Butterworth High-pass Filter Research Articles

Image enhancement based on fractional directional derivative

This paper introduces the directional derivative to fractional derivative and proposes a new mathematical method, fractional directional derivative (FDD), and gives the corresponding numerical calculation. Compared with the traditional fractional derivative, the coefficients of FDD along the eight directions in the image plane are not the same, which can reflect different fractional change rates along different directions and is benefit to enlarge the differences among the image textures. Experiments show that the capability of nonlinearly enhancing texture details by FDD is more obvious than those by the traditional fractional derivative and integer-order differentiation operators Laplacian, Butterworth high-pass filter.

Estimating Extracellular Spike Waveforms from CA1 Pyramidal Cells with Multichannel Electrodes

Extracellular (EC) recordings of action potentials from the intact brain are embedded in background voltage fluctuations known as the “local field potential” (LFP). In order to use EC spike recordings for studying biophysical properties of neurons, the spike waveforms must be separated from the LFP. Linear low-pass and high-pass filters are usually insufficient to separate spike waveforms from LFP, because they have overlapping frequency bands. Broad-band recordings of LFP and spikes were obtained with a 16-channel laminar electrode array (silicone probe). We developed an algorithm whereby local LFP signals from spike-containing channel were modeled using locally weighted polynomial regression analysis of adjoining channels without spikes. The modeled LFP signal was subtracted from the recording to estimate the embedded spike waveforms. We tested the method both on defined spike waveforms added to LFP recordings, and on in vivo-recorded extracellular spikes from hippocampal CA1 pyramidal cells in anaesthetized mice. We show that the algorithm can correctly extract the spike waveforms embedded in the LFP. In contrast, traditional high-pass filters failed to recover correct spike shapes, albeit produceing smaller standard errors. We found that high-pass RC or 2-pole Butterworth filters with cut-off frequencies below 12.5 Hz, are required to retrieve waveforms comparable to our method. The method was also compared to spike-triggered averages of the broad-band signal, and yielded waveforms with smaller standard errors and less distortion before and after the spike.

Non-Gaussian methods and high-pass filters in the estimation of effective connections

We consider several alternative ways of exploiting non-Gaussian distributional features, including some that can in principle identify direct, positive feedback relations (graphically, 2-cycles) and combinations of methods that can identify high dimensional graphs. All of the procedures are implemented in the TETRAD freeware (Ramsey et al., 2013). We show that in most cases the limited accuracy of the several non-Gaussian methods in the Smith et al. (2011) simulations can be attributed to the high-pass Butterworth filter used in that study. Without that filter, or with the filter in the widely used FSL program (Jenkinson et al., 2012), the directional accuracies of several of the non-Gaussian methods are at or near ceiling in many conditions of the Smith et al. simulation. We show that the improvement of an apparently Gaussian method (Patel et al., 2006) when filtering is removed is due to non-Gaussian features of that method introduced by the Smith et al. implementation. We also investigate some conditions in which multi-subject data help with causal structure identification using higher moments, notably with non-stationary time series or with 2-cycles. We illustrate the accuracy of the methods with more complex graphs with and without 2-cycles, and with a 500 node graph; to illustrate applicability and provide a further test we apply the methods to an empirical case for which aspects of the causal structure are known. Finally, we note a number of cautions and issues that remain to be investigated, and some outstanding problems for determining the structure of effective connections from fMRI data.

The frequency response of cerebral autoregulation

The frequency-response of pressure autoregulation is not well delineated; therefore, the optimal frequency of arterial blood pressure (ABP) modulation for measuring autoregulation is unknown. We hypothesized that cerebrovascular autoregulation is band-limited and delineated by a cutoff frequency for which ABP variations induce cerebrovascular reactivity. Neonatal swine (n = 8) were anesthetized using constant minute ventilation while positive end-expiratory pressure (PEEP) was modulated between 6 and 0.75 cycles/min (min(-1)). The animals were hemorrhaged until ABP was below the lower limit of autoregulation (LLA), and PEEP modulations were repeated. Vascular reactivity was quantified at each frequency according to the phase lag between ABP and intracranial pressure (ICP) above and below the LLA. Phase differences between ABP and ICP were small for frequencies of >2 min(-1), with no ability to differentiate cerebrovascular reactivity between ABPs above or below the LLA. For frequencies of <2 min(-1), ABP and intracranial pressure (ICP) showed phase shift when measured above LLA and no phase shift when measured below LLA [above vs. below LLA at 1 min(-1): 156° (139-174°) vs. 30° (22-50°); P < 0.001 by two-way ANOVA for both frequency and state of autoregulation]. Data taken above LLA fit a Butterworth high-pass filter model with a cutoff frequency at 1.8 min(-1) (95% confidence interval: 1.5-2.2). Cerebrovascular reactivity occurs for sustained ABP changes lasting 30 s or longer. The ability to distinguish intact and impaired autoregulation was maximized by a 60-s wave (1 min(-1)), which was 100% sensitive and 100% specific in this model.

