Application of Fabry-Pérot and fiber Bragg grating pressure sensors to simultaneous measurement of liquid level and specific gravity

An approach is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-pressure-sensor system comprising a fiber Bragg grating (FBG) pressure sensor and a Fabry-Pérot (FP) pressure sensor. In the FBG sensor, the pressure is derived from the FBG wavelength shift induced when the sensor is immersed in the liquid. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The advantageous concept of the dual-pressure-sensor system is atmospheric pressure compensation. The experimental results show that the FBG and FP pressure sensors have sensitivities of 0.1495 nm/kPa and 0.1569 μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the FBG wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors.     

The pore water pressure sensor based on Sagnac interferometer with polarization-maintaining photonic crystal fiber for the geotechnical engineering

The pore water pressure sensors with the six-hole suspended-core polarization-maintaining photonic crystal fiber (SC-PM-PCF) and commercial polarization-maintaining photonic crystal fiber (PM-PCF) are designed based Sagnac interferometer and calibrated in the laboratory. According to the theoretical analysis and calibration results, the transmission spectrum is very sensitive to the pore water pressure. It is found that the wavelength of the spectrum has a good linear relationship with variances of the surrounding pore water pressure, and the coefficient of wavelength–pressure of the commercial PM-PCF is 304.41 kPa/nm with the length of 35 cm as the sensing element while the coefficient of the SC-PM-PCF is 254.75 kPa/nm with the length of 100 cm. Finally, the two PM-PCF sensors are applied and compared with the conventional Pore water Pressure Transducers (PPTs) in a physical model test. It is found that measurements of the PM-PCF sensors are in good agreement with the results measured by the conventional PPTs.     

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.     

Monitoring of strain induced by heat of hydration,cyclic and dynamic loads in concrete structures using fiber-optics sensors

Advances in sensors technology provided an opportunity to monitor structures during different construction stages, as well as the behavior of concrete elements during hydration and strength gain. In this paper, embedded Fabry–Pérot fiber-optic sensors were utilized in an experimental investigation to study the hydration process in two different concrete volumes. In addition, the sensors performance under cyclic and torsional loading was investigated. The results showed that up to +300 μstrains could be developed until the final setting is reached. The increase in strain was accompanied by a 55 °C (130 °F) increase in temperature during the first 24 h. These values vary based on the nature of the mix and the concrete volume. In the cyclic and torsion tests, the fiber-optic sensors responded to load variations and were capable of recording samples responses as small as 1 μstrain.     

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%.     

A magnetic MEMS actuator using a permanent magnet and magnetic fluid enclosed in a cavity sandwiched by polymer diaphragms

A magnetic microelectromechanical systems (MEMS) actuator using a small permanent neodymium-magnet surrounded by magnetic fluid (MF) was developed and characterized. The magnet is enclosed in a cavity sandwiched by two identical thin PET-sheet diaphragms and is able to move smoothly due to the MF. The diaphragms deflect when an external magnetic force is applied to the magnet. This structure was adopted to prevent the diaphragms from being stiffened by attaching or fabricating a magnetic layer on the diaphragm surface and to secure the necessary volume of magnetic material. The magnets are 2–4 mm in diameter and the cavity is 5 mm in diameter and 1 mm in depth. The diaphragms are 20 μm in thickness. Experiments showed the displacement amplitude generated at the diaphragm center was in the range of 10–50 μm for attractive and repulsive magnetic force when magnetic flux density of 4–30 mT was applied. The response was within about 1 s. The deflection profile of the diaphragms can also be varied by changing the magnet position.     

Analysis of load-speed sensitivity of friction composites based on various synthetic graphites

The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient (μ) of friction composites containing synthetic graphite with different particle sizes (with similar crystallinity range) to braking pressure and sliding speed. The friction studies were carried out on a sub scale brake-test-rig, following 4 loads × 3 speeds experimental design. The best combination of performance properties was observed for the composite containing synthetic graphite with an average particle size of 410 μm. Other particle sizes which resulted in good performance were 38 and 169 μm. Very fine particle sizes were not beneficial for desired combination of performance properties. Regression analysis of μ following an orthogonal L₉(3 × 3) experimental design method revealed that the first order influences of sliding speed and braking pressure were significant. When all the combinatorial influences of braking pressure and sliding speed are taken into account together their simultaneous effects would be most effective in the range of graphite particle size ～80–250 μm.     

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.     

