Section 2: Physics of Ultrasound

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From this table it can be seen that ratios from one up to ten billion can be represented with a single or double digit number. Ease to work with numbers was particularly important in the days before the advent of the calculator or computer. The focus of this discussion is on using the dB in measuring sound levels, but it is also widely used when measuring power, pressure, voltage and a number of other things.
Use of the dB in Sound Measurements Sound intensity is defined as the sound power per unit area perpendicular to the wave. Units are typically in watts/m2 or watts/cm2. For sound intensity, the dB equation becomes: However, the power or intensity of sound is generally not measured directly. Since sound consists of pressure waves, one of the easiest ways to quantify sound is to measure variations in pressure (i.e. the amplitude of the pressure wave). When making ultrasound measurements, a transducer is used, which is basically a small microphone. Transducers like most other microphones produced a voltage that is approximately proportionally to the sound pressure (P). The power carried by a traveling wave is proportional to the square of the amplitude. Therefore, the equation used to quantify a difference in sound intensity based on a measured difference in sound pressure becomes:
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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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Page 259 and 260: Near field (near zone) or Fresnel z
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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: Why is the dB unit used? Use of dB
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
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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
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Section 2: Physics of Ultrasound

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