High Frequency Techniques Research Articles

Cascaded H–Bridge Multilevel Inverter: Review of Topologies and Pulse Width Modulation

Multilevel inverters (MLIs) have become more popular for medium-voltage and high-power applications. The cascaded H-bridge multilevel inverter (CHBMLI) is one of the three most popular topologies of MLIs. It was more reliable due to its fewer components per level. The number of possible output voltage levels is more than twice the number of DC sources, the most suitable topology for integration with renewable energy sources, easy to design, and has good performance with modularity. The main disadvantage of CHBMLI is the need for separate DC sources for each H-bridge. However, this can be considered as an advantage to be employed in renewable energy applications. This paper provides a review of CHBMLI topologies and pulse width modulation (PWM) techniques, including fundamental and high switching frequency techniques, such as selective harmonic elimination (SHE), space vector modulation (SVM), nearest level modulation (NLM), and Carrier-Based PWM.

An Effective Modulation Technique for Multi Level Inverters

High frequency modulation techniques play very important role in multilevel inverters MLIs. These techniques have several advantages over low frequency modulation methods where they provide lower harmonic contents and higher performance in real time adaptation. Multicarrier sinusoidal pulse width modulation MCSPWM is a common high frequency technique and control method for MLIs. The synchronization of carrier signals, complexity of hardware components and high cost are very important issues when implementing multicarrier MCSPWM in real time. This paper presents an efficient approach that can overcome the problems of multicarrier signals. The proposed approach combines the advantages of low and high frequency modulation techniques. Real time adaptation of modulation index can be achieved easily, and harmonics contents are reduced to very low levels as well. Simulation and comparison of the proposed approach with MCSPWM are presented. The proposed approach is applied and tested effectively with different topologies of MLIs.

Experimental demonstration of the strong impact of plasma excitation frequency range on electronic properties of silicon nitride/GaAs interfaces

Passivation/encapsulation of III–V electronic and photonic circuits and devices is often performed using plasma-enhanced chemical vapor deposited SixNy with a standard high frequency excitation of 13.56 MHz. The hypothesis of a possible higher passivation process efficiency for low frequency SixNy deposition on GaAs has been suggested by comparison with published work on high frequency. In this work, we report a direct experimental demonstration of the effect of the RF plasma source frequency on electronic properties of GaAs/SixNy interfaces during a passivation process. GaAs substrates from the same wafer are processed in the same reactor using the same plasma conditions except for the plasma excitation frequency and MIS structures are fabricated to probe interface electronic properties. Comparing interfaces obtained with a plasma source frequency below or over the ion transit frequency (∼ 2 MHz) shows drastic difference in electrical behavior. While Fermi level is pinned when a high frequency plasma (13.56 MHz) is used, a good modulation of surface potential is observed with a low frequency plasma (380 kHz), indicating an interface states density lower by orders of magnitude. X-ray photoelectron spectra analysis is performed in order to investigate GaAs/SixNy interface formation in relation with plasma excitation frequency. We show that a short exposure to the low frequency plasma results in the almost complete removal of native oxides species. To the contrary, a significant amount of oxides remains on structures treated by the high frequency technique. The low frequency plasma technique could be a better alternative to the standard high frequency, as it is less reliant on wet chemical treatments like ammonium sulfide passivation and could allow for processing at lower temperatures.

Characterization of transverse electron pulse trains using RF powered traveling wave metallic comb striplines

Advancements in ultrafast electron microscopy have allowed elucidation of spatially selective structural dynamics. However, as the spatial resolution and imaging capabilities have made progress, quantitative characterization of the electron pulse trains has not been reported at the same rate. In fact, inexperienced users have difficulty replicating the technique because only a few dedicated microscopes have been characterized thoroughly. Systems replacing laser driven photoexcitation with electrically driven deflectors especially suffer from a lack of quantified characterization because of the limited quantity. The primary advantages to electrically driven systems are broader frequency ranges, ease of use and simple synchronization to electrical pumping. Here, we characterize the technical parameters for electrically driven UEM including the shape, size and duration of the electron pulses using low and high frequency chopping methods. At high frequencies, pulses are generated by sweeping the electron beam across a chopping aperture. For low frequencies, the beam is continuously forced off the optic axis by a DC potential, then momentarily aligned by a countering pulse. Using both methods, we present examples that measure probe durations of 2 ns and 10 ps for the low and high frequency techniques, respectively. We also discuss how the implementation of a pulsed probe affects STEM imaging conditions by adjusting the first condenser lens.

