Fourth-order Butterworth Low-pass Filter Research Articles

Use of Filters to Smooth Out Signals Collected through Mobile Devices in the Static and Dynamic Balance Assessment: A Systematic Review

Background: When performing motion analysis using sensors, the signal often comes with noise and it is necessary to use filters to exclude unwanted frequencies. For this reason, the objective of this work was to carry out a systematic review on the filters used in data recorded from smartphone applications for static and dynamic balance assessment. Methods: A systematic literature review was performed on the PubMed, ScienceDirect, Scopus, Technology Research and Web of Science databases, using the search strategy: smartphone, “mobile technology”, evaluation, “postural stability”, and balance. Results: 427 articles were found (PubMed = 107; ScienceDirect = 67; Scopus = 106; Web of Science = 95; Technology research database = 52). After applying the inclusion criteria and removing duplicates, nine studies were eligible for this review. In these studies, the fourth-order Butterworth low-pass filter was the most applied (N = 6) and the cutoff frequency of 4 Hz (N = 2) was the most frequent. Conclusions: In general, few studies have adequately described the filter used in signal processing. This step, when hidden, negatively affects the reproducibility of studies. Understanding and describing the signal processing is important not only for the correct description of the results but also for the reproducibility of the studies.

A Low Power Low-Pass Fourth-Order Filter for WiMAX/LTE Receiver in CMOS 45nm Technology

In this paper, a [Formula: see text]-[Formula: see text] low-pass and low power filter with tunable in-band attenuation for WiMAX/LTE receiver is presented. The fourth-order filter consists of two cascaded biquad stages. The source-follower (SF) stage is used as a key building block in these biquads. In this paper, we have presented a circuit technique to reduce the nonlinearity of the SF stage resulting from unmatched signal swings at the gate and source terminals of the input transistor. The proposed SF stage, is used for design of a linear biquad which is then utilized in a fourth-order Butterworth low-pass filter. The simulation results of the filter for bandwidth of 10 MHz show that the IIP3 of the filter is equal to 8.22[Formula: see text]dBm, in-band noise density is 100[Formula: see text]nV/[Formula: see text]Hz and power consumption is 5.9[Formula: see text]mW. The supply voltage of the filter is equal to 1[Formula: see text]V.

Vortex search algorithm for the analog active filter component selection problem

Optimal selection of passive components is one of the most crucial design steps in analog active filter design problems. As the number of possible combinations increases, it becomes infeasible to perform an exhaustive search for optimum component values. Thus, intelligent algorithms are required for a fast and optimum selection of the passive component values. In this study, a newly proposed metaheuristic, the vortex search (VS) algorithm, is utilized for this purpose. To evaluate the performance of the VS algorithm, two different analog active filter topologies, the fourth-order Butterworth low-pass filter and the state variable low-pass filter, are used. The component values of the active filter topologies are selected within three different series of (E12, E24 and E96) passive components for both the resistors and the capacitors. The results are compared to other metaheuristics such as the particle swarm optimization (PSO2011), artificial bee colony (ABC), differential evolution (DE) and harmony search (HS) algorithms. It is shown that, the VS algorithm finds the minimum fitness values for both of the active filter topologies which in turn provides the optimum component values for each of the used component series.

Effects of Plyometric Training on Lower-Body Muscle Function in Novice Marathon Runners

Improvements in lower-body force production during concurrent endurance and explosive training have been reported in competitive runners, yet few studies investigate the effects of such training on muscle function in novice runners training for distances beyond 10,000 meters. PURPOSE: To investigate the impact of a plyometric training intervention on lower-body force and power production in novice runners training for a Marathon. METHODS: Students were recruited from a marathon training course. Participants were block randomized into two groups: plyometric/explosive speed training (PLYO) or core stability training (CORE). Squat jump (SJ) and counter-movement jump (CMJ) performance were evaluated using a force platform. Data were sampled at 1202Hz and filtered using a fourth-order Butterworth low-pass filter (50Hz). Dependent measures were peak force, average rate of force development (RFD), peak RFD and jump height, which were determined from the average of three jumps at the beginning and end of the 12-week intervention. A one-way analysis of covariance was conducted to discern between-group differences in jumping performance after the intervention. RESULTS: Vertical jump data were available for 20 participants (Mean ± SD: age = 20.4 ± 1.3 yr, height = 172.1 ± 9 cm, weight = 70.3 ± 10 kg, BMI = 23.5 ± 1.9 kg·m-2, 11 female). After adjusting for pre-intervention values, there was no significant difference between PLYO and CORE on post-intervention jump height during either SJ (p = 0.07, partial eta squared = 0.18) or CMJ (p = 0.57, partial eta squared = 0.02). Post-intervention values for peak force, average RFD and peak RFD did not differ between groups for either jump type. CONCLUSION: Jumping performance parameters were not affected by the 12-week PLYO intervention while concurrently training for a marathon. It appears that the high running volume associated with marathon training negatively influences the ability to increase lower-body force and power production in novice marathon runners. It is possible that one exposure per week of plyometric training performed after a 40-minute training run was insufficient to elicit adaptation in jumping performance. Future investigations should increase the frequency of plyometric training exposure and conduct this training before the days training run.

