Sensing Systems and Signal Processing
Dr Richard
Module Overview
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What will we cover?
Lecture Material
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Overview info:
• Who we are and how to contact us
• Over view of Module content
• Assessment criteria and format of the exam
Who we are
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Dr Richard 53 (CW 2, week 7)
A33a (week 11)
A47 content
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Sensing Systems and Signal Processing
This module covers a selection of topics where information is acquired from sensors and subsequently electronically processed.
Applications:
• acoustic
• non-destructive evaluation
• medical and bio-photonics.
Learning outcomes:
By the end of this module, students should be able to:
• Describe the operating principles of a variety of practical electronic sensors.
• Select from options when designing an overall sensing system
• Describe signal processing techniques typically employed with sensors.
Module content
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Timetable Week
Teachin g Week
Week Beginning
Teaching Activities / Teaching Topics
Assessment Release
Assessment Submission
L1 Module Introduction, NDE application, introduction to sensing, introduction to Matlab and formative exercise
Formative Matlab exercise
L2 Time domain and frequency domain signals
L3 Introduction to sensors
CW1 Matlab exercises.
Formative assessment optional submission Monday 9am
L4 Sensing Temperature
L5 Sensing light
L6 Signal conditioning and acquisition,
L7 CW 2 introduction
CW2 design exercise
CW1 submission, Thursday 3pm
L8 Bio-imaging applications, ultrasound applications
L9 Sensing Displacement
L10 Sensing Force
CW2 submission, Thursday 3pm.
11/04/22 – 25/04/22
L11 Sensing Chemicals, MRI
L12 Module Review, Revision, Example exam Q’s and solutions
Assessment
16/05/22-30/05/22
Assessment
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This 10 credit module is assessed by examination and coursework:
• Coursework 50%
• Examination 50%
Examination Information
• 2 hour exam
Example exam papers are on Moodle. Last year’s is the correct format as previous years were different.
Assessment
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Formative Exercise: Matlab exercises
0% of module assessment:
Date provided to students: week 20 (wb. 31/01/2022) Submission date: week 22 (Monday 14/02/2022, 9am) Method of submission: via Moodle
Coursework Part 1: Matlab exercises
25% of module assessment:
Date provided to students: week 22 (wb. 14/02/2022) Submission date: week 26 (Thursday 14/03/2022,3pm) Method of submission: via Moodle
Coursework Part 2: Sensing system analysis report
25% of module assessment:
Date provided to students: week 26 (wb. 14/03/2022) Submission date: week 33 (Thursday 04/04/2022, 3pm) Method of submission: via Moodle
More details on the exercises and assessment criteria are given on moodle.
Sensing and signal processing
What do these terms mean?
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what is ‘sensing’? what is ‘signal processing’?
Overview of generic sensing system
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Sensing Unit
Analogue Signal Processing
Sensing System
Display / Utilising information
Signal Processing
Overview of generic sensing system
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Measurands….
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Analogue signals, or continuous time signals, are quantities that vary continuously in time. For example the continuous voltage from a microphone.
Discrete signals, or digital or sampled signals are usually versions of analogue signals that have been sampled at equal instants in time. The process of sampling an analogue signal to form a discrete signal is known as digitisation or analogue to digital conversion. A discrete signal is usually characterised by a sampling frequency and a resolution, or bit depth.
Binary signals are pulse waveforms which exist in only two states, 0 and 1; for example a square wave.
Classes of Signals
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Periodic signals repeat, such as a fixed frequency sine wave which is continuous over all time.
Aperiodic signals have no observable periods but may not be random. Deterministic signals have a structure that when analysed allows one to
predict or determine the future course of the signal.
Random signals have no structure, but they do have properties. They are indeterministic in that the data could have occurred in any order and the signal would not appear to be different.
Stochastic signals combine both deterministic and random components. Most real engineering signals fall into this class because we have the ‘useful’ components of the signal with unwanted electronic noise superimposed.
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Sampling frequency is the number of samples of the signal that
are taken per unit time during the digitisation operation; the units
are samples per second, often expressed as Hz, samples s-1, or Ss-1.
Bit depth is the number of binary bits used to store the discrete signal, typically greater than eight and less than 64.
Signal to noise Ratio SNR is the ratio of the power in the signal to the power of the noise in the system. This tells you how well you will be able to detect your signal.
