Fibre Composite Electromagnetic Interference Shielding Materials
for use in Airborne Vehicles
Presented by Adrian BerghorstSchool of Mechanical Engineering
University of KwaZulu-Natal
Work completed by Denver Maharaj and Adrian Berghorst.Supervisor: Dr. Chris Von Klemperer
Slide 2 © CSIR 2006 www.csir.co.za
• Primary goal: Produce an electromagnetic shielding solution a for fibre reinforced polymer (FRP) airframe.
• Secondary goal: Produce a lightning protection solution for a fibre reinforced polymer (FRP) airframe.
Goals of the Research.
SeekerII graphic from: http://www.denel.co.za/Aerospace/UAV.asp
Graphic from: http://chamorrobible.org/gpw/gpw-20061026.htm
Slide 3 © CSIR 2006 www.csir.co.za
• Design a suitable FRP with adequate electromagnetic shielding efficiency (EMSE) and electrical conductivity.
• Design a suitable secondary bonding solution with adequate EMSE and electrical conductivity.
Areas of Research.
Slide 4 © CSIR 2006 www.csir.co.za
• Electromagnetic interference (EMI) is a disturbance or disruption in the performance of an electronic device due to the transmission of radiation from a source.
• EMI is prevented by placing a shield between the source and the device.
Electromagnetic Interference Information.
Slide 5 © CSIR 2006 www.csir.co.za
Lightning Strike Information.
• On average a commercial airliner is struck by lightning once a year.
• Lightning strikes the aircraft, the current travels along the skin, and exits at an extreme point.
• Eg: nose to vertical stabiliser.
Graphics from: http://www.cst.com
Slide 6 © CSIR 2006 www.csir.co.za
EMI Research
• EMI in aircraft may be classified into three sub-classes: 1. on-board systems 2.passenger carry-on devices3.externally generated EMI
• The frequency range of interest in this work is 800 MHz to 5 GHz.• Interference can range from slight static to interference with
avionics.• EMI interacts with a shielding material by reflection, absorption, or
transmission.
Slide 7 © CSIR 2006 www.csir.co.za
EMI Research – FRP Laminates
• Adding discontinuous filler materials to the resin.
• Including continuous aluminium mesh layer in the reinforcing.
• Using material with better electrical conductivity (carbon fibre as opposed to glass fibre).
Aluminium powder under a microscope.
Alumesh 401 when viewed at 100x magnification
Slide 8 © CSIR 2006 www.csir.co.za
• Materials used:• Carbon Fibre
• Stitched, woven, & Unidirectional.• Discontinuous Filler
• Aluminium, & Copper.• Resin
• LR20 (LH281 Hardener), & Prime 27 (Prime 20 slow Hardener)
• Continuous Mesh Layer• Alumesh 401
EMI Research – FRP Laminates
The Scientific Atlanta 5754 compact antenna range test set-up at the
University of Pretoria
Slide 9 © CSIR 2006 www.csir.co.za
• The best shielding solution was unidirectional carbon fibre laminates with filler and alumesh.
EMI Research – FRP Laminates
0
5
10
15
20
25
30
35
40
45
0 1000 2000 3000 4000 5000 6000
Frequency (MHz)
EM
SE
(d
B) Aluminium Plate
No Filler
7.5% Filler
15% Filler
0
5
10
15
20
25
30
35
40
45
0 1000 2000 3000 4000 5000 6000
Frequency (MHz)
EM
SE
(d
B) Aluminium Plate
No Filler
1 Ply
2 Ply
Hybrid powder doped unidirectional Metal mesh unidirectional
Slide 10 © CSIR 2006 www.csir.co.za
EMI Research – FRP Laminates
% Difference in Average Shielding Effectivness Relative to Aluminium Plate
-6
-4
-2
0
2
4
6
8
10
12A
l bas
e
0%al
7.5%
al
15%
al
7.5%
cu
15%
cu
7.5%
alcu
15%
alcu
1 la
yer
2 la
yers
Laminate
[%]
Unidirectional
Woven
Stitched
Slide 11 © CSIR 2006 www.csir.co.za
• Adding discontinuous fillers to the adhesive.
• Several different adhesives.
• Varying filler fractions.
EMI Research – Secondary Bonding
Adhesive samples prepared for inspection.
Slide 12 © CSIR 2006 www.csir.co.za
• Materials used• Adhesives
• Adekit H9940, Araldite 420, Cy221.
