Second‐harmonic component in the focused beam transmitted through a weakly dispersive liquid layer

1999 ◽  
Vol 105 (2) ◽  
pp. 957-957
Author(s):  
Shigemi Saito
Keyword(s):  
Liquid Layer ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Focused Beam

scholarly journals Optimal Design of Annular Phased Array Transducers for Material Nonlinearity Determination in Pulse–Echo Ultrasonic Testing

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5565
Author(s):  
Sungjong Cho ◽  
Hyunjo Jeong ◽  
Ik Keun Park
Keyword(s):  
Optimal Design ◽  
Ultrasonic Testing ◽  
Phased Array ◽  
Second Harmonic ◽  
Harmonic Wave ◽  
Harmonic Component ◽  
Beam Model ◽  
Sound Beam ◽  
Pulse Echo ◽  
Focused Beam

Nonlinear ultrasound has been proven to be a useful nondestructive testing tool for micro-damage inspection of materials and structures operating in harsh environment. When measuring the nonlinear second harmonic wave in a solid specimen in the pulse–echo (PE) testing mode, the stress-free boundary characteristics brings the received second harmonic component close to zero. Therefore, the PE method has never been employed to measure the so-called “nonlinear parameter (β)”, which is used to quantify the degree of micro-damage. When there are stress-free boundaries, a focused beam is known to improve the PE reception of the second harmonic wave, so phased-array (PA) transducers can be used to generate the focused beam. For the practical application of PE nonlinear ultrasonic testing, however, it is necessary to develop a new type of PA transducer that is completely different from conventional ones. In this paper, we propose a new annular PA transducer capable of measuring β with improved second harmonic reception in the PE mode. Basically, the annular PA transducer (APAT) consists of four external ring transmitters and an internal disk receiver at the center. The focused beam properties of the transducers are analyzed using a nonlinear sound beam model which incorporates the effects of beam diffraction, material attenuation, and boundary reflection. The optimal design of the APAT is performed in terms of the maximum second harmonic reception and the total correction close to one, and the results are presented in detail.

scholarly journals Control Strategy Based on Arm-Level Control for Output and Circulating Current of MMC in Stationary Reference Frame

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4160
Author(s):  
Waqar Uddin ◽  
Tiago D. C. Busarello ◽  
Kamran Zeb ◽  
Muhammad Adil Khan ◽  
Anil Kumar Yedluri ◽  
...  
Keyword(s):  
Reference Frame ◽  
Control Method ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Effective Control ◽  
Level Control ◽  
Circulating Current ◽  
Stationary Reference Frame ◽  
Pr Controller ◽  
Dc Component

This paper proposed a control method for output and circulating currents of modular multilevel converter (MMC). The output and circulating current are controlled with the help of arm currents, which contain DC, fundamental frequency, and double frequency components. The arm current is transformed into a stationary reference frame (SRF) to isolate the DC and AC components. The AC component is controlled with a conventional proportional resonant (PR) controller, while the DC component is controlled by a proportional controller. The effective control of the upper arm and lower arm ultimately controls the output current so that it delivers the required power to the grid and circulating current in such a way that the second harmonic component is completely vanished leaving behind only the DC component. Comparative results of leg-level control based on PR controller are included in the paper to show the effectiveness of the proposed control scheme. A three-phase, five-level MMC is developed in MATLAB/Simulink to verify the effectiveness of the proposed control method.

scholarly journals Control of MMC-Based STATCOM as an Effective Interface between Energy Sources and the Power Grid

Electronics ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 1264 ◽  
Author(s):  
Fatemeh Shahnazian ◽  
Ebrahim Adabi ◽  
Jafar Adabi ◽  
Edris Pouresmaeil ◽  
Kumars Rouzbehi ◽  
...  
Keyword(s):  
Reactive Power ◽  
Control Method ◽  
Second Harmonic ◽  
Power Grid ◽  
Harmonic Component ◽  
Current Control ◽  
Energy Sources ◽  
Stable Operation ◽  
Multilevel Converters ◽  
Steady State Operation

This paper presents a dynamic model of modular multilevel converters (MMCs), which are considered as an effective interface between energy sources and the power grid. By improving the converter performance, appropriate reactive power compensation is guaranteed. Modulation indices are calculated based on detailed harmonic evaluations of both dynamic and steady-state operation modes, which is considered as the main contribution of this paper in comparison with other methods. As another novelty of this paper, circulating current control is accomplished by embedding an additional second harmonic component in the modulation process. The proposed control method leads to an effective reduction in capacitor voltage fluctuation and losses. Finally, converter’s maximum stable operation range is modified, which provides efficiency enhancements and also stability assurance. The proficiency and functionality of the proposed controller are demonstrated through detailed theoretical analysis and simulations with MATLAB/Simulink.

