Microresonator interference fiber-optic sensor of relative air humidity

A novel type of fiber-optic sensor of relative air humidity is developed on the basis of the micromechanical silicon microresonator and silica gel. The output signal of such a sensor in the frequency form has low sensitivity to variations in the laser-source power and to random attenuations in the fiber. In the case of purely optical excitation of oscillations of the resonator, the sensitive element of such a sensor is completely passive because it does not contain any electronic circuits and components. The sensor showed high sensitivity at a relative humidity less than 75%, possibility to operate at temperatures below freezing, and low dependence of readings on air temperature. The dependence of the humidity mass adsorbed by silica gel on the relative air humidity was found to be linear, which simplifies sensor calibration.     

Mesoporous thin-film on highly-sensitive resonant chemical sensor for relative humidity and CO2 detection

Distributed sensing of gas-phase chemicals is a promising application for mesoporous materials when combined with highly sensitive miniaturized gas sensors. We present a direct application of a mesoporous silica thin film on a highly sensitive miniaturized resonant chemical sensor with a mass sensitivity at the zeptogram scale for relative humidity and CO(2) detection. Using mesoporous silica thin-film, we report one of the lowest volume resolutions and a sensitive detection of 5.1 × 10(-4)% RH/Hz to water vapor in N(2), which is 70 times higher than a device with a nontemplated silica layer. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10(-4)%/Hz and a volume resolution of 1.82 × 10(-4)% to CO(2) in N(2).     

High-sensitivity sensor of low relative humidity based on overlay on side-polished fibers

A low relative humidity (RH) sensor based on overlay on side-polished fiber is presented. The evanescent field from a single-mode optical fiber is coupled to a TiO/sub 2/ waveguide overlay. The transmission response exhibits sharp resonances whose central wavelengths are linearly shifted with RH. This behavior is due to the porous columnar nanostructure of the TiO/sub 2/ film. The water is adsorbed in the pores of the nanostructure changing the refractive index of the layer and causing a shift of the wavelength resonances. The response of the sensor is determined by the shape and size of the pores. The optical fiber evanescent field sensor developed has a linear response and high sensitivity (0.5 nm/% RH) for low RH (RH/spl sim/0%-15%) at 26.1/spl deg/C/spl plusmn/0.6/spl deg/C. The lack of hysteresis in the adsorption-desorption cycle has been checked. The development of a sensor with tailored response is envisaged using properly techniques to control the porosity of the material.     

Lanthanum doped barium stannate for humidity sensor

A few samples in the system Ba_1−xLa_xSnO₃ (x = 0.00, 0.01, 0.05 and 0.10) have been synthesized by the solid state ceramic route. Powder X-ray diffraction (XRD) pattern of the samples was recorded to confirm the formation of a single phase solid solution. The inferences drawn from the analysis of the X-ray diffraction pattern are that, the lattice parameter and bulk density decrease with increasing concentration of lanthanum. The resistance and capacitance of all the samples in the frequency range 20 Hz–1 MHz and relative humidity (RH) range 10–95% have been measured at 31 °C. It is observed that the frequency has more influence on the capacitance as compared to resistance. Among all the samples, the sample Ba_0.99La_0.01SnO₃ (bearing sample code BSL1) exhibits superior response to the change in humidity. The resistance of sample BSL1 changes almost three orders of magnitude where as capacitance changes only one order of magnitude within the RH range 10–95%. The variation of conductivity with RH for samples BSL0 and BSL1 is linear. The response and recovery time of these samples during adsorption and desorption of water vapor are less than 1 min. It is observed that at a particular relative humidity, temperature and frequency (i.e. for RH 10%, temperature 31 °C and frequency 1 kHz) conductivity of barium stannate increases sharply (almost four orders of magnitude) as dopant (La) concentration increases from 0 to 10 mol% which is explained in terms of charge compensation mechanism.     

Influence of concrete relative humidity on the amplitude of Ground-Penetrating radar (GPR) signal

In order to improve radar technique efficiency and to offer innovative applications as non-destructive evaluation tools for civil engineering structures, the authors studied the influence of concrete moisture on GPR sounding. The presence of water in concrete leads to modifications of its electromagnetic properties and thus to specific effects upon waveform characteristics. In particular, the paper focuses on amplitude variations during processes which consume free water (hydration, drying). Radar measurements were carried out on laboratory samples using a commercial ground-coupled antenna of 1.5 GHz central frequency, while relative humidity profiles of the concrete were provided by specific sensors placed at various heights through the concrete samples. An increase in the amplitude of signals propagating through the samples was observed during hydration and drying. Moreover, radargrams recorded during the test also show that the direct wave propagating at the surface of the samples, is ereatly influenced by the evolution of concrete moisture. Concrete hygrometric measurements performed at the same time provide quantitative information on the effect of moisture reduction on radar signals.     

Root-mean-square voltmeters for a broadband input signal

The error of root-mean-square voltmeters in a broadband voltage measurement is considered, and proposals are made for standardizing the metrological characteristics of those voltmeters so that the error of measurement of the signals can be evaluated. Several versions of an automatic error estimater to be incorporated into the voltmeter circuit are described. Translated from Izmeritel'naya Tekhnika, No. 4 pp. 33–36, April, 1997.     

