Thermal Burnout Research Articles

Functionalization of Carbon Electrodes with Nanotitania by Atomic Layer Deposition

Carbon fibers are materials with a very high surface area and are interesting for applications such as filters, fire-resistant heat insulation, photocatalysis, and capacitor electrodes. Moreover, thermal burnout can easily remove these fibers, making them ideal templates for high-precision coatings or keeping them within the coated structure, generating nanostructured composites. In this work, two different substrates, carbon felt and bacterial nanocellulose were coated by TiO2 with atomic layer deposition (ALD). After deposition, the templates were pyrolyzed or further removed by burnout in the air. The microstructure evolution of the 3D interlocked-fibers structures was characterized by scanning electron microscopy and nitrogen adsorption surface area after each step. Stable anatase was present as a single TiO2 phase even after heat treatment at 800°C. Moreover, electrochemical impedance spectroscopy and constant current charge-discharge were employed to investigate the electrochemical properties of the samples. Our results show that all samples display a uniform layer after ALD and that the surface area decreases with an increasing number of ALD cycles. After burnout, the 3D structures presented a straw-like appearance to the shells. Nonetheless, both samples presented a power density comparable to a porous NiO/C, with the pyrolyzed bacterial nanocellulose sample displaying a higher pseudocapacitance performance than the carbon-felt samples.

Impact of the structure on the thermal burnout effect induced by microwave pulses of PIN limiter diodes

Positive-intrinsic-negative (PIN) limiters are widely used to protect sensitive components from leakage power itself and adjacent high-power injection. Being the core of a PIN limiter, the PIN diode is possible to be burnt out by the external microwave pulses. Here, using a parallel computing program for semiconductor multi-physics effects designed by ourselves, we studied the influence of the thickness of the I layer and the anode diameter of the PIN diode on the maximum temperature change curve of the PIN diode limiter. The damage threshold criterion in the numerical simulation was first studied by comparing experimental results with simulation results. Then, we determined the impact of the structure on the thermal burnout effect induced by microwave pulses of PIN limiter diodes.

Thermal Burnout Effect of a GaAs PHEMT LNA Caused by Repetitive Microwave Pulses

The thermal burnout effect of a gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (PHEMT) low-noise amplifier (LNA) caused by repetitive microwave pulses is studied by theoretical analyses, simulations, and experiments. The theoretical model for thermal burnout under a single microwave pulse injection is first acquired by analyzing the power absorption in the electrical procedure and the heat distribution in the thermal procedure. By adopting two new assumptions and using the linear superposition theorem, the theoretical model for thermal burnout under a repetitive microwave pulse injection is acquired by further extension. Through derivation, the analytical relationship among the thermal burnout power threshold, the pulsewidth in a cycle, the pulse repetition frequency (PRF) and the pulse number is acquired. Because some assumptions and approximations are adopted, both the pulsewidth in a cycle and the total repetitive microwave pulselength must be between 10-ns scale and 1-μs scale. It shows that the theoretical results agree well with the simulation and experimental results. A minimum of two sets of data by experiment or simulation are needed to fit the analytical relationship. Therefore, experimental or simulation costs can be substantially reduced, and a helpful reference for

The influence of microwave pulse repetition frequency on the thermal burnout effect of a PIN diode limiting-amplifying system

This paper analyzes the influence of the microwave pulse repetition frequency on the thermal burnout effect of a PIN diode limiting-amplifying system. Based on the study of the single-shot microwave pulse thermal burnout effect and by introducing a new assumption that the heat dissipation of the electric field energy and the nonequilibrium carrier energy during the microwave pulse intervals can be neglected, the theoretical thermal burnout model in our previous study is extended to be suitable for repetitive microwave pulses. The theoretical relationship among the pulse number, the pulse repetition frequency, the pulse width and the thermal burnout power threshold is obtained by theoretical derivation. Because the assumptions are introduced, the theoretical relationship requires that both the whole length of a repetitive microwave pulse and the pulse width in a cycle of a repetitive microwave pulse should be between 10 ns and 10 μs. The results obtained by the theoretical relationship are in good agreement with the simulation results obtained by our self-designed device-circuit joint simulator, which verifies the correctness of the theoretical analyses, modeling and derivation. By fitting at least two sets of simulation or experimental data, the theoretical relationship can be used to predict the thermal burnout power thresholds of PIN diode limiting-amplifying systems under microwave pulse injections with different pulse parameters. It can greatly reduce the simulation or experimental costs and could be helpful for the design of a radio frequency receiver.

