Showing papers in "Sensors and Actuators A-physical in 2015"

Opto-electronic humidity sensor: A review

Abstract: The present paper reports the detailed study of various metal oxide nanomaterials as opto-electronic humidity sensor The sensor elements were fabricated and characterized as thin or thick film based on the semi-conducting metal oxide As semi-conducting metal oxides are known for their n-type conduction because of the presence of oxygen vacancies and change in refractive indices with the exposure of moisture therefore they were proven to be very good sensors for humidity Depending upon the need, the sensing materials were deposited either on the base of the prism or on the U-shaped borosilicate glass rods or on some other transparent substrates for opto-electronic sensing Light from LED or He–Ne laser was launched into the sensing element from one side and collected into the other side by optical power meter The mode of propagation of light was transmission, reflection or partially refraction Modulations in the intensity of light with changes in humidity were recorded Being optical in nature, such types of sensors are very useful for detection of moisture level at remote places or unmanned stations The primary purpose of this paper is to focus on the techniques used in these sensors

A review for optical sensors based on photonic crystal cavities

Abstract: This review covers photonic crystal cavities (PCCs) and their applications in optical sensors, with a particular focus on the structures of different PCCs. For each kind of optical sensor, the specific measurement principle, structure of PCC, and the corresponding sensing properties are all presented in detail. The summary of the reported works and the corresponding results demonstrate that it is possible to realize miniature and high-sensitive optical sensors due to the ultra-compact size, excellent resonant properties, and flexibility in structural design of PCCs. Finally, the key problems and new directions of PCCs for sensing applications are discussed.

3D printed molds for non-planar PDMS microfluidic channels

Abstract: This article introduces the use of three-dimensionally (3D) printed molds for rapid fabrication of complex and arbitrary microchannel geometries that are unattainable through existing soft lithography techniques. The molds are printed directly from computer-aided design (CAD) files, making rapid prototyping of microfluidic devices possible in hours. The resulting 3D printed structures enable precise control of various device geometries, such as the profile of the channel cross-section and variable channel diameters in a single device. We report fabrication of complex 3D channels using these molds with polydimethylsiloxane (PDMS) polymer. Technology limits, including surface roughness, resolution, and replication fidelity are also characterized, demonstrating 100-μm features and sub-micron replication fidelity in PDMS channels.

Real-time wind estimation on a micro unmanned aerial vehicle using its inertial measurement unit

Abstract: This paper presents an approach for a quadrocoper-based micro unmanned aerial vehicle (UAV) that estimates the wind vector (speed and direction) in real-time based on measurement data of its on-board sensors only. This method does not need any additional airspeed sensor or dedicated anemometer, and thus the micro UAV's valuable payload remains free for other sensors. Wind tunnel and field tests were used to evaluate the performance of the approach. In order to quantify its accuracy, experiments are presented where data was collected with an anemometer placed in an open field with the micro UAV in flight following a predefined trajectory around the anemometer and hovering at a defined position close to it.

A review of long range piezoelectric motors using frequency leveraged method

Abstract: This paper provides a comprehensive review of the literature regarding precision piezoelectric motors over long ranges based on the principle of repeating a series of small periodic step motions, named “frequency leveraged motors” in this paper. A summary of recent research into frequency leveraged motors is presented. Work is classified into three categories by different frequency driving methods, including ultrasonic motors, quasi-static motors (non-resonant motors), and motors combined resonant and quasi-static operations. Pros and cons of each motor type are discussed in term of their principle, structure, and performance. In addition, future perspectives and improvements of the frequency leveraged motor are also provided. It is summarized in such a way can provide a better understanding of the core characteristics of each type of long range piezoelectric motor. Moreover, it also aids in determining successful designs, suitability for applications and further research areas.

