Electrothermal Devices Research Articles

Direct Study of the Thermal Conductivity in Aluminum Nanowires

AbstractThermal conductivity and electrical resistivity of 1 μm long aluminum nanowires, 75, 100, and 150nm in width and 100nm thick, were measured at room temperature. The method consists of microfabricated electrothermal test devices and a model-based data processing approach using finite-element analysis (FEA). The electrical and thermal properties of the nanowires differ significantly from bulk values while electrical resistivity agrees well with theoretical prediction. Electron transport equation models, which adequately describe the resistivity data, consistently underestimate the thermal conductivity. Incorporating a phonon contribution of ˜ 21 W/m·K to the total thermal conductivity is found to accurately describe the measured values.

Electrothermal effects at the microscale and their consequences on system design

Electrothermal devices exhibit increasing secondary effects upon downscaling. These effects alter their temperature profiles and thermal energy distributions. Based on scaling laws, we show that the Thomson effect is increased over Joule heating as the structures are sized down. Thermal models are upgraded to take into account this secondary effect, and finite element simulations together with experimental runs validate them.

In-package MEMS-based thermal actuators for micro-assembly

The paper describes the first fabrication and experimental results in the on-going development of MEMS-based electrothermal actuation devices for lateral XY positioning of an optical fibre to a laser diode chip to improve their coupling efficiency and reduce the overall packaging cost. The deflection performance of bulk silicon U- and V-beam thermal actuators with and without fibre loading has been experimentally determined. This is a part of an investigation of the feasibility of an alternative method of performing micro-assembly tasks, i.e. by means of product-internal assembly functions.

Trapping of hydride forming elements within miniature electrothermal devices. Part 3. Investigation of collection of antimony and bismuth on a molybdenum foil strip following hydride generation

The interaction of stibine and bismuthine with a surface of bare and modified (Pt, Ir and Rh) molybdenum foil strips was investigated by atomic absorption spectrometry with a miniature hydrogen flame atomizer. Different trapping behavior of both analytes was observed contrary to selenium and arsenic hydrides. Maximum trapping efficiency of Sb and Bi is achieved at lower temperatures of 650–750 °C and 500–600 °C, respectively. Absence of hydrogen in argon does not affect trapping of these elements, whereas trapping of As and Se is feasible only in the presence of hydrogen. All used modifiers inhibit trapping of Bi and Sb when their amount exceeds 30 μg. Collected Sb is completely released at temperatures above 2200 °C, whereas a temperature of 1 200 °C is sufficient for vaporization of Bi. Aerodynamic conditions of the injected gas near the molybdenum surface play the same role in trapping both analytes as for As and Se. Maximum trapping efficiencies are achieved at total gas flow rates of 60–70 ml min − 1 and with a capillary distance of 2 mm. Trapping of Sb is not influenced within the whole interferent mass range of 0–30 μg of As and Se, and 0–300 ng of Bi. Trapping of other analytes is affected by 1 to 2 orders of magnitude higher amounts of concomitant hydrides. According to thermodynamic calculations, the competitive occupation of active sites on the molybdenum surface by the AsO (g) and SbO (g) species and the formation of the inactive analyte–interferent diatomic BiSe (g) and AsSe (g) species can probably be the reason for these interference effects.