The influence of microwave pulse width on the thermal burnout effect of an LNA constructed by a GaAs PHEMT

In this paper, the influence of microwave pulse width on the thermal burnout effect of a low noise amplifier (LNA) constructed by a GaAs pseudomorphic high electron mobility transistor (PHEMT) is theoretically analyzed and further verified with simulation and experimental results. By analyzing the electrical procedure and the thermal procedure, a theoretical model of the thermal burnout effect of the studied LNA is established according to the properties of microwave pulses and the structure of the LNA and GaAs PHEMT. Based on the theoretical model, the analytical relationship between the microwave pulse width and the thermal burnout power threshold is further obtained. According to the limitations caused by the approximations in the process of modeling, the available microwave pulse width range for the proposed analytical relationship is more than a nanosecond level and less than a microsecond level. The coefficients of the proposed analytical relationship can be determined by fitting at least two sets of simulation or experimental results, which can greatly reduce the simulation or experimental costs. Finally, the analytical relationship is verified by simulation and experimental results. The results show that the proposed analytical relationship is suitable to estimate the thermal burnout power threshold for a given microwave pulse width within the limit of microwave pulse width range.

The influence of microwave pulse width on the thermal burnout effect of a PIN diode limiting-amplifying system

This paper analyzes the influence of the microwave pulse width on the thermal burnout effect of a PIN diode limiting-amplifying system. Based on theoretical analyses and simulation, the relationship of the burnout effect on a PIN diode limiter and a PIN diode limiting-amplifying system is obtained first. By adopting an absorption efficiency factor, the theoretical model of the relationship between the microwave pulse width and the burnout power threshold for the PIN diode limiting-amplifying system is obtained. The proposed theoretical formulas can be determined by using at least two sets of simulation or measurement results to fit the constant coefficients, which can greatly reduce the simulation or experimental costs. The results obtained by the theoretical formulas are in good agreement with the numerical simulation results obtained by our self-designed device–circuit joint simulator, which verifies the correction of the theoretical analyses and modeling. The available microwave pulse width range for the proposed theoretical formulas is from 10ns to 10μs. In consideration of the potential threat of microwave pulses, the system-level study results obtained in this paper will be helpful for the design of the radio frequency receivers.

The Influence of Microwave Pulse Width on the Thermal Burnout Effect of an LNA Constructed by the SiGe HBT

This paper presents the influence of the pulse width on the thermal burnout effect of a low-noise amplifier (LNA) constructed by a silicon–germanium heterojunction bipolar transistor (SiGe HBT) when it is injected by microwave pulses. Based on the characteristics of microwave pulses and the structure of the SiGe HBT, a theoretical model to predict the impact of the pulse width and power on the thermal burnout effect of the LNA is established by solving the heat conduction equation. The derivation of the theoretical model requires the pulse width less than a microsecond level. Using at least two groups of simulated or measured results to fit the coefficients, the proposed theoretical model can predict the other effect of the pulse width, which can greatly reduce the experimental costs and guide the rational selection of the pulse width in numerical simulations. At last, the theoretical model is verified by numerical simulations and experimental measurements. The results show that within the scope of pulse width (less than the microsecond level) the burnout power threshold can be effectively reduced by increasing the pulse width.

Electro-thermal coupled modeling of PIN diode limiter used in high-power microwave effects simulation

A major failure mode of positive-intrinsic-negative (PIN) diode limiter is the diode junction thermal burnout due to the high-power microwave (HPM) irradiation. Based on the time domain circuit approach, an electro-thermal coupled model including junction transient self-heating effects is presented via analogous between thermal dynamic and electronic circuit topology. Moreover, the proposed model takes into account feedback updating of physical parameters as device junction temperature varying. The diode junction thermal behavior is simulated and verified by the device manufacture measurements. The PIN limiter circuit numerical results of the microwave pulse width dependence on power level under HPM interference validate the well-known semi-empirical Wunsch–Bell relationship. And the turning point value of microwave pulse width obtained in simulations is very close to that specified in Wunsch–Bell formula.