Extended PDMS stiffness range for flexible systems

Abstract: The use of polymers in the context of flexible systems such as flexible sensors leads to an incompatibility issue: on the one hand, the flexibility of the polymer must not be to the detriment of the fabrication process, e.g. excessive thermal expansion leading to process failure and on the other hand, certain applications will require high flexibility and also a specific mechanical stiffness, e.g. artificial skin, smart clothes, flexible screen. In other words, a compromise is necessary between rigidy for processing and controlled flexibility for applications. In this context it is crutial to be able to tune the mechanical properties of such polymers. Polydimethylsiloxane (PDMS) is a very versatile and useful soft polymeric material – Elastic modulus typically ≈1 MPa. This paper investigates the stiffness tunability of PDMS by varying the hardening agent to PDMS base ratio over 19:1 to 2:1, and using two extreme curing processes, i.e. 120 min at 100 °C and 2 days at 165 °C. It was observed that the stiffness of PDMS can be accurately controlled from 800 kPa to 10 MPa with a rupture limit higher than 20%. To our knowledge this is the highest reported elastic modulus in PDMS by combining mixing ratio and curing temperature. The impact of such a stiffness variation on potential functional properties such as the rupture limit, Poisson's ratio and material's wetting contact angle is also analysed. We observe that the wetting contact angle depends on the bulk mechanical properties of the PDMS. The observations will be of use to all technological communities who are engaged in using PDMS-type polymers for their specific applications.

Silicon diode temperature sensors - A review of applications

Abstract: Most of the variables measured in scientific investigations or engineering applications depend, by varying degrees, on temperature. This necessitates the simultaneous measurement of temperature along with the variable of interest in order to perform high fidelity temperature compensated measurements. Silicon diode based temperature sensors (or silicon thermodiodes) have the advantages of being low cost, having an absolute temperature measurement capability as well as providing the option of on-chip integration with electronic circuits and a wide temperature measurement range. Leveraging these advantages, engineers and scientists have used silicon thermodiodes in numerous and diverse applications. This paper identifies the common temperature measuring techniques, and focuses on the use and advantages offered by silicon diodes operated as temperature sensors in different drive modes. Finally it explores the published literature for summarizing the application areas where such sensors have been utilized successfully in recent years.

Fast response integrated MEMS microheaters for ultra low power gas detection

Abstract: Semiconducting metal oxide (SMO) gas sensors typically operate at a few hundred degrees Celsius and consume hundreds of milliwatts of power, limiting their application in battery-powered devices. An analytical model is presented for the optimization of the heater dimensions, which suggests the minimal power consumption is achieved when heat loss through air conduction and supporting beam conduction are equal. We demonstrate micromachined SMO sensors with optimized microheaters, which consume only ∼2 mW of power when operated continuously at 300 °C. We also measure an ultra-fast thermal response time of 33 μs via a transient temperature–resistivity response method. The short response time allows the heaters to be operated in ultra-short pulsing mode decreasing the average power consumption to the μW level. These micromachined SMO sensors are used in proof-of-principle experiments as ultralow power hydrogen sulfide SMO gas sensors.

Mid-IR optical sensor for CO2 detection based on fluorescence absorbance of Dy3+:Ga5Ge20Sb10S65 fibers

Abstract: The Dy3+ doped Ga5Ge20Sb10S65 bulk glass provides good emission efficiency in the middle IR with a better brightness than the blackbody sources. Sulfide single index fibers doped with Dy3+ (500-​3000 ppm) were drawn with optical attenuation of about 1-​3 dB​/m, suitable to develop fluorescence sources for chem. anal. by optical absorption in middle IR. They particularly present a broad emission around 4-​5 μm, making them attractive for CO2 detection. Considering the low cost and efficient Dy3+ pumping scheme by means of a com. laser diode, the Dy3+ sulfide fiber reveals potential for developing a CO2 optical sensor. Using the 4.35 μm broad emission of a Dy3+ doped Ga5Ge20Sb10S65 fiber combined with a differential measurement technique, the CO2 gas concn. measurement was carried out fruitfully. For this specific application, the CO2 detection threshold was fixed at about 400 ppm corresponding to atm. concn. and was successfully reached for a cell length of 1.5 cm with a resoln. of about 5​%. The sensitivity of the setup is mainly related to the size of the cell, deliberately reduced to develop a robust and compact system for natural geol. sites.