UHF Sensors Based Localization of Partial Discharge Sources in Air-Insulated Electrical Substation Using TDOA and Relative RSS Information

Time-difference of arrival (TDOA) based localization of partial discharge (PD) sources using Ultra High Frequency (UHF) technique often provides uncertain accuracy because of unavoidable errors in TDOA estimation between PD pulses. This paper presents a novel localization approach utilizing TDOA and relative received signal strength (RRSS) information together for improving the localization accuracy of PD sources within air-insulated substations (AIS). A complete PD localization system governed by this approach has been developed using multiple UHF PD sensors. The effectiveness of the proposed PD source localization approach has been validated through laboratory and field-based experiments in real-life AIS.

A new approach for microstructure imaging

A recurring issue with microstructure studies is specimen lighting. In particular, microscope lighting must be deployed in such a way as to highlight biological elements without enhancing caustic effects and diffraction. We describe here a high frequency technique due to address this lighting issue. First, an extensive study is undertaken concerning asymptotic equations in order to identify the most promising algorithm for 3D microstructure analysis. Ultimately, models based on virtual light rays are discarded in favor of a model that considers the joint computation of phase and irradiance. This paper maintains the essential goal of the study concerning biological microstructures but offers several supplementary notes on computational details which provide perspectives on analyses of the arrangements of numerous objects in biological tissues.

Impact of Surfactants on the Electrical and Rheological Aspects of Silica Based Synthetic Ester Nanofluids

This study reports experimental investigations of the effects of different surfactants (CTAB, Oleic acid and Span 80) on silica based synthetic ester nanofluids. The positive and negative potential observed for the ionic (CTAB) and non-ionic surfactant (Span 80) from zeta potential analysis indicates an improved stability. The optimization of nanofillers and surfactants is performed considering the corona inception voltage measured using ultra high frequency (UHF) technique and fluorescent fiber. Rheological analysis shows no significant variation of properties with shear rate, implying Newtonian behavior even with the addition of surfactant. In addition, the permittivity of the nanofluid is not much affected by adding surfactant but a marginal variation is noticed in the loss tangent with the effect of temperature. The fluorescence spectroscopy shows no change in the emission wavelength with the addition of silica nanofiller and surfactants. Flow electrification studies indicate an increase in the streaming current with the rotation speed and temperature, with a higher current magnitude observed in the case of nanofluids.

Surface imaging of breast implants using modern high-frequency ultrasound technology in comparison to high-end sonography with power analyses for B-scan optimization1.

This study aims to evaluate optimized breast implant surface-structure analysis by comparing high-end ultrasound technology with a new high frequency technique. This comparative study used new breast implants with different surfaces in an in vitro setting. Nine idle silicon or polyurethane (PU) breast implants were examined by two investigators in an experimental in vitro study using two high-end ultrasound devices with multi-frequency transducers (6-15 MHz, 9-16 MHz, 12.5-33 MHz).The ultrasound B-Mode was optimized using tissue harmonic imaging (THI), speckle reduction imaging (SRI, level 0-5), cross beam (high, medium, low) and photopic.Using a standardized ultrasound protocol, the implants were examined in the middle (point of highest projection) and lateral, by two independent examiners.Image evaluation was performed on anonymized digital images in the PACS. The aim was to achieve an artifact-free recording of the surface structure, the surface coating, the total image structures and, as far as possible, an artifact-free internal representation of the implants.For independent surface evaluation a score was used (0 = undetectability of surface structures, rich in artifacts, 5 = best possible, artifact free image quality). The quality of ultrasound imaging of breast implant surfaces after the optimization of B-Scan differed significantly comparing high-end ultrasound technology with modern high-frequency ultrasound technology (p < 0,05).The following setting has been found to be the best setting with the highest image quality:B-Mode, SRI value 3, Crossbeam high level with color coded imaging for B- mode. In the total examined frequency range of 6-33 MHz, the highest image quality was found in the average frequency range of 12.5-33 MHz at both measured points. For both devices, device 1 (high-end) and device 2 (high frequency) ultrasound, the image quality was in the12.5-33 MHz frequency range with an average image quality of 3.236. It was significantly higher, than in the lower frequency ranges and the same frequency range with THI. (p < 0,05). The image quality of the high-end sonography device was superior to the conventional high-frequency ultrasound device in all frequency ranges. High-end ultrasound imaging technology was superior in the quality of implant surface evaluation in comparison to high-frequency ultrasound sonography. The gained knowledge can serve as a basis for further multicenter clinical application and studies with the aim to develop an objective, precise tool to evaluate the implant and the surrounding tissue with ultrasound.

