Showing papers in "Sensors and Actuators A-physical in 2004"
TL;DR: In this article, the design of miniature generators capable of converting ambient vibration energy into electrical energy for use in powering intelligent sensor systems is described and experimental results are described and test results presented.
Abstract: This paper describes the design of miniature generators capable of converting ambient vibration energy into electrical energy for use in powering intelligent sensor systems. Such a device acts as the power supply of a microsystem which can be used in inaccessible areas where wires can not be practically attached to provide power or transmit sensor data. Two prototypes of miniature generator are described and experimental results presented. Prototype A is based around two magnets coupled to a coil attached to a cantilever; prototype B is based around four magnets. For prototype A, experimental results are given for its resonant frequency and its open circuit and loaded output as a function of vibration amplitude. For prototype B, experimental results are given for the generator's Q factor in air and vacuum, its output voltage as a function of vibration amplitude as well as its magnetic field strength. This generator has been tested on a car engine and shown to produce a peak power of 3.9 mW with an average power of 157 micro watts.
800 citations
TL;DR: In this paper, some critical issues and problems in the development of TiNi thin films are discussed, including preparation and characterization considerations, residual stress and adhesion, frequency improvement, fatigue and stability, modeling of behavior as well as functionally graded or composite thin films.
Abstract: TiNi thin films have attracted much attention in recent years as intelligent and functional materials because of their unique properties. TiNi thin film based micro-actuators will become the actuator of choice in many aspects in the rapidly growing field of micro-electro-mechanical systems (MEMSs). In this review paper, some critical issues and problems in the development of TiNi thin films are discussed, including preparation and characterization considerations, residual stress and adhesion, frequency improvement, fatigue and stability, modeling of behavior as well as functionally graded or composite thin films. Comparison is made of TiNi SMA micro-actuation with other micro-actuation methods. Different types of TiNi thin film based microdevices, such as microgrippers, microswitches, microvalves and pumps, microsensors, etc. are also described and discussed.
743 citations
TL;DR: In this paper, the authors describe the analysis, simulation and testing of a microengineered motion-driven power generator, suitable for application in sensors within or worn on the human body.
Abstract: This paper describes the analysis, simulation and testing of a microengineered motion-driven power generator, suitable for application in sensors within or worn on the human body. Micro-generators capable of powering sensors have previously been reported, but these have required high frequency mechanical vibrations to excite a resonant structure. However, body-driven movements are slow and irregular, with large displacements, and hence do not effectively couple energy into such generators. The device presented here uses an alternative, non-resonant operating mode. Analysis of this generator shows its potential for the application considered, and shows the possibility to optimise the design for particular conditions. An experimental prototype based on a variable parallel-plate capacitor operating in constant charge mode is described which confirms the analysis and simulation models. This prototype, when precharged to 30 V, develops an output voltage of 250 V, corresponding to 0.3J per cycle. The experimental test procedure and the instrumentation are also described.
598 citations
TL;DR: In this article, the capacitance between the two comb electrodes of a periodic interdigital capacitive sensor, based on conformal mapping techniques, is analyzed for any space and finger width as well as for any number of layers with different thickness and permittivity.
Abstract: The widespread use of interdigital electrodes in such applications as microwave filters, surface acoustic wave devices, electro-optic shutters as well as on chemical and biological sensing and even on the electrical and dielectric characterization of materials requires that we improve our description of their electrical performance. In this paper, we present new analytical expressions for the capacitance between the two comb electrodes of a periodic interdigital capacitive sensor, based on conformal mapping techniques. This proposed model is general and quite independent of the particular application and can be applied for any space and finger width as well as for any number of layers with different thickness and permittivity. The capacitance for a particular sensor configuration is a function of the dielectric permittivity of the materials, the fingers length and of two geometric non-dimensional parameters: (i) the ratio between the space and finger widths; (ii) the ratio between the thickness of the sensitive layer and the spatial sensor wavelength. Comparisons with previously published models as well as with experimental data and finite element analysis were made.
394 citations
TL;DR: In this paper, a 5mm diameter triaxial force sensor was developed for minimally invasive robotic surgery, which has a range of 2.5 n in axial direction and 1.7 n in radial direction.
