelectric nanogenerators) that utilize a unique integration of 0 dimensional to 3 dimensional nanomaterials to achieve remarkably high power intensity and long-term stability. Such battery-free soft wearable systems with highly efficient energy harvesting from the human body hold great promise for robotics and personalized healthcare applications.

There are two complementary requirements for implementing energy-harvested applications: the energy harvesting solution and the ultra-low power (ULP) requirements for the circuits. We address the ULP requirements by combining logically consistent design methodologies based on asynchronous streams to provide the essential blocks for a miniaturized ULP “mote.” First, we use an asynchronous stream data representation enabled by the use of continuous time Sigma-Delta modulators as analog-to-stream converters of sensor inputs. Second, we use Asynchronous Stream Processing (ASP) for ULP algorithms equivalent to DSP algorithms. Third we use Asynchronous Stochastic Computing (ASC) for ULP computations, including Machine applications such as Random Forest. Finally, we use Asynchronous Impulse Radio (AIR) UWB as a direct stream-to-radio mapping for compact wireless communication closes the loop for a ULP IoT mote from sensor input to wireless link.

Double rotor wind turbines are studied for improving wind energy harvesting. The location, size and number of blades of the second rotor are important factors which affect performance of the double rotor wind turbines. These and other blade parameters may influence the drag and output power characteristics of the wind turbine. In the present work, the drag forces acting on two double rotor wind turbine configurations are experimentally investigated using wind tunnel testing. The two configurations are cocurrent and counter current double rotor wind turbines. A single rotor wind turbine is used as a comparison reference to compare with the two double rotor wind turbine configurations. Models of the three horizontal axis wind turbines were produced using 3D printing technology and were tested in the wind tunnel while wind power augmentation was also evaluated. The experimental results revealed an increase in the value of drag coefficient when a second rotor is added. The increase on the drag coefficient depends on the configuration, the size and location of the second rotor. The drag coefficient for the counter current rotation double rotor is close to the single rotor wind turbine; however, an increase of about 25% on drag coefficient is observed for the case of cocurrent double rotor wind turbine.

Monitoring human health in real-time using wearable and implantable electronics (WIE) has become one of the most promising and rapidly growing technologies in the healthcare industry. In general, these electronics are powered by batteries that require periodic replacement and maintenance over their lifetime. To prolong the operation of these electronics, they should have zero post-installation maintenance. On this front, various energy harvesting technologies to generate electrical energy from ambient energy sources have been researched. Many energy harvesters currently available are limited by their power output and energy densities. With the miniaturization of wearable and implantable electronics, the size of the harvesters must be miniaturized accordingly in order to increase the energy density of the harvesters. Additionally, many of the energy harvesters also suffer from limited operational parameters such as resonance frequency and variable input signals. In this work, low frequency motion energy harvesting based on reverse electrowetting-ondielectric (REWOD) is examined using perforated high surface area electrodes with 38 µm pore diameters. Total available surface area per planar area was 8.36 cm² showing a significant surface area enhancement from planar to porous electrodes and proportional increase in AC voltage density from our previous work. In REWOD energy harvesting, high surface area electrodes significantly increase the capacitance and hence the power density. An AC peak-to-peak voltage generation from the electrode in the range from 1.57-3.32 V for the given frequency range of 1-5 Hz with 0.5 Hz step is demonstrated. In addition, the unconditioned power generated from the harvester is converted to a DC power using a commercial off-theshelf Schottky diode-based voltage multiplier and low dropout regulator (LDO) such that the sensors that use this technology could be fully self-powered. The produced charge is then converted to a proportional voltage by using a commercial charge amplifier to record the features of the motion activities. A transceiver radio is also used to transmit the digitized data from the amplifier and the built-in analog-to-digital converter (ADC) in the micro-controller. This paper proposes the energy harvester acting as a self-powered motion sensor for different physical activities for wearable and wireless healthcare devices.

This paper gives an overview about the available geothermal power plants. The second part there is a comparison between Geothermal Energy with other sources of Renewable Energy. The advantages and disadvantages of geothermal energy and power plant are discussed. Finally, a case study of a geothermal power plant located in Paris, France was simulated using System Advisor Model to observe the results. All the data input was obtained from a published research paper. Moreover, this study reviews the main functions of dry, flash and binary geothermal power plants.