Acoustics 4.ppt

Acoustics

1. Acoustic DiffractionMethod
(Determination of the velocity)
•This method is based on the fact that ultrasonic
waves which consist of alternate compressions and
rarefactions changes the density of the medium
through which theypass.
•This leads to a periodic variation of refractive index
of the liquid, such a liquid column is subjected to
ultrasonic waves constitutes an acoustical grating. If
monochromatic light is passed through the waves
the liquid causes the diffraction of light.
1

2. •Figure shows the experimental arrangement, standing
ultrasonic waves are produced ina liquidcontained
in a glass tube. The density and so the refractive index
of theliquid is maximum at thenodal point and
minimum at antinodal points. Hence thenodal area
actsas opaque region, while antinodal area
actsastransparent region forlight. Theliquid
column thus resembles therules grating.
2

3. 3
Thegrating period d equal to /λ/2 and is given by
d sine θ=mλ
Where
λ= wavelength of monochromatic light beam
m = order of minima.
Anacoustic diffraction grating produced bya liquid
column subjected toultrasonic waves

4. (1)Detection of flaws in metals(NDT)
Principle
•Ultrasonicwavesareusedtodetectthepresenceof
flawsordefectsintheformofcracks,blowholes
porosityetc.,intheinternalstructureofamaterial
•Bysendingoutultrasonicbeamandbymeasuring
thetimeintervalofthereflectedbeam,flawsinthe
metalblockcanbedetermined.
4
Applications of Ultrasonic Waves in Engineering

5. Experimental setup
Itconsistsofanultrasonicfrequencygeneratoranda
cathoderayoscilloscope(CRO),transmitting
transducer(A),receivingtransducer(B)andan
amplifier.
5

6. Working
•Inflaws,thereisachangeofmediumandthis
producesreflectionofultrasonicatthecavitiesor
cracks.
•Thereflectedbeam(echoes)isrecordedbyusing
cathoderayoscilloscope.
•Thetimeintervalbetweeninitialandflawechoes
dependsontherangeofflaw.
•ByexaminingechoesonCRO,flawscanbe
detectedandtheirsizescanbeestimated.
6

7. (2) Ultrasonic Drilling
•Ultrasonicsareusedformakingholesin
veryhardmaterialslikeglass,diamondetc.
•Forthispurpose,asuitabledrillingtoolbit
isfixedattheendofapowerfulultrasonic
generator.
•Someslurry(athinpasteofcarborundum
powderandwater)ismadetoflowbetween
thebitandtheplateinwhichtheholeisto
bemade
•Ultrasonicgeneratorcausesthetoolbitto
moveupanddownveryquicklyandthe
slurryparticlesbelowthebitjustremove
somematerialfromtheplate.
•Thisprocesscontinuesandaholeisdrilled
intheplate.
7

8. (3) Ultrasonic welding
•Thepropertiesofsomemetalschangeonheating
andtherefore,suchmetalscannotbeweldedby
electricorgaswelding.
•Insuchcases,themetallicsheetsarewelded
togetheratroomtemperaturebyusingultrasonic
waves.
8

9. (4) Ultrasonic soldering
•Metalslikealuminiumcannotbedirectly
soldered.However,itispossibletosoldersuch
metalsbyultrasonicwaves.
•Anultrasonicsolderingironconsistsofan
ultrasonicgeneratorhavingatipfixedatitsend
whichcanbeheatedbyanelectricalheating
element.
•Thetipofthesolderingironmeltssolderonthe
aluminiumandtheultrasonicvibratorremoves
thealuminiumoxidelayer.
•Thesolderthusgetsfastenedtoclearmetal
withoutanydifficulty.
9

10. (5) Ultrasonic cutting and machining
Ultrasonicwavesareusedforcuttingandmachining.
10
(6) Ultrasonic cleaning
Itisthemostcheaptechniqueemployedfor
cleaningvariouspartsofthemachine,electronic
assembles,armatures,watchesetc.,which
cannotbeeasilycleanedbyothermethods.

11. (7) SONAR
•SONARisatechniquewhichstandsforSound
NavigationandRanging.
•Itusesultrasonicsforthedetectionandidentification
ofunderwaterobjects.
•Themethodconsistsofsendingapowerfulbeamof
ultrasonicsinthesuspecteddirectioninwater.
•Bynotingthetimeintervalbetweentheemissionand
receiptofbeamafterreflection,thedistanceofthe
objectcanbeeasilycalculated.
•Thechangeinfrequencyoftheechosignalduetothe
Doppereffecthelpstodeterminethevelocityofthe
bodyanditsdirection.
11

12. •Measuringthetimeinterval(t)betweenthetransmitted
pulsesandthereceivedpulse,
•thedistancebetweenthetransmitterandtheremote
objectisdeterminedusingtheformula.,wherevisthe
velocityofsoundinseawater.
•Thesameprincipleisusedtofindthedepthofthesea.2
tv
d
12
1.Sonar is used in the location of shipwrecks and
submarines on the bottom of the sea.
2.It is used for fish-finding application .
3.It is used for seismic survey.
Applications of SONAR

13. Applications of Ultrasonics in Medicine
(1)Diagnosticsonography
•Medicalsonography(ultrasonography)isanultrasound-
baseddiagnosticmedicalimagingtechniqueusedto
visualizemuscles,tendons,andmanyinternalorgans,
theirsize,structureandanypathologicallesions.
13
Obstetric ultrasoundis primarily used to:
•Date the pregnancy
•Check the location of the placenta
•Check for the number of fetuses
•Check for physical abnormities
•Check the sex of the baby
•Check for fetal movement, breathing, and
heartbeat.

14. (2)Ultrasound therapeutic applications
• Morepowerultrasoundsourcesmaybeusedtocleanteethindental
hygieneorgeneratelocalheatinginbiologicaltissue,e.g.in
occupationaltherapy,physicaltherapyandcancertreatment.
• Extracorporealshockwavelithotripsyusesapowerfulfocused
ultrasoundsourcetobreakupkidneystones.
• WecanalsouseitinUltrasonicbloodFlowmeter
14

15. Ultrasound in research
•Scientistsoftenuseinresearch,forinstanttobreak
uphighmolecularweightpolymers,thuscreating
newplasticmaterials.
•Indeed,ultrasoundalsomakesitpossibleto
determinethemolecularweightofliquidpolymers,
andtoconductotherformsofinvestigationonthe
physicalpropertiesofmaterials.
•Ultrasoniccanalsospeedupcertainchemical
reactions.Henceithasgainedapplicationin
agriculture,thatseedssubjectedtoultrasoundmay
germinatemorerapidlyandproducehigheryields.
15