This letter presents micromachined two-dimensional array flextensional
transducers that can be used to generate sound in air or water. Indiv
idual array elements consist of a thin piezoelectric ring and a thin,
fully supported, circular membrane. We report on an optimum design for
an individual array element based on finite element modeling. We manu
facture the transducer in two-dimensional arrays using planar silicon
micromachining and demonstrate ultrasound transmission in air at 2.85
MHz. Such an array could be combined with on-board driving and an addr
essing circuitry for different applications. (C) 1998 American Institu
te of Physics.