Loss Of Signal Amplitude Research Articles

Acoustic Wave Velocities in Bridge Steels and the Effects on Ultrasonic Testing

Ultrasonic testing is utilized to ensure weld quality during the fabrication of steel bridges by identifying discontinuities that are classified as either acceptable or rejectable. The classification of a discontinuity can be affected by differences in the acoustic properties of the material under test and the reference standard used for calibration. Differences in wave velocity affect the refracted angle and amplitude of refracted shear waves. As a result, indications can be missed or incorrectly classified, or incorrectly located in the material. The objective of this research study was to characterize the acoustic wave velocities in a sample of contemporary steels to better understand the range over which velocities may vary for common steels. To address this objective, a series of velocity measurements have been conducted for shear waves propagating through different directions in steel plates of different strengths and reported manufacturing processes. The study also examines the loss of signal amplitude that results from changes in the refracted angle of shear waves used for the inspection of welds. Beam splitting that may occur in anisotropic materials and the potential impact on signal amplitudes is also presented. It was shown in the research that relatively small differences in velocity between the material under test and the reference standard cause a loss of sensitivity of the test. Data presented in the paper documents wave velocity and anisotropic ratios for a population of contemporary bridge steels used for the fabrication of steel bridges and an assessment of how velocity differences affect the amplitude of reflected shear waves.

Extending MIEZE spectroscopy towards thermal wavelengths.

A modulation of intensity with zero effort (MIEZE) setup is proposed for high-resolution neutron spectroscopy at momentum transfers up to 3 Å-1, energy transfers up to 20 meV and an energy resolution in the microelectronvolt range using both thermal and cold neutrons. MIEZE has two prominent advantages compared with classical neutron spin echo. The first is the possibility to investigate spin-depolarizing samples or samples in strong magnetic fields without loss of signal amplitude and intensity. This allows for the study of spin fluctuations in ferromagnets, and facilitates the study of samples with strong spin-incoherent scattering. The second advantage is that multi-analyzer setups can be implemented with comparatively little effort. The use of thermal neutrons increases the range of validity of the spin-echo approximation towards shorter spin-echo times. In turn, the thermal MIEZE option for greater ranges (TIGER) closes the gap between classical neutron spin-echo spectroscopy and conventional high-resolution neutron spectroscopy techniques such as triple-axis, time-of-flight and back-scattering. To illustrate the feasibility of TIGER, this paper presents the details of its implementation at the RESEDA beamline at FRM II by means of an additional velocity selector, polarizer and analyzer.

Temporal enhanced Ultrasound: A new method for detection of porosity defects in composites

Non-Destructive Evaluation (NDE) methods are commonly employed for identifying porosity, which is one of the most common manufacturing defects observed in composite structures. Among current widely used approaches are conventional ultrasonic methods such as pulse-echo analysis based on loss of signal amplitude. Application of these conventional ultrasonic methods, however, can be challenging in cases where the loss of signal is negligible, such as with porosity. In this paper, we propose Temporal-enhanced Ultrasound (TeUS) as a novel ultrasound-based imaging technique for NDE of composites. TeUS represents the analysis of a sequence of ultrasound images obtained from composites by varying an image acquisition parameter, such as the focal point, over the sequence. We present details on the analytical formulation of TeUS, followed by extensive simulation and experimental results to demonstrate the efficacy of TeUS for porosity detection, compared to a conventional ultrasound-based porosity detection method. The results indicate that TeUS has excellent sensitivity for identifying subtle changes in the level of porosity within composite samples, with the possibility to reduce the need for reference samples.

An analysis of the shadow effect for the short-offset transient electromagnetic method

The electromagnetic methods based on long-wire sources, whether in the time or frequency domain, are mainly detected in the far-source zone. Because the observation array is far away from the transmitting source, the amplitude and bandwidth of the signal have a large loss, which limits the detection depth and accuracy of these methods. In the near-source zone, the loss of signal amplitude and bandwidth is relatively small, conducive to improving the detection performance. However, the complex excitation field in the near-source zone makes the observation seriously affected by the source effect. This paper mainly researched the influence of the shadow effect (one of the source effects) on the observation of the short-offset transient electromagnetic method (SOTEM), which is a near-source time-domain method. The results show that the shadow effect has relatively limited influence only on the specific observation channels of the time series of observation data. Based on this, the research on eliminating shadow effects under single / multi-source, multi location and multi polarization excitation modes is carried out. The results show that using a single excitation source with multiple polarization directions or using excitation sources with different polarization directions can improve the detection accuracy of underground targets. All of these lays a foundation for further development of the SOTEM method.

