By John Rhea
SAN JUAN CAPISTRANO, Calif. - Designers at a California electronics company have developed a new way for vehicles to navigate when they are out of range of Global Positioning System (GPS) satellites.
Instead of the heavier and less-reliable electromechanical systems employing cantilever beam or pendulum inertial systems, engineers at Endevco Corp. of San Juan Capistrano, Calif., have put a variable-capacitance accelerometer on an array of three micromachined single-crystal silicon 2-inch wafers.
These navigational devices come in two versions, the model 7591 weighing 7 grams, and the model 7592 weighing 3.6 grams. They can withstand shock loads of as much as 10,000 Gs and can measure changes as little as +/- 2 G or as much as 100 G and operate at temperature ranges from -65 to 250 degrees Fahrenheit.
At the higher G loads and covering all three dimensions, the accelerometers are intended for measuring the trajectories of shoulder-launched anti-tank and anti-aircraft missiles, says Brian Link, marketing manager at Endevco.
He points out, however, that the same technology can also be applied to the two-dimensional problem of surface navigation. The wafers, fabricated at an Endevco facility in Sunnyvale, Calif., contain all the signal processing necessary for surface navigation, Link says; all they need is an external power source.
This is a dual-use technology based on the sensors used in down-hole oil drilling, where the devices have to withstand temperatures as high as 300 F. In addition to navigation for vehicles and missiles, Link says he also envisions applications in testing aircraft ejection seats, which generate forces of as much as 7 to 8 Gs.
The attraction of the electronic solution is the reduced size (about one-fourth the size of electromechanical accelerometers) and ruggedness. "They take a wallop and keep on working," Link notes. Offsetting these advantages is the high cost of the devices - about $300 apiece in OEM quantities of 1,000, vs. about $5 for the commercial accelerometers used in automobile airbags.
