This is a controversial device that is designed to generate a low level electromagnetic signal that emulates one that occurs naturally in the area between the planet and its ionosphere.
In nature, the resonant cavity is "plucked" by the continuous lightning strikes happening around the world. In this unit it is a simple low frequency oscillator that provides an alternating voltage to a long spiral antenna.
I regard these items as harmless metaphysical devices for people who enjoy that sort of thing. The only ones I object to are the ones sold at a high price by scammers and falsely touted to cure medical ailments.
There are two main variants of these. Simple units with an open ended antenna like this one, and others that pass very high current through the coils to create a strong pulsing magnetic field.
Because the brain produces low frequency alpha waves of a similar frequency when in an awake, but relaxed state, there is a vague notion that somehow the brain is in resonance with the earth. As such, many people claim that these units promote a relaxed state of mind. They may not really understand how the brain actually works.
A scary example of people trying to focus their mind forcefully, is the ones who apply electrodes to their ears and pass AC current across their brain. I regard that as high risk, and potentially interfering with the brain's operation.
This unit was a cheap one from AliExpress:-
https://www.aliexpress.com/item/1005008717401850.html
I paid about £2.50 for it.
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