The torsion pendulum dual oscillator (TorPeDO) is a double torsion pendulum consisting of two 60 cm beams each suspended by two parallel 60 cm suspension wires[1]. The two beams are orthogonal to each other, and share the same axis of rotation, as shown in figure 1. The beams have a design such that the centre of mass of both torsion pendulums are positioned at the same location in space. Gravitational forces attract the torsion beams causing them to rotate towards alignment with the direction of the potential. The two beams are mounted perpendicular to each other so gravitational forces will cause them to rotate differentially about the torsion axis. The torque experienced by the beams is a function of the magnitude of the gradient, and its angle with respect to the torsion-beam axis.

The TorPeDO is designed to be sensitive to low frequency gravitational forces, such as Newtonian Noise from seismic and atmospheric origin [2, 3] and gravitational forces from earthquakes [4]. In addition the sensor could potentially be used to investigate theories of semi-classical gravity [5, 6] and perform measurements of big G [7].

[1] McManus D. et al Class. Quantum Grav. 34 (2017) 135002
[2] Harms J et al 2013 Phys. Rev. D 88 122003
[3] Harms J 2015 Living Rev. 18 3
[4] Harms J et al 2015 Geophys. J. Int. 201 1416–25
[5] Yang H et al 2013 Phys. Rev. Lett. 110 170401
[6] Gan C G, Savage C M and Scully S Z 2016 Phys. Rev. D 93 124049
[7] Gundlach J H and Merkowitz S M 2000 Phys. Rev. Lett. 85 2869