Abstract: A 5 mm diameter tri-axial force sensor has been developed for minimally invasive robotic surgery. To define the required force range and resolution, a needle driver has been equipped with strain gauges. In vivo tests with different types of needles and tissue show that the required force range and resolution are, respectively, 2.5 N and 0.01 N. The new sensor is based on a flexible titanium structure of which the deformations are measured through reflective measurements with three optical fibres. It has a range of 2.5 N in axial direction and 1.7 N in radial direction.
354 citations
TL;DR: In this article, the use of highly stable ionic liquids to replace water is explored, which is due to the chemical breakdown of the water at relatively low operating voltages and the loss of water to evaporation when these devices are operated in air, causing a corresponding loss of performance.
Abstract: Nafion™membranes are known to operate as electromechanical actuators and sensors. The transduction in the material is caused by redistribution of the mobile cations in the material, which is made possible because the material is saturated with a solvent. Typically, the solvent used is water, although its use limits the performance of these materials. This is due to the chemical breakdown of the water at relatively low operating voltages and the loss of the water to evaporation when these devices are operated in air, causing a corresponding loss of performance. In the current work, the use of highly stable ionic liquids to replace water is explored. Ionic liquids have the advantage of greater electrochemical stability than water, thus offering the possibility of higher actuation voltages for these materials. Also, ionic liquids are known to be non-volatile and therefore will not evaporate out of the polymer as water will. In this work, the use of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid is demonstrated as a viable solvent for Nafion™polymer actuators and sensors. This ionic liquid melts at −9 °C and has an electrochemical stability Window of 4.1 V [Inorg. Chem. 35 (1996) 1168], making it a promising candidate to replace water in ionic polymer transducers. Experimental results indicate that Nafion™transducers solvated with this ionic liquid have improved staility when operated in air as compared to the same materials solvated with water, although the magnitude of the response is decreased as compared to the water samples at high frequencies. The main drawback associated with the use of ionic liquids is a reduction in the speed of the response as compared to water, although the initial results are promising and demonstrate the potential for this approach.
348 citations
TL;DR: In this article, a model describing the microstructure providing extremely strong and reversible tenso-resistive and piezo-resistant effects is proposed on the basis of atomic force microscopy of the conductive surface network of the composite.
Abstract: Electrically conductive polymer composites (ECPC) are shown as prospective large-size flexible pressure and stretch sensors for detecting of dangerous deformations and vibrations of vehicle parts. Reversible change of resistance dependent on stretch and pressure is obtained in electro-conductive polymer nanocomposites. At certain concentrations of carbon nano-particles a change of electrical resistance by more than four orders is observed at 40% relative stretch. The maximum sensitivity of nanocomposites is observed in the vicinity of the transition of electro-conductive percolation. Nanocomposites exhibit a very weak semiconductor-like temperature dependence of resistance. The tenso-resistive and piezo-resistive effects are found to be practically thermally stable in the region of 20–70 °C. A model description of the microstructure providing extremely strong and reversible tenso-resistive and piezo-resistive effects is proposed on the basis of atomic force microscopy of the conductive surface network of the composite. Reversibility of the effects is explained by higher mobility and stronger adhesion of carbon nano-particles to the polymer matrix compared to cohesion between them. The experimental data for tensile strain are in good agreement with theoretical equations derived from a model based on the change of particle separation under applied stress.
340 citations
TL;DR: In this paper, a hollow microneedle array with integrated, fluidic microchannels was used to extract interstitial fluid from human skin and verified by the in situ measurement of glucose concentration.
Abstract: This paper presents the design, fabrication and testing of a hollow microneedle array with integrated, fluidic microchannels. The microneedles are machined from single crystal silicon to a shank height of 250–350 μm with 300 μm center-to-center spacing. The needle size, density and shape are controlled by independent processing steps. Piercing of the protective stratum corenum layer of the skin by the microneedles, providing access to the living epithelial layers underneath, is successfully demonstrated. Filling of the integrated microchannels by capillary action with both non-biological fluids (glycerol, ethanol, surrogate interstitial fluid (ISF) and water) as well as biological fluids (ISF and whole blood) is demonstrated. The ability to extract interstitial fluid from human skin is successfully achieved and verified by the in situ measurement of glucose concentration. The microchip presented here represents the first step towards the realization of a transdermal, ISF extraction and analysis microsystem.
