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1.
Two piezoresistive ( n-polysilicon) strain sensors on a thin Si 3N 4/SiO 2 membrane with improved sensitivity were successfully fabricated by using MEMS technology. The primary difference between the two designs was the number of strips of the polysilicon patterns. For each design, a doped n-polysilicon sensing element was patterned over a thin 3 μm Si 3N 4/SiO 2 membrane. A 1000×1000 μm 2 window in the silicon wafer was etched to free the thin membrane from the silicon wafer. The intent of this design was to fabricate a flexible MEMS strain sensor similar in function to a commercial metal foil strain gage. A finite element model of this geometry indicates that strains in the membrane will be higher than strains in the surrounding silicon. The values of nominal resistance of the single strip sensor and the multi-strip sensor were 4.6 and 8.6 kΩ, respectively. To evaluate thermal stability and sensing characteristics, the temperature coefficient of resistance [TCR=(Δ R/ R0)/Δ T] and the gage factor [GF=(Δ R/ R0)/ ] for each design were evaluated. The sensors were heated on a hot plate to measure the TCR. The sensors were embedded in a vinyl ester epoxy plate to determine the sensor sensitivity. The TCR was 7.5×10 −4 and 9.5×10 −4/°C for the single strip and the multi-strip pattern sensors. The gage factor was as high as 15 (bending) and 13 (tension) for the single strip sensor, and 4 (bending) and 21 (tension) for the multi-strip sensor. The sensitivity of these MEMS sensors is much higher than the sensitivity of commercial metal foil strain gages and strain gage alloys. 相似文献
2.
We have developed a calorimetric sensor utilizing a thermoelectric device supported on a planar alumina substrate. By using a highly selective carbon monoxide (CO) oxidation catalyst and a non-selective platinum (Pt) catalyst, the device can be built to detect either CO or hydrocarbons with high selectivity. The CO oxidation catalyst comprises lead-modified platinum and exhibits excellent selectivity over the 200–400 °C temperature range. The thermoelectric device consists of two thick film junctions made of niobium pentoxide (Nb 2O 5)-doped titanium dioxide (TiO 2) and a lithiated nickel (Ni), which are supported on a planar alumina substrate. The thermocouple detects the difference in temperature due to different catalytic reactions over the two junctions and shows a high output signal because of the high Seebeck coefficient of Nb 2O 5-doped TiO 2 (−400 μV/°C). In gas bench tests, the sensor has a linear output of 0–2.75 mV over 0–1000 ppm of propylene and a response time of 2.5 s (at 90% of amplitude) at a gas temperature of 350 °C. An engine dynamometer evaluation shows that the response of the sensor parallels the change in CO and hydrocarbon constituent concentrations when the engine air-to-fuel ratio is varied. 相似文献
3.
A novel micromachined single wall carbon nanotube (SWCNT) reinforced nanocrystalline tin dioxide gas sensor has been developed. The presence of SWCNT in SnO 2 matrix was realized by a spin-on sol–gel process. The SWCNT/SnO 2 sensor's sensitivity for hydrogen detection has greatly increased by a factor of three, in comparison to that of pure SnO 2 sensor. The novel sensor also lowers the working temperature, response time and recovery time. The greatly improved performances are mainly attributed to the effective gas accessing nano passes through SWCNT plus the smaller distance between adjacent gas accessing boundaries formed by the distribution of tiny SWCNTs. Therefore, both the spatial requirement ( D ≤ 2 L, D is the distance between adjacent gas accessing boundaries and L is the space charge layer thickness) and surficial requirement (adequate gas activation area) are met and the maximum inherent sensitivity of SnO 2 is achieved. 相似文献
4.
NO 2 sensing properties of SnO 2-based varistor-type sensors have been investigated in the temperature range of 400-650°C and in the NO 2 concentration range of 15–30 ppm. Pure SnO 2 exhibited a weak nonlinear I– V characteristic in air, but clear nonlinearity in NO 2 at 450°C. The breakdown voltage of SnO 2 shifted to a high electric field upon exposure to NO 2 and the magnitude of the shift was well correlated with NO 2 concentration. Thus, SnO 2 exhibited some sensitivity to NO 2 as a varistor-type sensor. When SnO 2 particles coated with a SiO 2 thin film were used as a raw material for fabricating a varistor, the breakdown voltage in air was approximately the double that of pure SnO 2 and the sensitivity to 15 ppm NO 2 was enhanced slightly. However, the sensitivity to 30 ppm NO 2 decreased. The Cr 2O 3-loading on SnO 2 also led to an increase in the breakdown voltage in air, but the Cr 2O 3 addition was not effective for promoting the NO 2 sensitivity under the present experimental conditions. 相似文献
5.
