Interference Waveform Research Articles

Reflection of underwater sound from surface waves

A tank experiment has been conducted to measure reflection of underwater sound from surface waves. Reflection from a wave crest leads to focusing and caustics and results in rapid variation in the received waveform as the surface wave moves. Theoretical results from wavefront modeling show that interference of three surface reflected eigenrays for each wave crest produces complicated interference waveforms. There is good agreement between theory and experiment even on the shadow side of caustics where there are two surface reflected arrivals but only one eigenray.

Modeling the IEC 61000-4-4 EFT Injection Clamp

The paper analyzes the test setup required by the International Electrotechnical Commission (IEC) 61000-4-4 to evaluate the immunity of electronic equipment to electrical fast transients (EFTs), and proposes an electrical model of the capacitive coupling clamp, which is employed to add disturbances to nominal signals. The study points out limits on accuracy of this model, and shows how it can be fruitfully employed to predict the interference waveform affecting nominal system signals through computer simulations.

Cancelling ECG Artifacts in EEG Using a Modified Independent Component Analysis Approach

We introduce a new automatic method to eliminate electrocardiogram (ECG) noise in an electroencephalogram (EEG) or electrooculogram (EOG). It is based on a modification of the independent component analysis (ICA) algorithm which gives promising results while using only a single-channel electroencephalogram (or electrooculogram) and the ECG. To check the effectiveness of our approach, we compared it with other methods, that is, ensemble average subtraction (EAS) and adaptive filtering (AF). Tests were carried out on simulated data obtained by addition of a filtered ECG on a visually clean original EEG and on real data made up of 10 excerpts of polysomnographic (PSG) sleep recordings containing ECG artifacts and other typical artifacts (e.g., movement, sweat, respiration, etc.). We found that our modified ICA algorithm had the most promising performance on simulated data since it presented the minimal root mean-squared error. Furthermore, using real data, we noted that this algorithm was the most robust to various waveforms of cardiac interference and to the presence of other artifacts, with a correction rate of 91.0%, against 83.5% for EAS and 83.1% for AF.

Digital lock-in techniques for adaptive power-line interference extraction

This paper presents a simple digital approach for adaptive power-line (PL) or other periodic interference extraction. By means of two digital square (or sine) wave mixers, the real and imaginary parts of the interference are found, and the interference waveform is synthesized and finally subtracted. The described technique can be implemented in an open-loop architecture where the interference is synthesized as a complex sinusoid or in a closed-loop architecture for automatic phase and gain control. The same approach can be used for removal of the fundamental frequency of the PL interference as well as its higher harmonics. It is suitable for real-time operation with popular low-cost microcontrollers.

The Research on Method for Reduction of the Neutral Conductor Current in the Three-Phase Four-Wire Low-Voltage Distribution Line

In low-voltage distribution line of the three-phase four-wire system, the neutral conductor current increases by the current mainly on third harmonic wave which does not have the phase rotation under the condition in which a balance of the load was removed, when the harmonic generation equipment is contained for the load. The increase of such neutral conductor current is made to increase the waveform distortion of receiving end voltage, and various waveform interferences are arising. In order to reduce the neutral conductor current, the method for inserting the active filter for third harmonic wave near the load is proposed, and the protective effect of waveform interference is also reported.In this paper, the method for drastically reducing the neutral conductor current by the method using resonance phenomena of the LC which is simpler than active filter is proposed.

The impact of optical comb stability on waveforms generated via spectral line-by-line pulse shaping

Optical arbitrary waveform generation using the line-by-line pulse shaping technique has been shown to be sensitive to variations in the offset frequency of the input frequency comb due to time-domain waveform interference. Here we present a frequency-domain model that is able to predict waveform changes arising from offset frequency variations. In experiments we controllably shift the frequency of a comb derived from a phase-modulated CW laser, which allows us to quantitatively investigate waveforms generated by pulse shaping as a function of offset frequency. Experimental data are in excellent agreement with the predictions of our frequency-domain model. In addition, we propose and analyze new waveforms designed for monitoring of offset frequency variations by pulse shaping.

Evaluation of the shape and size of 3D cracks using microwaves

A method to evaluate the shape and size of a small 3D crack by microwaves was demonstrated. By considering the interference phenomenon occurring in the case of 3D cracks, a parameter reflecting microwave interference effect, which is a function of the position of the sensor in the direction of the crack length, was introduced into the usual dual frequency evaluation-equation. From the modified dual frequency equation, a new component named interference waveform, which is based on the amplitude of the reflection coefficient measured at two different frequencies, was obtained. On the other hand, based on the interference model, a corresponding interference waveform, which can be calculated from the assumed shape and size of a 3D crack, was also introduced. By comparing these two interference waveforms, the evaluation of the shape and size of the 3D crack were carried out. Four 3D fatigue cracks having different shape and size were treated. The shape and size of all the cracks were estimated well by using the proposed method.

