Project on Ultrasound
1.1 INTRODUCTION:
The human ear can hear the sound waves between 20 Hz to 20 kHz. This frequency range is known as “Audio Frequency Range”. The sound waves having frequencies above this audible range is known as “Ultrasonic Waves” or “Supersonic Waves”. Supersonic waves have the velocities higher than the velocity of sound i.e. more than 1200 km / hour. Ultrasonic waves can not be heard by a human being but a cat or dog may hear them. The wavelengths of ultrasonic waves are very small as compared to audible sound. The sound waves which have frequencies less than 20 Hz range are called “Infrasonic waves”
1.2 Production of Ultrasonic Wave:
The generator of ultrasonic wave is nothing but an oscillator, which can generate these high frequency waves. The ultrasonic waves can be produced by the following methods.
a) Magnetostriction Generator
b) Piezoelectric or Ultrasound Generator
a) Magnetostriction Effect
This effect is very useful in generating ultrasonic waves are known as Magnetostriction effect. This effect was first discovered by Joule in 1847 & subsequently used by G.W Pierre in an oscillator circuit. The Magnetostriction effect is that effect in which a rod of ferromagnetic material such as iron or nickel is placed in a magnetic field parallels to its length a small extension or contraction occurs is known as Magnetostriction effect. This change in length is found to be
i) Proportional to the applied field
ii) Is independent of the direction of the field applied
[pic]
Fig.1.1 - Variation of length with the applied magnetic field.
Figure shows that the length of nickel & iron rod changes with the impressed magnetic field. This change of length is independent of the sign of the field & only depends on the magnitude of the field & nature of the material. If the rod is placed inside a coil carrying a high frequency D.C. then it suffers the same change in length for each half cycle of
The human ear can hear the sound waves between 20 Hz to 20 kHz. This frequency range is known as “Audio Frequency Range”. The sound waves having frequencies above this audible range is known as “Ultrasonic Waves” or “Supersonic Waves”. Supersonic waves have the velocities higher than the velocity of sound i.e. more than 1200 km / hour. Ultrasonic waves can not be heard by a human being but a cat or dog may hear them. The wavelengths of ultrasonic waves are very small as compared to audible sound. The sound waves which have frequencies less than 20 Hz range are called “Infrasonic waves”
1.2 Production of Ultrasonic Wave:
The generator of ultrasonic wave is nothing but an oscillator, which can generate these high frequency waves. The ultrasonic waves can be produced by the following methods.
a) Magnetostriction Generator
b) Piezoelectric or Ultrasound Generator
a) Magnetostriction Effect
This effect is very useful in generating ultrasonic waves are known as Magnetostriction effect. This effect was first discovered by Joule in 1847 & subsequently used by G.W Pierre in an oscillator circuit. The Magnetostriction effect is that effect in which a rod of ferromagnetic material such as iron or nickel is placed in a magnetic field parallels to its length a small extension or contraction occurs is known as Magnetostriction effect. This change in length is found to be
i) Proportional to the applied field
ii) Is independent of the direction of the field applied
[pic]
Fig.1.1 - Variation of length with the applied magnetic field.
Figure shows that the length of nickel & iron rod changes with the impressed magnetic field. This change of length is independent of the sign of the field & only depends on the magnitude of the field & nature of the material. If the rod is placed inside a coil carrying a high frequency D.C. then it suffers the same change in length for each half cycle of
References: 1. ‘Fundamental of Acoustics’ by L.E. Kinsler & A.R. Frey; Wiley Eastern Limited (1963). 2. ‘Fundamentals of Ultrasonic’ by J. Blitz; Butterworth & Co-Publishers Limited (1969). 4. Edler I, Hertz CH. The use of ultrasonic reflectoscope for the continuous recording of movements of heart walls. Kungl Fzsiogr Sallsk i Lund Forhandl. 1954; Reproduced in Clin Physiol Funct Imaging 2004. 5. S. A. Kana (2003). Introduction to physics in modern medicine. Tsylor & Francis. 8. Bushberg JT (2002). The essential physics of medical imaging. Lippincott Williams & Wilkins. 14. Curie. J.P., Curie. (1880) Développement par pression de l 'é 'lectricite polaire dans les cristaux hémièdres à faces inclinées. C.R. Acad. Sci. (Paris). 15. Chilowsky C.M. Langévin. M.P. (1916) Procídés et appareil pour production de signaux sous-marins dirigés et pour la localsation à distances d 'obstacles sons-marins. 16. Langévin, M.P. (1928) Lés ondes ultrasonores. 17. Firestone, F.A. (1945) The supersonic reflectoscope for interior inspection. 18. Firestone, F.A. (1945) The supersonic reflectoscope, an instrument of inspecting the interior of solid parts by means of sound waves 19. Desch, C.H., Sproule, D.O. and Dawson, W.J. (1946) The detection of cracks in steel by means of supersonic waves 21. Tanaka, K. (1952) Application of ultrasound to diagnostic field. 22. Miyajima, G., Wagai, T., Fukushima, Y., Uchida, R. and Hagiwara, I. (1952) Detection of intracranial disease by pulsed ultrasound