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

Slide 21 © CSIR 2006 www.csir.co.za

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