Air Coupled Ultrasonic ImagingFor Non-Destructive Inspection
GTL UltrasonicsDavid LaveryMario MalavéAndrew Ray
Final Design ReportApril 23, 2009
Problem Overview Design AlternativesChosen Design DetailMarket AnalysisTransducer PerformanceCircuitry PerformanceSoftware PerformanceFinal Design SpecificationsUnresolved ProblemsProbable SolutionsTeam Performance Review
Air-Coupled Ultrasonics• Device for non-destructive inspection of
materials• Using novel polymer foam transducer• Incorporate new transducer material into
device to improve performance
Objectives• Develop a working ACU-NDI system using a novel
transducer material– Complete
• Reduce Cost– Complete
• Increase Efficiency– Partially Complete
• Mobile System– Incomplete
Unforeseen Obstacles• Electromagnetic Interference
– Overcome using circuit timing
• Poorly Conductive Transducer Surface– Overcome using compression contacts
• Highly Directional Signal– Overcome at cost of mobility
• High Impedance Between Air and Imaged Objects– Through Transmission Abandoned– Pulse-Echo Setup Used
Design AlternativesCylindrical Housing
•Portability
•Limited Circuitry Space•Poor Electrical Connections
Design AlternativesPlate Mounted
• Portability• Electrical Connection Issue
Resolved
• Poor Stability• Highly Variable Performance
Chosen Design•Best Performance
•Marginal Portability
•Expandable Circuitry
Design Tradeoffs• Excess Wire Length versus Expandability
– Potential for unwanted interference– Ease of circuitry redesign/expansion
• Portability versus Stability– Highly directional signal – Difficult to obtain useful data in handheld
operation
7.5mm Plexiglas
Copper Tape
BNC Fitting
Transducer Foam
Parts ListItem # Name Material Description
1 Base Plate 7.5mm Plexiglas Forms base of the transducer device
2 Side Support 7.5mm Plexiglas Supports front plate and back support
3 Back Support 7.5mm Plexiglas Holds BNC connector in place
4 Front Plate 7.5mm Plexiglas Mounting location for transducer and circuitry
5 Compression Plate 7.5mm Plexiglas Compression connection for transducer/electronics
6 BNC Connector Multiple Connects transducer to user output device
7 Copper Tape Copper Ground connection of piezoactive transducer
8 Transducer Polymer Foam Live connection of piezoactive transducer
Transducer Performance• High Quasi-Static Piezoactive coefficient
– 25-700pC/N• Low Acoustic Impedance
– 0.028MRayl
Transducer Performance• 200V 300kHz 100pulse/sec
– Maximum Unimpeded Transmission Distance356.3mm
– Peak-Peak Voltage Received20mV
– Minimal Signal Distortion
Silver Surface Etching• Photolithography Produces Exact
Shapes• Proof of Concept• Not Used for Transducers
Circuitry Alternatives• Amplifier and Band Pass Filter
– Eliminates Background Noise– High Gain– More Complex Circuitry
Circuitry Alternatives• Amplifier(s) Without Filters
– High Gain– Less Complex Circuitry– Noise Amplified With Signal
Performance ComparisonAmplifier Filter - Amplifier
Chosen Circuitry• Single Amplifier
– 35dB Gain– Less Complex - Fewer Failures– Fewer Points to Introduce Interference
Amplifier Parts ListItem # Name Description
U1 Op-Amp Analog Devices AD8001 800MHz GBW Operational Amplifier
R1 Resistor 180k Axial Lead Resistor
R2 Resistor 2k Axial Lead Resistor
Conn1 DIP Socket Mounting for Op-Amp to Allow Quick Replacement if Failure
Conn2 Sockets Sockets for Resistor R1 to Allow for Changes to Alter Gain
PCB Proto Board PCB to Mount Components On
Connection Alternatives• Single Adhesive Tape Contact
– Simple to Construct– Prone to Poor Connection– Impossible to Verify Contact
Connection Alternatives• Double Adhesive Tape Contacts
– Simple to Construct– Prone to Poor Connection– Possible to Verify Connection
Connection Alternatives• Double Mechanical Contact
– Complex to Construct– Unlikely to Lose Connection– Possible to Verify Contact
Connection Alternatives• Single Mechanical Contact
– Less Complex to Construct– Unlikely to Lose Connection– Impossible to Verify Contact
Mechanical Connection
Mechanical Connection
