I have been using cheap table top ultrasonic humidifiers with Frankincense oil to repel negs, and it seems to be working fairly well in the room it is used in.

I can't work out if it is the Frankincense oil that is doing all the neg repelling work or the ultrasound waves.

Has anyone had any experience with repelling negs with ultrasound only? Or using similar ultrasonic humidifiers with oils?