Vaccines can be delivered through the skin using ultrasound. This method doesn’t damage the skin and eliminates the need for painful needles. To create a needle-free vaccine, Darcy Dunn-Lawless at the University of Oxford and his colleagues mixed vaccine molecules with tiny, cup-shaped proteins. They then applied liquid mixture to the skin of mice and exposed it to ultrasound – like that used for sonograms – for about a minute and a half.
They were already terrified of phone signals.
Only fast ones though. Slower ones can’t penetrate the skin.
Hilariously enough, it’s closer to the other way 'round. Higher frequencies means more bandwidth but they can be blocked easier. Lower frequencies can go farther before being attenuated too much.