A novel approach to transform an open circuit series stub to a short circuit shunt stub for the implementation of high-pass butterworth filter

A new approach for transforming an open circuit series stub to short circuit shunt stub is presented.A mathematical identity is also derived. Additional transmission lines of particular lengths are also used while performing this transformation. The simulations and the experimental results verified that the derived mathematical identity can be used for the implementation of high-pass maximum flat Butterworth filter. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:497–501, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27354

CT and MRI Brain Images Registration for Clinical Applications

Registration is particularly challenging when fusing imagery from different sensors with different resolutions. Ridges are useful geometrical features for image registration. In this paper, first the performance of Gaussian and Butterworth high pass filters is analyzed on sharpening of images, then ridges are detected from CT and MRI brain images by using scale space primal sketch, and finally cross correlate the two 3D CT and MRI volumes for registration. Results are presented on number of images. The visual comparison shows that filters at cutoff frequency 100 MHz shows better quality. The comparative analysis show that Butterworth filter of order four yields more sharper images as compared to Gaussian filter. Finally, visual results after registration of MRI and CT images of the brain are presented, which can be useful in planning certain types of neurosurgical and ENT surgical procedures

Shannon Entropy Mapping of AF Rotors-Theoretical Extensions to a Novel Conceptual Paradigm

The pivot is critical to rotors maintaining AF. We have shown that high Shannon entropy (ShEn), a measure of information uncertainty, localises the pivot of rotors recorded with bipolar electrograms, and that targeted ablation of high ShEn EGMs is associated with termination in human AF This study evaluated ShEn colocalisation of rotors under conditions of: (i) rotor meander; (ii) electrogram filtering and (iii) effect of ShEn box size (iv) effect of myocyte model. Methods: Bipolar EGM recordings were studied in simulated (i) atrial (ii) ventricular and (iii) FitzHugh Nagumo rotors. Model meshes contained 100 × 100 elements with 0.5 mm spatial distance. Unipolar EGMs were calculated, which were used to construct bipolar EGMs. Spiral wave tip was localised with phase integration. ShEn was calculated as for each bipole. We simulated the effects of: (i) rotor meander, (ii) EGM filtering, with simulated high-pass Butterworth filters with cutoffs at 0.5, 10, and 30 Hz, (iii) ShEn box size in each model rotor system. Results: In each of the model systems, the highest region of ShEn colocalised with the pivoting region identified by the spiral wave tip. ShEn was inversely correlated with distance from the pivot (Pearson's r = −0.61, p < 0.001). The region of maximum Max ShEn colocalised with the pivot zone in ShEn box size from 0.01mV to 1 mV. Max ShEn remained colocalised with the pivot over a range of bipolar EGM cut-off frequencies, and with rotor meander, in each model system. Conclusion: These data confirm ShEn as a mechanistically based potential tool to map stable rotors.

