Cut-off Frequency Of Low-pass Filter Research Articles

Design and Characterization of a Digitally Tunable Gm-C Filter for Multi-Standard Receivers

This paper presents the design, simulation, prototyping, and measurement results of a digitally tunable fourth order Gm-C low-pass filter (LPF) for multi-standard radio receivers. The LPF cut-off frequency can be tunned by digitally selecting the transconductance of the basic reconfigurable operational transconductance amplifiers (OTAs) that compose the circuit. Four operation modes allow for control of the OTA transconductances and, consequently, the scaling of power consumption. The filter was designed and prototyped in a 1.8 V 180 nm CMOS process. The measurement results indicate that the configurability provides a cutoff frequency of 1.90/3.56/6.07/8.15 MHz with a power consumption ranging from 9.9 to 13.1 mW. The designed filter achieves an IIP3 of 8.17 dBm for a signal bandwidth of 8.15 MHz. The performance, in terms of power dissipation, noise, and cut-off frequency, is at the same order of magnitude compared to recent related works reported in the literature. The advantages are a compact area, small sensitivity to component mismatches, and low design complexity. The proposed filter presents electrical characteristics suitable for the application in radio receivers for multi-carrier WCDMA signals.

Optimizing Low Pass Filter Cut-off Frequency for Energy Management in Electric Vehicles with Hybrid Energy Storage Systems

Optimizing Low Pass Filter Cut-off Frequency for Energy Management in Electric Vehicles with Hybrid Energy Storage Systems

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%.

Stability Impacts of an Alternate Voltage Controller (AVC) on Wind Turbines with Different Grid Strengths

This paper studies the stability impact of the alternate voltage controller’s (AVC) low-pass filter (LPF) in a wind turbine’s grid-connected voltage source converter (VSC). A small-signal model of the grid-connected converter is designed with a grid-following synchronization control. More specifically, the non-linear state-space model of the grid-connected converter was developed, including the dynamics of both the inner and outer control loops of the converter, the dynamics of the elements of the electrical system, as well as the digital time delay. An eigenvalue-based stability analysis gives insight into the stability impacts of the outer-loop controllers. It is proven that the cutoff frequency of the AVC’s LPF affects the phase-locked loop (PLL) and AVC bandwidths of instability, as well as the corresponding critical oscillation frequencies. This phenomenon is observed in both weak and strong grids. Consequently, the small-signal stability regions of the PLL and AVC bandwidth can be identified for the range of the AVC’s LPF cutoff frequency under study. The stability regions of the PLL and AVC, which are obtained from the small-signal model, as well as the determined critical oscillation frequencies, are validated through time domain simulations and fast-Fourier transformation (FFT) analysis.

Systematic analysis of different low-pass filter cut-off frequencies on lumbar spine kinematics data and the impact on the agreement between accelerometers and an optoelectronic system

A necessary step in the validation of accelerometers for the measurement of spine angles is to determine the levels of agreement with current gold standard methods. However, agreement may be a function of filtering parameters. We aimed to (1) systematically determine the effect of different filter frequency cut-offs on the peak range of motion (ROM) during forward bending as measured by accelerometers and an optoelectronic (OE) system, (2) explore the influence of filtering on agreement between systems, and (3) determine the difference in peak ROM measurement between these systems. Accelerometers and OE sensors were attached at L2, L4, and S1 of 20 asymptomatic female participants for a guided flexion trial. Signals were then iteratively low-pass filtered with cut-off frequencies ranging from 14 Hz to 1 Hz and peak range of motion outcome measures were compared between systems. Peak ROM was minimally affected by filter cut-off frequency for both accelerometer and OE system. The difference in peak ROM between difference cut-off frequencies were maximum 0.66°, median 0.18° and minimum 0.06° for accelerometer derived values and maximum 0.23°, median 0.08° and minimum 0.03° for the OE system. The maximum difference across the filtering frequencies was 0.62° and the largest difference between the two systems (with outliers removed) was 0.82°. Cut-off frequencies ranging from 14 to 1 Hz had little effect of peak lumbar spine ROM during low velocity (6°/s) forward bending, regardless of motion capture method. Filtering cut-off frequency had little effect on the differences between the accelerometer and OE system and similar measurements can be achieved using accelerometers compared to OE systems.

