Acoustic Characterization of Materials

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Acoustic Characterization of Materials
Bernhard R. Tittmann - Group Leaderbrt4_at_psu.edu

• CAV Spring Workshop 2007
• May 8th and 9th

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Acoustic Characterization of Materials Group

• Faculty Members
• Bernhard R. Tittmann
• Joseph L. Rose
• Clifford Lissenden
• Al Segall
• Lawrence Friedman
• Joseph Cusumano
• Francesco Costanzo

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Presentation Overview

• Continuous, Noninvasive Liquid Level Measurement
• Noninvasive Water Pressure Measurement
• Aluminum Nitride High Temperature Transducer

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Continuous, Noninvasive Liquid Level Measurement

• Manton J. Guers, mjg244_at_psu.edu
• Daniel R. Zilinskis, drz115_at_psu.edu
• Dr. Bernhard R. Tittmann, brt4_at_psu.edu

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Current Level Sensing Technologies

• Predominately internally mounted devices
• Point
• Float switches, tuning forks
• Continuous
• Radar, ultrasonic beam
• Rods (floats, capacitance)
• Problem invasive
• Pressure vessel penetration
• External devices
• Ultrasonic sensor at a point pass/fail
• Need network of multiple sensors for a relatively
  continuous measurement
• Problem wiring and electronics

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Objectives

• Develop a continuous, noninvasive technique for
  liquid level measurement
• Robust design
• Usable on as many systems as possible
• Ability to measure any liquid through any
  thickness tank wall
• Simple design
• Minimal number of transducers, wires, and data
  processing
• Single channel operation

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Basic Principles

• Ultrasonic wave propagation is influenced by
  material properties
• At an interface, the reflection and transmission
  of ultrasonic waves is influenced by the acoustic
  impedance of each material
• Then the reflection factor is
• A change in the reflection factor produces a
  measurable change in the ultrasonic signal
• (i.e. distinguish between air and water)

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Basic Principles

• The effective impedance is proportional to how
  much of the ultrasonic beam is incident on air
  vs. water
• For a rectangular transducer, the amplitude of a
  particular reflection can be calculated with the
  equation

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Basic Principles
h

• For a circular transducer, the amplitude of a
  particular reflection can be calculated with the
  equations

r
for
for
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Results (1) Single, Round Transducer

• One inch round transducer, 250 kHz
• Observed relationship between water level and
  beam area close to theoretical prediction
• Center of transducer is more sensitive then edges

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Results (2) Array of Transducers

• 2 Transducers in Parallel (single channel
  acquisition)
• Gap in coverage
• Transducers must be well matched
• Poor results with 4 transducers

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Solution!

• Build a large piezoelectric strip transducer
• PVDF piezoelectric, copper tape electrodes
• Gel couplant

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Results (3) Rectangular PVDF Strip

• To match theory with experimental results, n
  equals of reflection (i.e. n2 for analyzing
  2nd reflection)
• The relation of liquid level to reflection
  amplitude is linear for a rectangular transducer

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Summary

• Homemade PVDF strip worked very well
• Rectangular geometry provides linear response
• Noninvasive
• Continuous
• Additional possibilities
• PZT
• AlN

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Noninvasive Water Pressure Measurement

• Manton J. Guers, mjg244_at_psu.edu
• Christopher J. Fontana, cjf173_at_psu.edu
• Dr. Bernhard R. Tittmann, brt4_at_psu.edu

Bechtel-Bettis
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Current Pressure Sensing Technology

• Mechanical gages, quartz resonators, bellows, and
  diaphragm based devices require contact with
  pressurized media (inside the pressure vessel)
• Many problems associated with penetrations into a
  pressure vessel
• Cost
• Leaks
• Inspection
• Possible obstruction

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Objectives

• Non-invasively measure water pressure
• Consider how to thermally insulate conventional
  transducer (high temperature operation)
• Investigate temperature effects and compensation

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Basic Principles

• As before, ultrasonic wave propagation is
  influenced by material properties
• In the case of measuring pressure, a change in
  impedance is caused by changes in operating
  pressure
• Increasing pressure, increases both density and
  acoustic velocity
• Increasing the impedance, decreases the
  reflection factor (higher pressure lower signal
  response)

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Basic Principles

• However, density and acoustic velocity are also
  influenced by temperature
• Similar order of magnitude temperature changes
  can corrupt the pressure measurement

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Bench Top Experiments

• Filled chamber 2/3 with water
• Control pressure with compressed air supply
• 0 to 1000 psi

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Bench Top Experiment Results (1)

• Technique works well, if data collected over
  short time intervals
• Minimal temperature influence
• Approximately 6 error theory vs. experiment

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Bench Top Experiment Results (2)

• Over long intervals the signal shifts
• Time (velocity) and amplitude (impedance)

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Heating Test Results (3)

• Used a heat gun to warm up vessel wall
• Thermal gradient (room temp to thermocouple)

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Thermal Protection for Conventional Transducer

• As part of this project, we also look at
  protecting a conventional transducer from high
  operating temperatures
• Metal buffer longer lower temperature, but get
  interference effects in ultrasonic signal

