Query: thin broadband noise absorption

Candidate papers:

abstract: Basic design rules are developed for the use of metallic nanostructures to realize broadband absorption enhancements in thin film solar cells. They are applied to a relevant and physically intuitive model system consisting of a two dimensional, periodic array of Ag strips on a silica coated Si film supported by a silica substrate. We illustrate how one can simultaneously take advantage of 1) the high near fields surrounding the nanostructures close to their surface plasmon resonance frequency and 2) the effective coupling to waveguide modes supported by the thin Si film through an optimization of the array properties. Following this approach, we can attain a 43% enhancement in the short circuit current as compared to a cell without metallic structures. It is suggested that 3 dimensional nanoparticle arrays with even larger boosts in short circuit current can also be generated using the presented framework. Photovoltaic (PV) cells can provide virtually unlimited amounts of energy by effectively converting sunlight into clean electrical power. Silicon has been the material of choice for PV cells due to low cost, earth abundance, non toxicity, and the availability of a very mature processing technology. The cost of current PV modules still needs to be significantly reduced and efficiency substantially increased to enable large scale implementation. Thin film, second generation Si solar cells may provide a viable pathway towards this goal because of their low materials and processing costs. Unfortunately the materials quality and resulting energy conversion efficiencies of such cells are still substantially lower than crystalline, wafer based cells. This is a direct result of the large mismatch between electronic and photonic length scales in these devices; the absorption depth of light in Si is significantly longer than the electronic (minority carrier) diffusion length in deposited thin film materials for photon energies close to the band gap. As a result, charge extraction from optically thick cells is challenging due to carrier recombination in the bulk of the semiconductor. If light absorption could be improved in ultra thin layers of active material it would lead directly to lower recombination currents, higher open circuit voltages, and higher conversion efficiencies. Conventional, planar anti reflection (AR) coatings do not provide high transmission efficiencies over the entire solar spectrum and do not enable effective light trapping to increase absorption. Light trapping schemes using diffusely scattering surface textures were first suggested in the 1980s and are by now fairly well understood. Texturing surfaces of thin film cells is not ideal as it leads to enhanced surface recombination. For this reason, some interesting alternative trapping configurations have been proposed that utilize structuring at length scales orders of magnitude larger than the cell thickness. More than a decade ago, it was first proposed to use the unique optical properties of metallic (i.e. plasmonic) structures to boost the efficiency of PV cells; those metallic nanostructures exhibit easily accessible collective electron oscillations known as surface plasmons. Surface plasmon excitations enable unparalleled light concentration and trapping. Since these pioneering efforts, plasmonics has also been used to enable new photodetector designs that exploit lateral and in depth light concentration to increase their signal to noise ratio and speed in the visible, near IR, and mid IR wavelength ranges. Recently, the use of metallic nanostructures for PV has received renewed attention with the availability of new nanofabrication tools and the growing understanding of their optical properties provided by the burgeoning field of plasmonics. In different cell designs both near field light concentration close to the individual particle resonance and effective light trapping by nanometallics have been explored. Experimentally, high peak enhancements in the tens of percent range at specific wavelengths and overall efficiency enhancements of 40% 8.3% and 8% have been achieved with the use of plasmonic structures for cells employing organics, a Si, and GaAs, respectively. Separate efforts have focused on increasing the more omni directional absorption characteristics for solar tracking and operation in diffuse sunlight. These results are very promising, although no detailed comparisons have yet been made to cells employing alternative light trapping technologies. Moreover, there is a clear need for effective optimization strategies that lead to broadband absorption enhancements over the entire solar spectrum. This type of optimization for nanostructured solar cells is now within the realm of possibilities; the recent advances in full field electromagnetic simulations and computer hardware have resulted in the development of extremely accurate and robust optimization tools that are now commonly used by the PV community. In this paper, we illustrate a straightforward and physically intuitive procedure to optimize the net overall absorption of a thin film Si solar cell over the entire solar spectrum; this simultaneously takes advantage of 1) the high near fields surrounding the nanostructures close to their surface plasmon C O M M U N IC A TI O N www.advmat.de
author_names: Ragip A Pala

