Advances in Ultraviolet Missile Approach Warning

Ludi Kruger

Saab Grintek Defence

Electronic Warfare South Africa 2019

International Conference and Exhibition

4-6 November 2019, CSIR, South Africa

Overview

2

Saab Grintek Defence Electro-optics

• Ultraviolet (UV)

• Near Infrared (NIR)

• Short Wave Infrared (SWIR)

• Medium Wave Infrared (MWIR)

• Long Wave Infrared (LWIR)

• SGD is working in all these wavelengths, including still investing in UV

3

Scope of presentation

• This presentation attempts to give an overview of useful new technologies applicable to ultraviolet missile approach warning

• This presentation is not:

• A comparison of UV and IR technologies

• A technical description of Saab products and technologies

• Of deep scientific nature4

Research in UV detection

• Research in UV detection in the following fields:

• Astronomy

• Cosmology

• Planetary studies

• Biological and medical applications

5

Ultraviolet MAW Values

• Solar blindness

• Sensitivity

• Field-of-view

• Discrimination between threats and clutter (sensor and algorithms)

• Response time

• High resolution not so important

• Cost relative to platform cost (but remember pilot)

6

The source and environment

7

A bit of science

8[1]

A bit of science

9[1]

Optics technology

10

Optics technology

• Aspheric optics

• Filters

• Curved image plane

• Multispectral lenses

• Nano-structured anti-reflection coatings

11

Aspheric lenses

• As the name implies, the surface(s) aren’t spherical

• Allows opportunity for:

• Fewer lenses

• More compact optical systems

• Better image quality

12

Aspheric lenses

13

[7]

Aspheric lenses

Advantages

• No spherical aberration

• Fewer, thinner lenses

Disadvantages

• More costly to grind

• Moulding softens the glass

• More expensive

14

Dielectric filters

• Dielectric or thin film filters deposited onto optics – lenses or windows

• Used as edge-, band pass- or band stop (notch) filters

• Traditional filters have wavelength shift for non-zero incidence angles

• New materials allow for less change with incidence angle

• Better control allows for better performance, e.g. less ripple

15

Curved image plane

• Enormous optical advantages of curved FPA

• Apple, Canon, Sony, Google and Samsung each have patent on curved sensor, but manufacturability a problem

• How to fabricate:

• Flexible

• OLED screens

• Flexible PCBs

• Spherical shapes require stretching

• Stretchable focal plane arrays have been proposed

• Fill factor actually increases because bridges not required

• SGD has used this concept in another system 16

[5]

Multispectral lenses

• GRaded INdex (GRIN) lenses have a parabolic decrease in refractive index from centre to edge

• GRIN lenses are sensitive to temperature, thickness, curvature and more

• Lens with flat optical power from 1-12 um demonstrated

• UV applicability to be confirmed

• 35% reduction in weight

• Human eye is example of this GRIN lens

• Optical systems are combined more

and more. This allows single set of

optics

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Nano-Structured Anti-reflection Coatings

• This is anti-reflective surface structure (ARSS), not coating

• AR coatings have much lower damage threshold than the material itself

• Look at concept of moth’s eye

• Theory: graded index layer on surface

• Height of bumps h=λ/2

• Etch, imprint or emboss

• Normal cleaning an be used

• Tested up to 45° - same transmission

• No effect on polarisation 18[14]

Detector and readout technology

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Detector and readout technology

• Image intensifier with resistive anode

• Digital Pulse Processing (DPP)

• Silicon Photon Multiplier (SiPM) / Single-photon avalanche diodes (SPAD)

20

Image Intensifier –Phosphor screen and imaging output

• The classic method

• Can use fibre taper

• Imaging sensor (e.g. CCD) used to digitise

21MCP cross section

[10]

Image Charge Detector

• [2]22

Image Charge Detector - Anode

23

[4]Tetra wedge anode

Resistive sheet anode

Detector withWedge and strip anode

Read-out for Image Charge Detector

24

• Four output ports have to be conditioned, amplified and compared

• Position of event can be determined

• Considered a “serial” device since simultaneous events can not be resolved

• Although this pile-up is rare

Charge coupled analogue read-out

25[2]

Charge coupled detector with DPP

26[2]

Charge coupled detector with DPP

• Higher pulse throughput

• Better noise performance

• Better accuracy

27[2]

Silicon Photon Multiplier

• Size of capacitor can be reduced - several 100 attofarads – single electron can give notable voltage change

• Fundamental limits: response time, timing jitter, efficiency and thermal noise

• Megapixel achieved.

