Introduction to the Physics of Ultrasound Sound? Sound is a longitudinal wave that travels in a straight line Sound requires a medium for traveling Range.

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<ul><li> Slide 1 </li> <li> Slide 2 </li> <li> Introduction to the Physics of Ultrasound </li> <li> Slide 3 </li> <li> Sound? Sound is a longitudinal wave that travels in a straight line Sound requires a medium for traveling Range of audible sound 20Hz -20kHz Range of audible sound 20Hz -20kHz </li> <li> Slide 4 </li> <li> Slide 5 </li> <li> When a longitudinal wave moves through a material, the particles of the material move backwards and forwards along the direction in which the wave is travelling. particles When a longitudinal wave moves through a material, the particles of the material move backwards and forwards along the direction in which the wave is travelling. particles The wavelength of a longitudinal wave can be measured as the distance between the centre of two compressions wavelength The wavelength of a longitudinal wave can be measured as the distance between the centre of two compressions wavelength </li> <li> Slide 6 </li> <li> Below is a picture of a longitudinal wave travelling along a spring. </li> <li> Slide 7 </li> <li> Ultrasonic wave is a longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20 kHz. Ultrasonic wave </li> <li> Slide 8 </li> <li> ULTRASONIC WAVE Frequency greater than audible sound (f&gt;20kHz). </li> <li> Slide 9 </li> <li> ULTRASONICS - Frequency greater than audible sound. INFRASONICS -Frequency lesser than audible sound SUPERSONIC Speed greater than sound. </li> <li> Slide 10 </li> <li> General Properties of Ultrasonics Acoustic waves Frequency &gt; 20kHz High energy waves Speed in a thin rod v = (Y/) 1/2, in liquid (K/) 1/2 in gas (P/ ) 1/2 Speed depends on frequency. Greater the frequency, higher the velocity Modes of propagation- longitudinal &amp; transverse Can be reflected, refracted &amp; diffracted </li> <li> Slide 11 </li> <li> Heating effect Stirring effect. Attenuation A=A 0 e x Can be transmitted through large distances Stationary waves are produced </li> <li> Slide 12 </li> <li> Piezo-electric effect When crystals like quartz, tourmaline etc. are subjected to stress along the mechanical axis, a P.D is developed across the perpendicular electrical axis. This is called Piezo electric effect Discovered by J &amp; P. Curie Converse of this effect is also possible. </li> <li> Slide 13 </li> <li> Converse piezo electric effect When a P.D is applied between the two opposite faces of a crystal, then stress or strain is induced along the perpendicular faces. If frequency of osculation is equal to the natural frequency of the crystal, resonance takes place and ultrasonics are produced. </li> <li> Slide 14 </li> <li> Krautkramer NDT Ultrasonic Systems Piezoelectric Effect Piezoelectrical Crystal (Quartz) Battery + </li> <li> Slide 15 </li> <li> Krautkramer NDT Ultrasonic Systems + The crystal gets thicker, due to a distortion of the crystal lattice Piezoelectric Effect </li> <li> Slide 16 </li> <li> Krautkramer NDT Ultrasonic Systems + The effect inverses with polarity change Piezoelectric Effect </li> <li> Slide 17 </li> <li> Krautkramer NDT Ultrasonic Systems An alternating voltage generates crystal oscillations at the frequency f U(f) Sound wave with frequency f Piezoelectric Effect </li> <li> Slide 18 </li> <li> Piezo electric crystals Piezoelectric crystal: a crystal that exhibits piezo electric effect is called piezo electric crystals Eg:- Quartz, tourmaline, Rochelle salt etc </li> <li> Slide 19 </li> <li> Piezoelectric Crystals The thickness of the crystal determines the frequency of the scanhead Low Frequency 3 MHz High Frequency 10 MHz </li> <li> Slide 20 </li> <li> Piezoelectric generator </li> <li> Slide 21 </li> <li> The circuit is basically a Hartley oscillator. The tank circuit produces high frequency alternating potential which is fed to the quartz crystal. </li> <li> Slide 22 </li> <li> Tank circuit To produce high frequency alternating potential. The frequency </li> <li> Slide 23 </li> <li> Piezoelectric generator This is based on the converse Piezo electric effect. When the frequency of oscillation coincides with the natural frequency of the crystal, resonance will take place. This principle is used for the production of ultrasonics. </li> <li> Slide 24 </li> <li> Frequency up to 15 MHz can be produced by this method. </li> <li> Slide 25 </li> <li> . </li> <li> Slide 