Direct Fabrication of IC Sacrificial Patterns via Rapid Prototyping Approaches

Patterns made from conventional wax materials in the Investment Casting (IC) process can easily be distorted, damaged, or broken in transportation or routine handling or due to exposure to heat. Alternatively, the strength and toughness of most Rapid Prototyping (RP) materials virtually eliminates this drawback due to their resistance to heat, humidity, and post curing. The current study is conducted to investigate the feasibility of using RP processes such as FDM and MJM to fabricate IC patterns from Acrylonitrile Butadine Styrene (ABS) and acrylate based materials respectively to be used directly in IC process. Evaluation of the effects of different internal pattern designs of the RP parts are conducted based on the thermal analysis approach and burnout properties of the RP patterns. Ceramic shell molds are fabricated on both RP patterns and subsequently placed in an oven which is gradually heated to 1000°C. The decomposition temperature and the residual ash of the RP pattern materials is determined and analyzed. Results show that the acrylate pattern ofMJMdecomposes rapidly compared to the ABS pattern from the FDM process. It is also observed that quasi and square hollow internal structures show better collapsibility or burnout properties, with no cracks, compared to cross pattern and cross hatch designs.

Sharp burnout failure observed in high current-carrying double-walled carbon nanotubefibers

We report on the current-carrying capability and the high-current-induced thermal burnout failure modesof 5–20 µm diameter double-walled carbon nanotube (DWNT) fibers made by an improveddry-spinning method. It is found that the electrical conductivity andmaximum current-carrying capability for these DWNT fibers can reach up to5.9 × 105 S m − 1 andover 1 × 105 A cm − 2 in air. In comparison, we observed that standard carbon fiber tended to be oxidized andburnt out into cheese-like morphology when the maximum current was reached, whileDWNT fiber showed a much slower breakdown behavior due to the gradual burnout inindividual nanotubes. The electron microscopy observations further confirmed that thefailure process of DWNT fibers occurs at localized positions, and while the individualnanotubes burn they also get aligned due to local high temperature and electrostatic field.In addition a finite element model was constructed to gain better understanding of thefailure behavior of DWNT fibers.

Milliwatt output levels and superquadratic bias dependence in a low-temperature-grown GaAs photomixer

A cw output power up to 0.8 mW is obtained from a low-temperature-grown (LTG) GaAs, 0.3 μm gap, interdigitated-electrode photomixer operating at room temperature and pumped by two modes of a Ti:Al2O3 laser separated in frequency by 0.2 GHz. The output power and associated optical-to-electrical conversion efficiency of 1% represent more than a sixfold increase over previous LTG-GaAs photomixer results obtained at room temperature. A separate LTG-GaAs photomixer having 0.6 μm gaps generated up to 0.1 mW at room temperature and up to 4 mW at 77 K. Low-temperature operation is beneficial because it reduces the possibility of thermal burnout and it accentuates a nearly quartic dependence of output power on bias voltage at high bias. The quartic dependence is explained by space-charge effects which result from the application of a very high electric field in the presence of recombination-limited transport. These conditions yield a photocurrent-voltage characteristic that is very similar in form to the well-known Mott–Gurney square-law current in trap-free solids.

Performance Of A Heat Pipe In A Microwave Field*

ABSTRACTThis paper describes a study of the feasibility of cooling high power microwave windows with heat pipes. The concept involves replacing a single conventional window with two thin windows which are separated in a manner to form—with the wave guide—an internal cavity where heat pipe operation occurs. The internal cavity is lined with a thin layer of capillary material and a working fluid is introduced.Thermal energy generated in the windows is conducted in the axial direction into the heat pipe cavity where it is transferred to the inside surface of the wave guide. The energy is then conducted in a radial direction through the wave guide and removed by conventional cooling techniques from the outer surface of the wave guide.Theoretical expressions have been developed for predicting thermal burnout fluxes, thermal resistances and vapor conditions during normal operation, and maximum working fluid head rises during vertical operation. A thermal test rig has been designed and fabricated which simulates...