Magnetostriction and application of ultrasonic waves

Magnetostriction along with Production, Properties, and Application of ultrasonic waves.

1. MAGNETOSTRICTION AND APPLICATIONS OF ULTRASONIC WAVES 15Z204 - MATERIALS SCIENCE Presented by Pranav Shankar Ramalingam - 17Z230 Preethi.S.V - 17Z231 Priyadarshini.S -17Z232

2. Outline In this Presentation, we will be discussing the following : What is Magnetostriction? Working and Result of Magnetostriction. What are ultrasonic waves? Production of ultrasonic waves by magnetostrsiction method. Properties of ultrasonic waves. Applications of ultrasonic waves (in the fields of science, engineering, medicine, etc).

3. What is Magnetostriction? Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions (expand or contract) during the process of magnetization. The effect was first identified in 1842 by James Joule when observing a sample of nickel.

4. Magnetostriction - Working Internally, ferromagnetic materials have a structure that is divided into domains, which are randomly oriented when the material is not exposed to a magnetic field and each domain is a region of uniform magnetic polarization. When a magnetic field is applied , the boundaries between the domains shift and the domains rotate ; both of these effects cause a change in the material’s dimensions.

5. Result of Magnetostriction The orientation of these small domains by the imposition of the magnetic field creates a strain field. As the intensity of the magnetic field is increased, more and more magnetic domains orientate themselves so that their principal axes of anisotropy are collinear with the magnetic field in each region and finally saturation is achieved.

6. Effect of increasing and decreasing applied or external magnetic field(H) on a ferromagnetic material can be seen here. The arrow mark indicates the change in value (increase or decrease) and direction of applied magnetic field.

7. Ultrasonic waves The sound waves are classified into three types on the basis of their frequencies. They are namely (i) infrasonic waves (sound waves of frequency below 20 Hz) (ii) audible sound waves (sound waves of frequency between 20 and 20kHz) (iii) ultrasonic waves (sound waves of frequency above 20kHz ). Ultrasonic Waves

8. Production of Ultrasonic waves The Ultrasonic waves are produced by a mechanical method using Galton's whistle. It is also produced by magnetostriction and piezoelectric oscillators. Let us discuss the magnetostriction oscillator in this section. MAGNETOSTRICTION METHOD To produce ultrasonic waves of frequencies up to 3MHz only. PRINCIPLE : The Magnetostriction oscillator is based on the principle of magnetostriction effect. When a ferromagnetic material is subjected to a varying magnetic field, the length of the ferromagnetic rod changes and the ferromagnetic rod is set into resonant vibration, whenever the frequency of the tank circuit coincides with the vibration of the ferromagnetic rod.

9. CONSTRUCTION : A ferromagnetic rod AB made up of Ni is clamped in the middle, C as shown. Coil of wires L 1 and L 2 are winded at the ends of A and B. One end of the coil L 2 is connected to the base of an NPN transistor and the other end of the coil L 1 is connected to the emitter and the negative terminal of a battery. A variable capacitor C 1 is connected across the coil L 1 . One end of the variable capacitor is connected to the collector circuit, whereas the other end of the variable capacitor is connected to the positive end of the battery through a milliammeter and a key K. Production of Ultrasonic waves Magnetostriction oscillator

10. Working - Magnetostriction Oscillator When the key is closed, the tank circuit (LC circuit) is set into oscillation with a frequency of vibration given by F= 1/(2π√(LC)) where L 1 =inductance of coil L 1 and C 1 =capacitance of the capacitor C 1 . An alternating EMF is produced due to the vibration of the tank circuit. This alternating EMF induces an alternating magnetic field. The length of the ferromagnetic material gets changed due to the alternating magnetic field. The change in the length of the ferromagnetic material induces an EMF in the coil L 2 .

11. The induced emf is fed into the base of the transistor and hence it gets amplified and it is fed into the tank circuit.Thus the oscillation is continuously maintained. The frequency of the oscillation of the tank circuit is varied by adjusting the variable capacitance value. If the frequency of the tank circuit matches with the frequency of vibration of the ferromagnetic rod, ultrasonic waves are produced and the ultrasonic waves are emitted from the ends of the rod as shown in the diagram. The frequency of ultrasonic waves produced is given by Where l is the length of the ferromagnetic material, Y is the Young’s modulus and ρ is the density of the ferromagnetic material. Working - Magnetostriction Oscillator

12. Properties of Ultrasonic waves The frequency of the Ultrasonic waves is greater than 20 kHz. The Ultrasonic waves are highly energetic. Because of their high frequency, they have intensity up to 10 kW(m)^-2. Like ordinary sound waves, Ultrasonic waves produce alternate compression and rarefaction, when they are propagating through liquid and gaseous medium. Ultrasonic waves produce Cavitation effect in liquids. The speed of the ultrasonic wave increases with the increase in its frequency. Ultrasonic waves are having a shorter wavelength. The Ultrasonic waves exhibit reflection and interference phenomenon similar to ordinary light waves. The Ultrasonic waves exhibit negligible diffraction effects.

13. Applications of Ultrasonic waves Science and engineering : 1. It is used to detect flaws or cracked in metals. 2.It is used to detect ships, submarines, iceberg etc, in ocean. 3. It is used for soldering aluminium coil capacitors, aluminium wires and plates without using any fluxes. 4. It is used to weld some metals which can’t be welded by electric or gas welding. Ultrasonic Welding Submarine-detection

14. Applications of Ultrasonic waves 5. It is used to cutting and drilling holes in metals. 6. It is used to form stable emulsion of even immiscible liquids like water and oil or water and mercury which finds application in the preparation of photographic films, face creams etc. 7. It act like a catalytic agent and accelerate chemical reactions. Ultrasonic homogenizers for liquid processing

15. Medicine : 8. It is used to remove kidney stones and brain tumours without shedding any blood. 9. It is used to remove broken teeth.It is also used in cavitation. Ultrasonic cavitation is a simple procedure that relies on sound waves to flush fat from the body instead of intensive surgery. 10. It is used for sterilising milk and to kill bacteria. 11. It is used to study the blood flow velocities in blood vessels of our body. 12. It is used as a diagnostic tool to detect tumours, breast cancer and also the growth of foetus can be studied. Applications of Ultrasonic waves

16. Applications of Ultrasonic waves 13. A Cheap Ultrasonic Range Finder Working - Everybody knows the speed of the sound in the dry air is around 340 m/s. Send a short ultrasonic pulse at 40 kHz in the air, and try to listen to the echo. Of course you wont hear anything, but with an ultrasonic sensor the back pulse can be detected. If you know the time of the forth & back travel of the ultrasonic wave, you know the distance, divide the distance by two and you know the range from the ultrasonic sensor to the first obstacle in front of it. Ultrasonic water depth detector