Miniaturized liquid film sensor (MLFS) for two phase flow measurements in square microchannels with high spatial resolution

Two miniaturized liquid film sensors (MLFS) based on electrical conductance measurement have been developed and tested. The sensors are non-intrusive and produced with materials and technologies fully compatible and integrable with standard microfluidics. They consist of a line of 20 electrodes with a purpose-designed shape, flush against the wall, covering a total length of 5.00 and 6.68 mm. The governing electronics achieve 10 kHz of time resolution. The electrode spacing of the two sensors is 230 μm and 330 μm, which allows measurements of liquid films up to 150 μm and 400 μm for sensors MLFS_A and MLFS_B, respectively. The sensor characteristics were obtained by imposing static liquid films of known thickness on top of the actual sensor. Further dynamic measurements of concurrent air-water flow in a horizontal microchannel were performed. The line of electrodes is placed across the flow direction with an angle of 3.53° from the direction of flow, allowing for a spatial resolution perpendicular to the flow of 14.2 μm for sensor MLFS_A and 20.5 μm for sensor MLFS_B. The high time and spatial resolution allows for fast and accurate detection of the presence of bubbles, and even measurement of film thickness and bubble velocity. Further information, such as the bubble shape, can be gathered based on the shape of the liquid layer underneath the bubble, which is particularly important for heat transfer studies in microchannels.     

Continuous accurate pH measurements of human GI tract using a digital pH-ISFET sensor inside a wireless capsule

This paper describes the design and implementation of a reliable, low-power pH-ISFET sensor inside a wireless diagnostic capsule for monitoring the pH of the human gastrointestinal (GI) tract. The sensitive element of the pH sensing device was an ion-sensitive FET (ISFET) with a threshold voltage that varies by concentration of hydrogen ions. An Ag/AgCl reference electrode that was surrounded by gel (mixed KCl) was applied in this pH-sensing device. An application-specific integrated circuit (ASIC) that is designed by a very large scale integration (VLSI) architecture was used as the interface between the pH sensing device and a wireless transceiver. Experimental results demonstrated that the pH sensitivity and operating range of the pH sensing device was 44.94 mV/pH and 1–11 pH; the device is linear. With the 18-bit Analog/Digital converter (ADC) module in the ASIC, the resolution could achieve 11,780 bits/pH. Moreover, the power dissipation of the pH-sensing device was only 0.048 mW while working in intermittent mode (duty cycle = 20%). Results from human experiments showed that this pH sensing device can work reliably for 136 h, and the pH data of sampled from the human GI tract can be received by a portable data recorder outside the human body in real time.     

Development and evaluation of a sensor glove for hand function assessment and preliminary attempts at assessing hand coordination

Quantitative measurement of hand kinematics can help us to better understand pathophysiological aspects of finger neural control and quantify hand impairments. A sensor glove was developed based on resistive bend sensors and resistive force sensors to monitor finger joint angles and forces exerted to objects by fingers. The validity and reliability of the glove were evaluated. A novel method was proposed to visualize and quantify the abnormality of the inter-joint coordination. The validity test indicated that the accuracy error of measuring joint angles was approximately ±6° and that of measuring forces was approximately ±8 g. The reliability test yielded an intraclass correlation coefficient of 0.9876 ± 0.0058 for the force sensors and 0.9561 ± 0.0431 for the bend sensors. The stability, accuracy and reliability of measuring joint angles were comparable with previous studies. The involvement of force sensors and the capacity of reflecting inter-joint coordination make the glove more comprehensive for hand function assessment.     

Development and evaluation of a two-axial shearing force sensor consisting of an optical sensor chip and elastic gum frame

We developed a promising shearing force sensor that is small in size and can measure shearing force along two axes independently. This sensor consists of an elastic gum frame and an optical sensor chip (6 mm × 6 mm × 8 mm). From the experimental results, the resolutions of the sensor along the x- and y-axes are found to be 0.070 N and 0.063 N. We also experimentally demonstrated that the sensor can separately measure shearing force along two axes. Finally, we demonstrated that the scale factor which correspond to resolution and linear portion which correspond to measuring range of the signals can be changed easily by using three types of elastic gum frame. This sensor can be embedded in the finger of a robot hand and use it to not only measure shearing force but also detect the slip phenomenon.     

