fig1 shows a piezoelectric film 1 forming a sensor element having contact surfaces 2 and 3 , the crystallographical axes of the sensors element being signed with x , y and z . monoaxially - oriented polymers direction x is chosen as the direction of the maximal stretch sensitivity parallel to the surface of the film . the direction of the initial tension is signed with x &# 39 ;. in most applications it will be advantageous to have angle α between the direction x of maximal sensitivity and direction x &# 39 ; of initial tension a value of zero or less than 45 degrees . contact surfaces 2 and 3 of film 1 are each formed by an electrically leading layer 4 &# 39 ;, 5 &# 39 ; consisting of metal evaporated on the film or of a conductive varnish . at least one of the contact surfaces 2 , 3 may be provided with an insulated electrical connection leading to a charge collector or directly to an electrical measuring chain . fig2 shows a sensor element 5 consisting of a flexible piezoelectric film attached to an electrically insulating tape 4 . for charge take off , leaders or printed leaders 6 and 7 are connected to the contact surfaces of the sensor element 5 . fig3 shows the sensor element of fig2 attached to pipe 8 , the free ends of the charge take off leaders 6 , 7 being schematically indicated . on the side facing the sensor element , tape 4 has a self - adhesive coating at least at the periphery portions projecting over sensor element 5 . when sticking tape 4 on pipe 8 , sensor element 5 is frictionally pressed against the pipe . variations of the diameter of pipe 8 therefore are transmitted to sensor element 5 by friction between pipe 8 and the piezoelectric film . the sensor element itself is not adhered to the pipe . fig4 shows a transducer according to the invention with the piezoelectric sensor element 9 being embedded between two tapes or foils 10 , 11 which are adhered or welded together . tape 10 is preformed like a cable binder . electrical connection of the electrodes of sensor element 9 to contact pins 13 and 14 is made by means of integrally casting in metal foil 12 and the foil - like end 15 of contact pin 14 . toothing 16 and catch 17 form a self - locking clasp so that this transducer can be simply and tightly around pipe 18 . tape 11 may consist of a material which improves friction transmission between the transducer and pipe 18 . in the embodiment of fig5 piezoelectric sensor element 21 again is embedded between two insulating tapes 19 , 20 forming a flexible measuring strip , the ends of which are clamped by means of strainer parts 22 , 23 and leader ends 24 , 25 . small windows 24 &# 39 ;, 25 &# 39 ; in the insulating tapes 19 , 20 provide electrical contact between the electrodes of sensor element 21 and leader ends 24 , 25 . strainer part 23 grips through aperture 22 &# 39 ; in strainer part 22 and is urged in the direction of stretch of the measuring strip by means of straining lever 27 which is rotatable by axis 26 . so the measuring strip surrounding pipe 28 is closed and provided with initial tension . this kind of a clasp is especially advantageous when the transducer is to be used for pressure measurements of pipes having nearly equal diameters . fig6 and 7 show a transducer which is particularly suitable for pressure measurements of injection pipes of diesel engines . piezoelectric film 31 is embedded between electrically insulating tapes 29 , 30 , thereby again forming a measuring strip which is strained around injection pipe 33 by snap - on spring 32 . only both the outer seating surfaces 32 &# 39 ; of spring 32 embrace injection pipe 33 by more than half of the circumference . the middle part of spring 32 does not touch pipe 33 or the measuring strip respectively and serves as a protective cover for the latter . the length of tapes 29 , 30 and piezoelectric film 31 is chosen as to cause initial stretch and tension when snapping spring 32 on pipe 33 . electrical connection of the electrodes of film 31 to leader ends 34 , 35 again is made by means of little windows 34 &# 39 ;, 35 &# 39 ; in insulating tapes 29 , 30 . fig8 and 9 show several single - sensor - elements , which are combined together . piezoelectric film 37 is applied to pipe 36 by means of an electrically leading adhesive . the outer surface of piezoelectric film 37 has a metal coating whereby some surface elements are uncoated along the circumference to achieve local separation to single elements . sensor element 37 and leading layers 38 are protected against outer influences by insulating foil 40 . the insulating foil 40 is provided at one of its end with electrically leading layers 39 . insulating foil 40 may be provided with leading layers 39 for instance by use of a copper coated foil at which the copper between leading layers 39 is etched away . leading layers 38 and 39 may be also glued with film 37 or insulating foil 40 , respectively , by means of an electrically leading adhesive . the measuring signals are lead to the periphery where they are taken off . member 41 serves to fasten the electrical connecting part of insulating foil 40 at pipe 36 and is glued with pipe 36 . due to the electrically leading connection between piezoelectric film 37 and pipe 36 , pipe 36 forms the common ground electrode for all layers 38 acting as charge take off electrodes .