Comparison of methods of derivation of the yank-time signal from the vertical ground reaction force–time signal for identification of movement-related events

Temporal changes in ground reaction force magnitudes reflect movement strategy, and thus underlying muscle activation patterns, during movement tasks. Speculatively, these changes may be observed more readily when the force–time signal is differentiated, yielding the yank-time signal. However, the differentiation process, including the signal filtering used before or after differentiation, can significantly affect the signal-to-noise ratio (SNR) and likelihood of meaningful inference. The aim of the present study was to compare three methods of deriving the yank-time signal: Method 1 derived the yank-time signal using 2nd-order central differentiation subsequent to application of a 4th-order Butterworth filter; Method 2 included the same process as Method 1 but additionally filtered the yank-time data with a Savitzky-Golay smoothing filter; and Method 3 directly and simultaneously derived and smoothed the yank-time signal using a Savitzky-Golay digital differentiation filter. The current analyses revealed Method 2 had the best SNR, followed by Methods 3 and 1, but caused a small loss of signal amplitude. With regards to timing of inflection points in the yank-time data, no significant difference was observed. Therefore, Method 3 led to the best derivation of the yank-time signal due to its efficiency and preservation of signal characteristics and good SNR. Also, a strong association between the first maximum point of the yank-time signal and the start of the downward movement of the body’s centre of mass during a countermovement jump, as identified by 3-D motion analysis, was observed. Thus, subtle events (e.g. start of downward movement) can be easily observed in the yank-time signal.

Data Correction Method for Improving the Spatial Resolution of a Position-Sensitive 10B Neutron Detector

A technique for correcting experimental data from a position-sensitive neutron detector with an active layer of solid boron-10, where the charge division method is used to determine the coordinate, is proposed. This technique relies on the signal amplitude loss in a distributed resistance circuit. Each resistance is connected to two adjacent wires of the anode (or to two adjacent strips of the cathode) of the detector. This readout method is simple to implement and does not require complex and expensive electronics. However, unlike the distributed delay line method, it requires that the nonlinear dependence of the coordinate both on the ratio of the measured amplitudes and on the sum of these amplitudes be taken into account when the neutron coordinate is calculated. Test measurements with a signal generator were conducted to determine the dependence of coordinates on the ratio of pulse amplitudes from two ends of the distributed resistance. This dependence is approximated by a third-order polynomial. At the same time, the coefficients of this polynomial depend on the sum of amplitudes of pulses at the outputs of two amplifiers connected to the two ends of the distributed resistance. The amplitude dependences of these coefficients are also approximated by third-order polynomials. Thus, the spatial resolution of the detector depends on the signal amplitudes and on the coordinate itself. It is possible to determine the signal amplitudes and neutron coordinates more accurately by correcting the data. The procedure also improves the integral uniformity of the coordinate distribution. Following the application of the proposed correction, the spatial resolution of the neutron detector improved from 2 to 1.5 mm along the x axis.

Experimental Results on the Open-Air Transmission of Macro-Molecular Communication Using Membrane Inlet Mass Spectrometry

Molecular communication (MC) is a method where the transmission of information involves the use of molecules rather than electromagnetic waves. In this letter, an open-air transmission MC experiment is conducted to study the signal behavior and the noise. A mass spectrometer is used as the detector, and an in-house-built odor generator is used as the transmitter. It is shown that the signal amplitude loss of the signal can be modeled by using advection–diffusion with decay equation. In addition, the noise of the system has shown to have similar characteristics to that of additive white Gaussian noise.

