Papers by Keyword: Attenuation

Abstract: Polyvinylidene Fluoride (PVDF) and Lead Zirconate Titanate (PZT) thin-film sensors can be used to detect acoustic emissions, and their low thickness (28µm PVDF sensors available) allow them to be embedded (positioned within a laminate). However, the characteristics and sensitivity of these sensors within composite structures require further study. The attenuation curves of PZT, silver ink metallised PVDF and gold metallised PVDF sensors, when mounted using a variety of couplants such as ultrasonic gel, resin, silicone adhesive and thin double-sided adhesive tape, have been generated. Investigations also include positioning the sensor within the laminate, as opposed to on the surface, and monitoring the performance changes with respect to the through-thickness position. The sensors coupled using resin have shown to generally have the highest amplitude, with the highest being the PZT yielding 88 dB at 5cm. Initial comparisons of signal detection by the sensors with respect to fibre orientation have shown that signal travelling along the fibres generally has higher amplitude when compared to at 45^o. This research is the first step toward identifying the preferred sensor type and position within the structure for damage detection.

Abstract: The Simulation of Crowd Sensing in Closed Space with the Attenuation Measurement of the Wi-Fi Signal is Proposed here. A Train Car is Used as the Test Environment of Interest. Experimental Validation is Performed for a Certain Range of Input Parameters which Include Permittivity of Human Body, Structure Materials and Sensor Placements. the Simulation Results Show that for all Cases, the Signal Strengths Associated with Masses of Human Body Reduce with Number of Passengers. the Number of Passengers can Be Estimated with Good Accuracy Using Linear Function with the R-Square Value over 0.97 and RMSE Value below 2. the Simulation Results Suggest that the Estimation Accuracy of Number of Passengers will Improve with Higher Number of Passengers and Multiple Transmitters in Neighbor Nodes can Affect the Overall Precision. the Experimental Validation Exhibits the same Trend as that of the Simulation. the Additional Experiment Indicates that the Passenger Body Movement Also has a Considerable Impact on the Estimation Accuracy.

Abstract: Silver nanoparticles (Ag NPs) are embedded in Er³⁺/Nd³⁺ co-doped lithium niobate tellurite glasses of the form (68-x)TeO₂-15Li₂CO₃-15Nb₂O₅-1Er₂O₃-1Nd₂O₃-(x)AgCl with x = 1,2 and 3 mol% via conventional melt-quenching technique. The ultrasonic attenuation shows the rate of sound energy reduction when an ultrasonic wave is propagating in a medium which is the lithium niobate tellurite glasses. The glass attenuation depends on the grain size, viscous friction, crystal structure, porosity and hardness. The existence of Ag NPs with an average size of 3.7 nm is confirmed using TEM analysis.

Abstract: It is shown that one of the express-methods for studying the internal structure and phase composition of geomaterial samples is broadband acoustic spectroscopy with laser sources of ultrasound. Theoretical assessment of time profiles and spectrums of opto-acoustic signals are presented. Numerical modelling of the spectrums and time profiles of ultrasound signals generated in opto-acoustic generators made of a different material is performed. The influence of diffraction and damping in rocks on the above characteristics is studied. The amplitude spectrum and time profiles of ultrasonic pulses transmitted through samples of marble of various thicknesses in which the most part of the characteristic grain sizes lies in the range of 500 μm - 1 mm are constructed. It has been established that, according to the amplitude spectrum of the original signal and the transmitted through the sample signal, it is possible to restore the characteristic dimensions of the grains.

Abstract: In this work, thermoplastic natural rubber (TPNR) composites were produced through melt blending method. Boron carbide (B₄C) as filler was added into the polymer blend (TPNR) with different weight percent from 0% to 30% and the effect of different B₄C contents on mechanical and thermal neutron attenuation properties of TPNR composites has been studied. The phase formation in composites was analyzed using XRD technique. From the results, it showed that the incorporation of B₄C fillers into TPNR matrix has enhanced the macroscopic cross section of the composites, however it lessens the tensile strength. Macroscopic cross section of the composites were increased from 3.34 cm^-1 to 14.8 cm^-1, while the tensile strength of the composites decreased from 3.79 MPa to 1.06 MPa with increasing B₄C from 0 wt% to 30 wt%. B₄C diffraction peaks were also increased in intensity with increasing B₄C content.

