Section 2: Physics of Ultrasound

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The units of the attenuation value in Nepers per meter (Np/m) can be converted to decibels/length by dividing by 0.1151. Decibels is a more common unit when relating the amplitudes of two signals.
Attenuation is generally proportional to the square of sound frequency. Quoted values of attenuation are often given for a single frequency, or an attenuation value averaged over many frequencies may be given. Also, the actual value of the attenuation coefficient for a given material is highly dependent on the way in which the material was manufactured. Thus, quoted values of attenuation only give a rough indication of the attenuation and should not be automatically trusted. Generally, a reliable value of attenuation can only be obtained by determining the attenuation experimentally for the particular material being used. Attenuation ∝ Frequency (f ) 2
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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
Page 79 and 80: Elastic Model / Shear Wave
Page 81 and 82: The Speed of Sound Hooke's Law, whe
Page 83 and 84: What properties of material affect
Page 85 and 86: Where V is the speed of sound, C is
Page 87 and 88: Q50: The principle attributes that
Page 89 and 90: E/N/G
Page 91 and 92: Examples of approximate compression
Page 93 and 94: Shear Wave Velocity: V S The veloci
Page 95 and 96: The applet below shows a longitudin
Page 97 and 98: http://www.ndt-ed.org/EducationReso
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Page 103 and 104: As can be noted by the equation, a
Page 105 and 106: The two velocities of sound are lin
Page 107 and 108: Sensitivity and resolution are two
Page 109 and 110: 2.5.2 Grain Size & Frequency Select
Page 111 and 112: Since more things in a material are
Page 113 and 114: Detectability variable: • pulse l
Page 115 and 116: Q7: When a material grain size is o
Page 117: Pulse Length: A sound pulse traveli
Page 120 and 121: Determining cross sectional area us
Page 122 and 123: Pulse volume rule-of-thumb: Competi
Page 124 and 125: When sound travels through a medium
Page 126 and 127: Scattering: Grain Size and Wave Fre
Page 128 and 129: Spreading/ Scattering / adsorption
Page 132 and 133: Attenuation can be determined by ev
Page 134 and 135: A o Ut A
Page 137 and 138: 2.6.3 Frequency selection There is
Page 139 and 140: Q94: In general, which of the follo
Page 141 and 142: Q7: When the material grain size is
Page 143 and 144: Transmission & Reflection Animation
Page 145 and 146: The following applet can be used to
Page 147 and 148: Reflection/Transmission Energy as a
Page 149 and 150: 2.8: Reflection and Transmission Co
Page 151 and 152: Since the amount of reflected energ
Page 153 and 154: Note that the reflection and transm
Page 155 and 156: If reflection and transmission at i
Page 157 and 158: Incident Wave other than Normal? -
Page 159 and 160: Further Reading (Olympus Technical
Page 161 and 162: Further Reading: Reflection & Trans
Page 163 and 164: 2.9: Refraction and Snell's Law
Page 165: V s1 Only If this medium support sh
Page 168 and 169: http://www.ni.com/white-paper/3368/
Page 172 and 173: Note that in the diagram, there is
Page 174 and 175: Snell Law
Page 176 and 177: Snell Law
Page 178 and 179: 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
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where D is the diameter of the tran
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Fresnel & Fraunhofer Zone 10dB, K-0
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Fresnel & Fraunhofer Zone
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Q: Where does beam divergence occur
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Q160 Beam divergence is a function
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Dead Zone - The interval following
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Dead Zone -The initial pulse is a t
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Dead Zone http://www.ni.com/white-p
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Q36: To eliminate the decrease in s
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Large Reflector Inverse Rule
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Small Reflector Inverse Square Rule
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Fundamental Frequency The lowest re
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Transducers Piezoelectric Thickness
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Application Case#1: The specimen's
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Application Case#2: Electromagnetic
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Q7: The resonance frequency of 2cm
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dB is a measures of ratio of 2 valu
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The Decibel The equation used to de
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Why is the dB unit used? Use of dB
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Use of the dB in Sound Measurements
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Since transducers and microphones p
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Sound Levels- Relative
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Practice:
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“Absolute" Sound Levels Whenever
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Absolute: The standard reference so
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Exercise: ANSWER Find the absolute
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Relative dB: Example Calculation 1
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Example Calculation 3 Consider the
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2.16 Practice Makes Perfect
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Q104: If an ultrasonic wave is tran
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学习总是开心事
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Section 2: Physics of Ultrasound

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