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Optical Data Processing
Published in Rajpal S. Sirohi, Mahendra P. Kothiyal, Optical Components, Systems, and Measurement Techniques, 2017
Rajpal S. Sirohi, Mahendra P. Kothiyal
Blocking filters [10, 11] are binary in nature; they remove a certain portion of the spectrum completely and allow the rest for image formation. They are of three types: low-pass filters, band-pass filters, and high-pass filters. Low-pass filters allow only low frequencies to pass through without attenuation. An example of a low-pass filter is a pin-hole placed on axis. If the diameter of the pinhole is 2d, it will pass frequencies up to d/λf when placed on axis at the back focal plane of the transforming lens. The frequency d/λf is the cut-off frequency. A band-pass filter allows a range of intermediate frequencies. An annular aperture is an example of a bandpass filter. If it is contained by a pair of diameters 2d1 and 2d2 (d2 > d1), the range of frequencies that is allowed is d1/λf to d2/λf. A high-pass filter permits only high frequencies to pass through. An opaque dot of diameter 2d will allow all frequencies above d/λf. Since the information about the edge of an object is contained in the higher frequencies, high-pass filtering is obviously used for edge enhancement. Figure 8.4 (a) gives an original image of a resolution test chart, and Fig. 8.4 (b) is its high-pass filtered image. Periodicity in a pattern can be removed by blocking filters. The removal of the raster scan in a television picture or of half-tone dots in a newspaper or periodical photograph can be also done by a blocking filter.
Laplace Transforms
Published in David V. Kalbaugh, Differential Equations for Engineers, 2017
An electrical low-pass filter is a circuit that responds to low frequency inputs with an output that closely matches the input, and responds to high-frequency inputs with an output that is nearly zero. That is, it allows low-frequency signals to pass through while blocking high-frequency signals. As an example application, if a signal consists of a low-frequency measurement corrupted with high-frequency noise, the measurement can be recovered by putting the signal through a low-pass filter. An nth order Butterworth filter is a circuit that performs the low-pass function as well as possible in a circuit with an nth order transfer function. A third-order Butterworth filter with cut-off frequency of one radian per second has transfer function () H(s)=vout(s)vin(s)=1s3+2s2+2s+1
Amplifiers and Filters
Published in Clarence W. de Silva, Sensor Systems, 2016
The purpose of a low-pass filter is to allow through all signal components below a certain (cutoff) frequency and block off all signal components above that cutoff. Analog low-pass filters are widely used as anti-aliasing filters in digital signal processing (see Chapter 6). An error known as “aliasing” enters the digitally processed results of a signal if the original signal has frequency components above half the sampling frequency (half the sampling frequency is called the Nyquist frequency). Hence, aliasing distortion can be eliminated if the signal is filtered using a low-pass filter with its cutoff set at the Nyquist frequency, before sampling and digital processing. This is one of the numerous applications of analog low-pass filters. Another typical application would be to eliminate high-frequency noise in a sensed signal.
Modelling and sizing techniques to mitigate the impacts of wind fluctuations on power networks: a review
Published in International Journal of Ambient Energy, 2022
M. V. Tejeswini, I. Jacob Raglend
The low-pass filter is a filter which permits signals lower than the cut-off frequency and attenuates the signals above the cut-off signal. There are three types of filter: active filter, passive filter and hybrid filter. Passive filters are made up of passive components (resistors, capacitors and inductors). It doesn’t consist of amplifying elements. Always their output will be less than the given input. The low-pass filter rejects and modifies the unwanted signals. The power electronic converter produces the harmonics. A filter circuit is used on the grid side converter to reduce the impact of harmonics on the grid. The converters used in DFIGs are modelled as ideal current source (Surinkaew and Ngamroo 2014). But in practice ideal case will not hold good. An AC filter is used on the grid side converter to remove some of the voltage harmonics of converter. The commonly used filter in grid side is L(inductor) and LCL(inductor capacitor inductor). The model of single-phase LCL filter is shown in (Mulolani, Althobaiti, and Alamoudi 2019). The resonant frequency is calculated using Equation (31)
Reducing the Cost of Calculations for Incremental Dynamic Analysis of Building Structures Using the Discrete Wavelet Transform
Published in Journal of Earthquake Engineering, 2022
Masoud Dadkhah, Reza Kamgar, Heisam Heidarzadeh
According to the above description, IDA consumes a lot of time and energy. Therefore, here a method is proposed to reduce the computational cost without a significant decrease in the precision of the results. Therefore, the earthquakes are filtered up to five levels with a discrete wavelet transform to obtain the main earthquake with fewer points. As can be seen from Fig. 1, a low-pass filter allows passing the low-frequency signals, while avoiding high-frequency signals. Also, a high-pass filter only passes high-frequency signals and does not pass low-frequency signals. Therefore, only high-frequency signals (Dj) pass through a high-pass filter, and only low-frequency signals (Aj) pass through a low-pass filter. In each level of decomposition, the calculated earthquake is applied to the structure, and IDA is performed. Finally, the responses of the frame are plotted for different intensities of the earthquake. The maximum response of the structure is plotted against the intensities of the earthquake for the IDA curve. Also, in this type of analysis, the behavior of the structure is considered to be nonlinear.
Identifying Stick-Slip Characteristics of a Smart Device on a Seismically Excited Surface Using On-Board Sensors
Published in Journal of Earthquake Engineering, 2022
Yunsu Na, Sherif El-Tawil, Ahmed Ibrahim, Ahmed Eltawil
Experiments for earthquake motions as mentioned earlier are conducted to compare the denoising performance of three different methods: low-pass filter, MODWT, MODWPT. The low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. In this study, a 25 Hz cutoff frequency is selected based on the work of (Skolnik and Wallace 2010). For MODWT and MODWPT, the denoising procedure has three steps. The first step selects a wavelet and a level N and then computes the wavelet decomposition of the signals at level N. The second step pertains to coefficients thresholding, i.e. it selects a threshold and applies soft thresholding to the detail coefficients for each level from 1 to N. The third step computes wavelet reconstruction based on the original approximation coefficients of level N and the modified detail coefficients of levels 1 through N. Details can be found in Donoho (1995). In this study, ‘db 1ʹ wavelet and level 3 are selected empirically.