Frequency Of High-pass Filter Research Articles

Determination of High-pass Filter Frequency with Deep Learning for Ground Motion

Determination of High-pass Filter Frequency with Deep Learning for Ground Motion

Vibration characteristics and cross-feedback control of magnetically suspended blower based on complex-factor model

The research of vibration characteristics and active control methods of the magnetically suspended blower (MSB) are conducted for mitigation of the vibration amplitudes and the dynamic displacements of rotor shaft of the MSB at high speed. Firstly, the dynamic models with four degrees of freedom (DOFs) of the rotor shaft in the MSB are established. Secondly, the vibration characteristics of rotor shaft considering the rotor unbalance and misalignment are analyzed using the complex-factor model. Furthermore, the complex-factor and complex-exponential function cross-feedback models are respectively used to suppress the vibration amplitudes and the dynamic displacements of rotor shaft. Both numerical simulation and experimental tests of the cross-feedback model are conducted to verify the models. It is shown that a wide cutoff frequency of low-pass filter (LPF) could mitigate the precession, and a wide cutoff frequency of high-pass filter (HPF) could suppress the nutation. The proposed complex-exponential function cross-feedback model could be used to reduce the precession amplitude of the rotor shaft by 38.88%, and mitigate its nutation by 60.42%.

Products of Interest

Products of Interest

Fast time-varying linear filters for suppression of baseline drift in electrocardiographic signals

BackgroundThe paper presents a method of linear time-varying filtering, with extremely low computational costs, for the suppression of baseline drift in electrocardiographic (ECG) signals. An ECG signal is not periodic as the length of its heart cycles vary. In order to optimally suppress baseline drift by the use of a linear filter, we need a high-pass filter with time-varying cut-off frequency controlled by instant heart rate.MethodsRealization of the high-pass (HP) filter is based on a narrow-band low-pass (LP) filter of which output is subtracted from the delayed input. The base of an LP filter is an extremely low computational cost Lynn’s filter with rectangular impulse response. The optimal cut-off frequency of an HP filter for baseline wander suppression is identical to an instantaneous heart rate. Instantaneous length of heart cycles (e.g. RR intervals) are interpolated between QRS complexes to smoothly control cut-off frequency of the HP filter that has been used.Results and conclusionsWe proved that a 0.5 dB decrease in transfer function, at a time-varying cut-off frequency of HP filter controlled by an instant heart rate, is acceptable when related to maximum error due to filtering. Presented in the article are the algorithms that enable the realization of time-variable filters with very low computational costs. We propose fast linear HP filters for the suppression of baseline wander with time-varying cut-off frequencies controlled by instant heart rate. The filters fulfil accepted professional standards and increase the efficiency of the noise suppression.

Points to consider for a validation study of iPS cell-derived cardiomyocytes using a multi-electrode array system

Human induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) provide a novel assay system to assess cardiac safety in drug development to overcome a problem of species difference in non-clinical testing during drug development. Using the multi-electrode array (MEA) platform, electrophysiological activities of iPS-CMs can be recorded easily to assess QT prolongation and proarrhythmic potential of drug candidates. Here we have established a standardized protocol to evaluate the possibility of iPS-CMs, and shared the protocol with an international consortium. To obtain reproducible and reliable experimental data from these cells, we determined the optimal experimental conditions, such as cell density, MEA coating, culture conditions, high-pass filter frequency, definition of early afterdepolarization or triggered activity, and calibration compounds. Based on the protocol, our validation study using 60 compounds is in progress. Thus, MEA-based experiments using iPS-CMs would be a standard testing method to evaluate QT prolongation and proarrhythmic potentials.

On the Design of AGC Circuits in IM-DD NRZ Optical Transmission Systems

This paper presents the investigation on the design of automatic gain control (AGC) circuits assumed to be robust against both bias and swing variations in the received unipolar digital signal. We have derived a small signal AGC general model that includes the impact of all relevant AGC components on the AGC transfer function. This model has been used for the calculation of AGC loop parameters of the specified AGC transfer function. The AGC robustness against signal level transients has been improved by introducing the second-order AGC loop. In ac-coupled receivers, the order and corner frequency of high-pass filter (HPF) placed in front of the AGC have been investigated. The HPF has been designed so that the input signal bias variations caused by signal level transients are compressed in acceptable limits, and so that bit-pattern bias variations do not significantly decrease the receiver performance. Signal swing and bias variations become very critical in optical systems using unipolar modulation format. Since the AGC design depends on its application, as an example, we have presented the AGC design concept in dispersion compensating 10.7 Gb/s intensity-modulated direct-detection (IM-DD) nonreturn-to-zero (NRZ) optical receiver using maximum-likelihood sequence estimation (MLSE).

