Showing papers in "Sensors and Actuators A-physical in 2016"

Evolution of 3D printed soft actuators

Abstract: Developing soft actuators and sensors by means of 3D printing has become an exciting research area. Compared to conventional methods, 3D printing enables rapid prototyping, custom design, and single-step fabrication of actuators and sensors that have complex structure and high resolution. While 3D printed sensors have been widely reviewed in the literature, 3D printed actuators, on the other hand, have not been adequately reviewed thus far. This paper presents a comprehensive review of the existing 3D printed actuators. First, the common processes used in 3D printing of actuators are reviewed. Next, the existing mechanisms used for stimulating the printed actuators are described. In addition, the materials used to print the actuators are compared. Then, the applications of the printed actuators including soft-manipulation of tissues and organs in biomedicine and fragile agricultural products, regenerative design, smart valves, microfluidic systems, electromechanical switches, smart textiles, and minimally invasive surgical instruments are explained. After that, the reviewed 3D printed actuators are discussed in terms of their advantages and disadvantages considering power density, elasticity, strain, stress, operation voltage, weight, size, response time, controllability, and biocompatibility. Finally, the future directions of 3D printed actuators are discussed.

Application of FBG sensors for geotechnical health monitoring, a review of sensor design, implementation methods and packaging techniques

Abstract: Fiber Bragg grating (FBG) sensor has been considered as a reliable sensor for health monitoring of structural and geotechnical projects. Various types of FBG based sensors have been proposed in past few decades and employed for health monitoring of many geotechnical structures. This paper presents an overview of the recent development and application of FBG based sensors for health monitoring of several key geotechnical structures, including soil nail systems, slopes, and piles. Different sensor design, implementation and packaging methods, advantages and limitations of using FBG based sensors in different projects are reviewed. Comparative analysis of using two mathematical methods for the prediction of ground movement using FBG sensor data are also carried out. The two typical mathematical methods include Finite Difference Method (FDM) and Numerical Integration method (NIM). Possible technical challenges of applying FBG sensors for geotechnical monitoring are discussed.

A review on coupled MEMS resonators for sensing applications utilizing mode localization

Abstract: In this paper, we review a recent technology development based on coupled MEMS resonators that has the potential of fundamentally transforming MEMS resonant sensors. Conventionally MEMS resonant sensors use only a single resonator as the sensing element, and the output of the sensor is typically a frequency shift caused by the external stimulus altering the mechanical properties, i.e. the mass or stiffness, of the resonator. Recently, transduction techniques utilizing additional coupled resonators have emerged. The mode-localized resonant sensor is one example of such a technique. If the mode localization effect is utilized, the vibrational amplitude pattern of the resonators changes as a function of the quantity to be measured. Compared to using frequency shift as an output signal, the sensitivity can be improved by several orders of magnitude. Another feature of the mode-localized sensors is the common mode rejection abilities due to the differential structure. These advantages have opened doors for new sensors with unprecedented sensitivity.

Low-cost flexible pressure sensor based on dielectric elastomer film with micro-pores

Abstract: We developed a low-cost flexible pressure sensor based on an elastomer film with uniformly distributed micro-pores as a dielectric layer. The dispersion of the micro-pores in the elastomer film results from the phase separation between a prepolymer material and deionized water to the elastomer, followed by the subsequent evaporation of the solvent within the polymer matrix after polymerization. Owing to the enhanced deformability by the pore structures, the relatively high sensitivity of 1.18 kPa−1 in the low pressure (

Shape memory alloy thin films and heterostructures for MEMS applications: A review

Abstract: In recent years, shape memory alloy (SMA) thin films have attracted significant attention from the scientific community and industry for their potential applications in the field of smart sensors and actuators, micro- and nano-electromechanical systems, aerospace, automobile, and biomedical. The present article focuses on the recent developments in the field of SMA thin films and their heterostructures with other materials for potential microelectromechanical systems (MEMS) applications. Various microdevices such as microgrippers, micropumps, microvalves, and cantilevers fabricated from binary and ternary SMA films have been discussed in detail. SMA thin films combined with various nitrides, oxides, and ferroelectric layers offer excellent surface modification and vibration damping at microscale for their use in harsh environments. The article encompasses the new paradigms in the field of SMA thin films that have been essentially developed by the authors and co-workers during the past 6 years.