A heap structure designed for secondary storage is suggested that tries to make the best use of the available buffer space in primary memory. The heap is a complete multi-way tree, with multi-page blocks of records as nodes, satisfying a generalized heap property. A special feature of the tree is that the nodes may be partially filled, as in B-trees. The structure is complemented with priority-queue operations insert and delete-max. When handling a sequence of S operations, the number of page transfers performed is shown to be O(∑ i = 1S(1/ P) log(M/P)( Ni/ P)), where P denotes the number of records fitting into a page, M the capacity of the buffer space in records, and Ni, the number of records in the heap prior to the ith operation (assuming P 1 and S> M c · P, where c is a small positive constant). The number of comparisons required when handling the sequence is O(∑ i = 1S log2 Ni). Using the suggested data structure we obtain an optimal external heapsort that performs O(( N/ P) log(M/P)( N/ P)) page transfers and O( N log2 N) comparisons in the worst case when sorting N records. 相似文献
6.
Integrated optical sensor chips suitable for high-resolution pH measurements are presented. The pH-sensitive swelling of a polymer membrane is detected by refractometry using a compact multi-channel sensor module. The signal transduction is achieved by means of chirped grating couplers which allow simple yet high functionality sensor modules to be built. The experiments have been performed with high sensitivity replicated polycarbonate TiO 2 waveguide sensor chips coated with an ultrathin photopatterned hydrogel membrane having functional groups which reversibly change from the neutral state to a charged state upon acidification. A resolution δpH <±1.1×10 −4 in terms of the pH (at pH 7.5) has been obtained in a dual-channel module with size 10×10×10 cm 3. 相似文献
7.
This paper describes the fabrication procedure as well as the sensing properties of new hydrogen sensors using Fe 2O 3-based thin film. The film is deposited by the r.f. sputtering technique; its composition is Fe 2O 3, TiO 2(5 mol%) and MgO(0–12 mol%). The conductance change of the film is examined in various test gases. The sensitivity to hydrogen gas is enhanced by treating the film in vacuum at 550 °C for 4 h and then in air at 700 °C for 2 h. The sputtered film is identified to be polycrystalline -Fe 2O 3 based on X-ray diffraction patterns. However, the surface layer is considered to be changed to Fe 3O 4 after heating in vacuum and then to γ-Fe 2O 3 after heating in air. The film is thus a multilayer one with a thin γ-Fe 2O 3 layer on a -Fe 2O 3 layer. The sensing mechanism is discussed based on measurements of the physical properties of the film, such as the temperature dependence of the sensor conductance, X-ray diffraction pattern, surface morphology, RBS (Rutherford back-scattering) spectrum and optical absorption spectrum. 相似文献
8.
The development of ordered porous nanostructured materials, such as polymeric Bragg gratings, offers an attractive platform for the encapsulation of chemical and biological recognition elements. To date, various types of polymer gratings have been developed with several demonstrated applications in switching, lasing, and display devices. Here, we focus on a new class of holographically ordered porous polymer (HOPP) gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. We present biochemical sensing using HOPP gratings that include a volatile solvent as the phase separation fluid. The resulting HOPP gratings are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of recognition elements. As a prototype, we developed an oxygen (O 2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. The resulting O 2 sensors performed across the full-scale range (0–100%) of oxygen in nitrogen, with a response time of less than 1 s. The O 2 sensor system uses a LED excitation source and a silicon photodiode detector. The ability of these HOPP reflection gratings to transmit or reflect a particular wavelength range, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest. 相似文献
9.
