Adaptive Pulse Repetition Frequency Technique for an Ultrasonic Transit-Time Gas Flowmeter for Hot Pulsating Gases

A technique of using an adaptive pulse repetition frequency (PRF) to operate an ultrasonic contrapropagation transit-time gas flowmeter (UFM) is introduced. This adaptive PRF technique allows transient measurements of hot (up to 450$^circhboxC$) and pulsating (up to 1.5 kHz) gas flows. Such conditions occur in the exhaust gas of a combustion engine. Here, a UFM with the widely used fixed PRF technique is not applicable, because the large gas temperature variations would prevent a reliable detection of ultrasonic pulse arrival times. Coherently reflected waves are generated within the gas because of the unavoidable acoustic impedance mismatch between the gas and the transducers, and, depending on the gas temperatures, these echoes overlap with the main signal. The adaptive PRF technique overcomes this problem and allows correct pulse detection over the whole temperature range required. The UFM utilizes special high-temperature-resistant capacitance ultrasonic transducers (CUTs) to meet the requirements in terms of operating temperature range and dynamic response. Results, which are obtained with a preliminary laboratory prototype, are presented for the exhaust gas mass flow rate in a$varnothing$50-mm pipe measured at gas temperatures of up to 450$^circhboxC$and at PRFs of up to 5.5 kHz, which is an increase in frequency response of one order of magnitude in comparison to existing measurement systems.     

A Capacitance Ultrasonic Transducer With Micromachined Backplate for Fast Flow Measurements in Hot Pulsating Gases

A novel high-temperature resistant capacitance ultrasonic transducer is presented. It is designed for an ultrasonic transit-time gas flowmeter and meets two main requirements not fulfilled by common piezoelectric transducers: First, a special construction based on an oxidized and patterned silicon backplate combined with a metallic membrane enables transducer operation at elevated gas temperatures of up to 600$^circhboxC$. Second, the geometry and material parameters were chosen to obtain a broadband device that allows high signal slew rates and pulse repetition rates. As proven by measurements in an automotive combustion engine test bed environment, this new transducer suits for internal combustion engine exhaust flow measurements in between the catalytic converter and the end of the exhaust pipe. Preliminary results for the exhaust mass flow (up to 160 kg/h) of a typical automotive engine measured with these novel transducers are given and compared with the mass flow calculated from fuel consumption and air/fuel ratio$(lambda)$.     

A Parallel Multiplexed Temperature Sensor System Using Bragg-Grating-Based Fiber Lasers

A parallel multiplexed temperature sensor scheme using a Bragg grating-based fiber laser approach has been developed and evaluated. Multiple laser cavities were formed as the active gain media of the system using a common broadband chirped fiber Bragg grating (CFBG) and several normal FBGs, which were used as optical feedback elements, in conjunction with different lengths of erbium-doped fibers (EDFs). These gain media were externally pumped by light from a 1480-nm laser diode (LD) through a 1480-nm 1$times$4 splitter. Normal FBGs were used as the wavelength-selective and sensing elements of the laser system. Simultaneous laser action at three different wavelengths corresponding to channels 1, 3, and 4, respectively, was obtained using this scheme. The temperature was measured over the range from room temperature (27$^circhboxC$) to a maximum of 540$^circhboxC$, which shows the potential of the scheme for quasi-distributed sensor applications.     

A Study of Hydrogen Sensing Performance of Pt–GaN Schottky Diodes

The performance of hydrogen-gas detectors based on Pt–GaN Schottky diodes with 24-nm-thick Pt contact was investigated. Current–voltage ($I$–$V$) Characteristics were measured in two ambients (e.g., synthetic air (20%$hboxO_2$in$hboxN_2$) and 1-vol.%$hboxH_2$in synthetic air) at different temperatures. The forward current of the diodes is found to increase significantly upon introduction of$hboxH_2$into the synthetic air ambient. Analysis of the$I$–$V$characteristics as a function of temperature demonstrated that the observed current increase is due to a decrease in the effective barrier height (BH) through a decrease in the Pt work function upon absorption of hydrogen. The decrease in the BH was measured as high as 30 and 152 meV at 25$^circhboxC$and at 280$^circhboxC$, respectively, upon introduction of$hboxH_2$into the ambient. The changes in the BH were completely reversible upon restoration of the synthetic air ambient. The sensitivity to the hydrogen gas was investigated in dependence on the operating temperature for 1-vol.% hydrogen in synthetic air. The changes in the forward bias at a constant current density of 3.2$hboxA/cm^2$was 90 and 330 mV at 25$^circhboxC$and at 310$^circhboxC$, respectively, upon introduction of 1-vol.%$hboxH_2$into the ambient. Additionally, a significant increase in the sensitivity and a decrease in the response and recovery times have been observed after increasing the operating temperature up to$sim hbox310 ^circhboxC$.     

