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MEMS Components for NMR Atomic Sensors

  • Author(s): Mohammednoor, Radwan M
  • Advisor(s): Shkel, Andrei M
  • et al.

This dissertation introduces a batch fabrication method to manufacture Micro-Electro-Mechanical System (MEMS) components for NMR atomic sensors, such as NMR gyroscope (NMRG) and NMR magnetometer (NMRM). The introduced method utilized a glassblowing process, origami-like folding, and a more traditional MEMS fabrication. We developed an analytical model of imperfections, including errors associated with micro-fabrication of MEMS components. In light of the developed error model and experimental evaluation of components, we predicted the effect of errors on performance of NMRG and NMRM. We concluded that with a realistic design, a 5mrad angular misalignment between coils and folded mirrors and a 100um linear misalignment between folded coils, it would be feasible to achieve an NMRG with ARW 0.1deg/rt-hr and an NMRM with sensitivity on the order of 10fT/rt-hz using MEMS technology.

A design process for miniaturized atomic vapor cells using the micro-glassblowing process was presented in this dissertation. Multiple design considerations were discussed, including cell geometry, optical properties, materials, and surface coating. The geometry and the optical properties were studied using experimentally verified analytical and Finite Element Models (FEM). The cell construction material and surface coating were the focus of our experimental study on factors that affect the transverse relaxation time (T2) of nuclear spins. We showed that the developed wafer-level coating process with Atomic Layer Deposition (ALD) of Al2O3 increased the relaxation time (T2), which is projected to reduce the ARW of NMR gyroscopes and the sensitivity of NMR magnetometers by four times.

Complementary to the developed atomic sensors components, an analog emulator for NMR atomic sensors was developed. The emulator represents the spin dynamics of atoms in an applied magnetic field that are governed by Bloch equations. Characterization of atomic sensors' components using the emulator was achieved by including one or more of those components with the emulator in a hardware-in-the-loop (HIL) configuration. Finally, we presented a comparison of the response between the NMR emulator and an actual NMR system, showing similarities of responses of the two systems and feasibility of using HIL configuration in development of micro-scale NMR sensors.

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