Carrier Frequency Component Research Articles

Resolution enhancement via guided filtering for spatial-frequency multiplexing single-shot high-speed imaging.

The frequency recognition algorithm for multiple exposures (FRAME) is a progressive single-shot high-speed videography technique that employs the spatial-frequency multiplexing concept to provide high temporal and spatial resolution. However, the inherent crosstalk from the zero-frequency component to the carrier-frequency component leads to resolution degradation and artifacts. To improve recovered frames' quality, we propose a FRAME reconstruction method using guided filters for a removal of the zero-frequency component, which can minimize the artifacts while enhance spatial resolution. A total variation (TV) denoising operation is involved to remove artifacts further to achieve optimized performances. Simulations and experiments were conducted to demonstrate the robust and efficient post-processing capability of the proposed method. With a two-frame experimental system, the results of a USAF 1951 resolution target reveal a 1.8-fold improvement in spatial resolution from 16 lp/mm to 28.5 lp/mm. For complex dynamic scenarios, the wide field of high-speed fuel spray was shot and the proposed method can resolve two droplets with a 30 μm distance which outperforms the traditional method.

State-space modeling approach for fringe pattern demodulation.

A spatial carrier fringe demodulation technique is proposed based on a state-space modeling approach for phase estimation. The fringe background intensity, carrier frequency, and phase quadrature components are considered to be the elements of the state vector, which are estimated simultaneously. The state estimation is performed using the extended Kalman filter. The simulation and experimental results are provided to demonstrate the performance comparison of the proposed method with popular and state-of-the-art methods in terms of noise robustness and phase estimation accuracy.

Reduction of Motor Drive System Loss by 5th Harmonic Superimposition PWM Control

Herein, the loss reduction of a motor drive system is experimentally studied by means of the 5th harmonic superimposition in the reference signal of a sinusoidal PWM inverter from the perspective of nonlinear magnetic characteristics. The measured data of the motor drive system loss exhibits a reduction of 1.5% in the condition when the superimposition rate is -0.15. More specifically, the motor core, copper and inverter losses are reduced. The results confirm the feasibility and efficacy of the proposed method. According to the fundamental research of a ring test with the same electrical steel as the motor, the magnetic characteristics of the B-H curve changes in the case of the 5th harmonic superimposition, which decreases the fundamental component of the current. Accordingly, the loss is considered to be reduced due to the decline in the fundamental current component and carrier frequency components.

Power Density and Temperature Rise Estimation at End-turn Stress Grading System of Large Rotating Machines under PWM Waveform

In this paper, the time-averaged power densities as well as the resulting temperature rise, on an end-turn stress grading (SG) system under PWM waveforms as functions of the carrier and the fundamental frequencies are systematically investigated by finite element method-based computations. A novel analytical approximation method to estimate the power densities and the temperature rises without time-consuming numerical computations are proposed. As a result, the maximum power density and the temperature rise increase nearly linearly with increasing fundamental and the carrier frequencies. It is suggested that power dissipations in the SG layer by the fundamental frequency component of a PWM waveform and those by the carrier frequency component can be clearly separated. Moreover, the estimated power densities and temperature rises based on the analytical approximations show reasonable agreement with the numerically computed ones, which indicates the validity of the proposed estimation method.

Residual Carrier Frequency Offset Estimation and Compensation for Commodity WiFi

The various offsets existed in the commodity WiFi devices greatly limit the use of ubiquitous WiFi signals for indoor applications. In this paper, we focus on the estimation and compensation of the residual carrier frequency offset (CFO) for the commodity WiFi devices. Specifically, we consider a distorted channel state information (CSI) model by taking into consideration various CSI errors such as packet detection delay (PDD) and CFO. We propose a multiscale sparse recovery algorithm to get rid of the effect of PDD and extract the carrier frequency component out of CSI. Then, we formulate the residual CFO estimation as a spectrum estimation problem and utilize the MUSIC algorithm to estimate the residual CFO. Real experiments and numerical simulations are conducted to evaluate the performance of the proposed method. The experimental results and simulation results show that the residual CFO is time-varying, and compared with existing methods, the proposed method can better estimate and compensate the residual CFO, and thus achieve better results.