A survey on actuators-driven surgical robots

Abstract: Robot-assisted surgeries have been integrated and leading to a paradigm shift in surgical fields. With the emergence of Minimally Invasive Surgery (MIS), especially Natural Orifice Transluminal Endoscopic Surgery (NOTES), there are various benefits such as a minimization of side effects, enhancement of precise surgical procedures, and faster recovery after the surgery that patients can take from. However, in order to effectively employ and exploit surgical robots, numerous technical challenges need to be addressed. Among these, actuators play a vital role. To provide deeper understanding on current actuators-driven surgical robot, this study will comprehensively review on four main types of transmission systems namely cable-driven mechanism, flexible fluidic actuators, smart material actuators, and magnetic actuators, in terms of conceptual designs, modelling, and control as well as their advantages and disadvantages. Profound discussions and recommendations for the future of actuators-driven surgical robots will be also pointed out to give the roadmap in the surgical field.

Piezoresistive natural rubber-multiwall carbon nanotube nanocomposite for sensor applications

Abstract: We explore, both experimentally and theoretically, the possibility to use a composite of natural rubber (NR) and multiwall carbon nanotubes (MWCNT) as a piezoresistive tensile sensor. As an essentially new feature relative to the previous work, we have performed a systematic study of the mechanism of the piezoresistance at large deformations in a wide range of MWCNT concentrations and crosslinking degrees of the host rubber material. In qualitative agreement with the previous work, the conductivity of the unstrained NR/MWCNT nanocomposite is shown to be adequately described by the percolation theory with the critical exponent evaluated to ∼2.31. Varying tensile stress-induced strains in the composite has been shown to results in a non-linear electrical response that cannot be described by simple modifications of the percolation theory. In order to explain the observed non-linear dependence of the resistance R of the composite on the strain e, we have developed a scaling theory that relates this resistance to the structural changes in the conducting MWCNT network caused by deforming the host NR. Based on the obtained results, we discuss the ways of using the highly stretchable conductive elastomer composites as an efficient piezoresistive tensile sensor.

Bi-resonant structure with piezoelectric PVDF films for energy harvesting from random vibration sources at low frequency

Abstract: This paper reports on a bi-resonant structure of piezoelectric PVDF films energy harvester (PPEH), which consists of two cantilevers with resonant frequencies of 15 Hz and 22 Hz. With increased acceleration, the vibration amplitudes of the two cantilever-mass structures are increased and collision occurs which causes strong mechanical coupling between the two subsystems. The experimental results show that the operating bandwidth is widened to 14 Hz (14–28 Hz) at an acceleration of 9.81 m/s2, and the peak output power can be 0.35 μW at a relatively low operation frequency of 16 Hz. Simulation and experiments with piezoelectric elements show that the energy harvesting device with the bi-resonant structure can generate higher power output than that of the sum of the two separate devices from random vibration sources at low frequency, and hence significantly improves the vibration-to- electricity conversion efficiency by 40–81%.

Cellulose nanocrystal/graphene oxide composite film as humidity sensor

Abstract: Cellulose nanocrystal/graphene oxide composite was reported as a humidity sensor in this study. The composite film was fabricated using simple blending the materials followed by oven drying. The composite film offers a unique advantages of cellulose combined with functionality of GO. It was capitalized to design renewable, flexible and cheap humidity sensor. Performance of the composite film as a humidity sensor was evaluated on the basis of relative capacitance change at different humidity level. Synthesized composite film was characterized using scanning electron microscope, Fourier transform infrared spectroscope, and X-ray diffraction. Environmental effect such as temperature was taken into account on the sensor performance. The sensing mechanism is explained on the basis of presence of hydrophilic functional groups in the composite. The linear and fast response of the developed sensor is advantageous.

Fabrication and characterization of V2O5 nanorods based metal–semiconductor–metal photodetector

Abstract: The fabrication and characterization of a metal–semiconductor–metal (MSM) visible photodetector based on V2O5 NRs are investigated. V2O5 nanorods (NRs) is synthesized on p-type Si(100) by spray pyrolysis method. The MSM photodetector is based on V2O5 NRs grown on Si(100) substrate. Structural and optical properties of the V2O5 NRs are studied using high resolution X-ray diffraction, field emission-scanning electron microscopy and photoluminescence spectroscopy. The results reveal an orthorhombic structure with preferred orientation along (001) plane of the prepared V2O5 NRs. Photoluminescence (PL) spectra show intensive and sharp green light emission at about 535 nm with high intensity. Upon exposure illumination to 540 nm (1.535 mW/cm2) at an applied voltage of 5 V, the device Exhibit 260.96 × 102 sensitivity; photodetector gain of device is 270, photoresponse peak of 0.948 A/W and photocurrent of 2.7 × 10−4A. The response and recovery times are determined as 0.787 s and 0.541 s, respectively; upon exposure to 540 nm light at 5 V applied bias. The obtained results indicate that the V2O5 NRs is a promising candidate for high performance as a MSM photodetector for commercially photoelectronic applications.

