Investigation of Ni-based thermal bimaterial structure for sensor and actuator application

Thermal bimaterial structures made of Ni and Ni-diamond nanocomposite for sensor and actuator application are proposed, fabricated, and tested. Two deflection types of thermal bimaterial structures, including upward and downward bending types, can be easily fabricated by controlling electroplating sequence of Ni and Ni-diamond nanocomposite. According to thermal performance measurement, the tip deflection of upward and downward types can reach about 82.5 μm and ?22.5 μm for a temperature change of 200 °C, respectively. In the condition, the thermomechanical sensitivity and output force are 412.5 nm/K and 97.0 μN for upward type thermal bimaterial structure; and ?112.5 nm/K and ?26.5 μN for downward type one. Due to the low electroplating process temperature (～50 °C) for both Ni-based layers, diminutive pre-deformation of as-fabricated structure and strong interlaminar bonding strength are verified by SEM and vibrational test. The resonant frequency of the structure remains unchanged after 10⁹ cycles.     

Spin-valve planar Hall sensor for single bead detection

The planar Hall effect (PHE) sensor with a junction size of 3 μm × 3 μm for a single micro-bead detection has been fabricated successfully using a typical spin-valve thin film Ta(5)/NiFe(16)/Cu(1.2)/NiFe(2)/IrMn(15)/Ta(5) nm. The PHE sensor exhibits a sensitivity of about 7.2 μV Oe^?1 in the magnetic field range of ±7 Oe approximately. We have performed an experiment to illustrated the possibility of single micro-bead detection by using a PHE sensor. A single micro-bead of 2.8 μm diameter size is secluded from 0.1% dilute solution of the Dynabeads^® M-280 dropped on the sensor surface and is located on the sensor junction by using a micro magnetic needle. The comparison of the PHE voltage profiles in the field range from 0 to 20 Oe in the absence and presence of a single micro-bead identifies a single Dynabeads^® M-280, the maximal signal change as large as ΔV ～ 1.1 μV can be obtained at the field ～6.6 Oe. The results are well described in terms of the reversal of a basic single domain structure.     

Development of an automation system to evaluate the three-dimensional oxygen distribution in wastewater biofilms using microsensors

In this paper the authors describe the development of an automation system applicable to environmental biofilm studies. The automation system controls a combined oxygen microsensor to measure the three-dimensional dissolved oxygen distribution in a wastewater biofilm sample. The biofilm is sampled from a rotating biological contactor in a municipal wastewater treatment plant. The automation system consists of a data acquisition system, a motion control system, and a computer program. The combined oxygen microsensor consists of a sensing electrode, a reference electrode, a guard cathode, an oxygen permeable membrane, and an electrolyte solution. The automation system allows the acquisition and storage of data from 4000 measurements from the microsensor and the precise positioning of the microsensor in order to measure 100 dissolved oxygen profiles in a 1000 μm × 1000 μm biofilm area. The three-dimensional profile shows that the dissolved oxygen concentration in the biofilm sample is highly heterogeneous and it revealed “pockets” of dissolved oxygen in deep sections of the biofilm sample. The automation system and the combined oxygen microsensor were proven to be tools that improve the quantity and quality of experimental results needed to understand important functions in biofilms used in wastewater treatment.     

Electroactive polymer based microfluidic pump

A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1 J/cm³ have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80 μm thick and 2.2 mm × 2.2 mm in lateral dimensions, showed an actuation deflection of 80 μm for an applied electric field of 90 MV/m. The microfluidic pump could pump methanol at a flow rate of 25 μl/min at 63 Hz with a backpressure of 350 Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively.     

Passive single chip wireless microwave pressure sensor

A novel micromachined passive wireless pressure sensor is presented. The device consists of a tuned circuit operating at 10 GHz fabricated on to a SiO₂ membrane, supported on a silicon wafer. A pressure difference across the membrane causes it to deflect so that an antenna circuit detunes. The circuit is remotely interrogated to read off the sensor data wirelessly. The chip area is 5 mm × 4 mm and the membrane area is 2 mm² with a thickness of 4 μm. Two on-chip passive resonant circuits were investigated: a meandered dipole and a zigzag antenna. Both have a physical length of 4.25 mm. The sensors show a shift in their resonant frequency in response to changing pressure of 10.28–10.27 GHz for the meandered dipole, and 9.61–9.58 GHz for the zigzag antenna. The sensitivities of the meandered dipole and zigzag sensors are 12.5 kHz/mbar and 16 kHz/mbar respectively.     

