Ultrasound reflection

Hiller, D., and Ermert, H., System Analysis of Ultrasound Reflection Mode Computerized Tomography, IEEE Trans. Sonic Ultrasonic SU-31, pp 240-250, (1984). 

Schlaberg, H.I., Yang, M., and Hoyle, B.S. (1997) Ultrasound reflection tomography for industrial processes. 17th Ultrasonics International Conference (U1 97), 1997, Delft. 

The greater the difference in acoustic impedance between the two materials the greater the fraction of ultrasound reflected. This has important consequences for the design and interpretation of ultrasonic experiments. For example, to optimize the transmission of ultrasound from one material to another it is necessary to chose two materials with similar acoustic impedance. To optimize the reflection coefficient materials with very different acoustic impedance should be used. The acoustic impedance of a material is often determined by measuring the fraction of ultrasound reflected from its surface. 

Ultrasound reflective spectroscopy application in the analysis of bubbly liquids has been known for many years. This technique is based on the transmission of ultrasound waves through a dispersion, and measuring the velocity and attenuation spectra. 

Part II of the book deals with lesser known aspects of US for the analytical chemists such as its use as an energy source for detection purposes. Thus, ultrasound-based detection techniques viz. US spectrometry in its various modes including ultrasound attenuation, ultrasonic velocity, resonant ultrasound, laser-generated, ultrasound reflection and acoustic wave impedance spectroscopies) are dealt with in Chapter 9. Finally, Chapter 10 is devoted to seleoted applioations of US spectrometry — mostly non-analytical applications from whioh, however, analytical chemists can derive new, interesting analytical uses for ultrasound-based deteotion techniques. 

Ultrasound is reflected at the boundary of two media possessing different acoustic impedances. 99.99% of ultrasound is reflected at the air-water boundary when an ultrasound beam is incident upon it from either side. Hence occurrence of air bubbles should be minimized in the coupling medium in order to avoid ultrasound reflection. The reflection coefficient for various interfaces may be estimated from the acoustic impedances of two media forming the interface using equations described in Refs. f... 

The ultrasound reflectivity of entrapped gas in echogenic liposomes allows real time image-guided drug and gene delivery. 

Buchanan KD, Huang S, Kim H, Macdonald RC, McPherson DD (2008) Echogenic liposome compositions for increased retention of ultrasound reflectivity at physiologic temperature. J Pharm Sci 97 2242-2249... 

By combining this technique with capacitive coupling or ultrasound reflection, wafer thickness and wafer flatness information is also obtained. A further step is to wafer-map the data. Using optical scanning, surface defect maps are generated (2.) and insulator thickness variations are measured ellipsometrically and displayed. As discussed further on, recombination lifetime maps can also be generated by non-contacting methods. 

Ultrasound reflects from a layer of oil between two bearing surfaces. The response of the oil film can be modelled using a quasi-static spring model. The proportion of the wave reflected depends on the stiffness of the oil film and its acoustic properties. Experiments have shown this spring model approach to be valid for the thickness of oil films typically encountered in the operation of hydrodynamic bearings. 

Resolution Study of Ultrasound Reflections in Bovine Vertebral Bones In-Vitro... 

This type of sensor typically includes infrared (IR) and ultrasound sensors. TRs detect the heat released from humans, and ultrasound sensors detect the movcnicnt of the human occupant (i.c., the device compares the reflection in different instants if they are different, something is moving in the sensor distance range). 

In a bath-type sonochemical reactor, a damped standing wave is formed as shown in Fig. 1.13 [1]. Without absorption of ultrasound, a pure standing wave is formed because the intensity of the reflected wave from the liquid surface is equivalent to that of the incident wave at any distance from the transducer. Thus the minimum acoustic-pressure amplitude is completely zero at each pressure node where the incident and reflected waves are exactly cancelled each other. In actual experiments, however, there is absorption of ultrasound especially due to cavitation bubbles. As a result, there appears a traveling wave component because the intensity of the incident wave is higher than that of the reflected wave. Thus, the local minimum value of acoustic pressure amplitude is non-zero as seen in Fig. 1.13. It should be noted that the acoustic-pressure amplitude at the liquid surface (gas-liquid interface) is always zero. In Fig. 1.13, there is the liquid surface... 

Essentially all imaging from medical ultrasound to non-destructive testing relies upon the same pulse-echo type of approach but with considerably refined electronic hardware. The refinements enable the equipment not only to detect reflections of the sound wave from the hard, metallic surface of a submarine in water but also much more subtle changes in the media through which sound passes (e. g. those between different tissue structures in the body). It is high frequency ultrasound (in the range 2 to 10 MHz) which is used primarily in this type of application because by using these... 

Ultrasound and X-ray imaging are routine in the clinic and examine endogenous molecules based on signal reflection and/or absorption. These are starting to find application in small animal research [53]. Currently, they provide primarily anatomical information, although addition of contrast agents promises new applications [54]. 

Fig. 11. Fundamental and harmonic imaging In the fundamental imaging mode (a), a narrow-band pulse of ultrasound (US) centered at a given frequency (e.g., 2.5 MHz) is emitted the sound reflected by the organs is used to create the image, (b) Microbubbles, because they are extremely compressible in comparison to organ tissue, not only reflect sound more efficiently than tissues but also emit harmonics. In the harmonic mode, the signal from the tissues is filtered out, leaving only the harmonics, resulting in specific imaging of the bubbles [37].

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