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This communication investigated the dust effect on microelectromechanical system (MEMS) thermal wind sensors, with an aim to evaluate performance in practical applications. An equivalent circuit was established to analyze the temperature gradient influenced by dust accumulation on the sensor's surface. The finite element method (FEM) simulation was carried out to verify the proposed model using COMSOL Multiphysics software. In experiments, dust was accumulated on the sensor's surface by two different methods. The measured results indicated that the output voltage for the sensor with dust on its surface was a little smaller than that of the sensor without dust at the same wind speed, which can degrade the measurement sensitivity and accuracy. Compared to the sensor without dust, the average voltage was reduced by about 1.91% and 3.75% when the dustiness was 0.04 g/mL and 0.12 g/mL, respectively. The results can provide a reference for the actual application of thermal wind sensors in harsh environments. [ABSTRACT FROM AUTHOR]

In this article, the benchmark drift of micromachined thermal wind sensor due to the packaging asymmetry has been analyzed and compensated. For the ideal wind sensors with symmetric packaging, the benchmark does not vary with speed and direction. However, for the real sensors, especially for handmade ones, packaging asymmetry problems are usually inevitable. Consequently, benchmark drifts with wind because of different thermal distribution in each direction, which was verified by the proposed lumped parameters model. The real sensors were tested in a wind tunnel and results showed the benchmark drift as well. The contribution of this work lies in the establishment of the equation of benchmark dependent on wind speed, which can predict benchmark value under different wind speeds by calibration at zero wind speed. This compensation method is extremely simple and convenient for industrial production. After compensation, the relative wind speed errors are reduced from 46 to 8% up to 30 m/s, and the wind direction errors are reduced from 30° to 7° over the full range of 360°. [ABSTRACT FROM AUTHOR]

In this article, a novel micro-electromechanical systems (MEMS) thermal wind sensor using the plastic injection packaging method was proposed. Compared with previous devices suffering from packaging asymmetry, the presented design can relieve the drift phenomenon and improve the accuracy of wind detection. Lumped parameter model and finite-element method (FEM) simulation were developed, and the sensor’s improvement was validated. By means of plastic injection molding process, the MEMS sensor chip based on ceramic substrate was encapsulated in a plastic carrier with low thermal conductivity of 0.96 W/($\text{m} \!\cdot \!\text{K}$). In addition, individual packaging was implemented by laser cutting, which ensures that the geometric center of the chip is almost coincident with that of packaging. The sensor, operated in the constant temperature difference (CTD) mode, was tested in the wind tunnel. The experimental results show that wind speed is measured up to 30 m/s with an accuracy of ±7%, while the direction is characterized over the full range of 360° with errors less than ±5°. Compared with the device in our previous work, the measurement accuracy of the proposed prototype sensor was improved by more than two times because of effective benchmark drift suppression. [ABSTRACT FROM AUTHOR]

Modeling of the packaged wind sensor operating on constant power (CP) mode is proposed in this paper. The proposed model is based on the theory of heat conduction and forced convection. The presented model indicates that the total output dc voltage is proportional to the square root of the wind speed, and ${V}_{x}$ , as well as ${V}_{y}$ , varies with the wind direction based on cosine function. The wind sensor is fabricated by microelectromechanical systems (MEMS) technology and packaged with the glue. The test is performed in the wind tunnel and the measured results indicate an agreement with the presented model. The relative error of voltage for the wind speed is less than 14% up to 30 m/s, while that for the wind direction is no more than 10.7% from 0° to 360°. [ABSTRACT FROM AUTHOR]

A self-heated double Wheatstone bridge configuration for a 2-D wind sensor is presented. Without a central heating element, eight thermistors are symmetrically arranged in two orthogonal directions, and four of them in each direction make up a Wheatstone bridge. The eight thermistors simultaneously act as the heating sources and temperature sensing elements. By applying the constant current supply to the bridge, the terminal voltage across the bridge and the bridge output voltage are utilized to measure the wind speed and direction, respectively. The 2-D wind sensor has been simulated numerically and fabricated directly on the ceramic substrate. Experiments demonstrate that the measured speed varies from 0 to 40 m/s with an error less than ±2 m/s while the measured direction spans from 0° to 360° with an error less than ±3° after calibration. The double bridge configuration greatly simplifies the measurement and control circuits for the 2-D wind sensor. [2018-0171] [ABSTRACT FROM AUTHOR]

