Low-frequency Interference Research Articles

Применение методов математической статистики для прогнозирования возникновения несимметрии напряжений в электрических сетях

In this paper a statistical analysis of the results of measuring the quality parameters of electric power of the traction substation Uryum 220/35/27.5/10 kV, RU – 35 kV, 1 SS, 35 kV overhead line (VL – 241) located in the Trans-Baikal Territory was performed using the methods of mathematical statistics and probability theory. A particular attention is paid to conducted low-frequency electromagnetic interference by the unbalance factor of the negative sequence voltage ( K 2 U ). Voltage unbalance is a fairly common phenomenon in electrical networks of various stress classes and one of the indicators by which the quality of electricity is estimated. Unbalance of stresses significantly affects consumers of electricity, including the supply network itself, and especially negatively it affects the process of ope­ration and the service life of electrical equipment. The relevance of this problem is confirmed by numerous studies on this issue and a significant amount of damage to consumers of electrical energy in service (especially in the Trans-Baikal Territory and the Far Eastern Regions). In the course of the research the form and parameters of the distribution law of a random continuously distributed quantity K 2 U are determined. To assess the degree of coincidence of the empirical and theoretical distributions, a three-fold test was carried out to verify the validity of the chosen distribution law using the Pearson's χ 2 , Kolmogorov, and ω 2 (Cramer – Mises – Smirnov) criteria. A theoretical logarithmically normal distribution is adopted. The authors determined the likelihood of conducted low-frequency electromagnetic interference on the coefficient of voltage unbalance negative sequence ( K 2 U ) for the studied object, besides, the estimation of the service life of the asynchronous motor within certain ranges was made. These ranges are selected basing on the existing interstate standard for the quality of electrical energy GOST 32144–2013. The research results are analyzed. The corresponding conclusions are presented.

Оценка работоспособности метода причинности по Грейнджерудля выявления однонаправленной связи при наличии общей внешней низкочастотной помехи

Оценка работоспособности метода причинности по Грейнджерудля выявления однонаправленной связи при наличии общей внешней низкочастотной помехи

Directional wave separation in tubular acoustic systems – The development and evaluation of two industrially applicable techniques

An acoustic device is used to evaluate internal features and defects within tubes by determination of the acoustic impulse response. This paper concerns methods of separating the total pressure wave measured in the device into its forward and backward travelling components, which facilitates computation of the acoustic impulse response. The device comprises a tube that has a speaker at one end and is axially instrumented with microphones. Unlike similar works, the methods presented in this paper were designed to be applied in an industrial context, they allow simple calibration and implementation using readily transportable equipment. Two wave separation algorithms are presented; the first is a known method that has been improved to provide simplified calibration and the second is a computationally inexpensive technique that has been adapted to improve its operational bandwidth. The techniques are critically evaluated using a custom built test rig, designed to simulate realistic tube features and defects such as constrictions, holes and corrosion. It is demonstrated that, although inter-microphone attenuation is not accounted for in the second algorithm, both algorithms function well and give similar results. It is concluded that the added sophistication of the first method means that it is less affected by low frequency interference and is capable of yielding more accurate results. However, in practical use as an evaluation tool, the benefits of including inter-microphone attenuation are outweighed by the additional calibration and computational requirements. Finally the output of the wave separation techniques is validated by showing agreement between experimental impulse response measurements and those obtained from a theoretically derived acoustic tube simulator.

Energy harvesting from electromagnetic interference induced in the human body

Energy harvesting using the human body as an antenna is presented. Low-frequency interference, mainly in the 40–60 kHz range, was generated from electronic ballast of a fluorescent light. Radiated electromagnetic energy was induced in a human body and a rectifier circuit converted induced energy into DC power. An input matching network of the diode rectifier was designed based on an equivalent source model of interference. A wristband-type harvesting module comprising a metal electrode designed to be in contact with the human skin was implemented. A power of −8.5 dBm was harvested from the body of a person with a height of 180 cm made to stand 60 cm below a fluorescent light with two 32 W lamps in a hemi-anechoic chamber. The proposed system can supply energy to the sensors used in body area networks.

On the nature of sources of audio-frequency electromagnetic interferences

It has been shown that metal elements of electronic equipment executing mechanical vibrations under exposure to the dc or low-frequency magnetic field could be sources of low-frequency electromagnetic interferences. The general solution of a boundary problem of electrodynamics was obtained that dealt with the electromagnetic field emission by a rod with circular cross-section made of metal of the non-ferromagnetic group under harmonic elastic oscillations in the dc magnetic field. A model example was considered for the situation where a source of low-frequency electromagnetic field was the rod with circular cross-section that executed longitudinal harmonic oscillations of compression–tension at the transverse dc magnetic field. An estimation of numerical values of the intensity of low-frequency magnetic field and the induced voltage of interference were also provided.

