Emitter Element Research Articles

Experimental research of metal hydride heat storage reactor processes

The results of the experimental research of thermal, mass exchange and dynamical characteristics of processes inside the low temperature metal hydride (MH) thermal energy storage system are presented. Single stage pressure driven MH heat storage system of closed cycle concept was studied and tested. Intermetallic compound (IMC) LaFe0.1Mn0.3Ni4.8 in the quantity of 5 kg was used as main hydrogen storage/heat emitter element in the reactor. Nominal maximum hydrogen capacity of the reactor is 850 st.l. with though resulting effective volume of cycled hydrogen ended up to be around 240-250 st.l. The reactor type and intermetallic alloy, which were used in the series of experiments, proved to be somewhat suitable for the task, but more advanced heat exchange design along with selection of different type of IMC promise to increase the cycled effective volume along with the system dynamics, resulting in greater thermal energy power output.

Electrostatic modeling of an in-plane gated field emission cathode

In this study, the authors develop an electrostatic model for an in-plane gated field emission cathode. This structure is based on two electrodes lying on the same plane. One electrode (bias electrode) allows biasing the field emitter element, a whisker in present study. The other electrode (gate electrode) is being used to electrostatically control the system. Our model points out the main geometrical parameters to be bias electrode characteristic size and whisker height, as confirmed by simulations. This model gives access to the extraction field experienced by the whisker emitter on its apex, in turn giving access to emission current dependencies on the various parameters of the model. The proximity of the gate as compared to the emitter apex enables low bias voltage to modulate the current with high susceptibility.

Generation of high power pulsed terahertz radiation using a plasmonic photoconductive emitter array with logarithmic spiral antennas

An array of 3 × 3 plasmonic photoconductive terahertz emitters with logarithmic spiral antennas is fabricated on a low temperature (LT) grown GaAs substrate and characterized in response to a 200 fs optical pump from a Ti:sapphire mode-locked laser at 800 nm wavelength. A microlens array is used to split and focus the optical pump beam onto the active area of each plasmonic photoconductive emitter element. Pulsed terahertz radiation with record high power levels up to 1.9 mW in the 0.1–2 THz frequency range is measured at an optical pump power of 320 mW. The record high power pulsed terahertz radiation is enabled by the use of plasmonic contact electrodes, enhancing the photoconductor quantum efficiencies, and by increasing the overall device active area, mitigating the carrier screening effect and thermal breakdown at high optical pump power levels.

An infrared-scene projector digital model

In infrared-scene projectors, an inherent variability for each emitter element manifests itself as fixed-pattern noise, or nonuniformity. This is unacceptable for valid sensor performance evaluation tasks. This article describes an infrared-scene projector digital model that will be used to simulate infrared-scene projection to assist algorithm development to eliminate this nonuniformity.

Chemical state sensitivity by PIXE, using solid state detectors

With accurate analog and digital signal processing, the stability of an X-ray line in a typical spectrum can be as good as 0.3 eV given appropriate precautions. In contrast, newly available atomic binding energy databases indicate that the difference between the Kα and Kβ X-ray energies can range over several eV, depending on the chemical state of the emitter element. In addition the Kβ ′ satellite structure varies significantly in energy and intensity depending on chemical state. It follows that PIXE spectra cannot be fitted with optimal accuracy if the database does not recognize these effects. On the positive side, it now appears worthwhile to investigate the possibility of deducing chemical information from the Kα–Kβ separation in PIXE spectra.

Spectrally selective, matched emitters for thermophotovoltaic energy conversion processed by tape casting

The thermophotovoltaic (TPV) generator converts radiant energy from a high temperature emitter element into electric power using infrared responding photovoltaic cells. Spectral control is a primary issue in TPV applications. Conventional TPV generators have relied on filters to achieve selectivity and spectral control with near-blackbody ceramic emitters. Several practical problems have limited the success of this approach, particularly the present lack of a satisfactory wide-band infrared filter. A new, spectrally selective emitter is described in this work, and will be called the “bandgap matched” emitter because its emissive power spectrum is very efficiently matched with the infrared response of the GaSb photovoltaic cell. The superior spectral efficiency has been achieved with a novel combination of spectrally active, transition metal dopants within an infrared-transparent magnesium oxide ceramic matrix. High mechanical integrity, thermal shock resistance, excellent heat transfer characteristics, and near-ideal spectral efficiency have been achieved by fabricating composite Co- or Ni-doped MgO from thin ceramic ribbons made by the tape casting process.

Base and collector resistances in heterojunction bipolar transistors

In heterojunction bipolar transistors (HBTs), the reverse base currents flow from the outer base periphery to the collector. The reverse base and collector resistances are therefore dominated by contact resistance, which is inversely proportional to the outer base and inner collector periphery lengths which are larger than the emitter lengths when the base and collector electrodes surround the emitter element. These resistances can be extracted from reverse Gummel (current vs V bc with V bc = 0) and from measurements of output resistances at zero collector voltage sweeps. We compare models with measurements where the base and collector peripheries decrease with increasing emitter diameters.

Thermal management of microwave power heterojunction bipolar transistors

A comprehensive study of the device layout effects on thermal resistance in thermally-shunted heterojunction bipolar transistors (HBTs) was completed. The thermal resistance scales linearly with emitter dot diameter for single element HBTs. For multiple emitter element devices, the thermal resistance scales with area. HBTs with dot geometrics have lower thermal impedance than bar HBTs with equivalent emitter area. The thermal resistance of a 200 μm 2 emitter area device was reduced from 266°C/W to 146°C/W by increasing the shunt thickness from 3 μm to 20 μm and placing a thermal shunt landing between the fingers. Also, power-added efficiencies at 10 GHz were improved from 30% to 68% by this thermal resistance reduction.