Vascular pedicle ligation techniques during laparoscopic colectomy

A variety of devices are available for pedicle ligation during laparoscopic colectomy including vascular staplers, clips, and electrothermal bipolar vessel-sealing devices. This study assesses their speed, reliability, and cost to guide surgeons in their choice for intracorporeal pedicle ligation. A prospective randomized study comparing laparoscopic vascular staplers and disposable clip appliers (S/C) with the LigaSure Atlas (LIG) was performed during elective right, left, and total colectomy. Cases were stratified by procedure. Failure was defined as any bleeding after proper pedicle ligation. The study included 48 S/C patients and 52 LIG patients with no differences in demographics, diagnosis, procedure, number of vessels ligated per procedure, or operative time. Failure occurred for 14 (9.2%) of the 152 vessels ligated in the S/C group, as compared with 5 (3%) of the 169 vessels ligated in the LIG group (p = 0.02). The median blood loss associated with device failure was 50 ml (range, 20-50 ml) in S/C group, as compared with 100 ml (range 25-800 ml) in the LIG group (p = 0.054). Major blood loss attributable to device failure and surgeon error occurred in only one LIG case. The mean cost per case of vessel ligation was significantly less in the LIG group (317 dollars +/- 0 dollars vs 400 dollars +/- 112 dollars; p < 0.001). The cost differences were greatest for total colectomy (LIG = 317 dollars +/- 0 dollars vs S/C = 565 dollars +/- 67 dollars; p = 0.002). Device failure, although more common in the S/C group, does not result in significant blood loss. The LigaSure Atlas is more cost effective during laparoscopic colectomy, especially total colectomy, and may allow the surgeon more versatility in its application.

Trapping of hydride forming elements within miniature electrothermal devices. Part 2. Investigation of collection of arsenic and selenium hydrides on a surface and in a cavity of a graphite rod

The interaction of arsenic and selenium hydrides with bare and modified graphite was investigated by atomic absorption spectrometry and by radiotracer technique using 75Se radionuclide in a laboratory made brass cylindrical chamber equipped with a vertical quartz tube torch for supporting miniature hydrogen diffusion flame atomizer. Strong interaction was observed at elevated temperatures above 800 °C. In contrast to the very often-reported data for conventional graphite tube atomizers, this high temperature interaction was also accompanied by a pronounced trapping of analytes at elevated temperatures close to 1100–1200 °C when modified graphite was used. Comparing modifiers tested (Ir, Pt and Rh), iridium appeared the only useful permanent modifier. Among various graphite-rod traps designed, the most efficient trapping of analytes was achieved in a graphite cavity. The net selenium trapping efficiencies of approximately 53% and 70% were found by radiotracer technique for the iridium-treated graphite surface and the iridium-treated graphite cavity, respectively. In contrast to the molybdenum surface, bare graphite did not exhibit any significant trapping effect. Trapping isotherms obtained at different temperatures displayed non-linear course in the range up to the upper limit of the analytical relevance of 100 ng of an analyte, indicating a limited trapping capacity of the modified graphite surface and the same trapping mechanism at low and elevated temperatures applied (300–1300 °C). Radiography experiments with 75Se radiotracer showed that a major part of selenium was collected within the small cavity of the graphite rod and that selenium was also deposited after the trapping and vaporization steps in the trap chamber and on the quartz tube wall of the burner. Complementary experiments performed with the conventional transversally heated graphite tube and with bare and thermally shielded injection capillaries for hydride introduction, showed that the pronounced trapping effect could not be observed at elevated temperatures in conventional systems equipped with the bare capillary. The losses of analytes in the non-shielded bare introduction capillary exposed to the heat decrease the transport efficiency of hydrides into the graphite tube, and consequently they cause reduction of the overall trapping efficiency at elevated temperatures.

Lasers and electrothermal devices in the treatment of lunotriquetral instability

Lasers and electrothermal devices in the treatment of lunotriquetral instability

Trapping of hydride forming elements within miniature electrothermal devices: part I. investigation of collection of arsenic and selenium hydrides on a molybdenum foil strip