Monopolar electromyographic signals recorded by a current amplifier in air and under water without insulation

It was recently proposed that one could use signal current instead of voltage to collect surface electromyography (EMG). With EMG-current, the electrodes remain at the ground potential, thereby eliminating lateral currents. The purpose of this study was to determine whether EMG-currents can be recorded in Tap and Salt water, as well as in air, without electrically shielding the electrodes. It was hypothesized that signals would display consistent information between experimental conditions regarding muscle responses to changes in contraction effort. EMG-currents were recorded from the flexor digitorum muscles as participant’s squeezed a pre-inflated blood pressure cuff bladder in each experimental condition at standardized efforts. EMG-current measurements performed underwater showed no loss of signal amplitude when compared to measurements made in air, although some differences in amplitude and spectral components were observed between conditions. However, signal amplitudes and frequencies displayed consistent behavior across contraction effort levels, irrespective of the experimental condition. This new method demonstrates that information regarding muscle activity is comparable between wet and dry conditions when using EMG-current. Considering the difficulties imposed by the need to waterproof traditional bipolar EMG electrodes when underwater, this new methodology is tremendously promising for assessments of muscular function in aquatic environments.

Source cancellation profiles of electroencephalography and magnetoencephalography.

Recorded electric potentials and magnetic fields due to cortical electrical activity have spatial spread even if their underlying brain sources are focal. Consequently, as a result of source cancellation, loss in signal amplitude and reduction in the effective signal-to-noise ratio can be expected when distributed sources are active simultaneously. Here we investigate the cancellation effects of EEG and MEG through the use of an anatomically correct forward model based on structural MRI acquired from 7 healthy adults. A boundary element model (BEM) with four compartments (brain, cerebrospinal fluid, skull and scalp) and highly accurate cortical meshes (~300,000 vertices) were generated. Distributed source activations were simulated using contiguous patches of active dipoles. To investigate cancellation effects in both EEG and MEG, quantitative indices were defined (source enhancement, cortical orientation disparity) and computed for varying values of the patch radius as well as for automatically parcellated gyri and sulci. Results were calculated for each cortical location, averaged over all subjects using a probabilistic atlas, and quantitatively compared between MEG and EEG. As expected, MEG sensors were found to be maximally sensitive to signals due to sources tangential to the scalp, and minimally sensitive to radial sources. Compared to EEG, however, MEG was found to be much more sensitive to signals generated antero-medially, notably in the anterior cingulate gyrus. Given that sources of activation cancel each other according to the orientation disparity of the cortex, this study provides useful methods and results for quantifying the effect of source orientation disparity upon source cancellation.

Pulsed-to-Continuous Read Signal Converter for Increasing Read Signal-to-Noise Ratio

The signal-to-noise ratio (SNR) of the read signal from an optical disc was improved by using a new signal conversion technology. Using this technology, a pulsed read signal was converted into a continuous signal without signal amplitude loss, which was unavoidable using conventional method. The technology was tested on a spin-stand, and it was demonstrated that the SNR can be improved by decreasing the incident laser pulse duty and the feasibility of improving the bit error rate over two magnitudes.

Neuronal field potential in acute hippocampus slice recorded with transistor and micropipette electrode

Arrays of planar electrodes are often applied to record spatial patterns of neuronal field potentials in acute brain slices. The approach is hampered by layers of inactive tissue caused by the cutting process and also by a film of bath electrolyte that may exist between the slice and the substrate. To address this issue, we used a micropipette electrode to measure the vertical profile of evoked field potentials across acute slices from mouse hippocampus. In this way, we found that the signal due to an excitatory postsynaptic potential (EPSP) at the bottom of the slice was about 40% of the maximum at its centre. The vertical profile was matched by a volume-conductor model with proper boundary conditions. Simultaneously, voltage transients caused by EPSPs were measured with a field-effect transistor in the substrate. The transistor signals were in agreement with the evoked field potentials at the bottom of the slice. The study demonstrates: (i) that the loss of signal amplitude from the centre of a slice to the bottom is modest, despite an inactive tissue layer; and (ii) that in principle, planar sensors are able to record the field potential at the bottom of a slice. The results raise questions about the small voltages that are often observed with planar metal electrodes and about the reconstruction of the neuronal activity from field potentials at the bottom of acute slices using current-source density analysis.