고속 전력선통신 모뎀용 수신단측 전류모드 대역통과 필터 설계

본 논문에서는 저전압 저전력 필터 설계에 적합한 전류모드 방식을 이용하여 고속 전력선통신(PLC)모뎀 수 신단의 1MHz~30MHz 차단주파수를 갖는 6차 대역통과 필터를 설계하였다. 3차 바터워스 고역통과 필터와 3차 체비세프 저역통과 필터를 종속연결로 구성하여 대역통과 필터를 설계하였다. 필터를 구성하기 위한 핵심로써 기존의 전류미러형 적분기에 비하여 증가된 이득 및 차단주파수를 가지는 새로운 전류모드 적분기를 설계하였다. 설계된 전류모드 적분기의 이득과 차단주파수는 각각 32.2dB 및 247MHz이였다. 설계된 6차 대역통과 필터의 차단주파수는 제어전압에 따라서 200KHz에서 50MHz까지 조정이 될 수 있으며 소비전력은 공급전압 1.8V에서 2.85mW이였다. 설계된 대역통과 필터는 1.8V, <TEX>$0.18{\mu}m$</TEX> CMOS 공정파라메터를 사용하여 검증되었다. In this paper a <TEX>$6^{th}$</TEX> 1MHz~30MHz bandpass filter for Power line communication(PLC) modem receiver is designed using current mode synthesis method which is good to design the low-voltage and low-power filter. The designed bandpass filter is composed of cascade connecting between <TEX>$3^{rd}$</TEX> Butterworth highpass filter and <TEX>$3^{rd}$</TEX> Chebychev lowpass filter. As a core circuit in the current-mode filter, a current-mode integrator is designed with new architecture which can improve gain and unity gain frequency of the integrator. The gain and the unity gain frequency of the designed integrator is each 32.2dB and 247MHz. And the cutoff frequency of the designed <TEX>$6^{th}$</TEX> bandpass filter can be controlled to 50MHz from 200KHz according to controlling voltage and the power consumption is 2.85mW with supply voltage, 1.8V. The designed bandpass filter was verified using a <TEX>$0.18{\mu}m$</TEX> CMOS parameter.

An R-peak detection method that uses an SVD filter and a search back system

In this paper, we present a method for detecting the R-peak of an ECG signal by using an singular value decomposition (SVD) filter and a search back system. The ECG signal was detected in two phases: the pre-processing phase and the decision phase. The pre-processing phase consisted of the stages for the SVD filter, Butterworth High Pass Filter (HPF), moving average (MA), and squaring, whereas the decision phase consisted of a single stage that detected the R-peak. In the pre-processing phase, the SVD filter removed noise while the Butterworth HPF eliminated baseline wander. The MA removed the remaining noise of the signal that had gone through the SVD filter to make the signal smooth, and squaring played a role in strengthening the signal. In the decision phase, the threshold was used to set the interval before detecting the R-peak. When the latest R–R interval (RRI), suggested by Hamilton et al., was greater than 150% of the previous RRI, the method of detecting the R-peak in such an interval was modified to be 150% or greater than the smallest interval of the two most latest RRIs. When the modified search back system was used, the error rate of the peak detection decreased to 0.29%, compared to 1.34% when the modified search back system was not used. Consequently, the sensitivity was 99.47%, the positive predictivity was 99.47%, and the detection error was 1.05%. Furthermore, the quality of the signal in data with a substantial amount of noise was improved, and thus, the R-peak was detected effectively.

Rapid dopaminergic and GABAergic modulation of calcium and voltage transients in dendrites of prefrontal cortex pyramidal neurons

The physiological responses of dendrites to dopaminergic inputs are poorly understood and controversial. We applied dopamine on one dendritic branch while simultaneously monitoring action potentials (APs) from multiple dendrites using either calcium-sensitive dye, voltage-sensitive dye or both. Dopaminergic suppression of dendritic calcium transients was rapid (<0.5 s) and restricted to the site of dopamine application. Voltage waveforms of backpropagating APs were minimally altered in the same dendrites where dopamine was confirmed to cause large suppression of calcium signals, as determined by dual voltage and calcium imaging. The dopamine effects on dendritic calcium transients were fully mimicked by D1 agonists, partially reduced by D1 antagonist and completely insensitive to protein kinase blockade; consistent with a membrane delimited mechanism. This dopamine effect was unaltered in the presence of L-, R- and T-type calcium channel blockers. The somatic excitability (i.e. AP firing) was not affected by strong dopaminergic stimulation of dendrites. Dopamine and GABA were then sequentially applied on the same dendrite. In contrast to dopamine, the pulses of GABA prohibited AP backpropagation distally from the application site, even in neurons with natural Cl− concentration (patch pipette removed). Thus, the neocortex employs at least two distinct mechanisms (dopamine and GABA) for rapid modulation of dendritic calcium influx. The spatio-temporal pattern of dendritic calcium suppression described in this paper is expected to occur during phasic dopaminergic signalling, when midbrain dopaminergic neurons generate a transient (0.5 s) burst of APs in response to a salient event.

