Finland sends electricity through air using sound waves and lasers for first time.

Scientists in Finland just pulled off something that once sounded impossible…sending electric power through the air. Using a mix of ultrasonic sound waves and laser beams, researchers managed to guide electricity without any physical wires. The test was done in controlled conditions, but it worked as planned. This moment is being seen as a serious step toward truly wireless power systems.

The research is being led by teams from the University of Helsinki and the University of Oulu. One method uses strong sound waves to shape the air itself, creating invisible paths that guide electric sparks. Scientists call this an acoustic wire. Another method uses lasers to help steer the energy safely and precisely across open space.

While this technology is still early and experimental, the future impact could be huge. Homes, factories, and smart devices could one day get power without plugs, cables, or contact points. That could change how cities are built and how devices are designed…

Table of Contents

Wireless Power via “Acoustic Wires” and Laser-Guided Discharges

In a recent Finnish proof-of-concept, researchers combined intense ultrasound and focused laser beams to steer electrical sparks through air – effectively creating a temporary “wireless wire” for electricity¹². The key physics is that a high-voltage spark heats the air, causing it to expand and become lower-density; this rarefied channel has a much lower breakdown voltage, so electricity preferentially travels through it. A focused ultrasonic field then pushes the hot, low-density air into its high-pressure regions (antinodes), confining the discharge along a chosen path¹². In other words, the ultrasound creates an “acoustic wire”: the discharge follows the acoustic focal zone. (In contrast, high-power laser pulses can ionize air directly to form a plasma conduit. Short laser pulses above a critical power self-focus in air and leave behind a narrow, conductive plasma channel acting like an electrical wire³⁴.)

Figure (Acoustic wire guiding). Without ultrasound (left), a high-frequency spark splits chaotically. With a focused 40 kHz ultrasonic field on (right), the purple discharge is confined to a single straight path. The sound field pushes the hot, lighter air into its antinodes, creating a low-density “wire” that the spark follows¹².

In the published demonstration (Irisarri et al., Science Advances 2025), the team used a small Tesla coil to create pulsed AC sparks and a custom ultrasonic emitter array to steer them. The Tesla coil ran at ~2.4 MHz carrier frequency, with amplitude modulation (~2.5 kHz, 50% duty), driven by a regulated 20–45 V supply at ~1 A⁶. The resulting spark currents were very low (microamp to milliamp scale), producing brief purple arcs of order a few centimeters. Surrounding the coil was an ultrasonic array of two concentric rings (17 cm diameter each) bearing 32 piezo transducers per ring, driven at 40 kHz⁷. The array generated standing-wave pressure maxima of order 1,500 Pa at the focal point. High-speed imaging showed that when the ultrasound was on, the spark would be drawn into the acoustic focal point in ~15–35 ms⁸ and then propagate along that path. With the ultrasound off, the same coil produced a branching, chaotic discharge.

Figure (Laboratory setup). (A) Side view of the ring of ultrasonic transducers (silver cylinders) around the Tesla coil electrode. (B) Top view: the 40 kHz standing-wave pattern (red overlay) traps the hot plasma (purple), confining it to a square channel. The array had 32×2 emitters as described in Irisarri et al.⁷.

Comparison with other wireless power methods: Unlike near-field inductive or capacitive coupling (which require coils or electrodes within centimeters), the acoustic/laser method uses radiative (propagating) energy. For context, tightly coupled inductive chargers (Qi standard) can achieve 30–60% efficiency at a few millimeters to centimeters range⁹. Resonant inductive systems (e.g. WiTricity) can work over ~0.5–1 m, reaching ~90% efficiency at 0.5 m for multi-kilowatt loads¹⁰, but efficiency falls off quickly beyond ~1–2 m. Microwave power-beaming (long-range radiative) has demonstrated tens of percent efficiency: e.g. William C. Brown’s 1975 experiment beamed 30 kW over 1.6 km at ~50% efficiency¹¹, while DARPA’s 2025 test delivered 800 W over 8.6 km at ~20% efficiency⁵. Laser beaming can also reach kilometers: NRL’s 2019 demo transmitted 400 W over 325 m (to run laptops via a solar receiver)¹². However, all such radiative methods face safety and atmospheric losses. By contrast, the Finnish acoustic-wire demonstration delivered only micro-watt to milliwatt levels, over centimeter distances (the setup used tiny sparks), so its power transfer efficiency is extremely low – essentially a physics demo, not a practical power system¹³¹⁴.