Accuracy is how close to the measured value is to the true value.
Precision is how close repeated measurements are to each other.
Non Destructive Evaluation (NDE)
Non destructive evaluation (NDE)
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Several terms used in the field e.g. Non destructive testing (NDT), non destructive evaluation (NDE), Non destructive inspection (NDI)
A decent definition is:
“Non destructive testing is the process of inspecting, testing or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system.” ASNT.org visited 06-2018
Encompasses many different techniques:
Magnetic Particle Testing (MT), Liquid Penetrant Testing (PT), Radiographic Testing (RT) Ultrasonic Testing (UT), Electromagnetic Testing (ET), Visual Testing (VT), Acoustic Emission Testing (AE), Guided Wave Testing (GW), Laser Testing Methods (LM), Leak Testing (LT), Magnetic Flux Leakage (MFL), Neutron Radiographic Testing (NR), Thermal/Infrared Testing (IR), Vibration Analysis (VA)
For many different application areas:
Non destructive evaluation (NDE)
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An event that changed an industry : Sioux City Airline disaster
Flight 232 took off from Stapleton airport, Colorado, July 19th 1989
An hour into the flight they ‘lost’ engine 2 and control of the plane.
Engine 2 was the tail mounted engine and when it disintegrated it damaged the 3 hydraulic systems for providing control of the plane – all at the same time – something that ‘shouldn’t’ have been possible.
This left the pilots with no way to control the plane, they ended up using thrust from the remaining engines to steer the plane.
Dropping altitude in a as controlled away as possible to spiral down towards the nearest airport.
https://en.wikipedia.org/wiki/United_Airlines_Flight_232
Non destructive evaluation (NDE)
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The Pilots attempted an emergency landing at Sioux city airport.
As they got the plane close to the runway, the tip of the right wing hit the ground spilling and igniting fuel.
The tail section broke off and the rest of the aircraft bounced along the ground and broke into several pieces.
Amazingly, 185 of the 285 people survived – due to the amazing skills of the pilots.
https://en.wikipedia.org/wiki/United_Airlines_Flight_232
Non destructive evaluation (NDE)
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The safety inspection team looking into the incident determined that the probable cause was the inadequacies in the inspection and quality control procedures in the engine overhaul facility.
This meant that a fatigue crack originating from a previously undetected metallurgical defect was not detected. The original defect was located in a critical area of the stage 1 fan disk.
As the crack grew, eventually it led to the catastrophic disintegration of the disk. As it flew apart the pieces had sufficient energy to breach the protective shroud and cause critical damage to the hydraulic systems on the plane.
Two failures here :
• undetected material defect
• undetected crack in critical location
https://en.wikipedia.org/wiki/United_Airlines_Flight_232
Ultrasound waves
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Ultrasound is a commonly used NDE technique and is used to characterise material and look for defects. Ultrasound is sound waves which have a frequency above 20KHz.
What are waves and how do they propagate?
Waves represent the movement of energy through a medium where there is no net movement of the medium.
If we look at the particle motion below we see that they trace out circles – the wave is moving left to right but the particles on average are in the same place, they only move locally.
https://www.saddleback.edu/faculty/jrepka/notes/waves.html
Ultrasound waves
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To move in circles there are two types of motion required:
• parallel to the direction of energy flow – P or
pressure / primary
• perpendicular to the direction of energy flow –
S or Shear/secondary waves
Combination of these motions gives rise to many types of wave modes.
The most common being bulk and surface waves.
Gases / liquids – don’t support shear modes as the forces between the atoms are too weak. Only get P waves in this case.
https://www.saddleback.edu/faculty/jrepka/notes/waves.html
Spatially Resolved Acoustic Spectroscopy
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Spatially Resolved Acoustic Spectroscopy
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Vsaw = fsig * λgen
Frequency ↓ Velocity
Higher f – Faster v
Lower f – Slower v
Spatially Resolved Acoustic Spectroscopy
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SRAS measures the Surface Acoustic Wave (SAW) velocity, this is the primary contrast mechanism
SAW velocity (typically ~3000ms-1 in metals) is determined by several effects:
• Crystallographic orientation: ±50ms-1 (Al), ±250ms-1 (Ti), ±500ms-1 (steel, Ni)
• Temperature (thermoelastic effect): -1 to -2ms-1 / oC (approx)
• Stress (acoustoelastic effect): -40ms-1/GPa (Al), -10ms-1/GPa (Ti), <-10ms-1/GPa
• Surface roughness
• Porosity/density
• Material variations (i.e. variations in surface coating thickness)
SAW amplitude (attenuation):
• Cracks / defects near the surface
Optical image: reflection of detection laser beam from sample surface • Surface condition, registration marks, obvious scratches etc.
