THEORY OF OPERATION 



Analysis indicated that comparatively low 

 level excursions of a disk electrode at a high 

 rate should provide sufficient flow, due to non- 

 linearity of the hydraulic coupling, that a 

 strong scrubbing action would occur, even in the 

 absence of cavitation, and that this scrubbing 

 might prevent or remove the normal biological 

 fouling. 



DESIGN 



A half -wavelength magnetostrictive tube was 

 rolled of sheet nickel and supported at the nodal 

 midpoint by three sets crews (Fig. 2). It was 

 excited at its resonant frequency of 32 Kcps by 

 an efficient solid-state driver of simple design. 



electrical noise pickup in the cable or electrode. 

 This precaution proved unnecessary, apparently 

 due to shielding precautions and effects of 

 symmetry. 



POTENTIAL FUTURE APPLICATIONS 



Success of this design has lead to several pro- 

 grams for further development. Design of a simi- 

 larly rugged pH cell using the antimony, antimony- 

 trioxide electrode is being evaluated. This cell 

 is typically erratic in its behavior, but a sur- 

 face contamination may be the reason. The appli- 

 cation of the self-scrubbing principle for 

 improving the thermal contact of thermistors, 

 platinum resistance thermometers and thermo- 

 couples in solutions and powders is underway. 

 Evidence shows that a considerable fraction of 



Fig. 2. Half -wavelength magnetostrictive tube. 



A 0.5- inch diameter brass endplate was rigidly 

 fastened to the tube and the exposed surface 

 heavily gold plated. The assembly was seated 

 with silicone rubber in a tube of Nylatron GS, 

 a molybdenum disulphide-filled nylon, which also 

 formed the bobbin for the exciting winding. The 

 winding was potted with an epoxy resin that 

 bonded the conductors mechanically and simul- 

 taneously offered chemical protection. Electri- 

 cal connection was made directly to the brass 

 plate by soft-soldering the copper center- 

 conductor of an unterminated miniature low-noise 

 coaxial cable (Microdot). The complete unit is 

 shown in Fig. 3- 



Power connections were to ordinary 115 volt 

 60 cps AC although any source could be utilized 

 by the semiconductor driver which requires a 

 total of 15 watts. The electronic design is 

 perhaps most notable because of the fact that 

 only twenty components are required, of which 

 twelve are in the power supply circuits. This 

 has allowed six months operation without a com- 

 ponent failure and should meet all requirements 

 of both inner and outer space. 



the boundary layer insulation effect can be 

 eliminated by sufficiently strong circulation. 



Heat flow from the magnetostrictive driver 

 losses, as well as from the energetics of fluid 

 reaction, must be considered in the design, 

 although the acoustic power is in the milliwatt 

 region and is of lesser importance. 



Electrode measurement of conductivity in natu- 

 ral environments, as opposed to the electrodeless 



3 ii R r\ 



transformer methods discussed earlierJ' 4 '' ?> u has 

 the advantage of utilizing basic measures of 

 length and current with greatly reduced complexity 

 and with higher accuracy than is possible with 

 electrodeless methods. 



A pi-section rejection filter was designed 

 and included to reduce anticipated ultrasonic 



30 



