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Near-Field Wireless Technology

Workshop Presented at IEEE RFID 2014, Orlando, FL April 8, 2014

Hans Schantz

on 2 December 2014

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Transcript of Near-Field Wireless Technology

Guglielmo Marconi

Lodge &

Inductive Wireless Telegraphy
Hertz Discovers Far-Field Wireless
Electrostatic Wireless
Origins of Wireless

Thomas Edison

William Henry Preece
Heinrich Hertz
Maxwell & Antenna Theory
High Frequency Wireless
Cellular Communications
Millimeter Wave
"Electrically Small" kR ~ 1
“An understanding of the mechanism by which energy is radiated from a circuit and the derivation of equations for expressing this radiation involve conceptions which are unfamiliar to the ordinary engineer.”
– Frederick Emmons Terman, 1932
"Maxwell’s field theory was believed to be good at all frequencies, but its language and some of its concepts were totally alien to most engineers of that period."
-Sergei Schelkunoff, 1970
Ghirardi, Alfred A., Radio Physics Course, New York: Farrar & Rinehart, Inc., 1930, p. 330
Wireless Applications

High Frequency/Far-Field Ideal For:
Long Range
Large Bandwidth
High Data Rate

Near-Field Links Ideal For:
Modest Data Rate
Short Range
Robust w.r.t. Blockage, Multipath
Near-Field Magnetic Induction (NFMI)
Auracomm founded 1995
RF 10-15MHz
Wireless Headset/Voice channel
Range < 2m
Acquired by Freelinc in 2007 (www.freelinc.com)
6DoF Magnetic Motion Tracking
Low Frequency AC or Pulsed DC
Polhemus Founded 1969
See: http://polhemus.com/
Ascension Technology Corporation Founded 1986
"Flock of Birds" Magnetic Tracking
See: http://www.ascension-tech.com/index.php
Radio Frequency Identification (RFID)
Encompasses a wide variety of technologies including:
10cm read at 120-150kHz
10cm-1m read at 13.56MHz
IEEE 1902.1
Data Rate: 1200 baud
Frequency: 131kHz
Range: <15m
See: http://www.visible-assets.com/
Friis' Law
Link Laws: Gain-Gain
Two link laws
"Like" Antennas
"Unlike" Antennas
Field Links
Modest data rate
Enhanced propagation
Range up to quarter wavelength (1MHz)
Robust in cluttered environment
No drops, no deadzones, no fading
Harald Friis, “A Note on a Simple Transmission Formula,” Proc. IRE, 34, 1946, pp. 254-256
Transfer Function
Asymmetry in reciprocity:
Transmitting transfer function is proportional to the time derivative of the receiving transfer function
Frequency domain:
Power ~ Signal Squared
Transmit power related to receive power by frequency squared:
UWB Antennas
Consider UWB antennas:
A constant gain antenna transmits a faithful copy of a voltage signal.
A constant aperture antenna receives a faithful copy of an incident signal.
Transmit Physics
Accelerating charges are not the source of radiation energy
Energy is stored in near-fields before decoupling and radiating away.
Gain or
Gain best describes transmit behavior
Aperture best describes receive behavior
H. G. Schantz, The Art and Science of UWB Antennas, Boston: Artech, 2005, p. 176.
H. G. Schantz, “Electromagnetic energy around Hertzian dipoles,” IEEE Antennas and Propagation Magazine, Vol. 43, No. 2, April 2001, pp. 50-62.
"L-POL" Link:
Link Laws: Gain-Gain
Near-Field Link
Laws: Gain-Aperture
Two link laws
"Like" Antennas
"Unlike" Antennas
"L-POL" Link:
Near-Field Link
Laws: Gain-Aperture
Hans Schantz, “Near-field propagation law & a novel fundamental limit to antenna gain versus size,” 2005 IEEE Antennas and Propagation Society International Symposium, Vol. 3A, 3-8 July 2005, pp. 237-240.
A.J. Compston, J.D. Fluhler, and H.G. Schantz, “A Fundamental Limit on Antenna Gain for Electrically Small Antennas,” 2008 IEEE Sarnoff Symposium, 28-30 April 2008, pp. 1-5.
Links Transition from Free-Space
Wavelength > Range
Slow monotonic variation in signal properties
Robust link that "ignores" most obstructions
Power Law Exponents
Links in Practice
Enhanced propagation
Range 20-60m
Near- & Far-Field Links Converge to Inverse r cubed
See also: Matt Reynolds, Low frequency indoor radiopositioning, PhD Thesis, MIT, February 2003
Far-Field Propagation
W. Honcharenko, “Modeling UHF Radio Propagation in Buildings,” Ph. D. Dissertation, Polytechnic University, Brooklyn, NY, 1993.
K. Siwiak, H. Bertoni, and S. Yano, “Relation between Multipath and Wave Propagation Attenuation,” Electronic Letters, Vol. 39, No. 1, January 9, 2003, pp. 142-143.
"Forty Years Ago: Maxwell’s Theory Invades
Engineering-and Grows with It," IEEE Trans. Ant. Prop. Vol. AP-18, No. 3, May 1970 p. 309-322.
Antenna Gain
Near-Field Gain Measurement
Measurement Results
Theory of Small Antenna Gain
Q-Limits & Gain
Ideal Quality Factor:
Generalized Small Antenna Gain
Gain Constant Depends Upon:
Electric vs. Magnetic
Shape/Form Factor

