Thermal Hysteresis in Thin-Film Platinum Resistance Thermometers

Thin-film platinum resistance thermometers (PRTs) are generally manufactured using the deposition of a thin platinum film on an alumina substrate and a laser-trimming method. Because of the strong adhesion between the platinum thin film and the alumina substrate, the PRTs inevitably have strain over the operating temperature range. This causes anomalies and instabilities in the resistance versus temperature characteristics (R?CT). The most prominent and observable effect of thermally induced strain is the thermal hysteresis in the R?CT characteristics. Thermal hysteresis is one of the main uncertainty factors in the calibration of industrial platinum resistance thermometers in laboratories. The thermal hysteresis for 30 thin-film PRTs was measured in the range of 0 °C to 500 °C in 100 °C steps. The thermal hysteresis was measured repeatedly using the same process, and the hysteresis decreased drastically with the repeated measurements. The thermal hysteresis was distributed from 16 mK to 156 mK for all sensors, and the lowest hysteresis was 1 mK to 11 mK in the test temperature range.     

Broadband magneto-dielectric response of particulate ferrite polymer composite at microwave frequencies

Complex permittivity and permeability of a magneto-dielectric composite material is studied using shielded, conductor-backed coplanar waveguide technique over X-band. The propagation constant over the test frequency range is evaluated using element-to-element correspondence of the ABCD matrix computed from scalar scattering parameters without modifying the coplanar structure. The mathematical formulation is verified by performing permittivity and permeability measurements for air over the range 9.5–12.045 GHz. Nano-sized nickel ferrite particles was synthesized using co-precipitation technique at different sintering temperatures. Average crystallite diameter is found to be 6.63–17.55 nm. The composite with 2% and 4% volume fractions is fabricated by reinforcing 6.63 nm ferrite particles in low density polyethylene matrix. The complex permittivity and permeability of the composite obtained from this method are also verified with cavity perturbation technique. The composite shows low saturation magnetization of 1.8745 emu/g and reduced hysteresis loss at room temperature.     

Temperature Dependent Magnetic, Dielectric Studies of Sm-Substituted Bulk BiFeO3

Bismuth ferrite- (BiFeO₃) ceramic is the most studied and attractive multiferroic material with low magnetization, moderate leakage current, and low polarization. Samarium substituted bulk BiFeO₃ prepared at low synthesis temperature ??600?°C by the sol?Cgel process. Room temperature X-ray diffraction (XRD) patterns confirmed the formation of perovskite structure Bi_0.9Sm_0.10FeO₃ (BSFO) phases. Present compositions possess high dielectric constant (????199) and low dielectric loss (tan????0.009) at room temperature for 100?Hz frequency. Room temperature dielectric permittivity and dielectric loss decreased with increasing frequency from 100?Hz to 10 MHz. As the temperature increased, an enormous increase in both dielectric permittivity and dielectric loss is observed at all frequency regions. Temperature dependent M?CH hysteresis loops were saturated. Spin glass-like ferromagnetic behavior is retained in M?CH hysteresis loops measured from the low temperature region and normal ferromagnetic behavior is observed in the high temperature region, both at room temperature and above ??350?K, 400?K, respectively. The origin of the ferromagnetic property in BSFO may be due to the presence of rare earth metal ions at the lattice sites of?BFO.     

Novel copolyester for a shape-memory biodegradable material in vivo

In this paper, we report the excellent shape-memory behavior of a novel Poly(glycol-glycerol-sebacate) (PGGS) terpolymer network for the first time. The polymer, with its crosslinked, three-dimensional networks acting as fixed phase, while its crystalline phase acting as a reversible one, meets the two necessary conditions to be the material that possesses shape-memory behavior, the response temperature of which is in the neighbourhood of human body temperature. The PGGS terpolymer, with a shape-memory ratio of above 99.5% and a recovery temperature of 37.5 °C, shows excellent shape-memory effect and a potential of being used directly in vivo.     

Thermal hysteresis in nonlinear media

One-dimensional thermal relaxation processes in media with nonlinear thermophysical properties are treated. Dynamic hysteresis is investigated theoretically in continuous and discontinuous nonstationary temperature fields. Boundary conditions are analyzed, for which a high-flow hysteresis process is realized. A quantitative estimate is given of irreversible variations in the material thermal state. Examples are given of constructing hysteresis branches. New properties are established for thermal shock waves propagating along the relaxing background.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 1, pp. 149–155, July, 1990.     