In this Letter, a differential piezoresitive wind speed sensor on a flexible substrate is proposed. Two piezoresistors with the same size are fabricated on the front surface and back surface of the substrate, respectively. When the wind blows towards the device, the flexible substrate is bent, increasing the resistance on the front surface and reducing that on the back surface. The proposed sensor is fabricated on a polyethylene terephthalate substrate. Wind speed experiments are performed in the wind tunnel and the results demonstrate that the sensor can measure the wind speed up to about 20 m/s. [ABSTRACT FROM AUTHOR]

This paper introduces a novel sensing element scheme to improve the accuracy of 2-D micromachined thermal wind sensor. The sensing element consists of eight heaters and eight thermistors placed on ceramic substrate. The octagon-arranged sixteen resistors are divided into two wind sensing groups, cross-type group and saltire-type group. These two groups monitor wind independently, and the final measured wind speed and direction are extracted from the measurement results of the two groups. Based on this octagon-sensing design, the sensor achieves higher accuracy for wind measurement, which is verified by the experiment. The results show that for the wind speed up to 33 m/s, the sensor has a measurement error less than ±1%, and the airflow direction over the full range of 360° is determined with a maximum error of ±1.5°. [2018-0045] [ABSTRACT FROM AUTHOR]

This paper presents the design, fabrication, and performance of a micromachined silicon thermal wind sensor with improved sensitivity. Deep reactive ion etching (DRIE) trenches are fabricated between the heater and the thermistors to suppress the lateral heat conduction in the chip. In addition, eight thermistors symmetrically arranged in four directions around the heater form two Wheatstone full-bridges, resulting in about 50% increase of the sensitivity with respect to four thermistors. Based on these two methods, the sensitivity of the micromachined silicon thermal wind sensor is improved remarkably, which is verified by the experiment. The results show that the measurement wind speed range is up to 33 m/s in constant voltage (CV) mode with the initial heating power of 256 mW. The sensitivity is measured to be 29.37 mV/ms−1 at the wind speed 3.3 m/s, achieving improvement of about 226%, compared with that of the traditional wind sensor. Wind direction measurement results show that airflow direction over the full range of 360° is determined with an accuracy of ±5°. [2017-0052] [ABSTRACT FROM AUTHOR]

This paper builds a complete analytical model for self-assembling microwave power sensor with thermopile and curled cantilever beam. The power sensor consists of a thermoelectric power sensor for low power detection from 0.1 mW to 100 mW and a capacitive power sensor for high power detection from 100 mW to 800 mW. The curled cantilever beam is designed to improve the dynamic range and microwave performance of the power sensor. The analytical model includes an electromagnetic model, a static mechanical model, and a stationary heat transfer model. The electromagnetic model takes the S-parameter of indirect-heating thermoelectric power sensor into consideration. The static mechanical model considers the fringing fields between the curled cantilever beam and the measuring electrode as well as the initial curling induced by the stress gradient. The experimental results show a good agreement with the theory and validate the effectiveness of the presented models. Furthermore, good performance of the power sensor has found. The measured return loss is lower than −25.5 dB at 8–12 GHz and the output of the power sensor has good linearity with the incident radio frequency power up to 600 mW. [ABSTRACT FROM AUTHOR]

