A practical MEMS gravimeter

Middlemiss, Richard Paul (2016) A practical MEMS gravimeter. PhD thesis, University of Glasgow.

Abstract

The ability to measure tiny variations in the local gravitational acceleration allows – amongst other applications – the detection of hidden hydrocarbon reserves, magma build-up before volcanic eruptions, and subterranean tunnels. Several technologies are available that achieve the sensitivities required (tens of μGal/√Hz), and stabilities required (periods of days to weeks) for such applications: free-fall gravimeters, spring-based gravimeters, superconducting gravimeters, and atom interferometers. All of these devices can observe the Earth tides; the elastic deformation of the Earth’s crust as a result of tidal forces. This is a universally predictable gravitational signal that requires both high sensitivity and high stability over timescales of several days to measure. All present gravimeters, however, have limitations of excessive cost (£70 k) and high mass (<8 kg).

In this thesis, the building of a microelectromechanical system (MEMS) gravimeter with a sensitivity of 40 μGal/√Hz in a package size of only a few cubic centimetres is discussed. MEMS accelerometers – found in most smart phones – can be mass-produced remarkably cheaply, but most are not sensitive enough, and none have been stable enough to be called a ‘gravimeter’. The remarkable stability and sensitivity of the device is demonstrated with a measurement of the Earth tides. Such a measurement has never been undertaken with a MEMS device, and proves the long term stability of the instrument compared to any other MEMS device, making it the first MEMS accelerometer that can be classed as a gravimeter. This heralds a transformative step in MEMS accelerometer technology. Due to their small size and low cost, MEMS gravimeters could create a new paradigm in gravity mapping: exploration surveys could be carried out with drones instead of low-flying aircraft; they could be used for distributed land surveys in exploration settings, for the monitoring of volcanoes; or built into multi-pixel density contrast imaging arrays.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Gravimetry, gravimeter, MEMS, gradiometry, geophysics.
• Subjects: Q Science > QC Physics; T Technology > T Technology (General); T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Funder's Name: Royal Society (ROYSOC), Engineering & Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Hammond, Professor Giles D.
• Date of Award: 2016
• Depositing User: Dr Richard Paul Middlemiss
• Unique ID: glathesis:2016-7788
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 18 Nov 2016 15:42
• Last Modified: 15 Nov 2017 08:47
• URI: https://theses.gla.ac.uk/id/eprint/7788