Justin S White

Edward S Barnard

John S Q Liu

Mark L Brongersma
title: Design of Plasmonic Thin Film Solar Cells with Broadband Absorption Enhancements
year: 2009

abstract: Airfoil broadband trailing edge noise is reduced by modification of the trailing edge geometry. A brush made of a single row of flexible polypropylene fibers is integrated in the trailing edge of a cambered airfoil. Far field acoustic measurements show a noise reduction potential reaching 3 dB on a wide frequency range. Due to high curvature of the incident flow, a secondary acoustic source partly masks the trailing edge noise reduction. Hot wire correlation measurements in the very near wake of the airfoil show that longitudinal as well as transversal length scales are affected by the brush. Span wise coherence length of boundary layer eddies falls off by 25 in the presence of a brush in the adequate frequency range, possibly explaining a 1.3 dB contribution to the noise reduction mechanism. Boundary layer turbulence exhibits a preferred coherence length l y v on a wide frequency range. l y v /d 2, is considered a proper brush design law, d being the diameter of the brush.
author_names: Arthur Finez

Emmanuel Jondeau

Michel Roger

Umr Cnrs

Marc C Jacob
title: Broadband Noise Reduction With Trailing Edge Brushes
year: 2010

abstract: Integrated optical modulators with high modulation speed, small footprint and large optical bandwidth are poised to be the enabling devices for on chip optical interconnects. Semiconductor modulators have therefore been heavily researched over the past few years. However, the device footprint of silicon based modulators is of the order of millimetres, owing to its weak electro optical properties. Germanium and compound semiconductors, on the other hand, face the major challenge of integration with existing silicon electronics and photonics platforms. Integrating silicon modulators with high quality factor optical resonators increases the modulation strength, but these devices suffer from intrinsic narrow bandwidth and require sophisticated optical design; they also have stringent fabrication requirements and limited temperature tolerances. Finding a complementary metal oxide semiconductor (CMOS) compatible material with adequate modulation speed and strength has therefore become a task of not only scientific interest, but also industrial importance. Here we experimentally demonstrate a broadband, high speed, waveguide integrated electroabsorption modulator based on monolayer graphene. By electrically tuning the Fermi level of the graphene sheet, we demonstrate modulation of the guided light at frequencies over 1 GHz, together with a broad operation spectrum that ranges from 1.35 to 1.6 um under ambient conditions. The high modulation efficiency of graphene results in an active device area of merely 25 um2, which is among the smallest to date. This graphene based optical modulation mechanism, with combined advantages of compact footprint, low operation voltage and ultrafast modulation speed across a broad range of wavelengths, can enable novel architectures for on chip optical communications.
author_names: Ming Liu

Xiaobo Yin

Erick Ulin-Avila

Baisong Geng

Thomas Zentgraf

Long Ju

Feng Wang

Xiang Zhang
title: A graphene based broadband optical modulator
venue: Nature
year: 2011

abstract: Broadband noise with profound low frequency profile is prevalent and difficult to be controlled mechanically. This study demonstrates effective broadband sound absorption by reducing the mechanical reactance of a loudspeaker using a shunt circuit through electro mechanical coupling, which induces reactance with different signs from that of loudspeaker. An RLC shunt circuit is connected to the moving coil to provide an electrically induced mechanical impedance which counters the cavity stiffness at low frequencies and reduces the system inertia above the resonance frequency. A sound absorption coefficient well above 0.5 is demonstrated across frequencies between 150 and 1200 Hz. The performance of the proposed device is superior to existing passive absorbers of the same depth (60 mm) which has lower frequency limits of around 300 Hz. A passive noise absorber is further proposed by paralleling a micro perforated panel with shunted loudspeaker which shows potentials in absorbing band limit impulse noise.
author_names: Yumin Zhang

Yum Ji Chan

Lixi Huang
title: Thin broadband noise absorption through acoustic reactance control by electro mechanical coupling without sensor.
venue: The Journal of the Acoustical Society of America
year: 2014

abstract: Noise random disturbances of signals poses a fundamental problem for information processing and affects all aspects of nervous system function. However, the nature, amount and impact of noise in the nervous system have only recently been addressed in a quantitative manner. Experimental and computational methods have shown that multiple noise sources contribute to cellular and behavioural trial to trial variability. We review the sources of noise in the nervous system, from the molecular to the behavioural level, and show how noise contributes to trial to trial variability. We highlight how noise affects neuronal networks and the principles the nervous system applies to counter detrimental effects of noise, and briefly discuss noise's potential benefits.
author_names: A Faisal