Influence of Nanofiller Dispersion on Electrical and Mechanical Properties of Epoxy Alumina Nanocomposites

The electrical and mechanical properties of the epoxy alumina nanocomposites depend on the uniform dispersion of the nanofiller in the epoxy matrix. Epoxy alumina nanocomposites were prepared using 1, 3, and 5 wt% of alumina nanofiller, and electrical and mechanical properties were analyzed using experimental and modelling studies. Water droplet initiated corona inception voltage (CIV) was identified using fluorescence fiber technique and by Ultra High Frequency (UHF) technique, under AC and DC voltages. The CIV formed due to water droplet have reduced drastically with increase in number of droplets and fluorescent fiber technique found to be more sensitive to identify water droplet initiated discharges. A micro mechanical model was proposed to analyse the combined effect of the interphase and agglomeration properties of the alumina nanoparticles on the tensile strength of epoxy alumina nanocomposites. Variation in ϕagg, Eagg, and E were analysed by adopting the non-parametric distribution of alumina nanoparticles and Young’s modulus increased with the increment in the alumina nanofiller dispersion level. The presence of aggregated particles exhibits a negative effect on the tensile properties of nanocomposites.

Combined application of ultrasonic and ultra high frequency techniques in the partial discharge detection and positioning of gas insulated switchgear

Partial discharge live detection of GIS can effectively find internal defects, but it is often interfered by surrounding environmental noise, which affects the correct identification and judgment of defect signals. This paper introduces the application of AE and UHF technique in the live detection of GIS, which successfully recognizes the external interference signal, analyzes the cause of abnormal partial discharge signal based on signal characteristics, and uses the method by calculating time difference to locate the source of the signal. An internal checking on the equipment were conducted based on the test results while the equipment were stopped, and verified the existence of floating fault inside GIS.

Partial discharge localisation in transformers using UHF technique: non-iterative method

The mathematical model of the Partial Discharge (PD) location detection system in transformers, using the Ultra High Frequency (UHF) technique, is a system of non-linear sphere equations. These non-linear equations are solved to determine the PD source co-ordinates. In this paper, a non-iterative method is studied to determine the PD location. For the study, a simulation-based system is modelled in an EM-solver. The UHF technique-based detection of the PD source location needs a minimum of four sensors. The non-iterative algorithm’s significant drawback is that it provides two solutions. However, in the present study, five sensors are positioned at specified coordinates to attain the real PD position (from the two obtained solutions) with higher accuracy.

Generation of Encrypted FSK RF Signals for Secured Communication Inspired with High Frequency Technique

The paper describes a secret data transmission method using high-frequency techniques. The data security system consists of two inter-related parts. One deals with the encryption of binary data using the RSA algorithm on software platform. The other introduces an innovative conception of implementing encrypted FSK signal generation simulated with microwave techniques & technologies. Here, it requires the simultaneous generation of a pair of two independent high-frequency signals with the help of reflex klystron. In this scheme, the high-frequency generator is biased by the repeller voltage and superimposed on a series of RSA encrypted binary data. So the system creates two high frequencies, one representative to the positive and the other one to the negative portion of the data referring in an FSK signal. The new concept has been also verified with the help of simulation and experiment.

