General: - Use ultrasound to investigate the reflection and transmission of sound. - Become familiar with the principles of operation of a simple ultrasound system. Specific: - Sense the position of...

ULTRASOUND
TABLE OF CONTENT:
    ITEM
    PAGE NO.
    ABSTRUCT:
    2
    INTRODUCTION:
    2
    EXPERIMENTAL PROCEDURE:
    2-5
    DISCUSSION:
    5
    CONCLUSION:
    5-6
ULTRASOUND:
ABSTRUCT:
The working principle of Ultrasound systems is to transmit a short burst of very high frequency sound and to listen to the echoes from objects or from sharp changes in sound speed and/or density within an object. In this experiment a single transducer was used for both transmitting and receiving sound and produces an output that represents the echo amplitude as a function of time. The general objectives of this experiment were to use ultrasound to investigate the reflection and transmission of sound and to be familiar with the principles of operation of a simple ultrasound system. More specifically purposes of this experiment were to sense the position of objects using reflected sound; to determine the range and angular resolution of an ultrasound system; and to measure the velocity of sound in various materials.
INTRODUCTION:
Amplitude of an acoustic signal can be indicated by its intensity, I, (W.m-2), which is acoustic power per unit area, or by the co
esponding pressure, p, (Pa). The two are related by
where rms p is the root mean square pressure (Pa) (square root of the mean of the squared pressure), ρ is density of the medium the wave is propagating in (kg.m-3), and v is the sound speed (m.s-1).
The electrical output of an ultrasonic transducer, and consequently the output of most ultrasonic systems, is proportional to the pressure. It is therefore proportional to the square root of the intensity.
The magnitude of a reflected echo depends on the characteristic acoustic impedance of the materials on either side of the reflecting boundary. The characteristic acoustic impedance is
The pressure reflection coefficient for normal incidence (ratio of reflected to incident acoustic pressure) is
Where, Z1 is the characteristic acoustic impedance of water and
Z2 is the characteristic acoustic impedance of the material.
EXPERIMENTAL PROCEDURE:
EQUIPMENT USED: The ultrasonic system used in this experiment is called the Medetech Ultrasonics Teaching Module (UTM) and operates at a frequency of 2.3 MHz. Its front panel layout is effectively a block diagram of the way the instrument works. The panel is divided into two main sections by the vertical
oken line: To the left of the line is the transmit section, which contains controls that alter the properties of the transmitted signal. The receive section is to the right of the line and contains controls that alter the way in which the received signal is processed. This unit is designed to use a conventional analogue oscilloscope (C.R.O.) as a display. The oscilloscope can be plugged into several different outputs to monitor the signal at different points in the receive chain.
PROCEDURE:
1. Basic operation
At first, the Perspex was filled tank with water to within a few centimeters of the top. After selecting the larger of the two transducers it was connected to the “transducer” connector on the UTM. The transducer was then mounted in a retort stand in such a way that it could be pressed up against one end of the tank (on the OUTSIDE).A generous blob of silicon grease was applied to the centre of the transducer face and it was then pressed up against the end of the tank. The purpose of the grease is to exclude all air from between the transducer face and the tank wall, which would otherwise dramatically attenuate the signal. Plain Perspex sheet was placed in the slot closest to the transducer and the...