Blood Pressure Simulation using an Arterial Pressure-volume Model

Using an arterial pressure-volume (APV) model, we performed an analysis of the conventional blood pressure estimation method using an oscillometric sphygmomanometer with computer simulation. Traditionally, the maximum amplitude algorithm (MAA) has been applied to the oscillation waveforms of the APV model to obtain the mean arterial pressure and the characteristic ratio. The estimation of mean arterial pressure and characteristic ratio was significantly affected by the shape of the blood pressure waveforms and the cutoff frequency of high-pass filter (HPF) circuitry. Experimental errors result from these effects when estimating blood pressure. To determine an algorithm independent of the influence of waveform shapes and parameters of HPF, the volume oscillation of the APV model and the phase shift of the oscillation with fast Fourier transform (FFT) were tested while increasing the cuff pressure from 1 mmHg to 200 mmHg (1 mmHg/s). The phase shift between ranges of volume oscillation was then only observed between the systolic and the diastolic blood pressures. The same results were obtained from simulations performed on two different arterial blood pressure waveforms and one hyperthermia waveform.

Optimal EMG signal bandwidth and interelectrode distance for the recording of acoustic, electrocutaneous, and photic blink reflexes

The bandwidth for the recording of the orbicularis oculi blink reflex electromyogram (EMG) response is optimal when low-frequency artifacts, such as motion artifacts and cross-talk from other muscles, are maximally suppressed, whereas true EMG signal power is maximally retained. The optimal bandwidth was investigated for acoustic, electrocutaneous, and photic blink reflexes. Reflexes were recorded with varying bandwidth and interelectrode distances of 12 and 36 mm. Power spectra of the EMG signals were calculated and compared with a theoretical spectrum of the uncontaminated EMG signal. For both electrode distances, the optimal bandwidth was on the average 28–500 Hz for acoustic and electrocutaneous blink reflexes and 12–500 Hz for photic blinks. Using photic stimuli, however, a high-pass filter frequency larger than 12 Hz (probably at least 30 Hz) in combination with occlusion of the eye will be necessary to avoid influences of retinal potentials. Given the optimal bandwidth, a larger electrode spacing may be expected to moderately improve the detectability of small blinks in all stimulus conditions.

Optimal EMG signal bandwidth and interelectrode distance for the recording of acoustic, electrocutaneous, and photic blink reflexes

The bandwidth for the recording of the orbicularis oculi blink reflex electromyogram (EMG) response is optimal when low-frequency artifacts, such as motion artifacts and cross-talk from other muscles, are maximally suppressed, whereas true EMG signal power is maximally retained. The optimal bandwidth was investigated for acoustic, electrocutaneous, and photic blink reflexes. Reflexes were recorded with varying bandwidth and interelectrode distances of 12 and 36 mm. Power spectra of the EMG signals were calculated and compared with a theoretical spectrum of the uncontaminated EMG signal. For both electrode distances, the optimal bandwidth was on the average 28-500 Hz for acoustic and electrocutaneous blink reflexes and 12-500 Hz for photic blinks. Using photic stimuli, however, a high-pass filter frequency larger than 12 Hz (probably at least 30 Hz) in combination with occlusion of the eye will be necessary to avoid influences of retinal potentials. Given the optimal bandwidth, a larger electrode spacing may be expected to moderately improve the detectability of small blinks in all stimulus conditions.

Illusory brightness step in the chevreul illusion

It is well known that a staircase luminance profile is not seen veridically, but appears as the scallopy-like Chevreul illusion. We have shown that adding thin lines (either light or dark) to the centre of each step creates an illusory brightness change at the point of the line. The regions between the added lines and the edges seem to be uniform, with a clear change in brightness at the point where the line was added. The conditions under which the illusion occurred were measured systematically, both by contrast matching and by annulment. One model that can readily account for the illusion is the local-energy model of feature detection (Morrone & Burr, 1988 Proceedings of the Royal Society of London B, 235, 221–245). Adding the bar to the step creates a peak in local energy at all scales. At the higher scales, the phase of the energy is near zero, the signal for a line; but at the lower scales the phase is near π/2, the signal for an edge. We propose that the edge signal of the lower scales causes the brightness illusion and that this brightness difference is structured by the feature defined sharply by the higher scales (even though that feature is not an edge). As well as predicting the existence of the illusion, simulations with the energy model predicted quantitatively the apparent contrast of the illusion as a function of stimulus contrast, bar-position and high-pass filter frequency.

