Attenuation Measurement Technique Research Articles

Phase analysis of signals using frequency-dependent attenuation for measurements of seismic waves

Attenuation refers to any decrease in the power of a propagated signal through a medium. Attenuation measurement techniques include ultrasonic, resonance bar, and stress-strain methods. The stress-strain method measures elastic and viscoelastic properties in the seismic frequency range. The signals received via attenuation measurement systems using the stress-strain method can be considerably weak. Moreover, the noise in these signals causes errors when estimating the signal phase-angle difference between the sample signal and probe signal, thereby reducing system precision and measurement accuracy. Accurate measurements of such phase differences are essential to the measurement of attenuation. A seismic-wave attenuation with frequency-dependent measurement based on the stress-strain method and digital signal processing techniques has been performed. The system estimates the attenuation of a rock by measuring the phase shift in the stress-strain cycle. As a preprocessing method, the finite impulse response band-pass filters are designed to eliminate the influence of noise and direct current offset while ensuring that the phase difference of the measured signal remains unchanged. Three methods for phase difference estimation, i.e., crosscorrelation, fast Fourier transform (FFT), and Hilbert transform are compared, for different signal-to-noise ratios, sampling frequencies, data sample lengths, and true phase differences. The results find that the phase difference estimation based on FFT is the best among all three methods and can effectively improve the precision of the experimental results. Simulation and measurement results further indicate that the attenuation measurement system achieves stable and reliable attenuation measurements in the range of 3–2000 Hz.

Rain Attenuation Study at Ku-Band over Earth-Space Path in South Korea

Rain attenuation measurement techniques are studied with appropriate prediction of rain attenuation at Ku-band for Koreasat 6. This is accomplished by the establishment of experimental setup in Mokdong at 12.25 GHz link. The databases are analyzed for three years, 2013 till 2015. During observation period, rainfall rate of 50 mm/hr is obtained which is measured by OTT Parsivel showing the signal attenuated by 10.7 dB for 0.01% of the occurrence. Comparison with the measured data demonstrates that the proposed technique provides sufficiently accurate estimation for Ku-band signal attenuation in site specifically whose effectiveness is performed through the statistical analysis against the established rain attenuation models. The proposed technique is judged through the error matrices where relative error margins of 52.82, 4.11, and 23.64% are obtained for 0.1%, 0.01%, and 0.001% of the occurrence.

Structural Health Monitoring Using Textile Reinforcement Structures with Integrated Optical Fiber Sensors.

Optical fiber-based sensors “embedded” in functionalized carbon structures (FCSs) and textile net structures (TNSs) based on alkaline-resistant glass are introduced for the purpose of structural health monitoring (SHM) of concrete-based structures. The design aims to monitor common SHM parameters such as strain and cracks while at the same time acting as a structural strengthening mechanism. The sensor performances of the two systems are characterized in situ using Mach-Zehnder interferometric (MZI) and optical attenuation measurement techniques, respectively. For this purpose, different FCS samples were subjected to varying elongation using a tensile testing machine by carefully incrementing the applied force, and good correlation between the applied force and measured length change was observed. For crack detection, the functionalized TNSs were embedded into a concrete block which was then exposed to varying load using the three-point flexural test until destruction. Promising results were observed, identifying that the location of the crack can be determined using the conventional optical time domain reflectometry (OTDR) technique. The embedded sensors thus evaluated show the value of the dual achievement of the schemes proposed in obtaining strain/crack measurement while being utilized as strengthening agents as well.