An overview of micro-force sensing techniques

Abstract: Due to the trend of miniaturization of devices, micromanipulation has been a hot topic in the last two decades. Unlike the macro world, the micro object is easy to be damaged if the contact force is not reliably detected and controlled. Hence, micro-force sensing is of great importance in micromanipulation, microassembly, medical applications, biomedical applications, materials science, dimension measurements and MEMS/NEMS for protecting micro-parts and micro-gripper from being damaged and ensuring the success of the manipulation process. This paper presents a survey of the recent methods of micro-force sensing. The working principle, detection accuracy, advantage and disadvantage of seven widely used force sensing methods are presented. Typical applications of each method in micro-assembly and micromanipulation are discussed. In addition, the comparisons among different kinds of force sensing approaches have been addressed. Moreover, another five promising micro-force sensing methods, which are confined to special component measurements or not widely used, are briefly introduced. Furthermore, two popular types of commercial micro-force sensors are listed to provide a guideline of selection for a specific application. The presented state-of-the-art overview is helpful to those engaged in micro-force sensing area to know the recent development and research tendency on micro-force sensing.

A precise embedded curvature sensor module for soft-bodied robots

Abstract: As an emerging field, soft-bodied robots require profoundly different approaches to sensing and actuation compared to their rigid-bodied counterparts. Electro-mechanical design, fabrication, and operational challenges due to material elasticity significantly complicate embedded, modular and precise proprioceptive feedback. This work presents a novel curvature sensor module to address the unique soft robotic specifications. The proposed device utilizes a magnet and an electronic Hall effect sensing component to accurately measure curvatures on a soft-bodied bending segment on a flexible circuit board, ensuring contact-free sensing. We verify performance of sensor modules on static and dynamic bending deformations based on a single initial calibration step. To the best of our knowledge, the presented device is the first modular and integrated soft-bodied sensor design that is demonstrated to be accurate up to 7.5 Hz with a root mean square error of 0.023 cm −1 between measured and actual curvature without filtering out the intrinsic noise, and available for use with soft-bodied kinematic bending chains.

Low frequency piezoelectric energy harvesting at multi vibration mode shapes

Abstract: A multi-degree of freedom micro-energy harvester has been designed, fabricated, and tested and sub 100 Hz natural frequencies have been achieved. This design's resonant frequencies at its first three mode shapes are within the low ambient vibration frequency range. The structure is fabricated from a silicon substrate with Aluminum Nitride (AlN) energy harvesting elements on thin silicon beams and uses a chip as a proof mass. The nonlinear stiffness due to stretching strain in the structure provides a wider harvestable frequency bandwidth in each mode. The nonlinear load-deflection equation for the second mode shape of the device, which corresponds to vertical oscillation and maximum harvester deflection, has been modeled using finite element simulation. The first three natural frequencies of 71.8, 84.5, and 188.4 Hz were measured experimentally for the presented harvester. A frequency bandwidth of 10 Hz has been obtained for the second mode shape under a base excitation of 0.2 g. A maximum open circuit voltage of 1 V and power output of 136 nW with a load resistance of 2 MΩ have been measured using this harvester. Using a synchronized switch harvesting on inductor (SSHI) electrical interface and Lead Zirconate Titanate (PZT), simulations estimate that the power output could be improved to ∼3.1 μW.

A force sensor based on three weakly coupled resonators with ultrahigh sensitivity

Abstract: A proof-of-concept force sensor based on three degree-of-freedom (DoF) weakly coupled resonators was fabricated using a silicon-on-insulator (SOI) process and electrically tested in 20 μTorr vacuum. Compared to the conventional single resonator force sensor with frequency shift as output, by measuring the amplitude ratio of two of the three resonators, the measured force sensitivity of the 3DoF sensor was 4.9 × 106/N, which was improved by two orders magnitude. A bias stiffness perturbation was applied to avoid mode aliasing effect and improve the linearity of the sensor. The noise floor of the amplitude ratio output of the sensor was theoretically analyzed for the first time, using the transfer function model of the 3DoF weakly coupled resonator system. It was shown based on measurement results that the output noise was mainly due to the thermal–electrical noise of the interface electronics. The output noise spectral density was measured, and agreed well with theoretical estimations. The noise floor of the force sensor output was estimated to be approximately 1.39nN for an assumed 10 Hz bandwidth of the output signal, resulting in a dynamic range of 74.8 dB.