Calculation of Band-Pass Filters with Fixed Frequencies of Infinite Attenuation

Introduction. When calculating band-pass filters (BPF) with infinite attenuation frequencies using the frequency conversion method, the parameters of the prototype – an inverse or quasi-elliptic low-pass filter (LPF) – are recalculated into BPF parameters according to conventional formulas. Using the selected low-pass filter cutoff frequency and the Q-factor of the band-pass filter, one can select at their discretion only one infinite attenuation frequency (attenuation pole). In order to suppress a pair of concrete frequencies in the attenuation band, the synthesis of BPF should initially fix the frequencies of maximum attenuation and the central frequency of the filter. The reverse transition toward the frequency response parameters of a low-frequency prototype is carried out using frequency conversion formulas.Aim. To develop of a method for calculating band-pass filters with fixed attenuation poles.Materials and methods. Odd-order filters with an additional capacitor in the transverse branch of the П-link and an inductance in the longitudinal branch of the Т-link were used as low-frequency prototypes of the BPF with attenuation poles. Approximation of the frequency response of a low-frequency prototype (inverse or quasi-elliptical LPF) was performed by methods based on solving systems of nonlinear equations.Results. A realizable transfer function (TF) of an n-th order LPF with attenuation poles was written as the ratio of the product of binomials and a polynomial of power n with real coefficients. Systems of equations were derived to determine amplitude-frequency response coefficients with a given frequency of maximum attenuation interference for both types of filters. Analytical expressions for the TF of the low frequency prototypes of 3th and 5th orders were recorded through the capacitances of the BPF circuits tuned to the central and suppressed frequencies, thus allowing the desired capacitances to be directly calculated. The BPF inductances were determined by formulas expressing the dependences of the BPF central frequency on the circuits parameters, taking into account the relationships given in the article. An example of calculating a 10th order quasi-elliptic BPF was provided.Conclusion. The proposed method can be used to determine the BPF parameters directly, without an intermediate calculation and subsequent transformation of the LPF prototype parameters. The given analytical expressions for the frequency response of the П- and Т-shaped BPFs of the 6th and 10th orders make it possible to verify the performed calculations and to correct the frequency response using inductances, when replacing the calculated capacitance values with their standard values.

WEWNĄTRZGRUPOWE PORÓWNANIE SKUTECZNOŚCI APARATÓW SŁUCHOWYCH W SZUMIE NA PODSTAWIE CZASÓW ODPOWIEDZI WERBALNEJ VRT

BackgroundVerbal response times (VRTs) are among the suggested markers for cognitive load during word recognition tasks. Measurements of VRT during hearing aid fitting can be a useful tool to obtain information about listening effort with different amplification parameters.Material and methodsA software program was developed to easily measure VRTs in speech recognition tests. The system plays 50 randomly chosen recorded words out of a set of 700 disyllables. Speech material can be presented together with pre-selected noise samples at different speech-to-noise ratios and processed with low-pass filters with selectable cut-off frequencies. The test is carried out in free field. A voice activity detector measures the time between the offset of the presented word and the onset of the repetition by the subject, which allows VRT and speech recognition scores to be quickly assessed. Tests were carried out with a group of 8 normal-hearing subjects to evaluate the effect of different filter parameters and a second group of 8 normal-hearing people to evaluate the effect of different speech-to-noise ratios on VRT. Finally, a group of 15 adult hearing-impaired subjects who used hearing aids were fitted under different conditions and the VRTs were compared between fittings.ResultsReducing the low-pass filter cutoff frequency or adding noise to the speech signal increased VRTs in normal hearing people, suggesting an inverse relationship between VRT and ease of listening. In the hearing-impaired group, VRTs with different fittings of the hearing aid showed differences that can be used as an indicator of listening effort.ConclusionsAdding a measurement of VRT to a regular word recognition test during hearing aid fitting could be useful for adjusting parameters or deciding between models or processing strategies, especially if recognition scores are high.

