Ultrasound frequency range

Figure 2. Effective clearing thresholds 7 for a 10-126 gm sample of MBBA in the ultrasound frequency range ( ) 0.4, (o) 1, (a) 3.2 MHz.

The ultrasound system should have more independent channels and allow the transmitter pulse to be individually adjustable in width and amplitude, and an increased frequency range for the logarithmic amplifier was desired. The digitization should be improved both with respect to sampling rate and resolution. 

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

Motion of fluids in which local velocities and pressures fluctuate irregularly, in a random manner. Predictive maintenance technique that uses principles similar to those of vibration analysis to monitor the noise generated by plant machinery or systems to determine their actual operating condition. Ultrasonics is used to monitor the higher frequencies (i.e., ultrasound) that range between 20,000 Hertz and 100 kiloHertz. 

Unlike vibration monitoring, ultrasonics monitors the higher frequencies, i.e. ultrasound, produced by unique dynamics in process systems or machines. The normal monitoring range for vibration analysis is from less than 1 Hertz to 20,000 Hertz. Ultrasonics techniques monitor the frequency range between 20,000 and 100 kHz. 

We have also examined the use of higher ultrasonic frequencies (500 kHz and 800 kHz) and found the trend in product distribution from carboxylate electrooxidation at platinum electrodes in methanol to be the same as under sonication in the 20 kHz to 40 kHz frequency range. However, we obtained better yields in spite of the usual reduced cell voltage requirements in the presence of ultrasound. There also seemed to be fewer of the numerous low-yield methoxylated species and other side-products. 

There are three distinct sets of ultrasound conditions based on frequency range and applications [5] ... 

Sonar and imaging technologies are based on sending out ultrasound pulses and receiving the echoes. The resolution capabilities depend upon the emitted pulses being sharp, and the sharper the pulse the more Fourier components it has. Therefore, for a transducer to emit and detect a sharp pulse it must be able to respond to a wide frequency range - that is it must have the broad band characteristic associated with low mechanical Q. The very lossy nature of the polymer phase endows the composite with this (Q < 10). 

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

The ultrasound typicaiiy used in common crystaiiization media (mainiy aqueous media) falls in the low-frequency range. 

For liquids, the velocity of ultrasound depends on the compressibility and density of the liquid. For suspensions, the velocity depends also on the drag of particles in the liquid under the influence of the ultrasonic wave. At low frequencies, small particles tend to move in phase with the liquid and the ultrasonic velocity may differ widely from that in the pure liquid. As particle size and ultrasonic frequency increases, the particles tend to lag more and more behind the movement of the liquid and the ultrasonic velocity approaches that of the suspension acting as a uniform fluid. There is a transition frequency range between complete entrainment and no entrainment of the particles that can be used to obtain particle size information. The hydrodynamic model of Marker and Temple [267 ] can be used to calculate ultrasonic velocity. This model takes into account the effects of fluid viscosity, of concentration, density and elastic modulus of both particles and fluid and can predict ultrasonic velocities accurately for volume fractions between 5% and 20%. Ultrasonic velocity measurements in the 50 kHz to 50 MHz can be used to determine particle size distributions in the range of about 0.1 to 30 pm. 

There is a correlation between sonochemical and sonoluminescence measurements, which is usually not observed. Sonoluminescence is the consequence that both the sonochemical production (under air) of oxidizing species and the emission of light reflect the variations of the primary sonochemical acts, which are themselves due to variations of the number of active bubbles. Pulsed ultrasound in the high-frequency range (> 1 MHz) is extensively used in medical diagnosis, and the effects of pulsed ultrasound in the 20-kHz range using an immersed titanium horn has been reported. ... 

Ultrasound at various frequencies in the range of 20 kHz to 16 MHz has been used for sonophoresis. These studies of sonophoresis can be classified into three categories based on the ultrasound frequency used, i.e., therapeutic, high-frequency, and low-frequency ultrasound. 

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. 

High-frequency, low-power ultrasound generally within the frequency range 0.5-20 MHz can be used to evaluate foodstuffs in terms of physical characteristics such as the degree of emulsification or the concentration of solids or gas. In... 

There is, however, a recent paper in English from a Bulgarian group on the sonoelectrochemical oxidation of sodium butyl xanthate [224]. These workers confirm the benefits of sonoelectrochemistry, but make the striking observation that in these xanthate flotation systems they obtain similar effects under 50-Hz irradiation (i.e. infrasound, within human hearing) to those at 20 kHz (ultrasound). Irradiation power details are not easy to compare from the report, but the result has considerable implications for sonoelectrochemical significance of cavitational phenomena, and further confirms that studies across the widest of frequency ranges are necessary for mechanistic elucidation. 

Active teehniques require external power, sueh as eleetronie or acoustic fields and vibration sourees. In the eleetrostatie field teehnique, both direct current and alternative eurrent ean be applied to a dieleetrie fluid. That causes a better bulk mixing of the fluid in the vieinity of the heat transfer surface [2]. Vibration teehniques are elassified as surfaee vibration and fluid vibration teehniques. Surface vibration impinges small droplets onto a heated surface to promote spray eooling. Both low and high frequeneies are used in surface vibration, espeeially for single-phase heat transfer. However, fluid vibration is a more practieal vibration enhaneement, due to the mass of most heat exehangers. Surface vibration eovers the frequency range from 1 Hz to ultrasound. 

Commonly used frequencies for ultrasound scanning range from 20kHz to 25 MHz. and the ultrasonic wavelength X is given by... 

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