A brush module for a rotating grinding brush, said brush module comprising: an elongate body part ; at least one abrasive cloth protruding from the body part ; a plurality of bristles extending from the body part essentially in the same direction as the abrasive cloth. A movable compacting punch is disposed in the die cavity and can move upwardly towards the die cavity opening to compact powder disposed in the cavity. Part of the guide wave energy leaks into the fluid in the form of bulk waves, reflects off the inner wall on the other side and enters back to the receiving transducer trailing the direct wave.