Impact and Removal of Ground-Penetrating Radar Vibration on Continuous Asphalt Concrete Pavement Density Prediction

Ground-penetrating radar (GPR) could be implemented for continuous asphalt concrete (AC) pavement density predictions during compaction process. However, vibrations during survey and the complexity of GPR data processing may impede its application. GPR antenna vibration affects the collected data, which could be mitigated through profile smoothing using decomposition approaches. A signal-processing technique is proposed for filtering vibration noise to allow for continuous AC density prediction from GPR data. During constant speed survey, low-pass filter cutoff frequency and length may be used during signal processing for profile smoothing. Nonstationary profile caused by inconsistent speed survey could be smoothed using wavelet transform. Empirical mode decomposition is suggested for utilization when sudden braking/accelerating occurs. Field tests using roller-mounted antennas were used to validate the process.

Automated Test Station for Low-Pass Filter Cut-off Frequency Measurements

The primary focus of this research paper is to study the automated test station to determine the cut-off frequency. The study was conducted for the low-pass filter in the frequency range 50Hz–100 KHz. Preliminary test was conducted using 10 filters whose cut-off frequencies were measured. The main blocks of the station are described, emphasizing some originality. The test results depict high degree of accuracy as such were manually checked to confirm the effectiveness of the test station. The automated test station was also developed to include provisions which allow the results to be stored in a spreadsheet file against each of the filter serial number. This is a unique feature of the measurement system

Adaptive identification of lowpass filter cutoff frequency for online vessel model tuning

Tuning of vessel models in real-time based on vessel measurements and weather information is of great interest in order to increase the safety and efficiency of marine operations. Vessel motion signals usually contain high-frequency noise. For an unbiased model tuning algorithm, it is essential to filter the noisy signals in order to identify the power of the wave-induced first-order vessel response. Lowpass filters with high accuracy should therefore be applied. However, it is a challenge to design such a filter since the optimal cutoff frequency can vary with sea states, vessel dimensions, vessel conditions, etc. This paper proposes a novel algorithm to adaptively search for the optimal cutoff frequency for a lowpass filter with high accuracy. The algorithm is fundamentally based on the facts that the vessel naturally acts as a lowpass filter and the energy from the high-frequency components, e.g., signal noise, is significantly smaller than that from the wave-induced vessel response. The algorithm is validated by 500 numerically simulated vessel motion signals with quite high noise levels and also by analysis of several on-site full-scale vessel motion signals. The improvements to the tuning results for the vessel parameters are demonstrated.

Optimization and visualization of phase modulation with filtered and amplified maximal-length sequence for SBS suppression in a short fiber system: a theoretical treatment.

We use a model to investigate both the temporal and spectral characteristics of a signal lightwave which has been spectrally broadened through phase modulation with a maximal-length sequence (MLS), which is a common type of pseudo-random bit sequence. The enhancement of the stimulated Brillouin scattering (SBS) threshold of the modulated lightwave in a fiber system is evaluated by numerically simulating the coupled three-wave SBS interaction equations. We find that SBS can build up on a nanosecond-level time scale in a short fiber, which can reduce the SBS suppressing capability of MLS modulation waveforms with GHz-level clock rate, if the sub-sequence ("run") lengths with the same symbol (zero or one) of the MLS extend over several nanoseconds. To ensure the SBS buildup is perturbed and thus suppressed also during these long sub-sequences, we introduce a low-pass filter to average the signal over several bits so that the modulation waveform changes gradually even during long runs and amplify the RF modulation waveforms to the level required for sufficient spectral broadening and carrier suppression of the optical signal. We find that the SBS suppression depends non-monotonically on the parameters of the filtered and amplified MLS waveform such as pattern length, modulation depth, and the ratio of low-pass filter cutoff frequency to clock rate for maximum SBS mitigation. We optimize the SBS suppression through numerical simulations and discuss it in terms of the temporal and spectral characteristics of the lightwave and modulation waveform using derived analytical expressions and numerical simulations. The simulations indicate that the normalized SBS threshold reaches a maximum for a RMS modulation depth of 0.56π and a ratio of filter cutoff frequency to clock rate of 0.54 and that MLS9 is superior to other investigated patterns.