Luc P J Selen

Daniel M Wolpert
title: Noise in the nervous system
venue: Nature Reviews Neuroscience
year: 2008

abstract: A Review of Materials Science. Vacuum Science and Technology. Physical Vapor Deposition. Chemical Vapor Deposition. Film Formation and Structure. Characterization of Thin Films. Epitaxy. Interdiffusion and Reactions in Thin Films. Mechanical Properties of Thin Films. Electrical and Magnetic Properties of Thin Films. Optical Properties of Thin Films. Metallurgical and Protective Coatings. Modification of Surfaces and Films. Emerging Thin Film Materials and Applications. Appendixes. Index.
author_names: Milton Ohring
title: The Materials Science of Thin Films
year: 1991

abstract: Passive materials provide sound absorption in a frequency band whose low frequency limit depends on its thickness. In general, sound absorption in the lower frequency range requires such bulky materials that the passive solution becomes impractical, except for special installations, such as anechoic chambers. On the other hand, active systems allow control of the input impedance of multilayer absorbers, affording low frequency absorption. When the properties of the passive system are properly combined with the active controller, it is possible to design broadband sound absorbers with an absorption coefficient close to unity from 100 Hz. These systems are named hybrid passive active absorbers. This paper describes the implementation of such a hybrid absorber, using a microperforated panel (MPP) as the passive material.
author_names: Pedro Cobo

A Fernandez
title: Hybrid Passive Active Absorption of Broadband Noise Using MPPs
year: 2006

abstract: The interest in mid infrared technologies surrounds plenty of important optoelectronic applications ranging from optical communications, biomedical imaging to night vision cameras, and so on. Although narrow bandgap semiconductors, such as Mercury Cadmium Telluride and Indium Antimonide, and quantum superlattices based on inter subband transitions in wide bandgap semiconductors, have been employed for mid infrared applications, it remains a daunting challenge to search for other materials that possess suitable bandgaps in this wavelength range. Here, we demonstrate experimentally for the first time that two dimensional (2D) atomically thin PtSe2 has a variable bandgap in the mid infrared via layer and defect engineering. Here, we show that bilayer PtSe2 combined with defects modulation possesses strong light absorption in the mid infrared region, and we realize a mid infrared photoconductive detector operating in a broadband mid infrared range. Our results pave the way for atomically thin 2D noble metal dichalcogenides to be employed in high performance mid infrared optoelectronic devices.The mid infrared technologies are essential to various applications but suffer from limited materials with suitable bandgap. Here the authors demonstrate that two dimensional atomically thin PtSe2 with variable bandgaps in the mid infrared via layer and defect engineering is highly promising for mid infrared optoelectronics.
author_names: Xuechao Yu

Peng Yu

Di Wu

Bahadur Singh

Qingsheng Zeng

Hsin Lin

Wu Zhou

Junhao Lin

Kazu Suenaga

Zheng Liu

Qi Jie Wang
title: Atomically thin noble metal dichalcogenide: a broadband mid infrared semiconductor
venue: Nature Communications
year: 2018

abstract: THz science is developing rapidly in Europe as well as the rest of the world. There is a strong interest in the exploitation of optical technologies in the THz frequency range in virtually all fields of basic and applied sciences of physics, chemistry, biology as well as medicine. Commercial interest in this field has also been growing, spurred by the potential of THz tools in quality control and the biotechnology sector. We will review some contrast mechanisms, which form the basis for real world applications of THz technology, in particular in the fields of applied chemistry and biotechnology. Whereas narrow bandwidth THz technology may become important for, e.g. real time imaging at larger standoff distances, we will concentrate on broad bandwidth THz technologies for spectroscopic identification of various substances. It has recently been established that the 0.1 5 THz spectral range contains unique fingerprints of a very large number of crystalline materials, including explosives, illicit drugs as well as most other chemicals in powder form. Since many packaging materials are transparent to THz radiation this fundamental property of crystalline compounds allows remote (contact free) sensing combined with chemical recognition. On the other hand, the THz spectrum of amorphous systems, including aqueous solutions, contains very little information about the detailed composition of the system. However, under certain conditions it is still possible to learn a great deal about amorphous systems with broadband THz spectroscopy. Amorphous systems of great biotechnological importance include DNA and proteins, both in aqueous solution and as dried matter. We will discuss methods for THz science and technology to attack the very complex problems involved in the extraction of useful new information, which may be difficult, expensive, or impossible to obtain with other methods, from minute amounts of biomaterial.
author_names: Bernd M Fischer