Smart artificial muscle actuators: Liquid crystal elastomers with integrated temperature feedback

Abstract: We present a smart, thermally stimulated liquid crystal elastomer actuator with an integrated heater and temperature sensor based on deformable polyimide wiring technology. Due to optimal thermal contact to the active material, heating from room temperature to the point of maximum contraction takes only 19.6 s; cooling requires only 5.6 s. The integrated temperature sensor allows closed-loop operation and characterize the thermomechanical properties of the material: open-loop positioning precision was found to be better than 45 μm and no inherent drift or hysteresis were observed. The maximum force generated by the actuator was 133 mN, corresponding to 76 kPa of stress. This ultra-compact actuator with integrated feedback is useful in applications that require large stroke in confined space.

Analytical modeling, simulations and experimental studies of a PZT actuated planar valveless PDMS micropump

Abstract: This paper presents analytical modeling, 3-D electro-fluid–structural simulations, fabrication and test of a piezoelectrically actuated PDMS based planar valveless micropump. The analytical model considers force balance in the nozzle-diffuser elements and at the fluid–membrane interface to predict the natural frequency and flow rate performance of the proposed micropump. The numerical model employs two-way fluid–structure coupling to represent fluid–structure interaction (FSI) between the membrane and working fluid by mapping displacement data from the membrane to the fluid and force data from the fluid to the surface of the membrane. Also, electro-structure coupling between deformation of a piezoelectric disk due to an applied voltage and resulting displacement of the membrane is considered. Based on the simulations, the circular shape of the chamber used in conventional micropump designs is modified to include a taper at the outlet, which provides a significant improvement (∼28%) in the flow rate. Numerical simulations are performed to study the effects of the nozzle-diffuser angle and size, chamber diameter and height and membrane diameter and thickness on the flow rate. Using simulation results, a suitable design of the micropump is identified and the proposed micropump is fabricated. Experiments are performed to study the effect of frequency and voltage on the flow rate and pressure-flow characteristics. The predictions of the analytical model and numerical simulations in terms of flow rate versus frequency and voltage and pressure-flow characteristics compare well with the corresponding experimental data (within 20%). Using a peak-to-peak voltage of 30 V, the micropump delivers a maximum flow rate of 20 μL/min and back pressure of 220 Pa. The proposed micropump is polymer based and thus suitable for low-cost and disposable applications.

Modeling and identification of asymmetric Bouc–Wen hysteresis for piezoelectric actuator via a novel differential evolution algorithm

Abstract: A novel modified Bouc–Wen (MBW) model is presented in this paper to describe the asymmetric hysteresis of piezoelectric actuator, and the parameter identification method is proposed based on a novel modified differential evolution (MDE) algorithm. In the MBW model, a polynomial-based non-lag component is used to realize the asymmetric hysteresis property. In the proposed MDE algorithm, a comprehensive trial vector generation strategy and the initial control parameters are investigated to balance the global and local search ability. The MDE-based parameter identification is compared with the classical differential evolution algorithm and the particle swarm optimization algorithm. The results demonstrate that the proposed MDE is superior to its competitors for identifying the asymmetric hysteresis of piezoelectric actuator.

High resolution microwave microstrip resonator for sensing applications

Abstract: A microwave planar resonator with a very high quality factor is presented for sensing applications. The proposed resonator uses an active feedback loop with a microwave amplifier to generate negative resistance to compensate the resonator's loss and increases the loaded quality factor of the system. This high quality resonator is based on a planar microstrip resonator with a primary quality factor of 200. The active loop technique increases the primary quality factor up to 15,480 with no other material in its surrounding environment when measured at 1.55 GHz resonance frequency. The high quality factor of the designed resonator provides very high resolution for detection of permittivity variation in its ambient environment with a theoretical resolution of 0.1 ppb (10−10). It is experimentally demonstrated that the small permittivity variations such as that of foam (with permittivity very close to air) can be detected. The circuit demonstrated a resolution of 26 dB in amplitude for a 1 MHz variation in the frequency domain.

