MEAST'HIN'd FORCKS AND WllAK IN S\\ ir< 1 1 1 .\( 1 Al'l-AUATrS h/ 



the open circuit voltage for a 4 per cent lead litanate l)ariinn litanate 

 ceramic for various baking temperatures and negali\-e biasing xoltages. 

 The optimum tempera! ui'e for a small grain size structure is lowered 

 about 50°C by the addition of the lead titanate. As can be seen the co- 

 ercive field is considerably increased and it apjx'ars safe to use a negative 

 field of (1000 volis per centimeter without any depolarization. In Section 

 1\' a system is described for which an ac voltage of this magnitude was 

 successfully used for many days with no change in sensitivity of the 

 (•(M'amic. The open circuit i)iezoelectric constant for the optimum ce- 

 ramic of Fig. 4 is 



Qco ^ in-s stat-coulombs -2 meters ,„v 



g33 = 3.82 X 10 T = l.lo X 10 — — -— (3) 



dyne JNemon 



Since the dielectric constant is about 1000, the effective ^33 piezoelectric 

 constant is about 



./33 = 310 X 10- ^tat coulombs ^ ^^^ ^ ^^-^ coulombs ^^^ 

 dyne JNewton 



Another property of interest is the stability of the piezoelectric proper- 

 ties of the ceramic o\'er a long period of time. While no very good com- 

 parisons have been made between the various baking conditions and 

 between barium titanate with and without additions, some long time 

 measurements have been made on four samples of the optimum 4 per 

 cent lead titanate used in the transducer of Fig. 3. Over a period of two 

 years during which they have been continuously used in a calibrated 

 oscillator, the calibration has not changed noticeably, i.e. less than 5 

 per cent. On accoimt of the superior voltage and time stability of the 

 lead titanate, barium titanate mixture, all of the elements used have 

 had this composition. 



Two types of units have been used for force measurements, one type 

 that responds to normal forces and tlie other to tangential forces. The 

 type responding to normal forces as shown by Fig. 5 is poled in the thick- 

 ness direction which is also the direction in which the force is applied. 

 The sensitivities for forces applied at points are given by the values of 

 Fig. 4. For example for typical units having the dimensions 0.1 cm by 

 0.1 cm in cross section and 0.05-cm thick will produce an open circuit 

 \'oltage of 2.7 volts for 100 grams applied to the ceramic. Such ceramics 

 have been used in measuring the dynamic forces when various parts 

 of the relay close or open. Fig. 6(a)'° shows the voltage generated when 

 the two relay contacts come together. The dynamic stress is somewhat 

 higher than the static stress and varies with time due to mechanical 