• Discontinuous Fillers• Aluminium, Copper, & Silver.
• Filler Fractions Tested• 0% → 15% by weight• 0% → 25% by volume
EMI Research – Secondary Bonding
The Scientific Atlanta 5754 compact antenna range test set-up at the
University of Pretoria
Slide 13 © CSIR 2006 www.csir.co.za
EMI Research – Secondary Bonding
Shielding Properties of Adhesives
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
750.
0000
1015
.625
0
1281
.250
0
1546
.875
0
1812
.500
0
2078
.125
0
2343
.750
0
2609
.375
0
2875
.000
0
3140
.625
0
3406
.250
0
3671
.875
0
3937
.500
0
4203
.125
0
4468
.750
0
4734
.375
0
5000
.000
0
Frequency (MHz)
EM
SE
(d
B) Solid Metal
Adekit (V)
Adekit (H)
Araldite (V)
Araldite (H)
Slide 14 © CSIR 2006 www.csir.co.za
• EMSE Ratio (Solid/Bonded) = 0.97 (3% difference)• Average Difference (Solid – Bonded) = 1.13 Db
Shielding Properties of Adhesives
-10.00
-5.00
0.00
5.00
10.00
15.00
20.00
Frequency (MHz)
EM
SE
(d
B)
Adekit (V)
Adekit (H)
Araldite (V)
Araldite (H)
EMI Research – Secondary Bonding
Slide 15 © CSIR 2006 www.csir.co.za
• Tested in accordance with ASTM B193-02, Standard test method for Resistivity of electrical conductor materials.
Electrical Conductivity – FRP Laminates
The RCL universal bridge circuit used to measure electrical resistance
Slide 16 © CSIR 2006 www.csir.co.za
• Average conductivity: 0.31 • Maximum Conductivity: 0.81• Minimum conductivity: 0.06
Electrical Conductivity – FRP Laminates
Conductivity
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
0.9000
-1 1 3 5 7 9 11 13 15
Filler [%] or Mesh Layers (5 = 1 layer & 15 = 2 layers)
Co
nd
uct
ivit
y [O
hm
/cm
]stitched al
stitched cu
stitched al+cu
stitched mesh
woven al
woven cu
woven al+cu
woven mesh
unidirectional al
unidirectional cu
unidirectional al+cu
unidirectional mesh
Slide 17 © CSIR 2006 www.csir.co.za
Electrical Conductivity – Secondary Bonding
• Tested in accordance with ASTM D 2739-72, Standard test method for volume resistivity of conductive adhesives.
Electrical conductivity sample according to ASTM D2739.
Slide 18 © CSIR 2006 www.csir.co.za
• Electrical conductivity in excess of 8.62
• Samples tested up to 25% filler by volume.
Electrical Conductivity – Secondary Bonding
24.97% (by volume), 72.37% (by weight) Cu in Araldite 420.
24.78% (by volume), 40.63% (by weight) Al in Adekit H9940.
Slide 19 © CSIR 2006 www.csir.co.za
• Tensile testing according to ASTM 638-02a, Standard test method for Tensile properties of plastics.
• Flexural testing according to ASTM 6272-02, Standard test methods for Flexural properties of unreinforced and reinforced plastics and electrical insulating materials by four-point bending.
Mechanical Strength – FRP Laminates
Tensile test
Flexural test
Slide 20 © CSIR 2006 www.csir.co.za
Mechanical Strength – FRP Laminates
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Mechanical Strength – FRP Laminates
Slide 22 © CSIR 2006 www.csir.co.za
• Lap Shear Testing According to ASTM D 1002– 01, Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal)
Mechanical Strength – Secondary Bonding
Sample in lap shear testing.
Slide 23 © CSIR 2006 www.csir.co.za
• Initial drop in strength• 66.3% Aluminium• 56.4% Copper• 41.4% Silver
Mechanical Strength – Secondary Bonding
• Lap shear testing to be done on volume basis
Slide 24 © CSIR 2006 www.csir.co.za
Conclusion• Better strength properties compared to orthodox
materials.• Better fatigue and corrosive properties.• Weight saving due to increased strength properties.• Long term cost saving.
• Higher initial cost compared with orthodox materials.• Difficulty in shielding from EMI.• Difficulty in conducting lightning strike.
Slide 25 © CSIR 2006 www.csir.co.za
Boeing 787 Dreamliner graphic from www.boeing.com
Denel SeekerII graphic from: http://www.denel.co.za/Aerospace/UAV.asp