the composite multi - transducer device of fig1 is given overall reference numeral 100 . the device 100 is made using the method described above . in this particular case , the electrodes are deposited using a mask that defines 25 electrodes that are adjacent and independent and of the shape shown in fig1 thereby forming 25 individual transducers that are capable of being fed separately . the assembly was then shaped to form , in the example , a cup having an opening of 100 mm and a radius of curvature of 160 mm . the piezoelectric material is of the pzt type and it constitutes about 25 % of the total volume . the 25 transducers respectively numbered 1 to 25 ( large digits ) are subdivided into five subgroups numbered 1 to 5 ( small digits ) which are fed in groups and individually as described below with reference to fig2 . the feeds to the groups 2 , 3 , 4 , and 5 are deposited on the sides and are referenced a 2 , a 3 , a 4 , and a 5 respectively . the transducer 1 constitutes a group on its own , and for practical reasons it is combined with group no . 2 to be fed from feed a 2 . the technique for making the multi - transducer composite device is conventional and as described by wallace arden smith at pp . 755 - 766 of ieee ultrasonic symposium , 1989 , and in particular with reference to fig2 . accompanying fig2 shows a block diagram of the cup - shaped multi - transducer device 100 of fig1 together with its electronic feeds . it can be seen that each individual composite piezoelectric transducer of the device 100 is associated with a pulse transformer which is given the same reference numeral as the number of the individual transducer that it feeds . there are therefore as many pulse transformers as there are transducers in the cup . thus , in this case , there are 25 pulse transformers which are grouped together to form four groups fed by four pulse generators . in this case , the four main groups 2 , 3 , 4 , and 5 are shown together with their associated pulse generators referenced g12 , g13 , g14 , and g15 . these pulse generators are controlled by a central control unit 110 , e . g . in the form of a computer and which contains , in the form of a file , all of the information necessary for individually controlling each of the 25 individual transducers . this is done by attributing control parameters to the transducers of the various electronic paths , and in particular phase delays and firing management , e . g . with respect to the number of shots and to the firing rate . this data is sent by the central control unit 110 to the pulse generator cards which are referred to as &# 34 ; pulse generators &# 34 ; via an interface card 112 , as shown in fig2 . each pulse generator card can control six to seven transducers independently . it is therefore necessary in this case to provide at least four cards , given that the central transducer 1 which constitutes a group on its own is controlled by the pulse generator referenced g12 . it will be understood that the pulses which are sent by the pulse generators are received by the pulse transformers for amplification and are transmitted to the transducers individually , thereby providing a high degree of flexibility in operation and making it possible to adjust the overall power of the multi - transducer composite piezoelectric device 100 at will . the central individual piezoelectric element referenced 1 in fig1 has been used to perform tests on the linearity of the sensitivity of the transducer element in terms of positive pressure p + as a function of the applied voltage . the results of these tests are given in the form of curves in fig3 where volts are plotted along the x - axis and pressure in bars is plotted up the y - axis giving the maximum pressure obtained as a function of the applied voltage . the resulting curve has a slope of 5 . 6 mbars / volt , which is remarkable . it is also surprising to observe that this curve is extremely linear regardless of the applied voltage and the pressure of the waves emitted to the focal point at the center of the cup , expressed in bars . in addition , aging tests have also been performed using the composite piezoelectric transducer 1 of fig1 with these tests being shown in the form of a curve in fig4 where number of shots x 1 , 000 is plotted along the x - axis and where the lefthand y - axis indicates pressure in bars . the curve showing pressure as a function of shots is plotted with asterisks *. the righthand y - axis gives impedance in ohms and the corresponding curve is plotted using small circles o . it can be seen that at an initial pressure of about 13 bars , this can be maintained essentially constant regardless of the number of shots , which is quite remarkable . similarly , the impedance of the composite piezoelectric material is kept essentially constant at around 1 ohm regardless of the number of shots , which is likewise remarkable and unexpected for the person skilled in the art . the invention thus makes it possible to achieve all of the above - announced determining technical advantages . in particular , the composite piezoelectric transducer of the invention , in particular when in the form of a multi - transducer device , can be used for making an acoustic or an ultrasonic therapy apparatus for therapy that may be destroying a concretion , destroying tissue such as a tumor , or treating bones . with reference to fig5 there can be seen a second embodiment of therapy apparatus of the present invention which has combined therapy and imaging functions , comprising a multi - transducer device of a type similar to that shown with reference to fig1 and 2 , in the form of a cup , but in which a plurality of transducers associated with an imaging function are disposed , in this case in two perpendicular lines 202 and 204 occupying planes of symmetry of the cup 200 , thereby obtaining image planes 203 and 205 that permanently contain the focal point f or center of the naturally - focusing spherically - shaped cup 200 . in addition , the other transducers of the cup 200 are distributed over four preferential sectors respectively referenced 206 , 207 , 208 , and 209 and which perform a therapy function . in this case also , there is a central control unit 110 , e . g . a computer , controlling ( via an interface 112 ) therapy pulse generators ( git ) or an imaging pulse generator ( gii ) respectively connected to the sectors of therapy transducers 206 , 207 , 208 , and 209 , or to the imaging transducers disposed on the lines 202 and 204 which are disposed orthogonally in this case . in a particularly preferred variant , a switch device 220 is included having a position a and a position b . when the switch is in its position a , the therapy pulse generator also causes the transducers in the imaging lines 202 and 204 to generate therapy pulses , i . e . when the switch is in position a , all of the transducers in the cup perform therapy , i . e . they operate at high power . in contrast , when the switch is in its position b , as shown in fig5 the therapy pulse generator controls the transducers in the therapy sectors 206 , 207 , 208 , and 209 only , while the imaging pulse generator gii controls the transducers disposed in the emitting lines 202 and 204 for imaging purposes so as to construct an echographic image of the region around the focus f occupying two perpendicular planes each including the point f . it will easily be understood that with the apparatus as shown in fig5 it is possible by appropriate programming of the interface 112 by the control unit 110 when the switch is in position a to make the pulse generators operate therapeutically to provide a sequence of therapy pulses per se controlling all of the transducers in the cup 200 , or else under reduced power in an imaging mode to control all of the transducers in the cup 200 at an imaging power . the apparatus thus provides most appreciable versatility in use . the invention thus covers all means constituting technical equivalants to the means described and various combinations thereof . it should be observed that all of the elements of the embodiments described with reference to fig1 to 5 form an integral portion of the invention and thus of the present description . the invention also covers any characteristic that appears to be novel over any of the prior art . the composite piezoelectric transducer of the invention can be used to perform medical hyperthermia or thermotherapy , or to damage tissue thermally , e . g . tumor tissue or varicose tissue , by causing a thermal effect selected from coagulation , necrosis , and volatilization thereof .
the invention relates to a composite piezoelectric transducer for making an acoustic or an ultrasonic therapeutic apparatus . the transducer may be a single large - size transducer or it may be a multi - transducer device and it advantageously emits ultrasonic waves that are focused on a focal point .