Normal ferroelectric to ferroelectric relaxor conversion in fluorinated polymers and the relaxor dynamics

To elucidate the molecular origin of the polarization dynamics in the ferroelectric relaxor poly(vinylidene fluoride—trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer, a broadband dielectric study was carried out in the frequency range from 0.01 Hz to 10 MHz and temperatures from −150°C to 120°C for the terpolymer and a normal ferroelectric P(VDF-TrFE) copolymer. The relaxation processes were also studied using dynamic mechanical analysis. It was shown that in the terpolymer, which was completely converted to a ferroelectric relaxor, there is no sign of the relaxation process associated with the ferroelectric-paraelectric transition which occurs in the P(VDF-TrFE) copolymer. In the copolymer, three additional relaxation processes have been observed. It was found that the relaxation process β_a, which was commonly believed to be associated with the glass transition in the amorphous phase, in fact, contains significant contribution from chain segment motions such as domain boundary motions in the crystalline region. In the temperature range studied, the terpolymer exhibits the latter three relaxation processes with the one (termed β_r) near the temperature range of β_a significantly enhanced. This is consistent with the observation that in conversion from the normal ferroelectric to a ferroelectric relaxor, the macro-polar domains are replaced by nano-polar-clusters and the boundary motions as well as the reorientation of these nano-clusters generate the high dielectric response. The experimental data also reveal a broad relaxation time distribution related for the β_r process whose distribution width increases with reduced temperature, reflecting the molecular level heterogeneity in the crystalline phase due to the random introduction of the CFE monomer in the otherwise ordered macro-polar domains. The random interaction among the nano-clusters as well as the presence of the random fields produces ferroelectric relaxor behavior in the terpolymer.     

Temperature dependence of ac-losses in multifilamentary Bi-2223 tapes between 4.2 K and Tc

The ac-losses of twisted multifilamentary Bi-2223/Ag tapes were measured in the temperature range between 4.2 K and the critical temperature T_c∼110 K. Stacks of tapes in perpendicular and in parallel field were investigated. The loss measurement is performed by the standard magnetisation technique, the absolute loss value is obtained by a calorimetric calibration measurement. For a fixed ac-field amplitude the energy loss per cycle Q is determined, at a given temperature, as a function of frequency f. The extrapolation to f→0 gives the hysteresis loss. Coupling losses are obtained from the slope of the loss curve Q(f) in the low frequency range ωτ?1. The measured total losses as a function of temperature show, at small field amplitudes, a minimum around 50 K. This is explained by the different temperature dependence of hysteresis and coupling losses. While coupling losses decrease with increasing temperature, hysteresis losses increase for field amplitudes below the penetration field. Coupling losses show a much weaker temperature dependence than the silver conductivity, which is explained by the existence of an interfacial resistance between filaments and silver matrix. Measured hysteresis losses were compared with available theoretical models and good agreement was found in parallel field.     

Solgel alumina coating for hollow waveguide delivery of CO(2) laser radiation

Solgel alumina films were prepared by use of the Yoldas process and were characterized optically and microstructurally. From nitrogen adsorption and electron microscopy, we determined that the material was highly porous, with pores and crystallites of the order of tens of nanometers in size. The infrared transmission and reflectance of the films were measured, and dispersion curves were calculated as a function of firing temperature by extracting the film optical constants from the reflectance and thickness data. The use of this material in a hollow waveguide structure for the delivery of CO(2) laser radiation for surgical applications is discussed. Calculated waveguide losses indicate that solgel-based alumina is a good candidate material for this application.     

Flexible polymeric rib waveguide with self-align couplers system

The authors report a polymeric based rib waveguide with U shape self-align fiber couplers system using a simple micromolding process with SU8 as a molding material and polydimethysiloxane as a waveguide material. The material is used for its good optical transparency, low surface tension, biocompatibility, and durability. Furthermore, the material is highly formable. This unique fabrication molding technique provides a means of keeping the material and manufacturing costs to a minimum. The self-align fiber couplers system also proves a fast and simple means of light coupling. The flexible nature of the waveguide material makes this process ideal for a potential wearable optical sensor.     