Analysis of high-Q,gallium nitride nanowire resonators in response to deposited thin films

Gallium nitride nanowires (GaN-NWs) are systems of interest for mechanical resonance-based sensors due to their small mass and, in the case of c-axis NWs, high mechanical quality (Q) factors of 10,000–100,000. We report on singly-clamped NW mechanical cantilevers of roughly 100 nm diameter and 15 μm length that resonate near 1 MHz and describe the behavior of GaN-NW resonant frequencies and Q factors following coating with various materials deposited by atomic layer deposition (ALD), including alumina (Al₂O₃), ruthenium (Ru), and platinum (Pt). Changes in the GaN-NW resonant frequencies with ALD deposition clearly distinguish conformal film growth versus island film growth. Conformal films lead to a stiffening of the NW and typically increase resonant frequency, whereas island films simply increase the NW mass and cause decreased resonant frequencies. We find that conformal growth of ALD alumina leads to stiffening of ～4 kHz per nm of alumina, in agreement with previously measured material properties. Conformal growth of Ru and Pt, respectively, qualitatively confirm our analytical predictions of positive and negative resonant frequency shifts. Island growth of ALD Ru has demonstrated a decrease in resonant frequency consistent with mass loading of ～0.2 fg for a 150 ALD-cycle film, also consistent with analytical predictions. Resonant Q factors are found to decrease with ALD film growth, offering the additional possibility of studying mechanical dissipation processes associated with the ALD-NW composite structures.     

A magnetoelectric energy harvester and management circuit for wireless sensor network

This paper presents an electromagnetic energy harvesting scheme by using a composite magnetoelectric (ME) transducer and a power management circuit. In the transducer, the vibrating wave induced from the magnetostrictive Terfenol-D plate in dynamic magnetic field is converged by using an ultrasonic horn. Consequently more vibrating energy can be converted into electricity by the piezoelectric element. A switching capacitor network for storing electricity is developed. The output of the transducer charges the storage capacitors in parallel until the voltage across the capacitors arrives at the threshold, and then the capacitors are automatically switched to being in series. More capacitors can be employed in the capacitor network to further raise the output voltage in discharging. For the weak magnetic field environment, an active magnetic generator and a magnetic coil antenna under ground are used for producing an ac magnetic field of 0.2–1 Oe at a distance of 25–50 m. In combination with the supply management circuit, the electromagnetic energy harvester with a rather weak power output (about 20 μW) under an ac magnetic field of 1 Oe can supply power for wireless sensor nodes with power consumption of 75 mW at a duration of 620 ms.     

A micro shear stress sensor based on laterally aligned carbon nanotubes

This paper reports the development of a micro thermal shear stress sensor that utilizes multiwalled carbon nanotubes as the sensing element. The sensor was fabricated by laterally aligning randomly distributed nanotubes into a 360 μm long and 90 μm wide conductive trace between two triangular shaped micro electrodes through the use of a high frequency AC electric field. During operation, the aligned nanotubes are electrically heated to an elevated temperature and surface shear stress is measured indirectly by the amount of convective heat transfer from the heated nanotubes to the surrounding fluid flow.The nanotube alignment process was primarily controlled by three different phenomena: dielectrophoresis, joule heating, and Brownian motion. Numerical simulations, together with experimental verifications, indicated that a successful alignment could only be realized if: (1) the dielectrophoretic force was positive, (2) the electro-thermal force was also positive, and (3) the dielectrophoretic force was high enough to overcome Brownian motion. The aligned nanotube trace has a room-temperature resistance of 580 Ω, which corresponds to a conductivity of 2.7 × 10⁴ S/m. The absolute temperature coefficient of resistivity ranges from 0.01 to 0.04% °C⁻¹. This is about one order of magnitude smaller than the highly doped polysilicon sensing material used in the MEMS micro shear stress sensor. The shear stress sensitivity of the nanotube trace operated at a 3% overheat ratio is found to follow the theoretical sensor power ∝ (shear stress)^1/3 relationship, provided the shear stress level is higher than 0.34 mPa. This result confirms the feasibility of using aligned multi-walled carbon nanotubes as a thermal shear stress sensing material.     