Modelling the effects of different fracture geometries and healing stages on ultrasound signal loss across a long bone fracture

The effect on the signal amplitude of ultrasonic waves propagating along cortical bone plates was modelled using a 2D Finite Difference code. Different healing stages, represented by modified fracture geometries were introduced to the plate model. A simple transverse and oblique fracture filled with water was introduced to simulate the inflammatory stage. Subsequently, a symmetric external callus surrounding a transverse fracture was modelled to represent an advanced stage of healing. In comparison to the baseline (intact plate) data, a large net loss in signal amplitude was produced for the simple transverse and oblique cases. Changing the geometry to an external callus with different mechanical properties caused the net loss in signal amplitude to reduce significantly. This relative change in signal amplitude as the geometry and mechanical properties of the fracture site change could potentially be used to monitor the healing process.

Resolution-Dependent Estimates of Multiple Sclerosis Lesion Loads

Changes in brain lesion loads assessed with magnetic resonance imaging obtained at 1.5 Telsa (T) are used as a measure of disease evolution in natural history studies and treatment trials of multiple sclerosis. A comparison was made between the total lesion volume and individual lesions observed on 1.5 T images and on high-resolution 4 T images. Lesions were quantified using a computer-assisted segmentation tool. There was a 46% increase in the total number of lesions detected with 4 T versus 1.5 T imaging (p < 0.005). The 4 T also showed a 60% increase in total lesion volume when compared with the 1.5 T (p < 0.005). In several instances, the 1.5 T scans showed individual lesions that coalesced into larger areas of abnormality in the 4 T scans. The relationship between individual lesion volumes was linear (slope 1.231) showing that the lesion volume observed at 4 T increased with the size of the lesion detected at 1.5 T. The 4 T voxels were less than one quarter the size of those used at 1.5 T and there were no consistent differences between their signal-to-noise ratios. The increase in signal strength that accompanied the increase in field strength compensated for the loss in signal amplitude produced by the use of smaller voxels. This enabled the acquisition of images with improved resolution, resulting in increased lesion detection at 4 T and larger lesion volumes.

Optical Clocks Based on Ultranarrow Three-Photon Resonances in Alkaline Earth Atoms

A sharp resonance line that appears in three-photon transitions between the 1S0 and 3P0 states of alkaline earth and Yb atoms is proposed as an optical frequency standard. This proposal permits the use of the even isotopes, in which the clock transition is narrower than in proposed clocks using the odd isotopes and the energy interval is not affected by external magnetic fields or the polarization of trapping light. With this method, the width and the rate of the clock transition can, in principle, be continuously adjusted from the MHz level to sub-mHz without loss of signal amplitude by varying the intensities of the three optical beams. Doppler and recoil effects can be eliminated by proper alignment of the three optical beams or by point confinement in a lattice trap. Light-shift effects on the clock accuracy can be limited to below a part in 10(18).

Time domain reflectrometry measurements of water content in coarse waste rock

Methods are presented to calibrate and implement a time domain reflectrometry (TDR) system to estimate the water content of coarse mine waste rock containing high solute concentrations in the pore water. High electrical conductivity of the pore water reduces the quality of TDR waveforms through the loss of signal amplitude. Zegelin-type probes with a resistive coating on the center conductor were used to obtain higher signal-to-noise waveforms. These probes must be calibrated prior to use. The TDR pulse travel-time measured in soils containing pore water with high solute concentrations increases systematically with solute concentration. Empirical calibrations are derived for waste rock with low and high electrical conductivity pore water. An ambient temperature correction is derived from observed diurnal fluctuations in the measured travel time to determine whether or not a detailed laboratory calibration for temperature effects is required. The variation of apparent dielectric permittivity with temperature is positively correlated with temperature at low water content and negatively correlated at high water content. This trend indicates the influence of water bound to mineral surfaces on the variation of apparent dielectric permittivity with temperature. Examination of our field data indicates that the effect of dissolved ions on the TDR calibration was great enough to justify a calibration that accounts for pore-water composition. The effect of ambient temperature was found to be small enough that an intensive laboratory calibration was not required.Key words: time domain reflectrometry, water content, mining.

