A new type of ultrasonic immersion transducer has been designed and constructed that has a wide bandwidth when used in water. It is a capacitive (electrostatic) device, using a micromachined backplate and a thin mica metallized membrane. It will be demonstrated that the field pattern of the device can be plotted experimentally using a miniature hydrophone, and the results will be compared favorably to theoretical predictions. The device has been produced as a plane piston, and also as a focusing device using both an annular transducer and a zone plate. The device has none of the ringing associated with piezoelectric devices, and hence is suitable for a wide range of applications.