An ultrasonic transceiver device for producing ultrasonic beams comprises a body vibratable at ultrasonic frequencies and an extensive surface for beam emanation, the device configured to produce an unfocused, or alternatively a focused, power beam for thermal tissue damage, the power beam being produced by vibration over the body of the transceiver and emanating from the extent of the surface, whereby the extensive surface becomes subject to convective cooling when immersed in a fluid by a chimney effect set up by said unfocused beam.