Integrated Heat-Flux Sensors for Harsh Environments Using Thermal-Spray Technology

Heat-flux sensors are widely used in thermal and heat-transfer engineering applications. Commercial heat-flux sensors currently available for harsh environments, however, remain limited due to complications in positioning/attaching the sensor onto the component, the inability to operate at high temperatures, and potentially altering or degrading the engineering device by the physical presence of the sensor. In this paper, heat-flux sensors have been fabricated for the first time entirely by using a thermal-spray technology. The sensors are fabricated directly onto engineering surfaces and consist of five to seven thermocouples arranged electrically in series and thermally in parallel, such that the heat flux is measured normal to the surface, on which the sensor resides. Devices are tested under both steady-state and transient conditions at temperatures up to 100$^circhboxC$. They exhibit a very good linearity between the heat flux and voltage output. Analytical modeling of the steady-state and transient responses is also presented and compared to experimental results. If successful, thermal-spray heat-flux sensors could represent a significant enabling technology for heat-flux sensing at high temperatures, in harsh environments, and in embedded sensor applications.     

175$^circhboxC$Silicon-Based Hybrid Charge Amplifier for 175$^circhboxC$and 100-mV/G Miniature Piezoelectric Accelerometer

High-temperature hybrid miniature silicon-based charge amplifier has been designed, fabricated, and tested. The charge gain$G_q approx 30 hboxmV/pC pm 1 hboxdB$at the reference frequency of 100 Hz. Frequency response deviation is$pm$1 dB at frequency range from about 0.5 Hz to about 10 kHz over the temperature range from$-55 ^circhboxC$to$175 ^circhboxC$. The maximum change in gain is$pm$5% over that temperature range. The maximum output signal is 5 V peak at voltage supply of$+$24 V. The charge amplifier compromises standard components, and it is built on the ceramic disk substrate with a diameter of about 8 mm. This circuit made possible the development of the industry's first 100-mV/G miniature (cube with side of 14 mm), lightweight (12.5 g), low-cost, and low-noise piezoelectric triaxial accelerometer with integral silicon-based electronics having operating temperature from$-55 ^circhboxC$to$175 ^circhboxC$. In the long-term active (with power supply) test, the circuit and the accelerometer operated at temperature of 175$^circhboxC$for 1000 h without any signs of degradation.     

A High-Resolution MEMS Piezoelectric Strain Sensor for Structural Vibration Detection

This paper presents the modeling, fabrication, and testing of a high-performance dynamic strain sensor. Using microelectromechanical systems (MEMS) technology, ZnO piezoelectric microsensors are directly fabricated on silicon and steel substrates. The sensors are intended to be used as point sensors for vibration sensing without putting an extra burden on the host structures. A model that incorporates piezoelectric effects into an RC circuit, representing the sensor architecture, is developed to describe the voltage output characteristics of the piezoelectric microsensors. It is shown that the sensitivity of microplanar piezoelectric sensors that utilize the $e_{31}$ effect is linearly proportional to sensor thickness but unrelated to sensor area. Sensor characterization was performed on a cantilever beam cut from a fabricated silicon wafer. The experimental data indicate that the overall sensor and circuit system is capable of resolving better than 40.3 nanostrain time domain signal at frequencies above 2 kHz. The corresponding noise floor is lower than 200 femto-strain per root hertz and the sensitivity, defined as the sensor voltage output over strain input, is calculated to be 340 V/$varepsilon$ . Micro ZnO piezoelectric sensors fabricated on steel hard disk drive suspensions also show excellent results. The sensor not only has a better signal-to-noise ratio but also detects more vibration information than the combination of two laser-doppler-vibrometer measurements in different directions.      