Abstract: The gamma ray and X-ray shielding properties of PVA containing different proportions of BaSO₄ as an aggregate have been investigated. The photon linear attenuation coefficients were measured by using ²⁴¹Am radioactive source (59.54 keV). Gamma rays were counted by a NaI(Tl) detector. It was found that the shielding efficiency increased when increasing the amount of BaSO₄ and specimen thickness. The linear attenuation coefficients were 0.085, 0.125, 0.179, and 0.189 for 0.2, 0.4, 0.6, and 0.8%w/v of BaSO₄. The X-ray attenuation test was performed using the diagnostic X-ray machine for energy of 45 kVp. The optical density of X-ray films was investigated. The results showed that the optical density of X-ray film decreased when increasing the amounts of BaSO₄.

Abstract: The propagation loss of water is important in sediment acoustics and underwater acoustics. The propagation loss in water is analyzed theoretically and an in-situ acoustic instrument of Attenuation Array is used to measure attenuation of water. Based on the first arrival cycle (FAC) judgment method, point judgment based data analysis method (PJDAM) and cross correlation based data analysis method (CCDAM) have the similar results of attenuation as 20.89±4.67 dB/m and 22.43±7.37 dB/m respectively in a wide range of measurement frequency changing from 100 to 300 kHz, which is close to the theoretical calculation of 22.64 dB/m in water using the Attenuation Array. The analysis method will be useful in in-situ acoustic measurement of seafloor surficial sediment.

Abstract: The communication signal attenuation compensation method for long distance communication is studied in this paper in order to improve the accuracy of the signal transmission. In long-distance communication, due to the shock pulse signal attenuation, the accuracy of signal is reduced. The use of auto-regressive integrated moving control method of error compensation can solve this problem. In the process of communication, the cumulative attenuation rate of communications network is used to establish auto-regressive integrated moving control model to achieve cumulative error compensation. The experiment results show that compensating the total amount of cumulative attenuation of signal in long-distance communication can reduce the attenuating property of communication network and achieve the requirements of communication.

Abstract: Attenuation coefficient is frequently-used for ultrasonic creep inspection in metals. However, in practical inspecting, e.g. thick wall weldment in high temperature pipings, it is usually difficult to measure the accurate propagating distance of ultrasound, which results in an inaccuracy of attenuation coefficient calculation. Therefore, a modified method for attenuation coefficient calculating was proposed here, in which the flight-time of ultrasound was substituted for propagating distance. The new calculated attenuation coefficient was named as flight-time-attenuation parameter, and had a unit as dB/us. A uniaxial tension creep experiment with pure lead was conducted to verify the detecting ability of this new parameter. Two piezoelectric wafers were pasted on the pure lead specimen, and ultrasonic testing was carried out simultaneously without interrupting the tension procedure. Attenuation coefficient and flight-time-attenuation parameter were calculated with inspecting signal acquired from creep specimen, and compared with each other. The results showed that two ultrasonic parameters had the same variation tendency along with creep procedure, and flight-time-attenuation parameter had a better sensitivity. Accordingly, the flight-time-attenuation parameter could be used for ultrasonic creep inspection in metals, and worked as a replacement of attenuation coefficient calculated with propagating distance. Another creep inspecting experiment with P91 steel weldments was conducted to verify the practicability of the new parameter, in which the new flight-time-attenuation parameter showed a good distinguishing ability for different creep status.

Abstract: The effect of stone powder content on the chloride diffusion coefficient and diffusion attenuation coefficient of chloride ion of mechanical sand (MS) concrete was studied. The results showed that the resistance to chloride ion permeability of MS concrete firstly increased and then decreased with the increase of the content of stone powder. The anti-permeability of the concrete which had moderate amount of stone powder was better than that of the natural river sand (NS) concrete. The diffusion attenuation coefficient of MS concrete was greater than that of the NS concrete, which was good for long-term durability of concrete structure.