Ultrasonic field analysis

FIGURE 14. Axial resolution improvement, (a) Low frequency poorly damped (b) high frequency poorly damped (c) high frequency highly damped. 

FIGURE 15. Lateral resolution improvement, (a) Poor lateral reso-lution potential (b) good lateral resolution potential. 

FIGURE 16. Composite material thickness measurement and defect location (A mode display), (a) Typical A mode display for a homogeneous material (b) typical A mode display for an inhomogeneous material. 

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Possible nondestructive testing techniques for adhesively bonded structures and composite materials will be introduced along with a literature survey of successes and applications to date. Emphasis on ultrasonic inspection will also be highlighted, including such topics as ultrasonic wave generation, wave velocity, dispersion, reflection factor, wave refraction, attenuation, ultrasonic field analysis, resolution, thickness and defect location measurement, and C-scan testing. 

The scheme of dispersion effects displayed in engineering materials of different structures was considered and an analysis of the causes of their occurrence was performed in our work. The spectrum of structural noise is considered as an element of unified spectral characteristics, reflected interaction of the ultrasonic field with given parameters and heterogeneous medium... 

An analysis of available literature data indicates the following possible mechanisms of heat and mass transfer alteration in an ultrasonic field ... 

A wealth of other data can be obtained from the use of US as an analytical method. Sonoelectrochemical analysis of trace metals [220] and organic compounds [221] has been reported. Ultrasonic atomisation [222] is used in many fields where a dispersion of liquid particles is required. Ultrasonic nebulisation (USN) is used for analysis of organic solutions in conjunction with ICP-AES/MS [223,224] and MIP-AES [225],... 

Peskin and Raco (P3) have given a theoretical analysis of both ultrasonic and electrostatic atomization from the point of view of liquid instability. They conclude that atomization with low frequency ac will require about twice the field strength as dc but that, by going to high frequency, lower fields are possible with conducting liquids. The value for the critical field for atomization given by these authors for a dc field is, however, smaller than that which would be calculated from Eq. (39) by a factor of (1/32)1/2. This presumably reflects the simplified one-dimensional model used in their derivation. 

As with any analytical technique, it is important for US spectrometry users to have a thorough understanding of its underlying physical principles and of potential sources of errors adversely affecting measurements. The basis of ultrasonic analyses in a number of fields (particularly in food analysis) is the relationship between the measurable ultrasonic properties (velocity, attenuation and impedance, mainly) and the physicochemical properties of the sample (e.g. composition, structure, physical state). Such a relationship can be established empirically from a calibration curve that relates the property of interest to the measured ultrasonic property, or theoretically from equations describing the propagation of ultrasound through materials. 

The potential of ultrasonic extraction for field-based extractions has been put into use in the industrial hygiene and environmental single-element analysis of, for example, lead from glass fibre filter ambient air samples [13,14] or from lead-based paint, urban dust and river sediment [15] hexavalent chromium from coal fly ash and paint chips [16] and strontium from river sediment [17]. Ultrasonic extraction has also proved effective as a prior step in multi-element determinations of heavy metals. 

Transmission electron microscopy was performed with a Philips EM420 and a Philips CM200 equipped with a field-emission gun and an EDAX detector for elemental analysis. Ground and ultrasonically dispersed (in dry -hexane) samples were brought on copper grids covered by a thin polymer film on which carbon was deposited. 

Because electrophoresis uses optical detection, this technique is limited to the analysis of dilute systems however, the recent development of electroacoustic methods has extended analysis to concentrated slurries containing up to 50% vol/vol solids [73], The electroacoustic effect is the response of charged particles to an applied alternating electrical or acoustical field [74], in contrast to the static field employed in electrophoresis. The acoustical response results from relative vibratory motion between particle and medium if the two phases differ in density. If an alternating electrical field is applied, charged particles vibrate in a back-and-forth motion in phase with the applied field, producing a sound wave whose pressure amplitude is proportional to the particle mobility and This technique is termed electrokinetic sonic amplitude (ESA). Alternatively, if an ultrasonic wave is applied, the particles vibrate at the sound... 

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