Sensors and Actuators最新文献

A simple, inexpensive and reliable wafer-to-wafer alignment technique is presented for use in the fabrication of microsensors and microactuators. The technique provides ±5 μm alignment precision and requires no special optical or mechanical fixtures.

The possibility of obtaining ion-selective membranes on ISFETs by chemical grafting of the silica insulator has been previously shown. The grafting only slightly modifies the electrical characteristics of the transistor (the dielectric permitivity and thickness being nearly unchanged), which makes it possible to perform differential measurements between an ion-sensitive FET and a reference FET. For the detection of silver ions, the sensitive membrane (dimethylamino)silane onto silicon dioxide; the reference FET is an ISFET fabricated by grafting an aliphatic chain onto silicon dioxide.

The response obtained, i.e., the difference between both source potentials versus a platinum pseudo-reference electrode, can be described with the site binding model.

The differential method allows a miniaturized reference electrode to be used. At the same time, the effects of drift, temperature and residual pH response are reduced.

Two-port acoustic wave sensors have been fabricated, which utilize shear horizontal (SH) acoustic plate modes (APMs) to probe a solid/liquid interface. These modes, excited and detected by interdigital transducers on thinned quartz plates, propagate efficiently with liquid contacting the device and allow sensing to be performed on the side of the device opposite the transducers. A number of sensing mechanisms have been discovered, including mass loading, viscous entrainment of the contacting liquid, and acoustoelectric coupling between evanescent plate mode electric fields and ions and dipoles in solution. The mass sensitivity of the APM device enables it to function as a microbalance in a number of sensing applications. A chemical sensor capable of detecting low concentrations of Cu²⁺ ions in solution has been constructed by chemically modifying the device surface with ethylenediamine ligands. The treated devices bind Cu²⁺ ions in a manner that can be reversed by the addition of acid to the solution.

A new design for a fiber optic tactile sensor array is presented. In this design, optical fibers are used both as the actual force-sensing elements and as the signal-transmission media. The tactile array is formed by appropriately arranging fibers into four overlapping layers, two active layers sand- wiched between two corrugation layers, forming a two-dimensional grid of fibers. When force is imparted to a given fiber intersection, small dis- tortions (microbend) appear in the stressed fibers, resulting in decreases in transmitted light intensity in these fibers. A prototype sensor of this type has been constructed and tested. Comparison of the test results to desired tactile sensor charac- teristics and to a popular commercially available tactile sensor indicate that the prototype sensor performs very well, out-performing the commer- cial sensor in a number of the tested categories.

A mass flow sensor based on the frequency shift of a resonating microstructure is being developed, using a measurement principle of the thermoanemometry type. The sensor is to be applied for mass flows up to 10 standard cubic centimeters per minute (sccm; 10sccm = 0.17 mg s^-1), with a high sensitivity, a high resolution and a fast response. Here we report on the first prototype consisting of a 2 μm thick membrane: the temperature elevation of the thermally excited vibrating membrane affects its resonance frequency. The three-dimemsional heat transfer within the membrane and the mass flow is modeled, and expressions are derived for the resonance frequencies of initially curved and stressed membranes. Experiments have been carried out for nitrogen flows of up to 500 sccm passing over thermally excited membranes. Predicted and measured values for the shift of the resonance frequency agree well. The sensitivity of the average temperature elevation to the mass flow is quite small: at 10 sccm the cooling effect of the mass flow is only 0.2% of the heat loss by conduction to the substrate. At a resonance frequency of 5.0 kHz, and an average temperature elevation of the mebrane of 8°C, this still leads to a frequency change of 13 Hz in the mass flow range from zero to 10 sccm. Suggestions are presented for increasing the sensitivity of the sensor.

