Current EMC Research at NIST
Perry Wilson
Electromagnetics Division
National Institute of Standards and Technology
ELECTROMAGNETICS DIVISION
B O U L D E R, C O L O R A D O
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NIST Organizational Structure
ELECTROMAGNETICS DIVISION
B O U L D E R, C O L O R A D O
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Electromagnetics Division
Perry Wilson, Div. Chief (Acting)
RF Electronics Group
Ron Ginley, GL
RF Fields Group
Mike Francis, GL (Acting)
Fundamental Microwaves
Materials Properties
High Frequency Devices
Field Parameters and EMC Applications
Antennas
Wireless Systems
ELECTROMAGNETICS DIVISION
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Magnetics Group
Ron Goldfarb, GL
Nano-Magnetics
Bio-Magnetics
Superconductivity
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Field Parameters and EMC
Applications Project
• Main Tasks
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Field strength calibration services (SP250)
Probe development
EMC facilities and test methods
Interference and propagation
Wireless systems
EMC standards and inter-comparisons
Short Courses
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Probe Development at NIST
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Open Area Test Site
30 m x 60 m OATS
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TEM Cells
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Fully Anechoic Chamber
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Fully Anechoic Chamber
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Cone and Ground Plane
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All Weather OATS
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Reverberation Chamber
ELECTROMAGNETICS DIVISION
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Reverberation Chamber
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Reverberation Chambers
• field uniformity
• low frequency limit
– mode density ≈ 1 mode/MHz
• independent paddle positions
8πV
f
2
v3
≈ (10 )−6
– frequency stirring
– position stirring
• spatial correlations
– de-correlation ≈λ/2
sin( kr )
ρ (r ) =
kr
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Reverberation Chambers
• antenna and test object response
– independent of directivity
•
•
•
•
•
2
2
E
1 0 λ
Pr =
2 η 4π
chamber Q
nested chambers for shielding measurements
cable shielding
multiple probe calibration
absorption cross section
– use as an exposure system for bio studies
ELECTROMAGNETICS DIVISION
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Reverberation Chambers
• enhanced backscatter
S11
2
= 2 S 21
2
ELECTROMAGNETICS DIVISION
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Reverberation Chambers
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Reverberation Chamber
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Orion Manned Orbiter SE
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Current EMC Research
• Develop SI traceable quantum based electric
field probe.
• Develop reverberation chamber based test
methods to simulate scattering rich wireless
link environments.
• Develop new shielding effectiveness test
methods.
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Quantum Based Field Probe
• Current techniques calibrate probes using a
“standard field”:
– Calculated field in a TEM cell
– TEM cell geometry
– Input power to TEM cell
– Probe placement inside TEM cell
– Calculated field in an anechoic chamber
– Gain of the transmit antenna
– Input power to the antenna
– Highly dependent and sensitive to the geometry of the relative positions of the
calibration probe and the standard source
– Accuracy order of 0.5 dB
– Sensitivity order of 0.5 V/m
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Quantum Based Field Probe
•
•
•
A probe based on atomic RF-resonance spectroscopy has the capability to
measure both very weak and very strong fields over a large range of
frequencies.
The feasibility of developing a technique that will allow direct SI units
linked RF electric field (E-field) measurements.
Uses the atomic transitions of Rydberg atoms as the RF field transducer as
a means for RF field detection:
– No antennas used
– No generation of a standard field for its operation
– Does not depend on any geometry considerations
– Allows for the direct measurement of the E-field
– Avoids the calculation uncertainties inherent in the TEM and anechoic
chamber techniques
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Quantum Based Field Probe
•Optically excite Rydberg atoms to an RF transition
•Arrival of an RF photon results in radiative decay of an optical photon
–Detect optical photon as a means to measure RF field
3
RF
2
Optical
Optical
1
Optical
4
DetectedPhoton
Photon
Detected
****Reference Gallagher****
ELECTROMAGNETICS DIVISION
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Detected Fluorescence
(dE0 )τ
Ωτ =
=π
2h
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Current Set-up
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Current Set-up
LIAD of Sodium Demonstrated at NIST, Boulder
Blue LIAD
excitation light at
455nm
Sodium cell
Laser beam
tuned to D2
Sodium transition
near 589nm
ELECTROMAGNETICS DIVISION
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Quantum Based Field Probe
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Fiber Core Probe
•Fill hollow core PBG fiber with Sodium gas.
•Small size~100um does not perturb microwave field. Microwave field is
uniform inside the fiber.
•Deliver pump light via fiber optics.
•Means for efficiently collecting much (80%) of the 815nm fluoresces since
atoms are inside the fiber.
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Scattering Rich Wireless Links
Office Corridor
Oil Refinery
Apartment Building
Subterranean Tunnels
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Reverberation Chamber
• Seek to simulate Rician K-factor over a large
range: k = direct power/scattered power.
