Acoustic properties measurement techniques

Anyone who has successfully used a microscope to image properties to which it is sensitive will sooner or later find himself wanting to be able to measure those properties with the spatial resolution which that microscope affords. Since an acoustic microscope images the elastic properties of a specimen, it must be possible to use it to measure elastic properties both as a measurement technique in its own right and also in order to interpret quantitatively the contrast in images. It emerged from contrast theory that the form of V(z) could be calculated from the reflectance function of a specimen, and also that the periodicity and decay of oscillations in V(z) can be directly related to the velocity and attenuation of Rayleigh waves. Both of these observations can be inverted in order to deduce elastic properties from measured V(z). 

As the design matures, the direct measurement of the acoustic properties becomes necessary. These properties include the longitudinal wave speed, the coefficient of attenuation and the acoustic impedance, which can be obtained from measurements of the reflection and transmission of sound by the material. Two acoustic techniques are available for these measurements, the impedance tube and the panel test. 

The acoustical properties for all samples were evaluated by using either a Toyo DDV-II Rheovibron viscoelastometer at 110 Hz, or a string apparatus developed at NRL-USRD, (8). In this latter instrument, dynamic Young s moduli and loss tangent were measured in the frequency range of 1-10 kHz, and master curves were obtained by using the time-temperature superposition technique, (9). 

Some, if not all, of the requirements of in-line measurement techniques are satisfied in tomographic techniques that provide spatially and temporally resolved data. The techniques utilize the inherent properties of the food material and include those based on magnetic, acoustic, optical, and electrical signals (Choi et al., 2002). These... 

The paper reports a noninvasive technique to measure the mechanical properties of the bulk soft tissues by a pulsed ultrasonic Doppler system. An ultrasonic transducer was used to measure internal displacement resulting from external acoustical perturbations. Measurements were made at four sites of 8 aboveknee residual limbs. The Young s moduli were found in a range of 53-141 kPa. Superficial tissue had a significantly higher modulus than the tissue beneath. 

The specific heat of both polymers was measured with the heat pulse technique in semiadiabatic fashion. The thermal conductivity was measured with a top loading He refngerator using the standard procedure. The acoustic properties, sound velocity and attenuation, were measured with the vibrating reed technique [16] in the frequency range (0.2 3) kHz. 

The acoustic microscopy s primary application to date has been for failure analysis in the multibillion-dollar microelectronics industry. The technique is especially sensitive to variations in the elastic properties of semiconductor materials, such as air gaps. SAM enables nondestructive internal inspection of plastic integrated-circuit (IC) packages, and, more recently, it has provided a tool for characterizing packaging processes such as die attachment and encapsulation. Even as ICs continue to shrink, their die size becomes larger because of added functionality in fact, devices measuring as much as 1 cm across are now common. And as die sizes increase, cracks and delaminations become more likely at the various interfaces. 

Following the publication of the first edition of Acoustic microscopy, two volumes were published of Advances in acoustic microscopy (Briggs 1995 Briggs and Arnold 1996). In these some of the concepts and applications were further developed, and new topics were introduced. Those two volumes serve as supplements to the second edition the material in them has not been repeated, though in a few places reference has been made to chapters in them. The main addition in this second edition is the chapter on ultrasonic force microscopy and related techniques. We trust that Acoustic microscopy will continue to serve as a helpful resource for further generations of microscopists who wish to image and measure elastic properties at high resolution. 

Heat is the most common product of biological reaction. Heat measurement can avoid the color and turbidity interferences that are the concerns in photometry. Measurements by a calorimeter are cumbersome, but thermistors are simple to use. However, selectivity and drift need to be overcome in biosensor development. Changes in the density and surface properties of the molecules during biological reactions can be detected by the surface acoustic wave propagation or piezoelectric crystal distortion. Both techniques operate over a wide temperature range. Piezoelectric technique provides fast response and stable output. However, mass loading in liquid is a limitation of this method. 

The major limitation of LA-ICP-MS is the need for standards that closely match the properties of the samples. In some cases it is possible to use NIST glass standard reference materials for calibration in the analysis of geological materials [67,68], Internal standardization employing MS signals from elements at known concentrations has been used to improve precision and accuracy. Other techniques, such as acoustic [69] and light scattering [70] measurements, have been used in an attempt to monitor the relative amount of material ablated. These approaches seem to work well for variations in the amount of material sampled for similar sample matrices but not for very different types of solids. Dual-sample introduction systems with either wet [71] or dry [72] aerosol introduction in addition to laser ablation have also been reported. 

Seismic refraction techniques can measure the density, thickness, and depth of geologic layers using sound (acoustic) waves transmitted Into the subsurface. These sound waves travel at different velocities In various soils and rock and are also refracted (or bent) at the Interface between layers, thereby affecting their path of travel. The time required for the wave to complete this path Is measured, permitting determination of the number of layers at the site as well as the sound velocity and depth of each layer. The wave velocity In each layer Is related to layer properties such as density and hardness. 

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