LTCC를 이용한 GPS와 WLAN 대역통과 여파기

본 논문은 LTCC를 이용하여 구현된 GPS와 WLAN용 대역통과 필터 설계방법을 제안한 것이다. 여기서 구현한 여파기는 버터워스 저역통과 여파기와 CRLH(Composite Right/Left-Handed) 전송선로의 고역통과 특성을 결합한 대역 통과 여파기를 설계하였다. 이렇게 설계된 여파기는 유전율 7.2의 그린쉬트를 이용한 LTCC 공정을 사용하여 1.5 GHz의 GPS와 2.4 GHz의 WLAN 대역의 대역통과 여파기를 제작하였다. 제작된 여파기의 삽입손실 결과는 1.5 GHz GPS대역에서 1.66 dB 또, 2.4 GHz WLAN 대역에서는 3.20 dB를 만족하는 대역통과 특성을 얻었다. This paper presents a bandpass fitler of GPS and WLAN band based on LTCC. The structure of bandpass fitler consists of a Butterworth lowpass fitler and highpass filter using CRLH (Composite Right/Left-Handed) transmission line. Using green sheet with dielectric constant 7.2, we fabricated the bandpass filter that satisfied GPS and WLAN band characteristics. We are implemented the bandpass filter at center frequency 1.5 GHz (GPS) and 2.4 GHz (WLAN). Its insertion loss are 1.66 dB at GPS and 3.20 dB at WLAN respectively.

A new method of obtaining perturbation vertical profiles in estimating the atmosphere gravity wave parameters

The gravity wave is the fundamental dynamic process in the atmosphere, and one of the important theoretical studies of atmosphere dynamics is to estimate the gravity wave parameters. Due to the inherent deficiency of the curve fitting method for the vertical perturbation profile (VPP), a new method is proposed in obtaining the profile for estimating the reasonable gravity wave parameters. Based on the features of cone of influence in wavelet transformation and its maximum value, which is considered as the critical value for background profile and perturbation profile, the VPP is obtained with a 10th-order Butter Worth highpass filter for the signal with the magnitude less than the critical value. With the Morlet wavelet and Fourier power spectrum analyses for the numerically simulated zonal wind and meridional wind, it is found that there are neither distinct background signals nor false signal including in the VPPs, which overcomes the deficiency of curve fitting method. Therefore, the proposed method is excellent compared with the widely used curve fitting method in obtaining the VPPs, and the reasonable atmosphere gravity wave parameters could be estimated with the new method.

Multiple-input adaptive seismic noise canceller for the attenuation of nonstationary coherent noise

Attenuation of coherent noise, typically weather generated noise and more specifically swell noise, is a major concern in seismic. Such noise, usually characterized by its low-frequency content and high amplitudes, is a common problem in seismic acquisition and, in particular, for marine data. We propose a multiple-input adaptive noise canceller as a solution to attenuate nonstationary coherent noise. This filter uses multiple noise sequences to estimate the noise contained in each trace. This noise estimate is then subtracted to obtain an estimate of the trace whose coherent noise has been attenuated. For the implementation of the adaptive filter, we use a variable step-size normalized least mean squares algorithm, as it is known for its simplicity and robustness. In addition, we demonstrate that variable step-size is necessary for this filter to adapt to the changing statistics of the seismic data. This method is tested on real marine seismic data and compared to a time-frequency median filter and a second-order high-pass Butterworth filter. We demonstrate that the multiple-input adaptive noise canceller is a powerful and efficient filter to attenuate swell noise while preserving the seismic reflections. Depending on the noise configuration, it can be used either by itself or in combination with a time-frequency median filter to obtain the best results.