A MEMS-based resonant-scanning lamellar grating Fourier transform micro-spectrometer with laser reference system

A lamellar grating Fourier transform infra-red (FTIR) micro-spectrometer is presented in which the device is electromagnetically actuated in resonant mode so as to achieve larger displacements with a lower driving voltage. By actuating at resonance, we can also have a design with a higher spring stiffness design such that the micro-spectrometer will have little influence from external perturbation. A data acquisition electronic system is designed such that the interferogram of the IR source can still be acquired at a fixed optical path distance (OPD) intervals. This is achieved by using a reference laser source. Working at a resonant frequency of 330 Hz, a 100 μm (bi-directional) displacement is achieved by the device with an input voltage of 2.2 V. A tunable laser source is used to demonstrate the system performance. The peak of the recorded spectra is very close to the actual wavelength of the IR, with a maximum difference of less than 5 nm.     

A 5 GHz LC-VCO frequency synthesizer for unlicensed band of WiMAX

This paper presents a low power and low phase noise CMOS integer-N frequency synthesizer based on the charge-pump Phase Locked Loop (PLL) topology. The frequency synthesizer can be used for IEEE 802.16 unlicensed band of WiMAX (World Interoperability for Microwave Access). The operation frequency of the proposed design is ranged from 5.13 to 5.22 GHz. The proposed Voltage-Controlled Oscillator (VCO) achieves low power consumption and low phase noise. The high speed divider is implemented by an optimal extended true single phase clock (E-TSPC) prescaler. It can achieve higher operating frequency and lower power consumption. A new frequency divider is also proposed to eliminate the hardware overhead of the S counter in the conventional programmable divider. The proposed frequency synthesizer consists of a phase-frequency detector (PFD), a charge pump, a low-pass loop filter, a VCO, and a frequency divider. The simulated phase noise of the proposed VCO is −121.6 dBc/Hz at 1 MHz offset from the carrier frequency. The proposed frequency synthesizer consumes 13.1 mW. The chip with an area of 1.048 × 1.076 mm² is fabricated in a TSMC 0.18 μm CMOS 1P6M technology process.     

Effect of micro-channel geometry on fluid flow and mixing

Understanding the flow fields at the micro-scale is key to developing methods of successfully mixing fluids for micro-scale applications. This paper investigates flow characteristics and mixing efficiency of three different geometries in micro-channels. The geometries of these channels were rectangular with a dimension of; 300 μm wide, 100 μm deep and 50 mm long. In first channel there was no obstacle and in the second channel there were rectangular blocks of dimension 300 μm long and 150 μm wide are placed in the flow fields with every 300 μm distance attaching along the channel wall. In the third geometry, there were 100 μm wide fins with 150° angle which were placed at a distance of 500 μm apart from each other attached with the wall along the 50 mm channel. Fluent software of Computational Fluid Dynamics (CFD) was used to investigate the flow characteristics within these microfluidic model for three different geometries. A species 2D model was created for three geometries and simulations were run in order to investigate the mixing behaviour of two different fluid with viscosity of water (1 mPa s). Models were only built to investigate the effect of geometry, therefore only one fluid with similar viscosity was used in these models. Velocity vector plots were used in the CFD analysis to visualise the fluid flow path. Mass fractions of fluid were used to analyse the mixing efficiency. Two different colours for water were used to simulate the effect of two different fluids. The results showed that the mixing behaviour strongly depended on the channel geometry when other parameters such as fluid inlet velocity, viscosity and pressure of fluids were kept constant. In two geometries lateral pressure and swirling vortexes were developed which provided better mixing results. Creation of swirling vortexes increased diffusion gradients which enhanced diffusive mixing.     

Miniature orthogonal optical scanning mirror excited by torsional piezoelectric fiber actuator

A novel optical scanner excited by a torsional piezoelectric fiber actuator is presented. The device consists of a piezoelectric fiber actuator generating torsional and longitudinal vibrations simultaneously and a specially designed metal frame transforming the two vibrations to orthogonal deflections of the mirror. Theoretical and experimental studies were performed on the structure. The changing trends of the vibration modes and resonant frequencies were obtained from finite element simulations. Samples with 1 mm × 1 mm mirrors were fabricated from PZT hollow fibers with a diameter of 1 mm and a stainless steel sheet with a thickness of 50 μm. A horizontal scanning angle of 17.9° and a vertical scanning angle of 2.6° were achieved at 6780 and 10,330 Hz under an applied voltage of 400 V_p–p.     

