This paper demonstrates improvements on semiconductor nanomembrane based high frequency pressure sensors that utilize silicon on insulator techniques in combination with nanocomposite materials. The low-modulus, conformal nanomembrane sensor skins with integrated interconnect elements and electronic devices could be applied to vehicles or wind tunnel models for full spectrum pressure analysis. Experimental data demonstrates that: 1) silicon nanomembrane may be used as single pressure sensor transducers and elements in sensor arrays, 2) the arrays may be instrumented to map pressure over the surfaces of test articles over a range of Reynolds numbers, temperature and other environmental conditions, 3) in the high frequency range, the sensor is comparable to the commercial high frequency sensor, and 4) in the low frequency range, the sensor is much better than the commercial sensor. This supports the claim that nanomembrane pressure sensors may be used for wide bandwidth flow analysis.
Recent work in the fabrication of self assembled quantum dot (QD) detectors for optical fiber sensors is reported in this
paper. The ability to develop the QD based devices and materials via the electrostatic self-assembly (ESA) process has
been demonstrated. The QD precursor nanocluster materials involved in ESA have been designed and synthesized to
proper size, stabilized in an aqueous-based solution, and functionalized to allow self-assembly. The optical fiber sensor
instrumentation has been developed to monitor the reflected optical power with the buildup of the QD layers on the fiber
endface during the ESA process. The results are confirmed by observing the effects of low-finesse QD Fabry-Perot
interferometric cavities formed via such processes on the ends of optical fibers. The photocurrent-voltage characteristics
show a diode-like behavior with linear photocurrent in the reverse bias and nonlinearity in the forward bias. It is
suggested that fast response times can be achieved due to the high carrier mobilities that arise in part due to structure of
the materials formed via the solution-based ESA process.
Recent work in the fabrication of self assembled quantum dot (QD) detectors on active structural fibers and
for the implementation of optical fiber sensors is reported in this paper. The ability to develop the QD
based devices and materials via the electrostatic self-assembly (ESA) process has been demonstrated by
Hand and Kang in prior work. The QD precursor nanocluster materials involved in ESA have been
designed and synthesized to proper size, stabilized in an aqueous-based solution, and functionalized to
allow self-assembly. Optical fiber sensor instrumentation has been developed to monitor the reflected
optical power with the buildup of the QD layers on the fiber endface during the ESA process. The results
are confirmed by observing the effects of low-finesse QD Fabry-Perot interferometric cavities formed via
such processes on the ends of optical fibers. The photocurrent-voltage characteristics show a diode-like
behavior with linear photocurrent in the reverse bias and non-linearity in the forward bias. It is suggested
that fast response times can be achieved due to the high carrier mobilities that arise in part due to structure
of the materials formed via the solution-based ESA process. This paper reviews this prior work and shows
examples of deposition of devices on both fiber endfaces and cladding surfaces.
Two different optical fiber-based sensor approaches are compared for the detection of hydrogen gas. The two sensors both use Fabry-Perot techniques that have been investigated for some time for other applications. One involves the use of an Extrinsic Fabry-Perot Interferometric (EFPI) sensor scheme, and the other uses a nanoFabry-Perot (nanoFP) cavity that is formed on the distal end of a fiber endface. It is found in general that the sensitivity of the EFPI sensor is higher than that of the nanoFP, but that its speed of response is slower.
Recent progress in nanostructured optical fiber-based sensors for the noninvasive, fast and quantitative measurement of volatile organic compounds (VOC) in human breath is reported. The sensor array, which is constituted with multilayered, interleaved metal nanocluster and polymer thin films on the distal ends of optical fibers, is fabricated by
the electrostatic self-assembly (ESA) process. Initial research and early sensor prototype demonstrations indicate that the
specific detection of acetone, ethane and other molecular targets in exhaled human breath is achievable. Moreover, the
selectivity and sensitivity of the system are significantly improved by incorporating an advanced data analysis model.
This paper presents recent progresses in the application of nanostructured optical fiber-based sensors for non-invasive, fast and reliable monitoring of respiratory airflow. Molecular-level self-assembly processing method is used to form multilayered inorganic nanocluster and polymer thin films on the distal ends of optical fibers to form such sensors. In order to optimize sensing performance, recent work has studies the synthesis process and the fundamental mechanisms for the change in optical reflection, specifically caused by exhaled air condensation on the coating surface. The physically small sensors fabricated by varying thin film chemistry, offer a full range of environmental relative humidity sensing from 0% to 100% with response times of microseconds, and mostly important, provide much higher sensitivity to breathing air, over 6 times larger than 100% relative humidity. The sensor performances in comparison with a medical nasal thermistor suggest such a thin film sensor an excellent device for advanced breathing airflow monitoring. All the features are appealing to clinical respiratory diagnosis and related sensor instrumentation design, and in good agreement with our analytical model.
This paper describes improvements that have been made in optical fiber biosensors based on thin films deposited onto the ends of optical fiber waveguides using molecular-level self-assembly processes. The properties of the sensor films may be varied by controlling both the chemistry and the morphology and ordering of the films during their fabrication. For example, multilayer segments of films having different indices of refraction may be deposited to form quarter wavelength stack filters whose reflection properties change as a function of concentration of target chemical that modifies the index of the outermost layer or layers. Prior work has shown that by using different chemicals in the self-assembled layers, correspondingly different target chemicals may be detected. These have included water vapor, ammonia, dichloromethane and others. Improvements have been made in the range of index of refraction that may be achieved in the individual layer segments, specifically over the range of 1.2 to 1.8 at visible and near-infrared wavelengths. This paper shows how such an improvement in index difference influences the minimum detectable chemical concentration difference detectable using this approach.
The paper describes the necessity and feasibility of digitizing output signal from the fiber-optic sensors (FOS), and how to realize the digital optics for FOS with intensity modulation. A method of obtaining information by using special optical fibers is described. The auto-adaptive optics technology is utilized to derive fiducial information. In order to increase computational flexibility, optical technology is used in place of several electronic technologies.
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