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3: Principle of a fluxgate magnetometer: (a) A ferromagnetic core is alternatively driven inand out of saturation by a primary drive coil. Changes in flux density are then sensed by the secondary coil; (b) Scheme of the induction signal with and without external magnetic field.
Source publication
This PhD thesis deals with the design, the technological implementation, and functional characterizations of a new type of monolothic 3D MEMS magnetometer. Other than for the classical approach used for 3D MEMS magnetometers, the sensor developed in this work is not based on the principle of Lorentz force, but takes advantage of magnetic material w...
Citations
... MNPs labeled with specific biomolecular species have proven a suitable tool for various biorecognition assays [19,20]. Figure 7.2 shows the measurement ranges of various magnetometers [18]. The next sections will introduce the different magnetic biosensor types and give an insight into the magnetic particles used to determine the presence of a virus species. ...
... The measurement ranges of various magnetic sensors (in units of Tesla). Reprinted from[18] with author's permission. ...
The magnetometer is an essential component in a number of scientific and technical disciplines, including instrumentation and space navigation. To detect magnetic fields, a traditional Lorentz force capacitive magnetometer utilizes transverse, parallel-plate combs. Due to the substantial squeeze-film damping effects, increasing the number of comb fingers reduces the quality factor, and hence does not increase the device’s sensitivity, thus restricting applications. To address this shortcoming, we propose a longitudinal comb transducer design for space navigation. Its structure consists of a proof mass and beams, acting as driving elements, and two pairs of longitudinal combs, acting as electrostatic sensing elements. The magnetic field is measured by using the displacement that the Lorentz force induces on the current-carrying beams. Differential capacitance is utilized to transduce the displacement into the electrical domain. The resulting MEMS magnetometer has been fabricated using a low-cost MEMS process. A test bed was set under near-vacuum conditions to measure the static capacitance and resonant frequency of the sensing element. The static capacitance was found to be 1.27 pF, while measurements at the resonance frequency of 35.4 kHz show a high quality factor of 200 and consequently a high sensitivity. The resolution is estimated to be 295nT/Hz\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$295 \,nT/\sqrt{Hz}$$\end{document}. With the exception of slight differences, these results were in accordance with the simulation.
Remarkable nanoscale electro-thermo-mechanical properties of silicon nanowires are increasingly studies. This experimental thesis investigates such properties for top-down fabricated monocrystal silicon nanowires.A four points bending set-up and a MEMS actuator are developed to apply ex situ and in situ mechanical stress on nanowires. Those devices are characterised in a cryogenic environment within a microprobe station. Electrical properties and piezoresistivity are studied using those systems. Moreover, the 3ω method measures the thermal conductivity of these nanowires.From buckling of silicon nanowires, unexpected high compressive stress (>100 MPa) was identified in top silicon layers of SOI substrates. Drift-compensated measurements show that p type silicon nanowires present large piezoresistive coefficients which decrease with temperature. Additionally, the MEMS device demonstrates the possibility to detect ample MEMS movements with sub-ångström resolution using the nanowires as piezoresistive nanogauges. The thermal conductivity was found consistent with previously reported values for silicon nanowires, and expectedly decreases with temperature.