Low temperature ethanol response enhancement of ZnO nanostructures sensor decorated with gold nanoparticles exposed to UV illumination

Abstract: To increase the ethanol sensing at low operating temperatures in ZnO nanostructure sensors, the gold nanoparticles were introduced to ZnO nanostructures (ZnO:AuNPs) by a sputtering technique. Then, the ethanol sensing characteristics were investigated under UV illumination at the temperatures in the range of 25–125 °C. It was found that the sensor response of ZnO:AuNPs sensor under UV illumination was remarkably improved. Moreover, the sensor based on ZnO:AuNPs under UV illumination exhibited the increasing of sensor response toward ethanol vapor with an increasing of UV illumination intensity from 0 to 4.1 mW/cm 2 . The sensor response enhancement mechanism can be explained by two main effects including sensor response enhancement due to an addition of AuNPs on ZnO nanostructures and UV illumination. The AuNPs added onto ZnO nanostructure strongly affect the chemical reaction change in the oxygen adsorption reaction resulting in a larger depletion layer width. As a result, the sensor response is enhanced to higher than that of ZnO nanostructure sensor. The sensor response enhancement due to UV illumination is explained by the formation of weakly bound oxygen ions from electron carriers being excited from band to band and oxygen molecule in air. This produces a thinner depletion layer width with the weakly bound oxygen ions due to the photo activation which are easily removed from the ZnO surface resulting in high sensor response with lower resistance.

Flexible screen printed thermoelectric generator with enhanced processes and materials

Abstract: This paper presents the fabrication and testing of bismuth tellurium (Bi1.8Te3.2) – antimony tellurium (Sb2Te3) based flexible thermocouples using screen printing technology for energy harvesting application. In this study, planar screen printed thermoelectric generators (TEGs) with three different printing processes were developed and coiled up to test. All thermocouples were printed on a flexible polyimide substrate. The dimension of each planer thermoleg is 20 mm × 2 mm while the thickness varied from 70.5 μm to 78 μm. The thermoelectric performance of TEGs using different binder systems A and B were investigated. For TEGs with binder A, the calculated Seebeck coefficient of a single thermocouple was in the range of 193–227 μV/K. At a temperature difference of 20 °C, the optimized power was 142 nW contributed by the cold isostatic pressed TEG with SbTe electrodes. Binder system B with lower viscosity was applied and proved to be able to decrease the resistivity of BiTe thick film, which increased the power factor (α2ρ). The power output of such coiled-up device increased to 444 nW with the same temperature difference. Higher output power could be realized by rolling up more planar thermocouples electrically connected. This work demonstrates that the low-cost screen printing technology and low-temperature curing materials are promising for the fabrication of flexible TEGs. Binder system that could help to generate a denser film was important to BiTe and SbTe based screen printable thermoelectric materials.

Flexible carbon nanotube nanocomposite sensor for multiple physiological parameter monitoring

Abstract: The paper presents the design, development, and fabrication of a flexible and wearable sensor based on carbon nanotube nanocomposite for monitoring specific physiological parameters. Polydimethylsiloxane (PDMS) was used as the substrate with a thin layer of a nanocomposite comprising functionalized multi-walled carbon nanotubes (MWCNTs) and PDMS as electrodes. The sensor patch functionalized on strain-sensitive capacitive sensing from interdigitated electrodes which were patterned with a laser on the nanocomposite layer. The thickness of the electrode layer was optimized regarding strain and conductivity. The sensor patch was connected to a monitoring device from one end and attached to the body on the other for examining purposes. Experimental results show the capability of the sensor patch used to detect respiration and limb movements. This work is a stepping stone of the sensing system to be developed for multiple physiological parameters.