Carbon nanotubes based strain sensors

This paper presents the design, fabrication and experimental results of carbon nanotubes (CNTs) based strain sensors. The sensors were fabricated by pressed CNTs tablets and elastic polymer beam. The diameter of multiwalled nanotubes (MWNTs) varied between 10 and 30 nm. The tablets of multiwalled CNTs having nominal thickness of 1.0 mm were pressed at a pressure of 200 and 300 MPa. The inter-electrodes distance (length) and width of the surface-type samples were in the range of 10–12 mm and 5–6 mm respectively. The DC resistance of the sensors having the strain sensitivity in the range of 50–80 in average increased under tension and decreased under compression.     

Measurement of fluid flow rate using nanocomposite silicone rubber sensor

This paper describes the use of an elastic nanocomposite sensor to measure the water flow rate in open and closed hydraulic circuits. A sensor was constructed of multiwalled carbon nanotubes (MWCNTs) dispersed in silicone rubber (SR) and subsequently tested to verify its ability to measure water flow rate. The results reveal that the correlation between the fluid flow rate and the pressure variation across the sensor entails that its electrical resistance can be correlated to the flow rate. The sensor constructed of 2 and 3 wt,% of MWCNTs in SR-based nanocomposite sensors exhibited a low percolation threshold. An electron microscope (HRSEM) was used to characterize the manufactured nanocomposite sensors and confirm the conductive networks. The variation in the electrical resistance of the sensor in terms of both water pressure and flow rate is described. The elastic sensor was calibrated to measure the water flow rate in the range of 0–35 l/min. The results show that an elastic sensor fabricated from MWCNTs dispersed in silicone rubber does exhibit sensitivity to the slight strain levels produced by dynamic water pressure and, as such, can be used to measure flow rate. In addition, the sensor's response to water flow in the presence of bubbles enables pump cavitation monitoring. This paper also investigates the reduction of sensor electrical conductivity in response to water immersion. The findings reveal that the elastic nanocomposite sensor could potentially be used as a liquid sensor to detect water leakage in hydraulic circuits.     

An all-fiber Fabry-Pérot interferometer for pressure sensing in different gaseous environments

A gas pressure sensor based on an all-fiber Fabry-Pérot interferometer (FFPI) is reported. The sensing head consists of a small section of silica rod spliced with a large offset between two single-mode fibers. The silica rod is used only as mechanical support so that an air cavity can be formed between both SMF. It is shown that the FFPI sensor is sensitive to gas pressure variation and when submitted to different gaseous environments, namely carbon dioxide, nitrogen and oxygen – sensitivities of 6.2, 4.1 and 3.6 nm/MPa, respectively, were attained. The refractive index change on nitrogen environment by means of gas pressure variation was also determined and a sensitivity of 1526 nm/RIU was obtained. The response of the sensing device to temperature variations in air was also studied and a sensitivity of −14 pm/°C was attained.     

Effect of ozone pretreatment on the physical and mechanical properties of particleboard panels made from bagasse

The main objective of this study was to investigate the applied properties of particleboard panels made from bagasse, which were either treated or not treated with gaseous ozone (O₃). Variable parameters were ozone exposure time (1–3 min) at 9 ppm and storage period (1–5 months). Other parameters such as resin content (12 wt%), hardener content (1 wt%), type of hardener (NH₄Cl), press closing time (5 mm/s), board density (0.70 g/cm³), and press pressure (30 kg/m²) were held constant. The experimental panels were tested for their mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR); and internal bonding strength (IBS) and physical properties in terms of water absorption (WA) and thickness swelling (TS) according to the procedures defined by EN standards. Overall results showed that all panels made from treated bagasse exceeded the EN standards for MOE, MOR, and IBS. However, WA and TS values decreased after ozone pretreatment compared to the un-treated (control) panels. Application of Duncan’s Multiple Range Test for the mean values of the results showed that the effects of both variables, except their interactions, on the mechanical and physical properties were highly significant (p ⩽ 0.01%). All the mechanical properties of the panels decreased when the treatment duration increased from 1 to 5 months.     

厚度效应对Pb(Zr0.53Ti0.47)O3薄膜微结构、铁电、介电性能的影响

用改进的溶胶-凝胶法在Pt(111)/Ti/SiO₂/Si(100)衬底上制备了不同厚度的高度(111)取向的Pb(Zr_0.53Ti_0.47)O₃薄膜.运用X射线衍射(XRD)和原子力显微镜(AFM)分析了薄膜的微结构,原子力显微镜表明厚度为0.3μm和0.56μm的PZT薄膜的晶粒尺寸和表面粗糙度分别为0.2～0.3μm、2～3μm和0.92nm、34nm.0.3μm和0.56μm PZT薄膜的剩余极化(Pr)和矫顽场(Ec)分别为32.2μC/²、79.9kV/cm, 27.7μC/cm²、54.4kV/cm;在频率100KHz时,薄膜的介电常数和介电损耗分别为539、0.066,821、0.029.     

