2. Introduction to the Physics of Ultrasound

3. Sound? Sound is a longitudinal wave that travels in a straight line
Sound requires a medium for traveling
Range of audible sound
20Hz -20kHz

5. 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.
The wavelength of a longitudinal wave can be measured as the distance between the centre of two compressions

6. Below is a picture of a longitudinal wave travelling along a spring.

7. Ultrasonic wave
Ultrasonic wave is a longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20 kHz.

8. Frequency greater than audible sound (f>20kHz).
ULTRASONIC WAVE
Frequency greater than audible sound (f>20kHz).

9. ULTRASONICS
- Frequency greater than audible sound.
INFRASONICS
-Frequency lesser than
audible sound
SUPERSONIC – Speed greater than
sound.

10. General Properties of Ultrasonics
Acoustic waves
Frequency > 20kHz
High energy waves
Speed in a thin rod v = (Y/ρ)1/2 ,in liquid (K/ρ)1/2 in gas (γP/ ρ)1/2
Speed depends on frequency. Greater the frequency, higher the velocity
Modes of propagation- longitudinal & transverse
Can be reflected, refracted & diffracted

11. Heating effect
Stirring effect.
Attenuation A=A0 e –αx
Can be transmitted through large distances
Stationary waves are produced

12. 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 & P. Curie
Converse of this effect is also possible.

13. 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.

14. Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect +
Battery
Piezoelectrical
Crystal (Quartz)
Krautkramer NDT Ultrasonic Systems

15. Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect +
The crystal gets thicker, due to a distortion of the crystal lattice
Krautkramer NDT Ultrasonic Systems

16. Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect +
The effect inverses with polarity change
Krautkramer NDT Ultrasonic Systems

17. U(f) Piezoelectric Effect Sound wave with frequency f
An alternating voltage generates crystal oscillations at the frequency f
Krautkramer NDT Ultrasonic Systems

18. Piezo electric crystals
Piezoelectric crystal: a crystal that exhibits piezo electric effect is called piezo electric crystals
Eg:- Quartz, tourmaline, Rochelle salt etc

19. Piezoelectric Crystals
The thickness of the crystal determines the frequency of the scanhead
Low Frequency
3 MHz
High Frequency
10 MHz

20. Piezoelectric generator

21. The circuit is basically a Hartley oscillator.
The tank circuit produces high frequency alternating potential which is fed to the quartz crystal.

22. Tank circuit
To produce high frequency alternating potential.
The frequency

23. 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.

24. Frequency up to 15 MHz can be produced by this method.

25. .

26. 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)

27. Magnetostriction
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

28. FREQUENCY
The frequency generated is given by

29. APPLICATIONS

30. DEPTH OF SEA

33. Bats navigate using ultrasound

34. ULTRASONIC MIXING

35. SOUND SIGNALING

36. SOLDERING & METAL CUTTING

39. CLEANING

41. STERILIZING

42. BIOLOGICAL EFFECT

43. MEDICAL FIELD

44. DIAGNOSIS
THERAPY

45. Ultrasound imaging: How does it work?
Need to clarify difference between probe and element
Mention coupling gel
An ultrasound element acts like a bat.
Emit ultrasound and detect echoes
Map out boundary of object

46. More about how it works…
Ultrasound probe
The probe contains a transmitter and a receiver.
A pulse of ultrasound is sent out by the transmitter.
skin
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
Body tissue
(muscle etc)

47. Ultrasound imaging: foetus feet
Pictures from
This is a 2D ultrasound scan
through the foot of a foetus. You can see some of the bones of the foot.

48. Ultrasound imaging: more surface rendering
Pictures from

49. Ultrasound imaging: imaging the heart
heart valves
atrium
ventricle
Pictures from

50. 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).

51. COAGULATION & CRYSTALLIZATION

52. FORMATION OF ALLOYS

53. TO FIND VELOCITY OF SOUND IN GASES & LIQUID

54. NON DESTRUCTIVE TESTING

55. 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

56. Aircraft Inspection
Nondestructive testing is used extensively during the manufacturing of aircraft.

57. Pulse echo system
Pulse transmission system
Pulse resonance system

58. Pulse echo system

59. back surface
echo

60. Ultrasonic Inspection (Pulse-Echo)
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 2 4 6 8 10
initial
pulse
crack
echo
crack
plate
Oscilloscope, or flaw detector screen

61. Pulse transmission system

62. Advantages of Ultrasonic testing
Simple and accurate
Very minute flows can be detected
Nature, size and location of defect can be accurately determined
Cheap method
Used as high speed testing
Large specimen can be inspected in a short time.

63. 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

64. Ultrasonic diffractometer.

65. Procedure

66. Diffraction takes place
d sin θ= nλ (1) where d= the distance between 2 nodal or antinodal planes
d= λa/2 or λa= 2d
V=טλa