The interaction of selenium and arsenic hydrides with surface of bare and modified (Pt, Ir and Rh) strips of the molybdenum foil was investigated by atomic absorption spectrometry employing miniature hydrogen diffusion flame as a simple atomizer and by radiotracer technique using 75Se-radionuclide as an indicator. In contrast to the recently reported data for tungsten atomizers, enhanced trapping was observed at the temperatures above 1000 °C, close to 1100–1200 °C, for the bare and modified molybdenum foil strips, irrespective of the analyte, and amount and type of the modifier deposited. When using a 75Se-radiotracer, the same selenium trapping efficiency of approximately 30% was found for the bare and rhodium-treated foils at the temperature of 1200 °C. Trapping isotherms of both analytes appeared to be very close to the linear fit even up to the upper limit of the analytical relevancy of 100 ng of an analyte, indicating a very high trapping capacity of the bare and modified surfaces. The influence of injection gas flow rate and capillary distance suggested that aerodynamic conditions of the injected gas near the molybdenum surface play significant role in trapping both analytes. The maximum trapping efficiency was reached for flow rates close to 60–70 ml min −1 and for a relatively short distance of 1–2 mm between the capillary orifice and the foil surface. Radiography experiments with 75Se-radiotracer showed that a major part of selenium was collected on a relatively small area, in the central part of the strip, opposite the orifice of the injection capillary. After trapping and vaporization steps, deposits of the selenium tracer were also found on the quartz tube wall of the trap chamber, close to the heated part of the strip.

Accomplishment and prospect of isas electric propulsion

The electric propulsion is one of the promising choices because of its high specific impulse when one would like to give a rise to the limited payload capability of the launch vehicle. Especially in a long-term mission or a high-energy mission, the electric propulsion provides less consumption of propellant or more payload mass under a given mass constraint of the satellite and the scientific probe. The Institute of Space and Astronautical Science (ISAS) has been developing a variety of electric propulsions for 30 years. These continuing efforts are now turning out to be an application era for the propulsion systems for near-Earth and/or interplanetary transportation of space probes with scientific missions in the 21st century. A magnetoplasmadynamic (MPD) arcjet successfully finished its space test onboard the Space Flyer Unit (SFU), a microwave ion engine is being developed for the asteroid sample return mission, and a DC arcjet is ready to be used for future orbit transfer or attitude control of Earth-bound satellites. The electric propulsions are divided into three major groups according to their plasma acceleration principles, electromagnetic, electrostatic and electrothermal devices. In ISAS, all the types of electric propulsions are studied as the high Δ V mission enablers and in this report these accomplishments and future prospects are introduced.

Semi-analytical modelling and simulation of the evolution and flow ofOhmically-heated non-ideal plasmas in electrothermal guns

In this paper, the Ohmic power input to the discharge capillary isrecovered and used to analyse the basic processes involved in electrothermal(ET) plasma devices operated in an ablation-controlled-arc regime. Such aninterplay between theory and experiment is necessary to reduce the number ofreasons which might be responsible for the reported discrepancies betweentheory and experiment, as well as to illuminate the subject of ablationcontrolled arcs. A consistent methodology for determining detailed compositionand thermodynamic functions of the non-ideal plasma generated in such devicesis presented and used in the present computations. Different non-idealityeffects, due to Debye-Hückel corrections in the Gibbs free energy, whichhave been ignored in prior publications, have been taken into account. Asemi-analytical model for an ET plasma source with non-ideal effects isdescribed and incorporated into a comprehensive computer code to simulateplasma evolution and flow in the discharge capillary. The model isone-dimensional, time dependent and uses the recovered Ohmic power input inthe source term of the energy equation. The developed code has been used toinvestigate the ablation process and has shown the inappropriateness of awidely used ablation model. Code predictions for different plasma parametersare presented, discussed, and compared to available experimental data.

Therapeutic heat:A historical perspective

The use of heat in the treatment of medical disorders can be traced throughout history. Refinements in the applicationof heat has led to the development of surgical lasers and electrothermal devices. Currently the Holmium:YAG (Ho:YAG) laser represents the arthroscopic laser of choice. Electrothermal surgical systems currently deliver either monopolar or bipolar radiofrequency energy. The safe and efficacious use of these devices is determined by an understanding of the basic science and clinical application of these surgical devices.

