MEASUREMENT OF PRESSURES 169 



of the disk is parallel to the wave front. This larger effect is a factor in 

 determining the best design and orientation of tourmaline gauges. It 

 has been found empirically that the most satisfactory arrangement for 

 general purposes consists of a stack of two or four disks in parallel, the 

 faces of the disks being set parallel to the direction of advance of pres- 

 sure. With this design the effects of internal reflections and the re- 

 sultant oscillations of response are reduced, and the transit time for a 

 required sensitivity is kept within reasonable limits. Some repre- 

 sentative tourmaline gauge designs of this and other types are described 

 in the next section. 



5.6. Piezoelectric Gauge Design and Performance 



A considerable variety of designs for piezoelectric gauges has been 

 evolved for various types of applications and as a result of experience 

 acquired in their use. The more detailed descriptions in this section are 

 confined primarily to gauge designs which have been developed by the 

 Woods Hole Laboratory and other cooperating groups. The material 

 presented is not, therefore, a complete summary of the developments 

 which have been made by all the various laboratories. The designs 

 discussed, or similar ones, have, however, been the ones most exten- 

 sively used and were employed in most of the explosion pressure meas- 

 urements given elsewhere in this book. 



As a result of the considerations outlined in sections 5.4 and 5.5, 

 tourmaline has been the most extensively used piezoelectric material, 

 both in the United States and in England. As mentioned in section 

 5.4, the pioneer development of tourmaline gauges was carried out in 

 England after 1919 in a continuing program of research employing 

 rather large units embodying a mosaic of crystals. Until quite recently, 

 the basic design employed by the Admiralty Research Laboratory was 

 used largely in England without major changes for measurements and 

 comparisons of large charges. ^^ Private communications have indi- 

 cated that a program of investigation on small charges employing 

 smaller gauges has been undertaken at the Admiralty Undex Works at 

 Rosyth, but no reports of this work were available at the time of this 

 writing. 



A considerable program of gauge development in the United States 

 began late in 1941 which was aimed chiefly at extending the range of 

 usefulness and precision obtainable with tourmaline gauges. The initial 

 efforts along these lines were made by A. B. Arons and E. B. Wilson, Jr. 

 at Harvard. Much later development work and construction of gauges 

 on their basic design, which might be called the hourglass gauge, was 

 carried out at the Stanolind Oil and Gas Co. Development Laboratory 

 under the direction of Daniel Silverman (104) and this group supplied 



^^ A standardized design is described by Bebb (6) . 



