Abstract: A transdermal delivery system including a first passive portion containing a substance for delivery in a reservoir and a second active portion that includes an ultrasonic source. The ultrasonic source includes piezoelectric element(s) that receive electrical stimulation and move radially. A support member fixed to one side of the piezoelectric element(s) restricts movement at that side, so the opposite side expands and contracts. A fulcrum attached to the support member opposite of the piezoelectric element(s) provides an anchor point about which the piezoelectric element(s) bends and flexes upon electrical stimulation. This provides a low ultrasound frequency with a smaller sized transducer than previously known. The active portion is applied to provide electrical stimulation for a certain length of time and removed, whereas the passive portion may remain for a longer duration. A feedback loop also monitors and adjusts the electrical stimulation to maintain a uniform or constant resonance frequency.