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Near-Field

Links Transition from Free-Space

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:

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

Gain Relation:

Near-Field

Links in Practice

  • Easier gain measurement - Q and size
  • Ideal free space links frequency independent:

Efficiency

& Gain

Q-Limits & Gain

Ideal Quality Factor:

Efficiency:

Choice of Frequency depends on:

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

Small Loop (TE1):

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.

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.

Example:

Wavelength > Range

  • Slow monotonic variation in signal properties
  • Robust link that "ignores" most obstructions

Received Power (dBm)

Near-

Field Links

Optimal

Small Loop Design

Generalized Small Antenna Gain

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

To maximize Q, maximize L for fixed length wire:

  • Maxwell/Gauss: d/l = 3.7
  • Brooks: l/d = 0.337 ~0.333; d/l = 2.97 ~3
  • 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

Gain Constant Depends Upon:

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

  • Frederick W. Grover, Inductance Calculations, New York: D. Van Nostrand Co., 1946, pp. 97-97.
  • James Clerk Maxwell, A Treatise on Electricity and Magnetism, 3rd ed., Vol. II, Oxford University Press, 1892, pp. 345-346.
  • H. B. Brooks, “Design of Standards of Inductance, and the Proposed Use of Model Reactors in the Design of Air-Core and Iron-Core Reactors,” Bureau of Standards Journal of Research, Vol. 7, No. 2, August 1931, pp. 289- 328, (Research Paper #342). See: http://1.usa.gov/1tL6Ium

Antenna Gain

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.

Gain Constant Value:

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

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

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

"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

Friis' Law

Ferrite Antenna Measurements

Near-Field Link

Laws: Gain-Aperture

Marconi

Lodge &

Far-Field

Wireless

Two link laws

  • "Like" Antennas
  • "Unlike" Antennas

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

Gain Measurements

Gain of Antenna Under Test Given Reference:

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.

Near-Field

Link Laws: Gain-Gain

Three Antenna Gain Measurement:

Wardenclyffe Tower

Tesla's Colorado Springs Experiments

Air Core Antenna Measurements

Oliver Lodge

1850-1940

Near-Field

Link Laws: Gain-Gain

Two link laws

  • "Like" Antennas
  • "Unlike" Antennas

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

Accelerating charges are not the source of radiation energy

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

High Frequency Wireless

Comparison

of Results

  • Gain best describes transmit behavior
  • Aperture best describes receive behavior

Evaluation of Magnetic & Electric Antennas

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.

Preece's

Inductive Wireless Telegraphy

  • VHF
  • UHF
  • Microwaves
  • Radar
  • Cellular Communications
  • Millimeter Wave
  • "Electrically Small" kR ~ 1
  • Railway Telegraphy
  • Inductive Wireless
  • Discovery of Far-Field Wireless
  • Re-discovery of Near-Field Wireless

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

William Henry Preece

1834-1913

UWB Antennas

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

Specifically:

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

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.

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:

Numerical Modeling

IEEE Lecture Series in Electromagnetics

NEC Validation

Excellent agreement!

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
  • NEC Validation

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

  • Range: 20-60m
  • Accuracy: 30cm-1m
  • Frequency ~1MHz
  • Capacity: ~80 tags

at 1Hz update

  • Q-Track Corporation

(www.q-track.com)

Encompasses a wide variety of technologies including:

  • 10cm read at 120-150kHz
  • 10cm-1m read at 13.56MHz

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

Average Energy Velocity for Various VSWR

Elemental Waves

Schantz, Hans G., “On the Superposition and Elastic Recoil of Electromagnetic Waves,” FERMAT, Vol. 4, No. 2, July-August 2014 [ART-2014-Vol4-Jul_Aug-002]. See also http://arxiv.org/abs/1407.1800

Energy Velocity

Average Energy Velocity of Standing Waves

Image Theory

Average Energy Velocity

where:

Schantz, Hans G., “On the Superposition and Elastic Recoil of Electromagnetic Waves,” FERMAT, Vol. 4, No. 2, July-August 2014 [ART-2014-Vol4-Jul_Aug-002]. See also http://arxiv.org/abs/1407.1800

Standing

Waves

Energy Velocity & Impedance

Energy velocity in terms of the normalized impedance…

Normalized Impedance

  • Elemental Waves
  • Image Theory
  • Impulses

-Symmetric

-Arbitrary

  • Harmonic Waves

"Pure" & "Impure" Waves

Harmonic Standing Waves

William Suddards Franklin (1863-1930) in 1909

Pure Wave

  • Progresses w/o change in shape
  • Impedance that of free space
  • Equal balance of electric and magnetic energy
  • Energy velocity = c

Impure Wave

  • Progresses w/o change in shape
  • Impedance not that of free space
  • Unequal mix of electric and magnetic energy
  • Energy velocity < c

Voltage and Current Waves

Power

Franklin, William Suddards, Electric Waves: An Advanced Treatise on Alternating-Current Theory, New York: The Macmillan Company, 1909, pp. 88-93. See Chapter 4. See: http://bit.ly/1rerFKe

Energy

Symmetric Impulses

Arbitrary Impulses

Gaussian Impulses

Spacetime Diagrams

Electromagnetic Newton's Cradle

Don't Cross the Streams!

E-Phase

H-Phase

EH-Phase Delta

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