Gain Measurements
Gain of Antenna Under Test Given Reference:
Three Antenna Gain Measurement:
E. Richards, H. Schantz, J. Unden, K. von Laven, A.J. Compston, and C. Weil, “Electrically Small Antenna Design for Low Frequency Systems,” 34th Annual Antenna Applications Symposium, 21-23 September, 2010.
IEEE Std. 149-1979, p. 96.
Gain Measurements
Air Core Antenna Measurements
Ferrite Antenna Measurements
of Results
Evaluation of Magnetic & Electric Antennas
Small Loop (TE1):
Loss Reduces Unloaded Q:
Loop Link Law
Link depends on loaded Q and size:
Easier gain measurement - Q and size
Ideal free space links frequency independent:
& Gain
J. S. McLean, “A re-examination of the fundamental limits on the radiation Q of electrically small antennas,” IEEE Transactions on Antennas and Propagation, Vol. 44, No. 5, pp. 672–676, May 1996.
David M. Pozar, “New Results for Minimum Q, Maximum Gain, and Polarization Properties of Electrically Small Arbitrary Antennas,” 3rd European Conference on Antennas and Propagation, 2009 (EuCAP 2009), 23-27 March 2009, pp. 1993-1996.
A.R. Lopez, “Harold A. Wheeler’s Antenna Design Legacy,” IEEE Long Island 2007 Systems, Applications and Technology Conference, 4 May, 2007, pp. 1-6.
Oleksiy S. Kim, Olav Breinbjerg, and Arthur D. Yaghjian, “Electrically Small Magnetic Dipole Antennas With Quality Factors Approaching the Chu Lower Bound,” IEEE Transactions on Antennas and Propagation, Vol. 58, No. 6, June 2010, pp. 1898-1906. See Eqn. 2b.
Herbert L. Thal, “New Radiation Q Limits for Spherical Wire Antennas,” IEEE Transactions on Antennas and Propagation, Vol. 54, No. 10, October 2006, pp. 2757-2763. See Eqn. 8b.
Kai Siwiak and Yasaman Bahreini, Radiowave Propagation and Antennas for Personal Communications, 3rd ed. Norwood, MA: Artech House, 2007, p. 359-360.
Constantine A. Balanis, Antenna Theory Analysis and Design, 2nd ed., New York: John Wiley and Sons, Inc., 1997, p. 762.
where for a well-matched antenna, unloaded Q is twice loaded Q.
See: Umar Azad, Hengzhen Crystal Jing, Yuanxun Ethan Wang, “Link budget and Capacity Performance of Inductively Coupled Resonant Loops,” IEEE Transactions on Antennas and Propagation, Vol. 60, No. 5, May 2012, pp. 2453-2461.
Equating L-POL Link Law:
Solving for gain:
Gain Relation:
Choice of Frequency depends on:
Noise Environment
Near-Field Range (1-3 times radiansphere)
Numerical Modeling
NEC and FEKO - Method of Moments
Validate gain relation
Validate link law
Validate field relation
Excellent agreement using simulated gain values
Near Field Intensities
Simulated gain results
"It is to be observed that the effective source of the emitted radiation is not at the oscillator itself, but at a quarter wave-length in advance of it. If it is to be assumed to start at the oscillator, the light will seem to travel too quickly; and Hertz found this to be the case.”

