Frequency, sound waves

Ultrasonic movement detectors utilize the principle of the Doppler effect on high-frequency sound waves. Ultrasonic movement detectors do not penetrate solid objects, but have smaller volume of coverage than microwave movement detectors. These units may also be affected by moving hot or cold air pockets in a room. 

Ultrasonics Use of ultrasonics involves the transmission of very high frequency sound waves through the metal whose thickness needs to be knownAn advantage of this technique is that access is only required to one side of the vessel or pipe wall (Fig. 19.58). A short burst of energy is transmitted via a transducer probe into the metal using the pulse-... 

William RT, Alfred LL (1927) The chemical effects of high frequency sound waves 1. A Preliminary Survey. J Am Chem Soc 49 3086-3100... 

The pioneering work on the chemical applications of ultrasound was conducted in the 1920 s by Richards and Loomis in their classic survey of the effects of high frequency sound waves on a variety of solutions, solids and pure liquidsQ). Ultrasonic waves are usually defined as those sound waves with a frequency of 20 kHz or higher. The human ear is most sensitive to frequencies in the 1-5 kHz range with upper and lower limits of 0.3 and 20 kHz, respectively. A brief but useful general treatment of the theory and applications of ultrasound has been given by Cracknel 1(2). 

In ultrasonic atomization, a liquid droplet is produced when powerful high frequency sound waves are focused onto the liquid. A liquid may be present in large volume and contained in a reser-... 

Ultrasonic detectors Emit high-frequency sound waves, and sense movement in a protected area by sensing changes in these waves. The sensor emits sound waves that stabilize and set a baseline condition in the area to be protected. Any subsequent movement within the protected area by a would-be intruder will cause a change in these waves, thus creating an alarm condition. 

The potential of sonochemistry was identified over sixty years ago in a wide ranging paper entitled The Physical and Biological Effects of High Frequency Sound-Waves of Great Intensity [13]. Over the few years which followed this paper a great deal of pioneering work in sonochemistry was carried out and, as a result of this, two reviews on the applications of ultrasound in polymer and chemical processes were published... 

Ultrasound is used to obtain information about the properties of a material by measuring the interaction between a high frequency sound wave and the material through which it propagates. This interaction depends on the frequency and nature of the ultrasonic wave, as well as the composition and microstructure of the material. The parameters most commonly measured in an ultrasonic experiment are the velocity at which the wave travels and the extent by which it is attenuated. To understand how these parameters are related to the properties of foods it is useful to consider the propagation of ultrasonic waves in materials in general. 

These nebulizers rely on a transducer made from a piezo-electric crystal which produces high frequency sound waves in the liquid in the nebulizing unit. The waves give rise to vertical capillaries of liquid ( fountains ) which, when the amplitude of the energy applied is sufficient, break up to provide an aerosol. 

This method consists of high-frequency sound waves (0.1-25 MHz) incident upon the test sample and measuring the energy of the reflected beam. Because of the flaws in the sample there will be loss in energy of the beam, known as attenuation. Cracks, laminations, shrinkage cavities, bursts, flakes, disbonds and other discontinuities can be detected by this method. 

Infrasound stations use very sensitive microbarometers to detect low frequency sound waves from atmospheric explosions. These stations are arrays and are able to determine accurately the location and size of an atmospheric explosion. Altogether there are 60 stations in the network as shown in Table 13.8. 

Because of the very small effects expected and, consequently, the immense experimental difficulties involved in measuring them, techniques are not yet well developed which make use of these properties. The bulk of the work has made use of the disturbing influence of high-frequency sound-waves on reacting solutions, and the remainder of this section will discuss briefly the application of acoustical methods to the study of chemical relaxation. 

An ultrasound device emits high-frequency sound waves that can pass through a material, he absorbed, or reflect off the surface of a material. Waves are reflected at the border between tissues with different densities, such as an organ and a tumor. The larger the difference in density, the greater the reflection. 

Wood, R.W. Loomis, A.L. The physical and biological effects of high frequency sound waves of great intensity. Philos. Mag. Ser. 7, 1927, 4 (22), 417-436. 

Ultrasound imaging is a non-invasive, portable and relatively inexpensive imaging modality, which is used extensively in the clinic. An ultrasound transducer (also called scanhead) sends short pulses of a high-frequency sound wave (1-10 MHz) into the body. At interfaces between two types of tissue, the wave will be refracted and part of the sound wave is reflected back due to Snells law. How much is reflected depends on the densities of the respective tissues, and thus the speed of the sound wave within the different tissues. In addition, parts of the sound wave are also backscattered from small structures at tissue boundaries or within the tissue. High-frequency sound waves propagate weU through soft tissue and fluids, but they are more or less stopped by air or bone. In clinical practice, this limitation is referred to as an acoustic window . The transducer not only sends the wave into the body but also receives part of the reflected and/or backscattered wave, also named echo . In clinical practice, ultrasound is used in a... 

In the case of a very high frequency sound wave, no diffraction occurs for light perpendicular to the direction of propagation of the sound wave. 

Ultrasonication A method for isolating solvent-extractable components of organic matter from samples of sediment or biota that uses high-frequency sound waves to agitate the sample in an organic solvent. 

In an acoustic atomizer, high-frequency sound waves are used to create capillary ripples that ultimately break up into droplets. Ultrasonic atomization can produce a fairly narrow droplet size distribution. 

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