Diagnosis of carbonation induced corrosion initiation and progression in reinforced concrete structures using piezo-impedance transducers

Abstract: In addition to chloride induced corrosion, the other commonly occurring type of rebar corrosion in reinforced concrete structures is that induced by the ingress of atmospheric carbon dioxide into concrete, commonly referred to as ‘carbonation induced corrosion’. This paper presents a new approach for detecting the onset and quantifying the level of carbonation induced rebar corrosion. The approach is based on the changes in the mechanical impedance parameters acquired using the electro-mechanical coupling of a piezoelectric lead zirconate titanate (PZT) ceramic patch bonded to the surface of the rebar. The approach is non-destructive and is demonstrated though accelerated tests on reinforced concrete specimens subjected to controlled carbon dioxide exposure for a period spanning over 230 days. The equivalent stiffness parameter, extracted from the frequency response of the admittance signatures of the PZT patch, is found to increase with penetration of carbon dioxide inside the surface and the consequent carbonation, an observation that is correlated with phenolphthalein staining. After the onset of rebar corrosion, the equivalent stiffness parameter exhibited a reduction in magnitude over time, providing a clear indication of the occurrence of corrosion and the results are correlated with scanning electron microscope images and Raman spectroscopy measurements. The average rate of corrosion is determined using the equivalent mass parameter. The use of PZT ceramic transducers, therefore, provides an alternate and effective technique for diagnosis of carbonation induced rebar corrosion initiation and progression in reinforced concrete structures non-destructively.

Mechanical behavior of strain sensors based on PEDOT:PSS and silver nanoparticles inks deposited on polymer substrate by inkjet printing

Abstract: Recently, inkjet printing technology has received growing attention as a method to produce low-cost large-area electronics, sensors, and antennas on polymer substrates. This technology relies on printing techniques to deposit electrically functional materials onto polymer substrates to fabricate electronic components or sensing elements. In this paper, we applied an inkjet printed technology for the development and characterization of films on a polymer substrate aiming at giving design considerations for the optimization of strain sensors or printed electronics obtained by inkjet printing. Two inks were tested over a polyimide substrate, a water-based conductive polymer, PEDOT:PSS, and a silver nanoparticles ink. Their sensing capabilities were investigated under tensile conditions and various strain histories (strain ramp; cyclic loading-unloading tests; application of constant strain over prolonged time) aiming at highlighting the correlation between electrical response, applied strain, time and mechanical histories. Furthermore, the mechanical viscoelastic response of the substrate was investigated under similar strain histories interpreting the results at the light of the substrate deformational characteristics and evaluating its influence.

A miniaturized electromagnetic vibration energy harvester using flux-guided magnet stacks for human-body-induced motion

Abstract: We present a miniaturized electromagnetic energy harvester (EMEH) that uses two flux-guided magnet stacks to harvest energy from common human-body-induced motions such as hand-shaking, walking, and slow running. We designed each magnet stack to increase the flux density within a given size of the harvester component, by guiding the flux lines through soft magnetic material and designed the miniaturized EMEH to up-convert the low-frequency vibration generated by human-body-induced motion to a high-frequency vibration by mechanical impact of a spring-less structure. Our use of a spring-less structure eliminates the challenges of designing a practical and reliable low-frequency (<5 Hz) oscillator. Our low-frequency oscillator couples the human-body-induced vibration to two high-frequency oscillators (electromagnetic transducer elements). Each high-frequency oscillator consists of the analyzed 2-magnet stack and customized helical compression spring. We fabricated a standard AAA battery sized prototype (3.9 cm3) and tested it with different human activities. We were able to generate a maximum 203 μW, 32 μW, and 78 μW average power from hand-shaking, walking, and slow running motion, respectively. This miniaturized structure yields a maximum average power density of 52 μW cm−3. We used a rectifier and multiplier circuit as the interface between the harvester and a wearable electronic load (wrist watch) to demonstrate the feasibility and capability of powering small-scale electronic systems from human-body vibration.