Low Sideband Radiation Beam Scanning at Carrier Frequency for Time-Modulated Array by Non-Uniform Period Modulation

A novel beam scanning method utilizing the carrier frequency component for time-modulated array (TMA) is proposed and a significant algorithm based on the non-uniform period modulation is implemented to suppress the maximum sideband radiation (SR) level. The signal in each channel is modulated by a pair of high-speed radio-frequency (RF) switches and totally three or four delay lines with different phases. In each modulation period, three selected delay lines are connected successively with proper pulse durations to keep the switches in ON states constantly and ensure the maximum efficiency in the feeding network. Additionally, in order to suppress the relatively higher SR generated by both switches and delay lines, each channel of the TMA system has a different modulation period, which will separate the harmonic components of different elements on the frequency axis. A desired relatively low maximum SR level without complicated optimization is obtained compared with uniform period modulation and optimization algorithms. Several numeric simulations are brought out to examine the performance of the proposed methods, and the results for comparison to existing methods are also provided. A group of experiments have been done to verify its effectiveness.

Automatic wavefront reconstruction on single interferogram with spatial carrier frequency using Fourier transform

Optical interferometry can be applied to obtain the wavefront phase and reconstruct the three-dimensional wavefront by analyzing interference fringes. Single interferogram analysis based on two-dimensional Fourier transform is proposed. This method just needs to acquire and analyze single interferogram to solve the wavefront phase. Compared with phase-shift method, Single interferogram analysis can reduce experiment cost and the limitation of measuring environment like vibration, airflow and noise, and meet the requirement of real-time and dynamic interferometry. Because the wavefront phase information is included in the carrier frequency components of single interferogram, an image edge detection method is used to automatically extract the center and boundary of the first-order carrier component of the spatial spectrum of the interferogram in the frequency domain.

Self-referencing mW-scale detection of sub-ns optical phase modulation in acetylene at 1530 nm.

Application of the phase memory of acetylene (C2H2) vibrational-rotational transitions in the 1520-1540nm wavelength range for a self-referencing homodyne detection of a sub-nanosecond optical phase modulation is reported. In the proposed configuration the collinearly propagating coherent dipole radiation of the excited molecule acts like a phase-locked reference wave (local oscillator) that enables transformation of the initial phase modulation into the intensity one. This technique does not need high light intensity and can operate in a linear range of the medium optical absorption. The linear optical phase demodulation (i.e., transformation of the phase-to-amplitude light modulation) is interpreted as an introduction of an additional phase shift to the carrier frequency component of the modulated signal in the maximum of the dispersion curve of a narrow optical absorption peak. It has been experimentally demonstrated with the bulk 10cm long cuvette filled with low pressure (∼2 Torr) acetylene at room temperature. Effective demodulation of the milliwatt-scale incident laser wave of a single- and multi-mode structure is shown. As expected, the response to the fast (<1 ns) phase modulation was quadratic when the acetylene inhomogeneous Doppler-broadened (∼500 MHz) absorption line is excited in its center and was linearized by tuning at one of the absorption line sides. It is of a differentiating (high-pass) type with the cutoff frequency determined by the total spectral width of the utilized absorption line. Expected detection resolution is determined by the photon noise of the incident light intensity.

Initial Rotor Position Detection Method of SPMSM Based on New High Frequency Voltage Injection Method

A novel initial position detecting strategy of sensorless control for the surface-mounted permanent magnet synchronous motor is proposed, the scheme combines the virtual high frequency (HF) voltage pulsating injection method with the carrier frequency component method. In order to improve the sensorless control performance, this method adds the virtual HF rotation frame based on the traditional HF pulsating injection method. At the same time, the carrier frequency component signals are utilized to detect a magnetic pole. The simulation and experimental results show that the proposed method does not require proportion-integration (PI) regulation. The novel magnetic pole judgment method can effectively improve the detecting performance of sensorless control in the long algorithm execution time, complex process, etc. The experimental results verified the correctness of the strategy.

Suppression of backscattering-induced noise by sideband locking based on high and low modulation frequencies in ROG.

Backscattering-induced noise is a dominant noise in a resonant optic gyroscope (ROG). This paper proposes a method to suppress the carrier and backscattering-induced noise with a sideband locking technique. The resonant cavity can be taken as a band-pass filter, and the carrier frequency component can be located at the stop-band while one sideband is locked to the cavity resonance. Then, the carrier will be suppressed by the cavity itself, which will reduce the interference with carrier backscattering. For the adoption of different modulation frequencies in clockwise (CW) and counter-clockwise (CCW) directions, the first-order sidebands of CW and CCW have a frequency offset to each other. Therefore, the first-order sideband backscattering can be eliminated when the sideband is locked to the cavity resonance. Also, both high and low modulation frequencies are applied to the phase modulator, which will further suppress the carrier, and the demodulation of low frequency will reduce the sensitivity to phase fluctuation noise in the system. The method has low requirements for parameter accuracy or device performance.

