Each vowel sound is a distinct shape of the mouth, tongue, and throat. When you say 'ah,' 'ee,' or 'oo,' not only does the air inside your head change, but so does the way radio waves pass through it. Researchers peered into this process using MRI scans taken right during speech and built a precise computer model of the head — from bones to soft tissues.

Then they sent radio signals at frequencies from 1 to 6 gigahertz (roughly the Wi-Fi range) through the model and compared the results with what sensors on the heads of two living people picked up. The picture matched: waves don't pass straight through like through glass; they scatter, much like light in fog. Each vowel produces its own pattern of bright and dark spots — maxima and minima of the signal.

The key finding is that the signal shape isn't random. It results from two things: how the head itself resonates (like a bell at certain notes) and where the receiving and transmitting antennas are placed. By changing the vowel, you slightly shift these resonances, and at the other end of the 'wire,' you see a characteristic peak or dip. It's like tuning a radio, except the knob is your jaw.

Such a model paves the way for devices that read silent speech: an antenna picks up a radio signal that has passed through the head, and software determines which vowel was pronounced based on its pattern — even if the lips never moved.