Design and optimization of piezoelectric impact-based micro wind energy harvester for wireless sensor network

Abstract: The purpose of the current study is to design and optimize a piezoelectric impact-based micro wind energy harvester (PIMWEH) as a power source for wireless sensor networks. First, using new PIMWEH design, numerical simulation, and experimental comparison analysis, we determined the most durable PIMWEH shape for application as a power source of WSNs. The experimental results show that the optimized PIMWEH generated 2.8 mW (RMS value) and did not crack within 40 h. Second, to supply power for sensor operation, we performed an experiment using a rectifying circuit, an AC–DC converter, and an electrical charger. The experimental results show a pure DC voltage signal of 3.3 V, and the output power was 1.0 mW (3.1 mW/cm3). A charging energy of 0.845 J was obtained in 24 min. Third, we calculated the efficiency of the PIMWEH to evaluate its performance. Using a three-step energy conversion process (using wind turbine, PZT, and LTC3588-1), an overall PIMWEH power conversion efficiency of 3.2% was obtained. For one day, the PIMWEH could supply power that is 6263–25055 times the power requirement of a commercialized ZigBee transmission. In addition, transmitting signals at intervals from 3.4 to 13 s was made possible.

Design and control of a novel compliant differential shape memory alloy actuator

Abstract: This paper presents the design and control of a novel compliant differential shape memory alloy (SMA) actuator with significantly improved performance compared to traditional bias and differential type SMA actuators. This actuator is composed of two antagonistic SMA wires and a mechanical joint coupled with a torsion spring. The differential SMA wires are utilized to increase the response speed, and the torsion spring is employed to reduce the total stiffness of SMA actuator and improve the output range. Theoretical models that include the stiffness equations of the SMA wire as well as the dynamics of three different SMA actuation systems are introduced and compared. Simulation and experimental results have proved that this new actuator can provide larger output angle compared to conventional SMA actuators under the same conditions. Moreover, regulation and tracking control experiments have demonstrated that this compliant differential SMA actuator achieves higher response speed compared to the bias SMA actuator using compatible PI controller. The tracking performance is further improved by the saturated PI controller.

Deep ultraviolet photodiodes based on the β-Ga2O3/GaN heterojunction

Abstract: A deep ultraviolet (UV) photodiode was fabricated using a heterojunction between β-Ga2O3 and GaN, and its UV sensitivity was investigated. A thin β-Ga2O3 layer was prepared on p-type GaN template substrate by gallium evaporation in oxygen plasma. The β-Ga2O3 layer had a (−2 0 1)-oriented crystal structure on (0 0 1) GaN. A device based on the β-Ga2O3/GaN heterojunction exhibited good rectifying properties. Under reverse bias, the current increased linearly with an increase in the deep-UV light intensity. The responsivity of the photodiode was highest under deep-UV light below a wavelength of 240 nm. The response time of the photodiode to deep-UV light was in the order of sub-milliseconds.

Size-dependent electromechanical buckling of functionally graded electrostatic nano-bridges

Abstract: This study explored the electromechanical buckling (EMB) of beam-type nanoelectromechanical systems (NEMS) by considering the nonlinear geometric effect and intermolecular forces (Casimir force and van der Walls force) based on modified couple stress theory. To model the system, a slender nanobeam made of functionally graded material (FGM) with clamped-guided boundary conditions, which is under compressive or tensile axial loads as well as symmetric and nonlinear electrostatic and intermolecular transverse loads, is used. Considering the Euler–Bernoulli beam theory and using the principle of minimum potential energy and the variational approach, the governing equation as well as the related boundary conditions is derived. To discretize the equation and its related boundary conditions, and to solve the equations, the generalized differential quadrature method (GDQM) is employed. Finally, after validation of the results, the effects of size, length, power law index, and the distance between the two fixed and movable electrodes on the bucking of the system are discussed and examined.