For the fabrication as step-down multilayer piezoelectric transformer, piezoelectric properties of Pb(Mg 1/3Nb 2/3)O 3–Pb(Zn 1/3Nb 2/3)O 3–Pb(Zr 0.52Ti 0.48)O 3 (PMN–PZN–PZT) ceramics were optimized by ZnO–Li 2CO 3 (ZL) and Pb 3O 4 content. Effects of the additions on the structure, bulk density and electrical properties of ceramics were investigated. The results revealed that the proper additions of ZL with Pb 3O 4 content could modify the electrical properties of the PMN–PZN–PZT ceramics. The composition sintered at 995 °C with 0. 01 wt.% ZL and 0.10 wt.% Pb 3O 4 content showed higher values, which were listed as follows: d33 = 256 pC/N, Kp = 0.60, Qm = 1910, r = 1032, tan δ = 0.0070 and r = 2.09 Ω. In addition, the step-down piezoelectric transformers with optimized PMN–PZN–PZT composites were fabricated and the characteristics as the output power and resistance loads were measured. Meanwhile, the step-down piezoelectric transformers sintered at 995 °C showed the favorable characteristics with a higher gain G of 0.204 and a lower temperature rise of 6 °C when the output power was 5 W, and the driving frequency were approximately constant (≈126 kHz) when the output power was from 5 to 13 W. Moreover, the maximum efficiency (90.2%) was obtained at load resistance of 10 Ω. 相似文献
10.
A surface acoustic wave (SAW)-based high-voltage sensor is described. The sensor consists of a SAW oscillator fabricated on a 10 mm × 10 mm 128° rotated Y-cut, X-propagating LiNbO 3 substrate. The voltage is applied to electrodes on the substrate, and the resulting electric field changes the propagation time of the SAW. The propagation time is directly related to the output frequency of the SAW oscillator. The high-voltage sensor offers a small-sized high-voltage measurement device with several attractive features: a high resolution (better than 0.2 V up to 2.4 kV, better than 0.4 V for higher voltages), a large range (−10 to +10 kV), a high input impedance (> 10 13 ω) and a low input capacitance (< 10 pF). The sensitivity amounts to 16 Hz V −1. 相似文献
11.
In our earlier study, we reported that at 300 °C, a 2.0 wt.% CeO 2-doped SnO 2 sensor is highly selective to ethanol in the presence of CO and CH 4 gases [F. Pourfayaz, A. Khodadadi, Y. Mortazavi, S.S. Mohajerzadeh, CeO 2 doped SnO 2 sensor selective to ethanol in presence of CO, LPG and CH 4, Sens. Actuators B 108 (2005) 172–176]. In the present investigation, we report the influence of ambient air humidity on the ethanol selective SnO 2 sensor doped with 2.0 wt.% CeO 2. Maximum response to ethanol occurs at 300 °C which decreases with the relative humidity. The relative humidity was changed from 0 to 80% for different ambient air temperatures of 30, 40 and 50 °C and the response of the sensor was monitored in a 250–450 °C temperature range. As the relative humidity in 50 °C air increased from 0 to 30%, a 15% reduction in the maximum response to ethanol was observed. A further increase in the relative humidity no longer reduced the response significantly. The presence of humidity improved the sensor response to both CO and CH 4 up to 350 °C after which the extent of improvement became smaller and at 450 °C was almost diminished. The sensor is shown to be quite selective to ethanol in the presence of humid air containing CO and CH 4. The selectivity passes a maximum at 300 °C; however it declines at higher operating temperatures. 相似文献
12.
TiO 2 thin films were prepared by spin-coating of a Ti butoxide-derived sol onto oxidized silicon wafers, followed by a heat-treatment at temperatures ranging from 500 to 800 °C. The film thickness after heat-treatment at 500 °C was 50 nm. Pt addition, with a Pt:Ti nominal atomic ratio ranging from 0.01 to 0.1, was achieved by adding solutions of Pt(II) acetylacetonate to the TiO 2 sols. The thin films were investigated by X-ray diffraction, evidencing that Pt promoted the structural transformation of the starting anatase phase of TiO 2 to rutile, with a more enhanced effect with increasing the Pt concentration and/or the heat-treatment temperature. High-resolution transmission electron microscopy evidenced that, when a Pt:Ti atomic ratio of 0.05 and a heat treatment at 500 °C were used, the TiO 2 contained both anatase and rutile phases and interspersed Pt nanocrystals (2–3 nm). This result allowed attributing the structural transformation in TiO 2 to the strain created by the Pt nanocrystals—a conclusion which was further corroborated by the observation that Pd-modified films, prepared under similar conditions, were only composed of anatase TiO 2 and did not contain any Pd nanocrystals. The films heat-treated at 500 °C were able to withstand a full microelectronic processing sequence, including dry etching for gas sensors sensitive area definition, Ti/Pt contact formation, and heater processing on the backside of the sensor substrates. H 2 gas-sensing tests evidenced that the anatase TiO 2 phase was much more sensitive than the rutile one. The presence of Pt further enhanced the gas-sensing properties, lowering the optimum sensor operation temperature to about 330 °C and allowing for the detection of a minimum H 2 concentration of about 1000 ppm. 相似文献
13.
