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Doppler-shifted laser self-mixing interferometry for enhanced detection sensitivity
摘要： Laser self-mixing interferometry (SMI) is a well-known measurement technique having been applied to the fields of geometrical quantities detection, medical treatment and industry manufacturing. Its detection sensitivity can be improved by frequency shifting towards the laser’s relaxation oscillation frequency (ROF), which has always been implemented by a pair of acousto-optic modulators (AOM). This manuscript presents a novel method based on Doppler effect for frequency shifting, which is based on a rotating disk and has the advantages of convenient adjustment and low cost. The theoretical analysis in the form of Doppler shift and time-delayed rate equations is followed, and simulative and experimental results are included to prove its validity. To our knowledge, this technique has not been used in practice till now, and the proposed structure, with these advantages, can find significant applications in designing high performance SMI sensors, and can extend SMI measurement to more kinds of non-cooperative surfaces.
关键词： Self-mixing interferometry,signal to noise ratio,Doppler shift,sensitivity,relaxation oscillation frequency
更新于2025-09-19 17:13:59
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Observation of water droplets oscillation due to laser induced Marangoni convection
摘要： In this paper, using experimental characterizations, we explore the motion of water droplets suspended in mineral oil under exposure of a focused continuous wave (CW) fiber laser beam. The laser beam exposure heats the surrounding oil medium as well. The temperature gradient generates thermocapillary (or Marangoni) convection flows. This approach uses infrared laser-induced thermocapillary-driven flow for manipulation of droplets in the range of 10 to 30 μm in diameter. The droplets are trapped in the convection flow and travel with thermocapillary convection flow (depending on the droplet sizes) along the streamline with high speed. This motion is observed at a certain critical power of the laser. The behavior of a droplet in response to thermally induced convection can be considered. we also examined the oscillatory behavior of the droplet on the xy plane. As expected, oscillation frequency/amplitude are linearly correlated to the droplet size.
关键词： Convection,Fiber laser,Marangoni force,Manipulation,Oscillation frequency,Thermocapillary,Temperature gradient
更新于2025-09-16 10:30:52
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[IEEE 2018 13th European Microwave Integrated Circuits Conference (EuMIC) - Madrid, Spain (2018.9.23-2018.9.25)] 2018 13th European Microwave Integrated Circuits Conference (EuMIC) - A Gain-Boosted 52–142 GHz Band-Pass Distributed Amplifier in O.13μm SiGe Process with f<inf>max</inf> of 210GHz
摘要： A band-pass gain-boosted distributed amplifier is proposed. The amplifier achieves a bandwidth of 90 GHz at center frequency of 97 GHz and operates up to frequencies as high as 0.67fmax of the transistors. A novel gain-boosted cascode structure as well as band-pass transmission lines are employed to significantly boost the bandwidth and the highest operation frequency of the amplifier. The amplifier shows an average gain of 14.4 dB from 52 GHz to 142 GHz in a 0.13-μm SiGe process with fmax of 210 GHz.
关键词： bandpass amplifiers,gain boosting,distributed amplifiers,millimeter-wave silicon RFICs,maximum oscillation frequency (fmax),SiGe
更新于2025-09-04 15:30:14
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The instability of terahertz plasma waves in cylindrical FET
摘要： In this paper, the Dyakonov-Shur instability of terahertz (THz) plasma waves has been analyzed in gated cylindrical ?eld effect transistor (FET). In the cylindrical FET, the hydrodynamic equations in cylindrical coordinates are used to describe the THz plasma wave in two-dimensional electronic gas. The research results show that the oscillation frequency of the THz plasma wave is increased by increasing the component of wave in the circumferential direction, but instability increment of the THz plasma wave are increased by increasing the radius of channel.
关键词： oscillation frequency,cylindrical ?eld effect transistor,THz plasma waves
更新于2025-09-04 15:30:14
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Analysis of Passivation Techniques in InP HEMTs and Implementation of an Analytical Model of <i>f</i> <sub/>T</sub> Based on the Small Signal Equivalent Circuit
摘要： This paper analyses, the influence of Si3N4-PECVD and Al2O3-ALD surface passivation on the DC and RF characteristics of InP HEMTs with different gate lengths 0.08 μm, 0.1 μm, 0.12 μm, and 0.15 μm. A significant improvement in maximum drain current IDS_MAX, transconductance gm_MAX and oscillation frequency fmax_MAX is obtained by scaling the thickness of the passivation layers An increase in gm_MAX and fmax_MAX, fT_MAX is observed by reducing parasitic capacitance w.r.t. the decrease in gate length. In addition, an analytical model of fT based on a small-signal equivalent circuit is developed, which consist of extrinsic parameters Rs, Rd, Cgs_ext and Cgd_ext and intrinsic parameters Cgsi, Cgdi, gmi and goi. The carrier transport is improved by increasing gmi, thus the transit time τt, the parasitic charging delay τext and the τpar are reduced by lowering the extrinsic capacitances. An excellent fitting between measured and simulated fT is achieved, which inturn leads a realistic way for further improvement in fT.
关键词： Passivation,Maximum Oscillation Frequency,Transconductance,Fabrication
更新于2025-09-04 15:30:14