Multiple cracks detection and visualization using magnetic flux leakage and eddy current pulsed thermography

Abstract: This paper investigates two non-destructive evaluation methods, magnetic flux leakage (MFL) and eddy current pulsed thermography (ECPT), for both artificial and natural multiple cracks (MC) detection and visualization. The detection capability and characteristics of MC visualization are verified and compared through simulations and experiments. Results show that, MFL testing reflects the surface shapes and orientations of MC by 3D magnetic field imaging. However, it is unable to evaluate the depth of artificial MC and detailed surface shapes of natural MC due to limitations of sensor array spatial resolution. ECPT shows more capability in MC visualization in detail from thermal images. The obtained thermal image sequences from ECPT demonstrate rich transient and pattern information to evaluate MC geometrical features. After discussion of the two methods with the probability of detection (POD) analysis, a promising new sensing structure which potentially combines both advantages of them is proposed to enhance the NDE performance for MC evaluation.

Kinetic energy harvesting from human walking and running using a magnetic levitation energy harvester

Abstract: For the first time, the power output of an electromagnetic magnetic levitation vibration energy harvester was studied when placed on 10 human participants while walking and running on a treadmill from 2 mph (3.2 km/h) to up to 7 mph (11.3 km/h). The power generated from the device when participants walked at 3 mph (4.8 km/h) averaged 71 μW. When running at 6 mph, the power increased to 342 μW. The testing on participants revealed that due to unique gaits and body structure, acceleration spectrum and damping can vary significantly between participants. Taller participants had a lower step frequency and therefore lower frequency acceleration content, signifying that a single design may not be optimal for all participants. Additionally, the estimated damping force varied largely between participants, from 3 to 8 mN. To minimize the effects of damping, the paper studies the effect of angle of attachment and damping reduction techniques using low friction materials and a guide rail system, which improve power output by over 50% when compared to the sub-optimal design.

Highly sensitive fast-response UV photodiode fabricated from rutile TiO2 nanorod array on silicon substrate

Abstract: An ultraviolet photodiode based on rutile TiO2 nanorods, which were grown on p-type Si substrate seeded with a TiO2 layer, was synthesized by radiofrequency reactive magnetron sputtering. Chemical bath deposition was performed to grow rutile TiO2 nanorods. X-ray diffraction and field emission-scanning electron microscopy were conducted to determine the structural and optical properties of the sample. The synthesized TiO2 nanorods exhibited tetragonal rutile structure. The device showed 3.79 × 102 sensitivity when it was exposed to 325 nm light (1.6 mW/cm) at 5 V bias voltage. In addition, the internal gain of the photosensor was 4.792 and the photoresponse peak was 460 mA/W. The photocurrent was 6.09 × 10−4 A. The response and recovery times of the PD were 50.8 and 57.8 ms, respectively, upon illumination of a pulsed UV light (325 nm, 1.6 mW/cm2) at 5 V bias voltage.

An electrostatically driven 2D micro-scanning mirror with capacitive sensing for projection display

Abstract: Bi-axial or two-dimensional (2D) MEMS micro-scanning mirrors (or micro-scanners) are considered the key component for laser scanning projectors. Many studies have shown the mechanical characterization of fabricated devices driven by various mechanisms. This work presents an electrostatically driven bi-axial micro-scanner with capacitive position sensing for Lissajous scanning projection. With the added sensing capability, a PLL (phase-locked loop)-based oscillator loop is developed to sustain mechanical resonance and to provide mirror position information, which are equally important for practical applications. The micro-scanner and the required circuits are implemented using bulk micromachining SOI (silicon on insulator) and 0.35-μm CMOS (complementary metal oxide semiconductor) technologies, respectively. The measured resonant frequencies of the bi-axial micro-scanner for the slow and fast-axis scans are 1.4 and 21.9 kHz, and the associated optical scan angles are 22.5° and 40°, respectively, under pulse modulation of 48 and 115 V pp . The fabricated micro-scanner is adopted in a laser beam scanning projection system to achieve WVGA (852 × 480) display resolution.

