An ultrasonic emitter apparatus for thermal treatment with focussed energy application comprises a resonant unit including a tubular cylindrical active element having an exterior surface facing in a radially outward direction and an interior surface facing in a radially inward direction, said active element being operative to generate ultrasonic vibrations in response to an applied signal, said resonant unit including a liquid disposed within the Interior of said active element, said resonant unit being resonant at an ultrasonic frequency and adapted to emit ultrasonic vibrations at said ultrasonic frequency principally in said radially outward direction.
