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Near-Field

Links Transition from Free-Space

See also: Matt Reynolds, Low frequency indoor radiopositioning, PhD Thesis, MIT, February 2003

Loop Link Law

Link depends on loaded Q and size:

Equating L-POL Link Law:

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.

Solving for gain:

Near-Field

Links in Practice

Example:

Q-Limits & Gain

Gain Relation:

Ideal Quality Factor:

Wavelength > Range

  • Slow monotonic variation in signal properties
  • Robust link that "ignores" most obstructions
  • Easier gain measurement - Q and size
  • Ideal free space links frequency independent:

Small Loop (TE1):

Choice of Frequency depends on:

  • Noise Environment
  • Near-Field Range (1-3 times radiansphere)

Received Power (dBm)

Near-

Field Links

Loss Reduces Unloaded Q:

References:

  • 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.

Power Law Exponents

  • Modest data rate
  • Enhanced propagation
  • Range up to quarter wavelength (1MHz)
  • Robust in cluttered environment
  • No drops, no deadzones, no fading

Maxwell & Antenna Theory

  • Enhanced propagation
  • Range 20-60m
  • Near- & Far-Field Links Converge to Inverse r cubed

“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

Near-Field Link

Laws: Gain-Aperture

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.

Significant path gain in near field!

"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

"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.

No frequency dependent path loss in far-field

Efficiency

& Gain

Efficiency:

Friis' Law

where for a well-matched antenna, unloaded Q is twice loaded Q.

Gain:

See:

  • 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.

Antenna Gain

Generalized Small Antenna Gain

Near-Field Link

Laws: Gain-Aperture

Marconi

Gain Constant Depends Upon:

  • Electric vs. Magnetic
  • Shape/Form Factor
  • Loading

Lodge &

Far-Field

Wireless

  • Near-Field Gain Measurement
  • Measurement Results
  • Theory of Small Antenna Gain

Two link laws

  • "Like" Antennas
  • "Unlike" Antennas

Gain Constant Value:

  • C ~ 4 Ferrite Loaded Loopsticks
  • C ~ 2 Air Core Loops
  • C ~ 1 Theory, Loops
  • C ~ 0.5 NEC Loops

Harald Friis, “A Note on a Simple Transmission Formula,” Proc. IRE, 34, 1946, pp. 254-256

Courtesy, Mount Holyoke College Archives and Special Collections

"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.

"L-POL" Link:

Tesla's Wireless Power Transfer

Guglielmo Marconi

1874-1937

  • High Voltage HF
  • Inductive Power Transfer
  • Wardenclyffe Tower

Near-Field

Link Laws: Gain-Gain

Tesla's Colorado Springs Experiments

Oliver Lodge

1850-1940

Near-Field

Link Laws: Gain-Gain

Two link laws

  • "Like" Antennas
  • "Unlike" Antennas

Wardenclyffe Tower

Ferrite Antenna Measurements

Hertz Discovers Far-Field Wireless

Transfer Function

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.

"L-POL" Link:

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:

Frequency dependent "path loss?"

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.

  • 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.

Overview:

Heinrich Hertz

1857-1894

Gain or

Aperture?

Transmit Physics

Near-Field

Origins of Wireless

Origins of

Near-Field Wireless

Air Core Antenna Measurements

Accelerating charges are not the source of radiation energy

Energy is stored in near-fields before decoupling and radiating away.

High Frequency Wireless

  • 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.

Near-Field

Gain Measurements

Gain of Antenna Under Test Given Reference:

Preece's

Inductive Wireless Telegraphy

  • VHF
  • UHF
  • Microwaves
  • Radar
  • Cellular Communications
  • Millimeter Wave
  • "Electrically Small" kR ~ 1

Three Antenna Gain Measurement:

  • Railway Telegraphy
  • Inductive Wireless
  • Discovery of Far-Field Wireless
  • Re-discovery of Near-Field Wireless

References:

  • 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.

Ghirardi, Alfred A., Radio Physics Course, New York: Farrar & Rinehart, Inc., 1930, p. 330

Motivation: Explore how electrically small antennas( ) work in near-field links.

Specifically:

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

Near-Field

Gain Measurements

William Henry Preece

1834-1913

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.

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

Comparison

of Results

Evaluation of Magnetic & Electric Antennas

Edison's

Electrostatic Wireless

Edison-

Guillard-Phelps

Link

Validation

Excellent agreement using simulated gain values

Thomas Edison

(1847-1931)

Fields

from Links

Antenna Factor relates Fields to Signal Voltage:

Solve for Gain:

Substitute into Link Law:

Solve for Electric Field Intensity:

Gain

Validation

Numerical Modeling

Simulated gain results

NEC and FEKO - Method of Moments

  • Validate gain relation
  • Validate link law
  • Validate field relation

6DoF Magnetic Motion Tracking

Near-Field Communications (NFC)

Near-Field Magnetic Induction (NFMI)

Near-Field Wireless Technology

Approach:

  • 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

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]

Dr. Hans G. Schantz, CTO

Q-Track Corporation

2223 Drake Avenue SW 1st Floor

Huntsville, AL 35805

h.schantz@q-track.com

Twitter: @aetherczar

  • Auracomm founded 1995
  • RF 10-15MHz
  • Wireless Headset/Voice channel
  • Range < 2m
  • Acquired by Freelinc in 2007 (www.freelinc.com)

Current &

Voltage in Small Loops

Apply Conservation of Energy:

Impedance of high Q resonant antenna:

Fields

Around Small Antennas

Near-Field

Wireless Applications

Wireless

Power Transfer

  • Antenna practice employs EIRP

Transmit Power:

Transmit Gain:

  • Electromagnetic theory employs dipole moment:

Turns: N

Current: I

Area: A

m

N

Overview

A

Fields from Dipoles, Moments & EIRP

  • WiTricity - MIT Demo (9MHz)
  • WiPower
  • Powermat Technologies
  • Qi - wireless power charging

I

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

Field from dipole theory:

Noting that:

Relate moment to EIRP:

Near Field Intensities

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

Near-Field Electromagnetic Ranging (NFER)

RuBee

IEEE 1902.1

Radio Frequency Identification (RFID)

Data Rate: 1200 baud

Frequency: 131kHz

Range: <15m

See: http://www.visible-assets.com/

Dipole

Fields from EIRP

Encompasses a wide variety of technologies including:

  • 10cm read at 120-150kHz
  • 10cm-1m read at 13.56MHz
  • Range: 20-60m
  • Accuracy: 30cm-1m
  • Frequency ~1MHz
  • Capacity: ~80 tags

at 1Hz update

  • Q-Track Corporation

(www.q-track.com)

  • Booth 351A

Field intensities may be written in terms of EIRP:

Transverse fields (Longitudinal) 6dB stronger....

Conclusion

Near Field

Impedance

Near Field

Phase Relations

Louis Sullivan

1856-1924

Heinrich Hertz

1857-1894

Hertz: Electric Waves, 1893, p. 152

"Form follows function."

What is

the "Near Field?"

See: Charles Capps, "Near Field or Far Field," EDN, August 16, 2001 pp. 95-102

Near Field

Impedance

Conclusion

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

Many Near-

Field Parameters

Low Frequency,

Near-Field Links

  • Multipath resistant
  • Good penetration
  • Bends, diffracts around obstructions
  • Robust Links

Superposition & Near-Fields

E-Phase

H-Phase

EH-Phase Delta

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