scholarly journals Second-harmonic generation in focused beam fields of phased-array transducers in a nonlinear solid with a stress-free boundary

2019 ◽  
Vol 1 (2) ◽  
pp. 117-125
Author(s):  
Hyunjo Jeong ◽  
Shu-zeng Zhang ◽  
Xiong-bing Li
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Phase Difference ◽  
Phased Array ◽  
Second Harmonic ◽  
Free Boundaries ◽  
Harmonic Components ◽  
Focused Beams ◽  
Pulse Echo ◽  
Focused Beam

Abstract In nonlinear acoustic harmonic generation in solids with stress-free boundaries, such a boundary is known to destructively change the second harmonic generation, and the pulse-echo method is not practically applicable. Focused beams have often been used for fluid nonlinearity and biomechanical imaging in pulse-echo test setups. This paper considers the focused beam fields of linear phased-array transducers to ensure that pulse-echo harmonic generation can be applied to solids with stress-free boundaries. The fundamental and second-harmonic beam fields that are focused and reflected at the stress-free and rigid boundaries are calculated and their properties are investigated in terms of the received average fields. The phase difference between the two second-harmonic components after reflection from the boundary—that is, the reflected and the newly generated second harmonic—is emphasized. The phase difference is used to explain the improved and accumulated second harmonic observed in the simulation results.

A new system for in vivo assessment of the degree of nonlinear generation using the second harmonic component in echo signals

2004 ◽  
Vol 30 (11) ◽  
pp. 1511-1516 ◽  
Author(s):  
Yasutomo Fujii ◽  
Nobuyuki Taniguchi ◽  
Iwaki Akiyama ◽  
Jing-Wen Tsao ◽  
Kouichi Itoh
Keyword(s):  
Second Harmonic ◽  
Harmonic Component ◽  
Nonlinear Generation ◽  
In Vivo Assessment ◽  
New System

scholarly journals Line Frequency Instability of One-Cycle-Controlled Boost Power Factor Correction Converter

Electronics ◽  
2018 ◽  
Vol 7 (9) ◽  
pp. 203 ◽  
Author(s):  
Rui Zhang ◽  
Wei Ma ◽  
Lei Wang ◽  
Min Hu ◽  
Longhan Cao ◽  
...  
Keyword(s):  
Power Factor ◽  
Power Factor Correction ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Input Voltage ◽  
Frequency Instability ◽  
Control Circuit ◽  
Line Frequency ◽  
Control Loops ◽  
Non Linear

Power Factor Correction (PFC) converters are widely used in engineering. A classical PFC control circuit employs two complicated feedback control loops and a multiplier, while the One-Cycle-Controlled (OCC) PFC converter has a simple control circuit. In OCC PFC converters, the voltage loop is implemented with a PID control and the multiplier is not needed. Although linear theory is used in designing the OCC PFC converter control circuit, it cannot be used in predicting non-linear phenomena in the converter. In this paper, a non-linear model of the OCC PFC Boost converter is proposed based on the double averaging method. The line frequency instability of the converter is predicted by studying the DC component, the first harmonic component and the second harmonic component of the main circuit and the control circuit. The effect of the input voltage and the output capacitance on the stability of the converter is studied. The correctness of the proposed model is verified with numerical simulations and experimental measurements.

Development of lateral interactions in the infant visual system

1992 ◽  
Vol 8 (1) ◽  
pp. 3-8 ◽  
Author(s):  
Samuel Sokol ◽  
Vance Zemon ◽  
Anne Moskowitz
Keyword(s):  
Visual System ◽  
Long Range ◽  
Short Range ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Frequency Component ◽  
Human Infants ◽  
Long Range Interactions ◽  
Harmonic Components ◽  
Inhibitory Interactions

AbstractThe development of lateral inhibitory interactions in the infant visual system, as reflected by the visual-evoked potential (VEP), was studied using a radial, asymmetrical windmill-dartboard stimulus. This contrast-reversing stimulus generates VEP responses with a strong fundamental frequency component and an attenuated second harmonic component (relative to that obtained using a symmetrical stimulus). These two harmonic components reflect distinct phenomena, and appear to be the result of short-range (the fundamental) and long-range (attenuated second harmonic) lateral inhibitory interactions elicited by differential luminance-modulation of contiguous spatial regions. We studied the development of the short-and long-range interactions at 100% and 30% contrast in human infants using both VEP amplitude and phase measures. Attenuation of the second harmonic (long-range interactions) was adult-like by 8 weeks of age while the strength of the fundamental (short-range interactions) was adult-like by 20 weeks suggesting a differential development of long-range and short-range interactions. In contrast, corresponding phase data indicated significant immaturities at 20 weeks of age for both the short-and long-range components.

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