https://www.saddleback.edu/faculty/jrepka/notes/waves.html
SRAS: applications
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What is it used for:
Grain imaging – looking at the shape, size, distributions of grains in metal samples. Orientation imaging – looking for the crystallographic orientation of grains in metal samples Defect detection – finding cracks or pores near the surface of samples
Grain Imaging
Orientation
SRAS: applications : grain imaging
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Example SAW velocity images
Steel Weld section
High resolution
Large Titanium samples
From velocity to orientation
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From Literature
All linked
Measured using SRAS
Material elastic constants
Knowing two - you can determine third
SAW phase velocity
Crystallographic orientation
Orientation information output
Measurement Measurement
Measurement Measuremaetn8t0°
at 100° MeasuremeMnet asurement
at 140° at 40°
Measurement Measurement at 160° at 20°
Measurement at 0°
SRAS: applications : orientation imaging
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Example images and simple how it works
SRAS: applications : Defect detection
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• Sample made by additive manufacturing
• Polished to look at with SRAS
• Optical image shows scratches and pores
• Acoustic image shows velocity and regions of no signal
• Acoustics see surface and sub-surface defects
SRAS optical
SRAS optical (magnified)
SEM surface image
SRAS acoustic
SRAS acoustic (magnified)
XCT subsurface image
SRAS : Block diagram
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Electronics chain
Generation System
Instrument controller
Output Images
Sample and stages
Stage controller
SRAS : Block diagram
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Generation
Laser Controller
Mask and Optics
TTL Trigger out
Light pulse→Absorbed
Local heating→Local thermal expansion launches sound pulse
SRAS : Block diagram
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Electronics chain
Delivery Optics
Collection optics
SRAS : sensing
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What sensing is taking pace in the SRAS instrument?
Obvious ones :
Sensing light – photodiodes for the probe beam Sensing light – for the camera image of the surface Position sensing – for control of the stages
Less obvious ones:
SAW velocity is sensitive to several different effects: Material, Crystallographic orientation, Temperature, Stress... Signal strength also sensitive to the Wave generation efficiency which is sensitive to many factors as well.
We will return to this instrument in the future and look at the details once we have covered the fundamentals to sensing and signal processing.
Formative Exercise Matlab
Formative Exercise
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Formative exercise
Released: today on Moodle https://moodle.nottingham.ac.uk/mod/resource/view.php?id=5110472 Submission : Via Moodle: https://moodle.nottingham.ac.uk/mod/assign/view.php?id=5684639
Monday 14th February 9am
Submission type: Pdf produced by MATLAB publish option. (explained shortly)
Formative Exercise
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Matlab® is available on all uni computers, see:
Software library : https://workspace.nottingham.ac.uk/display/Software/Matlab
“For personal use
The University licence also allows members of staff and students to install Matlab on their personally owned computers.
First create a Mathworks account if you have not already created one:
Staff and PGR;
Taught students (UG and PGT).
The follow the download instructions.”
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For those new to matlab I have added some matlab basics worksheets in a zip file in the following folder
https://moodle.nottingham.ac.uk/mod/folder/view.php?id=5110481
Work through these (you don’t need to do all the tasks to benefit from this) they cover various aspects of using matlab.
Additionally, We will use the second part of the seminar sessions for matlab help, which will give you an opportunity to ask questions related to your code and matlab. These sessions are your main source of getting coursework help.
We will not tell you if your solution is ‘correct’ but we will help you to debug any issues with your code.
Formative Exercise
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Example script on Moodle:
https://moodle.nottingham.ac.uk/pluginfile.php/7499759/mod_folder/content/0/Example_matlab_script.m?forcedownload=1
Saving .m as pdf example:
https://moodle.nottingham.ac.uk/pluginfile.php/7499759/mod_folder/content/0/To%20Save%20matlab%20as%20pdf.pdf?forcedownload=1
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