The Wee-g MEMS (MicroElectroMechanicalSensor) gravimeter is a precision accelerometer that has been developed between Physics & Astronomy (Prof. Hammond) and Engineering (Prof. Paul) at the University of Glasgow. The instrument is TRL5 and can be used to detect underground voids with applications in environmental monitoring, civil engineering and defence & security [1-4]. Wee-g uses a novel patented spring [5] to provide a low resonant frequency oscillator. Support under the National Quantum Technology Programme has enabled a field portable version to be deployed on active volcanoes (3 devices on Etna, Italy and 1 device on Poas, Costa Rica) and in Scotland/Ireland for water table monitoring.
The team is working towards a spinout opportunity (Quantrologee, which will be incorporated in November 2025) between the Universities of Glasgow (Wee-g) and Strathclyde (magnetometry), to deliver a dual gravity-magnetic sensor [6]. Industrial collaborators over the last 10 years include BP, Metatek, DSTL, QinetiQ, GCHQ and Schlumberger.
The Wee-g sensor (Fig 1) currently has a sensitivity of 20µGal/√Hz (1Gal=1cm/s2) and a bias stability of 2µGal after 256s, with typical signals of interest at the 10µGal level. The readout currently comprises a capacitive comb arrangement. Improving this sensitivity by an order of magnitude will yield a step change in signal-noise ratio, or it will enable an increase in the resonant frequency of the device thus making it more robust for field deployment.
This Ph.D. project will develop a new readout for the Wee-g sensor based on interferometry. This is well aligned to the activities of the Institute for Gravitational Research (Hammond is deputy director) which hosts a 10m interferometry and undertakes sub femtometer sensing within its 10m prototype interferometer at both 1064nm and 1550nm. Work also focusses on the development of squeezed light sources to reduce the shot noise at frequencies above 1kHz.
We propose to deploy a miniaturised interferometer on the Wee-g instrument. We will utilise commercial small form factor lenses and mirrors/beamsplitters that have come onto the market in the last 3 years. This will enable a new type of free-space interferometric readout. The project will further explore injection of squeezed light into the system to further supress shot noise by x2.
The project timeline comprises the following key activities;
Yr 1: modelling the interferometric readout, choosing either Michelson or Michelson with Fabry Perot-cavities (trading off dynamic range and sensitivity)
Yr 1-2: fabrication of a fixed interferometer initially, together with signal-noise analysis.
Yr 2: fabrication of an interferometer on the Wee-g accelerometer using pick-place tooling to align the optical components.
Yr 2: testing of the Wee-g interferometric readout
Yr 3: field trials at a series of well measured Glasgow gravity landmarks (Kelvin Building, bridges, railway tunnels in Botanical Gardens), and deployment to benchmark with DSTL instrument
Yr 3: injection of squeezed light into the interferometer using the light source at the Glasgow 10m interferometer for bench testing. Observing sub-shot noise performance.