312 citations
TL;DR: In this article, textile sensors for the equipment of a wireless monitoring suit are presented for the monitoring of electrocardiogram (ECG) and respiration rate of children in a hospital environment.
Abstract: In this paper, we present textile sensors for the equipment of a wireless monitoring suit. The suit is intended for the monitoring of electrocardiogram (ECG) and respiration rate of children in a hospital environment. Special attention is given to the dedicated sensor interface circuits. The sensors, which are entirely fabricated out of textile, are integrated in a prototype belt of the monitoring suit. The complete suit will not contain only the sensors, but also the interface, data handling, storage and transmission electronics. Therefore, distributed, miniaturized circuitry, textile interconnections, a textile antenna and hermetic packaging are developed.
311 citations
TL;DR: In this article, a finite element (FE) model was developed to design and optimize pMUTs for the operating range of 2-10 MHz in water and having maximized energy coupling coefficient.
Abstract: Piezoelectric micromachined ultrasonic transducers (pMUTs) are an example of the application of MEMS technology to ultrasound generation and detection, which is expected to offer many advantages over conventional transducers. In this work, we investigate pMUTs through novel design and fabrication methods. A finite element (FE) model, with original tools to measure device performance, was developed to design and optimize pMUTs. A pMUT for the operating range of 2–10 MHz in water and having maximized energy coupling coefficient was modeled, designed, fabricated, and tested for its resonance frequency and coupling coefficient. The model predictions for the resonance frequency were in excellent agreement with the measured values, but not as good for the coupling coefficient due to the variability in the measured coupling coefficient. Compared to conventional ultrasonic transducers, pMUTs exhibit superior bandwidth, in excess of 100%, and offer considerable design flexibility, which allows their operation frequency and acoustic impedance to be tailored for numerous applications.
276 citations
TL;DR: In this paper, a comparative study of two different electromechanical systems is presented in order to conceive autonomous portable generators capable of harvesting human mechanical energy, and the analytical models described in this paper present a high similarity and a duality in signal levels, adapted load and optimal working frequency, the two latters corresponding to the maximal electrical power generated.
Abstract: This paper presents the comparative study of two different electromechanical systems, in order to conceive autonomous portable generators capable of harvesting human mechanical energy. The first one is an electromagnetic system, made of a magnet in translation within a coil. The second one is a piezoelectric system, which is a PZT ceramic bar, polarised longitudinally, embedded at one end and constrained at the other end. The analytical models described in this paper present a high similarity and a duality in signal levels, adapted load and optimal working frequency, the two latters corresponding to the maximal electrical power generated.
TL;DR: In this article, an improved micro-scale thermoelectric generator (μ-TEG) is proposed based on polysilicon surface micromachining and is designed to convert waste heat into electrical power.
Abstract: As the power consumption of a large number of microelectronic devices has been continuously reduced in recent years, power supply units of a few microwatts have become sufficient for their operation. Our improved micro-scale thermoelectric generator (μ-TEG) is based on polysilicon surface micromachining and is designed to convert waste heat into electrical power. Since this device is compatible with standard CMOS fabrication processes, it can be easily integrated on chip level and matches the needs for low-cost and small-size systems. As thermoelectric materials, both, pure poly-Si and poly-Si 70% Ge 30% have been investigated. Emphasis was placed on a thermally optimized design and the reduction of the total electrical resistance of the generator. As a result of these improvements, a voltage of 5 V and an electrical power output of 1 μW for a matched consumer is achieved with generators of 1 cm 2 in size at a temperature drop of about 5 K.
TL;DR: In this paper, a novel microfabrication technology of 3D microstructures with inclined/rotated UV lithography using negative thick photoresist, SU-8, was presented.