A Fog-Removing Treatment Based on Combining High-Frequency Emphasis Filtering and Histogram Equalization

Fog may cause the impairment of image as well as the decrease in the distinguish ability. The present paper is to get rid of the weather’s influence from the impaired image. According to Retinex theory and exponential relationship between the degradation of the image and the depths of the scene points, it puts forward a fog-removing treatment based on combining high-frequency emphasis filtering and histogram equalization .Firstly, obtain the padding parameters and fill it. Secondly, filter the impaired image using Butterworth highpass filter of order 2. Through the padding parameters, Highpass filtering is not overly sensitive to the value of cutoff frequencies, as long as the radius of the filter is not so small that frequencies near the origin of the transform are passed. In which the gray-level tonality due to the low-frequency components was retained. Lastly, histogram balanced the image gotten last step. The simulation result based on Matlab shows his algorithm can effectively improve the visual effect scene under the condition of mist.

A New Implementation Method of Wavelet-Packet-Transform Differential Protection for Power Transformers

This paper presents an innovative implementation of the wavelet packet transform using Butterworth passive filters for differential protection of power transformers. The proposed implementation is based on designing cascaded stages of high pass 3$^{rd}$ order Butterworth filters with cut-off frequencies identical to the cut-off frequencies of wavelet packet transform associated digital quadrature mirror filters. These high pass filters are designed to extract the second level high frequency components present in the three-phase differential currents. The extraction of these frequency components is required in order to detect and classify transients in three-phase power transformers. The output of the designed Butterworth high pass filters is utilized to initiate a trip signal in case of internal fault currents. The 3$^{rd}$ order Butterworth high pass filters are designed to simplify their practical implementation as well as their integration with the differential protective relay for the tested power transformer. Different magnetizing inrush, through-fault and internal fault currents are investigated for different loading conditions. Performances of the proposed Butterworth passive filter-based differential relay are compared with those of the digital wavelet packet transform-based relay. Comparison results show that the Butterworth filter wavelet packet transform-based differential relay is able to provide a low cost good diagnosis and fast responses to internal fault currents.

An automated ECG-artifact removal method for trunk muscle surface EMG recordings

This study aimed at developing a method for automated electrocardiography (ECG) artifact detection and removal from trunk electromyography signals. Independent Component Analysis (ICA) method was applied to the simulated data set of ECG-corrupted surface electromyography (SEMG) signals. Independent Components (ICs) correspond to ECG artifact were then identified by an automated detection algorithm and subsequently removed. The detection performance of the algorithm was compared to that by visual inspection, while the artifact elimination performance was compared with Butterworth high pass filter at 30 Hz cutoff (BW HPF 30). The automated ECG-artifact detection algorithm successfully recognized the ECG source components in all data sets with a sensitivity of 100% and specificity of 99%. Better performance indicated by a significantly higher correlation coefficient ( p < 0.001) with the original EMG recordings was found in the SEMG data cleaned by the ICA-based method, than that by BW HPF 30. The automated ECG-artifact removal method for trunk SEMG recordings proposed in this study was demonstrated to produce a very good detection rate and preserved essential EMG components while keeping its distortion to minimum. The automatic nature of our method has solved the problem of visual inspection by standard ICA methods and brings great clinical benefits.

In vivo Doppler Ultrasound Quantification of Turbulence Intensity Using A High-Pass Frequency Filter Method

The objective of this investigation was to implement a high-pass frequency filter method to analyze Doppler ultrasound velocity waveforms and quantify turbulence intensity (TI) in vivo. Doppler velocity data were analyzed using two techniques, based on either ensemble averaging or high-pass frequency domain filtering of the periodic waveforms. The accuracy and precision of TI measurements were determined with controlled in vitro experiments, using a pulsatile-flow model of a stenosed carotid bifurcation. The high-pass filter technique was also applied in vivo to determine whether this technique could successfully distinguish between pertinent hemodynamic sites within the carotid artery bifurcation. Twenty-five seconds of Doppler audio data were acquired at three sites (common carotid artery [CCA], internal carotid artery [ICA] stenosis and distal ICA) within 10 human carotid arteries, and repeated three times. Doppler velocity data were analyzed using a ninth-order high-pass Butterworth filter with a 12-Hz inflection point. TI measured within the CCA and distal ICA was found to be significantly different ( p < 0.0001) for moderate to nearly occluded carotid artery classifications. Also, TI measured within the distal ICA increased with stenosis severity, with the ability to distinguish between each stenosis class ( p < 0.05). This investigation demonstrated the ability to precisely quantify TI using a conventional Doppler ultrasound machine in human subjects, without interfering with normal clinical protocols. (E-mail: david.holdsworth@imaging.robarts.ca)

