Ultrasonic Dehydration

Chapter 1

1 INTRODUCTION
This chapter reflects the general overview of the project work. This comprises of a brief description of ultrasonic and the piezoelectric transducers and transducer driver system followed by literature review. The objective, motivation and organization of the thesis are mentioned in this chapter.
1.1 Overview
A high power ultrasound system is used in a wide range of application where efficient and economical energy conversion is required. Two main part of this system are a power driver and a piezoelectric transducer.
The piezoelectric transducer generates mechanical energy in response to an applied electrical excitation. The ability of the transducer in energy conversion is reversible .it means the transducer can also

Hot air drying is a conventional method for dehydrating food but for heat sensitive materials ,this method can cause deteriorative changes .to have much more effective dehydration a high power ultrasound system is applied. In such a case ultrasound waves are generated using the ultrasound system and then contacted with food samples directly. In the intersection between ultrasound waves and samples, ultrasound waves penetrate in samples which results in contraction and expansion of material and moisture evaporation from samples [1, 11, 13,

Once ultrasound waves pass through fluids, some cavitational bubbles are generated and grow to a certain size then burst. Exploding of these bubbles increase the temperature and pressure of the liquid and dislodges sticking dirt from surfaces [15-20].
Also, an ultrasound transducer is used for cutting food products. Based on different food materials stiffness and softness, several cutting tools could be used for cutting food products. Ultrasound cutting at a frequency range 20-40 kHz is a suitable option for cutting all types of food products. Compared to conventional cutting methods this method is sharper and faster [2].
Velocity measurement in underwater vehicle is another applications of a piezoelectric transducer in which two transducer are used. One as a transmitter and another one as a receiver to estimate the velocity of the vehicle [21].
1.2.2 Biomedical