Reflection: acoustic

In such a system, the volume velocity at a given point and time can be expressed as  

Equation 11.5 allows us to state an expression for pressure in terms of the forward and backward volume velocities at a point in space and time in a similar way 

Rgure 11.7 A uniform tube with forward travelling wave, m+, and backward travelling wave u.  

---

Doppler Flow Meters. Doppler flow meters sense the shift in apparent frequency of an ultrasonic beam as it is reflected from air bubbles or other acoustically reflective particles that ate moving in a Hquid flow. It is essential for operation that at least some particles ate present, but the concentration can be low and the particles as small as ca 40 p.m. CaUbration tends to be influenced by particle concentration because higher concentrations result in mote reflections taking place neat the wall, in the low velocity portion of the flow profile. One method used to minimize this effect is to have separate transmitting and receiving transducers focused to receive reflections from an intercept zone neat the center of the pipe. 

Acoustic reflectance achieved by the measurement of the intensity of the reflection of a wave emitted at frequencies between 50 and 150MHz. A greater proportion of reflectance indicates widespread heterogeneity, as for example in fill, in coarse soil types, in highly fractured rock, or sometimes in cases of organic liquids present in the pore space. 

Demos, S.M., H. Alkan-Onyuksel, B.J. Kane, K. Ramani, A. Nagaraj, R. Greene, M. Klegerman, and D.D. McPherson, In vivo targeting of acoustically reflective liposomes for intravascular and transvascidar ultrasonic enhancement. J Am Coll Cardiol, 1999. 33(3) 867-75. 

G. Barnard, J. Bardin, J. Whiteley, Acoustic Reflection and Transmission Characteristics for Thin Plates , J. Acoust. Soc. Am.. 1975, 57, 57. 

Figure 4. Acoustic reflection from elastomer-steel plate systems.

In vivo targeting of acoustically reflective liposomes for intravascular and trans-vascular ultrasonic enhancement, J Am Coll Cardiol 33, 867-875. 

Fig. 4 The frequency shift depends on the acoustic reflectivity at the quartz-sample inter-...

The present configuration of the surface of the glacial drift in Long Island Sound is a deep central basin bounded by sills on the east and west. The submergence history of the Sound depends on the elevations of the lowest points on these sills relative to the sea level curve. On the Mattituck sill (to the east) this elevation is now -25 m. Sand is now being transported from east to west across the Mattituck sill and it is possible that the sill is now at a higher elevation than it was immediately after retreat of the ice. (More detailed acoustic reflection profile studies of the internal structure of the sill may answer this question.) The lowest point on the sill to the west (which has not yet been surveyed in as much detail) is higher than -20 m. (The locations of the saddle points on the eastern... 

Fig. 13. Structure of the bottom of Long Island Sound revealed by acoustic reflection profiles made with 7-kHz acoustic pulses. (Upper echo is produced by a 2(X)-kHz echo sounder.) (a) Section of end moraine capped by boulders and almost buried by marine mud. (b) Thick deposit of marine mud in central Long Island Sound on top of outwash sand with reflector above thought to be surface of lacustrine deposits, (c) Sand-to-mud transition zone in central Long Island Sound. In all records each division on the vertical scale is 600 mm.

Acoustic Tomography 5 cm no tracer necessary acoustic reflections on grain surfaces, no possibility for velocity measurements by steady state flow... 

The study done by American Acoustical and Insulation Materials Association (1974) showed that these concrete barriers are of very high acoustic reflectivity (95 % and above) and of low sound absorption. This means that concrete barriers are not effective in controlling and reducing traffic noise (Campbell 2000). 

---