activated and in particular ultrasonic tools may be designed to resonate vibrate in four modes as shown in fig1 a d in a first longitudinal mode of vibration illustrated in fig1 a an elongate tool 30 is energized to expand and contract essentially along its major axis tool 30 is provided with a threaded stud or post 31 for operatively connecting or coupling the tool to an electromechanical transducer assembly not illustrated a second type of mode fig1 b is called transverse wherein a differently designed tool 32 whips from side to side at its free tip in a third mode of vibration namely radial resonance the diameter of a tool 34 expands and contracts as illustrated in fig1 c torsional vibration as shown in fig1 d is also possible where a tool 36 is constrained to twist tools 32 34 and 36 are respectively provided with threaded studs 33 35 and 37 for operative attachment to transducer assemblies as before tools may alternatively be provided with a female threaded coupling that is a threaded bore for mechanical coupling with a threaded stud on an electromechanical transducer assembly not illustrated all of these modes are useful in generating a skin on a flowable particulate mass such as a meat product emulsion although some modes are preferred over others in this application one configuration that has proven effective for forming a skin on a cylindrical extrudate of particulate meat product is shown in fig2 a here a radial ring resonator tool 38 has been constructed with multiple electromechanical transducer assemblies 40 mechanically coupled via a threaded post and bore arrangement not visible to machined land areas 41 of an outer circumferential surface 42.