Resonant Wireless Power

Tesla's idea, the 2007 MIT proof, and an experiment you can build on your workbench

Tesla's Core Idea

In 1899, working in a temporary laboratory in Colorado Springs, Nikola Tesla did something that no one had done before: he lit 200 incandescent lamps from a distance of 25 miles, with no wires connecting them to the power source. His method was not magic. It was resonance.

Tesla had realized that the Earth itself behaves like a giant resonant cavity — a spherical shell of conductive ground surrounded by a conductive ionosphere, with a gap of insulating air between them. If you could drive an electrical oscillation at exactly the right frequency into this cavity, the energy would not dissipate randomly. It would travel through the Earth itself and emerge wherever a tuned receiver was waiting.

His Wardenclyffe Tower on Long Island (1901–1917) was the full-scale implementation of this idea: a 57-meter tower designed to pump oscillating current into the Earth at the planet's resonant frequency and deliver free, wireless power to anyone with a receiver. J.P. Morgan killed it. When Morgan realized that the system would allow anyone with a receiver to tap into the power — with no way to put a meter on it — he withdrew funding and refused to reinvest. The tower was demolished in 1917 for scrap. Tesla died broke in 1943.

The key insight Tesla was not trying to broadcast power through the air like a radio signal (which spreads out and loses energy as the square of distance). He was trying to drive a resonant standing wave through the Earth — like ringing a bell and having every tuned receiver in the world vibrate in sympathy. The energy would not be lost to radiation. It would be stored and redistributed by the resonant system.

He was 50+ years ahead of the theory that would formalize this. In 1952, German physicist Winfried Otto Schumann calculated the resonant frequency of the Earth-ionosphere cavity: approximately 7.83 Hz, with harmonics at 14.3, 20.8, 27.3, and 33.8 Hz. This is the Schumann Resonance — the actual heartbeat of the planet that Tesla had intuited experimentally before the mathematics existed to describe it.

Why It Actually Works — Resonant Inductive Coupling

The key physics principle is resonant inductive coupling, and it is different from simple inductive coupling (which is how a transformer works) in one important way: the coils must be tuned to the same resonant frequency.

In a transformer, two coils transfer energy because they are physically close. Move them apart and the coupling drops dramatically (as the cube of distance). In resonant inductive coupling, both coils form LC circuits (inductance + capacitance) tuned to the same resonant frequency. When one coil oscillates at that frequency, the other coil responds — at useful distances — because they share a resonant mode, not merely a magnetic field.

The analogy: two tuning forks of identical pitch. Strike one, and the other begins to vibrate, even across a room. A tuning fork of a different pitch is unaffected. That selectivity — that the energy goes specifically to a matched receiver and not to surrounding objects — is what makes this different from broadcast power.

The 2007 MIT Proof Marin Soljačić and colleagues at MIT (the WiTricity group) built two 60 cm diameter coils, tuned to the same resonant frequency (9.9 MHz), separated by 2 meters. With 60 watts of input, they delivered 45 watts to a light bulb connected to the receiving coil — 75% efficiency over 2 meters, through the air, with no physical connection. The coils were self-resonant helical structures, not wound around a core. The key paper is free online (see references below).

