XJTU twisting antenna sends an underwater signal on milliwatt power

A compact transmitter sent a signal from roughly 30 metres below the surface of Qiandao Lake to a receiver 115 metres away on shore. Xi'an Jiaotong University described the experimental system on November 12: its dimensions are roughly six centimetres on each side, and total power consumption is 10.4 milliwatts. Piezoelectric material drives a magnet through repeated twisting motions to generate a changing magnetic field.

Underwater communications face a problem that an ordinary phone largely avoids. Higher-frequency radio signals are strongly attenuated in water and other difficult environments. Lower frequencies can help with penetration, but their long wavelengths make conventional efficient antennas large. SLAC's account of its 2019 compact-antenna research explained the competing constraints: portability, radiation efficiency and bandwidth. A useful transmitter has to fit both its operating environment and its available energy supply.

Mechanical antennas are an established way to approach that trade-off. SLAC's roughly ten-centimetre device used a vibrating crystal. A 2025 Nature Communications paper described a centimetre-scale system in which piezoelectric ceramics rotated a magnetic disc, reporting underwater magnetic-field measurements at 100 metres with approximately 0.61 watts of input power. Neither mechanical actuation nor underwater magnetic communication began with the latest demonstration.

The Xi'an design uses back-and-forth twisting and resonance. The everyday analogy is a swing: small pushes delivered at the right rhythm can sustain a much larger motion. Here, the changing orientation of a magnet provides the changing magnetic field. The practical combination demonstrated is a complete small transmitter, milliwatt-level consumption and a water-to-shore link over a hundred metres.

Those numbers are not a universal performance ranking. Frequency, receiver sensitivity, propagation medium and information rate all affect what a communication system can do. A seawater experiment in the earlier paper and a freshwater lake trial are not interchangeable benchmarks. Our assessment is that the new design adds an engineering option for low-power links; simply dividing the two power figures would not establish a like-for-like efficiency improvement.

The consumer relevance is less about taking mobile broadband diving than about keeping underwater instruments working. Remote sensors need energy for both measurements and reporting them, and replacing their batteries can be a separate operational burden. A lower communication budget could leave more capacity for sensing or longer deployment. That is a system-design opportunity, rather than proof of a particular commercial battery life.

A field link is a meaningful milestone because the transmitter has moved beyond an isolated component measurement. Turning it into dependable equipment still means treating the transmitter, receiver and required messages as one system. The lake result supplies a concrete step in that direction, without making it the first small underwater antenna.

Original source published: Xi'an Jiaotong University, November 12, 2026, 15:23 Beijing time / 02:23 EST.