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- 2019
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- anharmonic Bloch oscillations
- coupled mode method
- array of waveguides
- active harmonic filter
- Multifunctional VSC
- unity power factor operation
- power quality improvement
- grid-connected SPV system
- renewable energy sources
- Optoelectronic Information Science and Engineering
- Electrical Engineering and Automation
- Shevchenko Pridnestrovskii State University
- Malaviya National Institute of Technology
- Academy of Sciences of Moldova
- IIITD&M Kancheepuram
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Fano Resonance on Nanostructured Lithium Niobate for Highly Efficient and Tunable Second Harmonic Generation
摘要： Second harmonic generation (SHG) is an important nonlinear process which is critical for applications, such as optical integrated circuit, nonlinear microscopy, laser, etc. Many challenges remain in the improvement of nonlinear conversion ef?ciency, since the typical value is of only 10?5 in nanostructures. Here, we theoretically demonstrate a periodic structure consisting of a lithium niobate (LN) bar and an LN disk, on a nanoscale (~300 nm) thin-?lm platform, which is proposed for a highly ef?cient SHG. By breaking the structure symmetry, a Fano resonance with a high Q, up to 2350 and a strong optical ?eld enhancement reaching forty-two folds is achieved, which yields a high conversion ef?ciency, up to 3.165 × 10?4. In addition to its strong second harmonic (SH) signal, we also demonstrate that by applying only 0.444 V on the planar electrode con?gurations of the nanostructured LN, the wavelength of SH can be tuned within a 1 nm range, while keeping its relatively high conversion ef?ciency. The proposed structure with the high nonlinear conversion ef?ciency can be potentially applied for a single-molecule ?uorescence imaging, high-resolution nonlinear microscopy and active compact optical device.
关键词： harmonic generation and mixing,lithium niobate,Fano resonance
更新于2025-09-23 15:22:29
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Changes in the Collagen Structure of Thyroid Nodule Capsules Determined by Polarization-Resolved Second Harmonic Generation Microscopy
摘要： Thyroid carcinomas represent a challenging problem as their differentiation from the much more frequent benign pathologies can be sometimes difficult. Automatic diagnostic approaches that can differentiate between malignant and benign thyroid nodules would be of great benefit for addressing thyroid pathologies. In this study we have used polarization-resolved second harmonic generation microscopy to investigate collagen organization in the fibrillar capsules surrounding human thyroid nodules. We demonstrate that imaging the collagen capsules at different laser beam polarization angles and fitting the second harmonic generation intensity with a theoretical curve can yield information on the nonzero components of the second order susceptibility tensor and the orientation of the collagen fibres. We have used this approach to differentiate between capsules surrounding the thyroid follicular adenoma and papillary carcinoma nodules. These results indicate that polarization-resolved second harmonic generation microscopy can provide additional information about the collagenous capsule surrounding thyroid nodules, which may complement intensity-based quantitative second harmonic generation microscopy and eventually traditional histopathologic examination.
关键词： second harmonic generation,thyroid nodules,collagen
更新于2025-09-23 15:22:29
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Nonlinear Analytic Solution of Eulerian Beam-Wave Interaction Theory Considering Harmonic Interaction of Traveling-Wave Tube Amplifiers
摘要： In this paper, a novel Eulerian nonlinear beam-wave interaction (BWI) theory considering harmonic interaction of a helix traveling-wave tube (TWT) is developed. Derived from this Eulerian model, the novel Eulerian nonlinear analytic solutions (the fourth-order analytic solution of fundamental and the second-order analytic solution of harmonic) are first obtained by the method of successive approximation. The analytic relationships between electric fields of fundamental/harmonic frequencies and electron phases are also found. Then, the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory are compared to a Lagrangian theory. C-band and Ku-band helix TWTs based on a single pitch section are included in the simulation. It is found that the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory agree well with the Lagrangian theory at 1-dB gain compression point. Interestingly, the saturation effects caused by electron overtaking cannot be found by the traditional Eulerian analysis but can be described by the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory. Moreover, Eulerian nonlinear analytic solutions are simpler and more accurately than existing approaches and, thus, allow analytical progress. This paper confirms that the Eulerian nonlinear analytic solutions can outperform the previous proposals.
关键词： analysis,nonlinear,traveling-wave tubes (TWTs),Eulerian,Analytic solution,beam-wave interaction (BWI),harmonic
更新于2025-09-23 15:22:29
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Time–frequency-based non-harmonic analysis to reduce line-noise impact for LIGO observation system
摘要： Gravitational waves (GWs) are the subjects of a new type of space observation that is expected to reveal new information on the early universe, neutron stars, and black holes. To reduce the impact of the widely used notch filter on GW observations, we propose the use of non-harmonic analysis (NHA) for the high-accuracy visualization of GWs. A simulated signal is used to compare the results obtained using short-time Fourier transform, Hilbert spectrum analysis, Hilbert–Huang transformation, and NHA. We demonstrate that NHA exhibits superior performance. In addition, we verify the analytical precision of NHA using actual data measured by the Laser Interferometer Gravitational-Wave Observatory (LIGO). We found that the high time–frequency resolution of NHA and the small influence that the analysis window has on this technique facilitate effective quantitative analysis, even for LIGO signals containing mixing noise. In addition, we achieve GW visualization up to the noise limit without using a notch filter.
