You talking about an ultra sonic cleaner If so ill tell you how they work as i validate them for hospital use,They basically send water molecules from one end of the bath to the other to validate i place a strip of tin foil in after a set period of time i remove the foil and it will look like a mini shotgun has been fired at it the weight of the foil will drop by over 50% Now if you use an ultrasonic cleaner use on its lowest setting for a short time.Do not buy a fixed power one you could destroy the coin  HTH