Design of multichord Hα detector arrays for the U-3M torsatron and identification of rotating plasma perturbations.

An Hα camera has been designed and installed in the U-3M torsatron for spatially and temporally resolved measurements. This device provides fast measurements of the emission brightness profile in the noisy environment of the radio frequency (RF) heated plasma. Unusual topology of diagnostics and the data acquisition system are applied. All the system components, including digitizers, are assembled in a single unit. It allows the suppression of a low-frequency electromagnetic interference by eliminating the ground loops. And the suppression of RF noises is achieved by eliminating the signal interface cables and digital interface cables in the design. The Wi-Fi interface is used to prevent a ground loop in the data transfer stage. The achieved sensitivity of our diagnostics is high enough for measuring the Hα emission from the low-density (ne ≈ (1-2)⋅10(10) cm(-3)) plasma with a temporal resolution of about 20 μs in the noisy environment. Different types of Hα emission fluctuations within the frequency range of 1-5 kHz and poloidal mode numbers m = 0 and m = 5 have been observed in U-3M. A simple technique of the line-of-sight data analysis, based on the U-3M magnetic surface asymmetry, is proposed and used for the spatial localization of the rotating mode and for the determination of mode numbers and its poloidal rotation direction using a single Hα array.

Periodic Carrier Frequency Modulation in Reducing Low-Frequency Electromagnetic Interference of Permanent Magnet Synchronous Motor Drive System

This paper introduces the periodic carrier frequency modulation (PCFM) for permanent magnet synchronous motor (PMSM) drive systems so as to reduce the low-frequency electromagnetic interference (EMI). PMSMs are widely used in many applications and they are usually fed by pulsewidth modulation (PWM) inverters. The EMI of PMSM, which results from the switch of power device, generates undesirable effects on the control system. Therefore, it is of importance to reduce the EMI of PMSM. The common mode (CM) conducted EMI model of the PMSM drive system is constructed to investigate the CM voltage. The simulations and experiments of PMSM fed by the fixed frequency PWM (FFPWM) and PCFM are implemented to analyze the CM conducted EMI. The CM EMI spectra of PMSM fed by the FFPWM and PCFM with different spreading frequency widths are compared to explore the influence of PCFM on the CM conducted EMI. The regular patterns on PCFM in reducing the CM conducted EMI of PMSM drive systems are revealed.

In-Phase Bias Modulation Mode of Scanning Ion Conductance Microscopy With Capacitance Compensation

The in-phase bias modulation (IPBM) mode of scanning ion conductance microscopy (SICM), which has advantages of both the dc mode and the traditional ac mode, is immune to low-frequency external electronic interference and potential drift while maintaining a high scanning speed. However, the IPBM mode still suffers from a low-signal-to-noise ratio (SNR). In this paper, we propose a capacitance compensation (CC) method to solve the problem in the IPBM mode of SICM. After CC, the signal level is significantly increased while the noise level remains unchanged. The increased SNR not only improves the image quality but also allows the system to work at a higher modulation frequency, thus increasing potential for fast scan. Experimental results verify the effectiveness of the IPBM mode of SICM with CC.

A 0.7 V, 40 nW Compact, Current-Mode Neural Spike Detector in 65 nm CMOS.

In this paper, we describe a novel low power, compact, current-mode spike detector circuit for real-time neural recording systems where neural spikes or action potentials (AP) are of interest. Such a circuit can enable massive compression of data facilitating wireless transmission. This design can generate a high signal-to-noise ratio (SNR) output by approximating the popularly used nonlinear energy operator (NEO) through standard analog blocks. We show that a low pass filter after the NEO can be used for two functions-(i) estimate and cancel low frequency interference and (ii) estimate threshold for spike detection. The circuit is implemented in a 65 nm CMOS process and occupies 200 μm × 150 μ m of chip area. Operating from a 0.7 V power supply, it consumes about 30 nW of static power and 7 nW of dynamic power for 100 Hz input spike rate making it the lowest power consuming spike detector reported so far.

Performance Analysis of Linear Induction Motor of Electromagnetic Catapult

Based on the operating principle of linear induction motor (LIM), this paper has analyzed the performance of the LIM consisting of a long sectioned transverse flux stator and a short flat aluminum mover, proposed the basic requirements and working modes of this special type of a catapult, described the optimal design methods of the LIM and discussed in detail some important parameters affecting the operating performance, such as the slot width, pole pairs, and the thickness of the mover. Then, the optimal system design and the discussion of performance are carried out based on the T-type equivalent circuit model with the covered and uncovered sections. The phase current, phase voltage, power capacity, and height are 11359 A, 3000 V, 409 MVA, and 1.73 m, respectively. The launch profile is also derived from the model. To verify the electromagnetic compatibility of the LIM, the 3-D magnetic model is established. The results show that the magnetic fields fall to the earth's ambient level at 1 m above the stator, which cannot bring low-frequency electromagnetic interference to the environment.