The design of polyaniline based sensor for the qualitative estimation of malonaldehyde

The detection of contaminated food in every stage of processing required new technology for fast identification and isolation of toxicity in food. Since effect of food contaminant are severe to human health, the need of pioneer technologies also increasing over last few decades. In the current study, MDA was prepared by hydrolysis of 1,1,3,3-tetramethoxypropane in HCl media and used in the electrochemical studies. The electrochemical sensor was fabricated with modified glassy carbon electrode with polyaniline. These sensors were used for detection of sodium salt of malonaldehyde and observed that a high sensitivity in the concentration range ∼1 × 10⁻¹ M and 1 × 10⁻² M. Tafel plots show the variation of over potential from − 1.73 V to − 3.74 V up to 10⁻⁵ mol/L indicating the lower limit of detection of the system.     

Multi-range sensors for the measurement of liquid film thickness distributions based on electrical conductance

The paper presents an approach toward an enhancement of the measuring range of high-speed sensors for the measurement of liquid film thickness distributions based on electrical conductance. This type of sensors consists of electrodes mounted flush to the wall. The sampling of the current generated between a pair of neighboring electrode is used as a measure of the film thickness. Such sensors have a limited measuring range, which is proportional to the lateral distance between the electrodes. The range is therefore coupled to the spatial resolution. The proposed new design allows an extension of the film thickness range by combining electrode matrices of different resolution in one and the same sensor. In this way, a high spatial resolution is reached with a small thickness range, whereas a film thickness that exceeds the range of the high resolution measurement can still be acquired even though on the costs of a lower spatial resolution. A simultaneous signal acquisition with a sampling frequency of 3.2 kHz combines three measuring ranges for the characterization of a two-dimensional film thickness distribution: (1) thickness range 0–600 µm, lateral resolution 2×2 mm², (2) thickness range 400–1300 µm, lateral resolution 4×4 mm², and (3) thickness range 1000–3500 µm, lateral resolution 12×12 mm². The functionality of this concept sensor is demonstrated by tests in a horizontal wavy stratified air–water flow at ambient conditions. Using flexible printed circuit board technology to manufacture the sensor makes it possible to place the sensor at the inner surface of a circular pipe.     

High immunity wafer-level measurement of MHz current

Wafer-level characterization of functional prototypes of solid state current sensors is usually the first step in the development stage, therefore a dedicated wafer-level measurement systems are required. Especially for MHz characterization, where electromagnetic interference issues became strongly relevant. Thus, for frequencies above 1 MHz, a sophisticated measurement techniques are needed, because parasitic couplings can significantly affect sensor response and other signal processing stages, causing errors or malfunction of the whole system. We propose technique for high immunity MHz current measurement by solid state sensor in wafer-level configuration. The system is especially well-suited for MHz characterization, where electromagnetic interference issues become highly relevant. We showed that balanced transmission provides possibility to reduce interference in the sensor biasing circuit of about 60 dB compared to single-ended method. The effectiveness of the proposed technique was tested in monitoring MHz current in the external line by single magnetoresistive sensors on wafer level.     

Identification and characterisation of steel corrosion using passive high frequency RFID sensors

High frequency RFID sensors are attractive in diverse applications where sensor performance is required at a low cost and dimension restriction. An approach adapting commercial passive 13.56 MHz RFID tags has been developed for sensing corrosion stage. This investigation includes balance of sensing and positioning of RFID sensors for corrosion detection by analysing real and imaginary parts of the complex impedance. With passive HF RFID sensors, real part and imaginary part of complex impedance have been extracted from the reader coil with VNA (vector network analyser) and delivering a unique capability for corrosion sensing with different atmospheric exposure time steel samples (1 month, 6 months, 10 months and 12 months). With different positioning (5–25 mm), features extraction based on the complex impedance with PCA (principal component analysis) has been designed for position-independent corrosion evaluation.     

