Torsion balances are almost ideal detectors of weak forces due to their low stiffness, noise and sensitivity to ground tilt. Their dynamics, however, make it difficult to measure forces that have sub-mm ranges. In Birmingham we are developing experimental techniques, based on previous work, to allow reliable measurements of the inverse square law of gravity down to mass separations of the order of 10mu m. This work has revolved around the superconducting torsion balance and the proof-of-concept air bearing suspension projects. I will discuss these experiments and my involvement in them. This has included designing, creating and implementing a capacitive displacement sensor for measuring the rotation of the test mass of the superconducting torsion balance, which could circumvent the inherent noise and instability associated with large stray-capacitances. This has also included experimentally demonstrating the in-situ tuning of the centre-of-buoyancy of a suspended mass on the air bearing suspension, which allows the possibility of decoupling ground tilt and horizontal accelerations originating from seismic noise from the rotational mode of the suspended mass, improving the sensitivity to signal torques.
Host: M. Aspelmeyer