Dependence of surface morphology on molecular structure and its influence on the properties of OLEDs

Most organic light-emitting diodes (OLEDs) have a multilayer structure composed of organic layers such as a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL) and an electron injection layer (EIL) sandwiched between two electrodes. The organic layers are thin solid films with a thickness from a few nano meters to a few tenths nano meter, respectively. Surface morphology of an organic thin solid film in OLEDs depends on the molecular structure of the organic material and has an affect on device performance. To analyze the effect of surface morphology of an organic thin solid film on fluorescence and electroluminescence (EL) properties, thin solid films of 4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran (DCM2) and new red fluorophores, (2E,2′E)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis[2-(2-thienyl)acrylonitrile] (ABCV-Th) and (2Z,2′Z)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis(2-phenylacrylonitrile) (ABCV-P) were investigated by atomic force microscopy (AFM). The samples for EL and AFM measurement were fabricated by the high-vacuum thermal deposition (8×10⁻⁷ Torr) of organic materials onto the surface of indium tin oxide (ITO)-coated glass substrate, in which the layer structures of samples for AFM measurement and those for EL measurement were ITO/NPB (40 nm)/red emitters (80 nm) and ITO/NPB (40 nm)/red emitters (80 nm)/BCP (30 nm)/Liq (2 nm)/Al (100 nm), respectively. The analysis based on AFM measurements well supported that the photoluminescence properties and the device performance were very much dependent upon surface morphology of an organic thin layer.     

The crystallographic change in sub-surface layer of the silicon single crystal polished by chemical mechanical polishing

The effect of the contact nominal pressure on the surface roughness and sub-surface deformation in chemical mechanical polishing (CMP) process has been investigated. The experimental results show that a better surface quality can be obtained at the lower pressure, and the thickness of sub-surface deformation layer increases with the increase of the pressure. In CMP process, polishing not only introduces amorphous transformation but also brings a silicon oxide layer with a thickness of 2–3 nm on the top surface. The atomic structure of the material inside the damage layer changes with the normal pressure. Under a higher pressure (125 kPa), there are a few crystal grain packets surrounded by the amorphous region in which the lattice is distorted, and a narrow heavy amorphous deformation band appears on the deformation region side of the interface. Under a lower pressure, however, an amorphous layer can only be observed.     

Electrolyte Jet Machining (EJM) of antibacterial surfaces

Electrolyte Jet Machining (EJM) has been performed on stainless steel surfaces with the aim of reducing bacterial retention through the generation of nanoscale surface morphology. Following initial EJM experiments aimed at investigating the influence of machining depth, machining speed and current density on the resulting surface roughness, three characteristic surfaces were produced with a current density of 10–18 A/cm² and a machining speed of 0.8–8 mm/s to obtain an arithmetic mean height (S_a) of 0.5–0.74 μm and a density of peaks (S_pd) of 0.25–1.26 μm⁻¹. Relatively large differences between the three surfaces in terms of S_pd allowed thorough investigation into the effects of surface feature size on bacterial retention to be performed. Reductions in the order of 90% compared to control samples were achieved for gram-positive Bacillus cereus and Staphylococcus aureus across the entire tested parameter range (S_pd = 0.25–1.26 μm⁻¹), while reductions in the order of 99% were achieved for gram-negative Escherichia coli and Pseudomonas aeruginosa for surfaces characterized by S_pd > 1 μm⁻¹. Not only do the results call attention to EJM as an innovative technology for producing antibacterial surfaces, they also highlight important differences in the behavior of gram-positive and gram-negative bacteria in relation to EJM-textured surfaces with nanoscale surface morphology.     

Experimental investigation on characteristics of venturi cavitating flow and Rhodamine B degradation in methanol solution

