well suited for application to the low frequency 

 problems associated with geophysics and/or ocean- 

 ography. A few examples of how solions have been 

 utilized in these fields are listed here. 



Microbarograph 



By choosing a "backup" pressure reference 

 chamber with the proper acoustic "leak, " very 

 minute atmospheric pressure changes (of the order 

 of 0.01 microbar) can be detected within the fre- 

 quency limits of the system. If this sensitivity 

 is excessive, a less sensitive transducer should 

 be chosen or an acoustic resistor should be 

 inserted in series with the transducer. A linear 

 operating range of 10,000:1 would place the maxi- 

 mum pressure limit around 100 microbars in the 

 case described. 



Detection of Small Oscillatory Water Currents 

 in the Ocean 



A device to detect small oscillatory water 

 currents has not been constructed but limited 

 investigation indicates the possibility of 

 designing such a transducer. Fluid flow through 

 a Venturi tends to create a pressure effect that 

 is proportional to the velocity of fluid flow. 

 A compound Venturi system coupled to a solion 

 transducer, with one Venturi "pointed" l80° away 

 from the other, could furnish a directional, low 

 velocity water current transducer. The same 

 effect also appears possible with the pitot tube, 

 but a "full wave" response would be more difficult. 



CONCLUSIONS 



Measurement of Vertical Pressure Gradient in the 

 Atmosphere or Ocean 



By coupling the solion flow detector to a long 

 rigid wall pipe, mounted in a vertical (or any 

 angle desired) position, dynamic differences in 

 pressure within the frequency and pressure 

 response of the transducer can be measured. 

 Again, 0.01 microbar of pressure change is detect- 

 able. Although changes in pressure (the dynamic 

 pressure) can be detected, static pressures can- 

 not. 



Oceanographic Bottom Pressure Transducer 



Again, by choosing a proper backup chamber 

 (pressure changes must be measured with respect 

 to some constant reference pressure), extremely 

 small changes in bottom pressure can be detected. 

 Pressure changes of the order of k x 10 ° inches 

 of water are theoretically detectable, so long 

 as the changes lie within the limits of the 

 system's frequency response. Housings have been 

 designed which physically protect the solion and 

 allow pressure measurements in the 1.0 cps to 

 0.001 cps frequency range. 



These are only a few of the many possible 

 applications of the solion. Solions have been 

 used extensively to measure ocean bottom pressure 

 signals in the study of the harbor seiche problem. 

 These transducers have been in operation for 

 approximately three years . Solions are also being 

 used in the study of low frequency atmospheric 

 noise. Reliability and stability have been 

 excellent . 



Some of the unusual characteristics of the 

 solion are: (l) low power consumption, (2) remote 

 operation capabilities, (3) high sensitivity, 

 (k) low pressure threshold capabilities, (5) very 

 low frequency response, (6) broad-band response 

 at low frequencies, (7) a reasonable temperature 

 coefficient that can be corrected with thermistors, 



(8) excellent stability and reliability and 



(9) surprisingly rugged construction, except for 

 diaphragm puncture. 



ACKNOWLEDGMENTS 



This work was sponsored by the Navy Department 

 through the Bureau of Naval Weapons and the 

 Office of Naval Research. 



A Solion Seismograph 



If the solion linear flow detector is coupled 

 to a long, horizontal column of fluid, say 

 mercury, and if the column is equally divided 

 about the solion (the same amount of column 

 length on each side of the transducer), there is 

 no net differential pressure across the solion 

 and its output is zero. Output will be obtained 

 when a shock signal, containing acceleration 

 components within the frequency response of the 

 solion system, is directed along the length of 

 the column. The pressure developed (and, by 

 Eqn. (7), the output current) will be propor- 

 tional to the length of the column of fluid, the 

 density of the fluid and the acceleration com- 

 ponent along the length of the column. Detection 

 of accelerations of the order of 10"" g is 

 readily possible. 



REFERENCES 



1. WILLARD, H. H., L. L. MERRITT and J. A. DEAN, 

 Instrumental Methods of Analysis , D. Van 

 Nostrand Co., New York, N. Y., 2nd Edition, 

 1951. 



2. K0LTH0FF, I. M. and J. J. LINGANE, 

 Polarography, Interscience Publ., New York, 

 N. Y., 2nd Edition, 1952. 



3 . OLSON, H . F . , Dynamical Analogies , D . Van 

 Nostrand Co., New York, N. Y. , 2nd Edition. 

 1958. 



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