Oliver Lodge, Modern Views of Electricity, 3rd ed., London: Macmillan & Co, Ltd., 1907, p. 303.
Oliver Lodge
Courtesy, Mount Holyoke College Archives and Special Collections
Frequency dependent "path loss?"
Kanda, Motohiso, “Time Domain Sensors for Radiated Impulsive Measurements,” IEEE Transactions on Antennas and Propagation, Vol. AP-31, No. 3, May 1983, pp. 438-444.
Hans Schantz, “d/dt, jω, Q, and UWB Antennas,” 2nd International Workshop UWB Radio Communications Proceedings, Inha, Korea, June 24, 2005, pp. 102-110.
No frequency dependent path loss in far-field
Significant path gain in near field!
Received Power (dBm)
Around Small Antennas

Antenna practice employs EIRP

Transmit Power:
Transmit Gain:
Electromagnetic theory employs dipole moment:
Turns: N
Current: I
Area: A

Current &
Voltage in Small Loops
from Links
Fields from Dipoles, Moments & EIRP
Fields from EIRP
Apply Conservation of Energy:

Impedance of high Q resonant antenna:
Antenna Factor relates Fields to Signal Voltage:

Solve for Gain:

Substitute into Link Law:

Solve for Electric Field Intensity:
Field from dipole theory:

Noting that:

Relate moment to EIRP:
Field intensities may be written in terms of EIRP:

Transverse fields (Longitudinal) 6dB stronger....
Motivation: Explore how electrically small antennas( ) work in near-field links.

Near-Field Links
Electrically Small Antenna Gain
Regulatory Near Fields
NEC Validation

High Frequency/Far-Field Ideal For:
Long Range
Large Bandwidth
High Data Rate

Near-Field Links Ideal For:
Modest Data Rate
Short Range
Robust w.r.t. Blockage, Multipath

Understand Electrically Small Antennas
Links, Gain, and Fields

Starting Point for Exploring How Near-Field
Links Solve Real-World Problems
Louis Sullivan

"Form follows function."
Gain Constant Value:
C ~ 4 Ferrite Loaded Loopsticks
C ~ 2 Air Core Loops
C ~ 1 Theory, Loops
C ~ 0.5 NEC Loops

Near-Field Wireless Technology
Dr. Hans G. Schantz, CTO
Q-Track Corporation
2223 Drake Avenue SW 1st Floor
Huntsville, AL 35805
Twitter: @aetherczar
Part One:
Origins of Near-Field Wireless
Survey of Applications
Introduction to the Near Field

Part Two:
Near-Field Links
Electrically Small Antennas
Regulatory Limits
Railway Telegraphy
Inductive Wireless
Discovery of Far-Field Wireless
Re-discovery of Near-Field Wireless
Origins of
Near-Field Wireless

Near-Field Communications (NFC)
NFC Forum Founded 2004
Data Rate: 106 kbit/s to 424 kbit/s
Frequency: 13.56 MHz
Range: ~10cm or less
[ISO/IEC 18000-3]
Near-Field Electromagnetic Ranging (NFER)
Range: 20-60m
Accuracy: 30cm-1m
Frequency ~1MHz
Capacity: ~80 tags
at 1Hz update
Q-Track Corporation
Booth 351A
Power Transfer
WiTricity - MIT Demo (9MHz)
Powermat Technologies
Qi - wireless power charging
Tesla's Wireless Power Transfer
Tesla's Colorado Springs Experiments
High Voltage HF
Inductive Power Transfer
Wardenclyffe Tower
Wardenclyffe Tower
Near Field
Phase Relations
Low Frequency,
Near-Field Links
Many Near-
Field Parameters
Multipath resistant
Good penetration
Bends, diffracts around obstructions
Robust Links
Hertz: Electric Waves, 1893, p. 152
EH-Phase Delta



Heinrich Hertz
What is
the "Near Field?"
See: Charles Capps, "Near Field or Far Field," EDN, August 16, 2001 pp. 95-102

Near Field
Near Field
Near Field
Superposition & Near-Fields
See: J.J. Fahie,
A History of Wireless Telegraphy
, 2nd ed. , Dodd Mead & Company, New York, 1901, pp. 135-161.
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