The influence of a galvanomagnetic stationary vortex current on the magneto-thermoelectric figure of merit of graded inhomogeneous bismuth-antimony alloys

We have studied the influence of a longitudinal graded inhomogeneity in crystals of bismuth-antimony solid solutions on their effective magnetoresistance, which is one of the parameters determining the efficiency (thermoelectric figure of merit) of a thermoelement operating in the presence of a transverse magnetic field. It is shown that, in a thermoelement operating under the action of an external magnetic field, the negative effect of the crystal inhomogeneity caused by the temperature gradient can be compensated for by its graded composition so as to provide for an increase in the thermoelectric figure of merit of the thermoelement.     

Efficiency of electrooptic spin-to-orbital angular momentum conversion in crystals

We introduce a figure of merit for the photon spin-to-orbital angular momentum conversion via electrooptic (EO) Pockels effect in single crystals. Relations for the effective EO coefficients are derived for different symmetry groups. We show that Bi₁₂TiO₂₀ crystals reveal the highest figure of merit among well studied crystalline EO materials. The efficiency of the spin-to-orbital angular momentum conversion is measured experimentally for a number of single crystals.     

稀土改性的钨酸铅晶体声光调制器

报导了一种基于稀土改性的钨酸铅晶体PbWO4 RE^3 (RE=La,Y或Cd)的声光调制器。根据实测的钨酸铅晶体中的声速数据,估算了PbWO4单晶的声光优值。结果表明其声光优值与目前常用的钼酸铅晶体十分接近。但是,PbWO4 RE^3 在光谱紫外区的截止波长为330nm使它可以在更短的波段工作,并具有抗紫外辐照的能力。该器件的中心频率为80MHz,带宽20MHz,在1W驱动功率下,一级衍射光的衍射效率为85％(He-cd激光,442nm)。     

Thermoelectric properties of carbon nanotube/silicone rubber composites

ABSTRACT

In this paper, we have studied the relevant physical quantities to the figure of merit of carbon nanotube (CNT)/polydimethylsiloxane composites at different loadings, and found that with increasing the CNT loadings, the electrical conductivity jumps several orders in magnitude at ‘threshold’, followed by a saturated plateau, and the Seebeck coefficient decreases by a small margin, and the thermal conductivity increases somewhat. According to the formula of the figure of merit, it is found that higher loading composites display a larger figure of merit. We hope the present study provides a new path to high-performance flexible thermoelectric materials.     

Efficiency of capturing a phase image using cone-beam x-ray Talbot interferometry

We assesses the efficiency of x-ray Talbot interferometry (XTI), a technique based on the Talbot effect for measuring a wavefront gradient, in terms of how quickly it can capture a high-quality phase image with a large signal-to-noise ratio for a given incident photon number. Photon statistics cause errors in the phase of the moiré fringes and impose a detection limit on the wavefront gradient. The relation between the incident photon number and the detection limit is determined, and a figure of merit of XTI for a monochromatic cone beam is then defined. The dependence of the figure of merit on optical system parameters, such as grating pitch and position, is then discussed. The effects of varying the pattern height and linewidth of the second grating are shown for rectangular and trapezoidal teeth. Finally, we show how to design a practical cone-beam Talbot interferometer for certain boundary conditions.     

High performance functionally graded and segmented Bi2Te3-based materials for thermoelectric power generation

Bi₂Te₃-based materials possess a figure of merit maximum over a narrow temperature range. When used in a generating mode over a large temperature difference the material operates at a substantially lower overall figure of merit than its maximum value. The conversion efficiency of a thermoelectric generator for low temperature waste heat recovery can be increased by employing functionally graded or segmented materials. In this work functionally graded p-type Bi₂Te₃-based thermoelectric materials have been prepared from melt by the Bridgman method using double doping technique. Segmented n-type thermoelement has been fabricated by joining two Bi₂Te₃-based materials with figure of merit maximum at 270 K and 380 K. The thermoelectric properties of the materials and a thermocouple comprised of p-type functionally graded and n-type segmented materials have been measured over a temperature range 200 K–450 K. The material efficiency of the thermocouple over the temperature gradient 223 K–423 K is estimated to be 10% compared with 8.8% for a standard Bi₂Te₃-based materials.     

Piezo-optic, photoelastic, and acousto-optic properties of SrB4O7 crystals

On the basis of studies of the piezo-optic effect, it has been shown that SrB(4)O(7) crystals can be used as efficient acousto-optic materials in the vacuum ultraviolet spectral range. The full matrices of piezo-optic and photoelastic coefficients have been experimentally obtained for these crystals. The acousto-optic figure of merit and the diffraction efficiency have been estimated for both the visible and deep ultraviolet spectral ranges.     

