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Effect of cold finger temperature on optical pulse modulation characteristics in a 2.59 terahertz quantum cascade laser
摘要： Terahertz (THz) frequency sources such as quantum cascade lasers (QCLs) offer a variety of new applications in far-infrared frequency bands. For better understanding of their behavior, a device-specific modeling approach is used to predict the optical output power under current modulation and chip temperature. This letter reports the numerical simulation of gain switching to evaluate temperature dependence for short pulse generation in QCLs. Modified rate equations are used for self-consistent computation of emitted THz optical power from QCLs. The device emits at 116 μm and is driven by various inputs such as haversine, tangential hyperbolic and square electrical pulses. From the simulation it is evident that the square input pulse requires the least magnitude current (0.83 A) at 15 K to generate pulses with minimum full width half maximum (FWHM). Moreover, when the peak amplitude of the square input signal is 1.01 A, it generates optical pulses with the least FWHM of 19.42 ps at 45 K. In the case of the haversine input with peak amplitude of 1.8A, a peak power of 27.86 mW is generated at 15 K.
关键词： cold finger temperature,rate equation model,numerical simulation,quantum cascade lasers,full width half maximum,gain switching,optical short pulses
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE Asia-Pacific Microwave Conference (APMC) - Singapore, Singapore (2019.12.10-2019.12.13)] 2019 IEEE Asia-Pacific Microwave Conference (APMC) - A Circularly Polarized Antenna Element Based on Open-ended Waveguide
摘要： Based on the open-ended rectangular waveguide structure, we proposed a circularly polarized antenna element with wide axial-ratio (AR) beam-width in this communication. Two rectangular notches are distributed on the wide sides of a rectangular waveguide in a 180° rotational symmetry to excite circular polarization. The simulated RHCP gain of the antenna is about 3.2 dBic at 11.5 GHz and the 3-dB AR beam-width is more than 120°. In addition, Owing to its simple configuration, the compact size (12(cid:2)(cid:2)6 mm2), this antenna element lays a good foundation for circularly polarized array antennas in wireless communication applications.
关键词： Circular polarization,End-fire antennas,Waveguide antennas,Wide beam-width
更新于2025-09-23 15:19:57
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The Interference Pattern of Plasmonic and Photonic Modes Manipulated by Slit Width
摘要： We demonstrate that the interference pattern of the plasmonic and photonic modes can be controlled by changing the slit width of a square slit structure. Based on the analyses of the plasmonic and photonic modes of slits with different widths, we theoretically derived the expressions of wavefield generated by a square slit. A far-field scattered imaging system is utilized to collect the intensity distribution experimentally. Various interference patterns, including stripes, square-like lattice array, and diamond-like lattice array, have been observed by adjusting the slit widths. In addition, the results were validated by performing finite-difference time-domain simulations, which are consistent with the theoretical and experimental results.
关键词： polarization,interference pattern,surface plasmon,slit width
更新于2025-09-23 15:19:57
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Comparative analysis of different cooling fin types for countering LED luminaires' heat problems
摘要： A significant problem with high-power LED luminaires is heat. Aluminum heat sinks have been extensively used as a solution. The most common method for heat sinks that increases surface area uses fins. In the present study, pin- and plate-fins were compared and it was observed that, in equal surface areas, better cooling was achieved by pin-fins. Thus, the study’s concentration narrowed to pin-fins and the results of different pin-fins were compared. Simulations of a sample group were conducted by using different numbers of fins, and the number of fins giving the lowest Tmax value (the highest junction point temperature) was accepted to be optimum for each group; then the optimum values were compared among the different groups. Keeping the base width of fins constant, optimum values were obtained for the same number of fins when the fin height was changed. However, keeping fin height constant, surface areas of optimum values and measured Tmax values were very close to one another other, even if the base width of fins was changed. The results have practical significance in designing high-power LED luminaires.
关键词： LED cooling,fin height,junction point temperature,base width,High-power LED luminaire,plate-fin heat sink,pin-fin heat sink
更新于2025-09-23 15:19:57
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Role of magnetic field on self focusing of super-Gaussian laser beam under relativistic effect
摘要： Considering an external magnetic field along the direction of propagation of laser, the self focusing of a super-Gaussian laser beam is studied when it propagates through the plasma at relativistic intensities. We consider the cyclotron motion of the electrons and use the tensor form of the plasma dielectric constant obtained based on the direction of the external magnetic field. For completeness, relativistic mass effect is incorporated in both the plasma frequency and electron cyclotron frequency. Using appropriate conditions, an equation for the beam width parameter is derived and solved. The equilibrium beam radius for a self trapped laser beam is also derived. Self focusing is better when cyclotron effects are taken into account. At higher intensity and higher spot size of the laser beam, self focusing becomes better.