The cascaded power sensor, including terminating-type one and capacitive-type one is modeled in this paper. The electric-heat-electric conversion model in the terminating-type power sensor is based on Fourier conduction equation, and the electric-force-electric conversion model in the capacitive-type power sensor is based on strain equation. Experiments are performed to verify the model. For the incident power from 1 to 100 mW, the measured sensitivity of the terminating-type is 0.124 mV/mW and the sensitivity of the model is 0.135 mV/mW. For the incident power from 100 to 150 mW, the sensitivity of the capacitive-type sensor is about 0.156 fF/mW, while the calculated sensitivity of the model is 0.165 fF/mW. The comparison demonstrates that the related error of the voltage is less than 9% and the related error of the capacitance change is less than 6%. [ABSTRACT FROM PUBLISHER]

This paper reports a high dynamic range power sensor based on GaAs process and MEMS technology. The proposed sensor consisted of the terminating-type sensor and the coupling-type sensor. The former measures low power while the latter is for high power detection. This device is designed and fabricated by GaAs MMIC process. In order to optimize microwave performance, impedance compensating technology by increasing the slot width of the CPW transmission line is developed. Related calculation and simulation are also presented in this paper. The microwave performance test reveals that the return loss is close to −28 dB@8 GHz, −27 dB@10 GHz and −26 dB@12 GHz, respectively. The microwave power response experiment is investigated from 1 mW to 150 mW. For the incident power less than 100 mW, the terminating-type sensor operates and the measured sensitivity is about 0.095 mV/mW@8 GHz, 0.088 mV/mW@10 GHz and 0.084 mV/mW@12 GHz, respectively. Related lumped equivalent circuit models of the loaded resistors are developed to explain the loss induced by the frequency of the signal. For the incident power with the improved dynamic range from 100 mW to 150 mW, the coupling-type sensor is adopted and the measured sensitivity is about 9.2 μV/mW@8 GHz, 8.6 μV/mW@8 GHz and 9.0 μV/mW@12 GHz, respectively. [ABSTRACT FROM AUTHOR]

A 2-D MEMS wind sensor based on $\Delta \text{P}$ (power difference) thermal feedback control is presented. The sensor consists of four outlying heaters and four inlying thermistors in two orthogonal directions on ceramic substrate. A $\Delta \text{P}$ thermal feedback control system is applied to eliminate the flow-induced temperature difference between upstream and downstream so as to achieve a temperature-balanced mode. This applied power difference among the four heaters is a measure for the wind speed and direction. Experimental results demonstrate that the measured speed varies from 0 to 40 m/s with an error less than ±0.5 m/s while the measured direction spans from 0° to 360° with an error less than ±2°. [2017-0286] [ABSTRACT FROM AUTHOR]

In this paper, a numerical model is established to describe the effect of temperature on the packaged thermoelectric power sensor in different environments. The thermal conductivity of the GaAs substrate and the Seebeck coefficient of the thermopiles both change with the surrounding temperature and then influence the output voltage of the sensor. The return loss of the packaged power sensor is measured to be −20 dB at 10 GHz and close to −12 dB at the edge of X-band. The temperature experiment is performed from 273 K to 363 K in the temperature chamber. An agreement between the measured results and the presented model is obtained and the temperature dependence factor is close to 0.15 mV/K at 10 GHz under the incident power of 50mW. Furthermore, calibration of the output voltage is accomplished from 273 K to 363 K and the compensated power with respect to the surrounding temperature is also recorded under 50mW. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents an X-band Wilkinson power divider which is completely compatible with GaAs monolithic microwave integrated circuit (MMIC). The novelty is that, GaAs is chosen for the realization for substrate because of its excellent microwave performance, and Au is used to fabricate transmission lines and air bridges due to its good electric properties. The measured return loss of port 1 is about −32 dB at the center frequency of 9 GHz and less than −16 dB over X-band. The insertion loss of port 2 and 3 is close to 3.3 dB at 8-12 GHz. The measured bandwidth for which the input return loss is less than −20 dB is about 3.2 GHz. For the miniaturized power divider, the measured return loss of port 1 is about −23 dB at the center frequency of 11 GHz and less than −13 dB over the band of 8-12 GHz. The measured insertion loss of port 2 and 3 is close to 3.5 dB over the X-band. The measured bandwidth of the miniaturized divider is less than 1.6 GHz. Comparison between the Wilkinson power divider and the miniaturized one shows that the shorter the quarter-wave transmission line is, the larger the impedance is. Meanwhile, the chip area reduction also leads to narrowed bandwidth of the power divider. The experiments demonstrate that the MMIC chip area of the power divider has been reduced by nearly 50% by capacitive loading, whereas the bandwidth is also narrowed by 50%. Therefore, the Wilkinson power divider applies to the situation if wide bandwidth is needed, while the miniaturized one is a better solution for small chip area. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:700-705, 2014 [ABSTRACT FROM AUTHOR]

