SENSORS, 2002 IEEE

The basic principles of a new surface acoustic wave (SAW) gas sensor are described. Being essentially a sensor of the mass-sensitive type, the proposed device possesses certain features of the thermometric SAW sensors and is not only sensitive to the vapors of volatile substances, but capable of detecting gases by their thermal properties as well. This principles consists of making a certain delay of heat fluxes between the substrate of sensitive SAW element (SAW delay line or SAW resonator) and working surface of the sensor's temperature stabilization system. In contrast to the known thermometric SAW sensors, the proposed sensor is characterized by high temperature stability and fast response. A variant of the sensor based on a LiNbO/sub 3/ is described and some results on detecting propane-butane mixtures are presented, glass spacers being a means providing heat flux delay between LiNbO/sub 3/ substrate and working surface of the sensor's temperature stabilization system.

Một cảm biến mới đã được thiết kế bằng cách sử dụng thiết bị SH-SAW. Chế độ sóng âm bề mặt ngang cắt (SH-SAW) có đặc điểm độc đáo là phản xạ hoàn toàn tại các cạnh tự do của vật liệu nền. Các SH-SAW được kích thích trên bề mặt của tinh thể LiTaO/sub 3/ với góc 36/spl deg/ YX và cạnh vuông góc của vật liệu nền đã được sử dụng để phản xạ các sóng này. Cả pha và biên độ của SH-SAW được phản xạ từ cạnh đã được đo lường như một phản ứng của đầu dò cảm biến. Nhiều thí nghiệm đã được thực hiện để xác minh cảm biến SAW loại phản xạ cạnh trong các chất lỏng nhớt và ionic. Kết quả thực nghiệm cho thấy cảm biến rất phù hợp cho việc phát hiện pha lỏng.

Trace level detection of H/sub 2/S is of immense interest in diverse fields ranging from gas and oil exploration to dentistry. In the present work 0.12 /spl mu/m thick sputtered SnO/sub 2/ films, and a novel SnO/sub 2/-CuO bilayer structure consisting of ultra thin (/spl sim/10 nm) CuO dotted islands (0.6 mm diameter) are investigated for H/sub 2/S gas sensing. With the SnO/sub 2/-CuO-dotted sensor, a high sensitivity of 7.3/spl times/10/sup 3/ at a low operating temperature of 150/spl deg/C is obtained with a fast response time of 14 seconds for 20 ppm of H/sub 2/S gas and a recovery time of 118 seconds under flowing air have been measured. The electronic and chemical interactions of the CuO catalyst layer on SnO/sub 2/ in the presence of H/sub 2/S have been analyzed in the light of space charge regions formed due to distributed p-type CuO islands on the n-type SnO/sub 2/ thin film surface. Dissociated hydrogen available from the CuO-H/sub 2/S interaction spills over and is found to be primarily responsible for the observed fast response characteristics.

In this paper, we present the first sensor ever built using films grown by supersonic beam of cluster oxides as sensing material. Supersonic cluster beams, produced by a pulsed micro-plasma cluster source have successfully used to prepare nanocrystalline thin films of TiO/sub 2/. The sensors, prepared by using different deposition parameters, were suitable for use in a gas sensor array for electronic nose. Sensors showed a quite good response to ethanol, methanol and propanol. Principal component analysis was used as method for testing the array capability in discrimination and recognition of the volatile compounds.

The vacuum packaged differential resonant accelerometer (DRXL) using gap sensitive electrostatic change effect is proposed by using the reverse surface micromachining (RSM) process based on the single crystal silicon. The differential frequency output is achieved by subtracting the resonant frequency between the two independent resonators, which has advantages with the wide input range and the good linearity. But the resonant accelerometer is fabricated using the epi-polysilicon surface micromachining process in the previous work. The residual and shear stress of the polysilicon result in the mismatch of the mechanical resonant frequency. The mismatch of the resonant frequency may demolish the advantages of the differential scheme because of the mechanical resonance characteristics. So, the single-crystal silicon was chosen for the accelerometer structure material because it has better mechanical properties than the polysilicon. The fabricated resonant accelerometer shows the nominal frequency of 6928 Hz and the sensitivity is about 10Hz in the /spl plusmn/10 G range. The bandwidth is more than 100 Hz.

This paper deals with Web sensors with particular attention to data structures and interfacing features described by IEEE1451 standard. A network architecture is proposed to reduce Web-sensor structural complexity. Transducer and electronic datasheets (TEDS) are directly interfaced to Internet through an HTTP-based protocol, that has been inspired by IEEE1451.2 Transducer Independent Interface (TII). Finally, a working prototype has been realized and some tests have been carried out to evaluate functionalities and real performances.

A novel micro-electro-mechanical digital-to-analog converter based on a bimorph thermal actuator (bimorph MEMDAC) is proposed in the paper. Driven by four-bit digital voltage of 5 V, it can produce out-of-plane deflection. Compared to the conventional bimorph thermal actuators driven by analog voltages, it could be controlled precisely by digital voltages. Finite element analysis, in which a three-layer model is used to improve the accuracy, shows that the maximum out-of-plane displacement and deflection angle is 22.1/spl mu/m and 0.228rad, respectively. The nonlinear error of the preliminary design is 0.5/spl mu/m. The error could be reduced to below 0.1/spl mu/m by design modifications.

We proposed and developed a novel transillumination laser CT imaging system using optical fiber based on an optical heterodyne detection method for biomedical use. The features of the imaging system are portability and robustness against environmental changes such as variable room temperature and unexpected vibrations. In addition, a motion-artifact-free image can be obtained because the measurements can be performed with the object fixed. In this paper, we experimentally investigate the fundamental imaging properties of the system in detail, which has spatial resolution of 500 /spl mu/m, dynamic range of more than 100 dB, and minimum detectable power of 10/sup -14/ W. Based on the facts, the system reconstructs tomographic images in a way similar to X-ray CT. Finally, we confirm the feasibility of fiber-optic-based laser CT by demonstrating the first tomographic image of a physical phantom.

Proposed the higher-order sensing method using preconcentrator with variable temperature in combination with the QCM sensor array to extract features of the samples. The rough separation among the compounds along the time axis enhanced the discrimination capability of the sensor array system. The results of the second-order sensing such as the images of the sensor responses and the loci on PCA space gave a lot of information on the samples. Moreover, the low-concentration flavors in water were discriminated using the proposed method. It was found that the system had robustness to humidity as well as enhanced discrimination capability.

This paper describes a new method for length and angle measurements of a sensor system which is based on a magneto-resistive sensor element. The system consists of the sensor element, a magnetic scale and a mixed signal ASIC which processes the sensor signals. The sensor signals are interpolated to achieve an enhanced resolution. The interpolation algorithm is implemented in the ASIC by a new architecture, where the essential procedure can be realized in the analogue subsystem. This new architecture will lead to a drastically reduced ASIC chip area. By using the signal symmetry all components can be used to process the sensor signals several times. This results in a topology with a minimum of components, which saves chip area, by the costs of some additional switching components.