No abstract

Pulsed ultrasound propagating in water was used at megahertz carrier frequencies (nominally 10-50MHz) to reflect and scatter from rough surfaces in the same way as light. We have considered noncontact ultrasonic techniques as complementary to optical techniques in several ways: (a) for specificapplications such as wet surfaces, (b) for rougher surfaces with average roughness, R(a) ≥ 0.1 µm, and (c) for (simultaneous) profilometry by time-of-flight measurements. Stylus and ultrasonic data are compared. An example of application to the manufacturing environment is for on-line, real-time sensor feedback and process control in the cutting or grinding of metals and ceramics.

We have developed a transducer which allows the benefits of Line-Focus Beam (LFB) acoustic minoscopy to be realized over large areas, using a conventional pulserreceiver. Experimental evidence is presented to show that the transducer is correctly modeled in detail by Green's function theory, and that all relevant wave speeds can also be predicted using a much simpler geometrical ray model. Data obtained by simply rotating the transducer a fixed distance above the specimen are presented using grey-scale plots which establish the ease with which anisotropy can be revealed.Finally, a grey scale plot of rotational-scan data recast in terms of velocity is shown to demonstrate the simultaneous detection of both surface and pseudo-surface waves in the same crystallographic orientation of a silicon specimen.

No abstract

Material dynamic elastic moduli can be readily obtained from a knowledge of the material's sound velocity(s) and density. One well-established ultrasonic technique for making the velocity measurements is the pulsed-wave transit-time technique. It is a versatile and potentially very accurate technique that can also assess the material elastic homogeneity and anisotropy. Here the many measurement and material factors affecting the precision of the method are addressed. A specific example of the effect of grain size on measurements in steel is presented in some detail.