In this paper, a novel in-line type frequency detector is proposed based on a MEMS membrane for X-band applications. In this design, the MEMS membrane stands above the signal line of the CPW transmission line and acts as a coupling capacitance. A certain percentage of the incident power, as a function of the frequency, is coupled to the microwave power sensors. Finally, the frequency of the incident RF signal is able to be deduced by measuring the output thermovoltage of the microwave power sensor based on the Seebeck effect. The design, lumped equivalent circuit model and simulation are presented. The in-line type power sensor is fabricated by the GaAs MMIC process based on MEMS technology. The measured return loss is less than −13 dB and the insertion loss is better than 1.3 dB over the frequency band of 8–12 GHz. The RF frequency measurement demonstrates that the output thermovoltage increases from 0.22 to 0.35 mV when the frequency varies from 8 to 12 GHz under the input power of 10 dBm. [ABSTRACT FROM AUTHOR]

An 8-12 GHz microwave frequency detector is presented, which is based on MEMS power sensors, by sensing the phase delay of two separated signals in two different tracks. The phase delay, proportional to frequency of the input microwave signal, leads to variation of the output power. Two different kinds of MEMS power sensors, a thermoelectric microwave power sensor and a MEMS capacitive power sensor, are adopted to measure the variation. The former is used for measuring the lower power while the latter for the higher one. The presented detector has been designed, optimized and fabricated successfully using the GaAs MMIC process. For the microwave signals of 10, 15 and 20 dBm, the measured result shows that the output thermovoltage decreases with the frequency based on the thermoelectric microwave power sensor and sensitivities of the detector better than 0.033, 0.110 and 0.343 µVMHz-1 are measured, respectively. Furthermore, the sensitivity of detector is directly proportional to the power of the input microwave signal. For the microwave signals of 24 dBm, the measured result shows that the capacitance decreases with the frequency based on the MEMS capacitive power sensor and the sensitivity of 0.013 fF MHz-1 is measured. The frequency measurement demonstrates the validity of the presented design. [ABSTRACT FROM AUTHOR]

In this letter, a differential capacitive power sensor is proposed based on the seesaw-type microelectromechanical systems (MEMS) membrane. When the microwave power is applied, the center part of the membrane is pulled down toward to the substrate. Meanwhile, the end parts are turned away from the substrate, because two anchors act like pivots. Hence, the capacitance between the center part and the electrodes increases, while the capacitance induced by the end parts decreases. This device is based on the MEMS technology and fabricated by GaAs monolithic microwave integrated circuit (MMIC) process. The tested return loss is about −29 dB at 1 GHz, −18 dB at 5 GHz, and −13 dB at 10 GHz. The insertion loss is better than 1.5 dB over 1–10 GHz. For the incident power from 1 to 100 mW, the measured capacitance change magnitude \Delta C\mathrm {in} increases from 0.1 to 7fF, while the capacitance change \Delta C\mathrm {out} magnitude varies from 0.1 to about 3 fF. Therefore, the sensitivity of the proposed power sensor is improved and on the order of 0.1 fF/mW. [2016-0014] [ABSTRACT FROM PUBLISHER]