关键词： Super-Gaussian laser,Moment theory,Beam width parameter,Self focusing,Relativistic nonlinearity
更新于2025-09-23 15:19:57
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Grid-connected photovoltaic system employing a single-phase T-type cascaded H-bridge inverter
摘要： This paper presents the control and application of a single-phase T-type nine-level cascaded H-Bridge (TCHB) multilevel inverter (MLI) topology. This paper focuses on the effectiveness of the TCHB and its control by presenting the inverter operation based on a PI current controller along with a Maximum Power Point Tracking (MPPT) scheme to realize a grid-tied photovoltaic (PV) system and a novel PWM method offering self-balancing at the DC-link capacitors. In order to attain gating signals for power transistors (IGBTs), the TCHB employs a PWM with one triangular carrier signal and eight reference signals. In addition, a mathematical modelling of the PWM method, along with a theoretical explanation of the self-balancing process has also been provided. To prove the effectiveness of the proposed TCHB topological design, it has been comparatively analysed against other fundamental MLI and symmetric CHB topologies. In addition, to corroborate the working of the control and the PV system application, levels ( ± 2Vdc, ± 2?Vdc, ± Vdc, ± ?Vdc, 0), simulation and hardware results have been presented.
关键词： Nine-level inverter,Pulse Width-Modulation (PWM),Grid-connected,Photovoltaic (PV) system,T-type cascaded H-bridge
更新于2025-09-23 15:19:57
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A Simple Method for the Evaluation of the Pulse Width of an Ultraviolet Femtosecond Laser Used in Two-Photon Ionization Mass Spectrometry
摘要： A simple method was proposed for on-site evaluation of the pulse width of an ultraviolet femtosecond laser coupled with a mass spectrometer. This technique was based on measurement of a two-photon ionization signal in mass spectrometry by translation of the prism in the pulse compressor of the femtosecond laser. The method was applied to optical pulses that were emitted at wavelengths of 267, 241, and 219 nm; the latter two pulses were generated by four-wave Raman mixing using the third harmonic emission of a Ti:sapphire laser (267 nm) in hydrogen gas. The measurement results show that this approach is useful for evaluation of the pulse width of the ultraviolet femtosecond laser used in mass spectrometry for trace analysis of organic compounds.
关键词： pulse width,mass spectrometry,ultraviolet femtosecond laser,ionization
更新于2025-09-23 15:19:57
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Performance Analysis of Mixed Carrier-pulse Width Modulation Scheme
摘要： This study deals with the performance analysis of Pulse Width Modulation (PWM) scheme for three phase voltage source inverter though intermingling of multiple carriers. The proposed PWM scheme using two groups of carriers (inverted Sine wave and Triangle wave), each group having carrier and its 90° shifted. The arbitrary selection of these carriers is based on the linear feedback shift registers value (‘0’ or ‘1’). This random carrier selection is serving to improve the spectral quality of the output of the inverter. This improved waveform has been derived from third harmonic injected sine PWM technique. Simulation results confirm the effectiveness of the proposed scheme in providing very less harmonic noises with minimum distortion and satisfactory fundamental component. This study also shows the implementation compatibility of the work with Field Programmable Gate Array environment.
关键词： Harmonic spread factor,voltage source inverter,linear feedback shift register,random pulse width modulation,pseudo random binary sequence
更新于2025-09-23 15:19:57
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[IEEE 2018 IEEE SENSORS - New Delhi, India (2018.10.28-2018.10.31)] 2018 IEEE SENSORS - Automated Technique Based on Image Processing for Accurate Diagnosis of Finger Clubbing
摘要： Medical observation has revealed that lung cancer, congenital heart defects, chronic lung infection, infection of the lining of heart chambers and a large number of other disorders mostly related to the lung and the heart is accompanied by the phenomenon of the “clubbing of the fingers”. It is actually a distortion of the general shape of the finger that now takes a bulging appearance, resembling a drumstick or a bird’s beak. Therefore finger clubbing can be treated as an early symptom of the onset of many such disorders. In this work, we have developed a software based on image processing techniques for the quantitative detection of finger clubbing. The image processing techniques undertaken in this work include lovi-bond angle detection and finger width profile monitoring by measuring Distal Phalange Depth-Inter Phalange Depth (DPD-IPD) ratio. Thus the system developed in this work provides an early manifestation of such disorders so that early diagnosis and effective treatment can be undertaken and the risk factor in such cases can be substantially reduced.
关键词： finger width profile,DPD-IPD ratio,finger clubbing,digital clubbing,lovi-bond angle
更新于2025-09-19 17:15:36
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Spectral-Efficient Reconstructed LACO-OFDM Transmission for Dimming Compatible Visible Light Communications
摘要： Dimming control is critical in practical visible light communication (VLC) systems to satisfy illumination demand. Upon exploiting multiple layers of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) signals for simultaneous transmission, layered ACO-OFDM (LACO-OFDM) constitutes a promising spectral-efficient modulation technique for VLC. However, dimming by integrating the industry-preferred pulse width modulation (PWM) to the LACO-OFDM scheme induces severe clipping noise due to the nonlinearity of LEDs. In this paper, we conceive a reconstructed LACO-OFDM (RLACO-OFDM) scheme incorporating the PWM technique for VLC to accommodate the dimming demands for indoor illumination, while maintaining a spectral-efficient communication link. Moreover, superior to its counterparts, the transmitted symbols in the RLACO-OFDM based VLC system can be readily recovered by a standard LACO-OFDM receiver while no additional detection of the PWM signal is required, which reduces the receiver complexity. Numerical results demonstrate that the proposed RLACO-OFDM is capable of realizing high spectral efficiency over a broad dimming range.
关键词： asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM),layered ACO-OFDM,pulse width modulation (PWM),Visible light communication (VLC),dimming control
更新于2025-09-19 17:15:36