High-Precision Electrolytic Capacitance Tilt Sensor

Tests of gravitational theory are at the forefront of current physics and astronomy research because Einstein’s theory of gravitation, General Relativity, is fundamentally inconsistent with the Standard Model of quantum mechanics. The study of gravity at small but measurable distances will probe new theories that are attempting to incorporate gravity into a consistent framework that includes all four fundamental interactions. 1 Laboratory tests of the gravitational inverse-square law are difficult because of the extreme weakness of gravity as compared to the other forces. At Humboldt State University, we are exploring the nature of short-range gravity at unprecedented levels using a novel parallel-plate torsion pendulum. Limitation and characterization of systematic errors are key factors in such gravitational tests. Due to the well-documented "tilt-twist" effect for torsion pendulums, 2 we need to characterize minuscule oscillations of the inclination of our apparatus. To this end, we are constructing a highprecision, electrolytic capacitance tilt sensor. The sensor is comprised of several aluminum rods partially submerged in a sodium bicarbonate solution. The aluminum rods each act as one side of a capacitor while the solution acts as the other. The dielectric between the rods and the solution is the naturally occurring oxide layer on the aluminum. Using a capacitance bridge circuit, the difference in capacitance between two rods yields a measure of the tilt of the sensor along one axis. As the apparatus' inclination changes, the surface area of the rods in solution also varies, thus changing the output of the bridge circuit. This paper addresses the design and characterization of the tilt sensor, as well as its relevance for short-range tests of gravity.