Research about the Sensorless Vector Control of Permanent Magnet Synchronous Motor Based on Two-stage Filter Sliding Mode Observer

In order to overcome the disadvantages of installing mechanical sensors and the problems of chattering and low observation accuracy in traditional sliding mode observer sensorless control, a two-stage filter Sliding Mode Observer (SMO) is proposed in this paper. By collecting the current and voltage of the Permanent Magnet Synchronous Motor (PMSM), the SMO algorithm is realized by using the state equation of the motor in the synchronous stationary coordinate system; the position of the rotor is estimated by the arc tangent function, the observation accuracy of the rotor position is improved by increasing phase compensation; the variable cut-off frequency filter is introduced to make the Low Pass Filter (LPF) cut-off frequency can be self-adjusted with the change of rotational speed, which improves the estimation accuracy of rotor position at different rotational speeds. Kalman filter is introduced to form a two-stage filter with variable cut-off frequency LPF, which greatly weakens the chattering of the motor and reduces the observation error. Finally, the simulation is carried out under MATLAB/Simulink. The simulation results show that the PMSM vector control system with two-stage filter sliding mode observer has high estimation accuracy, good dynamic and steady-state performance, strong anti-jamming ability and robustness.

Low-pass filter cutoff frequency affects sacral-mounted inertial measurement unit estimations of peak vertical ground reaction force and contact time during treadmill running

Inertial measurement units (IMUs) are popular tools for estimating biomechanical variables such as peak vertical ground reaction force (GRFv) and foot-ground contact time (tc), often by using multiple sensors or predictive models. Despite their growing use, little is known about the effects of varying low-pass filter cutoff frequency, which can affect the magnitude of force-related dependent variables, the accuracy of IMU-derived metrics, or if simpler methods for such estimations exist. The purpose of this study was to investigate the effects of varying low-pass filter cutoff frequency on the correlation of IMU-derived peak GRFv and tc to gold-standard lab-based measurements. Thirty National Collegiate Athletics Association Division 1 cross country runners ran on an instrumented treadmill at a range of speeds while outfitted with a sacral-mounted IMU. A simple method for estimating peak GRFv from the IMU was implemented by multiplying the IMU’s vertical acceleration by the runner’s body mass. Data from the IMU were low-pass filtered with 5, 10, and 30 Hz cutoffs. Pearson correlation coefficients were used to determine how well the IMU-derived estimates matched gold-standard biomechanical estimations. Correlations ranged from very weak to moderate for peak GRFv and tc. For peak GRFv, the 10 Hz low-pass filter cutoff performed best (r = 0.638), while for tc the 5 Hz cut-off performed best (r = 0.656). These results suggest that IMU-derived estimates of force and contact time are influenced by the low-pass filter cutoff frequency. Further investigations are needed to determine the optimal low-pass filter cutoff frequency or a different method to accurately estimate force and contact time is suggested.

An Improved ip − iq Harmonic Detection Method Based on Time-Varying Integral Duration

By analyzing harmonic related to instantaneous active current and instantaneous reactive current, we propose an improved harmonic detection method to remedy long response delay and low detection accuracy corresponding to harmonic of power system. This method introduces a series connection scheme composed of Low-Pass Filter (LPF) and a current average module firstly. Then, detection accuracy of harmonic current is enhanced by adaptive tuning cut-off frequency of LPF and integration time which was obtained by proposed algorithm of the current average module. Moreover, feedback loop is introduced to compensated delay caused by LPF. Simulations including uncontrollable rectifier and three-phase voltage type inverter show proposed method has many advantages such as high detection accuracy, low response delay and good generality. Our method provides reliable harmonic current detection for later harmonic suppression and harmonic compensation.

Spectral-Temporal Trade-Off in Vocoded Sentence Recognition: Effects of Age, Hearing Thresholds, and Working Memory.