DC–DC MMC for HVdc Grid Interface of Utility-Scale Photovoltaic Conversion Systems

This paper explores a utility-scale photovoltaic (PV) plant configuration based on a dc–dc stage interfaced directly to a modular multilevel converter (MMC) used for an HVdc power station. Since PV systems are dc by nature, the proposed solution has several advantages, such as full dc operation and step-up transformers avoidance with modular and reliable configuration. The contributions of this paper are the experimental validation of the proposed utility-scale configuration, while the conventional modulation stage has been further enhanced by including an adaptive phase-shifted modulation allowing improved voltage and current waveforms injected to dc grid under unbalanced power string operation. The enhanced performance is obtained by reducing the carrier frequency component of the converter voltage, generating an improved voltage ripple. Finally, experimental validation during steady-state and dynamic operation are presented to illustrate the behavior of the dc–dc MMC converter managed by the proposed modulation and control scheme.

Suppression of backscattering induced noise by the sideband locking technique in a resonant fiber optic gyroscope

Polarization fluctuation induced noise and backscattering-induced noise are the dominant noises in resonant fiber optic gyroscopes. This Letter proposes a new method to suppress the carrier and backscattering induced noise by the sideband locking technique. Besides choosing an optimized modulation depth and different clockwise and counterclockwise modulation frequencies, the sideband is locked to the cavity resonance. With the proper modulation frequency, the carrier frequency component locates at a position far away from the resonant frequency, and then it is suppressed by the cavity itself, which can be taken as a bandpass filter. The amplitude of the carrier frequency can be suppressed by 20–25 dB additionally by the cavity and the total intensity suppression ratio can reach 115.74 dB. The backscattering induced noise can be eliminated for the adoption of different frequencies. The method can realize a stable and high suppression ratio without high requirements for parameter accuracy or device performance.

Envelope following responses to Schroeder-phase harmonic stimuli

Recent studies suggest that peripheral nonlinearities only partially account for the envelope-following response (EFR) recorded at the scalp, with additional contributions from broadly tuned neurons in the central nervous system. The present study investigated this by measuring EFR to low and high-frequency stimuli designed to (1) optimize within-channel phase synchrony to produce maximal envelope modulation depth on the basilar membrane, or (2) optimize phase synchrony across multiple frequency channels to maximize envelope-related activity arising in the central nervous system. EFR was recorded in normal-hearing listeners using Schroeder-phase stimuli with harmonic components constrained to low and high-frequency ranges, as well to multi-frequency sinusoidally amplitude modulated tones as a function of component phase. Estimates of basilar membrane phase curvature varied across individuals. Response amplitudes and phase-locking values for the EFR varied as a function of carrier frequency range and component phase. The present results are consistent with an understanding of scalp-recorded EFR as a measure of central envelope processing extending beyond the initial encoding of the stimulus envelope arising in the periphery. The scalp-recorded EFR is thus not a direct index of envelope encoding in the auditory nerve.

An Analysis Approach for the Assessment of Pulse-width Modulated Carrier Frequency Spectral Components in Power Distribution Systems with Photovoltaic Resources

Power distribution systems may have photovoltaic resources, and these resources may interface with the AC system via pulse-width modulated inverters. The pulse-width modulated currents have high-frequency spectra due to the switching frequency, which is typically 2.0–20 kHz. These carrier frequency components are asynchronous to the “power frequency” (the “baseband,” which is 50 or 60 Hz). Residential photovoltaic resources are in the 2–5 kW range, and “utility-scale” photovoltaic resources may be in the range of 500 kW. The pulse-width modulated carrier frequency components of voltage and current propagate in the power distribution system, and the details of this propagation are described. Note that the pulse-width modulated voltages are not harmonics of the 60-Hz baseband frequency, nor are the several pulse-width modulated voltages generally synchronous with each other. The objective is to describe an analytical approach for the assessment of carrier frequency spectra in distribution systems with photovoltaic resources. Analysis tools and experience with those tools are given. Information is given to distribution engineers faced with systems with pulse-width modulated inverter resources and advice on frequency ranges of study, potential modeling inaccuracies, and software tools. The results of a study on an actual high penetration solar photovoltaic feeder are given.

