Chapter 1
WIA-COMM-009 (version 1.0.0, status Active, category COMM) describes wireless power transfer (WPT) as a family of technologies rather than a single product class. A phone pad, a 1 to 2 metre resonant link under a vehicle, a microwave beam to a rectenna, a laser aimed at a photovoltaic receiver and an orbital transmitter feeding a ground-side rectenna farm all move energy without a conductor. They differ in physics, power level and risk profile. The standard treats them under one vocabulary so that a system's mechanism, power, efficiency and legal authorisation can be described, compared and tested in the same way.
The scope is broad. It covers inductive power transfer (IPT, including Qi and AirFuel), capacitive power transfer (CPT), resonant power (the WiTricity approach), microwave transfer with rectennas, and laser beaming. It also covers EV dynamic (roadway) charging, space solar power, industrial WPT for robots, AGVs and cranes, and the safety and efficiency disciplines common to all of them: SAR limits, EMI/EMC compliance, foreign object detection and power control, impedance matching and beam steering. The guiding principle is the Korean phrase 홍익인간 (弘益人間), "benefit all humanity". The standard aims to make cable-free charging infrastructure broadly available and to support sustainable electrification.
The overview in the standard summarises the technology families in one comparison table. The ranges are indicative envelopes. For example, the Qi profile in the detailed inductive section gives a much shorter range, 0 to 5 mm, than the 0 to 5 cm shown here. Treat the table as a map of regimes, not a guarantee for any product.
| 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 |
Reading down the table, range grows by several orders of magnitude while efficiency falls. That trade-off is the main design constraint in the field, and the rest of this chapter builds on it.
The standard divides all WPT into two regimes by the distance between transmitter and receiver, measured against the wavelength λ. In the near field (d < λ/2π) power moves by reactive, non-radiative coupling. The coupling can be magnetic, as in IPT and resonant systems, or electric, as in CPT. In the far field (d > λ) power moves as radiation, as in microwave and laser beams. Between the two is a transition (Fresnel) region, bounded above by 2D²/λ, where D is the aperture diameter. The standard gives the efficiency scaling for each regime:
| 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. A near-field link degrades steeply once the separation exceeds the coil size. A far-field link degrades gently but starts from a much lower ceiling, because most of the radiated energy misses the receiver unless the aperture and beam are well designed.
The core relations the standard uses are short enough to quote:
Near-field (inductive):
P_rx = k² × Q₁ × Q₂ × P_tx
k = M / √(L₁ × L₂)
η = k² × Q₁ × Q₂ / (1 + k² × Q₁ × Q₂) (loosely coupled)
Far-field (Friis):
P_rx / P_tx = G_tx × G_rx × (λ / 4πd)²
L_path [dB] = 20 × log₁₀(4πd/λ)
Resonance:
f₀ = 1 / (2π√(LC))In the inductive relations, k is the coupling coefficient (0 to 1) and Q₁, Q₂ are the quality factors of the transmit and receive coils. M is the mutual inductance. The product k²·Q₁·Q₂ is the figure of merit: when it is much greater than 1, the theoretical efficiency tends toward 1. A loosely coupled pair can therefore still be efficient if its coils have high Q. This is why resonant systems, whose typical k is only 0.05 to 0.15, can work at distances where plain induction would fail. For the far-field equation, G_tx and G_rx are linear antenna or aperture gains and d is the link distance.
The standard also gives rules of thumb for k in coaxial coils. Good alignment with d < r gives k of 0.6 to 0.9. Moderate alignment with d ≈ r gives 0.3 to 0.6. Poor alignment with d > r gives k below 0.3. Coupling collapses with offset, which is why alignment tolerance appears in the data descriptors discussed later.
No WPT product consists of the wireless link alone. Every system follows the same chain:
DC → AC (Inverter) → Wireless Link → AC → DC (Rectifier)The overall efficiency is the product of the stages. The standard lists 92-98% for the inverter, 30-95% for the link (distance dependent) and 85-95% for the rectifier. As an illustration, a 95% inverter, an 85% link and a 90% rectifier give about 73% overall, even though no single stage looks poor. The lost energy is heat, given by P_loss = P_tx × (1 − η). Thermal management is therefore part of the physics from the start and should not be left to packaging.
The standard's design process starts with requirements (power level, distance, frequency constraints such as ISM bands and regulations, efficiency target and cost) and then selects a technology. Its selection guide is deliberately coarse:
| Power | Distance | Technology |
|---|---|---|
| < 100 W | < 10 mm | Inductive (Qi) |
| 100 W - 50 kW | 10 mm - 2 m | Resonant |
| > 1 kW | > 2 m | Microwave/Laser |
Capacitive transfer fills niches that induction handles poorly. It couples through a dielectric: capacitance follows C = ε₀·εᵣ·A/d, and transferred power rises with frequency and the square of voltage. Compared with inductive systems, it tolerates nearby metal well and dielectrics poorly, generates less EMI, and uses cheaper plates than coils. Its typical efficiency is 60-80% against 70-90% for inductive. The standard names underwater charging, harsh environments with no exposed conductors, contactless slip rings in rotating machinery and medical implants as natural uses.
