The present invention is directed to an ultrasonic repellent humidifier for dispersing insect repellant into the air as a micro fine repellent vapor. A repellent tank provides rhodinol and cedarwood oil based repellent to a repellent well. An ultrasonic transducer is positioned in the well beneath the level of the repellent. It vibrates, forming a repellant vapor that is drawn into a vapor duct by a forced air system and out of the unit, dispersing the repellent vapor into the surrounding air. The vibrating portion of the ultrasonic transducer that is exposed to the oil-based repellent is a ceramic material that inhibits residue from forming on the transducer that reduces its efficiency. The ceramic material may be formed on the metal case of the transducer or on the piezoelectric oscillation crystal, or it may be a separately replaceable disc.