In this paper, a novel 2.5-dimensional (2.5D) flexible wind sensor is proposed based on four differential plate capacitors. This design consists of a windward pillar, two electrode layers, and a support layer, which are all made of polydimethylsiloxane (PDMS) with different Young's moduli. A 2 mm × 2 mm copper electrode array is located on each electrode layer, forming four parallel plate capacitors as the sensitive elements. The wind in the xy-plane tilts the windward pillar, decreasing two capacitances on the windward side and increasing two capacitances on the leeward side. The wind in the z-axis depresses the windward pillar, resulting in an increase of all four capacitances. Experiments demonstrate that this sensor can measure the wind speed up to 23.9 m/s and the wind direction over the full 360° range of the xy-plane. The sensitivities of wind speed are close to 4 fF·m−1·s and 3 fF·m−1·s in the xy-plane and z-axis, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a novel wind speed sensor with dual layer inductors is proposed to realize improved sensitivity for the first time. Two inductors with same structure are fabricated on front and back surface of the flexible substrate. When the wind blows towards the substrate, the two inductors on both sides bend because of wind pressure. Consequently, the total inductance variation, as a measure for the wind speed, can be increased effectively because of mutual inductance effect. The proposed anemometer is fabricated on polyethylene terephthalate (PET) substrate. Wind speed experiments are performed in the special wind tunnel and the LCR meter is applied to record the inductance variation. It demonstrates that, compared to single-layer inductors, the dual-layer design can achieve a quadruple sensitivity for the wind speed up to 11.2m/s. The reason is that the mutual inductance contributes to the total variation equally as the two self inductance. [ABSTRACT FROM AUTHOR]

An analytic model of dual-layer-structure (DLS) microelectromechanical system (MEMS) thermal wind sensor was proposed in this article. Heat conduction and heat convective theory were applied to obtain the temperature difference between upstream and downstream under different wind speeds and directions. Simulation by finite element method (FEM) was performed to verify the proposed model. The DLS MEMS wind sensor was fabricated by commercial foundry with two polysilicon layers and one metal layer. After being packaged, the wind sensor was tested based on front surface sensing mode in the wind tunnel up to 33 m/s. The results demonstrated that the wind speed measurement agrees with the proposed model well and the average error of output voltage was no more than 8 mV. Moreover, the measured wind direction increased with the actual value marked on the base from 0° to 360°, which was consistent with the established model. Moreover, the average error was close to 3.7° and the maximum value was no more than 6.38°, which may be caused by asymmetry in scribing and packaging. [ABSTRACT FROM AUTHOR]

In this paper, the design, fabrication, and characterization of a robust MEMS thermal wind sensor utilizing ceramic film packaging are proposed. The ceramic film is fabricated by means of low temperature co-fired ceramic (LTCC) technology, achieving the excellent adhesion between silicon substrate and ceramic film without any thermal adhesive. The most important is that the adverse effects of the packaging on the performance of the thermal wind sensor can be minimized by adjusting the thickness and thermal conductivity of the ceramic film during the preparation of the ceramic slurry. The influences of thickness and thermal conductivity of ceramic film on the performance of sensor have been simulated by finite element method, and the results are in reasonable agreement with theoretical analysis. The proposed sensors were tested and calibrated in a wind tunnel. Experiments results demonstrate that the sensitivity of the proposed sensor is decreased only 4.7%, compared with the sensor without ceramic film. The maximum measurement error of the proposed sensor in wind speed and direction is 0.66 m/s and 5°, respectively. Compared with the sensor packaged with $250\mu \text{m}$ ceramic carrier, the heating power of the proposed sensor is reduced by nearly 50% and the sensitivity is increased by an order of magnitude at the same time. [ABSTRACT FROM AUTHOR]

• Finite element simulation of miniaturized housing structure for 3D packaged MEMS thermal wind sensor model. • Experiments are also done firstly, an agreement between simulation and experiment is obtained. • Provide a reference for the design and manufacture of MEMS thermal wind sensor miniaturization package. [Display omitted] This paper, for the first time, investigates the effects of miniaturized housing structure with various parameters on micro-electro-mechanical systems (MEMS) thermal wind sensors by simulation and experiments. Pillar diameter, number, height and curve-shaped top cover with different radian are considered to find out their influence on sensors performance. In the simulation, finite element method (FEM) software COMSOL is applied to simulate the 3D packaged sensor model. Then sensors with different housing parameters are tested in the wind tunnel based on thermal calorimetric principle, which uses flow-induced temperature gradient between symmetrically distributed thermistors to represent wind speed. An agreement between simulation and experiment is obtained, and the results demonstrate that the device's performance can be improved with smaller pillar diameter, more pillar number, and smaller pillar height. Moreover, the curved roof is designed, which provides a possibility for high wind speed measurement. [ABSTRACT FROM AUTHOR]

