Hairong Wang

Uncertainty estimation in measurement of micromechanical properties using random-fuzzy variables

Instrumented indentation testing mechanical properties of small volume materials can be affected by various factors during the measurement process, either in random or nonrandom characteristics, which can induce much uncertainty in the evaluation results. The traditional uncertainty estimation method, which is based on probability theory, is ineffective for the cases where some nonrandom effects are present. In this article, uncertainty estimation in measurement of hardness and elastic modulus by tester for micromechanical properties associated with random-fuzzy variables (RFVs) is presented. Uncertainty estimation results from both the traditional and RFV methods are derived and compared. Results show that the measurement uncertainties in hardness and elastic modulus can be effectively expressed in terms of RFVs under different levels of confidence, and all possible influencing effects on the uncertainties can be involved.

A micro oxygen sensor based on a nano sol-gel TiO2 thin film.

An oxygen gas microsensor based on nanostructured sol-gel TiO2 thin films with a buried Pd layer was developed on a silicon substrate. The nanostructured titania thin films for O2 sensors were prepared by the sol-gel process and became anatase after heat treatment. A sandwich TiO2 square board with an area of 350 μm × 350 μm was defined by both wet etching and dry etching processes and the wet one was applied in the final process due to its advantages of easy control for the final structure. A pair of 150 nm Pt micro interdigitated electrodes with 50 nm Ti buffer layer was fabricated on the board by a lift-off process. The sensor chip was tested in a furnace with changing the O2 concentration from 1.0% to 20% by monitoring its electrical resistance. Results showed that after several testing cycles the sensors output becomes stable, and its sensitivity is 0.054 with deviation 2.65 × 10−4 and hysteresis is 8.5%. Due to its simple fabrication process, the sensor has potential for application in environmental monitoring, where lower power consumption and small size are required.

Solid Potentiometric

A solid potentiometric CO₂ sensor has been developed using Li₃PO₄ as the electrolyte, Li₂TiO₃/TiO₂ as the reference electrode, and Li₂CO₃ as the sensing electrode. The Li₃PO₄ film was deposited on Al₂O₃ substrate by resistance heating evaporation. Two Pt electrodes with designed patterns were formed on the electrolyte film by micro fabrication technologies. The reference electrode and the sensing electrode were prepared by thick-film technology to cover part of the two Pt electrodes. Various properties were tested: sensitivity under different conditions, response and recovery properties, cross-interference performance, and stability. The values of ΔEMF/dec are 22 mV/dec, 45 mV/dec, and 78 mV/dec in accordance with the operating temperatures: 300°C, 400°C, and 500°C. At 500°C, the response time and recovery time are 30 s and 40 s, respectively, which is better than those of 400°C. When the thickness of Li₃PO₄ film is greater than 650 nm, the EMF output of the sensor changes little with change of the film thickness. From the results, it can be concluded that the optimal working temperature for the sensor is 500°C, and the optimal thickness of Li₃PO₄ is about 650 nm.

{\rm CO}_{2}

A potentiometric CO2 gas sensor based on Li3PO4 film with the thickness of 0.8 μm prepared by thermal evaporation method was developed. Au thin film with the thickness of 400 nm deposited by sputtering method was used as the metal electrodes of the sensor. Li2CO3 and Li2TiO3 with 10 mol. % TiO2 were used as the sensing and reference electrodes by screen printing the materials on the Au thin film electrodes, respectively. Response characteristics of the sensor to CO2 in the range of 250 ppm to 5000 ppm at different working temperatures were investigated. The electromotive force (EMF) values of the sensor were linearly dependent on logarithm of CO2 partial pressure at the temperatures between 420 °C and 530 °C. Dependence of response and recovery time, initial EMF, ΔEMF/dec on working temperature was presented. It can be found that the response time and recovery time reduced with the enhancement of working temperature and gradually reached to the limit when the temperature is above 500 °C. However, the maxi...

Sensor Using

A thin-film type potentiometric sensor has been prepared by the implementation of electro-beam evaporation, rf magnetron sputtering methods, and micromachining processes. Sn film was deposited on n-Si/SiO(2) (400 nm) substrate. A deposited LaF(3) film was applied as solid electrolyte and sputtered Pt film was used as the sensing electrode. The patterns of the Pt and LaF(3) were realized by the micromachining processes. The LaF(3) film was characterized by scanning electron microscopy and energy dispersive x ray. Saturated aqueous solutions were used to achieve controlled humidity environments. When the sensor was exposed to humidity environments, the electromotive force (EMF) of the sensor was examined. It was found that the sensor varies with the relative humidity (RH). The stable response curve was presented and non-Nernst behavior between the average EMF values and RH may be shown.