Cosputtered Metal and$hboxSiO_2$Layers for Use in Thick-Film MISiC$hboxNH_3$Sensors

High-temperature metal-insulator-silicon-carbide (MISiC) sensors are currently under development for use as$hboxNH_3$sensors in selective-catalytic-reduction (SCR) systems in diesel engines or non-SCR (NSCR) systems in boilers. The detection of$hboxNH_3$by these sensors requires the presence of triple points where the gas, the metal, and the insulator meet. These triple points have traditionally been located at the interface between the insulator and a porous metal. However, to facilitate the long-term stability of the devices when used in a harsh environment, a nonporous gate material would be preferred. Here, the behavior of the samples where such triple points have been introduced in a dense film through cosputtering of the insulator$(hboxSiO_2)$, and either Pt or Ir is studied. The$hboxNH_3$sensitivity of the materials was found to be in accordance with the earlier investigations on Si-based samples with cosputtered gate materials. Several metal-to-insulator ratios for each of the metals Pt and Ir were studied. The sensitivity of the layers as well as their selectivity to different concentrations of$hboxNH_3$at temperatures ranging from 150$^circhboxC$to 450$^circhboxC$was investigated. The films containing 60%–70% Pt or Ir were found to give a high sensitivity toward$hboxNH_3$. These samples were shown to be sensitive also to propylene and$hboxH_2$but were rather insensitive to NO and CO.     

液固两相流超声断面成像装置的研究

以水、泥沙构成的液固两相流为研究对象,制作了压电超声传感器、传感器阵列及超声波收发电路,构成了两相流断面超声投影数据采集系统,实现了计算机高速数据采集。实验验证,设计的压电传感器谐振频率达到200 kHz,发射角度大,接收灵敏度高;采用RC滤波方法,能够有效地滤除接收传感器受到的工频电磁干扰信号;收发传感器交替排列的传感阵列既可以获得最大数量的投影数据,又可以使强弱电电路分离,免受互扰;采集的投影数据能够反映固相流动状况。     

Benetzungswinkel und Grenzflächenenergien der geschmolzenen Metalle Bi,Pb, Cu und Ni in Kontakt mit festem Al2O3

Wetting Angles and Interfacial Energies of the Liquid Metals Bi, Pb, Cu and Ni in Contact with Solid Al₂O₃ Sessile drop experiments were used to determine the wetting angle (θ) between polycrystalline Al₂O₃ and the liquid metals Bi, Pb, Cu and Ni in argon-atmosphere. It was found that at their melting points the liquid metals do not wet the Al₂O₃ (θ > 90°). Using available literature data the work of adhesion and the interfacial energies in the investigated systems were calculated. Both show a linear dependence with temperature. The temperature coefficients were calculated. In the case of Cu and Ni the wetting behaviour is improved (θ < 90°) at higher temperature below the melting point of Al₂O₃.     

Ultrasonic Imaging in Hot Liquid Sodium Using a Plate-Type Ultrasonic Waveguide Sensor

This paper reports the first set of results from ultrasonic measurements for determining the imaging capability of a plate-type ultrasonic waveguide sensor in \(200\,^{\circ }\) C liquid sodium. This 10-m long plate-type waveguide sensor has been developed for viewing objects in opaque liquid sodium coolant for the applications in a sodium-cooled fast reactor (a next generation nuclear reactor). Various imaging capabilities of the waveguide sensor have already been demonstrated in water including ultrasonic beam steering, high resolution C-scan, and so on. However, water and liquid sodium have different acoustic properties and, more importantly, different wetting characteristics with stainless steel—the material for the waveguide sensor. For applications of the developed waveguide sensor in a real reactor environment, this research performs a set of necessary ultrasonic measurements in liquid sodium. The end section of the waveguide sensor which radiates an ultrasonic beam into the liquid sodium is coated with thin beryllium and nickel layers which can significantly improve the ultrasonic beam quality and wetting property of the stainless steel. A liquid sodium facility that consists of a glove box system, a sodium test tank, and an argon purification system has been built. The resolution and beam property are determined from ultrasonic C-scan experiments; a signal-to-noise ratio of over 10 dB and the resulting detection of a 1 mm wide slit can be achieved. The inherent issues associated with wetting of the waveguide sensor in liquid sodium are discussed based on the ultrasonic imaging results.     

