Mechanisms Of Ultrasound Irradiation Essay

674 words - 3 pages

INTRODUCTION

Ultrasound represents sound waves with frequencies greater than 16 kHz, higher than that could be heard by human. The upper limit of ultrasonic frequency is usually taken to be 5 MHz for gases and 500 MHz for liquids and solids [1] while the lower frequency limit is considered to be 20 kHz [2]. Ultrasound waves may be divided into two main areas [1, 3], Low Amplitude i.e. the propagation relates to the effect of medium on wave and High Amplitude in which the propagation is due to the effect of the wave on medium.

For many materials, low amplitude propagation has proved to be a powerful analytical technique for investigating the physico-chemical properties [4]. Low power ultrasonic irradiation does not produce any chemical changes, while high power ultrasound instigates permanent physical/chemical changes in the material [3, 5, 6]. High energy input produces cavitation and micro-streaming in liquids, heating, and surface-instability effects at liquid-liquid and liquid-gas interfaces [3, 7, 8].

Ultrasound has provided a method to explore some of primary properties of materials. Sonication offers a much better way to induce these physical and chemical changes with higher efficiencies and shorter processing times. An understanding of mechanisms for different effects of sound is important in connection with its applications in different fields (medicine, food, chemistry). There is considerable need to increase understanding of mechanisms in order to evaluate performances and limitations involved in its various applications.

This study explains the mechanisms of ultrasound irradiation with particular attention in the field of Nanomaterial synthesis.

POWER ULTRASOUND & ITS MECHANISM

Ultrasound waves require physical medium to propagate. These waves compress and stretch the spacing in the medium through which it passes. The average molecular distance varies as the molecules oscillate about their mean position when ultrasound crosses the medium (fig 1.2). When ultrasound passes through liquid, it exerts a negative pressure on the liquid. If the pressure is large enough that it exceeds the minimum molecular distance required to hold the liquid intact, the...

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