Applying shielding and ferrite materials
Alex Snijder
Field Application Engineer
Wurth Elektronik Nederland B.V
13 oktober 2015
Alex.Snijder@we-online.com
Agenda
Introduction
Types of shielding materials
Ferrites
Practical
Apr 2013 & ver7 | Hah | Public | Shielding
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EMC – Basic Phenomena
Electromagnetic Compatibility
Emission
(EMI)
Conducted
Conducted Emission
Immunity
(EMS)
Radiated
Radiated Emission
Conducted
Conducted Suscept.
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Radiated
Radiated Suscept.
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Electromagnetic Wave, E- & H-Field
EM wavelength: c = λ*f
λ = Wavelength
c = Speed of light
f = Frequency = 1/T
The E and H field are shifted 90 degrees in far field.
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Frequency relations – Wavelenght
0,03
0,05
c0
1
λ0 = =
f f ⋅ ε0 ⋅ μ 0
0,1
0,3
λ0 in m
physical constant
1
Examples:
3
VHF @ 100MHz λ0/4 = 75cm (FM Antenna)
10
30
WLAN @ 2.45 GHz λ0/4 = 3.125cm
100
300
1
3
10
30
100
300
1000
3000
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10000
f in MHz
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Common types of EM noise shields
Two main types: Metallic (Cu, Al, Steel ) and Ferrites (NiZn, MnZn and other materials)
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How Shields affect each component of EM waves
Ferrite
Metal
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Ferrite works better
at short distances
and it affects more
significantly the
magnetic field
Metal works at any
distance and it affects
more significantly the
electric field
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Electromagnetic Radiation
Near and far field
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Electrical Shielding: Apertures
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Unbalanced cable
Icm
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Cable shielding
-
Cable shield is part of the product
shield
-
Surface conductivity must be high
-
Most important is cable termination:
The connection between the cable
shield and the enclosure must be 360°
-
Unproperly terminated cables behave
like an antenna
Cable „perfect“ antenna:
-
30 MHz -> λ/4 = 2,5 m
-
3 GHz -> λ/4 = 25 mm
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High frequency connections
At high frequencies (>20KHz):
- Current flows mostly over
the surface of the conductor:
impedance increases
- Effect of parasitic
inductance is higher
Connections must be:
- As short as possible
- Maximum surface area
- Low impedance for RF signals
Ground connections are critical:
they are main source of common
mode noise
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Electrical Shielding: Apertures
-
Assembly
Access
Display
Connectors
Cable entry
Buttons
Ventilation
…
Maximum aperture dimension for 20dB
shielding effectiveness
-
30 MHz -> λ/20 = 0,5 m
-
3 GHz -> λ/20 = 5 mm
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Gaskets in more details
•
•
•
•
•
•
PU sponge core
Nickel / Cupper layer
Light weight
Helps to protection against rough
environmental conditions
(dust/humidity) IP 54
On request our WE-LT is also available
with conductive tape.
Customer-specific lengths and
stamped out patterns can be realized
on request.
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Gaskets in more detail
Material compatibility: Galvanic corrosion
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RETROFIT : Shielding
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STAR SERIES
- patented key technology
- prefixing cable system
- no cable squeezing
- patented closing device
- no unauthorised demounting possible
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COMMON OR DIFFERENTIAL MODE NOISE ?
PUT ALL LINES IN THE FERRITE
Level [dBµV/m]
Level [dBµV/m]
60
60
50
50
40
40
30
30
20
20
10
10
0
0
30M 40M 50M
70M
100M
200M
Frequency [Hz]
300M 400M
600M
30M 40M 50M
70M
100M
200M
Frequency [Hz]
300M 400M
600M
1G
1G
RESULT 1 : NO ATTENUATION
DIFFERENTIAL MODE NOISE
TRY ONE FERRITE ON EACH LINE
RESULT 2 : ATTENUATION
COMMON MODE NOISE
Or the noise don’t come from this cable
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POSITION : WHERE TO PLACE THE FERRITE
Design:
As close as possible to the
source of the noise
Ideally 20mm to 50mm from the
point of cable connectivity
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STAR-FIX and STAR-TEC IMPEDANCE
Ferrite NiZn
Impedance (Ohms)
10000
100
1
1
10
100
Frquency (MHz)
1 turn
2 turns
3 turns
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Fixation
- simple fixation
- prefixing possible
- UL94-V0
- available in grey and black
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Fixation
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Other STAR ferrite
STAR-RING with pin to fix it
Cable up to 27 mm
STAR-FLAT up to 50 pin
STAR-FLAT´s ribbon cable holding feature
prevents
sliding and cable crimping
(Possible with adhesive tape)
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Other ferrite
WE-NCF with pin to fix it
Cable up to 26,5 mm
Split Ferrite
Cable up to 26,5 mm
WE-SFA
Flat Ferrite
Clip plastic or metal
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Thanks for your attention
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