Within the near-field mechanisms, the key practical choices are coil design and compensation. Quality factor is Q = 2πf·L/R, so the engineering aim is to raise inductance relative to resistance:
Resonant links add a choice of compensation topology, which determines how the link behaves electrically:
| Topology | TX capacitor | RX capacitor | Characteristics |
|---|---|---|---|
| SS (Series-Series) | Series | Series | Constant current, simple |
| SP (Series-Parallel) | Series | Parallel | Constant current TX, voltage RX |
| PS (Parallel-Series) | Parallel | Series | Constant voltage TX |
| PP (Parallel-Parallel) | Parallel | Parallel | Constant voltage |
| LCC | L + C + C | Series/Parallel | Wide ZVS range |
Coupled-mode theory explains why such links need active control. Two coupled resonators split into two eigenmodes, ω₊ = ω₀√(1+k) and ω₋ = ω₀√(1−k), so the best operating frequency moves with coupling. That is why the standard lists frequency tracking (PLL) among its power-electronics controls, together with full-bridge or half-bridge inverters and a communication channel (ASK, FSK or Bluetooth).
The standard also records the established product profiles that this engineering produces. Qi (WPC) runs at 80-300 kHz and 5-15 W in its baseline profile, with an extended profile at 2 MHz and up to 100 W, and uses ASK modulation at 2 kbps over about 0-5 mm. AirFuel Resonant uses 6.78 MHz at 5-50 W over 0-50 mm, with Bluetooth Low Energy for communication. SAE J2954 for EV charging uses 85 kHz with four power classes (WPT1 3.7 kW, WPT2 7.7 kW, WPT3 11 kW, WPT4 22 kW), an air gap of 100-250 mm, misalignment tolerance of ±100 mm (X) and ±75 mm (Y), and grid-to-vehicle efficiency above 85%.
Wireless power puts energy into open space, where people, animals and metal objects may be present. The standard therefore treats safety as a design input. It lists four main considerations:
The standard's Phase 1 (data format) turns these ideas into descriptors that travel with a system. The system descriptor groups installations by mechanism and gives the mechanism-specific operating envelopes. IPT uses k of about 0.05-0.5, resonant systems high-Q LC tanks with k of 0.05-0.15, microwave beams use 2.45, 5.8, 24, 35 or 94 GHz, and lasers use near-IR or SWIR wavelengths of 808, 976 or 1550 nm. Space solar is modelled as an orbital transmitter feeding a ground rectenna farm. Each record carries the same canonical fields:
Two further descriptors reflect the physics above. The resonator descriptor holds topology (for example, planar coil with LCC compensation on the Tx side, matched LCC or series-parallel hybrid on the Rx side), Q factor (typically 100-500 for high-Q resonant designs), frequency stability across temperature, and the impedance-matching, per-receiver decoupling and SOTIF envelopes where the system operates in human-occupied space. The link descriptor holds per-link distance, the alignment envelope (lateral and angular tolerance before efficiency falls below policy) and a link budget that follows Tx power through free-space or coupling loss and Rx-side conversion to delivered DC power. This is the Friis and k²QQ relations expressed as data.
For beamed power, the microwave and laser envelope records transmitter aperture and gain, the beam-steering method (mechanical, electronic phased array or liquid crystal), rectenna count and per-rectenna conversion efficiency, and a beam-safety envelope. The central safety element is an interlock chain that gates the transmitter unless the receiver acknowledges its presence, so a beam cannot run unattended toward an unknown target.
Phase 2 groups the API surface into systems, links, safety tests, telemetry and regulatory data. The reference TypeScript SDK (@wia/comm-009) exposes the mechanisms as classes (InductiveWPT, ResonantWPT, MicrowaveWPT, LaserPowerBeaming, EVDynamicCharging). A shortened example from the standard shows a Qi-class charger and a microwave beam:
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}%`);
const microwaveWPT = new MicrowaveWPT({
frequency: 2.45e9, // Hz (2.45 GHz ISM band)
transmitPower: 1000,
antennaGain: 20, // dBi
beamSteering: true
});
const beam = await microwaveWPT.transmit({
targetLocation: { latitude: 37.7749, longitude: -122.4194 },
distance: 500, powerRequired: 100
});Note how the parameters mirror the physics. The Qi charger takes a frequency, a coil size, a FOD flag and a millimetre-scale alignment offset. The microwave transmitter takes an ISM-band frequency, antenna gain in dBi, beam steering and a distance. A command-line tool, wia-comm-009, offers the same calculations without code, with subcommands for inductive, resonant, microwave, laser and ev-dynamic scenarios, plus efficiency and safety analyses. For example, wia-comm-009 safety --power 1000 --distance 2 --frequency 2.45e9 checks a 1 kW, 2.45 GHz source at 2 m.
This chapter set out the shape of the standard. WPT is a continuum from near-field coupling to far-field beaming. Near-field links are governed by the coupling coefficient and the quality factors of the coils, far-field links by gain, wavelength and distance. Whatever the mechanism, the end-to-end result is the product of inverter, link and rectifier efficiencies, and the lost fraction becomes heat that must be managed. Technology choice follows power and distance. Inductive suits under 100 W at under 10 mm, resonant suits roughly 100 W to 50 kW out to 2 m, and microwave or laser suits long range. The established profiles (Qi, AirFuel Resonant, SAE J2954) fix frequency, power class and tolerance for their markets. Safety is built in through SAR limits, EMC compliance, foreign-object and living-object detection, and an interlock that stops a beam when no acknowledged receiver is present.
The standard captures all of this as structured records: a system descriptor with mechanism, frequency, power, efficiency profile, distance envelope and regulatory envelope; resonator and link descriptors that carry Q, alignment tolerance and the link budget; and a beaming envelope with its interlock chain. The SDK and CLI then exercise those same quantities.
The next chapter picks up the data side. It starts from the system descriptor and works outward to resonator, link and beaming records, showing how a design decision such as a compensation topology, an alignment tolerance or a rectenna array is written down so that another party can check the efficiency and safety claims against the physics set out here.