Acoustic properties absorption coefficient

Convection of heat via blood depends primarily on the local blood flow in the tissue and the vascular morphology of the tissue. Thermal diffusion is determined by thermal conductivity in the steady state, and thermal diffusivity in the unsteady state. In addition to these transport parameters, we need to know the volumes and geometry of normal tissues and tumor. In general, tumor volume changes as a function of time more rapidly than normal tissue volume. In special applications, such as hyperthermia induced by electromagnetic waves or radiofrequency currents, we need electromagnetic properties of tissues—the electrical conductivity and the relative dielectric constant. In the case of ultrasonic heating, we need to specify the acoustic properties of the tissue—velocity of sound and attenuation (or absorption) coefficient. 

In order to evaluate the acoustic properties of the various formulated composites, the sound absorption coefficients were determined by the impedance tube method according to ASTM E 1050-12. A soxmd absorption coefficients and impedance measurements instruments (Figure 16.3) made by Walen Audio Technologies, Maharashtra, India was adopted. The sample diameter was 100 mm, and each value represented the average of six samples. The soxmd absorption coefficients were measured in six frequencies 100, 200,400, 800,1600 and 3200 Hz. 

For studies of dilute polymer solutions, measurements of high precision are necessary to obtain the small differences between the properties of solutions and solvent. Apparatus for pulse propagation in such solutions at 20 MHz has been described by Miyahara, Wada, and Hassler," and for variable path interferometry by Cerf, and for standing waves by Miyahara. jjj jjjg latter method, the frequency can be varied continuously from 1 to 20 MHz. At lower frequencies (10 to 700 kHz), the free decay of waves in a spherical vessel can be measured. In such measurements, the data are ordinarily left in terms of M (or simply velocity and attenuation, or the acoustic absorption coefficient identified in Chapter 18) with no attempt to convert them to K. ... 

This chapter first provides an introduction to the acoustic properties of textiles, which include propagation, absorption, and scattering of sound. The properties can be characterized by various parameters such as flow resistance, transmission loss, absorption coefficient, and scattering coefficient. Test and evaluation methods for obtaining these parameters are discussed. Based on the acoustic properties of the textiles, acoustics designers can make use of textiles in buildings and office environments to optimize sound quaUty depending on particular requirements. 

Most textiles that are used for acoustic purposes show open porosity due to many interconnected pores or voids inside. The acoustic performance of a porous textile is mainly determined by its (air) flow resistivity, which is an intrinsic property of the textile and is a measure of how easily air can enter and pass through a porous textile material (Cox and D Antonio, 2009). Flow resistivity, also known as static flow resistivity, is related to acoustical properties and plays a critical role in the calculation of many intrinsic acoustic properties of porous textiles, such as the characteristic impedance, the propagation constant, and the sound absorption coefficient. In the S.l. Unit system, flow resistivity is quoted in units of Nsm" and is defined as the unit-thickness specific flow resistance o (Morfey, 2001),... 

The dramatic change in the local movement of polymer chains at Tg leads to large changes in a host of physical properties. These properties include density, specific heat, mechanical modulus, mechanical energy absorption, dielectric coefficients, acoustical properties, viscosity, and the rate of gas or liquid diffusion through the polymer, to name a few. Any of these properties can be used, at least in a crude manner, to determine T ... 

The local variations of mineral content were determined from synchrotron radiation micro-computed tomography (SR-pCT). By means of a monochromatic x-ray beam, SR-pCT directly provides accurate 3-D maps of Ae linear attenuation coefficient within the sample. The absorption depends on the amount of mineral content which can be related to the differences in gray levels in reconstracted images. As acoustic microscopy and SAXS provide information about the surface properties, the corresponding surface is extracted from the 3D reconstraction of the bone mineral density. 

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