Browsing by Subject "Joule heating"

Now showing 1 - 4 of 4

Open Access
Analytic thermal modeling for dc-to-midrange modulation frequency responses of thin-film high-Tc superconductive edge-transition bolometers
(Optical Society of America, 2001) Fardmanesh, M.
Thin-film superconductive edge-transition bolometers are modeled with a one-dimensional analytic thermal model with joule heating, film and substrate materials, and the physical interface effects taken into consideration. The results from the model agree well with the experimental results of samples made of large-meander-line Yba2Cu3O7-x films on crystalline SrTiO3, LaAlO3, and MgO substrates up to 100 kHz, the limits of the experimental setup. Compared with the results of the SrTiO3 substrate samples, the results from the model of the LaAlO3 and the MgO substrate samples deviate slightly from the measured values at very low modulation frequencies (below ∼10 Hz). The deviation increases for higher thermal-conductive substrate materials. When the model was used, the substrate absorption and the thermal parameters of the devices could also be investigated. © 2001 Optical Society of America.
Open Access
DC characteristics of patterned YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconducting thin-film bolometers: artifacts related to Joule heating, ambient pressure, and microstructure
(Institute of Electrical and Electronics Engineers, 1998-06) Fardmanesh, M.; Scoles, K.; Rothwarf, A.
Joule heating due to the bias current and resistance of the material in patterned YBa2Cu3O7-x superconducting films on 250-500-mu m-thick MgO, LaAlO3, and SrTiO3 crystalline substrates, results in a number of effects: 1) a temperature rise in the film with respect to the measured temperature at the bottom of the substrate; 2) a possible thermal runaway, which may be local or uniformly distributed in the film, depending upon the dimensions of the superconducting pattern relative to that of the substrate; 3) an apparently sharper normal-to-superconducting transition in the measure R versus T curve; and 4) decrease of T-c to 60 K (Delta T-x > 20 K) after being subjected to high-bias currents j similar to 10(5) A/cm(2) under vacuum, with recovery of T-c after exposure to room atmosphere. The magnitude of R at Tc-onset is found to be dependent on bias current in granular samples, with a lower R at currents higher than some on-set value. The slope of R versus T in the transition region in our granular samples is found to be lower at higher bias currents, since the widening of the transition overcomes the shift caused by the Joule heating. These various phenomena impact the responsivity of bolometers made from these films, as well as the predictions of possible attainable responsivity and speculations of mechanisms occurring in the films. In particular, misinterpretation of the Joule heating sharpening of the R versus T curve has led to predictions of responsivities over one order of magnitude higher than are justified, and shifts in properties of the films due to heating have been misinterpreted as nonequilibrium responses of the films.
Open Access
Modeling of Joule heating and convective cooling in a thick-walled micro-tube
(Elsevier Masson, 2017) Cole, K.D.; Çetin B.
The heating of a fluid in a metallic micro-tube can be realized at the inlet and/or within a certain section of micro-scale heat and fluid flow devices by using Joule heating which is a heat generation mechanism that occurs when an electric current is passed through the metallic wall. For the thermal analysis of fluid flow in an electrically heated micro-tube, the solution of conjugate heat transfer (to include effect of the axial conduction through the channel wall) together with Joule heating is required. An analytic solution is presented for conjugate heat transfer in an electrically-heated micro-tube in this study. The solution is obtained in the form of integrals by the method of Green's functions for the hydrodynamically fully-developed flow of a constant property fluid in a micro-tube. The current analytical model can predict the fluid temperature for a given wall thickness, wall material and applied voltage across the micro-tube. The effects of the wall thickness and the wall material on the normalized temperature distribution and the effectiveness parameter are discussed. The comparison of the normalized temperature for Joule heating and a spatially uniform heating is also presented. © 2017 Elsevier Masson SAS
Open Access
Response analysis and modeling of high temperature superconductor edge transition bolometers
(Springer, 2004) Fardmanesh, Mehdi; Narlikar, A. V.
One of the promising devices made of high temperature superconducting (HTSC) materials are edge transition bolometers. Since the discovery of high-temperature superconductors, many works have been focused on the application of these materials in different types of bolometers for the near to far infrared wavelength regime [l]-[9]. They can be used to detect electromagnetic radiation over the whole spectrum from x-ray to the far-infrared [1], [9]-[13]. The superconductor bolometers typically consist of patterned thin or thick superconducting films deposited on crystalline substrates such as MgO, SrTiO3, and LaA103. Their operation is based upon their steep drop in the resistance, R, at their transition temperature, Tc. The detector is typically held at a temperature close to the middle of the superconducting transition, where the dR/dT is maximum. When the detector is illuminated its temperature rises by an amount proportional to the input radiation power resulting in a ΔR. The response obtained by the above mechanism is the so called the bolometric, or equilibrium response, as opposed to typically faster non-bolometric or intrinsic response caused by other mechanisms such as direct depairing. A typical response of an YBCO sample versus temperature at low frequencies is shown in Figure 1.1.