Optical fiber distributed temperature sensor using short term Fourier transform based simplified signal processing of Raman signals

A simplified technique using short term Fourier transform to reduce the errors in distributed temperature measurement with a Raman scattering based optical fiber sensor system is presented. The two main sources of errors are differential attenuation to anti-Stokes and Stokes signal by fiber and local change in Stokes due to change in temperature. The proposed technique compensates these errors and extracts correct temperature profile in spite of practical difficulties encountered in applying the theoretical concept. Moreover proposed technique is less complex, self-reliant, can tolerate variation in laser power, requires less dead zone and suits automation using embedded solution. Results of measurement carried out, using the system developed at RRCAT, Indore, for two hot zones having spatial width of 1.9 m (kept at 56 °C) and 1.5 m (kept at 78 °C), located at 47 m and 85 m respectively, show that these parameters can be recovered with significantly small errors.     

Sensory platform architecture for IN SITU monitoring the thermal comfort in rural environments – The case study at Federal Rural University of Amazonian,Brazil

This research presents an IN SITU sensory platform developed through the integration of air temperature and relative humidity sensors on an ecosystem in order to obtain some thermal characteristic of the rural environments. This sensory platform contains an expert system to detect the behaviors of environmental variables that result in risk or without risk alert to the thermal comfort for human and animal health. For this, the expert system analyses the environmental thermal conditions of the UFRA University, through temperature and humidity index (THI). The THI values estimated (processed) from data of temperature and relative humidity during the year 2012. Four intervals of THI were used to classify human health performance (THI < 74: comfort, 74 ⩽ THI < 79: hot; 79 ⩽ THI ⩽ 84: too hot, and THI > 84: extremely hot), and two intervals to classify animal production (79 ⩽ THI ⩽ 84: dangerous and THI > 84: emergency). The Amazon is located in the equatorial region and has a warm and humid climate that the prevailing mode reveals an alternation of two seasons throughout the year, hot and humid summer and rainy winter. The results that the most critical period occurs between May and October, although it was observed in every day of every year, the THI values during the hottest hours of the day (15:00 pm) range between 75.9 and 86.3, where humans and animals can suffer some degree of thermal stress, affecting negatively both. Therefore, we consider this platform as a good solution for thermal monitoring, which is based on IN SITU measurement technologies for rural environments.     

Cost effective refractive index sensor based on optical fiber micro cavities produced by the catastrophic fuse effect

We propose a refractive index optical fiber sensor based on the micro cavities generated through the fiber catastrophic fuse effect. This sensor was tested in the measurement of solutions with refractive indices ranging from 1.3320 to 1.4280. The linear dependence of the reflection spectra modulation period as function of the surrounding environment refractive index leads to a resolution of 3 × 10⁻⁴ RIU. The proposed sensor is an innovative solution based on optical fiber damaged by the fuse effect, resulting in a cost effective solution.     

Optimal estimation of the relevant information coming from a variable reluctance proximity sensor placed in a car undergoing performance tests

Today's automotive industry has a soaring interest in efficient, reliable and robust sensors able to make intelligent driving decisions that can save millions of lives every year. To that end, the sensors used in today's cars are being provided with microprocessors and application-specific integrated circuit technologies that incorporate a certain amount of intelligence into the sensors themselves. In this paper, an inverse square-root adaptive filtering algorithm for recursive least-squares estimation (QR-RLS) is used to improve the response of a wheel speed sensor placed in a car undergoing performance tests. Such an algorithm is used to carry out an optimal estimation of the relevant signal coming from the sensor, which is buried in a broad-band noise background where we have little knowledge of the noise characteristics. The results of the experiment are satisfactory, a significant improvement of 32.5 dB in the signal-to-noise ratio at the QR-RLS adaptive filter output was achieved. Also, in order to compare classical filtering techniques with optimal adaptive filtering techniques, the signal coming from the wheel speed sensor was also filtered by using a second-order lowpass digital Butterworth filter. The results of comparing the aforementioned filters show that the optimal adaptive filter is superior to the classical filter.     

