574 
Because the crystal is small, the output must be amplified before 
it is fed into a ecathode-ray tube. However, this gage has the advantage that 
it can be used to study explosions of charges smaller than those required 
with the Keys type of gage. 
PART 2. TMB PICKUP ELEMENTS 
Two materials which satisfy all of the specified requirements for a 
high-impedance pickup are quartz and tourmaline crystals. Their piezoelec- 
tric properties are described in detail in References (6) to (14). 
Quartz crystals have been used in the measurement of rapidly chang- 
ing pressures in internal combustion engines (15). More recently the Naval 
Ordnance Laboratory has been developing a quartz indicator for the measure- 
ment of underwater explosion pressures (16). The two types of Taylor Model 
Basin piezoelectric gages use quartz and tourmaline, respectively. 
THE TMB QUARTZ GAGE 
When an "X-cut" plate of quartz* is subjected to a compressional 
force normal to its parallel faces, equal and opposite charges proportional 
to the force appear at these faces. Quartz is not sensitive to isotropic 
pressure and a quartz crystal forming the sensitive element of a pressure 
gage must be housed in a case so that the pressure will act only on the faces 
perpendicular to the electric axis. Quartz plates have been subjected to 
pressures up to 50,000 pounds per square inch in a testing machine, and the 
relationship between charge and pressure has been found to be linear over 
this full range (17). 
The present TMB quartz gage has passed through several stages in 
its evolution. The earliest form had a large crystal and a plastic housing; 
a subsequent model used a double crystal and a brass housing; the gage de- 
scribed in this report is considerably smaller than the previous models and 
is of the single-crystal type. The techniques applied in the construction 
and assembly of a quartz gage at the Taylor Model Basin are described in the 
Appendix. 
An idea of the progressive reduction in size, to obtain a high nat- 
ural frequency of vibration for the quartz-mount system, is presented in Fig- 
ure 2. In its present form the pickup element consists of a cylindrical 
quartz crystal 1/16 inch thick and 1/4 inch in diameter, housed in a brass 
cylindrical mount 7/32 inch high and 1/2 inch in diameter; see Figure 3. A 
brass tube, integral with this cylinder, contains the wire conductor attached 
a plate of quartz is said to be "X-cut" if its plane is perpendicular to an electric axis of the 
crystal. 