{\rm Li}_{3}{\rm PO}_{4}

The infrared absorption gas sensor detects CH4, CO, CO2, and other gases accurately and rapidly. However, temperature and humidity have a great impact on the gas sensors performance. This article studied the response of an infrared methane gas sensor under different temperatures and humidity conditions. After analyzing the compensation methods, a back propagation neural network was chosen to compensate the nonlinear error caused by temperature and humidity. The optimal parameters of the neural network are reported in this article. After the compensation, the mean error of the gas sensors output was between 0.02–0.08 vol %, and the maximum relative error dropped to 8.33% of the relative error before compensation. The results demonstrated that the back propagation neural network is an effective method to eliminate the influence of temperature and humidity on infrared methane gas sensors.

Film as the Electrolyte

In this paper, we investigated the sensing properties of sandwich structure of TiO2/Pd/TiO2 thin films at various operating temperatures and oxygen partial pressures. The nanostructure TiO2 thin films were prepared by the sol-gel method. Various thickness of Pd buried layer was deposited by magnetron sputtering of a pure Pd target. The films were characterized using X-ray diffraction analysis and SEM. It was found that TiO2/Pd/TiO2 thin films have the p-type behavior while the pure TiO2 thin film is n-type semiconductor materials. We found that the structure of TiO2/Pd/TiO2 thin films with 10 s sputtering Pd layer has a better stability at 240 °C.

Response characteristics of a potentiometric CO2 gas sensor based on Li3PO4 solid electrolyte using Au film as the electrodes

A potentiometric SO2 gas sensor based on Li3PO4 solid electrolyte has been developed using Au as the reference electrode and Li2SO4/V2O5 as the sensing electrode. The Li3PO4 film was deposited on Al2O3 substrate by resistance heating evaporation. Two Au films with designed patterns were formed on the Li3PO4 film by micro-fabrication technologies. The sensing electrode covers one electrode partly using thick-film technology. The electromotive force values between the sensing electrode and the reference electrode were measured and various characteristics were studied including sensitivity, response characteristics, and stability and selectivity. According to the results, we conclude that an optimal working temperature of the SO2 sensor is 500 °C, the measurement range is 0-100 ppm, the sensitivity is about 32.47 mV/dec, the response and the recovery time is about 5 min and 10 min, respectively. And the stability and the selectivity of the sensor are good, making it have potential in SO2 measurement of living environment.

Humidity response properties of a potentiometric sensor using LaF3 thin film as the solid electrolyte

To characterize the subsurface mechanical damage (SSD) of the polished optics, the material remove rate of the polished K9 glasses based on HF acid etching was investigated. The etching of optics is assumed to be isotropic, a polished K9 sample with special designed pattern was tested to find out the constancy of etching rate versus time. As the etching rate was determined, the polished samples were progressively etched till the SSD disappeared visually. During etching, topographies of the surface revealed the evolution of the subsurface damages, and by recording and comparing topographies, we may get the distribution of the SSD at every depth. The thickness of etched material refers to the depth of SSD as the subsurface damages were totally exposed. Compared with the Magnetorheological finishing tamper polishing, this method of measuring SSD is low-cost and simple.

BACK PROPAGATION NEURAL NETWORK MODEL FOR TEMPERATURE AND HUMIDITY COMPENSATION OF A NON DISPERSIVE INFRARED METHANE SENSOR

Electromotive force (EMF) transient curves presented that the sensor showed good repeatable response in the humidity environments using ambient atmosphere as the carrier gas at different temperatures. The 90% response time and recovery time were within 40 s and 50 s, respectively. The sensor also presented stable response characteristics in 75.1% RH and 83.6% RH humidity environments using N(2), 5% O(2), and 50% O(2) as the carrier gases, respectively. The EMF always increased with the partial pressure of oxygen in certain relative humidity. However, the ΔEMF was decreased with the increase of O(2) content in the carrier gas under the condition of the variation of relative humidity from 75.1% to 83.6%. These phenomena revealed that the sensor was sensitive to water vapor without oxygen in the sample gas and too much water vapor had adverse effect on the response to oxygen. Non-Nernst behavior of the sensor was discussed in detail.