Chapter 3
WIA-COMM-009 (version 1.0.0, status Active, published 2025-12-26) treats wireless power transfer (WPT) as a single problem space. That space runs from a phone resting on a charging pad to a laser beam crossing hundreds of kilometres. These systems have little in common mechanically, but the standard groups them because they share one underlying mechanism, electromagnetic coupling between a transmitter and a receiver. They also share one dominant tradeoff, which is that efficiency falls as distance grows.
The key-feature list names ten capabilities:
The standard separates the regimes by the distance between the two ends, measured against the wavelength of the field in use. Inside roughly λ/2π the field is reactive and non-radiative. Energy sloshes between the coils or plates, and the receiver draws from that stored field. Beyond about one wavelength the energy radiates and obeys the Friis relation. The region between the two is a transition zone, bounded at its far edge by 2D²/λ, where D is the aperture diameter.
| Regime | Distance | Dominant mechanism | Efficiency scaling |
|---|---|---|---|
| Near-field | d < λ/2π | Reactive coupling | ∝ (1 + d²/r²)⁻³ |
| Fresnel | λ/2π < d < 2D²/λ | Transition | ∝ 1/d |
| Far-field | d > 2D²/λ | Radiation | ∝ 1/d² |
Here r is the coil or plate radius. The table explains why a coil that works well at a few millimetres is useless at a few metres. Near-field efficiency collapses with a steep cube-law term once the gap exceeds the coil radius. Far-field links lose power more gradually, but they need large apertures and tightly controlled beams to deliver anything usable.
Two relations anchor the rest of the standard. For near-field magnetic coupling:
P_rx = k² × Q₁ × Q₂ × P_tx
k coupling coefficient (0-1)
Q₁,Q₂ quality factors of the TX and RX coilsFor far-field radiation:
P_rx = P_tx × G_tx × G_rx × (λ / 4πd)²
G_tx, G_rx antenna gains
λ wavelength
d distanceEverything else in the standard is a refinement of these two. Coil design is an effort to raise k and Q. Rectenna and beam-steering design is an effort to raise gain and keep the beam on target. Both efforts aim to push the received fraction of transmitted power higher.
The standard states its purpose through the principle of 홍익인간 (benefit all humanity): cable-free charging infrastructure that is safe, efficient and interoperable. The scope covers consumer electronics, electric vehicles, industrial systems and space-based solar power.
The standard's central summary is a ladder of technologies, each fitting a band of distance and power. The figures below are the ranges given in the standard's core-concepts table.
| Technology | Range | Efficiency | Power | Frequency |
|---|---|---|---|---|
| Inductive (Qi) | 0–5 cm | 70–90% | 5–15 W | 80–300 kHz |
| Resonant | 10 cm–2 m | 40–80% | 1–11 kW | 6.78 MHz |
| Microwave | 1–1000 m | 10–50% | 1 W–100 kW | 2.45–24 GHz |
| Laser | 100 m–1000 km | 10–40% | 1 W–1 MW | IR/Optical |
Each step to the right trades efficiency for reach. Alongside this ladder the implementation guidelines give a selection rule of thumb. Below 100 W at under 10 mm, choose inductive. From 100 W to 50 kW at 10 mm to 2 m, choose resonant. Above 1 kW and beyond 2 m, choose microwave or laser. The ranges overlap at the edges, which signals that selection is a design judgement and not a lookup. Frequency limits, regulatory constraints, the efficiency target and the cost budget all enter the decision.
The headline efficiency of a wireless link is not the efficiency of the whole system. The standard describes every WPT system as a conversion chain:
DC → AC (Inverter) → Wireless Link → AC → DC (Rectifier)Typical per-stage figures are 92–98% for the inverter, 30–95% for the link depending on distance, and 85–95% for the rectifier. The overall efficiency is the product of the stages. A link that is excellent on paper can therefore disappoint at the wall socket if the inverter and rectifier are poorly chosen. This is why the optimization guidance spends as much effort on power electronics as on the coupling itself.
For the inductive case, the standard gives the loosely coupled efficiency expression, valid when k² is much less than 1:
η = k² × Q₁ × Q₂ / (1 + k² × Q₁ × Q₂)When k²Q₁Q₂ is much greater than 1, η approaches 1, which is the theoretical limit. The practical reading is that a weak coupling coefficient can be compensated by high quality factors. Quality factor is defined as Q = 2πf·L/R. Raising it means reducing series resistance, for example with Litz wire to tame skin effect above about 20 kHz, or with ferrite to concentrate flux. Mn-Zn ferrite suits below 1 MHz and Ni-Zn above it. Higher frequency permits smaller coils but raises AC losses, which is why Qi settles in the 80–300 kHz range, resonant systems use the 6.78 MHz ISM band, and EV systems use 85 kHz for better penetration and efficiency.
