Ultrasound transmission time

Research at the IKV in Aachen, Germany, has shown that the measurement of ultrasound transmission time (UTT) yields a useful quantity to characterize the thermodynamic condition of the polymer melt [68]. Advantages of the UTT measurement are  

Commercial applications of UTT measurement started in 1976 however, the method has not found widespread use. An important application in extrusion is the noncontacting temperature measurement of heat-sensitive materials. Protruding temperature sensors can easily cause degradation with such materials. The UTT measurement, pressure compensated, can be used for stock temperature control in a similar fashion as with the conventional melt temperature sensor (see Section 4.6). 

The UTT measurement can be used in total extrusion line control. The use of UTT measurement reportedly has resulted in considerable technical improvements in product performance in several extrusion operations [68]. It should be noted, however, that the pressure compensation is rather involved and that the accuracy of the resulting temperature is only as good as the pressure measurement. In this respect, the melt temperature measurement by IR radiation is less complicated (see Section 4.3.1). 

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With ultrasound velocity tomography the local speed of ultrasound in a cross section of the subject under study is computed from a large set of ultrasound transmission times. These calculations (reconstructions) are based upon a model that describes the propagation of ultrasound in a medium. In its simplest form the ultrasonic pulses are supposed to travel along straight pathways from transmitter to receiver. The measured transmission times depends on the velocity distribution v(jc, y) in the plane of reconstruction ... 

In this paper a method is described to measure accurately the three-dimensional geometry of the isolated, working canine heart during the cardiac cycle. Times of flight of ultrasonic pulses are measured with high accuracy for many directions through the object under study. These transmissions times are then used to reconstruct the ultrasound velocity distribution in the plane of measurement. 

In an early study, Greenleaf et al. [4] reported reconstructions of ultrasonic velocity from time-of-flight profiles. Since then there has been periodic activity in using ultrasound to determine the transmission properties attenuation or refractive index. 

Ultrasounds can be applied to chemical systems by using ultrasonic baths or probes. Although baths are more widely used, probes are more efficient as a result of (a) the lack of uniformity in the transmission of ultrasounds (in baths, only a small fraction of the total liquid volume in the immediate vicinity of the ultrasound source experiences the effects of cavitation) and (b) the decline in power with time, which leads to exhaustion of the energy applied to baths. Both phenomena result in substantially decreased experimental repeatability and reproducibility. For this reason, the use of baths should be restricted to cleaning operations and removal of dissolved gases, their intended applications. A wide variety of commercially available ultrasonic baths exists ranging from laboratory to industrial-scale models. 

Later the magnetic stirrer is operated in a defined manner and dispersion begins. The graph plotting transmission versus time provides a measure for dispersion velocity. When the transmission curve reaches a plateau the best possible (stationary) dispersion obtainable with this device has been reached. By applying ultrasound to the liquid the degree of dispersion can be further increased in most cases. The test results may be used to define several characteristic dispersion conditions of the material e.g. the ratio of transmission at a given time to transmission at stationary dispersion or final dispersion due to ultrasound. 

In principle, the ultrasonic techniques described for solid-liquid flow measurement can be applied to measure air flow rate and particle velocity. Direct measurement of air flow rate by measuring upstream and downstream transit times has been demonstrated. But, the Doppler and cross-correlation techniques have never been applied to solid/gas flow because the attenuation of ultrasound in the air is high. Recent developments have shown that high-frequency (0.5-MHz) air-coupled transducers can be built and 0.5-MI Iz ultrasound can be transmitted through air for a distance of at least 1 in. Thus, the cross-correlation technique should be applicable to monitoring of solid/gas flow. Here, we present a new cross-correlation technique that does not require transmission of ultrasonic waves through the solid/gas flow. The new technique detects chiefly the noise that interacts with the acoustic field established within the pipe wall. Because noise may be related to particle concentration, as we discussed earlier, the noise-modulated sound field in the pipe wall may contain flow information that is related to the variation in particle concentration. Therefore, crosscorrelation of the noise modulation may yield a velocity-dependent correlation function. 

Acoustic sensors have been less frequently used on robots. They are generally based on the use of a pulsating ultrasound source (ca. 40 kHz) and the accurate measurement of the time interval between transmission and reception of the pulse. 

In 1841, Swiss physicistJean-Daniel Golladon conducted experiments regarding sound transmission in Lake Geneva he determined that sound traveled more than four times faster in water than in air. In 1881, French physicist Pierre Gurie, who is well known for his work regarding ionizing radiation, discovered the piezoelectric effect, which later made the development of the ultrasound transducer possible. 

Thermal scanning microscopy Temperature-time profile Time/temperature resolved pyrolysis mass spectrometry Thermal ultraviolet Thermal volatilisation analysis Thermal wave infrared imaging Transmission X-ray microscopy Total-reflection X-ray fluorescence (c/r. TRXRF) Ultrasonic force microscopy Ultraviolet photoelectron spectroscopy Ultrasound... 

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. 

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