Abstract: This paper presents a novel microfabrication technology of three-dimensional (3D) microstructures with inclined/rotated UV lithography using negative thick photoresist, SU-8. In exposure process, a photomask and a SU-8 coated substrate are fixed together, and tilted or tilted and rotated to a UV source. The reflected UV at the interface between the resist and the substrate is also exploited as well as the incident UV. With the 3D microfabrication technology, various 3D microstructures are easily fabricated such as oblique cylinders, embedded channels, bridges, V-grooves, truncated cones, and so on. The angles between fabricated structures and normal lines are 19.5°, when the incident angle of UV in air is 32°. Thus, the refractive index of SU-8 and the maximum refractive angle at the interface between SU-8 and air are expected about 1.6 and 39°, respectively.
TL;DR: In this article, an inductive power system is presented, capable of remotely powering implantable monitoring and stimulating devices, with an efficiency of 36% over a distance of 3 cm. Optimisation of the power transfer efficiency and the misalignment tolerance was obtained using a self developed design tool.
Abstract: An inductive powering system is presented, capable of remotely powering implantable monitoring and stimulating devices. The system is capable of delivering at least 50 mW, with an efficiency of 36% over a distance of 3 cm. The power transfer frequency is 700 kHz. Optimisation of the power transfer efficiency and the misalignment tolerance was obtained using a self-developed design tool. Bi-directional data-transmission is integrated in the system: amplitude modulation is applied for the downlink transmission, absorption modulation for the uplink transmission. Our new system is capable of transmitting data at a maximal bit rate of 60,000 bits/s.
TL;DR: In this paper, an analytical approach to the static, dynamic, and stability analysis of the microstructures subjected to electrostatic forces is presented, which has the advantages of full analytical description, explicit physical meanings, and agrees well with the reality under small deflection.
Abstract: An analytical approach to the static, dynamic, and stability analysis of the microstructures subjected to electrostatic forces is presented in this paper. The present model has the advantages of full analytical description, explicit physical meanings, and agrees well with the reality under small deflection. The stiffness of a microstructure will be softened periodically with the frequency of applied voltage and the variation increases with increasing the magnitude of applied voltage. The dynamic instabilities may occur below the pull-in voltage. The instable regions appear not only near the multiples of resonant frequencies but also near some fractions of resonant frequency differences. Furthermore, the instable regions expand with increasing the applied voltage.
TL;DR: In this article, a SU-8-based polymerase chain reaction (PCR) chip with integrated platinum thin film heaters and temperature sensor is presented, which is capable of fast thermal cycling.
Abstract: We present a SU-8 based polymerase chain reaction (PCR) chip with integrated platinum thin film heaters and temperature sensor. The device is fabricated in SU-8 on a glass substrate. The use of SU-8 provides a simple microfabrication process for the PCR chamber, controllable surface properties and can allow on chip integration to other SU-8 based functional elements. Finite element modeling (FEM) and experiments show that the temperature distribution in the PCR chamber is homogeneous and that the chip is capable of fast thermal cycling. With heating and cooling rates of up to 50 and 30 °C/s, respectively, the performance of the chip is comparable with the best silicon micromachined PCR chips presented in the literature. The SU-8 chamber surface was found to be PCR compatible by amplification of yeast gene ribosomal protein S3 and Campylobacter gene cadF. The PCR compatibility of the chamber surfaces was enhanced by silanization.
TL;DR: In this paper, a new masking technique for glass etching in concentrated hydrofluoric acid (HF) was proposed, which was applied to fabricate microfluidic components for a micro-peristaltic pump to be integrated in a micro polymerase chain reaction (PCR) device.
Abstract: A new masking technology for wet etching of glass, to a depth of more than 300µm, is reported Various mask materials, which can be patterned by standard photolithography and metal etching processes, were investigated for glass etching in concentrated hydrofluoric acid (HF) A multilayer of metal, Cr/Au/Cr/Au, in combination with thick SPR220-7 photoresist, was found to be ideal for this purpose Through holes etched from both sides of a 500µm thick Pyrex glass wafer were obtained Pinholes, created in the glass by failure of simple metal masking when subjected to HF etching, were successfully eliminated using the new masking technology In addition, the lateral undercutting of glass caused by the under-etching of the Cr mask was minimized to 27% of the etching depth With these advantages, this newly developed masking method was successfully applied to fabricate microfluidic components for a micro-peristaltic pump to be integrated in a micro polymerase chain reaction (PCR) device These components include through holes for liquid accessing and electrical contacting and a 200µm thick pump diaphragm This new masking technology also adds to the methods available to fabricate the microfluidic devices in glass substrates
TL;DR: In this paper, a new wireless power technique for micro-systems based on low frequency ( −3 at 2-3 kG) was proposed. But this method is not suitable for large-scale systems.