ANN Fed High Gain Luo Converter based Reduced Switch Multilevel Inverter for Single Phase Network Bridged PV Arrangement

In the present scenario photovoltaic (PV) systems feature resonant interest in the recent researches. The amount from the PV frame is highly oscillated due to temperature variation. In this proposed work, the ANN based MPPT algorithm extracts maximum energy from the PV system by benefit of high gain DC-DC Luo converter, the Luo converter produced voltage is given to the single phase grid through reduced switch seven level inverter. The proposed seven level inverter is controlled by high frequency technique multicarrier modulation technique. The PI controller based closed loop grid synchronization is implemented for solving the power quality issues. The multilevel inverter reduce the total harmonics distortion in the output AC voltage waveform. The developed work is carried out using Matlab software-based simulation with various solar irradiation and degree. Keywords: Artificial Neural Network

The Hyperfine Transition for the Definition of the Second

AbstractThe unit of time of the International System of Units (SI), the “atomic second” was defined through a constant of physics in 1967. It is derived from the frequency of the hyperfine transition of the atom of cesium 133. From the astronomical definition of the second until today, the accuracy of the realization of the second has improved by eight orders of magnitude, with a rate that has increased since the development of the cesium frequency standards, to reach parts in 1016 for the best clocks today. In 2018, when the new SI was adopted, the time metrology community proved that a new generation of frequency standards operating in optical wavelengths has uncertainties at the level of 10–18, and challenge the implementation of high accurate frequency and time comparison techniques to decide on a revision of the definition of the second. Herein, the progress in the definition and realization of the second from astronomy until today is reviewed, an inventory of the present resources is assembled and a brief view for the future given.

First principles research on the dynamic conductance and transient current of black phosphorus transistor

The validity of high frequency technique and time-domain measurement to nanoscale electronic devices provides an imperious demand to explore the ultrafast electron dynamics and nonlinear responses accompanied with material science in theory. In this work, we carried out a first principles calculation to research the dynamic response in both frequency and time domain of a nanoscale Cu/black phosphorus (Cu/BP) transistor. The system shows n-type transport behaviors due to the charge transfer from the Cu/BP contact to the central BP section, which is different from the p-type pristine BP transistor. By adjusting the gate voltage, on-off ratio of conductance can reach up to 103 which is expected to further increase with the length of the central BP section. The Cu/BP transistor always shows capacitive-like behaviors even at high frequency, and cut-off frequency is estimated up to 75 THz. Transient current evolution shows abundant quantum scattering behaviors, and two important time scales were analyzed. The tune-on time is comparable to the Fermi velocity of pristine BP, and is roughly independent of the magnitudes of bias voltages. The relaxation time is roughly hundreds of femtoseconds, which corresponds to the cut-off frequency up to a point and can be further reduced by dephasing effect. The rapid response of hundreds of femtoseconds indicates that the Cu/BP transistor maybe work as high frequency nanoscale electronic device.

Recently Developed Reduced Switch Multilevel Inverter for Renewable Energy Integration and Drives Application: Topologies, Comprehensive Analysis and Comparative Evaluation

Recently, multilevel inverters (MLIs) have gained lots of interest in industry and academia, as they are changing into a viable technology for numerous applications, such as renewable power conversion system and drives. For these high power and high/medium voltage applications, MLIs are widely used as one of the advanced power converter topologies. To produce high-quality output without the need for a large number of switches, development of reduced switch MLI (RS MLI) topologies has been a major focus of current research. Therefore, this review paper focuses on a number of recently developed MLIs used in various applications. To assist with advanced current research in this field and in the selection of suitable inverter for various applications, significant understanding on these topologies is clearly summarized based on the three categories, i.e., symmetrical, asymmetrical, and modified topologies. This review paper also includes a comparison based on important performance parameters, detailed technical challenges, current focus, and future development trends. By a suitable combination of switches, the MLI produces a staircase output with low harmonic distortion. For a better understanding of the working principle, a single-phase RS MLI topology is experimentally illustrated for different level generation using both fundamental and high switching frequency techniques which will help the readers to gain the utmost knowledge for advance research.

A review of ultrasound detection methods for breast microcalcification.