Cochlear implant (CI) signal processing degrades the spectral components of speech. This requires CI users to rely primarily on temporal cues, specifically, amplitude modulations within the temporal envelope, to recognize speech. Auditory temporal processing ability for envelope modulations worsens with advancing age, which may put older CI users at a disadvantage compared with younger users. To evaluate how potential age-related limitations for processing temporal envelope modulations impact spectrally degraded sentence recognition, noise-vocoded sentences were presented to younger and older normal-hearing listeners in quiet. Envelope modulation rates were varied from 10 to 500 Hz by adjusting the low-pass filter cutoff frequency (LPF). The goal of this study was to evaluate if age impacts recognition of noise-vocoded speech and if this age-related limitation existed for a specific range of envelope modulation rates. Noise-vocoded sentence recognition in quiet was measured as a function of number of spectral channels (4, 6, 8, and 12 channels) and LPF (10, 20, 50, 75, 150, 375, and 500 Hz) in 15 younger normal-hearing listeners and 15 older near-normal-hearing listeners. Hearing thresholds and working memory were assessed to determine the extent to which these factors were related to recognition of noise-vocoded sentences. Younger listeners achieved significantly higher sentence recognition scores than older listeners overall. Performance improved in both groups as the number of spectral channels and LPF increased. As the number of spectral channels increased, the differences in sentence recognition scores between groups decreased. A spectral-temporal trade-off was observed in both groups in which performance in the 8- and 12-channel conditions plateaued with lower-frequency amplitude modulations compared with the 4- and 6-channel conditions. There was no interaction between age group and LPF, suggesting that both groups obtained similar improvements in performance with increasing LPF. The lack of an interaction between age and LPF may be due to the nature of the task of recognizing sentences in quiet. Audiometric thresholds were the only significant predictor of vocoded sentence recognition. Although performance on the working memory task declined with advancing age, working memory scores did not predict sentence recognition. Younger listeners outperformed older listeners for recognizing noise-vocoded sentences in quiet. The negative impact of age was reduced when ample spectral information was available. Age-related limitations for recognizing vocoded sentences were not affected by the temporal envelope modulation rate of the signal, but instead, appear to be related to a generalized task limitation or to reduced audibility of the signal.

Human Frequency Following Responses to Filtered Speech.