A high dynamic range microwave power sensor compatible with the gallium arsenide monolithic microwave integrated circuit process is presented. The power sensor consists of a thermoelectric power sensor and a capacitive power sensor for low and high power detection, respectively. To improve the dynamic range and optimise the impedance matching characteristic, the curled cantilever beam is utilised and the slot width of the coplanar waveguide transmission line is modified. The measured return loss is lower than –25.5 dB at 8–12 GHz. The output of the power sensor shows good linearity with the incident radio frequency power. For the incident power from 0.1 to 100 mW, the obtained sensitivities by a thermoelectric power sensor are about 0.0842, 0.0752 and 0.0701 mV/mW at 8, 10 and 12 GHz, respectively. For the incident power from 100 to 400 mW, the measured sensitivities by the capacitive power senor are about 0.0400, 0.0301 and 0.199 fF/mW at 8, 10 and 12 GHz, respectively. [ABSTRACT FROM AUTHOR]

With the rapid development of microfluidic platforms in high-throughput single-cell culturing, laborious operation to manipulate massive budding yeast cells (Saccharomyces cerevisiae) in replicative aging studies has been greatly simplified and automated. As a result, large datasets of microscopy images bring challenges to fast and accurately determine yeast replicative lifespan (RLS), which is the most important parameter to study cell aging. Based on our microfluidic diploid yeast long-term culturing (DYLC) chip that features 1100 traps to immobilize single cells and record their proliferation and aging via time-lapse imaging, herein, a dedicated algorithm combined with computer vision and residual neural network (ResNet) was presented to efficiently process tremendous micrographs in a high-throughput and automated manner. The image-processing algorithm includes following pivotal steps: (i) segmenting multi-trap micrographs into time-lapse single-trap sub-images, (ii) labeling 8 yeast budding features and training the 18-layer ResNet, (iii) converting the ResNet predictions in analog values into digital signals, (iv) recognizing cell dynamic events, and (v) determining yeast RLS and budding time interval (BTI) ultimately. The ResNet algorithm achieved high F1 scores (over 92%) demonstrating the effectiveness and accuracy in the recognition of yeast budding events, such as bud appearance, daughter dissection and cell death. Therefore, the results conduct that similar deep learning algorithms could be tailored to analyze high-throughput microscopy images and extract multiple cell behaviors in microfluidic single-cell analysis. [ABSTRACT FROM AUTHOR]

In this paper, we present a robust, low-power and wide-range MEMS thermal wind sensor, which is based on a glass reflow process. A general analytical model is first proposed for obtaining the heater's temperature and the temperature distribution on the sensor surface. Based on this model, the effect of the sensor's geometry and package on the sensor's performance is investigated. These results demonstrate how the measurement range and the sensitivity of the sensor can be optimized with a change in structural geometries. Besides, it has shown that the package structure of the sensor is also important for obtaining the required performance. Then, calculated results are validated with 2-D finite element method (FEM) solver CMOSOL. It is found that although there is some deviation between theoretical and simulation results, the model can have good reference value for latter MEMS thermal wind sensor design. Finally, the sensor is characterized in a wind tunnel. At a constant heating power of 14.5 mW, measurement results show that the sensor can detect airflow speeds of up to 33 m/s, with an accuracy better than 0.5 m/s at low speeds and 5% Full-Scale at high speeds. Airflow direction can be determined in a 360° range with an accuracy better than 5°. In addition, the sensor also shows a good repeatability. [ABSTRACT FROM AUTHOR]