Classifying household and locomotive activities using a triaxial accelerometer

The purpose of this study was to develop a new algorithm for classifying physical activity into either locomotive or household activities using a triaxial accelerometer. Sixty-six volunteers (31 men and 35 women) participated in this study and were separated randomly into validation and cross-validation groups. All subjects performed 12 physical activities (personal computer work, laundry, dishwashing, moving a small load, vacuuming, slow walking, normal walking, brisk walking, normal walking while carrying a bag, jogging, ascending stairs and descending stairs) while wearing a triaxial accelerometer in a controlled laboratory setting. Each of the three signals from the triaxial accelerometer was passed through a second-order Butterworth high-pass filter to remove the gravitational acceleration component from the signal. The cut-off frequency was set at 0.7 Hz based on frequency analysis of the movements conducted. The ratios of unfiltered to filtered total acceleration (TAU/TAF) and filtered vertical to horizontal acceleration (VAF/HAF) were calculated to determine the cut-off value for classification of household and locomotive activities. When the TAU/TAF discrimination cut-off value derived from the validation group was applied to the cross-validation group, the average percentage of correct discrimination was 98.7%. When the VAF/HAF value similarly derived was applied to the cross-validation group, there was relatively high accuracy but the lowest percentage of correct discrimination was 63.6% (moving a small load). These findings suggest that our new algorithm using the TAU/TAF cut-off value can accurately classify household and locomotive activities.

Tunable photonic filters: a digital signal processing design approach

Digital signal processing techniques are used for synthesizing tunable optical filters with variable bandwidth and centered reference frequency including the tunability of the low-pass, high-pass, bandpass, and bandstop optical filters. Potential applications of such filters are discussed, and the design techniques and properties of recursive digital filters are outlined. The basic filter structures, namely, the first-order all-pole optical filter (FOAPOF) and the first-order all-zero optical filter (FOAZOF), are described, and finally the design process of tunable optical filters and the designs of the second-order Butterworth low-pass, high-pass, bandpass, and bandstop tunable optical filters are presented. Indeed, we identify that the all-zero and all-pole networks are equivalent with well known principles of optics of interference and resonance, respectively. It is thus very straightforward to implement tunable optical filters, which is a unique feature.

Derived gravity field of the seismogenic upper crust of SE Germany and West Bohemia and its comparison with seismicity

The gravity field of the seismogenic upper crust was derived from the Bouguer gravity map by applying the Butterworth high-pass filter in the wave-number domain. The cutoff wavelength of the filter was 110 km, to pass the gravity signals of structures within the 18 km thick seismogenic layer. The derived residual gravity map reveals potential stress concentrating structures, which may cause seismicity provided they lie within the existing zones of weakness. Furthermore we derived a shaded relief map of the horizontal gravity gradient, which highlighted the tectonic lines accompanied by density contrast. The directional analysis of this map shows three dominant strike directions. The most prominent one is the Hercynian NW-SE strike direction represented by the Franconian Line, the Gera-Jachymov Fault Zone and the Elbe Zone. The second dominant strike is the Rhenisch NNE-SSW trending represented by the Upper Rhine Graben Zone, Rheinsberg- Heldburg Line and several Proterozoic volcanic belts in the Tepla-Barrandien Unit. The third pronounced trending of the ENE-WSW direction is represented by the Erzgebirge and Eger Graben gravity low. The N-S trending Rostock-Leipzig-Regensburg Zone(Pritzwalk-Naab Lineament) is not distinctly reflected in the derived gravity maps, although many fault segments have a meridian direction. The relative reactivation potential of some pre-existing fault systems identified in the gravity map was studied with respect to the wide range of the recent stress configuration determined in the West Bohemia/Vogtland region. The resulting diagrams show that the steep NNW-SSE to N-S faults (represented by some segments of the Marianske Lazně Fault Zone) are oriented favourably for reactivation. On the contrary, the orientation of the ENE-WSW faults limiting the Eger Graben (Litoměřice Fault, etc.) is unfavourable for reactivation for all dip values