Papers by Keyword: Acoustic Impedance

Abstract: The work is focused on an attempt to develop a route for the fabrication of piezoceamic-polymer composites having (1-3) type connectivity. The process included the extrusion of rods of diameter approximately 200 mm. A commercial piezoelectric, PC-5 was modified by addition of a lithium/bismuth based glass former together with excess PbO to lower the sintering temperature to about 1000 °C. The fast firing sintering was employed. The rods were assembled and impregnated with an epoxy resin to form 1-3 composites containing approximately 50 and 20 vol% piezoceramic. The measurement values showed that, the piezoelectric constant, d₃₃ = 232 pCN^-1 and 215 pCN^-1, thickness electromechanical coupling coefficient, k_t = 0.51 and 0.5 and the mechanical quality factor, Q_m = 14 and 5 for the composites containg PZT rods at 50 vol% and 20 vol% respectively. Their acoustic impedances were 5.1 and 3.6 for the 50 vol% and 20 vol% of PZT rods respectively. The results show that with lower volume% of PZT could result in lower acoustic impedance which can be further improved for biomedical imaging and hydrophone applications.

Abstract: Ultrasonic parameters of CuO: Diethylamine-Isopropaonol binary nanofluids at six different concentrations have been reported at three different temperatures like 298K, 308K and 318K. The acoustical parameters such as Ultrasonic sound velocity (v), Compressibility (β), Inter molecular free length (Lf), Acoustic impedance (Z) are calculated from experimental data. The variation of these parameters with composition of the mixture helps us in understanding the nature and extent of interaction between particles and the binary liquid mixtures. Keywords Ultrasonic velocity, Compressibility, Acoustic impedance, Inter molecular free length, Nanofluids

Abstract: The present experimental investigation was carried out in order to explore the possible molecular interactions of D(+) mannose with mixed solvent of aqueous NaCl, KCl , MgCl₂ and CaCl₂at 303 K. Experimental values of densities and ultrasonic velocities were carried out of the ternary mixture solution D(+) mannose with aqueous NaCl ,KCl, MgCl₂ and CaCl₂. Aqueous alkali metal halides (NaCl ,KCl , MgCl₂ and CaCl₂ ) were added under different molalities with D(+) mannose. The related and relevant parameters correlated to the present study such as adiabatic compressibility K_s, acoustic impedance Z, apparent molal volume ф_v, apparent molal adiabatic compressibility, ф_Ks, and partial molal volume ф⁰_v and partial molal adiabatic compressibility, ф^o_Ks at infinite dilution. The present investigation has exploited the possible molecular associations such as ion-ion, ion-solvent, solute-solute and solute-solvent interactions in these systems. It has been observed that there exist strong solute-solvent interaction and complex formation between in these ternary systems.

Abstract: This article presents a comprehensive investigation in the acoustic characteristics of flame-retardant PET mesh composite fabric and PU foam with the various bulk density of foam and weight ratio of vermiculite. By using impedance tube, absorption coefficients and acoustic impedance of composite material which play an important roles in the estimation of the wave propagation passing through the specific material will be obtained. Results showed that foam with higher bulk density not only increased the material characteristics in the absorption but more importantly, cause the wider band for absorption. With the inclusion of vermiculites, the level of absorption of composite material will obviously increase, especially for the higher frequencies. Instead of 20wt% for vermiculites, the highest absorption coefficient can be found under the 15wt%. On the other hand, acoustic impedance of composite material presented in this article will slowly decrease with frequencies, and the influences of these two parameters are focused on the lower frequency range.

Abstract: With the development of techniques, the acoustic performance of 3C electroacoustic products, such as earphone, headphone, microspeaker and etc., will be paid much attention. Ventilation material which is often used in the front and rear side of the product is also an important component to affect the acoustic performance. Depending on the diverse manufacture processes and materials, there are many kinds of ventilation materials, including paper, mesh, poron, nonwoven and etc.. This study aims to investigate acoustic characteristics of these ventilation materials, including air permeability, reflection coefficient, and acoustic impedance. The result indicates that mesh with different code number shows similar air permeability. Meanwhile, the reflection coefficients of each mesh material have no significant variation with the frequency. For the lower frequencies, the level of acoustic impedance is much related to the structure or material used. With the increment of frequency, the acoustic impedance of all the materials will converge to a certain value even for the higher density material.

Abstract: This work presents an experimental characterization of three types of ground commonly found in urban centers regarding their absorption properties with respect to sound propagation: asphalt, grassland and soil. A brief theoretical background is presented, and the experimental procedure is discussed in detail. With basis on experimental results, it is concluded that grassland ground is mostly absorbent for all tested frequencies, whereas asphalt and soil are reflexive for low frequencies and absorbent for high ones.

Abstract: The propagation of the stress wave in axial direction during the impact between the front-end-coated projectile and the substrate coated by ceramic films is described by the stress wave theorem. The impact process is numerically simulated by ANSYS/LS-DYNA, where the shell unit is used for precision. The effects of thickness of the front-end coating on the interfacial stress are discussed in detail. Dependence of different ceramic films are also considered. Simulation results show that interfacial normal stress is much greater than tangential stress. The interfacial normal stress is greatest when the thickness of the projectile coating is 0.2 mm. The interfacial tangential stress increases slightly as the thickness of coating increases. Similar stress history in the interface occurs when the acoustic impedance of the films are close. Greater acoustic impedance results in smaller stress.

Abstract: Microhardness and sound velocity were measured in case of differently prepared solder samples. The used Pb-10Sn solder samples were melted then cooled down applying different cooling rates. These procedures caused variant microstructure thus different microhardness and sound velocity values. The sound velocity was measured by means of scanning acoustic microscopy. Characterization of solder materials by acoustic microscopy gives the possibility to non-destructively estimate mechanical and reliability parameters of the given material.

Abstract: A non-contact ultrasonic system to monitor the yogurt fermentation process through a stainless steel reactor wall is described. During the process, the acoustic impedance was determined by using multiple reflections of ultrasound within the stainless steel wall. Thus, the wall was part of the measurement system. By basing on measurement multiple reflections, the instrument sensitivity is increased by the power of the reflection coefficient. Experimental results show that the acoustic impedance changes continuously while pH declines. It is very useful, especially on production scale for yogurt that the acoustic impedance measurement does not demand a liquid transparent to ultrasound. Also, this noncontact sensing method can reduce the risk of food contamination from measuring instrument, and contribute to hygienization for food manufacture industries.

Abstract: A piezoelectric ceramic(lead niobium lithium zirconate titanate, P(LN)ZT), sulphoaluminate cement and polymer were used to fabricate polymer modified cement based piezoelectric composites by cut-filling technique. The influence of P(LN)ZT volume fraction on the electromechanical properties and acoustic impedance of composite was investigated. Comparing with P(LN)ZT Piezoelectric ceramic, the vibration at thickness mode of 1-3 type piezoelectric composite is strengthened, and the electromechanical quality factor is reduced. When P(LN)ZT volume fraction is 30.86%, the acoustic impedance value is 8.24 M rayl, which is close to that of the concrete (9.0 M rayl), and this is suitable for the non destructive inspection.