关键词： Noise reduction,Non-harmonic analysis,Gravitational wave
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE Power & Energy Society General Meeting (PESGM) - Portland, OR, USA (2018.8.5-2018.8.10)] 2018 IEEE Power & Energy Society General Meeting (PESGM) - A Study on Control Strategy of PV inverter for Harmonic Mitigation in A Microgrid
摘要： This paper presents a study of the control strategies of three-phase grid-connected photovoltaic inverter to mitigate its harmonic current output and improve the power quality of the grid. The operation principle and topology of the PV inverter is analyzed by establishing the state-space mathematical model based on the adaptation of proportional resonant (PR) and quasi-proportional resonant (QPR) controllers. According to the characteristics of the PR and QPR controllers, the theories for mitigating harmonic currents are reviewed. A three-phase ac microgrid with grid-connected inverter systems is then built on Matlab/Simulink and the performances of the inverter controllers for harmonic mitigations are verified by comparing the simulation results.
关键词： quasi-PR controller,Three-phase grid-connected PV system,harmonic compensation,inverter
更新于2025-09-23 15:22:29
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[IEEE 2018 Applications of Electromagnetics in Modern Techniques and Medicine (PTZE) - Rac?awice (2018.9.9-2018.9.12)] 2018 Applications of Electromagnetics in Modern Techniques and Medicine (PTZE) - Electrical Parameters of Chosen Organs of Abdominal Cavity and Their Influence on Electromagnetic Waves Propagation
摘要： The electrical conductivity and relative permittivity of chosen organs of abdominal cavity for the popular range of VHF and LF have been presented. They have been used for determining a dielectric loss angle of the wave's penetration into particular organs where the wave may be propagated. The change in the wavelength and its speed in the organ and the conventional depth of its penetration were computed. A considerable signification was made assuming that the electromagnetic wave hits directly from the air to the organ and there exists only the running wave moving in the direction of axis "z", described for the electrical component (analogous formula is valid for the magnetic component by relationship (2).
关键词： flat,harmonic electromagnetic waves,well- and weakly-conducting media,organs and tissues of abdominal cavity
更新于2025-09-23 15:22:29
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[IEEE 2018 25th International Conference "Mixed Design of Integrated Circuits and System" (MIXDES) - Gdynia, Poland (2018.6.21-2018.6.23)] 2018 25th International Conference "Mixed Design of Integrated Circuits and System" (MIXDES) - Optimization of Class-D Amplifier Output Stage for Piezoelectric Actuator Control
摘要： Design of a piezoelectric driver for a microelectromechanical actuator in a small form factor for laser telecommunications is introduced. The driver introduces a number of challenges due to its size and power limitations as a Microelectromechanical Systems (MEMS) actuator. Because of the small form factor, the driver must be integrated into the actuator itself, which limits its size and power. The efficiency of a linear amplifier becomes a major drawback due to the dissipated heat of only 20 W for the Laser Telecommunications Module (LTM), low efficiency of a linear amplifier becomes a major drawback due to the dissipated heat. Switching Class-E amplifiers provide exceptional efficiency compared to non-switching solutions at a price of high frequency harmonics, which allows for higher output power without additional heat dissipation. The efficiency, however, comes at a price of high frequency harmonics, which must be reduced by implementing a High-Energy-Efficiency Interference (HEEI) and Total Harmonic Distortion (THD). Driving a capacitive load, such as a piezoelectric actuator, at a high frequency with a Class-E amplifier requires a matching network to achieve the desired output power. The measurements were performed on a custom-made driver model for piezoelectric stack actuators with 270 V peak-to-peak voltage, 500 kHz switching frequency and a range of capacitive load from 2.1 nF to 20 nF.
关键词： Actuator,Driver,Amplifier,Distortion,LTM.2,Output Stage,SMPS,Class-E,Total,LTM,THD,MEMS,Harmonic,Transmission,Telecommunications,Laser,Module,High-Energy-Efficiency,HEEI,Interference,Piezoelectric,Microelectromechanical
更新于2025-09-23 15:22:29
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Enhancement of attosecond pulse in water window region by using pump-probe approach
摘要： An effective scheme to enhance the harmonic yield and the attosecond (as) pulse signal from H+2 has been proposed by using the pump-probe laser field. It is found that with the help of the multi-cycle pump pulse, H+2 can be steered into the resonance ionization regions, where the ionization probability can be remarkably enhanced. Thus, the harmonic yield can be remarkably enhanced when a sequential mid-infrared probe pulse is added. Further, by modulating the phase of the probe pulse and by adding a controlling pulse, the harmonic cutoff can be extended up to the water window region. Finally, by the Fourier transformation of the selected harmonics on the harmonic supercontinuum, the water window attosecond pulses as short as 25 as can be obtained.