Photonic crystal slabs with hexagonal air holes fabricated by selective area metal organic vapor phase epitaxy

It is shown that the photonic crystal slab (PCS) with hexagonal air holes has band gaps in the guided mode spectrum, which can be compared to that of the PCS with circular air holes, thus it is also a good candidate to be used for the PC devices. The PC with hexagonal air holes and a = 0.5 μm and r = 0.15 μm was fabricated successfully by selective area metal organic vapor phase epitaxy (SA-MOVPE). The vertical and smooth sidewalls are formed and the uniformity is very good. The same process was also used to fabricate a hexagonal air hole array with the width of 0.1 μm successfully. The air-bridge PCS with hexagonal air holes and a = 0.3 μm and r = 0.09 μm was also fabricated successfully by SA-MOVPE. Further optimization of the growth conditions for the sacrificial layer and the selective etching of the GaAs cap layer is also needed. Our experimental results indicate that SA-MOVPE is a promising method for fabricating PC devices and photonic nanostructures.     

Design,simulation and validation of a novel uncooled infrared focal plane array

This paper describes a novel single-layer bi-material cantilever microstructure without silicon (Si) substrate for focal plane array (FPA) application in uncooled optomechanical infrared imaging system (UOIIS). The UOIIS, responding to the radiate infrared (IR) source with spectral range from 8 to 14 μm, may receive an IR image through visible optical readout method. The temperature distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array, which is consisted of two materials with mismatching thermal expansion coefficients. In order to obtain a high detection to the IR object, gold (Au) film is coated alternately on silicon nitride (SiN_x) film in the flection beams of the cantilevers. And a thermal–mechanical model for such cantilever microstructure is proposed. The thermal and thermal–mechanical coupling field characteristics of the cantilever array structure are optimized through numerical analysis method and simulated by using the finite element simulation method. The thermal–mechanical rotation angle simulated and thermal–mechanical sensitivity tested in the experiment are 2.459 × 10⁻³ and 3.322 × 10⁻⁴ rad/K, respectively, generally in good agreement with what the thermal–mechanical model and numerical analysis forecast, which offers an effective reference for FPA structure parameters design in UOIIS.     

A 24-h forecast of ozone peaks and exceedance levels using neural classifiers and weather predictions

A neural network combined to a neural classifier is used in a real time forecasting of hourly maximum ozone in the centre of France, in an urban atmosphere. This neural model is based on the MultiLayer Perceptron (MLP) structure. The inputs of the statistical network are model output statistics of the weather predictions from the French National Weather Service. These predicted meteorological parameters are very easily available through an air quality network. The lead time used in this forecasting is (t + 24) h. Efforts are related to a regularisation method which is based on a Bayesian Information Criterion-like and to the determination of a confidence interval of forecasting. We offer a statistical validation between various statistical models and a deterministic chemistry-transport model. In this experiment, with the final neural network, the ozone peaks are fairly well predicted (in terms of global fit), with an Agreement Index = 92%, the Mean Absolute Error = the Root Mean Square Error = 15 μg m⁻³ and the Mean Bias Error = 5 μg m⁻³, where the European threshold of the hourly ozone is 180 μg m⁻³.To improve the performance of this exceedance forecasting, instead of the previous model, we use a neural classifier with a sigmoid function in the output layer. The output of the network ranges from [0,1] and can be interpreted as the probability of exceedance of the threshold. This model is compared to a classical logistic regression. With this neural classifier, the Success Index of forecasting is 78% whereas it is from 65% to 72% with the classical MLPs. During the validation phase, in the Summer of 2003, six ozone peaks above the threshold were detected. They actually were seven.Finally, the model called NEUROZONE is now used in real time. New data will be introduced in the training data each year, at the end of September. The network will be re-trained and new regression parameters estimated. So, one of the main difficulties in the training phase – namely the low frequency of ozone peaks above the threshold in this region – will be solved.     

Design and modeling of a novel microsensor to detect magnetic fields in two orthogonal directions

In this paper, we present the design and modeling of the electrical–mechanical behavior of a novel microsensor to detect magnetic fields in two orthogonal directions (2D). This microsensor uses a simple silicon resonant structure and a Wheatstone bridge with small p-type piezoresistors (10 × 4 × 1 μm) to improve the microsensor resolution. The resonant structure has two double-clamped silicon beams (1000 × 28 × 5 μm) and an aluminum loop (1 μm thickness). The microsensor design allows important advantages such as small size, compact structure, easy operation and signal processing, and high resolution. In addition, the microsensor design is suitable to fabricate using silicon on insulator (SOI) wafers in a standard bulk micromachining process. An analytical model is developed to predict the first bending resonant frequency of the microsensor structure using Macaulay and Rayleigh methods, as well as the Euler–Bernoulli beam theory. Air and intrinsic damping sources of the microsensor structure are considered for its electrical–mechanical response. The mechanical behavior of the microsensor is studied using finite element models (FEMs). For 10 mA of root mean square (RMS) excitation current and 10 Pa air pressure, this microsensor has a linear electrical response, a fundamental bending resonant frequency of 52,163 Hz, and a high theoretical resolution of 160 pT.     

