"Breathing" ring effect

Hi guys, it’s my first time trying to reach out for help in this forum and I hope that I didn’t asked this question in the wrong section.
Anyway, I’m trying to make an healing effect form an university project and I need to create a pulsing ring in the center of my effect. I managed to create the impulse but i need it to be like a “breathing” effect; with this I mean that I want to change the intensity of the opacity of the effect over time, making it look like if it’s breathing.
Any ideas of how I can obtain such a thing?