Experimental investigation of performance reliability of macro fiber composite for piezoelectric energy harvesting applications

Abstract: Macro fiber composite (MFC) has been extensively used in actuator/sensor/harvester applications. Fatigue due to cyclic high electric fields in actuator applications has been studied extensively. However, fatigue failure of MFC due to high stress or strains in energy harvesting applications has attracted little attention. The aim of the study is to obtain the upper limit of dynamic strain on MFC which can be used as failure limit in the design process of piezoelectric energy harvesters (PEHs). The examined PEH is comprised of a cantilever beam made of aluminum and a patch of MFC bonded at its root for power generation. Energy harvesting tests are conducted at various base accelerations around 30 Hz (near resonant frequency) and the voltage output and maximum strain on MFC are measured. Severe loss in the performance of the harvester is observed within half million cycles of testing at high strain amplitude. Hence several reliability tests for extended periods of time are carried out at various strain amplitudes. The harvesters are tested at resonant frequencies around 30 Hz and 135 Hz for over 20 million and 60 million cycles, respectively. Degradation in voltage output, change in natural frequency and formation of cracks are considered as failures. Based on the experimental results, an upper limit of 600 μϵ is proposed as the safe amplitude of strain for reliable performance of MFC. Tensile tests are also carried out on MFC patches to understand the formation of cracks and shift in resonant frequency at low strains. It is observed that cracks are formed in MFC at strains as low as 1000 μϵ. The observations from this work are also applicable to MFC bending actuators undergoing cyclic strains.

A low voltage silicon micro-pump based on piezoelectric thin films

Abstract: We fabricated a functional micro-pump made of silicon and PZT thin films with standard MEMS technology. This pump can self-prime, works in both ways and pumps both air and water. Typical figures in water are 3.5 μL/min-flow rate at 1 Hz, no downstream pressure and 24 V-actuation voltage. At this voltage, the micro-pump valves withstand 32 mbar downstream pressure. The main advantage of this micro-pump based on piezoelectric films compared to its bulk counterparts is that it allows for low voltage operation. Less than 50 μW are needed to actuate the pump membranes at 1 Hz.

Low frequency (LF) RFID sensors and selective transient feature extraction for corrosion characterisation

Abstract: In this paper, Low Frequency (LF) RFID sensing system is used to characterise marine atmospheric corrosion on steel samples. Considering the conductivity and permeability variation in the corrosion layer, optimisation of sensing sensitivity and communication distance of commercial RFID tags placed on both coated and uncoated samples (exposure duration between 1 and 12 months) for impedance matching and appropriate operation frequencies are analysed. To balance the communication distance between RFID reader and tag and to match the impedance variation of RFID tags on metallic samples, a concept of wireless power transfer (WPT) through strongly coupled magnetic resonance (SCMR) method at RFID is applied. Static and transient features are extracted and selected to characterise corrosion. To enhance the sensing sensitivity to corrosion characterisation, further experimental studies have been carried out using ferrite sheets. The proposed LF RFID sensing system has been validated using commercial RFID tags with different feature extractions and selection of features for corrosion characterisation.

Liquid level measurement based on a no-core fiber with temperature compensation using a fiber Bragg grating

Abstract: An optical fiber sensor for simultaneous measurement of liquid level and temperature is proposed and experimentally demonstrated. The sensor is formed by the integration of a no-core fiber (NCF) with a fiber Bragg grating (FBG).When the liquid level is changed, the interference fringe of the NCF would shift while the Bragg wavelength of the FBG remains the same. On the other hand, the interference fringe of the NCF and the Bragg wavelength of the FBG would shift simultaneously with the variation of temperature. Thus the liquid level sensor with dynamic temperature compensation can be easily achieved by using the temperature sensing property of FBG. For 10 pm wavelength resolution, the resolution of the sensor is 0.046 cm and 1.1 °C in liquid level and temperature, respectively. The fabrication of the proposed sensor is very simple and it is characterized by the dynamic temperature compensation, which makes it desirable in liquid level measurement.

Improve efficiency of harvesting random energy by snap-through in a quad-stable harvester

Abstract: In response to the defects of the bi-stable energy harvester (BEH), we develop a novel quad-stable energy harvester (QEH) to improve the harvesting efficiency. The device is made up of a bimorph cantilever beam having a tip magnet and three external fixed magnets. By introducing the repulsion forces between magnets, the function of potential energy of the QEH is given. It owns four potential wells. It is proved that the quad-stable harvester can cross the barriers and realize snap-through easier. Validation experiments were performed by frequency sweeping and random excitations. Results show that compared to the BEH the frequency bandwidth of snap-through of the novel device is much wider. The QEH can make a dense snap-through in response under random excitation, and give out a large output voltage. This shows that the proposed QEH is more effective in energy harvesting applications.

