Range Of Frequency Components Research Articles

An FFT-based beam profile denoising method for beam profile distortion correction

The accurate verification of beam parameters is mandatory for treatment safety in particle therapy, therefore, the systematic uncertainties of the segmented ionization chambers and detector arrays used as beam monitors, must be measured. In this study, a Fast Fourier Transform (FFT) based denoising method is proposed to remove noise from the pencil beam profile signal in both the spatial and spatial-frequency domains. In the spatial domain, the bias caused by noise was corrected, and the noise outside the 4 σ range of the spot center was discarded. Then, in the spatial-frequency domain, thanks to the Gaussian shape of the signal’s magnitude spectrum, the 4 σ range of frequency components was extracted to eliminate the signal fluctuation caused by noise. In addition, low amplitude high-frequency components are finely removed by thresholding to reduce the distortion of beam profile signals. The performance of the proposed method was verified through simulation experiments in terms of the coefficient of determination ( R 2 ) and signal-to-noise ratio (SNR). Results show that SNRs of the denoised signals are more than six times higher than those of the original signals and R 2 of the denoised signals is larger than 0.9. The denoising capability of the presented method was verified by an X-ray radiation experiment. R 2 of the denoised signal achieves 0.96 from 0.60, and the fitting errors of beam parameters ( μ and σ ) also decrease by denoising without increasing the radiation intensity and the integration time.

An Overview on the Investigation of Power Quality Problems and Harmonic Exclusion in the Power System Using Frequency Estimation Techniques

The present research paper is based on a survey on the Investigation of Power Quality Problems and Harmonic Exclusion in the Power System using the Frequency Estimation Technique. The majority of FD approaches are openloop, and they are based on Fourier series analysis in most cases. When applied to frequency domain approaches, Fourier series analysis is a powerful mathematical tool that allows users to acquire a wide range of frequency components by multiplying the input by a set of trigonometric functions (sine/cosine) at various frequencies. Typically, the discrete implementation of the Fourier series, also known as the Discrete Fourier Transform, is used to compute results. DFT can be done quickly and simply using computer technology, and it can be used to estimate the grid signal parameters with improved selectivity and greater steady-state accuracy than other methods. The A/D conversion process of the input signals is required for the real-time implementation of the DFT, which necessitates the repeated sampling and updating of the input signals. However, in order to compute the N samples, this approach necessitates the use of N2 complex multiplication and N2–N complex addition. As a result, it was not extensively used prior to the introduction of the microprocessor.

Wavelet transform based coherence analysis of freak wave and its impact

The present paper presents the results of a wavelet transform-based coherence analysis of freak wave and its impact. Wavelet transform has been used as a tool in analyzing signals in the time domain as well as in the frequency domain. The analysis was applied to laboratory-generated freak waves. The wavelet transform of the time history of the freak wave and its impact force revealed that a wide range of frequency components were contained in them. The coherence analysis was conducted on the wave and its impact force time histories. The coherence analysis revealed that some high-frequency components were highly correlated with the impact forces. The present study demonstrates that the wavelet transform can be an alternative tool in the analysis of strongly nonlinear freak wave and its impact.

Frequency analysis of the acoustic emission signals from PZT ceramics during the application of AC fields

Abstract Frequency analysis of Acoustic Emission signals in the range of 100–1200 kHz obtained from PZT ceramics during the application of limited and continuous cycles of ac field was undertaken to understand the fatigue behaviour of these ceramics. In the limited cycles experimentation, lower fields yielded higher range of frequency components (200–900 kHz) and higher fields yielded lower range of frequency components (200–500 kHz) at differnt temperatures of 60° C and 160° C. During continuous application of ac field, the initial stages of application yielded higher frequency components (100–850 kHz) and with increasing time of application, the frequency components of acoustic emission signal shifted towards lower frequency (less than 400 kHz). Electrical discharge induced cracking, resulted in the emission of frequency components in the range of 100–275 kHz.

Facilitation effect of auxiliary noise stimuli on response of isolated frog muscle spindle to sinusoidal movements.

Receptor potentials and impulse patterns were recorded from isolated frog muscle spindles using sinusoidal and superimposed random stretches as stimuli with different sinus-to-noise ratios. The entire dynamic amplitude range of the spindle receptor was evaluated by measuring the sensory response at different levels of static stretch. Auxiliary random stimuli provoked rectified fast depolarizing receptor potential transients; their amplitude and slope grew larger with increasing intensity of the noise stimulus and with increasing prestretch level. Due to this strongly nonlinear behavior of the transducing site the frequency and size of the receptor potentials evoked by the auxiliary input signal increased during the stretching phase of the sinusoidal movement. Since the fast depolarizing receptor potential transients provided a powerful trigger for the action potential encoding site, auxiliary random stimuli effectively enhanced the afferent discharge rate, especially during the stretching phase of the sinusoidal movement. Auxiliary noise stimuli could even activate the afferent discharge to an otherwise subthreshold sinusoidal stretch. It is assumed that by the same mechanism the transfer characteristic of the receptor is broadened towards higher frequencies. Since auxiliary random stimuli increased the nonlinear properties of all receptor response components, a "linearizing" approximation technique only partially describes the receptor's transfer properties. The facilitation effect recorded in the differentiated muscle spindle when random stimuli were superimposed on sinusoidal displacements closely resembled the excitation of afferent firing when passive stretching interacted with active fusimotor innervation. A hypothesis is proposed to explain both effects by the same mechanism acting upon the transducing sensory endings: Since passive random stretches as well as active twitching of the intrafusal muscle fibers exhibited almost the same range of frequency components, we propose that both stimuli also generate the same kind of receptor potentials; namely, those fast-rising depolarization transients of the receptor potential, which vigorously drive the encoding site. In general, these experiments explain how the specific response of a neuron can be facilitated by an additional unspecific (noisy) input.