Hanspeter Helm

Peter Uhd Jepsen
title: Chemical Recognition With Broadband THz Spectroscopy
venue: Proceedings of the IEEE
year: 2007

abstract: Fundamentals and Basic Terminology Introduction Noise Control Strategies Acoustic Field Variables Wave Equations Mean Square Quantities Energy Density Sound Density Sound Power Units Spectra Combining Sound Pressures Impedance Flow Resistance The Human Ear Brief Description of the Ear Mechanical Properties of the Central Partition Noise Induced Hearing Loss Subjective Response to Sound Pressure Level Instrumentation for Noise Measurement and Analysis Microphones Weighting Networks Sound Level Meters Classes of Sound Level Meter Sound Level Meter Calibration Noise Measurements Using Sound Level Meters Time Varying Sound Noise Level Measurement Data Loggers Personal Sound Exposure Meter Recording of Noise Spectrum Analysers Intensity Meter Energy Density Sensors Sound Source Localization Criteria Introduction Hearing Loss Hearing Damage Risk Hearing Damage Risk Criteria Implementing a Hearing Conservation Program Speech Interference Criteria Psychological Effects of Noise Ambient Noise Level Specification Environmental Noise Level Criteria Environmental Noise Level Surveys Sound Sources and Outdoor Sound Propagation Introduction Simple Source Dipole Source Quadruple Source (Far Field Approximation) Line Source Piston in an Infinite Baffle Incoherent Plane Radiator Directivity Reflection Effects Reflection and Transmission at a Plane/Two Media Interface Sound Propagation Outdoors, General Concepts Sound Power, its Use and Measurement Introduction Radiation Impedance Relation between Sound Power and Sound Pressure Radiation Field of a Sound Source Determination of Sound Power Using Intensity Measurements Determination of Sound Power Using Surface Vibration Measurements Some Uses of Sound Power Information Sound in Enclosed Spaces Introduction Low Frequencies Bound between Low Frequency and High Frequency Behavior High Frequencies, Statistical Analysis Transit Response Porous Sound Absorbers Panel Sound Absorbers Flat and Long Rooms Applications of Sound Absorption Auditorium Design Partitions, Enclosures and Barriers Introduction Sound Transmission through Partitions Noise Reduction vs Transmission Loss Enclosures Barriers Pipe Lagging Muffling Devices Introduction Measures of Performance Diffusers as Muffling Devices Classification of Muffling Devices Acoustic Impedance Lumped Element Devices Reactive Devices Lined Ducts Duct Bends or Elbows Unlined Ducts Effect of Duct End Reflections Duct Break Out Noise Line Plenum Attenuator Water Injection Directivity of Exhaust Duct Vibration Control Introduction Vibration Isolation Types of Isolators Vibration Absorbers Vibration Neutralizers Vibration Measurement Damping of Vibrating Surfaces Measurement of Damping Sound Power and Sound Pressure Level Estimation Procedures Introduction Fan Noise Air Compressors Compressors for Chillers and Refrigeration Units Cooling Towers Pumps Jets Control Valves Pipe Flow Boilers Turbines Diesel and Gas Driven Engines Furnace Noise Electric Motors Generators Transformers Gears Transportation Noise Practical Numerical Acoustics Introduction Low Frequency Region High Frequency Region: Statistical Energy ANalysis
author_names: David Alan Bies

Colin H Hansen
title: ENGINEERING NOISE CONTROL: Theory and Practice
year: 1988