Printed electrodes structures as capacitive humidity sensors: A comparison

Abstract: This work discusses about four planar printed capacitive sensors with different geometrical layouts, fabricated by inkjet printing on a flexible substrate and used as humidity sensors. In particular, we show a comparison among interdigitated electrodes, meandered electrodes, spiral electrodes, and serpentine electrodes in terms of fabrication yields, sensitivities to relative humidity as well as thermal drift taking into account frequency dependencies. In addition, numerical simulations have been performed to further investigate the characteristics of these sensors. All sensors present similar behavior in frequency with humidity. Taking into account sensitivity within the same sensing area, the highest value is achieved by serpentine electrodes, followed by spiral electrodes, interdigitated and meandered electrodes, in this order. The best configuration will be dependent on the specific application and its requirements.

Fiber Bragg grating based sensing system: Early corrosion detection for structural health monitoring

Abstract: Fiber optic sensors have been widely used in chemical and biomedical applications and are now being extended to structural health monitoring (SHM) in the civil engineering field. Due to the destructive nature of tests for corrosion monitoring, a non-destructive system was developed to monitor rebar corrosion via fiber Bragg grating (FBG). In this study, two different methods are proposed and tested; FBG with Polydimethylsiloxane (PDMS) coating and bare FBG. FBG sensors were embedded on the specimen to monitor the expansion strain caused by rebar corrosion, and their performances were monitored by observing the Bragg wavelength shift. A significant wavelength shift for the FBG without coating was observed on day 17, whereas for the PDMS coating, the significant wavelength shift occurred on day 10. This proves that PDMS coated FBGs have a higher sensitivity for corrosion detection as compared to non-coated ones. The overall results of both methods after etching have shown a good linear response. Strain induced by the corrosion shows good linear response as corrosion rate increased. Corrosion rate were calculated from the conventional weight loss measurement method. These sensors can be installed for real-time and non-destructive SHM monitoring in civil engineering.

A tensural displacement amplifier employing elliptic-arc flexure hinges

Abstract: To increase the effective actuation stroke of piezoelectric stack actuators and giant magnetostrictive actuators, displacement amplifiers are usually employed to provide mechanical amplification. In this work, a novel symmetric two-stage lever-type amplifier called tensural displacement amplifier is proposed, in which all the flexural hinges are loaded in tension and bending rather than compression and bending when deflected. The tensural displacement amplifier does not have the potential problems buckling may cause because all the compliant members are loaded in tension. In addition, the proposed amplifier exhibits higher lateral frequency when deflected due to the stress stiffening effects of the tensural hinges. The kinetostatic model for the tensural displacement amplifier was established, based on which an amplifier whose amplification ratio exceeds 40 was designed. The amplification ratio of the design was further verified by the finite element model and prototype test.

Theoretical modeling and analysis of two-degree-of-freedom piezoelectric energy harvester with stopper

Abstract: Piezoelectric energy harvesting techniques provide a promising way to transform the vibration energy into electric energy. Since the voltage output peak can drop due to the frequency excitation moving away from the resonance region, the on broadening the bandwidth of operation frequency has drawn great attention. In the paper, a novel two-degree-of-freedom piecewise-linear piezoelectric energy harvester is proposed to achieve wide operation frequency bandwidth by combining the multimodal harvesting technique and nonlinear method. Based on the average method, the analytical solution of the proposed device is achieved. From analytical and experiment results, at an excitation acceleration of 0.3 g, as the excitation frequency is up sweeping, the system achieves frequency bandwidth operation of 7.4 Hz which is about 5.2 times higher to that of conventional two-degree-of-freedom linear harvester, and the power outputs for the first and second resonances can reach up to 429 μW and 411 μW, respectively. Due to the close agreement between the calculated values and experiment results, the analytical solution and the theoretical model could be applied to further MEMS fabrication process and optimized design.

All-fiber multipath Mach⬜Zehnder interferometer based on a four-core fiber for sensing applications

Abstract: A novel, simple and compact optical fiber sensor based on multipath Mach-Zehnder interferometer (m-MZI) is proposed and experimentally demonstrated. The device consists of a segment of four-core fiber (FCF) spliced between two single-mode fibers (SMFs). When the m-MZI is kept straight, an obvious interference pattern appears in the transmission spectrum. Compared with previously reported optical fiber modal interferometers, higher phase sensitivity can be obtained in our scheme due to the multipath interference configuration embedded in one fiber. The maximum fringe visibility of the interference resonance dips exceeds 23 dB. The interference fringe of the FCF would shift with the variation of strain, temperature, refractive index (RI) and curvature. So it is possible to measure these parameters by simply monitoring the wavelength shifts. Experimental results show that the sensitivities of the sensor in strain, temperature, RI and curvature are 1.78 pm/μe, 209 pm/°C, 91.39 nm/RIU and 20.18 nm/m↙1, respectively. To the best of our knowledge, the multi-purpose sensing applications of the sensor have been experimentally investigated for the first time. Moreover, the proposed sensor has the advantages of high fringe visibility and simple fabrication process.

