High-resolution micromachined interferometric accelerometer

Abstract

We demonstrate a promising type of microfabricated accelerometer that is based on the optical interferometer. The interferometer consists of surface-micromachined interdigital fingers that are alternately attached to a proof mass and support substrate. Illuminating the fingers with coherent light generates a series of diffracted optical beams. Subangstrom displacements between the proof mass and frame are detected by measuring the intensity of a diffracted beam. The structure is fabricated with a two-mask silicon process and detected with a standard laser diode and photodetector. We estimate that the minimum detectable acceleration is six orders of magnitude below the acceleration of gravity, i.e., 2 μg/Hz in a 1 Hz bandwidth centered at 650 Hz.

Tools for the Design of Miniaturized Analytical Systems

“…This is based on interference of a reference laser beam by the one reflected by the cantilever. An alternative approach is to use interdigitated cantilevers as an optical diffraction grating [156,157]. One part of the light is reflected at the interface between the fibre and the surrounding media, and the other part is reflected at the cantilever back into the fibre.…”

“…The cleaved end of an optical fibre is brought close to the cantilever surface. An interferometric sensor for the AFM with a cantilever micromachined into the shape of interdigitated fingers to form a diffraction grating has been presented [156,157]. These two beams interfere inside the fibre, and the interference signal can be measured with a photodiode.…”

High resolution quartz flexure accelerometer based on laser self-mixing interferometry

“…However, for many military and civilian navigation applications, improved accuracy or performance is not necessarily the most important issue, and the most important issue is to meet the performance at a reduced cost and size, especially when incorporating the global positioning system into the inertial navigation system to eliminate inertial sensors' output drifts over time. 4 Considering the above application background, the micromechanical type has a tiny size but limited accuracy that hardly exceeds microgram, 5 while the electrostatic type shows super high resolution but complicated structure and an expensive production cost. 6,7 Comparatively, the traditional pendulous type QFA has extremely simple setup and a competitively low cost; 8 however, its resolution has always been limited to the range of microgram mainly due to the parasitic phenomenon of the differential capacitance that is adopted to measure the displacement of the pendulous reed, which acts as the moving proof-mass of the pendulous accelerometer.…”

An accelerometer incorporating a laser microencoder for a wide measurable range

“…Accelerometers fabricated using micromachining technology are based mainly on the change of the frequency of a microresonator [1], which is expected to have an ultrahigh Q value owing to its ultrasmall structure. Measurements of displacements of a movable microstructure that corresponds to a seismic mass have been reported; these measurements may be based on capacitance [2][3][4][5], a tunneling current [6], or diffraction [7]; they may be made with an optical fiber [8][9][10][11][12][13] or a split photodiode [14]; or they may use strain detection [15,16] based on an MOS structure. Although accelerometers based on resonators promise higher sensitivity, it is difficult to control the vacuum conditions and feed back the changes.…”