关键词： High-order harmonic generation,pump-probe pulse,charge resonance enhanced ionization,single attosecond pulse,harmonic enhancement
更新于2025-09-23 15:21:21
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Ultrafast X-ray Transient Absorption Spectroscopy of Gas-Phase Photochemical Reactions: A New Universal Probe of Photoinduced Molecular Dynamics
摘要： Time-resolved spectroscopic investigations of light-induced chemical reactions with universal detection capitalize recently on single-photon molecular probing using laser pulses in the extreme ultraviolet or X-ray regimes. Direct and simultaneous mappings of the time-evolving populations of ground-state reactants, Franck?Condon (FC) and transition state regions, excited-state intermediates and conical intersections (CI), and photoproducts in photochemical reactions utilize probe pulses that are broadband and energy-tunable. The limits on temporal resolution are set by the transit- or dwell-time of the photoexcited molecules at specific locations on the potential energy surface, typically ranging from a few femtoseconds to several hundred picoseconds. Femtosecond high-harmonic generation (HHG) meets the stringent demands for a universal spectroscopic probe of large regions of the intramolecular phase-space in unimolecular photochemical reactions. Extreme-ultraviolet and soft X-ray pulses generated in this manner with few-femtosecond or sub-femtosecond durations have enormous bandwidths, allowing the probing of many elements simultaneously through excitation or ionization of core?electrons, creating molecular movies that shed light on entire photochemical pathways. At free electron lasers (FELs), powerful investigations are also possible, recognizing their higher flux and tunability but more limited bandwidths. Femtosecond time-resolved X-ray transient absorption spectroscopy, in particular, is a valuable universal probe of reaction pathways that maps changes via the fingerprint core-to-valence resonances. The particular power of this method over valence-ionization probes lies in its unmatched element and chemical-site specificities. The elements carbon, nitrogen, and oxygen constitute the fundamental building blocks of life; photochemical reactions involving these elements are ubiquitous, diverse, and manifold. However, table-top HHG sources in the “water-window” region (280?550 eV), which encompasses the 1s-absorption edges of carbon (284 eV), nitrogen (410 eV), and oxygen (543 eV), are far from abundant or trivial. Recent breakthroughs in the laboratory have embraced this region by using long driving-wavelength optical parametric amplifiers coupled with differentially pumped high-pressure gas source cells. This has opened avenues to study a host of photochemical reactions in organic molecules using femtosecond time-resolved transient absorption at the carbon K-edge. In this Account, we summarize recent efforts to deploy a table-top carbon K-edge source to obtain crucial chemical insights into ultrafast, ultraviolet-induced chemical reactions involving ring-opening, nonadiabatic excited-state relaxation, bond dissociation and radical formation. The X-ray probe provides a direct spectroscopic viewport into the electronic characters and configurations of the valence electronic states through spectroscopic core-level transitions into the frontier molecular orbitals of the photoexcited molecules, laying fertile ground for the real-time mapping of the evolving valence electronic structure. The profound detail and mechanistic insights emerging from the pioneering experiments at the carbon K-edge are outlined here. Comparisons of the experimental methodology with other techniques employed to study similar reactions are drawn, where applicable and relevant. We show that femtosecond time-resolved X-ray transient absorption spectroscopy blazes a new trail in the study of nonadiabatic molecular dynamics. Despite table-top implementations being largely in their infancy, future chemical applications of the technique will set the stage for widely applicable, universal probes of photoinduced molecular dynamics with unprecedented temporal resolution.
关键词： time-resolved spectroscopy,photochemical reactions,high-harmonic generation,X-ray transient absorption spectroscopy,nonadiabatic molecular dynamics
更新于2025-09-23 15:21:21
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Design of Microstrip Bandpass Filters Based on Stair-Step Patch Resonator
摘要： In this research article, single pole bandpass filter using stair-step patch topology based on symmetrical and asymmetrical step impedance resonators has been designed for industrial, scientific and medical (ISM) band application. This filter has been modeled by Microwave Office simulator using RT/Duroid substrate constant of 10.8, the substrate thickness of 1.27mm, loss tangent of 0.0023 and copper metallization thickness of 0.035 mm. To enhance the stopband levels of filter response, two microstrip bandpass filters have been designed as two-pole configurations based on edge, and cross-coupled stair-step patch resonators using the same simulator tool and substrate specifications. The proposed filters have compact sizes of (0.311λ(cid:2917)(cid:2925) x 0.233λ(cid:2917)(cid:2925)) for single pole filter, (0.578λ(cid:2917)(cid:2925) x 0.24λ(cid:2917)(cid:2925) )for two-pole edge coupled filter and (0.566λ(cid:2917)(cid:2925) x 0.234λ(cid:2917)(cid:2925))for two-pole cross-coupled filter designed at center frequencies of 2.4, 2.46 and 2.41 GHz respectively. These filters have interesting insertion loss and return loss magnitudes, narrow band frequency responses, second harmonic suppression and good stopband levels. Apart from ISM band applications, the proposed filters can be adopted in WLAN systems and Bluetooth applications for short range devices. The experimental results for designed filters are of good consistency with the simulations.
关键词： ISM band applications,stair-step patch resonator,filter compactness,narrow band frequency response,Microstrip bandpass filters,second harmonic frequency blocking
更新于2025-09-23 15:21:21