Pt-loaded metal oxides [WO 3/ZrO 2, MO x/TiO 2 (MO x = WO 3, MoO 3, V 2O 5), WO 3 and TiO 2] equipped with interdigital Au electrodes have been tested as a NO x (NO and NO 2) gas sensor at 500 °C. The impedance value at 4 Hz was used as a sensing signal. Among the samples tested, Pt-WO 3/TiO 2 showed the highest sensor response magnitude to NO. The sensor was found to respond consistently and rapidly to change in concentration of NO and NO 2 in the oxygen rich and moist gas mixture at 500 °C. The 90% response and 90% recovery times were as short as less than 5–10 s. The impedance at 4 Hz of the present device was found to vary almost linearly with the logarithm of NO x (NO or NO 2) concentration from 10 to 570 ppm. Pt-WO 3/TiO 2 showed responses to NO and NO 2 of the same algebraic sign and nearly the same magnitude, while Pt/WO 3 and WO 3/TiO 2 showed higher response to NO than NO 2. The impedance at 4 Hz in the presence of NO for Pt-WO 3/TiO 2 was almost equal at any O 2 concentration examined (1–99%), while in the case of Pt/WO 3 and WO 3/TiO 2 the impedance increased with the oxygen concentration. The features of Pt-WO 3/TiO 2 are favorable as a NO x sensor that can monitor and control the NO x concentration in automotive exhaust. The effect of WO 3 loading of Pt-WO 3/ZrO 2-based sensor is studied to discuss the role of surface W-OH sites on the NO x sensing. 相似文献
14.
This paper describes some new techniques for the rapid evaluation and fitting of radial basic functions. The techniques are based on the hierarchical and multipole expansions recently introduced by several authors for the calculation of many-body potentials. Consider in particular the N term thin-plate spline, s( x) = Σ j=1N djφ( x− xj), where φ( u) = | u| 2log| u|, in 2-dimensions. The direct evaluation of s at a single extra point requires an extra O( N) operations. This paper shows that, with judicious use of series expansions, the incremental cost of evaluating s( x) to within precision ε, can be cut to O(1+|log ε|) operations. In particular, if A is the interpolation matrix, ai,j = φ( xi− xj, the technique allows computation of the matrix-vector product Ad in O( N), rather than the previously required O( N2) operations, and using only O( N) storage. Fast, storage-efficient, computation of this matrix-vector product makes pre-conditioned conjugate-gradient methods very attractive as solvers of the interpolation equations, Ad = y, when N is large. 相似文献
15.
Oxide semiconductors have been examined to develop NO x sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al 3+, Sc 3+, Ga 3+ or In 3+, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NO x has been fabricated. Many kinds of interference gases, such as C 3H 6, CO and SO 2, have been found to have only a slight influence on the sensor response to NO. The influence of O 2 and H 2O is also negligible, except for the cases of 0% H 2O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases. 相似文献
16.
LaFEO 3 and Ca xLa 1−xFeO 3 ceramic powders have been prepared by the coprecipitation method from La(NO 3) 3, Fe(NO 3) 3 and Ca(NO 3) 2 aqueous solutions. The orthorhombic perovskite phases of LaFeO 3 and Ca xLa 1−xFeO 3 are characterized by X-ray diffraction patterns. The sensors fabricated with those powders have high sensitivity to alcohol. Partial substitution of La 3+ in LaFeO 3 with Ca 2+ can enhance the sensitivity of the materials to reducing gases. The resistance of an LaFeO 3 sensor in air, vacuum and alcohol-containing air has been measured. Complex impedance spectroscopy has been used to try and analyse the gas-sensing mechanism. According to the experimental results, it can be deduced that the surface adsorptive and lattice oxygen govern the sensing properties of LaFeO 3 and Ca xLa 1−xFeO 3 ceramics. 相似文献
17.