Thickness measurement using liftoff point of intersection in pulsed eddy current responses for elimination of liftoff effect

Abstract: Pulsed eddy current (PEC) responses would intersect at a point for a nonferrous plate when only liftoff distance is varied. In this paper, the behaviors of liftoff point of intersection (LOI) points due to a plate with varying conductivity and thickness were investigated and interpreted in physics by means of simulations and experiments. LOI points result from the invariance of the phase spectrum of PEC responses to liftoff effect, and the time of LOI points would increase with an increase of phase spectrum. Subsequently, the signatures of LOI points were compared with the peak heights and time to peaks of PEC signals and their derivatives. The results demonstrate that the signatures of LOI points possess the comparable performances in terms of sensitivity, linearity and measurement range. Moreover, the signatures of LOI points are immune to liftoff variations in nature, which shall enhance the accuracy and reliability of PEC evaluation.

A new design and a fabrication approach to realize a high performance three axes capacitive MEMS accelerometer

Abstract: This paper presents a new fabrication approach and design for a three axis capacitive MEMS accelerometer that is capable of measuring externally applied accelerations in three orthogonal axes. Individual lateral and vertical axis accelerometers are fabricated in the same die on an SOI wafer which is anodically bonded to a glass substrate. Handle layer of the SOI wafer is used as the top electrode for the vertical axis accelerometer. This accelerometer has a 2 mm 2 perforated electrode area anchored to the glass substrate by four beams. The lateral axis accelerometers on the other hand, have comb finger structures with a 2.7 × 4.2 mm device size and anchored to the glass substrate by six folded beams. Rest capacitance of the vertical axis accelerometer is designed to be 8.8 pF, and it is 10.2 pF for the lateral axis accelerometers. The system level performance results are obtained using analog readout circuitry integrated to each axis separately. The x- and y-axis accelerometers show a noise floor and bias instability equal or better than 13.9 μg/√Hz and 17 μg, respectively, while the z-axis accelerometer shows 17.8 μg/√Hz noise floor and 36 μg bias instability values.

A three-axis force fingertip sensor based on fiber Bragg grating

Abstract: Fiber Bragg grating (FBG) based force sensing technology receives much attention from various research communities in robotics. In this paper, we investigate a three-axis FBG force sensor for robot finger. A special separated elastic structure with six FBGs attached has been designed for three-axis force sensing. Strain distribution and dynamic performance of the proposed structure are simulated by using finite element analysis (FEA). Six FBGs with different wavelengths were arrayed along a single fiber and divided into three groups to measure Fx, Fy, and Fz, respectively. The experimental results demonstrate that the sensor possesses good linearity, weak coupling, and creep resistance.

Calibration and performance assessment of an innovative high-temperature cavitometer

Abstract: This paper describes a series of systematic experimental studies to evaluate the performance of a high-temperature cavitometer under well-controlled conditions. The cavitometer was specifically designed for measurements in liquid metals: it operates through a long tungsten waveguide (probe), providing thermal protection to the piezo sensing elements placed outside the hot area, and with sufficient bandwidth to enable the monitoring of broadband acoustic emissions associated with cavitation activity. It was calibrated electrically, and acoustically, at kHz and MHz frequencies, and so can be used to estimate acoustic pressures (in Pa), providing physical, and consequently practical, meaning to cavitation measurements within liquid metals. Results obtained from ultrasonic sources in a cylindrical vessel using water showed that the cavitometer is a reliable and robust device for characterizing direct field acoustic pressures and broadband emissions from the resulting cavitation. Additionally, preliminary characterization of the real-time acoustic pressures during ultrasonic processing of liquid aluminium (Al) in a standard clay-graphite crucible were performed for the first time. The use of the calibrated cavitometer will establish a more generalized approach for measuring the actual acoustic pressures over a broad range of liquid temperatures within a sonicated medium, demonstrating its potential use as a tool for optimizing, controlling, and scaling-up processes.