Page 27 - PEN eBook October 2025

AEROSPACE AEROSPACE

Mid-field exploits resonant frequencies between In practice, this formula gives the free-space baseline,
transmitter and receiver circuits. Tolerating but real-world factors—oxygen and water vapor
misalignment and enabling greater distances, it’s absorption, rain, or fog scattering—further degrade
ideal for powering implanted medical aids or mobile beam quality, especially over long distances.
robotics.
MICROWAVE VS. LASER IN WPT
Far-field WPT involves transmitting electromagnetic There are two options for beaming energy over vast
energy over long distances, typically using highly distances: microwave and laser.
directional beams. At the receiving end, rectennas
(rectifying antennas) capture this energy and convert it Microwaves operate in the gigahertz range, providing
into DC electricity for powering drones, satellites, and a resilient and well-proven method for wireless energy
energy harvesters. beaming. Microwaves exhibit strong penetration in
adverse weather conditions (such as clouds and rain),
A practical example is space-based solar power and high safety tolerance owing to relatively low energy
(SBSP), where a satellite equipped with solar panels density. They’re already used in space-to-Earth (S2E)
Power from space (Source: Enel Green Power)
converts sunlight into electrical energy and transmits energy transfers via rectenna arrays, though they need
it to Earth via microwaves or lasers. On the ground, large antennas and face limitations in beam focus and
Beaming Power Across rectennas receive and convert the transmitted energy bandwidth.
into usable electricity.
Lasers, using infrared or visible light, offer high beam
the Void: Can Satellites of circular geosynchronous orbit at ~35,786 km above precision and dual capabilities for energy and data
A satellite in geostationary orbit (GEO), a special case
transmission.
the equator, remains fixed relative to the surface
Help Fuel the Planet? by matching Earth’s rotation, enabling continuous transmission, they’re more susceptible to atmospheric
While lasers offer high beam precision for S2E energy
transmission of microwave energy to ground-based
interference and require complex safety and thermal
receivers.
systems. Efficiency can also suffer outside ideal
By Filippo Di Giovanni, contributing writer for Power Electronics News A satellite in GEO experiences predictable eclipses of conditions.
up to 75 minutes near orbital midnight, occurring daily
during the roughly three weeks before and after the Choosing the right method depends on the mission:
As energy demand is soaring and the call for are permittivity and permeability of the vacuum. spring and fall equinoxes.
sustainable solutions grows louder, engineers are ▶ Microwaves suit energy delivery from satellites
turning to space as an untapped frontier. In the toolbox The transport of electromagnetic energy through Transmitting antennas in such systems are often to Earth.
of green energy production techniques, one of the most space is described by the Poynting vector , which phased-array or high-gain directional types, with
ambitious ideas is the wireless transmission of energy represents the directional energy flux. It is given by the parabolic reflectors frequently used to focus energy. ▶ Lasers are better for powering drones or
from orbiting satellites to Earth using microwaves or vector product: A rectenna typically consists of a receiving antenna, a deep-space assets.
lasers. This concept, once confined to science fiction, low-pass filter, a rectifying diode, and a DC filter.
is turning into a technological reality.
PARAMETERS AFFECTING WPT EXPERIMENTS
THE PHYSICS BEHIND WIRELESS WPT EFFICIENCY WPT began with Heinrich Hertz and was followed
POWER TRANSMISSION Efficient WPT depends on frequency, beam by Nikola Tesla’s wireless energy experiments, but
Wireless power transmission (WPT) is based on is perpendicular to and , and its magnitude divergence, conversion efficiency, and environmental it didn’t take off until 1964, when William C. Brown
the ability of electromagnetic waves to carry energy represents the rate at which electromagnetic energy interference. Higher frequencies enable tighter beam demonstrated a model helicopter powered solely
through free space without requiring a physical passes through a unit area per unit time, expressed in focusing and improved directivity but suffer greater by microwaves. In the 1970s, NASA explored using
transmission medium. watts per square meter. atmospheric attenuation. microwaves to beam solar energy from space to Earth,
leading to the invention of rectennas, which convert
Fundamentally, WPT is governed by Maxwell’s MODES OF TRANSMISSION In free space, the Friis transmission formula gives the microwave energy into DC electricity. Early tests
equations, one of the greatest achievements of human Depending on the range to be covered and frequency, maximum received power: achieved 54% efficiency, and the concept still inspires
intellect. It utilizes electromagnetic fields and, in there are three modes of implementing WPT: near-field, innovations in wireless power systems today.
some cases, electromagnetic radiation and resonance mid-field, and far-field.
phenomena, to efficiently transfer energy from a source REQUIREMENTS FOR 5-GW SBSP
to a receiver. In short-range applications such as in wireless SBSP offers continuous, weather-independent solar
charging pads, near-field is used, which is based on energy collection. Orbital platforms can operate above
The electric field and magnetic field store magnetic or electric field coupling between coils or the atmosphere, receiving a constant solar flux of
energy with volumetric densities (in joules per cubic plates. Such mode is limited by tight alignment, its linking received power to transmitted power, antenna ~1.36 kW/m —roughly 4× the long-term average of
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meter) of and , respectively, where and efficiency degrading rapidly with distance. gains, wavelength λ, and distance d. ~0.34 kW/m at Earth’s surface.
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