• K-factor is affected by:
– Absorber (Q of the chamber)
– Types of antennas (directive, omni)
– Position orientation of the antennas
• Replicate measured power delay profiles
(PDP)
• Standards measurements: TRP and TIS
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Example: Stamping Factory
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Example: Stamping Factory
Measurements at engine stamping plant
0
o delay-spread=277ns * mean-delay=290.5ns
o delay-spread=122ns * mean-delay=130.1ns
o delay-spread= 67ns * mean-delay=71.2ns
o delay-spread=168ns * mean-delay=137.8ns
-5
o delay-spread=175ns * mean-delay=142.7ns
o delay-spread=128ns * mean-delay=105.8ns
reverb
chamber
Power Delay Profile (dB)
o delay-spread=173ns * mean-delay=176.1ns
1 absorber
3 absorbers
7 absorbers
flint metal, drg-drg, 10m
flint metal, drg-drg, 50m
flint metal, drg-drg, 80m
flint metal, drg-drg, 110Bm
-10
-15
stamping plant
-20
-25
-30
0
200
400
600
800
1000
time (ns)
1200
1400
1600
1800
2000
Reverb chamber bounds measurement
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Antenna Effect
Mean Power Delay Profile (100 steps)
Mean Power Delay Profile (100 steps)
-60
-60
Power Delay Profile (dB)
-70
-80
-90
-100
-110
-120
-130
0
Horns
500
1000
Delay (ns)
1500
2000
Horn Indirect 1, Absorber A
Horn Indirect 2, Absorber A
Horn Indirect 1, Absorber B
Horn Indirect 2, Absorber B
Horn Indirect 1, Absorber C
Horn Indirect 2, Absorber C
Omni Direct CoPol, Absorber B
Omni Direct XPol, Absorber B
-70
Power Delay Profile (dB)
Horn Indirect 1, Absorber A
Horn Indirect 2, Absorber A
Horn Indirect 1, Absorber B
Horn Indirect 2, Absorber B
Horn Indirect 1, Absorber C
Horn Indirect 2, Absorber C
Horn Direct CoPol, Absorber B
Horn Direct XPol, Absorber B
-80
-90
-100
-110
-120
Omnis
-130
0
500
1000
Delay (ns)
1500
2000
•Different antenna types can impact PDP
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Realistic PDPs
•Measurements made in Denver
urban canyon last summer
•Channel characterization and
PASS device measurements
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Simulating Realistic PDPs
• Pulse generator used to
amplitude modulate RF,
creates short-duration pulse
• Fading simulator replicates
delayed, scaled versions
• Reverb chamber introduces
exponential profile
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Simulating Realistic PDPs
• Using multiple, overlapping pulses, we can create many
difficult PDPs.
-34
fitted simulated data
measured Data Denver
-36
-38
PDP [dB]
-40
-42
-44
-46
-48
-50
-52
-54
0
100
200
300
400
500
600
700
800
900
Delay [ns]
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Shielding Effectiveness: Nested
Chambers
Sample
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Enclosure Shielding Effectiveness
• IEEE 299 Standard Method for Measuring the
Effectiveness of Electromagnetic Shielding
Enclosures:
– Physically large, electrically large enclosures
– Physically small, eclectically large enclosures
– Physically small, electrically small enclosures
• Problem with physically small enclosures: may not
accommodate paddle, large antenna.
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Small Enclosure SE
• From Hill we have for a planar interface
(chamber wall away from edges, corners):
t
E y ( x,0, z )
2
ELECTROMAGNETICS DIVISION
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=2
2
E0
3
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Small Enclosure SE
• Thus a small monopole and frequency stirring
can be used to measure a field related to the
center of the enclosure.
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SE Comparison
port 3
port 2
port 2
port 1
port 1
port 4
Mode-Stirred with a Horn Antenna: SE => S31
Mode-Stirred with a Monopole Antenna: SE => S41
port 3
port 2
port 2
port 1
port 1
port 4
Frequency Stirring with a Horn Antenna: SE => S31
Frequency Stirring with a Monopole Antenna: SE => S41
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SE Comparison
(a) open aperture
(c) narrow slot aperture
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(b) half-filled aperture
(d) generic aperture
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SE Comparison
(b) half-filled aperture
(a) open aperture
20
18
16
SE(dB)
14
12
10
8
mode_stirring_horn
6
freq_stirring_horn
4
mode_stirring_monopole
freq_stirring_monopole
2
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Frequency (MHz)
(c) narrow slot aperture
ELECTROMAGNETICS DIVISION
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(d) generic aperture
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Aircraft SE
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Space Shuttle Endeavour SE
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