Design,simulation and experiment of electroosmotic microfluidic chip for cell sorting

A microfluidic cell sorting chip has been developed using micromachining technology, where electroosmotic flow (EOF) is exploited to drive and switch cells. For this electroosmotically driven system, it is found that the effect of induced hydrostatic pressure caused by unequal levels in solution reservoirs is not negligible. In this work, the numerical simulation of EOF and opposing pressure induced flow in microchannels is presented and the velocity profiles in the microchannels are measured experimentally using microparticle imaging velocimetry (PIV) system. The result shows that the final resulting velocity is the superposition of the two flows. A total volume of 0.305 μl is transported in the 50 μm microchannel and the back flow occurs after 240 s transportation. The task of sorting cells is realized at the switching structure by adjusting the electric fields in the microchannels. The performance of the cell sorting chip is optimized by investigating the effect of different switching structures. A Y-junction switching structure with 90° switching angle is highly recommended with simulated leakage distance of 53 μm and switching time of 8 ms.     

Design and performance of a microcantilever-based hydrogen sensor

This paper describes the design of, and the effects of basic environmental parameters on, a microelectromechanical (MEMS) hydrogen sensor. The sensor contains an array of 10 micromachined cantilever beams. Each cantilever is 500 μm wide×267 μm long×2 μm thick and has a capacitance readout capable of measuring cantilever deflection to within 1 nm. A 20-nm-thick coating of 90% palladium–10% nickel bends some of the cantilevers in the presence of hydrogen. The palladium–nickel coatings are deposited in ultra-high-vacuum (UHV) to ensure freedom from a “relaxation” artifact apparently caused by oxidation of the coatings. The sensor consumes 84 mW of power in continuous operation, and can detect hydrogen concentrations between 0.1 and 100% with a roughly linear response between 10 and 90% hydrogen. The response magnitude decreases with increasing temperature, humidity, and oxygen concentration, and the response time decreases with increasing temperature and hydrogen concentration. The 0–90% response time of an unheated cantilever to 1% hydrogen in air is about 90 s at 25 °C and 0% humidity.     

Design and fabrication of a new MEMS capacitive microphone using a perforated aluminum diaphragm

In this paper, a novel single-chip MEMS capacitive microphone is presented. The novelties of the method relies on the moveable aluminum (Al) diaphragm positioned over the backplate electrode, where the diaphragm includes a plurality of holes to allow the air in the gap between the electrode and the diaphragm to escape and thus reducing acoustical damping in the microphone. Spin-on-glass (SOG) was used as a sacrificial and isolating layer. Backplate is monocrystalline silicon wafer, that it is more stiff. This work will focus on design, simulation, fabrication and characterization of the microphone. The structure has a diaphragm thickness of 3 μm, a diaphragm size of 0.5 mm × 0.5 mm, and an air gap of 1.0 μm. The results show that the pull-in voltage is 105 V, the initial stress of evaporated aluminum diaphragm is around 1500 MPa and the zero bias capacitance of microphone is 2.12 pF. Comparing with the previous works, this microphone has several advantages: the holes have been made on diaphragm, therefore no need of KOH etching to make back chamber, in this way the chip size of each microphone is reduced. The fabrication process uses minimal number of layers and masks to reduce the fabrication cost.     

Ultra high performance planar InGaAs PIN photodiodes for high speed optical fiber communication

This paper reports a front-illuminated planar InGaAs PIN photodiode with very low dark current, very low capacitance and very high responsivity on S-doped InP substrate. The presented device which has a thick absorption layer of 2.92 μm and a photosensitive area 73 μm in diameter exhibited the high performance of a very low capacitance of 0.47 pF, a very low dark current of 0.041 nA, a very high responsivity of 0.99 A/W (79% quantum efficiency) at λ = 1.55 μm, the 3 dB bandwidths of 6.89 GHz (−5 V), 7.48 GHz (−12 V) for bare chips and 4.48 GHz (−5 V), 5.02 GHz (−12 V) for the devices packaged in TO can, respectively. Furthermore, the developed PIN photodiodes possess high breakdown voltage of less than −25 V.