Key Papers and References

Paper	Why It Matters	Access
Kurs et al., "Wireless Power Transfer via Strongly Coupled Magnetic Resonances," Science 317(5834), 83–86 (2007)	The foundational MIT WiTricity experiment. 75% efficiency at 2 meters.	science.org
Bobowski et al., "Non-radiative mid-range wireless power transfer: An experiment for senior physics undergraduates," American Journal of Physics 86:623 (2018)	Written specifically to let you reproduce the MIT result at home. Full coil specs, all parts listed. Free PDF.	arxiv.org/abs/1812.00513
Tesla, "The Problem of Increasing Human Energy," Century Illustrated Magazine (June 1900)	Tesla's own description of his global wireless power vision, in his words. Freely available.	pbs.org/tesla
Tesla, Colorado Springs Notes, 1899–1900 (Nolit, Belgrade, 1978)	Tesla's actual laboratory notebook. Available through academic libraries and archive.org.	archive.org
W.O. Schumann, "Über die strahlungslosen Eigenschwingungen einer leitenden Kugel," Zeitschrift für Naturforschung A, 7(2), 149–154 (1952)	The paper that formalized the Earth resonance Tesla intuited. The Schumann Resonance.	German; summary available at Wikipedia
Hackaday.io — resonant LC coil demo	Practical build guide, commodity parts, circuit diagrams, 10W LED at 75 cm demonstrated.	hackaday.io/project/174181
Instructables — High-Range Wireless Power	Step-by-step guide targeting the 2-foot transfer range of the MIT demo.	instructables.com

The Home Experiment — What You Will Build

You will build two identical LC resonator coils, drive one with an oscillating signal, and light an LED or small lamp connected to the other — with no wire between them. This is the MIT experiment scaled to workbench size. Total cost: $30–60. Total build time: 2–4 hours.

What You Will Need

Magnet wire (enameled copper wire) — 28 or 30 AWG, 100 feet minimum. Available at electronics suppliers or Amazon. ~$8
PVC pipe or cardboard tube — 4 inches diameter, 8 inches long. Two pieces (one per coil). ~$3
Capacitors — 820 pF polypropylene film capacitors (Qty: 4, two per coil). Critical: use polypropylene, not ceramic — you need high Q. ~$5
IRFP460 N-channel MOSFET — or IRFZ44N for lower voltage. ~$4
ZVS driver circuit — a Royer oscillator. You can buy a pre-built ZVS driver board on Amazon for ~$4, or build from the Hackaday schematic.
12V DC power supply — 3–5A. An old laptop power brick works.
LEDs — 3 or 4 white LEDs, or a single 10W LED module (~$3)
Multimeter — to verify resonant frequency

⚠ Safety note The transmitter coil operates at 12V but generates a strong oscillating magnetic field. Keep pacemakers, credit cards, and magnetic storage media away from the coil while operating. Do not scale up the input voltage without understanding the physics — higher voltage increases field strength rapidly.

Building the Coils

Wind 100 turns of 28 AWG magnet wire tightly around your 4-inch PVC pipe. Leave 4 inches of wire at each end as leads. Sand the enamel off the last inch of each lead. Do this twice — both coils must be identical. Uniform winding matters: the inductance must match between the two coils.

Attach two 820 pF capacitors in parallel across the ends of each coil. This sets the resonant frequency: f = 1 / (2π √(LC)). For 100 turns on a 4-inch form with ~100 µH inductance and 1640 pF total capacitance, you get roughly 350 kHz. The exact frequency matters less than having both coils identical.

Connect the transmitter coil to the ZVS driver output. The ZVS driver will automatically find and lock to the coil's resonant frequency — that's what it does. Power it with your 12V supply.

Connect your LED(s) across the receiver coil ends. Place the receiver coil parallel to the transmitter, 6 inches apart to start. Power on the transmitter. The LEDs should light.

Move the receiver coil back in 2-inch increments. Note the distance at which the LEDs dim noticeably. This is your coupling range. At resonance, properly wound coils transfer energy usefully at 1–2 coil diameters of separation.

What You Are Experiencing

When the LEDs light up with no wire between the coils, you are watching exactly what Tesla was attempting at Wardenclyffe — energy transferred through the resonant coupling of two tuned systems, not through a physical connection. The only difference between your workbench and Tesla's tower is scale and medium. Tesla's transmitter was trying to use the Earth itself as the resonant medium. You are using the air between your coils.

For the book Document every step. Measure input power (voltage × current into the ZVS driver) and output power (voltage × current through the LED). Calculate efficiency. Compare to the Kurs et al. 75% figure. You will probably get 20–50% at 6 inches, dropping to 5–15% at 18 inches. That's real data. That's a real experiment. That's a chapter.