Effect of heat treatment on an AISI 304 austenitic stainless steel evaluated by the ultrasonic attenuation coefficient

AbstractThe properties of metals can be substantially changed by various methods, one of them is using heat treatment processes. Moreover, ultrasonic testing is the most preferred and effective, nondestructive testing technique for characterization of mechanical material properties. Austenitic stainless steel AISI 304 serves in many applications due to high strength and corrosion resistance. In certain applications, it is important to evaluate the mechanical properties of AISI 304 stainless steel. In this study, the ultrasonic method (attenuation measurement technique) is used to evaluate the hardness of AISI 304 stainless steel samples which were heat treated at different levels. Due to the heat treatment process, each sample has its specific microstructure and hardness which attenuate ultrasonic waves appropriately. The ultrasonic and hardness test show that it is possible to evaluate the hardness of AISI 304 stainless steel by ultrasonic attenuation coefficient. In addition, the relationship between ultrasonic attenuation coefficients and time of heat treatment is investigated.

Monitoring moisture movements in building materials using X-ray attenuation: Influence of beam-hardening of polychromatic X-ray photon beams

X-ray attenuation measurements are commonly used as a non-destructive method to monitor internal concentration changes of moisture (i.e., moisture content) and other chemical compounds in porous building materials. The technique provides direct measurements of moisture content changes through analysis with a composite model consisting of a dry porous material and a thickness of water equivalent to the moisture content of the material. The current formulation of this composite model relies on certain assumptions, including a monochromatic X-ray photon beam source (i.e., X-ray photons of a single, consistent energy) and that interactions between the X-ray photons and the materials (water and porous material) are independent. However, X-ray sources typically used by researchers in this field of study produce X-ray photon beams over a spectrum of energy levels, or polychromatic X-ray photons. Implications of this inconsistency are introduced and discussed. This paper presents both an overview of fundamental descriptions of the X-ray attenuation measurement technique and results from a parametric experimental study of various porous construction materials, including calcium silicate board, aerated autoclaved concrete, clay brick, cementitious materials, and wood. Results from the parametric investigation indicate the attenuation coefficient of water is dependent on the type and thickness of the porous material.

Wave attenuation measurement technique for nondestructive evaluation of concrete

Nondestructive testing (NDT) that uses ultrasonic waves is a reliable experimental technique for characterisation of materials in existing concrete structures and for safety evaluations of these structures. The wave velocity is related to the stiffness of material and the wave attenuation can be used to evaluate damaged concrete structures. This paper proposes an experimental technique to quantitatively measure the wave attenuation using contact ultrasonic transducer for NDT. The proposed technique is subject to interference as a result of the transducer-coupling condition. Unbiased attenuation can be obtained by self-compensating the signals measured in a lead–zirconate–titanate ceramic material inserted between a conventional transducer and a sample. The reproducibility and relevancy of the proposed technique are demonstrated using examples of the technique applied to cement paste and concrete. Also, the relevancy of the attenuation measurements for damage evaluation of cement-based material is demonstrated based on a theoretical attenuation model.

Attenuation-Measurement Technique With a Small Mismatch Uncertainty Using Phase Characteristics of Multiple Reflected Signals

An accurate radio-frequency and microwave attenuation-measurement technique with a small mismatch uncertainty for continuous-frequency application has been developed by shifting the phase characteristics of the multiple reflected signals. A loss-measurement system in four different phase networks is set for this purpose by introducing two low-reflective lines (airlines) where the phase-shift values are already known. From substitution-loss measurements carried out for variable attenuators as devices under test, the attenuation is simply obtained, which is unrelated to the source and load reflection coefficients of ΓG and ΓL, respectively. Experimental measurements on a 10-dB step attenuator performed with a 40-mm length of airlines at almost continuous frequencies from 12.3 to 14.1 GHz are demonstrated and show a good agreement with measurements where the test ports are impedance-matched.

