A polarization‐independent optical sensor is created by fabricating a concentric gold ring grating with a period of 900 nm on the end facet of an optical fiber. The sensing function of this ...miniaturized device is realized by sending white light as a probe to the gold rings and collecting the response signal in the back‐reflection through the optical fiber. A pronounced peak due to the Rayleigh anomaly of the gold ring grating is observed in the reflection spectrum, the center wavelength of which is sensitive to the change in the environmental refractive index of the fiber end facet. Theoretical analysis not only shows excellent agreement with the experimental results, but also gives insights into the mechanisms of this kind of sensor. Using the center position of the Rayleigh peak as the response signal, a high sensitivity dλ/dn of 900 nm per unity refractive index is realized for this sensor and a resolution of Δn/n ≈ 1% is demonstrated in preliminary experiments. The sensitivity is solely determined by the period of the grating.
A sharp peak in the reflection spectrum due to the diffraction anomaly of a gold nanoring grating on the end of an optical fiber is used as a probe signal of the refractive index change in the surrounding medium. The sensitivity is determined by the period of the grating. The rotational symmetry of the rings and optical fiber about a common axis makes the sensor response polarization‐independent.
Electrospray emitters are an obvious choice for miniaturized thrusters for a variety of applications on small satellites (e. g., CubeSats), as well as for other micropropulsion purposes. They are ...inherently small and require a relatively low electric power for operation, and therefore, they fulfill the requirements imposed due to the small volume of CubeSats. Electrospray emitters of the internally wetted capillary type were fabricated by 3D microlithography in the SU-8 photopolymer down to capillary diameters of about 10 μm. Thus, the emitters are an order of magnitude smaller in lateral dimensions than those fabricated by advanced 3D printing methods and still half an order of magnitude smaller than those made by planar photolithography in SU-8. Fabrication methods and process parameters are presented. Furthermore, the preliminary results of the electric characterization of the emission behavior are shown. The experiments show promising results regarding the fabrication quality and extraction behavior.
Miniaturized Electrospray Thrusters Henning, Torsten; Huhn, Katharina; Isberner, Leonard W. ...
IEEE transactions on plasma science,
2018-Feb., 2018-2-00, Letnik:
46, Številka:
2
Journal Article
Recenzirano
Electrospray thrusters are a promising micropropulsion technology for CubeSats, among others, because they have the potential to provide high specific impulse. They avoid moving parts and allow a ...high degree of miniaturization. In combination with fabrication technologies from microelectromechanical systems (MEMS), miniaturization of individual emitters to the range of tens of micrometers brings with it a new concept of constructing and scaling thrusters, namely, by numbering-up the microthrusters to a device of suitable thrust. The current state of the art is briefly reviewed with an emphasis on MEMS technology. Furthermore, preliminary results, which indicate the feasibility of fabricating electrospray emitters in nonsilicon MEMS technology, notably by 3-D microlithography (two-photon lithography) are presented.
The flow of water and steam in an electrically powered micro heat exchanger consisting of an array of 68 wavy microchannels in parallel, each 200-μm wide, 100-μm deep and approximately 40-mm long, ...was investigated by high-speed videography. Semi-quantitative, time- and space-resolved information about the void fraction was extracted by pixel intensity calculations. Fluctuations at sub-audio frequencies (pulsation) were always visible in the microchannel array. Pulsation at the outlet reached a minimum with increasing heating power, but below the power required to achieve complete evaporation. This minimum was accompanied by a shift in the lateral distribution of channels filled with more steam or water. The differences between the test device and typical devices for applications in thermal and process engineering are also identified.PUBLICATION ABSTRACT
An internally wetted capillary-type electrospray thruster design is presented. The capillary emitters are optimized for fabrication using 3D micro lithography and can achieve sub 10-micrometer ...capillary diameters with an aspect ratio of over 20. Also provided is a design for a completely modular integrated extraction electrode that comprises an electrode carrier produced by 3D micro lithography and a thin metal film. The electrode orifices, distance to emitters, and size are all customizable thanks to the modularity of the design, which is compatible with any electrospray thruster type. The design provides alignment precision within 5 micrometers of the emitter tip and electrode orifice. While our new electrode achieved reproducible extraction, instability is still present. The data on emission from these emitter-electrode stacks is presented, as well as in situ microscopic optical observation of individual emitters. The images demonstrate emission in multiple extraction modes, microfluidic behaviour of the capillaries in space-like conditions, and interactions of the emission modes with the integrated electrode.
In this article, heat transfer in microstructure devices and its application in laboratory and industry will be described. Basic principles of microstructure heat exchangers made of metal, ceramics, ...and polymers will be presented. A variety of laboratory prototype applications will be shown, as well as some examples for industrial use of not only microstructure heat exchangers, but also microstructure devices as chemical reactors. A brief outlook will describe possible future application fields.
The promising performance of microchannels has given rise to intensive research on pressure drop and heat transfer characteristics of flows at the small scale. To check the classical models and to ...validate new ones, experiments need to be conducted, which are particularly difficult given the characteristic dimensions involved and the magnitude of the fluxes to be measured. Although more care has been devoted lately to the design of experiments in terms of control of the geometry and of the boundary conditions, the uncertainties which inevitably affect each measurement do not seem to have been given the proper consideration. Correctly calculating uncertainties not only allows a correct assessment of the experimental data obtained, but can also be used to decide which measurements need to have the highest precision to achieve a certain accuracy, thus saving money on the others. In this paper, a quantitative criterion is given to assess the accuracy achievable in the determination of the friction factor in the laminar regime for the flow of a fluid in a circular microtube. The influence of the six quantities (pressure drop, outlet pressure, temperature, length, diameter and volume flow rate) measured to determine
f in the laminar regime are studied separately and when combined. It is found that at low Reynolds numbers flow rate and pressure drop measurements are determinant for the final value of the uncertainty, while at larger Reynolds numbers the influence of the accuracy in measuring the hydraulic diameter prevails and also limits the minimum value that the total uncertainty can take.
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