Acoustic reflectometry

A number of methods are available for the characterization and examination of SAMs as well as for the observation of the reactions with the immobilized biomolecules. Only some of these methods are mentioned briefly here. These include surface plasmon resonance (SPR) [46], quartz crystal microbalance (QCM) [47,48], ellipsometry [12,49], contact angle measurement [50], infrared spectroscopy (FT-IR) [51,52], Raman spectroscopy [53], scanning tunneling microscopy (STM) [54], atomic force microscopy (AFM) [55,56], sum frequency spectroscopy. X-ray photoelectron spectroscopy (XPS) [57, 58], surface acoustic wave and acoustic plate mode devices, confocal imaging and optical microscopy, low-angle X-ray reflectometry, electrochemical methods [59] and Raster electron microscopy [60]. 

Acoustic time domain reflectometry operates on the principle that the velocity of sound and ultrasound increases in gases and decreases in liq-... 

Af/f is small whenever rq,2 is close to one. Conversely, since the QCM only works well when the normalized frequency shift Af/ff is small, it makes sense to assume 1. Equation 39 shows that quartz crystals are acoustic re-flectometers. The results of QCM measurements can therefore be easily compared to data obtained with other forms of ultrasonic reflectometry [57,58]. It is well known from optical techniques such as elUpsometry [59] or surface plasmon resonance (SPR) spectroscopy [60] that a film thickness can be inferred from a measurement of the reflectivity. The same applies to acoustics. 

The chapter is organized as follows. Section 8.2 provides a short reminder of what acoustic shear waves can and cannot do. Shear waves have distinct advantages (compared to other surface anal3Ttical techniques like optical reflectometry or atomic force microscopy [AFM]), but there are also some caveats to be kept in mind. Section 8.3 briefly summarizes some predictions from simple planar models of slip. An experimental result, which stands as an example for an experience in the authors laboratory, is presented in section 8.4. Section 8.5 provides the results from FEM calculations. Section 8.6 discusses nonlinear phenomena and acoustic streaming, in particular. 

Acoustic wave transmission and reflection have been used extensively throughout the twentieth century for nondestmctive testing. In the latter part of the twentieth century ultrasound techniques were developed for the noninvasive imaging of fetuses and internal organs in the health-care industry. In 1995 the first application of ultrasonic time-domain reflectometry (UTDR) for characterizing membrane processes was reported (Bond et al., 1995). This chapter will provide an overview on the developments in applying UTDR for membrane and membrane process characterization. 

Evans et al. (2005) recently reported significant improvements in the scanning acoustic microscopy technique as well as in the extension of ultrasonic reflectometry to the... 

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