Visualization of plasma-fluid mixing through X-ray shadowgraphy

Changes induced by the impact of a hot plasma jet on a fluid have been recorded using X-ray shadowgraphy. The process is of particular importance in the operation of electrothermal acceleration devices. Sets of frames taken every 40 mu s reveal details of the interaction. Fluid erosion is observed to occur only at the fluid extremity directly hit by the plasma. The erosion rate has been evaluated for the initial collision stages when the volume accessible to the fluid remains constant; the measured values range between 100 m/s and 200 m/s. >

Determining Ultratrace Metal Concentrations by Inductively Coupled Plasma Emission Spectrometry

The use of electrothermal vaporization devices (ETV) to introduce analytes into inductively coupled plasma (ICP) for determination by atomic emission spectroscopy (AES) provides detection limits in picograms but requires solution concentrations higher than nanogram‐per‐litre levels. Determination of metal concentrations lower than nanograms per litre requires a preconcentration step. The method of controlled potential electrodeposition of metals into mercury film on glassy carbon electrodes for ETV‐ICP‐AES is described. The method can be used for simultaneous multielemental determination of trace and ultratrace concentrations of metals in water. Modification and optimization of the technique are discussed. Also included are the results of determinations of eight trace elements.

Determining Ultratrace Metal Concentrations by Inductively Coupled Plasma Emission Spectrometry

The use of electrothermal vaporization devices (ETV) to introduce analytes into inductively coupled plasma (ICP) for determination by atomic emission spectroscopy (AES) provides detection limits in picograms but requires solution concentrations higher than nanogram‐per‐litre levels. Determination of metal concentrations lower than nanograms per litre requires a preconcentration step. The method of controlled potential electrodeposition of metals into mercury film on glassy carbon electrodes for ETV‐ICP‐AES is described. The method can be used for simultaneous multielemental determination of trace and ultratrace concentrations of metals in water. Modification and optimization of the technique are discussed. Also included are the results of determinations of eight trace elements.

Atomic Absorption Determination of Lead, Bismuth, Selenium, Tellurium, Thallium and Tin in Complex Alloys Using Direct Atomization from Metal Chips in the Graphite Furnace

Atomic absorption spectrometry utilizing electrothermal atomization devices has proven to be the best technique available for the analysis of complex alloys for trace elements of metallurgical interest. The determination of lead, bismuth, selenium, tellurium, thallium, and tin was successfully demonstrated by direct atomization from complex, nickel-base alloy chips with commercial atomic absorption furnace equipment. The determination was carried out by first milling metal chips from the bulk sample. The sample was transferred directly to the furnace and atomized immediately with no preatomization heating cycle. A series of cast alloy standards containing the trace elements were prepared by additions to a nickel-base alloy, then subsequently analyzed by established analytical methods. Of the three commercial atomizers studied, the Perkin-Elmer model HGA 2100 proved to be the most suitable for direct determination of the trace elements of interest. The coefficient of variation of absorbance measurements varied from 7% for bismuth which is easily atomized to 25% for tin which is more difficult to atomize.

Development of a regeneratively cooled 30-kw arcjet engine

The development of a fully regenerative-cooled 30-kw arcjet engine including a summary of the successful continuous 500-hr endurance test, is presented. This direct current arcjet engine, which uses hydrogen as the propellant, operated satisfactorily at an average measured thrust of 0.745 Ib and demonstrated a total impulse of 1.34 million Ib-sec during the described endurance test. Numerous analytical as well as experimental heat-transfer studies were required in order to substantiate the basic design philosophy, full regenerative-cooling using gaseous hydrogen. This electrothermal engine demonstrated a performance of 55% in over-all thruster efficiency at a specific impulse of 1000 sec, resulting in a 20% improvement in efficiency over a radiation-cooled 30-kw arcjet engine developed during 1962. The results of this development program indicated that the 30-kw arcjet engine described in this paper is one of the most advanced electrothermal propulsion devices at this power level yet reported.