Abstract: This paper presents a new wireless powering technique for microsystems based on low frequency ( −3 at 2–3 kG). Comparing with other remote powering techniques, this method possesses much higher voltage generation efficiency per generator volume.
TL;DR: The development of a self-powered system, specifically for sensor applications that can be energised on a test rig by an electromagnetic vibration-powered generator, that enables wireless operation without the use of a battery with a finite service life is detailed.
Abstract: Over recent years there has been a growing interest in the field of micro-systems and their applications across a wide range of areas, including sensor-based systems able to operate with full galvanic isolation. This paper details the development of a self-powered system, specifically for sensor applications that can be energised on a test rig by an electromagnetic vibration-powered generator. This enables wireless operation without the use of a battery with a finite service life. The results of two systems designed for remote sensing in condition monitoring applications are discussed. The first system uses a liquid crystal display to provide the system output; the second uses an infra-red link to transmit the data output.
TL;DR: In this article, the authors present an overview of optical fiber-optic intensity-based measurement and Fabry-Perot Interferometer (FPI) for vibration sensing.
Abstract: Vibration monitoring of machinery is reducing the overall operating costs of industrial plants. Conventional vibration sensors, based on capacitive or piezoelectric principles, are limited in application due to the problem of electrical isolation. Fibre-optic based instrumentation is thus an attractive alternative method of vibration measurement in the vicinity of electrical substation. This paper discusses several techniques of vibration sensing using optical fibre technology and assesses their potential for use on electromechanical equipment. Firstly an overview of sensor based on In-Fibre Bragg Gratings is presented, and its potential for the measurement of strain and vibration is assessed. Secondly, vibration sensing using fibre-optic intensity-based measurement is presented and then Fabry-Perot Interferometer (FPI) for vibration sensing is critically reviewed. Of these, the FPI is the most attractive since it can easily be configured within a reflective fibre-optic probe. However, reported FPI sensors have been highly sensitive to measurement errors caused by mechanical vibration, temperature, and acoustic waves. This paper reviews technological developments of FPI to vibration sensing in extreme electromechanical environments and also for non-contact measurement. Finally this paper presents an overview of dual-wavelength technique for assessment of vibration signature.
TL;DR: In this article, the authors investigated flow characteristics of low Reynolds number laminar flow through gradually expanding conical and planar diffusers and quantified the results from numerical analysis in terms of pressure loss coefficient.
Abstract: Flow characteristics of low Reynolds number laminar flow through gradually expanding conical and planar diffusers were investigated. Such diffusers are used in valveless micropumps to effect flow rectification and thus lead to pumping action in one preferential direction. Four different types of diffuser flows are considered: fully developed and thin inlet boundary layer flows through conical and planar diffusers. The results from the numerical analysis have been quantified in terms of pressure loss coefficient. The variation of pressure loss coefficient with diffuser angle is presented for Reynolds numbers of 200, 500 and 1000. The pressure loss coefficients have been used to calculate the diffuser efficiency for two different types of nozzle-diffuser elements. The general trend of variation of pressure loss coefficient with diffuser angle was found to be similar to that for high Reynolds number turbulent flow. However, unlike at high Reynolds numbers, pressure loss coefficients at low Reynolds numbers vary significantly with Reynolds number. It was also observed that trends of variation in the pressure loss coefficient with Reynolds number are different for small and large diffuser angles. Also, at low Reynolds numbers, the pressure loss coefficients for a thin inlet boundary layer are not always smaller than those for fully developed inlet boundary layer, in contrast to the behavior for high Reynolds number flows. Contrary to past claims, flow rectification is shown to be indeed possible for laminar flows. The two different types of nozzle-diffuser elements considered led to pumping action in opposite directions. Further, it was observed that flow rectification properties of both kinds of nozzle-diffuser elements improved with increasing Reynolds number.
