474 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



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DEPOLING FIELD IN KILOVOLTS PER CENTIMETER 



Fig. 2 — Open circuit voltage for 500 grams force for normal barium titanate 

 under depoling voltages. 



the effect of additives. The data of Fig. 2 show^ the effect of firing tem- 

 perature on the initial open circuit voltage for sample disks 0.775 cm 

 in diameter and approximately 0.15 cm thick. The variation of voltage 

 with thickness and area was taken account of by multiplying the meas- 

 ured voltage by the area and di\dding by the thickness. 



The open circuit voltage was measured by using the circuit of Fig. 

 3. A barium titanate cylinder and metal horn described in a previous 

 paper," vibrating at 18,000 cycles, strikes the sample a blow at its central 

 position. The voltage generated is applied to the input of a high resistance 

 tube similar to the one shown by Fig. 1, and then actuates a cathode 

 ray tube. The voltage corresponding to the height of the peak is cali- 

 brated by putting a known voltage in series with the ceramic across a 

 small resistance R and hence the magnitude of the open circuit voltage 

 can be quantitatively determined. The value of the mechanical blow 

 applied to the polarized ceramic can be adjusted by controlling the drive 

 on the ceramic cylinder. With the feed back circuit described in the 



