Air Coupled Ultrasonic Imaging For Non-Destructive Inspection

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/