Large Piston Motion Research Articles

Nondestructive On-Site Detection of Soybean Contents Based on An Electrothermal MEMS Fourier Transform Spectrometer

A portable spectrophotometer has been developed to provide on-site detection of soybeans’ moisture, protein, and fat contents in a nondestructive manner. The core module of this soybean analyzer is a micro Fourier transform infrared spectrometer (μFTIR) based on an electrothermal microelectromechanical systems (MEMSs) mirror. The electrothermal MEMS mirror is capable of generating a large piston motion of 320 μ m at only 8.5 Vdc. The tilting of the MEMS mirror plate during its piston scanning affects the spectral repeatability of the μFTIR. In this paper, the effect of the MEMS mirror tilting on the spectral repeatability is analyzed and an automatic tilt realignment algorithm is developed to maintain high spectral repeatability, which is better than 0.01 in long term use. The μFTIR module has a footprint of 125 mm × 90 mm with a height of 50 mm. The whole instrument is designed for portability and on-site operation as well as the convenience of loading soybeans. More than 300 samples of soybeans are collected, 80% of which are used to establish a prediction model using chemometrics methods. The standard error is no more than 3% when using the prediction model to test the remaining 20% samples.

Miniaturizing Fourier Transform Spectrometer With an Electrothermal Micromirror

An amplitude-division Fourier transform spectroscopy system has been constructed. The system design hinges on an electrothermally actuated micromirror with large piston motion. The micromirror is composed of electrothermal mesh actuators and can generate up to 95 μm usable linear optical path difference of the system at only 0.8 V dc . A custom electrical system is developed to control the micromirror and data processing is implemented to extract the spectrum from interferograms. The system can achieve a spectral resolution of 5 nm at 532 nm.

A thermal bimorph micromirror with large bi-directional and vertical actuation

This paper reports a novel large vertical displacement (LVD) microactuator that can generate large piston motion and bi-directional scanning at low driving voltage. A LVD micromirror device has been fabricated by using a unique deep reactive ion etch (DRIE) post-CMOS micromachining process that simultaneously provides thin-film and single-crystal silicon microstructures. The bimorph actuation structure is composed of aluminum and silicon dioxide with an embedded polysilicon thermal resistor. With a size of only 0.7 mm × 0.32 mm, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at 6 V dc. This device can also be used to perform bi-directional rotational scanning through the use of two bimorph actuators. The micromirror rotates over ±15° at less than 6 V dc, and over ±43° (i.e., >170° optical scan angle) at its resonant frequency of 2.6 kHz.

Sound Radiation from a Reciprocating Compressor Orifice without Valve

As a first step toward the acoustic radiation modeling of a reciprocating air compressor, the suction and exhaust valves were removed and the compressor was made to cycle air through a single circular orifice. The theoretical model incorporates the aharmonic and large piston motion by thermodynamically modeling the flow in the cylinder. The flow through the orifice was modeled as compressible. Contraction coefficients on an ON-OFF basis were used to account for streamline effects in the orifice section. The farfield acoustic spectrum was predicted by treating the orifice as a monopole source radiating into an infinite halfspace. Agreement between theoretical prediction and experimental measurements was encouraging. A small rise in both the predicted and measured frequency spectrum was hypothesized to be a Helmholtz resonator effect, since it occurred in the expected frequency band. The theoretical calculations were carried out using both a conservation of mass and momentum approach and a conservation of mass and energy approach. Small differences in the results of these two approaches were observed. Finally, with a desire to simplify future models, influences of individual terms in the equations on instantaneous mass flow rates were evaluated.

Sound Radiation from a Reciprocating Compressor Orifice without Valve

As a first step toward the acoustic radiation modeling of a reciprocating air compressor, the suction and exhaust valves were removed and the compressor was made to cycle air through a single circular orifice. The theoretical model incorporates the aharmonic and large piston motion by thermodynamically modeling the flow in the cylinder. The flow through the orifice was modeled as compressible. Contraction coefficients on an ON-OFF basis were used to account for streamline effects in the orifice section. The farfield acoustic spectrum was predicted by treating the orifice as a monopole source radiating into an infinite half-space. Agreement between theoretical prediction and experimental measurements was encouraging. A small rise in both the predicted and measured frequency spectra was hypothesized to be a Helmholtz resonator effect since it occurred in the expected frequency band. The theoretical calculations were carried out using both a conservation of mass and momentum approach and a conservation of mass and energy approach. Small differences in the results of these two approaches were observed. Finally, because of our desire to simplify future models, influences of individual terms in the derived equations on instantaneous mass flow rates were evaluated.