A solid composite electrolyte with high proton conductivity based on antimonium pentoxide with additives of phosphoric acid has been obtained. A potentiometric solid-state gas sensor using this electrolyte has been developed for detecting small amounts of hydrogen (10–2000 ppm) in gas mixtures at ambient temperature. The sensor consists of the reference electrode: Ag or Ag/(Ag + Ag 2SO 4), the solid composite electrolyte and H 2-sensitive electrode: Pt or Pd. The electromotive force (e.m.f.) of the sensor varies logarithmically with H 2 concentration for hydrogen partial pressures in the range 100–2000 ppm and depends on the oxygen partial pressure. The slope of e.m.f.-log( pH 2) dependence is 170 and 200 mV for Pt and Pd, respectively, which exceeds the Nernst value, presumably due to the formation of a mixed potential. The sensor can operate at a wide range (20–95%) of a relative humidity. 相似文献
18.
Solid-electrolyte-based electrochemical SO x sensors fabricated with MgO-stabilized zirconia and Li 2SO 4---CaSO 4---SiO 2 (4:4:2 in molar ratio) exhibit fairly good sensing characteristics for 2–200 ppm SO 2 in air at 600–750 °C, with the e.m.f. responses following the Nernst equation for the two-electron reduction of SO 2. The 90% response and 90% recovery times to 20 ppm SO 2 are 10 s and 7 min at 650 °C, and 10 s and 3 min at 700 °C, respectively. It is further found that the sensor exhibits excellent selectivity to SO x in the coexistence of CO 2 and NO x, and good long-term stability. The sensor is simple in structure, easy to prepare, and quite tough chemically and mechanically. These features should ensure practical use for this SO x sensor. 相似文献
19.
For an ordered set W = { w1, w2,…, wk} of vertices and a vertex v in a connected graph G, the (metric) representation of v with respect to W is the k-vector r( v | W) = ( d( v, w1), d( v, w2),…, d( v, wk)), where d( x, y) represents the distance between the vertices x and y. The set W is a resolving set for G if distinct vertices of G have distinct representations. A new sharp lower bound for the dimension of a graph G in terms of its maximum degree is presented. A resolving set of minimum cardinality is a basis for G and the number of vertices in a basis is its (metric) dimension dim(G). A resolving set S of G is a minimal resolving set if no proper subset of S is a resolving set. The maximum cardinality of a minimal resolving set is the upper dimension dim+(G). The resolving number res(G) of a connected graph G is the minimum k such that every k-set W of vertices of G is also a resolving set of G. Then 1 ≤ dim(G) ≤ dim+(G) ≤ res(G) ≤ n − 1 for every nontrivial connected graph G of order n. It is shown that dim+(G) = res(G) = n − 1 if and only if G = Kn, while dim+(G) = res(G) = 2 if and only if G is a path of order at least 4 or an odd cycle. The resolving numbers and upper dimensions of some well-known graphs are determined. It is shown that for every pair a, b of integers with 2 ≤ a ≤ b, there exists a connected graph G with dim(G) = dim+(G) = a and res(G) = b. Also, for every positive integer N, there exists a connected graph G with res(G) − dim+(G) ≥ N and dim+(G) − dim(G) ≥ N. 相似文献
20.
We report on electrical responses of tungsten oxide thin film ozone sensors based on a tungsten trioxide (WO 3)/tin oxide (SiO 2)/Si structure with interdigitated Pt electrodes. The influence of O 2 concentration in the sputtering gas and working temperature of the sensor are investigated. Sensitivity to ozone increases with O 2 content in the sputtering gas. It reaches its highest value for sensors fabricated with 50% O 2. For these sensors, the best ozone sensitivity and shortest response and recovery times are obtained at a working temperature of 523 K. Ozone sensitivity is compared to other ozone sensors. 相似文献
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