TL;DR: In this article, a hybrid fluorescence detection microsystem by heterogeneous integration of a CdS thin-film filter, an (In, Ga)N thinfilm blue LED, and a disposable PDMS microfluidic device onto a Si PIN photodetector substrate is described.
Abstract: Microassembly of a hybrid fluorescence detection microsystem by heterogeneous integration of a CdS thin-film filter, an (In, Ga)N thin-film blue LED, and a disposable PDMS microfluidic device onto a Si PIN photodetector substrate is described. The CdS thin film filter was deposited directly onto a photodetector by pulsed-laser deposition. A thin-film (In, Ga)N LED was then transferred by a novel “pixel-to-point” laser lift-off process from the sapphire growth substrate to the silicon photodetector substrate. The final integration step was achieved by positioning a disposable polymer microfludic device onto the excitation/detection subsystem. Pixel-to-point transfer is potentially an enabling microassembly process for the fabrication of multicolor fluorescence-based bioassays and chemical detection microsystems.
TL;DR: A novel tactile sensor system, specifically designed to detect and quantify in real time tissue characteristics in a manner analogous to the human hand, is presented and suggested that it may prove useful in applications involving robotics in the biomedical field and can be incorporated in the next generation of virtual operating systems.
Abstract: A novel tactile sensor system, specifically designed to detect and quantify in real time tissue characteristics in a manner analogous to the human hand, is presented. To date, no modality that is capable of detecting the hardness and/or softness of tissues has been developed. The emerging requirement to build smart robotic manipulation for the next generation of virtual systems, incorporating hand-like-tactile feedback, continues to challenge developers in biomedical instrumentation. To satisfy this need we present a novel sensor system, consisting of a combination of a piezoelectric transducer (PZT) and a pressure sensor element. The system is designed with a feedback circuit, made with a disc-shaped PZT sensor element and a phase shift circuit acting as the oscillating circuit. Upon contact with a test object, this system responds to its physical properties by changing its resonance frequency in accordance with the object’s acoustic impedance. It is suggested that this sensor may prove useful in applications involving robotics in the biomedical field and can be incorporated in the next generation of virtual operating systems.
TL;DR: In this paper, a micromachined scanning probe cantilever was designed to be resonant at an exact integer integer multiple of the fundamental resonance frequency, which enables sensing of non-linear mechanical interactions between the atomically sharp tip at the free end of the cantilevers and a surface with unknown mechanical properties.
Abstract: We present a micromachined scanning probe cantilever, in which a specific higher-order flexural mode is designed to be resonant at an exact integer multiple of the fundamental resonance frequency. We have fabricated such cantilevers by reducing the stiffness of the third order flexural mode relative to the fundamental mode, and we have demonstrated that these cantilevers enable sensing of non-linear mechanical interactions between the atomically sharp tip at the free end of the cantilever and a surface with unknown mechanical properties in tapping-mode atomic force microscopy. Images of surfaces with large topographical variations show that for such samples harmonic imaging has better resolution than standard tapping-mode imaging.
TL;DR: In this article, a novel actuation mechanism is presented, which makes use of the antagonism of intrinsic magnetic and shape recovery forces acting on a ferromagnetic shape memory alloy (SMA) microactuator.
Abstract: A novel actuation mechanism is presented, which makes use of the antagonism of intrinsic magnetic and shape recovery forces acting on a ferromagnetic shape memory alloy (SMA) microactuator in a magnetic field. This mechanism is associated with large actuation and small biasing forces in each actuation direction resulting in a large stroke. Since no additional biasing elements are required, extremely compact designs are possible. As a demonstrator, an optical microscanner of 7 mm×3 mm×5 mm size is presented showing large scanning angles up to 120° in off-resonance mode. The scanning performance keeps frequency independent below a critical frequency, which is determined by heat transfer times.
TL;DR: In this article, a bridge-type flexure hinge mechanism was developed and optimized to amplify the displacement of a multilayer piezostack, which has a high amplification ratio in a relatively small size.