An eight-position self-calibration method for a dual-axis rotational Inertial Navigation System

Abstract: An eight-position self-calibration method for a dual-axis rotational Inertial Navigation System (INS) is provided in this paper. By experiencing two more positions with tilt attitudes than those experienced in a conventional six-position method, not only constant biases, scale factor errors, and misalignment errors, but also g-dependent biases can be calibrated. Field tests indicate that, after the calibration and compensation of the g-dependent biases, both a latitude error and a longitude error remain within a small range over time. In contrast, by using the conventional six-position method, a latitude error is several times larger and a longitude error diverges rapidly over time. Compared with the six-position method, accuracy of the dual-axis rotational INS is significantly improved more than 50% by the eight-position self-calibration method. The self-calibration method is feasible both in static and over a ship at the dockside.

Cladless few mode fiber grating sensor for simultaneous refractive index and temperature measurement

Abstract: In this work, we have demonstrated a cladless few-mode fiber grating sensor for simultaneous measurement of refractive index (RI) and temperature. The proposed sensor is fabricated from an etched few-mode Fiber Bragg Grating (FMFBG) that can support two Bragg wavelengths, in which the sensitivities for each Bragg wavelength to the changes of RI and temperature are different. A mode coupling theory is used to describe the sensing principle of the proposed sensor and the simulation result finding that an etched diameter of 14.1 μm can get the better performance for optimal the power confinement of etched FMFBG. Experimental results show that the proposed sensor has the RI sensitivities for both λ 01 and λ 11 are estimated to be 1.183 nm/RIU and 4.816 nm/RIU respectively, and temperature sensitivities for λ 01 and λ 11 are 9.62 ± 0.08 pm/°C and 9.52 ± 0.13 pm/°C respectively. With the assistance of 3 × 3 characteristic matrix, discrimination measurements of temperature and RI has been demonstrated and the deviations in RI and temperature measurements are ±8 × 10 −4 RIU and ±1 °C respectively.

A highly sensitive Mach–Zehnder interferometric refractive index sensor based on core-offset single mode fiber

Abstract: A highly sensitive refractive index (RI) sensor based on all-fiber Mach–Zehnder interferometer (MZI) was simulated and demonstrated. It was fabricated by splicing a section of single mode fiber (SMF) between two SMFs with a slight core offset at two splicing joints, which were used to excite cladding modes and couple the core mode to cladding modes. And then the interference between the core and cladding modes was utilized to measure sounding RI and the sensitivity of the sensor was enhanced by tapering fiber. Experimental results showed that the measured RI sensitivity could be up to 78.7 nm/RIU in the range of 1.333–1.374. Meanwhile, the sensor has the advantages of simple structure, small size, high sensitivity and low cost.

High quality barium titanate nanofibers for flexible piezoelectric device applications

Abstract: Piezoelectric and ferroelectric nanostructures and devices have attracted extensive attention because they can realize the conversion between mechanical and electrical energies for sensors and energy harvesting applications. In the present work high quality lead-free BaTiO 3 nanofibers were obtained by a sol-gel based electrospinning technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and piezoresponse force microscopy (PFM) were utilized to characterize the morphologies, phase and domain structures along with the nanoscale electromechanical response. Well-crystallized BaTiO 3 fibers were obtained with good local piezoelectric response ( d 33,eff of ∼40 pm/V using PFM). Further, a flexible piezoelectric device was fabricated by combining aligned BaTiO 3 nanofibers and a PDMS polymer matrix. An inter-digital electrode on a flexible substrate was incorporated to enhance the output signal. The proposed device displayed an output peak–peak voltage of ∼0.45 V at a load resistance of 1 MΩ under a periodic bending excitation of ∼45 Hz. It has the advantages of small-size, ease of processing, high flexibility and strain tolerance, and high-sensitivity to external vibration at low-frequency which may open up a range of new applications.

Optimization of power consumption for gas sensor nodes: A survey

Abstract: The Wireless Sensor Network (WSN) technology has recently been used, rather successfully, in a huge number of monitoring applications. However, the monitoring of combustible gases with WSN stands out from typical applications where the wireless communications function is much more power hungry than the sensing one. The reason behind this “dissonance” is in using catalytic or semiconductor sensors that ensure a trade-off among the safety requirements, performance and power consumption. This work provides a survey of intrinsic power optimization techniques with a special focus on recent advances in power management, sensor fabrication, sensing circuits, and measurement procedures. The paper concludes with providing a future outlook in the area.