基于频域分解的水声信号宽带盲波束形成

盲波束形成算法可以在不知道阵的流型、信号及干扰方位的情况下,仅根据各阵元接收的数据恢复信号。由于水声信号为宽带信号,为了充分利用宽带信息,提出利用频域分解的方法获得满足窄带条件的信号,并利用窄带盲波束形成JADE（Joint Approximate Diagonalisation of Eigen-matrices）算法进行处理。对宽带盲波束形成算法进行了理论推导和仿真实验。研究结果表明,盲波束形成算法相对于常规波束形成在信号恢复方面有优越性。     

Application of coulometric electrolytic cells in absolute humidity hygrometers

We present data from studies of coulometric electrolytic cells with platinum, rhodium, and platinum–iridium electrodes. We describe the experimental apparatus, the procedure, and the results of a study of the dependence of the measurement error in analysis of inert gases, nitrogen, hydrogen, and oxygen at temperatures of 20 and 50°C. We give recommendations for use of coulometric electrolytic cells in hygrometers with measurement range 0–1000 ppm.     

宽带DRFM干扰机信号处理模块设计

目的:提高数字射频存储器(DRFM)干扰机的瞬时带宽、处理能力和灵活性等性能。方法:结合DRFM原理与信道化接收技术,提出了高性能宽带DRFM干扰机信号处理模块的设计方案,并据此采用先进的信号处理器件和高性能ADC、DAC设计硬件平台,完成相应的软件设计。结果:对硬件平台的性能参数进行测试,实验表明其瞬时带宽可达4 GHz,信号最大存储深度约为200 ms,最小转发延迟约为600 ns。结论:该原型机可实现对新体制雷达的有效干扰。     

Capacitive sensor for relative angle measurement

Based on a capacitive angle and angular rate sensor, a sensor measuring the relative angle between two rotating shafts has been developed. Two rotatable electrodes are placed between two sensor plates. The relative angle between the two rotors and the absolute position of the rotor blades are calculated from measurements of the capacitive coupling between different transmitting stator segments and a single receiving electrode. A prototype of this sensor has been developed with a range of the relative angle of /spl plusmn/7.5/spl deg/ with a resolution of 0.1/spl deg/.     

Thin plasma-polymerized layers of hexamethyldisiloxane for humidity sensor development

The response of resistive-type sensors based on thin hexamethyldisiloxane layers to relative humidity (RH) was evaluated. Humidity sensitive layers were plasma polymerized at low frequency glow discharge using a capacitively coupled parallel plate reactor. The sensor design comprises the absorbing layer deposited on clean glass substrate with comb-shape aluminum electrodes (interdigitated structure). The change in electrical impedance of the sensing film was monitored as the device was exposed to humidity. The variation of the plasma-polymerization parameters resulted in different humidity sensing properties which could be correlated to the results of Fourier transform infrared spectroscopy (FTIR). The deposited films exhibited a detectable response to RH ranging from 30 to 95% with low hysteresis, good reproducibility and stability in long-term use. Films with a greater thickness showed a significant decrease in the humidity sensing capability. FTIR analysis revealed the presence of SiH bonding groups, which are frequently linked to the film density. The increase in the plasma discharge power induced also a significant decrease in the diffusion process of water vapor inside the sensitive layer bulk.     

Possibilities for accurate control of the relative humidity of air

Studies considering the control of relative humidity are analyzed.     

Photocatalytic ozone sensor based on mesoporous indium oxide: Influence of the relative humidity on the sensing performance

Mesoporous In₂O₃, synthesized by a nanocasting procedure, is used as a resistive gas sensor for ozone in very low concentrations (from 20 ppb to 2.4 ppm) at room temperature. Its sensing performance is substantially increased by illumination with blue light (460 nm, 2.7 eV). For low ozone concentrations the sensor response increases with increasing humidity. However, higher humidity also results in the occurrence of a saturation of the response at lower ozone concentrations; this is rationalized by assuming a poisoning of surface active sites by hydroxyl groups.     

纳米氧化铝薄膜湿度传感器的研制

研究了阳极氧化三氧化二铝多孔膜的制备工艺,采用两步阳极氧化法和独特的后处理工艺获得了孔洞分布均匀、孔径大小一致且耐水合的多孔氧化膜,分析了传感器的湿敏特性:传感器的湿滞<2%,响应时问<10s,恢复时间<40s,性能非常优良.     

Impact of morphology on high-speed humidity sensor performance

Capacitive-based humidity sensors were fabricated using unique nanostructured aluminum-oxide thin films. These sensors exhibited extremely fast desorption response times as short as 42 ms. In this paper, we present the effects of varying the thin-film porosity on sensor performance. Specifically, we look at the capacitive response and the desorption response time of the sensors. It was found that increased porosity tends to decrease the desorption response time and increase the relative humidity where the devices become sensitive.