Download Electromagnetic Shielding Techniques for Inductive

Ronan Dunne
Supervisor: Dr. Maeve Duffy
Co Supervisor: Liam Kilmartin
Inductive power transfer is a method of
transferring power wirelessly from a source to an
object requiring power.
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Inductive coupling - Inductive coupling involves the use
of magnetic fields to stimulate the movement of current
through a wire
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Nikola Tesla – Tesla coil.
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Recent developments in technology
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Charging Platforms for mobile devices
Biomedical applications
Advantage: No hazardous, inconvenient cables
and wires.
Charging Platform
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Contains inbuilt transmitter coils which induce a
current in the receiver coils in the mobile devices
when they are brought close to the platform.
Transmitter & receiver coils must be close together
as the magnetic fields they produce are small.
Bigger the magnetic field, the less efficient it
becomes.
Improve efficiency - implement resonant circuits in
both the Primary and Secondary sides of circuits.
Biomedical applications:
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The transmitter and receiver coils in these devices
are much further apart resulting in low inductive
coupling levels.
Inductive coupling is used to transfer pulses from
the externally worn transmitter to the implanted
receiver circuit.
These pulses are applied to the relevant nerve
endings
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Build demonstrator circuit
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Investigate Electromagnetic shielding
techniques
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Verify calculations and results by applying
analytic and finite element analysis techniques
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Demonstrator circuit
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Transmitter and receiver coils
Resonance
Electromagnetic shielding
Calculations (Matlab) & Simulations (Maxwell)
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Mutual Inductance
Inductance of different coils
Shielding Effectiveness
Transmitter coil is connected to power source
which produces a magnetic field.
• For a current to be induced, must add a receiver
coil inside the transmitter coils magnetic field.
• receiver coil must be close to the transmitter coil
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Built demonstrator circuit which contains
transmitter and receiver coils.
Capacitors were added to create resonance on
the primary and secondary sides which
improves power produced.
Inductive power transfer was shown by
creating enough power to light an LED.
By adding resonance circuits that have the
same resonance frequency the current can
tunnel from the transmitter to the receiver coil.
• This improves the efficiency of energy transfer
as energy is not scattered in all directions.
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Vs without capacitor (w/o resonance):
Frequency(Khz)
300
"
"
Distance (mm)
55
40
20
10
Secondary Voltage (V pk-pk)
0.12
0.14
0.18
0.22
Vs increased by 5.06V (pk-pk)
Vs with 1nF capacitor, resonating @ 630Khz:
Capacitor (nF)
1
"
"
"
Frequency(Khz)
630
"
"
"
Distance (mm) Secondary Voltage (V pk-pk)
55
0.88
40
1.38
20
2.9
10
5.28
Vs increased by 2.72V (pk-pk)
Vs with resonance on both sides:
Primary Cap (Nf) Secondary Cap (nF) Frequency(Khz) Distance (mm) Secondary Voltage (V pk-pk)
4.7
1
630
55
1.44
"
"
"
40
2.16
"
"
"
20
5
"
"
"
10
8
Vs with magnetic material added to core of receiver coil:
Frequency(Khz) Primary Capacitance
Secondary Cap (nF)
Distance (mm)
Secondary Voltage (V pk-pk)
270
30.38
1
55
3.48
"
"
"
40
5.52
"
"
"
20
11.1
"
"
"
10
19.5
Vs increased by 11.5V(pk-pk)
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Matlab was used to programme formulas and
Maxwell was used to simulate results.
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Mutual Inductance between two planar windings
Formula for Mutual Inductance
Magnetic field around the winding
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Power across diode was calculated in Excel
using results measured on oscilloscope.
The Following results were calculated:
@ Vp = 2V (Pk-Pk)
P = 885W
@ Vp = 4V (Pk-Pk)
P = 16.3 mW
@ Vp = 6V (Pk-Pk)
P = 45.0 mW
@ Vp = 8V (Pk-Pk)
P = 81.9 mW
@ Vp = 10V (Pk-Pk) P = 118 mW
EM shielding is the process of limiting the flow
of EM fields by using a barrier made to block
the magnetic fields.
• Several tests to compare shielding performance
of different materials.
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No shield
Ferrite shield
Copper shield
Ferrite and Copper shield
Secondary Voltage Vs with ferrite
Vs with
Vs with
Distance (mm)
(V pk-pk)
Shield
Copper shield double layer
55
1.44
1.2
0.88
0.64
40
2.16
1.76
1.32
0.84
20
5
3.4
2.4
1
10
8
5.12
4.56
1.2
SE = 16.48dB
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Maxwell used to simulate the effects of
different shielding techniques by placing the
plates within the magnetic field created by the
transmitter coil.
Magnetic field without ferrite plate
Magnetic field with ferrite plate
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The demonstrator circuit clearly shows Inductive
power transfer by creating enough power to light an
LED.
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implementing resonance circuits, increases power produced.
Adding magnetic material also increases power.
Electromagnetic Shielding was used to block magnetic
fields. It was proved that a double layer substrate made
of copper and ferrite acts as the best shield. Satisfactory
results of up to 16.5dbs were produced.
Maxwell was used to simulate behaviour of magnetic
fields and to verify results.