Hysteresis in Transport Critical-Current Measurements of Oxide Superconductors

We have investigated magnetic hysteresis in transport critical-current (I_c) measurements of Ag-matrix (Bi,Pb)₂Sr₂Ca₂Cu₃O_10–x (Bi-2223) and AgMg-matrix Bi₂Sr₂CaCu₂O_8+x (Bi-2212) tapes. The effect of magnetic hysteresis on the measured critical current of high temperature superconductors is a very important consideration for every measurement procedure that involves more than one sweep of magnetic field, changes in field angle, or changes in temperature at a given field. The existence of this hysteresis is well known; however, the implications for a measurement standard or interlaboratory comparisons are often ignored and the measurements are often made in the most expedient way. A key finding is that I_c at a given angle, determined by sweeping the angles in a given magnetic field, can be 17 % different from the I_c determined after the angle was fixed in zero field and the magnet then ramped to the given field. Which value is correct is addressed in the context that the proper sequence of measurement conditions reflects the application conditions. The hysteresis in angle-sweep and temperature-sweep data is related to the hysteresis observed when the field is swept up and down at constant angle and temperature. The necessity of heating a specimen to near its transition temperature to reset it to an initial state between measurements at different angles and temperatures is discussed.     

Dielectric properties of La-modified antiferroelectric PbZrO3 thin films

Lead zirconate is a room temperature antiferroelectric material, which exhibits double polarization hysteresis characteristic in the presence of external field. A transformation from antiferroelectric to paraelectric behavior through a ferroelectric phase has been exhibited upon addition of La-to pure lead zirconate thin films, which were confirmed from dielectric, hysteresis and pyroelectric and micro Raman analyses. Thin films of pure and La-modified lead zirconate were processed using A-site vacancy formula Pb_(l−1.5x)La_XZrO₃ by pulsed excimer laser ablation technique. Pyroelectric coefficient increased gradually from 55 to 190 μC cm⁻² K⁻¹ with the addition of 0 to 9 mole% of La to pure lead zirconate. The transition temperature has been reduced to room temperature (∼34 °C) with addition of a 9 mole% of La-to lead zirconate. Presence of antiferroelectricity in pure lead zirconate thin films is due to antiparallel shifts of Pb-ions in (110) direction and reduction of transition temperature is attributed to creation of A-site vacancies would have caused enhancing of ferro-and paraelectric behavior with La-addition.     

Impact of Waveguide Filling Material on Near-Field Microwave Inspection of Carbon-Loaded Composites

The advent of carbon loaded composite materials gave a boost to many industries. This is because of their light weight, durability and strength. As new structures utilizing carbon loaded composites are built, the need for a reliable nondestructive testing technique increases. A carbon-loaded composite testing poses a challenge to most nondestructive testing and evaluation (NDT&E) techniques. Microwave NDT&I techniques main challenge is the lossy nature of carbon, especially at high microwave frequencies. Lower frequencies penetrate deeper in carbon-loaded composites, however, to operate at lower frequencies the size of the waveguide probe increases significantly which degrades the resolution rapidly. Open-ended rectangular waveguide sensors filled with a dielectric material will be used to inspect carbon-loaded composites. The filling of the waveguide reduces the frequency of operation and keeps the small size of the waveguide (i.e. increases the penetration depth and maintains the resolution). However, varying the waveguide filling material dielectric properties will have an impact on the measurement parameters optimization process and consequently on the detection sensitivity. In this paper, the use of the waveguide filling material as an optimization parameter will be investigated. Carbon-loaded composites with disbonds will be inspected and the variation of the dielectric properties of the loading material of rectangular waveguide probes for carbon loaded composites inspection will be assessed.     

新型三元聚合物给体材料的合成及在有机太阳能电池中的应用

以吡咯并[3,4-c]吡咯二酮(DPP)为A单元,苯并[1,2-b∶4,5-b′]二噻吩(BDT)和萘为D单元,合成了一种新型2D/A型三元共轭聚合物太阳能电池给体材料(PDPP-BDT-NT),通过核磁共振氢谱(1 H NMR)对其结构进行了表征,通过热重分析、紫外-可见吸收光谱(UV-Vis)、循环伏安法对其热学性质、光物理性能及能级结构进行了研究。PDPP-BDT-NT具有较好的热稳定性,热分解的温度为401℃,有较宽的吸收光谱,可覆盖300~900nm,最高占据轨道(HOMO)能级为-5.35eV。以聚合物PDPP-BDT-NT为给体材料,PC60BM为受体材料,制备了一系列有机聚合物太阳能电池,在大气质量(AM)为1.5G,功率为100mW·cm-2模拟的太阳光照射下,有机聚合物太阳能电池的光电转化效率(PCE)可达2.09%。甲醇处理后,有机聚合物太阳能电池的PCE可达2.34%。     