Impact of low-frequency pulsed electromagnetic fields and interference currents in the formation of heterotopic ossification after total hip instalation in the hip joint

Due to the extension of life expectancy, the number of elderly people increases, and thus the number of disease and injuries of the locomotor system, especially the hip joint. One of the persistent trend is an increasing trend in the number of patients with coxarthrosis and implanted total hip endoprosthesis. One of the postoperative complications that occurred after implantation a total hip endoprosthesis is heterotopic ossification (HO). HO is the most common complication that occurs after the implantation a total hip endoprosthesis with recorded cases in the range of 9-90%. HO are insufficiently understood phenomenon, which is characterized by the formation of bone in periarticular tissues. We prospectively followed patients who implanted total hip endoprostheses in the department of orthopedics ZC in Kos. Mitrovica in 2008. and 2009. year. We examined the influence of physical agents on the prevention of HO near the hip joint. In these patients the treatment was carried out kinesiotherapeutic at the Center for Rehabilitation Health Center Kosovska Mitrovica, as well as pulse therapy low frequency magnetic field frequency of 30 Hz, 30 minutes, 8 mT intensity and 15 minutes interferential current, 0-100 Hz frequency. All patients were on the rehabilitation of one month (20 days). Based on this research we confirmed the assumption that the use of low frequency pulsed magnetic fields, interference currents and kinesitherapy prevents HO in patients after implantation of total endoprosthesis of the hip joint.

The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

AbstractThe Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).

Method of adaptive filtering of pulse-wave low-frequency distortions

Different methods of correcting the low-frequency distortions of pulse-wave signal have been considered. A correction method based on forming a reference signal of adaptive filter and using low-frequency filtering of initial biosignal is proposed. The efficiency of different methods of pulse-wave filtering is investigated under the conditions of exposure to interferences of different intensity. It has been found out that the proposed method of filtering low-frequency interferences makes it possible to obtain the lowest distortions in signal processing as compared to the model signals free from manifestation of distorting effects.

Design, analysis and implementation of a buck–boost DC/DC converter

A novel buck–boost converter is presented in this study. This converter is based on Cuk converter. Therefore it inherits all the advantages of Cuk converter such as low output voltage ripple and minimal radio frequency interference. In addition, some implementation problems of KY converters are solved. The proposed converter has higher voltage gain in step-up mode in comparison with Cuk converter. Moreover, this converter expands the continuous conduction mode (CCM) operational region. In the suggested topology, the gate of the switch is referenced to ground, so this converter does not need a floating gate drive. Simulation results of the suggested converter are presented in different operational conditions. To verify the operation of the proposed converter, experimental results are provided using a hardware prototype that operates in both CCM and discontinuous conduction mode.

Performance Comparison of Windowing Techniques for ECG Signal Enhancement

Electrocardiogram (ECG) signal is generally corrupted by various artifacts like baseline wander, power line interference (50/60 Hz) and electromyography noise and these must be removed before diagnosis. The task propounded in this article is removal of low frequency interference i.e. baseline wandering and high frequency noise i.e. electromyography in ECG signal and digital filters are implemented to delete it. The digital filters accomplished are FIR with various windowing methods as of Rectangular, Hann, Blackman, Hamming, and Kaiser. The results received are at order of 300, 450, 600. The signal taken of the MIT-BIH database which contains the normal and abnormal waveforms. The work has been in MATLAB where filters are implemented in FDA Tool. The result received for entire FIR filters with various windows are evaluated the waveforms, power spectrums density, signal to noise ratio (SNR) and means square error (MSE) of the noisy and filtered ECG signals. The filter which shows the excellent outcomes is the Kaiser Window.

Optimal Signal Amplitude of Orthogonal Frequency-Division Multiplexing Systems in Dimmable Visible Light Communications

Visible light communications (VLC) using the intensity modulation of light-emitting diodes (LEDs) provides a new communication medium to overcome the shortage of radio spectrum, and allows reuse of LED lighting infrastructures. Orthogonal frequency-division multiplexing (OFDM) was introduced to VLC for its merits in mitigating the fading effects resulting from delay spread, and in avoiding low-frequency ambient interference. Noise and clipping are two major factors that degrade the performance of OFDM in VLC. A larger signal easily overcomes noise, but experiences impairment by clipping. Therefore, degradation due to clipping has a trade-off relationship with that due to noise, depending on the signal amplitude of OFDM. In this paper, the optimal signal amplitude in the trade-off is obtained by simulation when the dimming and LED intensity are given. The former indicates a user's requirement for lighting, and the latter represents the channel quality. The required LED intensity-to-noise ratio, as the channel quality that guarantees dimming as well as an adequate bit-error rate (BER), is also discussed.