Hydrodynamic cavitation (HC) commonly occurs within industrial pipelines and its unsteady flow characteristics are of great significance for energy conservation and efficiency improvement. This study investigates the effects of methanol concentration (0–20 wt%) on the cavitating flow characteristics and the degradation of Rhodamine B (RhB) under operating conditions of a 0.7 MPa pressure drop, temperature of 30 °C, 200 passes through a venturi reactor, and an initial RhB concentration of 40 μmol/L. The transient cavitation behavior was monitored using a high-speed camera. The cavitation images show that the presence of methanol generates more stable bubbles, which results in less violent bubble collapse. The pressure pulsation and vibration induced by cavitation flow were synchronously measured using high-frequency pressure and acceleration sensors. The spectral analyses of the pressure pulsation indicate that methanol has no effect on the dominant frequency (∼5.5 Hz) at different positions, and the amplitude initially increases with increasing methanol concentration and then stabilizes. The pressure pulsation intensity increases due to the increased vapor pressure of the solution. The vibration spectral analyses show that methanol has little effect on the peak frequencies, which occur near 4.0 kHz and 14.3 kHz of the low and high-frequency bands, respectively, whereas the peak amplitude decreases with increasing methanol concentration. The per-pass degradation model of RhB in methanol solution considering pyrolysis of methanol was verified for the first time and show to adequately describe the experimental data. The degradation percentage and per-pass degradation factor decrease with increasing methanol concentration. The reduced surface tension of the solution prolongs the bubble lifespan and prevents bubble coalescence, thus weakening the vibration and degradation performance. The results provide important insight for cavitation applications and degradation modeling of mixed solutions.     

Compaction behavior and permeability property tests of preforms in vacuum-assisted resin transfer molding using a combined device

A device was designed to study compaction behavior and permeability of preforms in vacuum-assisted resin transfer molding, consisting of a pressure control module, a pressure test module, a thickness test module, and an experimental plate. It can also be used to test the effects of resin flow and the post-filling process on the thickness variation of preforms. Four tests were conducted with the device: (1) compaction tests on preforms of 1, 15, 20, and 25 layers in dry and wet states; (2) in-plane permeability tests on preforms of 1, 5, 10, and 20 layers; (3) transverse permeability tests for 20 layers preforms; (4) determination of the effects of resin flow and post-filling time on preform thickness variation with two liquids. The results show the in-plane permeability decreases as the number of layers increases, and the value for 20 layers is about 62% of one layer. Preform thickness is affected by the liquid viscosity and post-filling time, and the averaged thicknesses of edible oil and Cycom890 resin were 2.12 and 2.03 mm, respectively, at post-filling times of 30 and 40 min, which represent a decrease by 1.9% and 2.9%, respectively, compared with the cases in which there was no post-filling process.     

Parameters optimization on surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process

With the advance of contemporary technology, high precision surface finishing techniques for optical glasses are of great concern and developing to meet the requirements of the effective industrialized processes. Not only the used tools but also process parameters have great influence on the surface roughness improvements. In this paper, surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process has been presented. For the same purpose, a tool for executing ultra precision polishing was designed and manufactured. Taguchi's experimental approach, an L₁₈ orthogonal array was employed to obtain the optimal process parameters. ANOVA analysis has also been carried out to determine the significant factors. It was observed that about a 98.33% improvement on surface roughness from (R_a) 0.360 μm to (R_a) 0.006 μm has been achieved. The experimental results show that a surface finished achieved can satisfy the requirements for optical-quality surface (R_a < 12 nm). In addition, the influence of significant factors on surface roughness improvement has been discussed in this study.     

Feasibility assessment of magnetic resonance-thermometry on pancreas undergoing laser ablation: Sensitivity analysis of three sequences

Laser ablation (LA) is a minimally invasive technique for the treatment of tumors as an alternative to surgical resection. The light absorbed by tissue is converted into heat, and causes irreversible cell damage when temperatures higher than 60 °C are reached. The knowledge in real time of temperature may be particularly beneficial for adjusting laser settings applied during treatment and to be notified in real time about its end-point. As a consequence, several techniques for temperature monitoring within the tissue have been investigated along the last decades. In the field of LA, particularly attractive are non-invasive methods. Among these techniques, thermometry based on the analysis of Magnetic Resonance Imaging (MR-thermometry) has gaining large acceptance in this field. MR-thermometry allows estimating the temperature variation thanks to the thermal dependence of several MRI parameters, among others the most promising are T₁ relaxation time, and proton resonance frequency shift.The aim of this study is to assess the sensitivity of MRI thermometry using three T₁-weighted sequences (i.e., Inversion Recovery Turbo-FLASH, IRTF, Saturation Recovery Turbo-FLASH, SRTF, and FLASH) using an 1.5-T MR scanner on healthy swine pancreases undergoing LA. The reference temperature was measured by MRI-compatible fiber optic sensors (fiber Bragg grating sensors). The sensitivity of the proposed techniques was estimated and compared. The thermal sensitivity of the three sequences was −1.47 ± 0.08 °C⁻¹, −0.95 ± 0.05 °C⁻¹, and −0.56 ± 0.04 °C⁻¹ for IRTF, SRTF and FLASH, respectively. Results show that the proposed technique may be adequate for temperature monitoring during LA.