[3]

28

SiPM Readout

29[ref]

Silicon Photon Multiplier

• 2D doped silicon imagers combined with integrated red rejection filters

• UV sensitive Si detectors with tailorable out of band rejection now possible

• [9]

30

Single-Photon Avalanche Diode

• Follow up to:

• Photomultiplier tubes (PMTs)

• Microchannel plates (MCPs)

• Electron-multiplying charge-coupled devices (EMCCDs)

• e.g. SPAD implementation of CMOS

• Operation in Geiger mode

31

[9]

Processing and algorithms

32

Algorithm development

• Neural networks (Artificial Intelligence (AI)) initially limited and fixed parameters

• What input parameters

• Number of hidden layers

• Activation functions

• Thresholds

• Doors opened now for neural network to choose its own parameters

• Computing power and technology allows for much more data to be given to network during training

• Deep learning33

[12]

Increasing input data

• Concept was shown to generate additional input patterns

• Take “benign” image and project threat into it

• This multiplies the available input data to train neural networks with

[13]

34

Performance optimisation

35

Performance optimisation

• Parameters that can be optimised

• Resolution

• Frame rate

• Sensitivity

• Performance in noise

• Reliability

• Neural network as discussed

• Amount of pre-processing (at sensor)

• Raw data recording for later optimisation

• Large amounts of data can be handled 36

Performance verification

37

Performance Verification –Stimulators

• UV Stimulators

• RUAG Missim

• Textron Griffen-50

• Textron Mallina-180

• Textron Phantom

38

Performance Verification –The UV LED

• Early stimulators use halogen lamps – wide wavelength band

• UV LEDs then became available and common

• Be aware of centre wavelength and bandwidth

39

Performance Verification –Complexities

• Algorithms became more complex

• More parameters needed as input

• More difficult to fool systems

• Moving platforms even more complex to stimulate

40

Acknowledgements

• EWSA conference organisers

• Saab Grintek Defence management and colleagues

41

References1. Ratheon IR Wall Chart, http://www.ratheon.com, 2007

2. Jonathan S. Lapington; James S. Milnes; Martin Page; Martin B. Ingle; K. Rees, Novel electronic readout systems for photon-counting imagers, Proceedings Volume 4128, Image Intensifiers and Applications II; (2000) https://doi.org/10.1117/12.405872

3. Lapington, J, Detector Technologies for WSO, World Space Observatory Detector Workshop, Leicester, Space Research Centre, University of Leicester, 3-5 December 2007

4. J.S. Lapington, J. Howorth, J. Milnes, A Reconfigurable Image Tube using an External Electronic Image Readout, Space Research Centre University of Leicester and Photek Ltd, http://www.photek.com/support/Papers/A_Reconfigurable_Image_Tube_using_an_External_Electronic_Image_Readout.pdf

5. K. Renshaw, Z. Ma, Hemispherical focal plane arrays for wide field-of-view imaging, CREOL, The College of Optics and Photonics, Univ. of Central Florida (USA), SPIE 2017 proceedings 10209-14.

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References6. A. M. Boyd, Optical design of athermal, multispectral, radial GRIN lenses, Excellital

Qioptiq, SPIE 2017 10181-9

7. “Vinayraiofh”, Asperic Lens: Its Advantages and Drawbacks, 7 October 2015, https://opticaldesignblog.wordpress.com/2015/10/07/aspheric-lens-its-advantages-and-drawbacks/

8. J. Ma, Y. Zhang, X. Wang, L. Ying, S. Masoodian, Z. Wang, D. Starkey, W. Deng, R. Kumar, Y. Wu, S. A.Ghetmiri, Z. Yu, S-Q Yu, G. Salamo, E. Fossum, J. Liu, Prospects and fundamental limitations of room temperature, non-avalanche, semiconductor photon-counting sensors, SPIE 2017 10212-8

9. S. Nikzad, M. Hoenk , A. D. Jewell, J. J. Hennessy, A. G. Carver, T. J. Jones, T. M. Goodsall, E. T. Hamden, P. Suvarna, J. Bulmer, F. Shahedipour-Sandvik, E. Charbon, P. Padmanabhan, B. Hancock and L. D. Bell, Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials, Sensors, 21 June 2016

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References10.Photek Ltd, Image Intensifier Application Note, Version Date 02/15

11.S. D. Wolter, J. A. Greenberg, Classification-free threat detection based on material-science-informed clustering, Elon Univ. (USA), Duke Univ. (USA). SPIE 2017 10187-20

12.Neural Network Using Python and Numpy, https://www.python-course.eu/neural_networks_with_python_numpy.php, 2 November 2019

13.T.W. Rogers, N. Jaccard, E. J. Morton, L.D. Griffin, A deep learning framework for the automated inspection of complex dual-energy x-ray cargo imagery, Univ. College London and Rapiscan Systems Ltd, SPIE 2017 10187-21

14.L. E. Busse, J.A. Frantz, L. B. Shaw, S. S. Bayya, G. Villalobos, Antireflective surface structures on infrared optics, U.S. Naval Research Lab and Scotera Defense Solutions Inc, SPIE 2017 10181-18

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“

”

All men plume themselves on the improvement of society, and no man improves.

- Ralph Waldo Emerson

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Thank you

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