Ultrasound sound frequency ranges

The easily accessible frequency range of sound and ultrasound waves confines the range of applicability of... 

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... 

Figure 1.1. Frequency ranges of sound and ultrasound. (Reproduced with permission of Wiley-VCH — modified — Ref [8].)...

Sound waves are mechanical vibrations in a solid, liquid or gas. Ultrasound is the same, but at a frequency higher than the range audible to humans (viz. 1 Hz to 16 kHz). The lowest ultrasonic frequency is normally taken to be 20 kHz (i.e. 20 000 cycles per second). The top end of the frequency range is limited only by the ability to generate the signals frequencies in the gigahertz range (upwards of 1 billion cycles per second) have been used in some applications. 

Ultrasound sound at frequencies above the audible range (i.e., above about 20 kHz). 

The term ultrasound describes sound waves with a frequency range from 16kHz up to several megahertz. Vibrational motions are transmitted by oscillating devices into a fluid and cause pressure waves. This varying sound pressure is superimposed on the static pressure of the liquid. Fluids are generally capable... 

Ultrasound is sound pitched above the frequency bond of human hearing. It is a part of sonic spectrum ranging from 20 kHz to 10 MHz (wavelengths from 10 to 10 cm). The application of ultrasound in association with chemical reactions is called sonochemistry. The range from 20 kHz to aroimd 1 MHz is used in sonochemistry, since acoustic cavitation in liquids can be efficiently generated within this frequency range. However, common laboratory and industrial equipment typically utilize a range between 20 and 40 kHz. 

As we have seen, defoaming of foams prepared from dilute, low-viscosity, aqueous surfactant solutions has been reported mainly with ultrasound in the frequency range of 20-25.8 kHz. The only reported exception to this concerns the extremely weak effect described by Komarov et al. [60] in the frequency range of 2-7 kHz. If we reasonably ignore the latter, then we can use the plot of the sound velocities for 0.99 < 0.999 shown in Figure 7.21 to estimate the range of wavelengths... 

These electromechanic effects result in sound generation in the audible frequency range up to some kilohertz (8739). Higher harmonics may cause ultrasound (91). Therefore these effects lead to an electroacoustic response which can be exploited in applications such as speakers or headphones. The frequency characteristics and the achievable maximum vibration amplititde are two parameters that are decisive for the application of this material in such devices. As already mentioned, both depend very strongly on the quality of the alignment of the Sc FLC polymer, the layer structure (chevron, bookshelf, or other), the existence of zigzag defects in the sample, and the... 

The chemical effects of ultrasound do not arise from a direct interaction with molecular species. Ultrasound spans the frequencies of roughly 15 kH2 to 1 GH2. With sound velocities in Hquids typically about 1500 m/s, acoustic wavelengths range from roughly 10 to lO " cm. These are not molecular dimensions. Consequently, no direct coupling of the acoustic field with chemical species on a molecular level can account for sonochemistry or sonoluminescence. 

Its unit is hertz (s ), corresponding one cycle per second. Pure tone consists of one frequency, but normally all sounds are a mixture of many frequencies. In the audio range, frequency varies normally from 20 Hz to 16000 Hz. The size of the audio range depends on the sensitivity of the listener s ears. When the frequency is below 20 Hz, it is called infrasound, while for frequencies over 16000 Hz, it is called ultrasound. 

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). 

The first area involves low amplitude (higher frequency) sound and is concerned with the physical effect of the medium on the wave and is commonly referred to as low power or high frequency ultrasound . Typically, low amplitude waves are used for analytical purposes to measure the velocity and absorption coefficient of the wave in a medium in the 2 to 10 MHz range. Information from such measurements can used in medical imaging, chemical analysis and the study of relaxation phenomena and this will be dealt with later. 

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... 

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