0–3 composites consisting of carbon black and vanadium oxide conductive fillers in polyethylene, a polyurethane, and polyvinyl alcohol have been developed for use as chemical sensors. Polymer matrices loaded with conductive filler near the percolation threshold swell reversibly in the presence of liquid and gaseous solvents, disrupting the conductive pathways and proportionally increasing the resistance. The magnitude of the swelling (which usually dominates the magnitude of ΔR) depends on the solubility of a given solvent in the polymer. For non-polar materials, the swelling can be predicted by considering the difference in solubility parameters of polymer and solvent, although the overall magnitude of ΔR may also be influenced by particle morphology, the percolation behavior for the system of interest, and other undefined solvent/polymer/filler interactions. The response time of the sensor is determined primarily by the sample thickness and the diffusion of the solvent through the polymer. Response times will play a role in determining the selection of a sensor for a particular application.

Non-contact electrooptical techniques offer the possibility of using automatic measurement for on-line dimensional analysis and quality control. In this paper a simple method, based on optical image elaboration using filtering techniques in the Fourier plane, is presented. The method enhances the signal-to-background ratio and can eliminate undesired spatial components in the image light distribution. The result of pre-filtering is a quasi- digital presentation of the object profile that reaches the CCD camera directly.

A preliminary implementation of the system is described, both for one- and two-dimensional ob- jects, and significant experimental results are pre- sented.

A sensor is described for identifying and quantifying different components in a gas mixture by decoding information from a modulated output signal. The system operates by passing the unknown gas into a reaction chamber containing a heated catalytic filament. The output products of the chamber are detected by an electrochemical sensor. The concentration of the reaction products is modulated by varying the temperature of the catalytic filament periodically. A theory is presented for analyzing the modulated output signal. The validity of the analysis is confirmed by experiments conducted with benzene, CO and HCN, and by a computer simulations. It appears to be possible to identify different species in the inlet gas stream provided the species undergo chemical reactions in the reactor that have different activation energies. The signal magnitude at peaks or valleys in the output is directly proportional to concentration, even though a steady-state condition is not reached. The approach may be generalized to other detector systems.

This paper describes the micro Stirling engine, a miniaturized Stirling engine the length, width, or height of whose body measure no more than several centimeters. The steps taken both to establish the design concept and actually to produce a microactuator are discussed. Geometrical scale analysis and computer simulation are used to investigate how the design parameters change when the engine size is reduced. This analysis and simulation enable a micro Stirling engine with an approximately 0.05 cm ³ piston swept volume (equivalent ot the displacement of a gasoline is approximately 10 mW at 10 Hz. Problems of scaling down the engine to a maximum length of several millimeters are discussed.

Electrostatic force generation may offer distinct advantages over more familiar magnetostatics at size scales approaching microns. The fabrication of very small electrostatic actuators is becoming technologically feasible, but is extremely difficult, so that mathematical modelling of actuator designs is likely to be very important in the advancement of this technology. Modelling involves difficulties not only in finding solution (typically numerical) to a mathematical problem, but more important, it requires that the mathematical problem be well formulated. This in turn requires an understanding of, and intuition for, what electrostatic effects are likely to be revelant, as well as an appreciation for the behavior of materials in electrostatic interactions and for the impact on other machine components (bearing, loads, etc). The well-established lore of magnetostatics is not of much use as a guide in this task for several reasons: magnetic materials tend to be either highly permeable (i.e. ferromagnetic) or to have no magnetic effect. By contrast, there are no electrostatically inert materials; the relative dielectric constant ε of any solid (of normal density) is of order two or greater, and thus any solid element of an electrostatic configuration has a significant influence on the field. Also, the sources of magnetic fields, currents or magnetization, can be specified with some confidence, while the sources of the electrostatic field, electric charge and polarization, are much more elusive and subject to change. It is the purpose of this paper to point out some of the effects that must be taken into account if a mathematical model is to give an adequate representation of the behavior of an actualy system. To do this we sketch a brief list of the types of electrostatic elements and interactions (conductors, dielectrics, compensated and uncompensated electrets, ferroelectrics, image forces, dielectrophretic forces, etc.) and use this list as background for discussing some electrostatic effects that may be important in the design or modelling of microactuators. For some of these effects, applicable results are reported from experimental investigations carried out with both a small (several hundred micron scale) electrostatically actuated device (‘SCOFSS’) built to study aspects of microelectromechanical design and of control via electrostatic actuation, and the ‘Wobble Motor’, a successful electrostatic microactuator.