The coupling coefficient itself comes from geometry. The standard gives the mutual inductance of two coaxial circular coils and defines k = M / √(L₁ × L₂). As a rule of thumb it quotes k of 0.6–0.9 for excellent alignment with a gap smaller than the coil radius, 0.3–0.6 when the gap is about the radius, and below 0.3 beyond that. Misalignment therefore does the same damage as extra distance, which is why alignment appears as an explicit parameter whenever a link is requested.
Efficiency also determines the cooling load. Lost power is P_loss = P_tx × (1 − η). The standard's worked example is an 11 kW EV charger at 90% efficiency, which dissipates 1,100 W as heat. It maps that onto cooling options: natural convection below 50 W, forced air for 50–500 W, and liquid cooling above 500 W. A "small" efficiency gap is therefore a thermal design problem as well as an energy cost.
The standard is delivered in four phases: a data format (system, resonator, microwave/laser, safety and space-solar envelopes), an API, protocols for each technology family, and ecosystem integration. The unifying idea is that a WPT installation is described as a registered system, and energy flows only through an explicit link between a registered transmitter and a registered receiver.
The TypeScript SDK (@wia/comm-009) models each technology as its own class: InductiveWPT, ResonantWPT, MicrowaveWPT, LaserPowerBeaming and EVDynamicCharging. An inductive Qi-compatible charger is configured with its operating point and a foreign-object-detection switch:
const qiCharger = new InductiveWPT({
standard: 'Qi',
frequency: 87000, // Hz
maxPower: 15, // Watts
coilDiameter: 0.05, // meters
foreignObjectDetection: true
});
const session = await qiCharger.startTransfer({
deviceId: 'phone-12345',
requestedPower: 10, // W
alignment: { x: 0, y: 0, z: 0.005 } // meters
});
console.log(`Transfer efficiency: ${session.efficiency}%`);
console.log(`Power delivered: ${session.powerDelivered} W`);The pattern is: configure the hardware envelope once, then request transfer sessions that carry a device identity, a requested power and a measured alignment. The session reports the delivered power and the efficiency actually achieved. The microwave class follows the same shape but swaps the geometry for far-field parameters: frequency, transmit power, antenna gain in dBi, and whether beam steering is enabled. A transmit call then names a target location, a distance and the power required, and returns the beam efficiency and received power.
The service interface exposes the same model over HTTP and a streaming channel:
POST /wireless-power-transfer/v1/systems # register WPT system
GET /wireless-power-transfer/v1/systems/{id} # fetch system record
POST /wireless-power-transfer/v1/links # establish link
GET /wireless-power-transfer/v1/links/{id}/state # current link state
POST /wireless-power-transfer/v1/safety/test # run safety self-test
WS /wireless-power-transfer/v1/telemetry/stream # live link telemetry
GET /wireless-power-transfer/v1/regulatory/{id} # regulatory authorisation statusRegistering a system returns a stable systemId. Opening a link carries the per-link parameters: alignment, requested power and link duration. The important design choice is that link creation is also a validation step. The endpoint checks the request against the regulatory envelope. A microwave-beaming link needs a current operator authorisation. A laser-beaming link needs the safety scanner's self-test to have passed within its documented validity window. Endpoints are discoverable through /.well-known/wia-wireless-power-transfer.
For engineers who prefer a shell, the CLI mirrors the technology families and adds calculators. A few of its invocations from the standard show the range of scenarios:
wia-comm-009 inductive --standard Qi --power 15 --frequency 87000
wia-comm-009 resonant --distance 1.0 --power 3300 --frequency 6.78e6
wia-comm-009 microwave --frequency 2.45e9 --distance 100 --power 1000
wia-comm-009 efficiency --technology resonant --distance 0.5 --coupling 0.6
wia-comm-009 safety --power 1000 --distance 2 --frequency 2.45e9The last two commands matter most in design practice. They let a designer test whether a proposed distance, coupling or exposure level is plausible before any hardware exists.
The standard devotes a protocol section to each family, and each family fails in a different way.
Inductive and resonant. The cited near-field standards are Qi from the Wireless Power Consortium, AirFuel Resonant, and SAE J2954 for EV charging. Qi runs at 80–300 kHz baseline, with 5–15 W baseline power and ASK modulation as its communication link (2 kbps). AirFuel Resonant sits at the 6.78 MHz ISM band and uses Bluetooth Low Energy for communication. SAE J2954 operates at 85 kHz with four power classes (WPT1 at 3.7 kW, WPT2 at 7.7 kW, WPT3 at 11 kW and WPT4 at 22 kW). It specifies an air gap of 100–250 mm, a misalignment tolerance of ±100 mm in X and ±75 mm in Y, and a grid-to-vehicle efficiency above 85%. For an EV, positional tolerance is a first-order requirement because a driver cannot park to the millimetre. In the standard's example, a resonant system at 6.78 MHz is built from a 0.5 m transmitter coil and a 0.3 m receiver coil. This shows that resonant systems accept larger gaps and looser alignment than a Qi pad does, at the price of a more demanding quality-factor budget.