通过PVDF传感器测量振动板结构的声辐射模态伴随系数

基于声辐射模态理论进行ASAC控制系统中的一个重要内容就是获得声辐射模态伴随系数。以简支板为例,设计了一种新的PVDF(POLYVINYLIDENE FLUORIDE聚偏氟乙烯)压电传感器,用来测量板的前3阶声辐射模态伴随系数。由仿真计算结果表明,在中低频率,测量第一阶声辐射模态伴随系数时,只需要在板布置两条PVDF传感器即可;测量第二、三阶声辐射模态伴随系数时,可在板上布置多条传感器能得到比较精确的结果。同时PVDF传感器测量的结果与理论相符,说明这种新型PVDF压电传感器的设计是可行的。     

A highly sensitive Pb(Zr,Ti)O3 thin film ultrasonic micro-sensor with a grooved diaphragm

A highly sensitive piezoelectric ultrasonic micro-sensor with a grooved multilayer membrane was developed by a Si-based MEMS technique. The groove was located at one-quarter of the distance away from the edge of the membrane and opened into piezoelectric layer. The piezoelectric layer Pb(Zr,Ti)O(3) (PZT) was 2.2 microm thick and was prepared by a sol-gel method. The prepared PZT film was pure perovskite and showed a highly (100) textured structure. The sensitivity of the fabricated piezoelectric ultrasonic sensor without the groove structure was 100 microV/Pa. In comparison, the sensitivity of the ultrasonic sensor with the groove structure was about 500 microV/Pa, which is 5 times that without the groove structure. The diaphragm having grooves showed a corrugate-like structure that was formed by residual stress. The high sensitivity of the membrane with the grooved diaphragm is considered to relate to the corrugate-like structure.     

Multichannel Temperature Sensing by Differential Coherence Multiplexing

The method of differential coherence multiplexing is demonstrated for multichannel temperature sensing. The idea of the method is to introduce into the conventional coherence-multiplexed sensor array a chain of stable etalon interferometers connected to the interrogating interferometer in parallel to the sensor chains. Optical delays of sensor interferometers are obtained from the phase shift of the interference maximums of the etalon and sensor coherence peaks. The technique is inherently insensitive to low-frequency phase noise in the interrogating interferometer and does not require any means for measurement of the optical path difference of the interrogating interferometer. Multiplexed temperature sensing is demonstrated in a chain of four extrinsic Fabry–PÉrot temperature sensors in the range of 400$^circ hboxC$with a root-mean-square noise of 0.005$^circ hboxC$. Theoretical estimations show a possibility of increasing the dynamic range to the units of$10^5$.     

A highly sensitive Pb(Zr,Ti)O/sub 3/ thin film ultrasonic micro-sensor with a grooved diaphragm

A highly sensitive piezoelectric ultrasonic micro-sensor with a grooved multilayer membrane was developed by a Si-based MEMS technique. The groove was located at one-quarter of the distance away from the edge of the membrane and opened into piezoelectric layer. The piezoelectric layer Pb(Zr,Ti)O₃ (PZT) was 2.2 mum thick and was prepared by a sol-gel method. The prepared PZT film was pure perovskite and showed a highly (100) textured structure. The sensitivity of the fabricated piezoelectric ultrasonic sensor without the groove structure was 100 muV/Pa. In comparison, the sensitivity of the ultrasonic sensor with the groove structure was about 500 muV/Pa, which is 5 times that without the groove structure. The diaphragm having grooves showed a corrugate-like structure that was formed by residual stress. The high sensitivity of the membrane with the grooved diaphragm is considered to relate to the corrugate-like structure.     