Performance tests of a new non-invasive sensor unit and ultrasound electronics

Industrial applications involving pulsed ultrasound instrumentation require complete non-invasive setups due to high temperatures, pressures and possible abrasive fluids. Recently, new pulser-receiver electronics and a new sensor unit were developed by Flow-Viz. The complete sensor unit setup enables non-invasive Doppler measurements through high grade stainless steel. In this work a non-invasive sensor unit developed for one inch pipes (22.5 mm ID) and two inch pipes (48.4 mm ID) were evaluated. Performance tests were conducted using a Doppler string phantom setup and the Doppler velocity results were compared to the moving string target velocities. Eight different positions along the pipe internal diameter (22.5 mm) were investigated and at each position six speeds (0.1–0.6 m/s) were tested. Error differences ranged from 0.18 to 7.8% for the tested velocity range. The average accuracy of Doppler measurements for the 22.5 mm sensor unit decreased slightly from 1.3 to 2.3% across the ultrasound beam axis. Eleven positions were tested along the diameter of the 48.4 mm pipe (eight positions covered the pipe radius) and five speeds were tested (0.2–0.6 m/s). The average accuracy of Doppler measurements for the 48.4 mm sensor unit was between 2.4 and 5.9%, with the lowest accuracy at the point furthest away from the sensor unit. Error differences varied between 0.07 and 11.85% for the tested velocity range, where mostly overestimated velocities were recorded. This systematic error explains the higher average error difference percentage when comparing the 48.4 mm (2.4–5.9%) and 22.5 mm (1.3–2.3%) sensor unit performance. The overall performance of the combined Flow-Viz system (electronics, software, sensor) was excellent as similar or higher errors were typically reported in the medical field. This study has for the first time validated non-invasive Doppler measurements through high grade stainless steel pipes by using an advanced string phantom setup.     

Impact location determination on thin laminated composite plates using an NIR-FBG sensor system

An integration of Structural Health Monitoring (SHM) into composite structures contribute towards the development of smart composites structure. Smart-structure offers an ability have a continuous and real-time information of its circumstances under critical loading applications. One of the main objectives in this research study was the development of the Fiber Bragg grating (FBG) sensor system for SHM of thin composite laminates. Not only that, this work has been utilizing the FBG sensors in the Near Infra-red (NIR) range; ∼830 nm, as an alternative to the applications of the conventional 1550 nm FBG sensors. The capability of this sensor system was validated with the impact location determination test on a thin composite plate. It showed a very promising result whereby the relative error falls below 10%.     

Effects of flow patterns and salinity on water holdup measurement of oil-water two-phase flow using a conductance method

This research investigates the effects of flow pattern and salinity of oil-water two-phase flow on water holdup measurement using a conductance method. Firstly, vertical upward oil-water two-phase flow experiment is conducted in a 20 mm inner diameter (ID) pipe, in which the salinities of aqueous solutions are set as 151 ppm, 1003 ppm, 2494 ppm and 4991 ppm respectively. Experimental water-cut and mixture velocity are set as 80–100% and 0.0184–0.2576 m/s. In the experiment, three different flow patterns, i.e., dispersed oil-in-water slug flow (D OS/W), dispersed oil-in-water flow (D O/W) and very fine dispersed oil-in-water flow (VFD O/W) are observed and recorded by a high speed camera. Meanwhile, we collect the response of Vertical Multiple Electrode Array (VMEA) conductance sensor excited by a sine voltage signal. The result shows that, for VFD O/W, the water holdup from VMEA sensor shows a satisfied agreement with that of quick closing valve (QCV) method under certain salinities, i.e., 1003 ppm as well as 2494 ppm. For D OS/W flow and D O/W flow characterized by dispersed oil droplets with various sizes, considerable deviations of water holdup between VMEA sensor and QCV method under four kinds of salinity aforementioned are presented. Afterward, according to experimental analysis along with theoretical deviation, it is concluded that the deviation of the measurement system reaches its minimum when reference resistance in the measurement circuit and salinity of the aqueous solution satisfy constraint conditions, and the accuracy of water holdup using the conductance method can be improved through adjusting reference resistance to match the salinity of water phase. Finally, the recurrence plot algorithm is utilized to identify typical flow patterns mentioned above and it shows satisfied results on comprehending the discrepancies among different flow patterns, demonstrating that the recurrence plot algorithm can be effectively applied in flow pattern identification regarding oil-water flows.     