There is increasing interest in using the frequency following response (FFR) to describe the effects of varying different aspects of hearing aid signal processing on brainstem neural representation of speech. To this end, recent studies have examined the effects of filtering on brainstem neural representation of the speech fundamental frequency (f0) in listeners with normal hearing sensitivity by measuring FFRs to low- and high-pass filtered signals. However, the stimuli used in these studies do not reflect the entire range of typical cutoff frequencies used in frequency-specific gain adjustments during hearing aid fitting. Further, there has been limited discussion on the effect of filtering on brainstem neural representation of formant-related harmonics. Here, the effects of filtering on brainstem neural representation of speech fundamental frequency (f0) and harmonics related to first formant frequency (F1) were assessed by recording envelope and spectral FFRs to a vowel low-, high-, and band-pass filtered at cutoff frequencies ranging from 0.125 to 8 kHz. FFRs were measured to a synthetically generated vowel stimulus /u/ presented in a full bandwidth and low-pass (experiment 1), high-pass (experiment 2), and band-pass (experiment 3) filtered conditions. In experiment 1, FFRs were measured to a synthetically generated vowel stimulus /u/ presented in a full bandwidth condition as well as 11 low-pass filtered conditions (low-pass cutoff frequencies: 0.125, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, and 8 kHz) in 19 adult listeners with normal hearing sensitivity. In experiment 2, FFRs were measured to the same synthetically generated vowel stimulus /u/ presented in a full bandwidth condition as well as 10 high-pass filtered conditions (high-pass cutoff frequencies: 0.125, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, and 6 kHz) in 7 adult listeners with normal hearing sensitivity. In experiment 3, in addition to the full bandwidth condition, FFRs were measured to vowel /u/ low-pass filtered at 2 kHz, band-pass filtered between 2-4 kHz and 4-6 kHz in 10 adult listeners with normal hearing sensitivity. A Fast Fourier Transform analysis was conducted to measure the strength of f0 and the F1-related harmonic relative to the noise floor in the brainstem neural responses obtained to the full bandwidth and filtered stimulus conditions. Brainstem neural representation of f0 was reduced when the low-pass filter cutoff frequency was between 0.25 and 0.5 kHz; no differences in f0 strength were noted between conditions when the low-pass filter cutoff condition was at or greater than 0.75 kHz. While envelope FFR f0 strength was reduced when the stimulus was high-pass filtered at 6 kHz, there was no effect of high-pass filtering on brainstem neural representation of f0 when the high-pass filter cutoff frequency ranged from 0.125 to 4 kHz. There was a weakly significant global effect of band-pass filtering on brainstem neural phase-locking to f0. A trends analysis indicated that mean f0 magnitude in the brainstem neural response was greater when the stimulus was band-pass filtered between 2 and 4 kHz as compared to when the stimulus was band-pass filtered between 4 and 6 kHz, low-pass filtered at 2 kHz or presented in the full bandwidth condition. Last, neural phase-locking to f0 was reduced or absent in envelope FFRs measured to filtered stimuli that lacked spectral energy above 0.125 kHz or below 6 kHz. Similarly, little to no energy was seen at F1 in spectral FFRs obtained to low-, high-, or band-pass filtered stimuli that did not contain energy in the F1 region. For stimulus conditions that contained energy at F1, the strength of the peak at F1 in the spectral FFR varied little with low-, high-, or band-pass filtering. Energy at f0 in envelope FFRs may arise due to neural phase-locking to low-, mid-, or high-frequency stimulus components, provided the stimulus envelope is modulated by at least two interacting harmonics. Stronger neural responses at f0 are measured when filtering results in stimulus bandwidths that preserve stimulus energy at F1 and F2. In addition, results suggest that unresolved harmonics may favorably influence f0 strength in the neural response. Lastly, brainstem neural representation of the F1-related harmonic measured in spectral FFRs obtained to filtered stimuli is related to the presence or absence of stimulus energy at F1. These findings add to the existing literature exploring the viability of the FFR as an objective technique to evaluate hearing aid fitting where stimulus bandwidth is altered by design due to frequency-specific gain applied by amplification algorithms.

Filtration Selection and Data Consilience: Distinguishing Signal from Artefact with Mechanical Impact Simulator Data.

A large variety of data filtration techniques exist in biomechanics literature. Data filtration is both an 'art' and a 'science' to eliminate noise and retain true signal to draw conclusions that will direct future hypotheses, experimentation, and technology development. Thus, data consilience is paramount, but is dependent on filtration methodologies. In this study, we utilized ligament strain, vertical ground reaction force, and kinetic data from cadaveric impact simulations to assess data from four different filters (12 vs. 50Hz low-pass; forward vs. zero lag). We hypothesized that 50Hz filtered data would demonstrate larger peak magnitudes, but exhibit consilience of waveforms and statistical significance as compared to 12Hz filtered data. Results demonstrated high data consilience for matched pair t test correlations of peak ACL strain (≥ 0.97), MCL strain (≥ 0.93) and vertical ground reaction force (≥ 0.98). Kinetics had a larger range of correlation (0.06-0.96) that was dependent on both external load application and direction of motion monitored. Coefficients of multiple correlation demonstrated high data consilience for zero lag filtered data. With respect to in vitro mechanical data, selection of low-pass filter cutoff frequency will influence both the magnitudes of discrete and waveform data. Dependent on the data type (i.e., strain and ground reaction forces), this will not likely significantly alter conclusions of statistical significance previously reported in the literature with high consilience of matched pair t-test correlations and coefficients of multiple correlation demonstrated. However, rotational kinetics are more sensitive to filtration selection and could be suspect to errors, especially at lower magnitudes.