Thermoelastic generation of cylindrical Rayleigh waves and whispering gallery modes by pulsed-laser excitation

An analytical model of cylindrical surface waves excited thermoelastically by a pulsed-laser line source is presented. The laser-generated transient response of the cylindrical Rayleigh wave and the first three whispering gallery (WG) modes of an aluminum cylinder are calculated from the model using residue theory and the fast Fourier transform technique. The superposed wave form of the four transient modes is in excellent agreement with the wave form obtained from experiment and reveals that the peaks observed in experimental data are the result of wave-form interference from the superposition of all WG modes.

Seismic Detection and Characterization of the Altiplano-Puna Magma Body, Central Andes

— The Altiplano-Puna Volcanic Complex (APVC) in the central Andes is the product of an ignimbrite “flare-up” of world class proportions (de Silva, 1989). The region has been the site of large-scale silicic magmatism since 10 Ma, producing 10 major eruptive calderas and edifices, some of which are multiple-eruption resurgent complexes as large as the Yellowstone or Long Valley caldera. Seven PASSCAL broadband seismic stations were operated in the Bolivian portion of the APVC from October 1996 to September 1997 and recorded teleseismic earthquakes and local intermediate-depth events in the subducting Nazca plate. Both teleseismic and local receiver functions were used to delineate the lateral extent of a regionally pervasive ∼20-km-deep, very low-velocity layer (VLVL) associated with the APVC. Data from several stations that sample different parts of the northern APVC show large amplitude Ps phases from a low-velocity layer with Vs ≤ 1.0 km/s and a thickness of ∼1 km. We believe the crustal VLVL is a regional sill-like magma body, named the Altiplano–Puna magma body (APMB), and is associated with the source region of the Altiplano–Puna Volcanic Complex ignimbrites (Chmielowski et al., 1999).¶Large-amplitude P–SH conversions in both the teleseismic and local data appear to originate from the top of the APMB. Using the programs of Levin and Park (1998), we computed synthetic receiver functions for several models of simple layered anisotropic media. Upper-crustal, tilted-axis anisotropy involving both Vp and Vs can generate a “split Ps” phase that, in addition to the Ps phase from the bottom of a thin isotropic VLVL, produces an interference waveform that varies with backazimuth. We have forward modeled such an interference pattern at one station with an anisotropy of 15%–20% that dips 45° within a 20-km-thick upper crust. We develop a hypothesis that the crust above the “magma body” is characterized by a strong, tilted-axis, hexagonally symmetric anisotropy. We speculate that the anisotropy is due to aligned, fluid-filled cracks induced by a “normal-faulting” extensional strain field associated with the high elevations of the Andean Puna.

Horizontal transition from fast to slow structures at the core–mantle boundary; South Atlantic

Recent tomographic studies of the deep mantle have revealed large-scale low-velocity zones beneath Africa and relatively fast velocity zones beneath South America. Here we conduct a concentrated core–mantle boundary (CMB) study across this transition zone from fast to slow beneath the South Atlantic. Deep South American earthquakes recorded in Africa provide S and ScS waveform data at core-grazing distances of 85–105°. The waveform interference pattern produced at these ranges provides an excellent sample of the CMB structure in the vicinity of the ScS bounce point which can be used to map out regions of low-velocity zones (<5% reductions) and the more extreme ultra-low-velocity zones (>10% reductions). The strongest anomalies occur at the western edge roughly beneath the Tristat Plateau with weaker structures to the east beneath the so-called ‘Great Africa Plume’. These results agree with dynamic models where strong local upwellings develop at the edges of D″ (fast) structures.

Waveform detection with RBF network – Application to automated EEG analysis

Automated detection of different waveforms in physiological signals has been one of the most intensively studied applications of signal processing in the clinical medicine. During recent years an increasing amount of neural network based methods have been proposed. In this paper we present a radial basis function (RBF) network based method for automated detection of different interference waveforms in epileptic EEG. This kind of artefact detector is especially useful as a preprocessing system in combination with different kinds of automated EEG analyzers to improve their general applicability. The results show that our neural network based classifier successfully detects artefacts at the rate of over 75% while the correct classification rate for normal segments is as high as about 95%.