Performance evaluation of a cheap,open source,digital environmental monitor based on the Raspberry Pi

We report on the design, construction and evaluation of a low-cost digital environmental monitoring system based on a popular micro-computer board and mass market digital sensors. The system is based around the use of open source software and readily available digital sensors, providing key parameters required for environmentally-controlled calibration laboratories: air temperature, pressure and humidity. Each system logs data at set intervals with front-panel display, web page graphical display and email alerting when exceeding set tolerances. The sensors have been calibrated at the National Physical Laboratory using standards traceable to the SI. Long term stability of the system is estimated and in addition to monitoring of laboratory environments for regulatory purposes, the systems can also be used to provide on-demand values for local refractive index with an expanded (k = 2) uncertainty of 1.1 × 10⁻⁷ as required for many optical-based measuring systems.     

Evaluation of aspects affecting measurement of three-axis accelerometers

In order to set integrated procedures involving geotechnical and structural aspects finalized to buildings diagnostics, uncertainty aspects are discussed concerning three-axis accelerometers and inclinometers for a distributed sensor network. This network allows to operate in a selective manner, preferring the most critical situations. To this aim, the main aspects affecting the measurement uncertainty of sensors to be used for building diagnostic should be known. As the firstly step of the uncertainty evaluation procedure, we focused on the calibration of sensors used for the task. The requirement of low cost and complexity of sensors and test benches was considered. Experimental results show that satisfactory calibration accuracy could be achieved, also for the low frequency range, 0–10 Hz. Systematic errors are minimized and main parameters affecting uncertainty are identified, such as: the motion positioning of the accelerometer with respect to the vertical axis, the imposed motion law, the parameter used as the reference and, finally, the real radial positioning of the sensor. Requirements to be satisfied by the sensor are also analysed.     

Development and evaluation of a compact 6-axis force/moment sensor with a serial structure for the humanoid robot foot

In order to walk safely, forces and moments exerted on humanoid robot foot should be measured and used for controlling the robot. This paper describes the development and evaluation of a six-axis force/moment sensor used under humanoid robot foot. The developed sensor is capable of measuring 400 N horizontal force, 1000 N vertical force, 20 N·m moment about the horizontal axis and 10 N·m moment about the vertical axis using rectangular cross-sectional beams. The structure of the sensor is newly modeled, and the sensing elements are simulated by using finite element method (FEM). Then the sensor is fabricated by attaching strain gages onto the beams. Finally, a characteristic test of the developed sensor is carried out, and the output from FEM analysis agrees with those from the characteristic test.     

Development of high-precision micro-roundness measuring machine using a high-sensitivity and compact multi-beam angle sensor

With recent development in advanced manufacturing, demand for nanometric accuracy in dimensional metrology has increased dramatically. To satisfy these requirements, we propose a high-accuracy micro-roundness measuring machine (micro-RMM) using a multi-beam angle sensor (MBAS). The micro-RMM includes three main parts: the MBAS, a rotary unit, and a bearing system. The MBAS has been designed and established in order to improve motion accuracy of the micro-RMM. The dimensions of the MBAS are 125(L) mm × 130(W) mm × 90(H) mm. Compared with other methods, an MBAS is less susceptible to spindle error (stage-independence) when detecting angles, can maintain high sensitivity with miniaturized size, and can be used conveniently at the factory level. The optical probe, reported in this paper, is based on the principle of an autocollimator, and the stability is improved when using the MBAS. Unlike multi-probe methods, the micro-RMM is constructed to realize roundness measurement by using only one probe, which is less susceptible to instrumental errors. Experimental results confirming the feasibility of the multi-beam angle sensor for roundness measurement are also presented.     

Surface roughness measurement based on fiber optic sensor

The multi-wavelength fiber sensor for measuring surface roughness and surface scattering characteristics were investigated. In this paper, specimens with different surface roughness were analyzed by using 650 nm, 1310 nm and 1550 nm laser as the light source, respectively. The working distance of 2 mm was chosen as the optimum measurement distance. The experimental results indicate that multi-wavelength fiber sensor can accurately measure surface roughness, and can effectively reduce the unsystematic error. The light scattering intensity ratio has a good linear relationship with the surface roughness. The minimum relative error of the surface roughness is 2.92%, the maximum relative error is 13.4%, and the average relative error is about 7.48%. The accuracy for measuring surface roughness by multi-wavelength fiber sensor is about twice as large as that by single-wavelength fiber sensor.