Rayleigh backscattering noise suppression based on real-time heterodyne receiver for loop-back WDM-PON.

In this paper, we propose a Rayleigh backscattering (RB) noise mitigation scheme based on the use of real-time heterodyne receiver for loop-back wavelength division multiplexing passive optical network (WDM-PON). Heterodyne detection has been utilized to increase the upstream receiver sensitivity, while an electro-absorption modulator (EAM) is used to simultaneously turn heterodyning bipolar signal into single polar signal and mitigate accumulated carrier RB noise. With the help of the nonlinear negative-slope transfer function of EAM, low frequency interference noise is suppressed successfully. RB noise mitigation performance is studied over 45-km single mode fiber (SMF) transmission, and the optical-signal-to-Rayleigh-noise-ratio (OSRNR) is reduced to 15.6 dB, when bias voltage of EAM is at -4 V. Through utilizing this real-time heterodyne receiver in single fiber loop-back structure, upstream error free transmission is realized with receiver sensitivity of -25 dBm.

Design considerations for high-Q bandpass microwave oscillator sensors based upon resonant amplification

A series of microwave resonant oscillator sensors were designed and characterized using bandpass planar and volumetric electrical resonators having loaded quality factor (Q) values in the range of 2 to 20. The use of these resonators in positive feedback circuits yielded sensor Q-factors of up to 2 × 107, demonstrating Q-factor amplifications on the order of 106. It is shown that the Q-factor amplification can be increased in a positive feedback system through the selection of feedback loop group delay, allowing use of resonators with lower static, loaded Q-factor values. A low-frequency electromagnetic interference sensing application is demonstrated for two resonant oscillator configurations, showing considerable frequency sensitivity to 45 kHz emitters.

An unusually powerful mode of low-frequency sound interference due to defective hair bundles of the auditory outer hair cells.

A detrimental perceptive consequence of damaged auditory sensory hair cells consists in a pronounced masking effect exerted by low-frequency sounds, thought to occur when auditory threshold elevation substantially exceeds 40 dB. Here, we identified the submembrane scaffold protein Nherf1 as a hair-bundle component of the differentiating outer hair cells (OHCs). Nherf1(-/-) mice displayed OHC hair-bundle shape anomalies in the mid and basal cochlea, normally tuned to mid- and high-frequency tones, and mild (22-35 dB) hearing-threshold elevations restricted to midhigh sound frequencies. This mild decrease in hearing sensitivity was, however, discordant with almost nonresponding OHCs at the cochlear base as assessed by distortion-product otoacoustic emissions and cochlear microphonic potentials. Moreover, unlike wild-type mice, responses of Nherf1(-/-) mice to high-frequency (20-40 kHz) test tones were not masked by tones of neighboring frequencies. Instead, efficient maskers were characterized by their frequencies up to two octaves below the probe-tone frequency, unusually low intensities up to 25 dB below probe-tone level, and growth-of-masker slope (2.2 dB/dB) reflecting their compressive amplification. Together, these properties do not fit the current acknowledged features of a hypersensitivity of the basal cochlea to lower frequencies, but rather suggest a previously unidentified mechanism. Low-frequency maskers, we propose, may interact within the unaffected cochlear apical region with midhigh frequency sounds propagated there via a mode possibly using the persistent contact of misshaped OHC hair bundles with the tectorial membrane. Our findings thus reveal a source of misleading interpretations of hearing thresholds and of hypervulnerability to low-frequency sound interference.

Bioelectric signal detrending using smoothness prior approach

Bioelectric signals such as electromyogram (EMG) and electrocardiogram (ECG) are often affected by various low-frequency trending interferences. It is critical to remove these interferences from the recordings so that the critical features of the bioelectric signals could be clearly observed. In this study, an advanced method based on smoothness prior approach (SPA) was proposed to solve this problem. EMG and ECG signals from both the MIT-BIH database and the experiments were employed to evaluate the detrending performance of the proposed method. For comparison purposes, a conventional high-pass Butterworth filter was also used for the detrending of the EMG and ECG signals. Two numerical measures, the correlation coefficient (CC) and root mean square error (RMSE) between the clean data and the detrended data, were calculated to evaluate the detrending performance. The results showed that the proposed SPA method outperformed the high-pass filtering method in reducing various kinds of trending interferences and preserving the desired frequency contents of the EMG and ECG signals. The study suggested that the SPA method might be a promising approach in detrending bioelectric signals.