Breast microcalcifications are one of the important imaging features of early breast cancer and are a key to early breast cancer diagnosis. Ultrasound imaging has been widely used in the detection and diagnosis of breast diseases because of its low cost, nonionizing radiation, and real-time capability. However, due to factors such as limited spatial resolution and speckle noise, it is difficult to detect breast microcalcifications using conventional B-mode ultrasound imaging. Recent studies show that new ultrasound technologies improved the visualization of microcalcifications over conventional B-mode ultrasound imaging. In this paper, a review of the literature on the ultrasonic detection methods of microcalcifications was conducted. The reviewed methods were broadly divided into high-frequency B-mode ultrasound imaging techniques, B-mode ultrasound image processing techniques, ultrasound elastography techniques, time reversal techniques, high spatial frequency techniques, second-order ultrasound field imaging techniques, and photoacoustic imaging techniques. The related principles and research status of these methods were introduced, and the characteristics and limitations of the various methods were discussed and analyzed. Future developments of ultrasonic breast microcalcification detection are suggested.

Field Applications of Ultra High Frequency Techniques for Defect Detection in GIS

The reliable and stable operation of power apparatus is important for the development of GIS. It is important to utilize condition monitoring technologies and anticipate possible failures in advance. Many papers have been published about the partial discharge detection with UHF or X-ray in laboratory, but seldom in field application. Thus, many engineers at project sites are not familiar with the current professional diagnosis techniques. Recently, during the GIS routine data analysis obtained by partial discharge online monitoring system, it was found that the UHF monitoring signals’ developing trend of the 220 kV GIS No. 2 high-voltage side of transformer in phase C at an actual station was abnormal and needed further detection. In order to precisely investigate the problem and then guide the operation and maintenance activities, a series of professional diagnoses were conducted. Three new types of partial discharge detection and positioning methods were applied for accuracy, including UHF partial discharge detection based on multi-stage amplified signal demodulation and multiple weighted averages processing; the partial discharge detection based on the signal radiation hole of insulation disk at the ground connection; and the positioning method based on UHF-SHF. After a series of troubleshooting works, the partial discharge defects have been diagnosed, and the case can be referred in the field monitoring of GIS.

Review and Comparison of Clock Jitter Noise Reduction Techniques for Lowpass Continuous-Time Delta-Sigma Modulators

It is well known that continuous-time Delta-Sigma modulators are very sensitive to clock jitter effects. In literature, a number of techniques have been proposed to cope with them. In this brief, we present a detailed review and comparison of the reported techniques. While the effectiveness to reduce clock jitter effects may be of most importance in this comparison, we also consider other performance metrics such as circuit complexity and overhead to implement the technique, power consumption overhead of technique, synthesis complexity incurred in system-level design, extensibility of the technique from single-bit to multi-bit operation, and robustness to process variation. When clock jitter is relatively large, the fixed-width pulse feedback technique is most effective to reduce clock jitter effects among all techniques at high sampling frequency, while switched-capacitor-resistor and switched-shaped current techniques have best performance at medium frequency or below.

Understanding the dielectric properties of pressboard material thermally aged in Dibenzyl Disulphide (DBDS) included transformer oil

Surface Discharge Inception Voltage (SDIV) of unaged and copper sulphide diffused Oil Impregnated Pressboard (OIP) material was studied by adopting Ultra High Frequency (UHF) technique. Copper sulphide diffusion into OIP material was carried out by thermal aging of pressboard material in Dibenzyl Disulphide (DBDS) added transformer oil. The SDIV reduces with increase of thermal aging temperature. The current pulse injected in positive and negative half cycle during the surface discharge of the AC shows the rise time of 0.8ns and 1ns respectively. The FFT analysis of UHF signal measured during surface discharge process has shown frequency content in the range 0.7–1.2 GHz with its dominant frequency at 0.9 GHz. The life of the charge presented on the pressboard increases with thermal aged specimen. Energy dispersive spectroscopy (EDS) analysis of OIP material indicates presence of copper and sulphur content. Frequency Domain Dielectric Spectroscopy (FDDS) studies indicate the permittivity(er), dissipation factor (tan(δ)), conductivity (σdc) increases and relaxation time (τ), coefficient (α) decrease with OIP material (in air / Nitrogen) aged at higher temperature in DBDS added transformer oil. Cole-Cole double relaxation model was used to understand the dielectric parameters of copper sulphide diffused OIP material. The DC conductivity of pressboard material aged in DBDS included transformer oil follows Arrhenius law and the activation energy decreases with increase in temperature of thermal aging.