Section 2: Physics of Ultrasound

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Absolute: The standard reference sound pressure in air or other gases is 20 µPa, which is usually considered the threshold <strong>of</strong> human hearing (at 1 kHz). Actual Sound pressure → ↖ Standard reference pressure 20 μMpa Absolute: Sound pressure level in dB as a ratio to standard reference in logarithmic scale. 76db= 20log(P/20 μPa) Log(P/20 μPa)=3.8dB P= 10 3.8 x 20 μPa =126191 μPa http://www.ncvs.org/ncvs/tutorials/voiceprod/equation/chapter9/index.html
Exercise: Find the absolute sound level in μPa for the following measurement <strong>of</strong> air traffic noise.
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Section 2: Physics of Ultrasound
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2.0: Ultrasound Formula http://www.
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Ultrasonic Formula
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2.1: Wave Propagation Ultrasonic te
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Acoustic Spectrum
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Acoustic Wave - Node and Anti-Node
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http://hyperphysics.phy-astr.gsu.ed
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2.2: Modes of Sound Wave Propagatio
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Longitudinal and shear waves
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Longitudinal and shear waves
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2.2.3 Longitudinal Wave Also Knows
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Longitudinal wave: Longitudinal wav
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2.2.4 Shear waves (S-Waves) In air,
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Shear waves
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Q10: For a shear wave travelling fr
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Rayleigh waves are a type of surfac
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Q29: The longitudinal wave incident
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The major axis of the ellipse is pe
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Surface wave
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Surface wave has the ability to fol
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Surface wave - One wavelength deep
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Love Wave http://web.ics.purdue.edu
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Other Reading: Rayleigh Waves Surfa
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Q110: What kind of wave mode travel
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2.2.6 Lamb Wave: Lamb waves propaga
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Types of Wave New! • Plate wave-
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Plate or Lamb waves are similar to
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With Lamb waves, a number of modes
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Symmetrical = extensional mode Asym
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Symmetrical = extensional mode
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The form is determined by whether t
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Q1: The wave mode that has multiple
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Dispersion refers to the fact that
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Thickness Limitation: One can not g
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Spring model- A mass on a spring ha
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In terms of the spring model, Hooke
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Elastic Model / Longitudinal Wave
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Elastic Model / Shear Wave
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The Speed of Sound Hooke's Law, whe
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What properties of material affect
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Where V is the speed of sound, C is
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Q50: The principle attributes that
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E/N/G
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Examples of approximate compression
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Shear Wave Velocity: V S The veloci
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The applet below shows a longitudin
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http://www.ndt-ed.org/EducationReso
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Java don’t work? http://jingyan.b
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Java don’t work? http://jingyan.b
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As can be noted by the equation, a
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The two velocities of sound are lin
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Sensitivity and resolution are two
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2.5.2 Grain Size & Frequency Select
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Since more things in a material are
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Detectability variable: • pulse l
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Q7: When a material grain size is o
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Pulse Length: A sound pulse traveli
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Determining cross sectional area us
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Pulse volume rule-of-thumb: Competi
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When sound travels through a medium
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Scattering: Grain Size and Wave Fre
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Spreading/ Scattering / adsorption
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The units of the attenuation value
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Attenuation can be determined by ev
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A o Ut A
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2.6.3 Frequency selection There is
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Q94: In general, which of the follo
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Q7: When the material grain size is
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Transmission & Reflection Animation
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The following applet can be used to
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Reflection/Transmission Energy as a
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2.8: Reflection and Transmission Co
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Since the amount of reflected energ
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Note that the reflection and transm
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If reflection and transmission at i
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Incident Wave other than Normal? -
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Further Reading (Olympus Technical
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Further Reading: Reflection & Trans
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2.9: Refraction and Snell's Law
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V s1 Only If this medium support sh
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http://www.ni.com/white-paper/3368/
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Note that in the diagram, there is
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Snell Law
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Snell Law
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Example: Snell’s Law L-wave and S
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Snell Law: First critical angle
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Q155 Which of the following can occ
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Q: When angle beam contact testing
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Snell Law: http://techcorr.com/serv
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More on Snell Law Like light, when
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http://www.ndtcalc.com/calculators.
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Mode Conversion http://www.ndt-ed.o
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Snell's Law holds true for shear wa
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In the applet below, the shear (tra
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Creep wave
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Beyond the first critical angle, on
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Note that the applet defaults to co
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Offset of Normal probe above circul
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Refraction and mode conversion at n
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Q118: At the water-steel interface,
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Q72. In a water immersion test, ult
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Q53. The term used to determined th
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The absolute noise level and the ab
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Sound Volume: Area x pulse length M
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Acoustic Volume: w x w y ∆t
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Determining cross sectional area us
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4. Decreases in materials with high
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Pulse Length Affect Resolution
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Transducer cut-out http://ichun-che
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UT Transducer
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UT Transducer- Surface creep wave t
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UT Transducer
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When the origins of the two interac
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However, as stated previously, soun
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Q5: Acoustic pressure along the bea
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Of course, there are more than two
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2.12.3 Fresnel & Fraunhofer Zone Fr
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The Near Field (Fresnel)- Wave Inte
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Fresnel / Fraunhofer Zone
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Near field (near zone) or Fresnel z
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Near/ Far Fields
Page 263 and 264: where D is the diameter of the tran
Page 265 and 266: Fresnel & Fraunhofer Zone 10dB, K-0
Page 267 and 268: Fresnel & Fraunhofer Zone
Page 269 and 270: Q: Where does beam divergence occur
Page 271 and 272: Q160 Beam divergence is a function
Page 273 and 274: Dead Zone - The interval following
Page 275 and 276: Dead Zone -The initial pulse is a t
Page 277 and 278: Dead Zone http://www.ni.com/white-p
Page 279 and 280: Q36: To eliminate the decrease in s
Page 281 and 282: Large Reflector Inverse Rule
Page 283: Small Reflector Inverse Square Rule
Page 287 and 288: Fundamental Frequency The lowest re
Page 289 and 290: Transducers Piezoelectric Thickness
Page 291 and 292: Application Case#1: The specimen's
Page 293 and 294: Application Case#2: Electromagnetic
Page 295 and 296: Q7: The resonance frequency of 2cm
Page 297 and 298: dB is a measures of ratio of 2 valu
Page 299 and 300: The Decibel The equation used to de
Page 301 and 302: Why is the dB unit used? Use of dB
Page 303 and 304: Use of the dB in Sound Measurements
Page 305 and 306: Since transducers and microphones p
Page 307 and 308: Sound Levels- Relative
Page 309 and 310: Practice:
Page 311: “Absolute" Sound Levels Whenever
Page 316 and 317: Exercise: ANSWER Find the absolute
Page 318 and 319: Relative dB: Example Calculation 1
Page 320 and 321: Example Calculation 3 Consider the
Page 322 and 323: 2.16 Practice Makes Perfect
Page 324 and 325: Q104: If an ultrasonic wave is tran
Page 326 and 327: 学习总是开心事
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Section 2: Physics of Ultrasound

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