Terahertz and Sub-Terahertz Tunable Resonant Detectors Based on Excitation of Two Dimensional Plasmons in InGaAs/InP HEMTs

Plasmons can be generated in the two dimensional electron gas (2DEG) of grating-gated high electron mobility transistors (HEMTs). The grating-gate serves dual purposes, namely to provide the required wavevector to compensate for the momentum mismatch between the free-space radiation and 2D-plasmons, and to tune the 2DEG sheet charge density. Since the plasmon frequency at a given wavevector depends on the sheet charge density, a gate bias can shift the plasmon resonance. In some cases, plasmon generation results in a resonant change in channel conductance which allows a properly designed grating-gated HEMT to be used as a voltage-tunable resonant detector or filter. Such devices may find applications as chip-scale tunable detectors in airborne multispectral detection and target tracking. Reported here are investigations of InGaAs/InP-based HEMT devices for potential tunable resonant sub-THz and THz detectors. The HEMTs were fabricated from a commercial double-quantum well HEMT wafer by depositing source, drain, and semi-transparent gate contacts using standard photolithography processes. Devices were fabricated with metalized transmission gratings with multiple periods and duty cycles. For sub-THz devices, grating period and duty cycle were chosen to be 9 ?m and 22%, respectively; while they were chosen to be 0.5 ?m and 80% for the THz device. The gratings were fabricated on top of the gate region with dimensions of 250 ?m x 195 ?m. The resonant photoresponse of the larger grating-period HEMT was investigated in the sub-THz frequency range of around 100 GHz. The free space radiation was generated by an ultra-stable Backward Wave Oscillator (BWO) and utilized in either frequency modulation (FM), or amplitude modulation (AM) experiments. The photoresponse was measured at 4K sample temperature as the voltage drop across a load resistor connected to the drain while constant source-drain voltages of different values, VSD, were applied. The dependence of such optoelectrical effect to polarization of the incident light, and applied VSD is studied. The results of AM and FM measurements are compared and found to be in agreement with the calculations of the 2D-plasmon absorption theory, however, a nonlinear behavior is observed in the amplitude and the line-shape of the photoresponse for AM experiments. For detection application, the minimum noise-equivalent-power (NEP) of the detector was determined to be 235 and 113 pW/Hz1/2 for FM and AM experiments, respectively. The maximum responsivity of the detector was also estimated to be ~ 200 V/W for the two experiments. The far-IR transmission spectra of the device with nanometer scale period was measured at 4 K sample temperature for different applied gate voltages to investigate the excitation of 2D-plasmon modes. Such plasmon resonances were observed, but their gate bias dependence agreed poorly with expectations

IMECE2008-68886 EXPERIMENTAL NONLINEAR VIBRATION ANALYSIS OF PIEZOELECTRICALLY ACTUATED MICROCANTILEVERS

ABSTRACT With daily growth of using microcantilevers in microelectromechanical systems, comprehensive analysis on their dynamical behavior is necessary since they are mostly utilized as the main sensing device. In this paper, the out-ofplane vibrations of the piezoelectrically actuated microcantilever are experimentally investigated. The microcantilever is covered with a piezoelectric layer on its top surface through which it can be excited by applying the voltage to the piezoelectric actuator. The nonlinear frequency response of the microcantilever is studied and shift in natural frequency due to nonlinearity is examined. By observing the subharmonics of the fundamental frequencies at 2X and 3X, it is experimentally shown that there exist cubic and quadratic nonlinearities in the microcantilever. A mathematical model based on these experimental tests is then proposed and verified. The out-of-plane measurements provide the ability to observe both transversal and torsional modes. In addition, the modes in which the microcantilever acts like a plate are observed. INTRODUCTION Microcantilevers find many applications in nanomechanical sensors/actuators and especially piezoelectrically-actuated microcantilevers have recently received considerable attention since they are capable of better actuation. The sensing/actuating operation is based on static and dynamic deflections of the microcantilevers. However, measurement of the dynamic vibrations of the microcantilever is the base sensing strategy. Therefore, a nonlinear comprehensive experimental study on the frequency response of these microcantilevers seems to be essential since in such small scale even very small excitations can provide large amplitude and consequently nonlinear vibration

LS-DYNA Simulation of Hemispherical-punch Stamping Process Using an Efficient Algorithm for Continuum Damage Based Elastoplastic Constitutive Equation

Abstract. An efficient integration algorithm for continuum damage based elastoplastic constitutive equations is implemented in LS-DYNA. The isotropic damage parameter is defined as the ratio of the damaged surface area over the total cross section area of the representative volume element. This parameter is incorporated into the integration algorithm as an internal variable. The developed damage model is then implemented in the FEM code LS-DYNA as user material subroutine (UMAT). Pure stretch experiments of a hemispherical punch are carried out for copper sheets and the results are compared against the predictions of the implemented damage model. Evaluation of damage parameters is carried out and the optimized values that correctly predicted the failure in the sheet are reported. Prediction of failure in the numerical analysis is performed through element deletion using the critical damage value. The set of failure parameters which accurately predict the failure behavior in copper sheets compared to experimental data is reported as well

A study on anti-diabetic and anti-hypertension herbs used in Lorestan province, Iran

Introduction: Diabetes and hypertension are amongst the most prevalent diseases in the world, while they can be controlled and prevented, create many problems and complications for affected patients. This study was aimed to identify and report the most important and effective herbs for diabetes and high blood pressure treatment in Lorestan province (West of Iran). Methods: By gathering and integrating indigenous data from local inhabitants of Lorestan, Iran, the goal of this study was accomplished. Data were gathered by cooperation of the agents of public health services network all over the towns of Dorud, Boroujerd, Khorramabad, Aleshtar, Poledokhtar, Aligoodarz, Nurabad and Kouhdasht. Results: Results of this study showed that there were overall 17 medicinal plants which were used for treatment and controlling of diabetes and high blood pressure. Conclusion: Medicinal plants reported in this study are indigenous to the Lorestan province. Some of the foresaid herbs seem to have some unknown therapeutic effects which are reported in this study for the first time, and some others have various known therapeutic effects mentioned in other similar studies. It is essential for researchers to find out the actuality of clinical effectiveness of the herbs and their active substances. Once the positive effects of these herbs proved, it would be possible to produce drugs which are useful in curing and controlling diabetes and hypertension.</p

Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy

Infrared spectroscopy is a powerful tool for basic and applied science. The molecular spectral fingerprints in the 3 um to 20 um region provide a means to uniquely identify molecular structure for fundamental spectroscopy, atmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise, coherent laser sources with broad, tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can enable the above-mentioned applications. Here, we leverage robust fabrication and geometrical dispersion engineering of silicon nanophotonic waveguides for coherent frequency comb generation spanning 70 THz in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides significant spectral broadening and engineered spectra targeted at specific mid-infrared bands. We use this coherent light source for dual-comb spectroscopy at 5 um.Comment: 26 pages, 5 figure