A theoretical comparison of attenuation measurement techniques from backscattered ultrasound echoes

Accurate characterization of tissue pathologies using ultrasonic attenuation is strongly dependent on the accuracy of the algorithm that is used to obtain the attenuation coefficient estimates. In this paper, computer simulations were used to compare the accuracy and the precision of the three methods that are commonly used to estimate the local ultrasonic attenuation within a region of interest (ROI) in tissue; namely, the spectral log difference method, the spectral difference method, and the hybrid method. The effects of the inhomgeneities within the ROI on the accuracy of the three algorithms were studied, and the optimal ROI size (the number of independent echoes laterally and the number of pulse lengths axially) was quantified for each method. The three algorithms were tested for when the ROI was homogeneous, the ROI had variations in scatterer number density, and the ROI had variations in effective scatterer size. The results showed that when the ROI was homogeneous, the spectral difference method had the highest accuracy and precision followed by the spectral log difference method and the hybrid method, respectively. Also, when the scatterer number density varied, the spectral difference method completely failed, while the log difference method and hybrid method still gave good results. Lastly, when the scatterer size varied, all of the methods failed.

A Simple RF Attenuation Measurement Technique With a Small Mismatch Uncertainty

An accurate radio frequency (RF) and microwave attenuation measurement method is described, where source and load do not have to be matched to the line impedance and where the contribution of a mismatch effect to the uncertainty is reduced to about 0.002 dB. From loss measurements carried out for variable attenuators, as well as for attenuators of fixed attenuation values as devices under test, which are fitted to quarter-wavelength lines in three different configurations, the attenuation is simply obtained and is unrelated to the source and load reflection coefficients of Gamma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> and Gamma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> , respectively. Experimental results on a 10-dB step attenuator measurement at frequencies from 1 to 17 GHz show good agreement with measurements where the source and load are impedance matched. The technique is effective even with Gamma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> and Gamma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> higher than 0.1.

Effectiveness of hearing protector devices in impulse noise verified with transiently evoked and distortion product otoacoustic emissions

This study aimed to evaluate the effect of impulse noise on otoacoustic emissions (OAEs) while a passive non-linear earplug or an active level-dependent earmuff was worn.Since none of the standardized attenuation measurement techniques, REAT (real ear at threshold), ATF (acoustic test fixture), or MIRE (microphone in real ear), is designed to test both types in real-wearing condition, OAEs, suitable for detecting subtle changes in the functional integrity of the cochlear outer hair cells, are used.First, DPOAEs (distortion product) and TEOAEs (transiently evoked) of 24 subjects were compared before, immediately after gunfire practice, and after one hour of non-exposure. Secondly, both types of OAEs were evaluated in 31 subjects before and after exposure during a five-day military practice.Significant differences existed between the ears in most cases; the emissions from the right ear had a tendency to be more robust. There were no significant changes in OAEs either before and after exposure, or in the second experiment over multiple days. These findings suggest that the HPDs are able to prevent cochlear damage.

An attenuation measurement technique for rotating planar detector positron tomographs

This paper presents a new attenuation measurement technique suitable for rotating planar detector positron tomographs. Transmission measurements are made using two unshielded positron-emitting line sources, one attached to the front face of each detector. Many of the scattered and accidental coincidences are rejected by including only those coincidences that form a vector passing within a predetermined distance of either line source. Some scattered and accidental coincidences are still included, which reduces the measured linear attenuation; in principle their contribution can be accurately estimated and subtracted, but in practice, when limited statistics are available (as is the case with the multi-wire Birmingham positron camera), this background subtraction unacceptably increases the noise. Instead an attenuation image having the correct features can be reconstructed from the measured projections. For objects containing only a few discrete linear attenuation coefficients, segmentation of this attenuation image reduces noise and allows the correct linear attenuation coefficients to be restored by renormalization. Reprojection through the segmented image may then provide quantitatively correct attenuation correction factors of sufficient statistical quality to correct for attenuation in PET emission images.