偏转磁芯铁氧体材料的磁滞损耗分析

对偏转磁芯所采用的铁氧体材料的磁滞损耗特性进行了分析,得出了磁滞损耗功率与频率、磁通密度和温度的经验公式。对磁滞回线中涡流的影响进行了分析,得出在目前应用的偏转频率下,磁芯损耗中磁滞损耗占主要部分。根据经验公式,对计算磁滞损耗的方法和在计算温度分布中的应用进行了介绍。     

Investigation of phase transformations by in-situ neutron diffraction in a Co-Re-based high temperature alloy

In-situ neutron diffraction at high temperatures was used to investigate phase transformation in a Co-Re-based alloy. Stability of carbides and transformation of Co matrix from ε (hcp) to γ (fcc) phase were studied. The ε ? γ phase transformation exhibited a large hysteresis with temperature. The alloy has a complex microstructure with Cr₂₃C₆, TaC and σ phase stable over a wide temperature range. The hysteresis is the result of composition interplay between Co-matrix and other phases, e.g. Cr-carbide and σ. TaC is stable at high temperatures up to 1300 °C.     

Room Temperature Exchange Bias in Multifunctional Sb<Subscript>2</Subscript>FeO<Subscript>6</Subscript> Multiferroic

Sb₂FeO₆ was prepared and its crystal structure was examined using x-ray diffraction (XRD). From the latter, it was found that the former adopted the tetragonal structure with space group P42/mnm. Room temperature hysteresis loop (M- H) measurements clarified the evidence of exchange bias. Semiconducting-like behavior was predominant where the correlated barrier hopping is the principal mechanism. The gained results pushed us to classify the Sb₂FeO₆ as a type-I multiferroic material.     

Determination of PRT Hysteresis in the Temperature Range from −50 °C to 300 °C

This paper discusses the contribution of hysteresis to the measurement uncertainty of industrial platinum resistance thermometers (IPRTs). Hysteresis is one of the sources of uncertainty that has so far not been sufficiently researched and documented. The term hysteresis applies to any system that is path dependent; the output depends on the history of the input. In our case, thermal hysteresis results in different resistance values at the same temperature point, depending on whether the temperature was increasing or decreasing. The reason for such behavior is related to the construction of the thermometer (strain due to thermal expansion and contraction) and also to possible moisture inside the encapsulation. In the process of evaluation of the calibration and measurement capabilities (CMCs) of IPRTs within Working Group 8, the Consultative Committee for Thermometry (CCT WG8) concluded that the uncertainty due to hysteresis is not uniformly defined and not always added to the total uncertainty of the resistance thermometer under calibration. In order to estimate the uncertainty contribution due to the hysteresis and compare different procedures, resistance measurements were carried out on a number of IPRTs of different qualities and tolerance classes. The temperature span was between ?50 °C and 300 °C, which is the most frequent temperature range in the practical use of IPRTs. The hysteresis was then determined in different ways (change of resistance at the ice point and at the midpoint temperature according to the ASTM International Standard E644 and according to the new version of IEC Standard 60751), and a comparison of results was made.     

Fracture surface roughness in highly deformable polymers

The fracture surface roughness was determined for five highly deformable polymers (styrene-butadiene rubber, two ethylene-propylene rubbers, low density polyethylene and plasticized polyvinyl chloride) as a function of rate and temperature. The mechanical hysteresis for the same materials was also measured as a function of rate, temperature and strain amplitude. Although the surface roughness does not correlate with crack velocity, it does so uniquely with the effective hysteresis in the material surrounding the propagating crack. A simple physical explanation is advanced for the universal dependence of roughness on hysteresis in these materials.On leave of absence from the Bridgestone Tyre Company, Research Department, 2800-Ogawa Higashi-Machi, Kodairy-shi, Tokyo, Japan.     

Dielectric, magnetic and electrical properties of ZnFe2O4 ceramics

The polycrystalline sample of ZnFe₂O₄ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction studies of the compound showed the formation of a single-phase compound at room temperature. Studies of dielectric properties (ε_r, tan δ) of the above compound as a function of frequency in a wide temperature range show dielectric anomalies signifying existence of possible ferroelectric to paraelectric phase transition in the material. The confirmation of this assumption was made with observation of ferroelectric hysteresis loop at room temperature. Magnetic measurement exhibits anti-ferromagnetic nature of the sample. Studies of the zero-field cooled and the field-cooled magnetization in dc field provided the blocking temperature T_B. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between the microstructure (i.e., bulk, grain boundary, etc.) and electrical parameters of the material. Detailed studies of impedance parameters have provided an insight into the electrical properties and understanding of types of relaxation process in the material. The temperature variation of dc resistivity/conductivity exhibits negative temperature coefficient of resistance behaviour of the material. The frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.