The following table summarizes key attributes:

Method	Power Efficiency	Typical Range	Safety/Exposure	Cost/Complexity	Maturity
Ultrasonic “acoustic wire” (Helsinki lab)	Negligible (microwatts over cm)¹³	cm (lab-scale)	Moderate – intense ultrasound (160 dB eq.) but non-ionizing¹⁵	Moderate (arrays of transducers)	Experimental (2025)
Inductive coupling (e.g. Qi pads)	30–90% at mm–cm gaps⁹	~0–5 cm	Low (magnetic fields at kHz)¹⁶	Low–moderate (coils)	Commercial (phones)
Resonant inductive (e.g. EV charging)	~90% at ~0.5 m¹⁰, falls to <30% at 1–2 m	~0.5–2 m	Moderate (strong kHz/MHz fields)	Moderate (tuned coils)	Emerging (some EV systems)
Microwave beaming	~50% (short distance)¹¹; ~20% (km-scale)⁵	10s m–km (LOS)	High (ionizing/thermal hazard, strong RF)¹⁵	High (antennas, RF amps)	Prototype (space solar, demo)
Laser (optical) beaming	~20% (long-range)⁵; up to 50% with optimized PV¹⁷	10s m–km (LOS)	Very high (eye/skin hazard, requires safety interlocks)⁴	High (high-power lasers, PV receivers)	Demonstrations (demos, DARPA)
RF harvesting (“Wi-Fi power”)	≪1% (μW from ambient)¹⁸¹⁴	10s–100s m	Low (low-power RF)	Low (chips/antennas)	Commercial (sensors)

(Sources as cited above; “range” indicates useful distance under ideal lab/demo conditions. “Safety” rates risk to humans/devices.)

Safety and Hazards: Each method has distinct concerns. The Finnish ultrasound experiment itself did not involve any strong electromagnetic fields, but high-intensity ultrasound can heat tissue or cause mechanical harm if misdirected (though 40 kHz is above human hearing, animals may be affected). The researchers note that using ultrasound is safer for eyes and skin than powerful lasers⁴. However, continual 160+ dB fields would likely require shielding in practice. The arc discharges themselves produce ozone and nitrogen oxides, which are irritants, and generate broadband EM interference. Laser beaming carries severe eye/skin hazards (invisible infrared can blind), requiring strict controls. Microwave power lines must avoid personnel exposure (FCC/ICNIRP limits) and can interfere with communications. The DailySun fact-check warns that these lab sparks deliver only trivial power and “do not transmit electricity at practical scale,” underscoring that current demonstrations are far from consumer-safe, full-scale systems¹⁵¹⁴.

Applications & Implications: In theory, an “acoustic wire” could enable contactless high-voltage routing or new kinds of switches. The authors suggest uses like contactless haptic feedback, patterned plasma treatments, or flexible circuit routing¹⁹. However, they emphasize these are fundamental physics results, not a turnkey power source¹⁵. In contrast, laser (and microwave) power-beaming is already being explored to power remote drones, sensors, and even UAV charging tethers. For example, DARPA and companies (EMROD, PowerLight) are developing laser-beamed power stations to charge drones in flight or transmit solar power from space⁵¹². Still, even these aim for specialized cases (mile-scale line-of-sight links) and could take years to commercialize. The Finnish work hints at a future where device designs might incorporate onboard receivers (PV cells or antennas) and need no plugged cables, but any urban “wireless grid” would require orders-of-magnitude more power and stringent safety nets than today’s demos allow.

Challenges and Open Questions: The key barriers are efficiency, alignment, and power scaling. The acoustic-wire method has so far only steered tiny spark pulses; sustaining a continuous current or delivering kilowatts would require far larger, more powerful arrays and dealing with losses in the discharge. Timing control is another issue: unlike lasers that ionize before each pulse, ultrasound takes milliseconds to form the guiding channel⁶²⁰. Real-world deployment must address atmospheric turbulence, moving targets, and the risk of unintended arcing. For laser beaming, mirror or atmospheric distortion can defocus the beam; optimizing the PV receiver spectrum and cooling is crucial. All methods must also grapple with regulation (spectrum/eye-safety standards) and the need to integrate with existing infrastructure. Current research is expanding into multi-beam steering, phased arrays, and new materials to improve conversion efficiency²¹¹⁷. Ultimately, the technology is at a proof-of-concept stage: further work is needed on power handling, safety protocols, and cost reduction before any practical “wireless power cables” become reality.

Sources: This analysis draws on the original Helsinki-led publication on acoustic guiding²¹, official University news releases¹⁴, and coverage of related technologies⁵¹²¹⁵. The table and comparisons incorporate known benchmarks from wireless power literature⁹¹⁰¹¹. All cited findings are from peer-reviewed or authoritative sources as noted.