Microwave. A microwave link is a radiating system, so the engineering concerns are aperture, gain and pointing. Antenna gain follows G = 4π·A_eff/λ². Beam steering uses a phased array, where the phase shift at element n is Φₙ = 2π·d·sin(θ)/λ, or a retrodirective array, which uses phase conjugation to aim the beam back toward a pilot signal. The receiver is a rectenna: antenna, matching network, rectifier (Schottky diodes or GaN HEMTs) and DC filter. The standard cites state-of-the-art rectenna efficiencies of 82% at 2.45 GHz, 85% at 5.8 GHz and 70% at 24 GHz, each quoted at a stated power density. Typical applications are drone charging, remote IoT sensors, disaster relief and forward military bases.
Laser. A laser link replaces the rectenna with photovoltaic cells matched to the laser wavelength. The overall efficiency is η_total = η_laser × η_transmission × η_PV, which the standard places at roughly 5–25% in typical conditions. Wavelength is therefore a system-level decision. The standard tabulates the choices:
| Wavelength | Laser type | Atmospheric transmission | PV match | Safety |
|---|---|---|---|---|
| 450 nm | Diode | Poor (Rayleigh) | Si good | Eye hazard |
| 808 nm | Diode | Good | GaAs/Si | Eye hazard |
| 980 nm | Diode | Good | GaAs | Eye hazard |
| 1064 nm | Nd:YAG | Excellent | InGaAs | Eye safe-ish |
| 1550 nm | Fiber | Excellent | InGaAs | Eye safe |
The table captures the tension in laser design. Wavelengths with the best atmospheric transmission and cell match are not necessarily the safest for the eye. Beam geometry follows a Gaussian profile, with divergence θ = λ/(π·w₀), so a larger beam waist gives a tighter beam at distance. For eye safety the standard defines a Maximum Permissible Exposure and gives approximate values for a 1064 nm continuous-wave beam: about 2 W/m² for the eye and about 1000 W/m² for the skin. Applications include space power relay, lunar polar base power, helicopter-to-ground relief power, underwater links where light penetrates better than RF, and hazardous areas where sparks and EMI must be avoided.
Capacitive, EV dynamic and space solar. CPT couples through electric fields, with C = ε₀·εᵣ·A/d, so the dielectric and plate geometry set the coupling. EV dynamic charging extends the static case to a roadway, and the CLI includes a simulation for it taking vehicle speed, power and efficiency. Space solar power combines orbital generation with the microwave or laser transmission machinery above.
Safety in the standard is layered, and each layer addresses a different failure of the physics. Human exposure is bounded by a SAR limit of under 2 W/kg, referenced to FCC and ICNIRP, and by IEEE C95.1 exposure limits. Electromagnetic interference is bounded by FCC Part 15 and EN 55011. Metal debris trapped between coils is the characteristic near-field hazard. It heats up and detunes the link, so the standard calls for foreign object detection by Q-factor monitoring and thermal sensing, with FOD and living-object-protection (LOP) sensors in the safety integration step. Heat generally is handled through the loss budget in §3.2, and EMI through shielding. The measurement toolchain it names includes CISPR 11 and FCC Part 15 for EMC and IEEE 1528 or IEC 62209 for SAR.
Regulatory coverage reaches well beyond the transmitter hardware. The standards cross-walk lists, among others, SAE J2954 and J2847/6 for EV WPT, IEC 61980 for the EU, IEC 60825-1 for laser safety, ISO 14117 for implantable medical devices, ITU-R Radio Regulations for frequency allocation, and ITU-R P.676 and P.838 for atmospheric loss. Microwave beaming adds national licensing of frequency and transmit power. The standard also notes that the cross-walk is informative, and implementers must obtain authoritative texts from the issuing bodies. The API's link-level checks in §3.3 are how these requirements show up in software. A link cannot be established unless the matching authorisation or self-test is current. As a conformance layer, the standard also defines a supply-chain, attestation and governance process, but it is the same machinery used across the whole standards family and is not specific to wireless power.
The cost table in the implementation guidelines gives a sense of what the safety and conversion stack costs in practice. For an EV Level 2 stationary installation, the components include a transmit coil ($200–500), a receive coil ($300–600), power electronics ($500–1,500), control and communication ($100–300) and installation ($500–1,000). The total is $1,600–3,900 against a stated target of under $2,000. The numbers show that coil and ferrite design is only part of the budget, and the power electronics and installation labour are comparable.
Summary. This chapter framed WIA-COMM-009 around a few ideas that recur throughout the book:
The next chapter moves from this overview to the technical foundation. It develops the formulas introduced here, such as mutual inductance, quality factor, Friis path loss and Gaussian beam spread, into the design relationships that the standard's data format and protocols build on.