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Possible Calibration Scheme

• Use of buffer rod provides a second interface
  reflection to work with (more information)
• Ideally, buffer-vessel reflection provides a
  temperature measurement (heat transfer solution)

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Summary

• Change is ultrasonic signal over 0-1000 psi can
  be measured
• Measurement is very sensitive to temperature
• Current effort coupled-field FEM to
  parametrically investigate pressure and
  temperature

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Aluminum Nitride - High Temperature Transducer

• David A. Parks, dxp261_at_psu.edu
• Dr. Bernhard R. Tittmann, brt4_at_psu.edu

Bechtel-Bettis
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Objectives

• Desire to perform the pressure and level
  measurements at high operating temperatures
• Conventional transducer are not acceptable

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Piezoelectric Transducer Concept

• Electric field converted to stress and
  vise-versa (solid media)
• seE
• e piezoelectric stress constant
• Stress is coupled to the solid
• s2T12 s1
• T transmission coefficient

pulse
scope
u1
E
u2
defect
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Typical Material Utilized

• Single Crystal
• periodic arrangement of atoms is unbroken
  throughout entire solid
• certain structures have separated centers of
  charge hence a dipole moment
• Poled Poly-crystal
• Application of an electric field at elevated
  temperatures causes dipoles within the many
  domains to develop a preferential orientation

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Phase Transitions Destroy Piezoelectricity

• As temperature increases the Gibbs free energy is
  dominated by the entropy
• Results in phase transitions to more symmetric
  crystal structures
• Symmetry eliminates separation between charge
  centers
• Aluminum Nitride is stable as a hexagonal
  structure over a large temperature range

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Two Prototypes

• Prototype 1 obtained first

• Prototype 2 obtained after careful consideration

5 mm
14 X14 mm
2 mm
0.45 mm
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Preliminary Results Prototype 1

• Signals Remained Strong up to 300 C
• One reflection discernable above noise in a 50 mm
  steel block
• Complaint evaporated at 350 C
• Potential replacement couplants include
• Liquid metals with extremely high boiling
  temperature 2000 C Ga, In, or Fr

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Broadband vs. Tone-Burst

• Steady state response and resonance can be used
  to ones advantage to obtain large amplitudes

• Pulse excitation causes transient response to
  dictate amplitudes of oscillation

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Axial Resolution

• Resolution limited by pulse duration
• Prototype 1 elements required tone burst
  excitation (reflection illustrated at right)
• In this case dgt15.5mm
• Broadband pulse is desirable therefore we must
  maximize transient response
• Output
• Attenuation within specimen and Beam spread

Sample speed of sound c
d
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Beam Control

• Near Field
• Angle of Divergence
• Attenuation proportional to f4 is a minor effect
  in Rayleigh region lgtgtd

a
N
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Transient Response Analysis

• Solving the equation of motion for the element
  via Laplace transform readily gives the truncated
  result
• Particular element thickness gives maximal output
• Also creates a focused beam
• High frequency element and thus attenuation
  effects are somewhat greater but still minor

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Prototype 2 Elements RT
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Summary

• Transient response has been maximized and
  broadband pulses excitation works
• The element rings for longer than desirable and
  this can be eliminated via a backing layer or
  multiple elements out of phase
• High temperature coupling will be investigated
  Indium is a likely prospect

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References

• J. Krautkramer, H. Krautkramer Ultrasonic
  Testing of Materials Springer Verlag 1990
• Emmanuel P. Padadakis Bell Telephone
  Laboratories Ultrasonic Attenuation Caused by
  Scattering in Polycrystalline Metals November 30
  1964 http//scitation.aip.org/getpdf/servlet/GetP
  DFServlet?filetypepdfidJASMAN000037000004000711
  000001idtypecvipsprognormal 2006
• K. Goebbels, S. Hirsekorn, H. Willems The Use of
  Ultrasound in the Determination of Microstructure
  a Review http//ieeexplore.ieee.org/iel5/10284/32
  717/01535361.pdf?arnumber1535361 
• Victor Giugiutiu, Sergey E. Lyshesvski
  Micromechatronics CRC Press 2004
• Bray, D.E. 2002. Ultrasonic stress measurement
  and material characterization in pressure
  vessels, piping, and welds. ASME PVP Conference
  Proceedings, 124 326-335.
• Greenwood, M.S. J.A. Bamberger. 2004.
  Self-calibrating sensor for measuring density
  through stainless steel pipeline wall. ASME
  Journal of Fluids Engineering, 126189-192.
• Kinsler, L. et al. 2000. Fundamentals of
  Acoustics 4th ed. Wiley Sons.
• Lin, S. and H. Zhang. 2004. A new method for
  nondestructive measuring pressure based on the
  Rayleigh wave. Proceedings of IEEE
  Instrumentation and Measurement Technology
  Conference, 2332-2336.
• Rose, J.L. 1999. Ultrasonic Waves in Solid Media.
  Cambridge Press.
• Shull, P. Ed. 2002. Nondestructive Evaluation.
  Marcel Decker, Inc.
• Tittmann, B.R. 2005. Sonic pressure vessel
  sensor. ASME J of Pressure Vessels and Piping,
  127226- 229.

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