Connection Resistance• Mechanical Connections
– 6.3 Ω, 5.8 Ω, 4.5 Ω, 4.9 Ω
• Adhesive Connections– 368K Ω, 630 Ω, ∞ Ω, ∞ Ω
Chosen Connection Design
• Double Mechanical Contact– Ability to Check Connection– Low Connection Resistance– Higher Performance– Greater Reliability
Software Performance
• Wavelet Transform vs. Fourier Transform• Advantages of the Wavelet Transform• Ultrasonic Applications• Analyzing Received Signal
Fourier TransformCross products of changing complex exponentials (varying sinusoids)
Continuous Wavelet TransformCross products of a scaled and shifted wavelet
Wavelet Transform vs. Fourier Transform
Predefined Wavelets
Scaled Wavelet
Generated OutputFourier Transform (Spectrum)
Wavelet Transform (Scalogram)
Advantages of the Wavelet Transform• Detect transients in a signal• Analyze non-stationary signals
– All order statistics of the signal are changing with time• Detect changing statistics even in the presents of noise
– If the noise remains constant throughout the process (stationary noise)
• Scalogram not depended on a windowing– Short-Time Fourier Transform (STFT) uses window to generate a
spectrogram
STFT Example (T=25ms)
STFT Example (T=1000ms)
Wavelet Transform Example 1
Wavelet Transform Example 2
Ultrasonic Applications
• Pass through transducers– Received signal will contain frequency
components that change with time• Transient region detection
– This can be used to characterize different materials
– Due to different impedances of the materials
Analyzing Received SignalLabVIEW Analysis of reflected data • Data extracted from the oscilloscope via Ethernet port• Analyzed with the “Mexican Hat” wavelet (reflection configuration)
Analyzing Received Signal 1
Analyzing Received Signal 2
Results
• Emitting on different surfaces using reflection– Wavelet Analysis showed slight statistical changes– Amplitude changes are present in the ultrasonic
signal• Wavelet transform results can be improved if a
pass through transducer is used
Damping DetectionLabVIEW Analysis of reflected data• Detect amplitude changes with configurable thresholds
Analyzing Received Signal
Final Specifications• Refer to Specs Handout• Key Specifications
– 356.3mm transmissible distance– 7mm flaw detected 10 out of 10 times– 2mm flaw detected 2 out of 10 times
Unresolved Issues• Pass-through capability
– Leads to software issues• Compact mobile system
– As a result of meeting other performance specifications
Probable Solutions• Pass-through
– Increase power to transducer– Identify better material– Circuitry design
• Mobile System– Add internal storage capacity– Create pass-through capability
Market Analysis• Frequently used couplants used for
transmission– Oil, glycerin, and water– Success with air can open a new market of devices
• Possible Device Users– Aviation/Aerospace companies; Boeing, Lockheed
Martin, NASA• NASA Space Shuttle
– Currently uses Laser Dynamic Range Imager (LDRI)
• Only provides superficial data• Air Coupled Ultrasonics (ACU) provides information deeper
than the surface
Updated Parts Cost TablePart Description Quantity Unit Price Price
2'x2' Printed Circuit Board (PCB) 2 $3.45 $6.90 Operational Amplifiers (Op-amp) 3 $1.25 $3.75 Resistor 10 $0.90 $9.00 Capacitor 5 $0.95 $4.75 BNC Connectors 4 $5.00 $20.00 200mm x 200mm Plexiglas Sheet 1 $10.00 $10.00 Cellular Polypropylene Foam (1m) 1 $15.00 $15.00 DC Power Supply (400 W) 1 $100.00 $100.00 Cable (10 ft BNC) 1 $20.00 $20.00 Mounting Hardware Kit 1 $20.00 $20.00 LabVIEW Software (Student Version) 1 $80.00 $80.00 Project Total $289.40
Cost Analysis• 60 Engineering hour for each group member
– $50/hr give a cost of $9000 in labor• 21.7% profit at a sales price of 2,500 ($541 per unit sold)
Team Performance• Deviations from Schedule
– Etching Research– Transducer Construction– Circuit Design
• Obstacles to Achievement– Lower Power Transducer– Surface Reflection Used
Major Deviations
Works Cited• http://www.mathworks.com• http://www.conceptualwavelets.com/
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