Flow Sensor Arrays Research Articles

Selective Growth Method of Carbon Nanotubes by Chemical Vapor Deposition

Carbon nanotubes (CNTs) are potentially useful for developing functional nanodevices such as thermal probes, flow sensor arrays, and AFM probes. Controlling the growth position of CNTs grown by chemical vapor deposition (CVD) is crucial to fabrication of these nanodevices. We propose an easy, non-lithographic process of making CNT sensor probes using CVD. Growth positions of CNTs were precisely controlled by depositing a patterned barrier layer above the catalyst layer. Then, the CNTs were grown from the exposed catalyst layer using CVD. This method is easily applied to assembling bridged CNTs. We used focused ion beam etching to remove the barrier layer and expose the catalyst membrane. Through the proposed method, we made a bridge of CNTs at the tip of a Si edge. This type of bridge can be used as the nanoprobes for local sensing of physical properties.

Fault-tolerant sensor integration for micro flow-sensor arrays and networks

Distributed micro flow-sensor arrays and networks (DMFSA/N), built from collections of spatially scattered, cooperating intelligent and redundant micro flow-sensor nodes, can improve the accuracy and reliability of system. However, it is unrealistic to expect all the sensor nodes and communication links in the system to function properly all the time. This paper is based on an earlier research, in which a DMFSA/N with a cluster architecture and fault-tolerant time-out Protocol (FTTP) was developed. In this paper, a fault-tolerant sensor integration algorithm (FTSIA) is proposed and evaluated in simulations. Experimental results showed that the FTSIA could always give reliable results even when certain portion of the sensors yielded faulty information. Furthermore, the results from FTSIA were significantly more accurate than the mean of sensor readings (popularly applied in industry) if some of the sensors produced faulty readings. Finally, the application of the proposed FTSIA is illustrated by measuring flow pressure using a pressure sensor array of eight sensors.

Scalable microbeam flowsensors with electronic readout

In this paper, we present a scalable microchannel-embedded cantilever flowsensor with electronic readout. The scalable nature of the sensor addresses the need to realize arrays of flowsensors to characterize localized flow patterns. The electronic readout addresses the need to integrate flowsensors in microfluidic channels for closed-loop flow control. The in-channel nature of the flowsensor provides a wide choice for the cap material (e.g., PDMS, glass, silicon, etc.) enabling division of labor between integrated circuit (IC) and microfluidic foundries. This also holds promise for large-scale integrated microfluidic systems. The cantilever beam is placed inside a microfluidic channel in such a way that it utilizes drag forces to cause a flow-induced stress underneath the beam anchor. A Wheatstone bridge of piezoresistors placed directly under the anchor converts the flow-induced stress into a differential output voltage. We present an analytical model and 3-D simulations for the proposed flowsensor. Flowsensors fabricated by standard photolithography were tested to experimentally verify the validity of the model and simulation results. A flow sensitivity (unamplified) of 0.5 ppm/(/spl mu/L/s) was measured with first generation devices with water flow from 10 /spl mu/L/min to 100 /spl mu/L/min. Through experimental results, it is also shown that scaling down the size of the flowsensor results in higher sensitivity. We present a prediction on the noise-floor of flow measurement based on the results obtained using these prototype flowsensors.

Improvement of surface acoustic wave gas and biosensor response characteristics using a capacitive coupling technique.

As for many other electronic devices and circuits, electrical contact to surface acoustic wave sensors is usually made using bonding wires. This technique is known to result in reliable contact under most conditions, but it does so with several disadvantages. First, electrical contact is not reversible, impeding replacement of sensor devices. Second, bonding wires are quite delicate and should not be exposed to high gas or liquid flows. Third, the presence of bonding wires may limit the potential to miniaturize a sensor housing or flow cell. Therefore, a capacitive coupling technique was developed to replace bonding wires. This permitted redesign of flow cells and sensor arrays, resulting in flow cell volumes of 80 microL to 60 nL. As a consequence, response times were reduced to 1-2 s in gas sensing and a few minutes in liquid sensing, respectively. At the same time, sensor devices can be easily replaced, and the system is less susceptible to malfunction.

MEMS Devices and Applications in Aerospace and Civil Engineering

J ‘‘Examination of Bulge Test for Determining Residual Stress, Young’s Modulus, and Poisson’s Ratio of 3C-SiC Thin Films,’’ describe their study of a test that is based on plate mechanics, and illustrate its capabilities within their work on silicon carbide fabrication. Another important topic within MEMS ~and its nanoscale counterpart, NEMS! research is biochemical sensing, for which dissolvable hydrogels can serve as indicators. Aluru and his colleagues from the University of Illinois, in a paper entitled ‘‘Mathematical Modeling and Simulation of Dissolvable Hydrogels,’’ present a mathematical model for hydrogel behavior with comparisons between model and experimental results. Three papers are contributed by researchers in the MEMS community describing the development of devices that can revolutionize aerospace and civil engineering practice. My colleagues from Carnegie Mellon, Xie ~now at the University of Florida! and Fedder, report on the development of vibratory gyroscopes in a paper entitled ‘‘Integrated MEMS Gyroscopes.’’ In a paper entitled ‘‘Capacitive Micromachined Ultrasonic Transducers: Theory and Technology,’’ Khuri-Yakub and his coworkers from Stanford give the reader comprehensive insight into the design, behavior, and performance of ultrasonic transducers. Liu and his coworkers, from the University of Illinois, contribute a paper entitled ‘‘Two-Dimensional Micromachined Flow-Sensor Array for Fluid Mechanics Studies’’ in which they describe the development of two novel sensors for use in fluid mechanics; they start with the physical concepts, show the development of the MEMS process and the device design, and then illustrate the results with experimental studies. I wish to thank the authors of these papers, as well as others who responded with interest and whose papers may appear in future issues of this Journal. The ideas they describe are stimulating, their research practices are exemplary, and their writing is excellent. They set a high standard and we are the beneficiaries. Irving J. Oppenheim Carnegie Mellon University