Accounting for maintenance in a computer memory reliability prediction model

This paper reviews the benefit of periodic maintenance for improving the reliability of computer memory protected by error detection and correction (EDAC), and presents a new memory reliability model that accounts for such maintenance. Mean time to failure (MTTF) has been the traditional figure of merit for assessing the benefit of memory maintenance. This paper proposes failure probability calculated at maintenance intervals as a more meaningful figure of merit for periodically maintained systems and presents examples using the new model.     

Growth and characterization of 300-µm thick bi-substituted gadolinium Iron garnet films for an optical isolator

A 300-µmm thick magnetooptic Bi-substituted gadolinium iron garnet film grown by liquid-phase epitaxy shows large magnetooptic figure of merit of 270 deg/dB at 1.3-µmm wavelength (Faraday rotation coefficient: - 1530 deg/cm, and optical absorption coefficient: 1.3 cm^-1) and is a promising material for a "vertical type" optical isolator at 1.3-µmm. At 0.8-µm the figure of merit of 23 deg/dB is obtained.     

Pyroelectric energy conversion: optimization principles

In the framework of microgenerators, we present in this paper the key points for energy harvesting from temperature using ferroelectric materials. Thermoelectric devices profit from temperature spatial gradients, whereas ferroelectric materials require temporal fluctuation of temperature, thus leading to different applications targets. Ferroelectric materials may harvest perfectly the available thermal energy whatever the materials properties (limited by Carnot conversion efficiency) whereas thermoelectric material's efficiency is limited by materials properties (ZT figure of merit). However, it is shown that the necessary electric fields for Carnot cycles are far beyond the breakdown limit of bulk ferroelectric materials. Thin films may be an excellent solution for rising up to ultra-high electric fields and outstanding efficiency. Different thermodynamic cycles are presented in the paper: principles, advantages, and drawbacks. Using the Carnot cycle, the harvested energy would be independent of materials properties. However, using more realistic cycles, the energy conversion effectiveness remains dependent on the materials properties as discussed in the paper. A particular coupling factor is defined to quantify and check the effectiveness of pyroelectric energy harvesting. It is defined similarly to an electromechanical coupling factor as k2=p2theta0/(epsilontheta33cE), where p, theta0, epsilontheta33, cE are pyroelectric coefficient, maximum working temperature, dielectric permittivity, and specific heat, respectively. The importance of the electrothermal coupling factor is shown and discussed as an energy harvesting figure of merit. It gives the effectiveness of all techniques of energy harvesting (except the Carnot cycle). It is finally shown that we could reach very high efficiency using 1110.75Pb(Mg1/3Nb2/3)-0.25PbTiO3 single crystals and synchronized switch harvesting on inductor (almost 50% of Carnot efficiency). Finally, practical implementation key points of pyroelectric energy harvesting are presented showing that the different thermodynamic cycles are feasible and potentially effective, even compared to thermoelectric devices.     

Effect of nonstoichiometry on the thermoelectric properties of Tl<Subscript>4</Subscript>TiS<Subscript>4</Subscript> crystals

Stoichiometric (1), Tl₂S-enriched (2), and TiS₂-enriched (3) Tl₄TiS₄ crystals (with deviations from stoichiometry within the homogeneity range of the ternary compound) have been grown by the Bridgman method, and their thermoelectric properties have been studied by the Harman technique. All of the crystals have a high thermoelectric figure of merit. The highest figure of merit is offered by crystal 1 at positive thermoelectric powers and by crystal 3 at negative thermoelectric powers. The thermoelectric properties of crystal 2 were found to irreversibly degrade over time.     

Preparation and Thermoelectric Properties of Polycrystalline Si<Subscript>0.4</Subscript>Ge<Subscript>0.6</Subscript>

Polycrystalline Si_0.4Ge_0.6 was prepared by electron-beam float-zone melting, and its thermoelectric properties were studied in the intrinsic region. The samples were found to be p-type, with a room-temperature resistivity from 5 to 20 Ωcm. The thermoelectric figure of merit of the alloy in the intrinsic region (500–1000 K) is lower than that of heavily doped alloys. Above 1000 K, a sharp rise in its thermoelectric figure of merit would be expected.     

梯度热电材料的研究进展

热电材料梯度化是在保证各组分单一材料的热电性能的基础上,拓宽其应用温度范围,使各组分材料都能工作在最佳温区,以确保热电材料在一定的工作温度范围内具有较高的ZT值,保证其高的热电转换效率.介绍了热电材料的研究基础及其梯度化设计,对梯度热电材料在国内外的研究进展进行了综述并对未来的研究趋势进行了展望.     