Evaluation of Uncoated and Coated Time Domain Reflectometry Probes for High Electrical Conductivity Systems

High sample electrical conductivity reduces the quality of a time domain reflectrometry (TDR) waveform by the loss of signal amplitude. Two strategies are examined to obtain higher signal/noise waveforms: (i) waveform differencing by remote diode shorting and (ii) covering probe conductors with resistive coatings. Experiments using electrically conductive water solutions (0–5 dS m−1) and three‐rod Zegelin type probes show conventional dual‐tangent waveform analysis and waveform differencing using manual short circuits can accurately determine travel time but the remote diode shorting method can be systematically biased by the electrical properties of the diodes used. Three‐rod Zegelin‐type probes with a high resistance coating on the central rod permit collection of analyzable waveforms for solutions with electrical conductivities at least as high as 70 dS m−1 Dual‐tangent analysis of the raw waveform is found to be more accurate than the remote diode shorting method within water solutions and within silica sand saturated with an electrically conductive water solution. The probe coating creates a nonlinear relationship between the apparent dielectric permittivity estimated using a coated probe and the actual sample apparent dielectric permittivity. Experimental measurements of this relationship can be fitted using an equation of the form for a coaxial cell. A three‐rod coated probe with a single diode at the probe head is a practical means to collect interpretable waveforms in media with high electrical conductivity. However, measurements of travel time alone may not be sufficient to determine water content in soils with high concentrations of dissolved ions in the soil water solution.

A scintillating fibre hodoscope for high rate applications

A scintillating fibre hodoscope was developed for application in a high rate environment such as the central region of external beam experiments. It accommodates rates of several 10 6 s −1 per fibre channel while maintaining a time resolution of about 400 ps . Its central elements are highly efficient radiation-hard scintillating fibres and a photomultiplier tube capable of operating at such rates without appreciable loss of signal amplitude.

Effect of pH and surface functionalities on the cyclic voltammetric responses of carbon-fiber microelectrodes.

Carbon electrodes are useful for the detection of oxidizable species with cyclic voltammetry. In particular, carbon-fiber microelectrodes have been employed for the measurement of several neurotransmitters in brain tissue. However, during cyclic voltammetry with carbon-fiber electrodes the current varies with changes in concentration of some inorganic cations as a result of their interaction with surface functional groups. The electrode's response to the hydronium ion is a particular concern because its voltammetric response occurs over a broad range of potentials that overlap those of neurotransmitters of interest such as dopamine. This is especially a problem in vivo because simultaneous changes of dopamine and pH frequently occur in brain tissue. In this work, voltammetric current changes are shown to arise from pH dependent shifts in the peak potentials of background voltammetric waves that arise from species confined to the carbon-fiber electrode surface. Polishing the electrode with alumina suspended in cyclohexane in an environment containing lowered oxygen, a method previously demonstrated to remove oxides from the carbon surface, leads to a substantial reduction in the sensitivity to pH changes. However, this is accompanied by a loss in signal amplitude for dopamine. The dopamine response can be restored using the cation exchanger Nafion without significantly increasing the pH response. To investigate which oxide functional groups play a direct role in the electrode's current responses to changes in pH, surface-confined carbonyl and alcohol functionalities were chemically modified. In both cases, the modification did not affect the carbon-fiber electrode's responsiveness to changes in pH. Nonetheless, the polishing technique proved to be effective in reducing pH interferences in in vivo applications.

Development of highly reactive hardening agents for MP tapes

The reactivity of isocyanate groups was examined using molecular orbital calculations and magnetochemical measurements. We found a linear relationship between the logarithm of kinetic constants for the addition reaction of the phenylisocyanates with 2-ethylhexanol and the atomic charges of the carbon atoms in the isocyanate group. A linear relationship was also found between the kinetic constants and the 13 C chemical shifts of the same carbon. On the basis of these relationships, a new hardening agent consisting of Cl-substituted phenyldiisocyanates (CPDI) was synthesized. The degree of cross-linking of the binder film was improved by using the new highly reactive hardening agent. Furthermore, the loss of signal amplitude of MP tape using the new agent was less than that using the conventional agent in pause mode test.

Removal of brown stain on magnetic head by a chelating agent on magnetic tapes

We found that a chelating agent on magnetic tape can drastically suppress the loss of signal amplitude caused by brown stains. After a streaming-mode test using MP tape on which a chelating agent was coated, we found no brown stain on the magnetic head. A chelating agent on magnetic tape is able to prevent from formation of brown stains. In addition, we found that a chelating agent on magnetic tapes can remove brown stain, already on the magnetic head. It is suggested that a chelating agent reacts with the iron oxide of brown stains to make metal complexes, and that the complexes can be removed easily by chemical lapping.