Radiative quantum efficiency in an InAs/AlSb intersubband transition

The quantum efficiency of an electroluminescent intersubband emitter based on InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two series of oscillations periodic in 1/B are observed, corresponding to the elastic and inelastic scattering of electrons of the upper state of the radiative transitions. Experimental results are accurately reproduced by a calculation of the excited state lifetime as a function of the applied magnetic field. The interpretation of these data gives an exact measure of the relative weight of the scattering mechanisms and allows the extraction of material parameters such as the energy dependent electron effective mass and the optical phonon energy.Comment: 4 pages, 5 figure

Heat Treatment Improvement of Dairy Products via Ohmic Heating Processes : Thermal and Hyrodynamic Effect on Fouling

Fouling and consequently cleaning of heat exchangers in the dairy industry are nowadays a significant issue still not solved for the processing of quite a large variety of products. Ohmic heating processes for food products a priori are well known to minimize the fouling phenomenon due to a totally different way of heating food by admitting the current directly in the product. Such a technology could be a good alternative to counter both fouling and cleaning aspects when pasteurizing or sterilizing dairy desserts known to generate large amounts of soil on heated surfaces. The aim of this experimental study was to investigate the respective roles of both the hydrodynamic parameters and surface electrode temperatures on the fouling phenomenon when heating a simple dairy mix designed to mimic dairy product behaviors

Properties of contactless and contacted charging in MEMS capacitive switches

The dielectric charging in MEMS capacitive switches is a complex effect. The high electric field during pull-down causes intrinsic free charge migration and dipole orientation as well as charge injection. The macroscopic dipole moment of the first two mechanisms is opposite to the one arising from charge injection. This causes partial compensation hence mitigates the overall charging and increases the device lifetime. The charging due to intrinsic free charge migration and dipole orientation can be monitored under contactless electric field application in the pull-up state. The paper investigates the characteristics of contactless charging and compares them with the ones of contacted charging. The characteristics of the discharging process that follows each charging procedure are also presented

Fouling and Cleaning of Modified Stainless Steel Plate Heat Exchangers Processing Milk Products

Fouling of heat exchangers in dairy industries is still quite a severe problem both technically and economically. Altering the surface properties of the heating surfaces would be a way of solving this issue. Modified steel surfaces were tested in an Alfa Laval V2 plate heat exchanger throughout dairy product sterilization. The behavior was analyzed for 8 different surface treatments, such as coatings (Diamond Like Carbon [DLC], Silica, SiOX, Ni-P-PTFE, Excalibur®, Xylan®) and ion implantation (SiF+, MoS2). All fouling and cleaning experiments were carried out in standard and well-controlled operating conditions. After fouling, no significant difference could be seen between all the modified steels and the reference by statistical variance analysis. Cleaning efficiency of Ni-PPTFE appeared significantly the best. It could be suggested that the free surface energy plays a predominant role and the roughness a minor role in the level of fouling and cleaning efficiency

On-chip circularly polarized circular loop antennas utilizing 4H-SiC and GaAs substrates in the Q/V band

This paper presents a comprehensive assessment of the performance of on-chip circularly polarized (CP) circular loop antennas that have been designed and fabricated to operate in the Q/V frequency band. The proposed antenna design incorporates two concentric loops, with the outer loop as the active element and the inner loop enhancing the CP bandwidth. The study utilizes gallium arsenide (GaAs) and silicon carbide (4H-SiC) semiconductor wafer substrates. The measured results highlight the successful achievement of impedance matching at 40 GHz and 44 GHz for the 4H-SiC and GaAs substrates, respectively. Furthermore, both cases yield an axial ratio (AR) of less than 3 dB, with variations in bandwidths and frequency bands contingent upon the dielectric constant of the respective substrate material. Moreover, the outcomes confirm that utilizing 4H-SiC substrates results in a significantly higher radiation efficiency of 95%, owing to lower substrate losses. In pursuit of these findings, a 4-element circularly polarized loop array antenna has been fabricated for operation at 40 GHz, employing a 4H-SiC wafer as a low-loss substrate. The results underscore the antenna’s remarkable performance, exemplified by a broadside gain of approximately 9.7 dBic and a total efficiency of circa 92%. A close agreement has been achieved between simulated and measured results

Electron scattering spectroscopy by a high magnetic field in quantum cascade lasers

We present a detailed experimental and theoretical study of a GaAs∕AlGaAs mid-infrared quantum cascade laser (QCL) under a strong magnetic field. The emitted power and the magnetoresistance show strong oscillations as a function of B , due to a magnetic field modulation of the lifetime of the upper state of the laser transition. The analysis of these oscillations shows a modulation of the electron lifetime due to inelastic (LO-phonon emission) and elastic scattering mechanisms. We show that at low temperature, the interface roughness scattering is the most efficient elastic relaxation mechanism; it becomes dominant whenever LO-phonon emission is inhibited by the magnetic field. By comparing experimental and theoretical results, we are able to estimate the relative weight of elastic and inelastic scattering. The magnetic field is thus a powerful spectroscopic tool to study the scattering mechanisms in QCL active regions

Properties of contactless and contacted charging in MEMS capacitive switches

The dielectric charging in MEMS capacitive switches is a complex effect. The high electric field during pull-down causes intrinsic free charge migration and dipole orientation as well as charge injection. The macroscopic dipole moment of the first two mechanisms is opposite to the one arising from charge injection. This causes partial compensation hence mitigates the overall charging and increases the device lifetime. The charging due to intrinsic free charge migration and dipole orientation can be monitored under contactless electric field application in the pull-up state. The paper investigates the characteristics of contactless charging and compares them with the ones of contacted charging. The characteristics of the discharging process that follows each charging procedure are also presented. © 2013 Elsevier Ltd. All rights reserved