Reliability and robustness of optimization properties for stabilization of the upright stance as determined using posturography

Diagnostic value of static posturography depends on its methodological features, measurement properties, and on computational methods that extract meaningful information from the postural sway i.e. the center-of-pressure (CoP) displacements. In this study, we assessed the reliability and robustness of the postural system based on the optimization properties of the CoP signal: descending, local and global stability, and convergence. For the analysis, we used CoP data from 146 participants (104 [71%] female, age 46 ± 23 years, body mass index 23.6 ± 3.4 kg/m2) recorded while standing quietly on a foam surface without visual input. Reliability was estimated using the intraclass correlation coefficient from a single (ICC2,1) and averaged (ICC2,3) measurements. Robustness was assessed through main and interaction effects for the signal duration (60, 30 s), sampling frequency (100, 50 Hz), and lowpass filtering cutoff frequency (10, 5 Hz). The observed reliability depended on the use of average or single measurements as it was excellent for the stability property (ICC2,k ≥ 0.772); excellent-to-acceptable (ICC2,3 ≥ 0.540) or excellent-to-unacceptable (ICC2,1 ≥ 0.281) for the descending property; and excellent-to-unacceptable (ICC2,3 > 0.295; ICC2,1 > 0.122) for the convergence property. Robustness analysis showed large main effects of signal duration (ω2 ≤ 0.834, p < 0.001), sampling frequency (ω2 ≤ 0.526, p < 0.001), and the lowpass filter cutoff frequency (ω2 ≤ 0.523, p < 0.001) on the optimization properties; but all two-way and three-way effects varied from medium to trivial. Reliability is thus excellent to acceptable for deriving the descending, stability, and convergence properties from the average of three measurements. Those optimization properties are robust to the interaction but not the main effects of methodological sources of variation of posturography.

Effects of low-pass filter combinations on lower extremity joint moments in distance running

Inverse dynamics is a standard tool in biomechanics, which requires low-pass filtering of external force and kinematic signals. Unmatched filtering procedures are reported to affect joint moment amplitudes in high impact movements, like landing or cutting, but are also common in the analysis of distance running. We analyzed the effects of cut-off frequencies in 94 rearfoot runners at a speed of 3.5 m/s. Additionally, we investigated whether the evaluation of footwear interventions is affected by the choice of cut-off frequencies. We performed 3D inverse dynamics for the hip, knee and ankle joints using different low-pass filter cut-off frequency combinations for a recursive fourth-order Butterworth filter. We observed fluctuations of joint moment curves in the first half of stance, which were most pronounced for the most unmatched cut-off frequency combination (kinematics: 10 Hz; ground reaction forces (GRFs): 100 Hz) and for more proximal joints. Peak sagittal plane hip joint moments were altered by 94% on average. We observed a change in the ranking of subjects based on joint moment amplitude. We found significant (p < 0.001) footwear by cut-off frequency combination interaction effects for most peak joint moments. These findings highlight the importance of cut-off frequency choice in the analysis of joint moments and the assessment of footwear interventions in distance running. Based on our results, we propose to use matched cut-off frequencies around 20 Hz in order to avoid large artificial fluctuations in joint moment curves while at the same time avoiding a severe removal of physiological high-frequency signal content from the GRF signals.

A low-cost electro-cardiograph machine equipped with sensitivity and paper speed option

The price of electrocardiograph (ECG) machine on the market is very high. Currently, the technology used is still very complicated and ineffective, and the ECG machine cannot be connected to other devices. A new development of a low-cost ECG machine with a customized design was needed to integrate the machine with other devices. Therefore, the purpose of this study is to develop a low-cost ECG machine which can be connected to other devices and equipped with sensitivity and paper speed setting. So that portable ECG machines can be produced and used at small clinics in the society. In this study, the main controller of the 12 channels ECG machines was supported by ATMEGA16 microcontroller, that is available on the market at low prices. The main part of the ECG amplifier is built using a high common mode rejection ratio (CMRR) instrumentation amplifier (AD620) and a bandpass filter which the cutoff frequency for highpass filter and lowpass filter are 0.05 Hz and 100 Hz, respectively. In order to complement the previous study, some features were introduced such as selectivity and motor speed option. In this study, 10 participants are involved for data acquisition,and an ECG phantom was used to calibrate the machine. The performance of the ECG machine was evaluated using standard measurement namely relative percentage error (% error) and uncertainty (UA). The result shows that %error from all of the feature is less than 2% and the UA is 0.0 which shows that the ECG machine is feasible for diagnostic purposes.