Effect of electronic-ballast fluorescent lighting on wireless infrared links

Fluorescent lamps driven by electronic ballasts emit an infrared (IR) signal that is periodically modulated at rates of tens of kilohertz, and which can severely impair the performance of IR wireless links. The impact of fluorescent interference can potentially be reduced by highpass electrical filtering, but such filtering induces intersymbol interference (ISI). The authors present expressions for the bit error rate (BER) of systems using on-off keying (OOK) and pulse-position modulation (PPM) in the presence of both a deterministic interfering signal and ISI. They have measured the interference waveforms from lamps driven by 22 and 45 kHz ballasts, and have used the measured waveforms to evaluate the performance of IR links using OOK and 2, 4, 8 and 16 PPM at bit rates of 1, 10, and 100 Mbit/s. When the fluorescent interference is normalised to the signal power required in the absence of this interference, the penalties incurred by OOK are found to be essentially independent of bit rate. At 1 Mbit/s, PPM suffers approximately the same penalties as OOK, but as the bit rate is increased, the degradation of PPM becomes progressively much smaller. In the absence of measures to prevent ISI, first-order highpass filtering is not effective in improving the performance of OOK, but can substantially improve PPM link performance at bit rates of 10 and 100 Mbit/s.

Characteristics of orthogonal slow frequency hopping/16‐quadrature amplitude modulation system with an interference immunity decoding method for digital land mobile communications

AbstractThis characteristics of a slow frequency‐hopping system using 16‐ary quadrature amplitude modulation (SFH/16‐QAM) to provide superior spectral efficiency and high‐quality transmissions in digital land mobile communications is investigated. In this method, highly efficient transmissions are realized with 16‐QAM through fading distortion compensation based on the injection of pilot symbols; but, since 16‐QAM alone provides insufficient immunity to interference, several strategies are required for applications to cellular systems. Here, a new interference immune decoding method is proposed that is based on an improvement in error‐correction methods. In the orthogonal SFH, since mutually different hopping patterns are used for each cell, the interference waveforms from other cells are randomized with respect to the desired waveform. By using this property, the level of the interference superimposed on the desired waveform is detected and estimated from the gaps of inserted periodic slots, and the interference immunity of 16‐QAM with minimum weighted Euclidean distance decoding is improved. Computer simulations of frequency selective fading shows that the proposed method has strengths relative to the near‐far problem and is especially effective for utilization in the cellular system uplink. The introduction of voice activated control is shown to be effective in the downlink. Also, as a result of the frequency diversity realized through SFH, performance degradations due to slow fading are slight.

Constructions of particular random processes

This paper reviews how to construct sets of random numbers with particular amplitude distributions and correlations among values. These constructions support both high-fidelity Monte Carlo simulation and analytic design studies. A variety of constructions is presented to free engineering models from "white or normal" limitations embodied in many current simulations. The methods support constructions of conventional stationary and normally distributed processes, nonstationary, nonnormal signal and interference waveforms, nonhomogeneous random scenes, nonhomogeneous volumetric clutter realizations, and snapshots of randomly evolving, nonhomogeneous scenes. Each case will have specified amplitude statistics, e.g., normal, log-normal, uniform, Weibull, or discrete amplitude statistics; and selected correlation, e.g., white, pink, or patchy statistics, clouds. or speckles. Sets of random numbers with correlation, nonstationarities, various tails for the amplitude distributions, and multimodal distributions can be constructed. The paper emphasizes aspects of probability theory necessary to engineering modeling.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive detection using low rank approximation to a data matrix

Using an accurate formula for the error in approximating a low rank component, we calculate the performance of adaptive detection based on reduced-rank nulling. In this principal component inverse (PCI) method, one temporarily regards the interference as a strong signal to be enhanced. The resulting estimate of the interference waveform is subtracted from the observed data, and matched filtering is used to detect signal components in the residual waveform. We also present a generalized likelihood-ratio test (GLRT) for adaptively detecting a low rank signal in the presence of low rank interference. This approach leads to a test which is closely related to the PCI method and extends the PCI method to the case where strong signal components are present in the data. A major accomplishment of the work is our calculation of the statistics of the output of the matched filter for the case in which interference cancellation and signal detection are carried out on the same observed data matrix. That is, no separate data is used for adaptation. Examples are presented using both simulated data and real, active-sonar reverberation data from the ARSRP, the Acoustic Reverberation Special Research Program of the Office of Naval Research.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A moving-mirror Michelson interferometer for probing transient plasma plumes

A modified Michelson interferometer was used to probe the electron density in plasma plumes produced by pulsed XeCl laser ablation of Al2O3. With one of the mirrors of the interferometer translating steadily, the phase angle of the sinusoidal interference signal was tracked and the XeCl laser was fired whenever the detected phase angle matched a predefined value. The transient interference waveform produced by the plasma plume was then synchronously captured. This moving-mirror interferometer features minimal vibration isolation, fast response time (∼10 ns), powerful noise rejection, and a detection limit of a thousandth of a fringe shift, or ∼1015 electrons per cm3 for mm size plumes.