Optimal late potential criteria for reducing false positive signal-averaged electrocardiograms

The purposes of this study were to determine for signal-averaged electrocardiograms in normal subjects: (1) the incidence of false positives for various filter frequencies and late potential criteria and (2) reproducibility over time. In 46 normal volunteers, the QRS vector magnitude was bidirectionally high-pass filtered at 25, 40, and 100 Hz. As high-pass filter frequency increased, QRS duration decreased from 98 ± 9 to 92 ± 9 msec ( p < 0.0001), terminal QRS root mean square voltage decreased from 60 ± 41 to 14 ± 9 μV ( p < 0.0001), and terminal QRS low amplitude signal duration increased from 27 ± 7 to 41 ± 14 msec ( p < 0.0001). For individual parameters, the incidence of false positive tests ranged from 2% to 41%, whereas there were no false positive tests for the combination of abnormal QRS duration plus either root mean square voltage or low amplitude signal duration. Measurements were repeated after 6.4 ± 0.3 months in 26 subjects and were highly reproducible at all filter settings. The potentially high incidence of false positive tests with some criteria has important implications for the use of signal-averaged electrocardiography as a screening test in patient populations with various arrhythmia risks.

Effects of Filtering on Right Ventricular Electrograms Recorded from Endocardial Catheters in Humans

Criteria for identifying electrically abnormal myocardium based on analysis of electrogram, amplitude, duration, and morphology have recently been proposed as an aid to catheter mapping in humans. Electrogram characteristics are likely to be influenced by analog filtering and the distance between recording electrodes. These parameters can be varied and differ among electrophysiology laboratories. To determine the magnitude of the effect of low pass and high pass filtering and interelectrode distance on human bipolar right ventricular electrograms eight patients were studied. The signal from a single bipolar electrode pair was recorded simultaneously on five channels with variable filtering. As the high pass filter frequency increased above 10 Hz, the electrogram duration and amplitude decreased. The decrease in amplitude was described by a monoexponential function with a 30% decrease in amplitude at a filter setting of 30 Hz and a 69% decrease at a filter setting of 100 Hz. As the low pass filter frequency decreased from 2,500 to 250 Hz, electrogram characteristics were not significantly altered. Low pas filtering at 100 Hz decreased electrogram amplitude slightly. Neither high nor low pass filter settings or interelectrode distance affected electrogram timing. However, filtering could markedly alter electrogram morphology, introducing the possibility for errors in visual assessment of electrograms. Electrogram duration increased linearly with increasing distance between recording electrodes. The effects of filtering on electrograms were similar regardless of interelectrode spacing. Thus, varying the high pass filter setting over a range that is used clinically (from 1 to 100 Hz) can substantially alter electrogram duration, amplitude, and morphology. Low pass filtering at 250 Hz and above had no effect on these electrograms although it is possible that alterations would be observed in signals from areas of slow conduction that we did not study.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of high-pass filter frequency and slope on BAEP amplitude, latency and wave form

The effects of increases in analogue high-pass filter frequency and slope on the BAEP were investigated in a group of 20 subjects. Frequency effects were additionally compared to the wide-band recorded signal and slope effects to a zero-phase shift filter, all filters being digitally simulated. Absolute amplitude, latency and interpeak latency were significantly reduced by both progressive filter frequency and steepness. Additionally, different effects on the ascending and descending limbs of waves I, III and V were observed which explain wave form distortions. The results suggest that filtering should be limited to, at most, 6 dB/oct and 100 Hz frequency.

Use of signals in the terminal QRS complex to identify patients with ventricular tachycardia after myocardial infarction.

Small, high-frequency electrocardiographic signals were recorded from the body surface in 39 patients with and 27 patients without ventricular tachycardia (VT). All patients were in normal sinus rhythm, had a previous myocardial infarction, were not taking antiarrhythmic drugs, and did not have bundle branch block. Bipolar X, Y, Z leads were signal averaged and processed by a bidirectional digital filter that allowed low-amplitude signals to be detected in the terminal QRS complex and ST segment. The high-pass filter frequency was 25 Hz. Patients with VT had a lower amplitude of high-frequency signal in the late QRS complex. In the last 40 msec of the filtered QRS complex, the patients with VT had 14.9 +/- 14.4 microV of high-frequency signal; patients without VT had 73.8 +/- 47.7 microV (p less than 0.0001). Ninety-two percent of the patients with VT had less than 25 microV of high-frequency voltage; only 7% of patients without VT had less than 25 microV (p less than 0.0001). Patients with VT had a longer QRS duration than those without VT, 139 +/- 26 vs 95 +/- 10 msec (p less than 0.0001). The QRS duration was longer than 120 msec in 72% of the patients with VT but in none of the patients without VT (p less than 0.0001). In all patients there was no separate and discrete high-frequency signal in the ST segment. Advanced signal processing of the ECG accurately identified the patients in the study with VT after myocardial infarction.