26 </li> <li> Magnetostriction Magnetostriction is a property of magnetic materials that causes them to change their shape when subjected to a magnetic field. The effect was first identified bby James Joule James Prescott Joule, (1818 1889) </li> <li> Slide 27 </li> <li> When a ferromagnetic rod is placed in an alternating M.F, with its length parallel to the field, the length of the rod increases and decreases rapidly (or the rod vibrates) This phenomena is known as Magnetostriction. This principle is used to produce ultrasonic waves Magnetostriction </li> <li> Slide 28 </li> <li> FREQUENCY The frequency generated is given by </li> <li> Slide 29 </li> <li> APPLICATIONS </li> <li> Slide 30 </li> <li> DEPTH OF SEA </li> <li> Slide 31 </li> <li> Slide 32 </li> <li> Slide 33 </li> <li> Bats navigate using ultrasound </li> <li> Slide 34 </li> <li> ULTRASONIC MIXING </li> <li> Slide 35 </li> <li> SOUND SIGNALING </li> <li> Slide 36 </li> <li> SOLDERING &amp; METAL CUTTING </li> <li> Slide 37 </li> <li> Slide 38 </li> <li> Slide 39 </li> <li> CLEANING </li> <li> Slide 40 </li> <li> Slide 41 </li> <li> STERILIZING </li> <li> Slide 42 </li> <li> BIOLOGICAL EFFECT </li> <li> Slide 43 </li> <li> MEDICAL FIELD </li> <li> Slide 44 </li> <li> DIAGNOSIS THERAPY </li> <li> Slide 45 </li> <li> Ultrasound imaging: How does it work? An ultrasound element acts like a bat. Emit ultrasound and detect echoes Map out boundary of object </li> <li> Slide 46 </li> <li> More about how it works The probe contains a transmitter and a receiver. A pulse of ultrasound is sent out by the transmitter. The pulse is reflected from a surface and returns to the receiver. The ultrasound machine measures how long it takes for the pulse to return Ultrasound probe Body tissue (muscle etc) skin </li> <li> Slide 47 </li> <li> Ultrasound imaging: foetus feet This is a 2D ultrasound scan through the foot of a foetus. You can see some of the bones of the foot. </li> <li> Slide 48 </li> <li> Ultrasound imaging: more surface rendering </li> <li> Slide 49 </li> <li> Ultrasound imaging: imaging the heart heart valves atrium ventricle </li> <li> Slide 50 </li> <li> Why Use Ultrasound? Ultrasound is very safe. There is no firm evidence that it does any harm to the body (or the baby in the case of pregnancy scans). X-rays are potentially dangerous, particularly to young children and pregnant women (they damage the unborn baby). </li> <li> Slide 51 </li> <li> COAGULATION &amp; CRYSTALLIZATION </li> <li> Slide 52 </li> <li> FORMATION OF ALLOYS </li> <li> Slide 53 </li> <li> TO FIND VELOCITY OF SOUND IN GASES &amp; LIQUID </li> <li> Slide 54 </li> <li> NON DESTRUCTIVE TESTING </li> <li> Slide 55 </li> <li> Non destructive testing is a new method of testing of material Without destruction of the material This can be used to detect the imperfections like flaws, cracks, breakings, cavity, airpockets, discontinuities etc in material </li> <li> Slide 56 </li> <li> Aircraft Inspection Nondestructive testing is used extensively during the manufacturing of aircraft. </li> <li> Slide 57 </li> <li> Pulse echo system Pulse transmission system Pulse resonance system </li> <li> Slide 58 </li> <li> Pulse echo system </li> <li> Slide 59 </li> <li> back surface echo </li> <li> Slide 60 </li> <li> High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws. Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features that reflect sound. f plate crack 0246810 initial pulse crack echo Oscilloscope, or flaw detector screen Ultrasonic Inspection (Pulse- Echo) </li> <li> Slide 61 </li> <li> Pulse transmission system </li> <li> Slide 62 </li> <li> Advantages of Ultrasonic testing 1.Simple and accurate 2.Very minute flows can be detected 3.Nature, size and location of defect can be accurately determined 4.Cheap method 5.Used as high speed testing 6.Large specimen can be inspected in a short time. </li> <li> Slide 63 </li> <li> Ultrasonic diffractometer To find the velocity and wavelength of ultrasonics a quartz crystal is set into vibrations in a liquid using an R.F oscillator. Ultasonics produced This makes the liquid an aquastic grating Collimated sodium light allowed to fall normally on the grating </li> <li> Slide 64 </li> <li> Ultrasonic diffractometer. </li> <li> Slide 65 </li> <li> Procedure </li> <li> Slide 66 </li> <li> Diffraction takes place d sin = n--------(1) where d= the distance between 2 nodal or antinodal planes d= a /2 or a = 2d V= a </li> </ul>

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