Effect of Grain Boundary on the Wettability and Interfacial Morphology in the Molten Bi／Cu System

The wetting behavior of molten Bi on polycrystalline Cu substrate and single crystal Cu substrate was studied by the sessile drop method in the temperature range from 673 to 873K. At low temperature the wetting behaviors of molten Bi on both types of Cu substrate were similar. However, at high temperature, the equilibrium contact angle of polycrystalline Cu substrate was lower than that of single crystal Cu substrate, because the preferred dissolution of grain boundaries leads to a smaller liquid/solid interracial energy for polycrystalline Cu substrate. The formation mechanism of arrow-shaped Cu grains at the Bi/single crystal Cu interface is also discussed.     

Analysis according to the change in structure of ultrasonic sensors and the change in pressure inside the tank for measurement of fuel amounts in compressed natural gas (CNG) tank

The present study is a fundamental research for precise measurement of fuel amounts in a compressed natural gas (CNG) tank where an analysis of receiving sensitivity was conducted as a result of changes in the contact surface shape in the number of piezoelectric element of the ultrasonic sensor as well as in the internal pressure of the tank. Experiments were conducted as a function of changes in the contact surface shape between the ultrasonic sensor and outside of the aluminum tank and in the number of piezoelectric element as well as in the internal pressure of the tank. According to the experimental results, it could be confirmed that the maximum receiving sensitivity value was increased by about 60 % when the contact surface shape of the transmission and receiving ultrasonic sensors compared with the ultrasonic sensor in the Line-Line shape selected as the reference model was changed to the surface. As a whole, the highest receiving sensitivity values were observed when the transmission sensor of surface shape produced as multiple piezoelectric elements and the receiving sensor of surface shape produced as a single piezoelectric element were used. It could be confirmed that receiving sensitivities were improved at the same voltage value as a result of changes in the contact surface shape of the ultrasonic sensor and in the number of piezoelectric elements.     

A novel sensor for monitoring acoustic cavitation. Part II: Prototype performance evaluation

For Part I see ibid., vol.50, no.10, p.1342 (2003). This paper describes a series of experimental studies to evaluate the performance of newly developed sensors for monitoring broadband acoustic emissions generated by acoustic cavitation. The prototype sensors are fabricated in the form of hollow, open-ended cylinders, whose inner surface is made from a thin film of piezoelectric polymer acting as a passive acoustic receiver of bandwidth greater than 10 MHz. A 4 mm thick coating of special acoustical absorber forms the outer surface of the sensor. The layer functions as a shield to cavitation events occurring outside the hollow sensor body, allowing megahertz acoustic emissions emanating from within the liquid contained in the sensor to be monitored. Testing of the new sensor concept has been carried out within the cavitating field provided by a commercial ultrasonic cleaning vessel operating at 40 kHz whose power output is rated at 1 kW. It is demonstrated that the prototype cavitation sensors are able to record a systematic increase in the level of the high-frequency acoustic spectrum (>1 MHz) as electrical power to the cleaning vessel is increased. Through careful control of the experimental conditions, reproducibility of the high frequency "energy" associated with the cavitation spectrum was found to be typically /spl plusmn/25%.     

Grain boundary diffusion and wetting in the analysis of intergranular penetration

Intergranular penetration of liquid bismuth has been analysed in two pure metals, Cu at 500 °C and Ni at 700 °C, used either as polycrystals or as oriented bicrystals. At the liquid/solid interface, large grooves have developed in Cu–Bi, while micrometer-thick films were observed in Ni–Bi. The bismuth concentration measurements obtained by Auger electron spectroscopy indicate a zone of monolayer Bi segregation followed by a diffusion-type profile over a distance of the order of 100 μm for Cu–Bi and a nanometer-thick film followed by similar diffusion-type profile for Ni–Bi. In both cases the kinetics of intergranular penetration and embrittlement has been shown to be parabolic. It is concluded that no wetting occurs in Cu–Bi system at 500 °C while Bi wets Ni at 700 °C. It is postulated that the mechanism of intergranular penetration operates at a very tip of the penetration front, as opposed to the tip of liquid Bi film observed by scanning electron microscopy, and must be based on diffusion rather than wetting phenomena. Some suggestions are formulated for the future research in the area of intergranular penetration that can be split in two phenomena: grain boundary wetting above the wetting transition temperature and grain boundary diffusion below.