Markers of Postmatch Fatigue in Professional Rugby League Players

The aim of the present study was to identify neuromuscular, biochemical, and endocrine markers of fatigue after Rugby League match play. Seventeen elite Rugby League players were monitored for a single match. Peak rate of force development (PRFD), peak power (PP), and peak force (PF) were measured during a countermovement jump (CMJ) on a force plate pre and postmatch play. Saliva and blood samples were collected 24 hours prematch, 30 minutes prematch, 30 minutes postmatch, and then at 24-hour intervals for a period of 120 hours to determine plasma creatine kinase concentration ([CK]) and salivary cortisol concentration ([sCort]). There were significant (p < 0.05) decreases in PRFD and PP up to 24 hours postmatch with PF significantly (p < 0.05) decreased immediately postmatch. The [sCort] significantly (p < 0.05) increased from 24 hours prematch to 30 minutes prematch and up to 24 hours postmatch compared with 24 hours prematch. Plasma [CK] significantly (p < 0.05) increased 30 minutes postmatch with a peak occurring 24 hours postmatch and remained elevated above 24 hours prematch for at least 120 hours postmatch. There were significant (p < 0.05) correlations between the increase in [CK] and reduction in PRFD 30 minutes postmatch and 24 hours postmatch. The [sCort] was significantly (p < 0.05) correlated with the reduction in PF 30 minutes postmatch. Results demonstrate that neuromuscular function is compromised for up to 48 hours after match play. Elevated [CK] despite 120-hour recovery indicate that damage to muscle tissue after Rugby League match play may persist for at least 5 days postmatch. Despite the prolonged presence of elevated [CK] postmatch, strength training 48 hours postmatch may have resulted in a compensatory increase in PRFD supporting the inclusion of strength training during the short-term postmatch recovery period.

Mixed-integrator-based bi-quad cell for designing a continuous time filter

A new mixed-integrator-based bi-quad cell is proposed. An alternative synthesis mechanism of complex poles is proposed compared with source-follower-based bi-quad cells which is designed applying the positive feedback technique. Using the negative feedback technique to combine different integrators, the proposed bi-quad cell synthesizes complex poles for designing a continuous time filter. It exhibits various advantages including compact topology, high gain, no parasitic pole, no CMFB circuit, and high capability. The fourth-order Butterworth lowpass filter using the proposed cells has been fabricated in 0.18 μm CMOS technology. The active area occupied by the filter with test buffer is only 200 × 170 μm2. The proposed filter consumes a low power of 201 μW and achieves a 68.5 dB dynamic range.

Characterisation of vortex shedding in vascular anstomosis models using pulsed doppler ultrasound

Vortex shedding at vascular anastomoses were investigated in vitro using a 20 MHz pulsed-wave Doppler velocimeter. Centreline velocity measurements were made at various axial distances in simplified polyurethane models of proximal and distal end-to-side anastomoses of angles 15, 30, 45, 60 and 80° using pulsatile flow waveforms similar to those in femoropopliteal bypass grafts. The in-phase and quadrature Doppler signals were recorded and the maximum frequency waveform, averaged over 64 cycles, was obtained using short-time Fourier transform. A fourth-order Butterworth low-pass filter was employed to separate the vortex velocity signal from the convective velocity. The vortex signal envelope was calculated using a Hilbert transform method and the vortex amplitude was taken as the maximum of this envelope. The results show that higher vortex amplitude were found in the proximal anastomoses and under resting flow conditions. Although the vortex amplitudes generally increased with angles of anastomosis, they were found to be higher in the 60° than in the 80° proximal anastomosis. The vortex structures were investigated using spectrograms and these show prominent features at 40–50 Hz indicative of the short-duration oscillatory signals during the decelerative phase of systole expected from the passage of vortices. The study indicates that flow disturbances due to vortex shedding may be a common feature in femoropopliteal bypass grafts.

The effect of digital lowpass filters on the maximum velocity of saccadic eye movements

The present paper is a study of how the inaccuracy of coefficients of digital lowpass filters may distort the maximum angular velocities of saccadic eye movements. Maximum velocity is one of the most important parameters of saccades. There are several diseases which decrease the maximum velocities of saccades. It was investigated how a fourth order Butterworth lowpass filter can affect maximum velocities. The lowpass filter has been tested by simulation as well as real eye movement data recorded electro-oculographically and photoelectrically. The coefficients of digital lowpass filters should be computed and applied with sufficient accuracy to prevent filters from altering the maximum velocities a phenomenon which might lead to erroneous diagnosis.