A Strategy for the Design of the LCR Filter in a Series Voltage Compensator

SUMMARYIn this paper, we propose a strategy for the design of the LCR filter in a series voltage compensator and investigate our method by performing simulations and experiments. In the proposed method, first, the inductance is derived from the ratio of the maximum amplitude of the ripple current to the amplitude of the fundamental current, which is denoted as . Second, the capacitance is derived from the ratio of the ripple voltage to the fundamental voltage. Third, the resistance R is determined from the rate of decrease of the carrier frequency component and the settling time.

Second harmonic generation of ultrashort pulses in refractive-index-linear-modulating nonlinear crystals

We present a theoretical model to deal with second harmonic generation (SHG) of ultrashort pulses in refractive-index-linear-modulating (RILM) nonlinear crystals. New coupled-wave equations were derived based on plane wave propagation. Under the undepleted-pump approximation, the analytic solutions for SHG of ultrashort pulses were obtained. The second harmonic (SH) pulse width and the efficiency were optimized in terms of the RILM parameter and the chirp coefficient of fundamental pulses. The results show that modulation of the refractive index (RI) in nonlinear crystals leads to a spectral localization of SHG that compensates the group velocity mismatch (GVM) and therefore compresses SH pulses. The modulation complicates the SHG process, which determines the pulse width, and the conversion efficiency varies with length and bandwidth. Especially, an overshooting compression phenomenon was found, which arose mainly from internal interference of the carrier frequency component in a SH pulse.

Drift Correction in a Porphyrin-coated ZnO Nanorods Gas Sensor

Photoconductivity and gas sensitivity cooperate in porphyrins coated ZnO nanostructures. However, in organic coated semiconductors the former is regulated by a number of mechanisms, involving the charge transfer in the organic layer. Since organic layers are poor conductors these processes are quite slow and the sensor may exhibits a long time drift before to be operative as gas sensor. In this paper we show that under light modulation, the carrier frequency component of the signal is free of drift and it can readily indicate the interaction with volatile compounds.

A Design Strategy for the LCR Filter and Carrier Frequency in a Series Voltage Compensator

In this paper, we propose the LCR filter design method and the carrier frequency decision method in the series voltage compensator. In this proposed design method, the filter Lf is calculated from the peak value of the ripple current, and the filter Cf is calculated from the ripple voltage component. The damping resistance is calculated from the percentage of the elimination of the carrier frequency component and the settling time. We verify a model equipment in the experiment, and the experimental results agree well with the calculated design values.

Twin Image Authentication by Distributed Data Hiding (TIADDH)

In frequency domain steganography, use of gray scale images for secret data hiding has already been proved authentic. But to enhance the level of authenticity and secrecy of steganography and also to increase the volume of data to be hidden, pairs of gray scale carrier images are used in the proposed work. Each image is considered as a collection of contiguous blocks. The spatial values in each block of size 2 x 2 are first converted to frequency components by applying Discrete Cosine Transform (DCT). Then a message digest is generated for the payload/secret data. Both the payload data and the generated message digest are fabricated within the carrier frequency components. The first frequency component of each block is not used for embedding but is used for re-adjustments to maintain the quantum values positive and non-fractional in spatial domain and also to reduce the integrated noise due to embedding of payload. Further, to enhance the strength of secrecy of the embedded message a method has been devised which deduces pseudo-random positions for embedding and subsequent extraction of secret data bits. Finally, each block of frequency components is reverted back into spatial domain by applying Inverse Discrete Cosine Transform (IDCT). The results, after experimenting with the proposed technique, establish its superiority over other similar techniques in terms of capacity and imperceptibility. Keywords: Image Authentication, Digital Watermarking, Steganography, DCT, IDCT, MSE, PSNR, IF, SSIM

A Strategy for the Design of the LCR Filter in a Series Voltage Compensator

SUMMARY In this paper, we propose a strategy for the design of the LCR filter in a series voltage compensator and investigate our method by performing simulations and experiments. In the proposed method, first, the inductance Lf is derived from the ratio of the maximum amplitude of the ripple current to the amplitude of the fundamental current, which is denoted as {%Irip}. Second, the capacitance Cf is derived from the ratio of the ripple voltage to the fundamental voltage. Third, the resistance R is determined from the rate of decrease of the carrier frequency component and the settling time.