Download - Advanced Instrumentation for Acousto-Ultrasonic Based Structural Health Monitoring · Acousto-Ultrasonic Based Structural Health Monitoring Joel Smithard, Steve Galea, ... • 4 Optical

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Advanced Instrumentation for Acousto-Ultrasonic Based Structural

Health Monitoring

Joel Smithard, Steve Galea,

Stephen van der Velden, Ian Powlesland,

Cedric Rosalie, and Nik Rajic

Aerospace Division

UNCLASSIFIED – Approved For Public Release

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Outline

▪ AUSAM+ overview

▪ Hardware

▪ Firmware and Software

▪ Operational Modes

▪ First-Of-Class Assessment

▪ System Demonstration

▪ MatLab Scripting

▪ Array of 16 sensing elements

▪ Acousto-Ultrasonic ‘fingerprint’

▪ Wrap-up


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AUSAM overview

115 x 65 x 20 mm; size comparison to IPhone

• Instrument Bandwidth 50 kHz – 5 MHz for actuation and response

– High order Lamb waves provide a richer source of AU information

• Interrogate using PZTs and FBGs


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AUSAM Hardware ▪ USB 2.0: power and communications

▪ High Voltage PZT Amplifier

▪ 50 KHz to 5 MHz frequency

▪ Drive on any channel(s)

▪ Receive on any channel(s)

▪ 1 to 1024 synchronous averages

▪ External isolated trigger in/out

▪ External Temperature and Strain measurements

▪ Connect up to 62 units

Drive:

• Maximum 200Vp-p drive pulse• Arbitrary function generator• Drive capacitive loads up to 10nF

• Monitoring of drive load voltage and current

Receiver:

• 4 independent low noise receiver channels• 4 independent optical PIN diode channels• 4 Optical DC power measurements

• Independent gain control from -4.5dB to 55dB


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AUSAM Firmware and SoftwareCan replace

with Raspberry Pi; connect over

wireless

Can replace with Python; wireless to

Raspberry Pi


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AUSAM+ MatLab Object


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%%Setup

ausam_master = AusamModel( 'bitfile', ‘..\aushmiv.bit', 'serial', '1606000DLL');

ausam_slave1 = AusamModel(……

ausam_slave2 = AusamModel(……

…….

ausam_slave1.Hardware.Unit(2).Leds='hhhhhhhh'; %LEDs driven by hardware function, eg LED1=trigger

ausam_slave1.Hardware.Unit(2).TriggerControl = 11363; % one wire mode;

…….

% set channel gains (dB)

gain = 43.5;

ausam_master.Hardware.Unit(2).Channel(1).Gain = gain;

ausam_master.Hardware.Unit(2).Channel(2).Gain = gain;

…….

skew = 11.51e-3;

ausam_master.Hardware.Unit(2).Channel(1).Skew = skew;

ausam_master.Hardware.Unit(2).Channel(2).Skew = skew;

-----

AUSAM+ Scripting (setup)


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%%Trigger done get/use the data

ausam_master.Hardware.Unit(2).Channel(1).RequestADC;

ausam_master.Hardware.Unit(2).Channel(2).RequestADC;

…….

% Data has now been moved from actual hardware to the MatLab object.

PVDF_Array_element_16 = ausam_master.Hardware.Unit(2).Channel(4).Data;

PVDF_Array_element_15 = ausam_master.Hardware.Unit(2).Channel(3).Data;

……..

PVDF_Whole_Array = [PVDF_Array_element_1; PVDF_Array_element_2; ...

figure(5),imagesc(fliplr(PVDF_Whole_Array'))

% Plot all channels

figure(1)

subplot(2,2,1)

plot(ausam_master.Hardware.Unit(2).Channel(1).Data)

subplot(2,2,2)

……

%Do some magic with it☺

factor = ((2/2^12)/(10^(ausam_master.Hardware.Unit(2).Channel(4).Gain/20))); %gets ADC counts to volts

[HT] = AUSAM_GenerateHilbertTransform(ausam_master.Hardware.Unit(2).Channel(4).DataCounts*factor);

…….

AUSAM+ Scripting (get the data)


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The AUSAM+ operates in three typical modes.

1. Generating an excitation drive signal

2. Performing an EM impedance sweep

3. Active interrogation• pulse-echo

• pitch-catch

The first two modes focus on acquiring large excitation signals while the active interrogation modes focus on acquiring small AU responses.

Operational Modes


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▪ Acquisition system

▪ Drive amplifier

▪ Noise/Crosstalk

▪ ElectroMechanical (EM) Impedance

▪ Photodiodes

▪ Auxiliary functions

▪ User functionality


First-Of-Class Testing (FOCT)

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Drive amplifier (FOCT)


Frequency sweep using a five cycle Hanning windowed

sinusoidal signal, at maximum amplitude, applied to a 1 nF

precision capacitor

Improvement

possible; not

limited by

hardware

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Drive amplifier (FOCT)

The PSD of the AU response of a

PZT element on an aluminium

plate, in a pitch-catch

configuration, when the actuator

element is excited at 500 kHz

1.2 MHz 100 Vp

excitation signal

applied to a 1 nF

capacitor

PSD of 500kHz response AUSAM and LeCroy

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Noise/Crosstalk (FOCT)

Cha has 1 nF capacitor using

100 mm long twisted pair wire,

other channels open circuit

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ElectroMechanical (EM) Impedance (FOCT)


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3 mm thick aluminium plate with 10 and 6.3 mm diameter PZT discs.

All the data collected were from a single Hanning windowed sinusoidal drive pulse (ie. no averaging was applied)

PZT System Demonstration


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Impedance magnitude

10mm element


6.3mm element

Reduction indicating good bond

Reduction indicating good bond

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150 kHz pulse-echo and pitch-catch

Drive Pulse Unfiltered Filtered

pulse-echo

10mm

pitch-catch

6.3mm

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1.5 MHz pulse-echo and pitch-catch

Drive Pulse Unfiltered Filtered

pitch-catch

6.3mm

pulse-echo

10mm

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4 AUSAM+ units: 16 Element Sensor


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AUSAM+ Sensitivity vs LeCroy DSO

LeCroy

AUSAM+


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16 Element Sensor Array: Wave Front


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‘Fingerprint’ Ball Impact 100mm From Array (2D FFT)

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frequency-thickness (MHz-mm)

wavenum

ber

(rad/m

)

A0

SH0

S0

A1

S1

S2

0 0.5 1 1.5 2 2.5 3 3.5 4 4.50

500

1000

1500

2000

‘Fingerprint’ Active Acousto-Ultrasonic Drive


Acousto-Ultrasonic sweeps 0.1–2.5MHz, 100kHz steps

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• A new small, robust, flexible instrument for Acousto-Ultrasonic interrogation.

• Excite and monitor Lamb waves at frequencies up to 5 MHz.

• Sinusoidal excitations of 200 Vp-p in the frequency range 200 kHz to 1.5 MHz while providing usable drive strength at frequencies 50-200kHz & 1.5-5 MHz.

• The device was shown to have a relatively low noise floor and low electrical crosstalk between acquisition channels.

• The performance of an in-built EM Impedance capability compared well to that of a commercial Impedance Analyser.

• The module provides the ability to undertake strain and temperature measurements.

• The compact AUSAM+ is small and light enough to find SHM application in a vast array of situations.

• The Matlab hardware object provides enormous versatility allowing the user to easily interface with the hardware functionality thus permitting the development of customised in-house GUIs for a wide variety of activities and applications.


Wrap-up

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Questions

[email protected]