Control of the deposition ratio of Bi2Te3 and Sb2Te3 in a vacuum evaporator for fabrication of Peltier elements

This article reports the main problem and the corresponding solution of the co-evaporation of Bi2Te3 and Sb2Te3 films for the fabrication of Peltier elements. This main problem consists in the control of the deposition rates of the two elements: Bi or Sb and Te, which have very different vapor pressures. The control of the deposition ratio was achieved by means of a PID controller, which permitted the fabrication of thin-film Peltier elements that produce a temperature gradient in the order of 2C between their hot and cold junctions, when measured at free air conditions.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/18142/2004.Agencia de Inovação (MPYROM)

On-chip array of thermoelectric peltier microcoolers

This article reports on the theoretical modelling, the Finite Element Modelling (FEM) simulation, the fabrication process and preliminary results of the first on-chip thermoelectric microcooler array (64 pixels arranged in a 8×8 array), with each pixel independently controlled. This microcooler array uses co-evaporated V–VI compounds of Bi2Te3 and Sb2Te3 as thermoelectric layers, and can be fabricated using planar thin-film technology, lithography and wet etching, on top of a silicon wafer where the CMOS electronic circuits were previously made

An experimental evaluation of the incidence of fitness-function/search-algorithm combinations on the classification performance of myoelectric control systems with iPCA tuning

BACKGROUND: The information of electromyographic signals can be used by Myoelectric Control Systems (MCSs) to actuate prostheses. These devices allow the performing of movements that cannot be carried out by persons with amputated limbs. The state of the art in the development of MCSs is based on the use of individual principal component analysis (iPCA) as a stage of pre-processing of the classifiers. The iPCA pre-processing implies an optimization stage which has not yet been deeply explored. METHODS: The present study considers two factors in the iPCA stage: namely A (the fitness function), and B (the search algorithm). The A factor comprises two levels, namely A(1) (the classification error) and A(2) (the correlation factor). Otherwise, the B factor has four levels, specifically B(1) (the Sequential Forward Selection, SFS), B(2) (the Sequential Floating Forward Selection, SFFS), B(3) (Artificial Bee Colony, ABC), and B(4) (Particle Swarm Optimization, PSO). This work evaluates the incidence of each one of the eight possible combinations between A and B factors over the classification error of the MCS. RESULTS: A two factor ANOVA was performed on the computed classification errors and determined that: (1) the interactive effects over the classification error are not significative (F(0.01,3,72) = 4.0659 > f( AB ) = 0.09), (2) the levels of factor A have significative effects on the classification error (F(0.02,1,72) = 5.0162 < f( A ) = 6.56), and (3) the levels of factor B over the classification error are not significative (F(0.01,3,72) = 4.0659 > f( B ) = 0.08). CONCLUSIONS: Considering the classification performance we found a superiority of using the factor A(2) in combination with any of the levels of factor B. With respect to the time performance the analysis suggests that the PSO algorithm is at least 14 percent better than its best competitor. The latter behavior has been observed for a particular configuration set of parameters in the search algorithms. Future works will investigate the effect of these parameters in the classification performance, such as length of the reduced size vector, number of particles and bees used during optimal search, the cognitive parameters in the PSO algorithm as well as the limit of cycles to improve a solution in the ABC algorithm

Thermoelectric micro converters for cooling and energy scavenging systems

This paper describes the fabrication process of thermoelectric microconverters, based on n-type bismuth telluride (Bi2Te3) and p-type antimony telluride (Sb2Te3) thin films. Materials are fabricated by thermal co-evaporation with thermoelectric properties comparable to those reported for the same materials in bulk form (used in conventional macro-scale Peltier modules). Absolute value of Seebeck coefficient in the range 150-250 μVK-1 and in-plane electrical resistivity of 7-15 μΩm were obtained. Influence of fabrication parameters on thermoelectric properties is reported. The films were then patterned by photolithography and wet-etching techniques, using HNO3/HCl based etchants. Influence of composition and concentration of etchants in the process is reported. A microcooler was fabricated and analysed by infrared thermal imag

On chip thermoelectric microcoolers

The present work reports the fabrication and characterization of a planar Peltier microcooler on a flexible substrate. The microcooler was fabricated on flexible Kapton© polyimide substrate, 12 µm in thickness, using Bi2Te3 and Sb2Te3 thermoelectric elements deposited by thermal co-evaporation. The cold area of the device is cooled using four pairs of thermoelectric elements, connected in series with aluminum/nickel contacts. Flexible substrates add uncommon mechanical properties to the composite filmsubstrate and enable their integration with many novel types of electronic devices. Films were deposited by coevaporation of Bismuth and Tellurium or Antimony and Tellurium to obtain Bi2Te3 or Sb2Te3 compounds, respectively. The performance of Peltier microcooler is analyzed by infrared image microscopy, on still-air and under vacuum conditions, and the temperature difference between the cold side and the hot side of the device is recorded and it’s comparable with literature available for Peltier microcoolers on rigid substrates.Agencia de Inovação (MPYROM) and Portuguese Foundation for Science and Technology (SFRH/BD/18142/2004)

Fabrication of flexible thermoelectric microcoolers using planar thin-film technologies

The present work reports on the fabrication and characterization of a planar Peltier cooler on a flexible substrate. The device was fabricated on a 12 νm thick Kapton(c) polyimide substrate using Bi2Te3 and Sb2Te3 thermoelectric elements deposited by thermal co-evaporation. The cold area of the device is cooled with four thermoelectric junctions, connected in series using metal contacts. Plastic substrates add uncommon mechanical properties to the composite film-substrate and enable integration with novel types of flexible electronic devices. Films were deposited by co-evaporation of tellurium and bismuth or antimony to obtain Bi2Te3 or Sb2Te3, respectively. Patterning of the thermoelectric materials using lift-off and wet-etching techniques was studied and compared. The performance of the Peltier microcooler was analysed by infrared image microscopy, on still-air and under vacuum conditions, and a maximum temperature difference of 5 °C was measured between the cold and the hot sides of the device. © 2007 IOP Publishing Ltd

Anti-de Sitter curvature radius constrained by quasars in brane-world scenarios

This paper is intended to investigate the luminosity due to accretion of gas in supermassive black holes (SMBHs) in the center of quasars, using a brane-world scenario naturally endowed with extra dimensions, whereon theories formulated introduce corrections in the field equations at high energies. SMBHs possess the necessary highly energetic environment for the introduction of these corrections, which are shown to produce small deviations in all SMBH properties and, consequentely, corrections in the accretion theory that supports quasars radiative processes. The radiative flux observed from quasars indicates these deviations, from which the magnitude of the AdS$_5$ bulk curvature radius, and consequently the extra dimension compactification radius is estimated.Comment: 11 pages, RevTeX, Eq.(2) and (3) expanded, and comments thereon update