Lateral Resolution In Seismic Reflection-A Physical Model Study

SUMMARY Physical seismic model experiments have been undertaken to study the detectability and lateral resolution of buried linear reflecting targets (slits in an aluminium plate) which might simulate a range of interesting geological structures, e.g. fracture zones, fault blocks, reefs, facies changes, cavities. The reflector length was varied from one-thirtieth to over 20 wavelengths. The depth of burial was 17 wavelengths. Even the smallest target yielded discernible diffractions on receivers located in the shadow zone of the reflector. The lateral extent of the reflector can be accurately determined in the subwavelength range by utilizing together the amplitude, frequency, moveout and polarity information contained in the composite diffractionlreflection signals. As the reflector length increases, the amplitude and travel time increase, but the predominant frequency decreases. The dominant polarity of the interference waveform changes as the reflector length exceeds one wavelength. For targets extended horizontally more than one wavelength, the time difference between the two edge-diffracted waves is a good measure of reflector extent. In the case of an inclined reflector, the moveout pattern of the two diffractions was asymmetrical, forming a convergence zone (and higher amplitude) on the downdip side of the shotpoint. The offset at which the diffraction wavelets merge serves to define the reflector dip. The reflector length can be estimated from the time separation between the two weaker diffractions observed on receivers located updip of the shot, after appropriate correction for target inclination.

Locally optimum detection in moving average non-Gaussian noise

Detection algorithms that are locally optimum Bayes, and also asymptotically optimum, are developed for both coherent and incoherent signaling for arbitrary interference and signal waveforms when the dependence in the noise samples is represented by a moving-average model. This leads to receiver structures, which are prewhitened versions of the locally optimum detectors in the independent case. A probability-of-error expression (in the ideal-observer symmetric case), the processing gain, and the minimum-detectable signal are derived in both cases. These demonstrate, by means of an expression comparing performance between this and the independent case, that for the same large sample size (n>>1), an improvement in performance is always achieved when the noise samples are dependent, without any additional complexity in receiver structure. >

Scalp topography of human somatosensory evoked potentials: The effect of interfering tactile stimulation applied to the hand

A detailed topographical analysis of human SEPs in response to median nerve stimulation was performed, with and without concurrent tactile stimulation of the hand. Twenty-eight recording sites on the scalp and neck were referred to earlobe and non-cephalic reference electrodes. The following components were identified in the control wave form: N10, N11, N13, P14, N19, P20, P22, N22, N29, P30 and P44. The interference wave form showed significant attenuation of P14, N19, P20, P22 and N29, while P30 was abolished. N10, N11, N13 and N22 remained unchanged and P44 was enhanced. In the interference wave form there also appeared an N33 component, supplanting P30 over the posterior contralateral quadrant, and a P36 frontally. The pattern of changes was best demonstrated by subtracting the interference from the control response to derive a ‘difference’ wave form. This consisted of ‘P’14, ‘N’19, ‘P’21, ‘P’32 and ‘N’36 components. The last 2 were of large amplitude over the posterior contralateral quadrant and frontal cortex, respectively, and overlapped for at least 10 msec of their duration. The results indicate that the interfering effect occurred at the level of the brain-stem or above. The topography of the difference wave form suggests that the ‘P’32 and ‘N’36 components may be attributable to a generator situated in the posterior bank of the central sulcus (Brodmann's area 3b), concerned with the processing of input from cutaneous mechanoreceptors. It is proposed that the P22 and N22 components of the control and interference wave forms may be due to a generator located at the bottom and in the anterior bank of the central sulcus (area 3a).

A wave shaping method for NRZ pulses

A now method of generating intersymbol interference (ISI) and jitter-free signalling waveforms is presented. The method is based on a feedback ramp generator followed by a triangular-to-sine converter. Because the system operates on the transitions of the data stream, there is no problem of phase slipping with respect to the data clock at the regenerators.