Abstract: A piezoelectric actuator using bridge-type flexure hinge mechanisms is developed and optimized to amplify the displacement of a multilayer piezostack. The developed hinge mechanism has three-dimensional structure to reduce its size, so it has a high amplification ratio in a relatively small size. The developed mechanisms are modeled by matrix methods assuming flexure hinges as 6 degree-of-freedom spring elements to show the validity of the proposed hinge mechanism. To verify the derived matrix model, displacement and frequency experiments are performed. The experimental result shows that the displacemental error between the matrix model and experiments is below 10%. This indicates that the deformation of the hinge in the parasitic direction should be considered for more exact estimation of the amplification of the bridge-type hinge mechanism. Using the developed matrix model, an optimization is performed to estimate the performance of the hinge mechanism.
TL;DR: In this article, a single-stage axial microturbine with a rotor diameter of 10 mm was developed for the first step in the development of a microgenerator that produces electrical energy from fuel.
Abstract: A single-stage axial microturbine has been developed with a rotor diameter of 10 mm. This turbine is a first step in the development of a microgenerator that produces electrical energy from fuel. The turbine is made of stainless steel using die-sinking electro-discharge machining. It has been tested to speeds up to 160,000 rpm and generates a maximum mechanical power of 28 W with an efficiency of 18%. When coupled to a small generator, it generates 16 W of electrical power, which corresponds to an efficiency for the total system of 10.5%.
TL;DR: In this paper, a new approach of enlarging the measurement range of a thermal calorimetric flow sensor is presented, based on the fact that the response of these kind of sensors tends to saturate at a certain flow ratio, so the widening of the flow range can be achieved by increasing the number of sensing elements of the sensor.
Abstract: A new approach of enlarging the measurement range of a thermal calorimetric flow sensor is presented. It is based on the fact that the response of these kind of sensors tends to saturate at a certain flow ratio, so the widening of the flow range can be achieved by increasing the number of sensing elements of the sensor. This implies only a redesign of the flow sensor device, which is fabricated with an existing standard low cost technology. This approach has been implemented achieving measurement ranges from 0.1 up to 8 SLM by placing three different pairs of sensing resistors on the same membrane. Characterisation results and a simulation-based procedure to design flow sensors according to specific applications are included.
TL;DR: In this paper, a tool-wear monitoring in a high-speed machining process on the basis of the analysis of different signals' signatures in the time and frequency domains is presented.
Abstract: The monitoring of high-speed machining processes is a key issue for ensuring better use of new machine-tool capabilities. An investigation of tool-wear monitoring in a high-speed machining process on the basis of the analysis of different signals’ signatures in the time and frequency domains is presented in this paper. Sensorial information from relevant sensors (i.e., dynamometer, accelerometer and acoustic-emission (AE) sensor) is compared and analyzed, assessing the deviation in representative variables in the time and frequency domains. The time- and frequency-domain analysis confirms the relevance of cutting-force and vibration signals’ signatures for tool-wear monitoring in high-speed machining (HSM) processes. Likewise, the spectrum analysis of AE signals corroborates that AE sensors are very sensitive to changes of tool condition, with increasing amplitudes of up to 160 kHz for worn tools.
TL;DR: In this article, the properties of a capacitance type thermally carbonized porous silicon (TC-PS) humidity sensor at room temperature have been reported, and the repeatability is excellent but the hysteresis above 60% of relative humidity should be reduced.
Abstract: We report the properties of a capacitance type thermally carbonized porous silicon (TC-PS) humidity sensor at room temperature. Several constructions to use porous silicon as a miniaturized humidity sensor material have been introduced earlier. In these applications, poor long-term stability of PS is most often improved by thermal oxidation. However, thermally carbonized PS surface has been found to be at least as stable in humid atmosphere, and in addition to that, the thermal carbonization also maintains the originally large specific surface area of PS. Indeed, our sensor shows good sensitivity over a wide range of relative humidity. The repeatability is excellent but the hysteresis above 60% of relative humidity should be reduced. The effect of measurement frequency on the sensitivity is also demonstrated.