Method comparison study on soot-selective techniques

In a long-term field study at two locations with different air pollution levels several soot-selective measurement techniques were compared with a thermochemical method which measures non-extractable carbon (NEC) detecting the evolved CO2 by means of coulometric titration. The attenuation measurement technique (aethalometer) and the aerosol photoemission method showed good correlations to NEC for concentrations ranging from 1.6μg/m3 to 40.8μg/m3. The specific mass absorption coefficient of black carbon with respect to NEC varied between 8.4m2/g and 13.7m2/g with respect to the measurement sites, but the σ value was found to remain constant at each site independent of seasonal or meteorological variations. The ratio of photoelectric signal to NEC varied between 16 fA·(μg/m3)−1 and 33 fA·(μg/m3)−1 depending on the age of the aerosol. The diurnal variations of that ratio showed strong similarities to the traffic patterns. Additionally a slight temperature dependence of this ratio was found for the aged aerosol with a proportionality factor of − 0.35 fA·(K·μg/m3)−1. With the reflectance measurement technique (smoke shade method) reliable NEC determination was not possible for NEC concentrations ⩽ 5 μg/m3.

Measurement of attenuation using a normalized amplitude spectrum

In conventional material evaluation and attenuation measurement, methods employing multiple ultrasonic echoes in the thickness direction of the samples are often used to calculate the reflection and attenuation coefficients. The successive echoes must be well resolved, and there is consequently a minimum thickness of material which can be tested for a given frequency transducer. For thin specimens, a high frequency probe may be used, but this may be problematic for composite laminates since the reflections from the individual plies can cause interference. In this paper, an alternative method based on the amplitude spectrum of the reflections from the specimen is presented. The technique deduces the attenuation coefficients by using the spectral amplitudes at the anti-resonance (or resonance) frequencies of the normalized amplitude spectrum, and has the advantage that it does not require that the successive echoes be separated in time. Measurements made on glass, epoxy, and composite laminate specimens are used to compare our attenuation measurement technique with the standard method.

Attenuation and ratio—National standards

In national standards laboratories, the popular attenuation measurement techniques are: RF, IF, vector IF, and AF substitution; power ratio, voltage ratio, time-interval ratio, and six-port methods; and a procedure that employs a Josephson junction in a superconducting ring. These nine techniques are briefly described, the dynamic ranges and accuracies achieved with them are reported, and their relative merits are discussed. The later sections are devoted to: attenuation measurement techniques used in industry and elsewhere, voltage doubling circuits, attenuation traveling standards, errors and uncertainties associated with attenuation measurements, and international attenuation comparisons. An analysis of the results obtained in four recent international comparisons is included.

Ultrasonic attenuation tomography of soft tissues

In this paper we show that one can measure integrated attenuation for a soft-tissue structure simply by measuring the center frequencies of the incident and transmitted pulses. Except for a multiplicative constant, the integrated attenuation is equal to the difference of these two frequencies . Also, this method is independent of transmittances at tissue - tissue and tissue - couplant interfaces . Since the attenuation information is derived from frequency shifts rather than the signal amplitudes, this new method is somewhat insensitive to a partial loss of signal caused by beam refraction. This technique is based on the power spectra of transmitted ultrasonic pulses approximating Gaussian functions. The validity of this approach has been checked by computer simulation. Tomographic reconstructions of the experimental data using the various attenuation measurement techniques are presented.

Ultrasonic attenuation tomography of soft tissues.

In this paper we show that one can measure integrated attenuation for a soft-tissue structure simply by measuring the center frequencies of the incident and transmitted pulses. Except for a multiplicative constant, the integrated attenuation is equal to the difference of these two frequencies. Also, this method is independent of transmittances at tissue-tissue and tissue-couplant interfaces. Since the attenuation information is derived from frequency shifts rather than the signal amplitudes, this new method is somewhat insensitive to a partial loss of signal caused by beam refraction. This technique is based on the power spectra of transmitted ultrasonic pulses approximating Gaussian functions. The validity of this approach has been checked by computer simulation. Tomographic reconstructions of the experimental data using the various attenuation measurement techniques are presented.

Underwater Light Attenuation Measurements

Light attenuation measurement techniques will be discussed and typical data presented. Measurements taken near San Clemente island will be presented of the volume attenuation coefficient, diffuse attenuation coefficient, and spectrographic characteristics. Typical volume attenuation measurements taken in the north Pacific at depths to 6000 feet will also be presented.