Epitaxially grown Bi-substituted iron garnet films for magneto-optic devices

The growth conditions and magnetooptical properties of films of Bi-substituted iron garnets are described. The chemical composition of TmBiFe-Ga garnet films grown from a PbO,B2O3flux has been determined using the radiotracer technique of chemical analysis. The maximum value of the figure of merit (Faraday rotation per unit optical attenuation) found for these films is 2.5 deg/dB at 560 nm. Annealing experiments show that the lead incorporated in these films does not appreciably influence the optical absorption. Using a flux of Bi2O3,MeO2(with Me = Si,Ce), Bi-substituted iron garnet films have been grown. For (TmBiFeGa) garnet films a value of the figure of merit of 3.5 deg/dB at 560 nm is obtained. The Faraday rotation and the optical absorption are measured in the visible for (YBiFeGa)8O12films grown on a large lattice constant substrate. The figure of merit at 560 nm was found to be 4.7 deg/dB.     

制备工艺对n型Bi_2Te_3基材料热电性能和抗压强度的影响

以商用区熔(ZM)n型Bi2Te3基材料为原料,采用简单研磨结合放电等离子烧结技术(ZM+SPS)和熔体旋甩(MS)结合放电等离子烧结技术(MS+SPS)制备了n型Bi2Te3基块体热电材料.对三种不同工艺制备出样品的微结构、热电性能和力学性能进行了研究.FESEM微结构表征结果表明:区熔样品的晶粒粗大,有较强的取向性;经SPS烧结后,晶粒细化,取向性大为降低;而区熔样品经MS+SPS后,晶粒得到进一步细化,且没有明显的取向性.对三组样品进行的热电性能和抗压强度测试,结果表明:区熔原料最大ZT值为0.72(430K),抗压强度仅为40MPa;经SPS后,样品的最大ZT值为0.68(440K),抗压强度为110MPa,相比区熔样品提高了175%;MS+SPS样品的最大ZT值为0.96(320K),其室温ZT值相比区熔样品提高了64%,抗压强度相比区熔样品提高了400%,达到200MPa.     

液闪测量3H活度TDCR与ESCR法的比较

基于TDCR与ESCR两种不同的液体闪烁测量方法,使用两台液体闪烁计数器分别测量3H系列猝灭源,探测效率均随着猝灭程度的增加而降低,TDCR方法具有较高的探测效率,且测量值的偏差总体较小;采用ESCR方法测量猝灭指数较大的3H样品时,宜提前基于所用闪烁液的体积对3H的优值因子进行调试,并使用多组低测量效率的猝灭标准源来拟合猝灭曲线。     

Multicriteria optimality for iterative encoding of computer-generated holograms

We propose a new multicriteria method for the determination of computer-generated holograms (CGH's). For this purpose, the direct binary search (DBS) algorithm for computing CGH's has been modified to converge on a new error function that defines the optimal trade-off among different criteria. This approach allows us to control the trade-off between the amplitude error and the diffraction efficiency and to provide a rigorous figure of merit. Comparisons among different encoding methods show that the best results are obtained with a modified version of the DBS method combined with the iterative Fourier transform algorithm.     

Exo-reversible staging of coolers in series and in parallel

Serial and parallel staging of exo-reversible coolers are formulated, analyzed and compared. The parallel staging includes an extensive parameter which is the proportion of combined stages. This extensive free parameter affects the intensive factors of specific power and figure of merit. Serial staging reduces the 1st Law efficiency and parallel staging improves the 2nd Law efficiency. Comparison of a parallel with a serial staging under common cooling capacity and cooling range, shows that it is always possible to find a parallel arrangement of lower specific power and more compact. Some results are demonstrated on staging of Joule-Thomson cryocoolers (below and above the Joule-Thomson inversion temperature).     

热电材料新进展

本文评述了热电材料研究的最新发展，指出它在制冷技术和能源工程上的广阔应用前景，系统地分析了影响品质因子提高的各种因素，指出了提高品质因子的一些可能途径。     

Precision Measurement of Antenna System Noise Using Radio Stars

This paper reviews the National Bureau of Standards (NBS) preision noise measurements program for antenna systems which have been made using Cassiopeia A and the moon. The Earth Terminal Measurement System (ETMS) was developed by NBS to make measurements of figure of merit (G/T), and the noise equivalent flux (NEF). The accuracy of the noise measurements are, typically, between 5 and 15 percent for systems with antenna gains between 51 and 65 dB and frequencies between 1 and 10 GHz. Key words?antenna gain; antenna half-power beamwidth; atmospheric loss; Cassiopeia A; earth terminal measurement system; figure of merit; moon; noise equivalent flux; noise measurement; radio stars; satellite communication.