Evaluation of a Continuously Variable Calculable Capacitor

We describe key components of a new calculable capacitor and evaluate advantages as well as shortcomings of the current design. The unique features include an interferometer using multiple tunable lasers that measure the absolute cavity length in a continuous fashion. Diamond-turning technology offers a cost-effective alternative for fabricating nearly perfect cylinders for the main electrodes. It also enables us to adopt a compact capacitor structure that can be automated by positioning the movable guard electrode using a linear actuator. The resultant salient feature is its continuous tunability over a range of 0.1 pF, enabling nonlinearity testing of capacitance bridges.