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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 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]

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]

A thermal wind sensor utilizes the fact that airflow over a heated plate will cool it asymmetrically, with the upstream part of the plate being cooled more than the downstream part. In the temperature-balanced (TB) mode, the heating power may be distributed spatially in the sensor such that any flow-induced temperature gradient is cancelled. Information about the airflow can be extracted in the distribution of heating power in the sensor. Ideally, the influence of changes in the ambient temperature on the sensor’s output can be eliminated if in the whole measurement range the temperature sensor sensitivities are equal. However, because of the temperature dependency of the material properties of the airflow and the sensor, it may have a temperature drift. This paper, for the first time, investigates temperature effects of the ceramic microelectromechanical system (MEMS) thermal wind sensor based on the TB mode. The sensor consists of four outlying heaters and four inlying thermistors in two orthogonal directions on a ceramic substrate. When working in the TB mode, it could measure wind speed and wind direction by applying a power difference on the upstream and downstream heaters, so that the flow-induced temperature gradient is eliminated. Theoretical analysis has been developed which takes the variations of thermophysical properties in the sensor and the control circuits into account. Experiments for testing wind speed and direction have been performed in a wind tunnel with an adjustable ambient temperature. It shows that the wind speed is linearly influenced by the ambient temperature while the wind direction is inherently unaffected by ambient temperature variations. After compensation, the sensor shows a credible performance with an error of less than ±1m/s in wind speed and ±2° in wind direction in a temperature range from 0 °C to 30 °C. [ABSTRACT FROM AUTHOR]

This paper presents a semi-empirical model for the temperature effect of a micromachined 2-D anemometer. The anemometer consists of a self-heated double Wheatstone bridge. 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 both heating and sensing elements. The terminal voltage across the bridge and the bridge output voltage, under the constant current supply, are utilized to measure the wind speed and direction, respectively. The semi-empirical model has taken the thermal physical properties of the air, sensor substrate, and thermistors into account. It shows that the measurement of wind direction has a weak temperature dependence due to the symmetric config uration of the self-heated double Wheatstone bridge, which suppresses the temperature drift. The temperature compensation has been performed by means of the semi-empirical model. The experimental measurements demonstrate that, when the air temperature changes from 270 to 310 K, the wind speed varies from 0 to 30 m/s with an error less than ±1.5 m/s while the wind direction spans from 0° to 360° with the weak temperature dependence. [ABSTRACT FROM AUTHOR]

A 2-D anemometer sensor on a ceramic substrate is proposed, modeled, simulated, and fabricated. The sensor consists of four outlying heaters and four inlying thermistors arranged in two orthogonal directions on a ceramic substrate. The heaters are driven by power feedback control circuits, while the thermistors measure the temperature distribution on the surface of the sensor. By applying a power difference on the upstream and downstream heaters, the flow-induced temperature gradient is canceled via the temperature-balanced mode, and both wind speed and direction can be extracted by the applied power difference. An analytical model of the 2-D anemometer sensor is developed for the applied power difference as a function of wind speed and direction. The finite-element method simulations have been utilized to demonstrate the analytical model. The sensor was fabricated directly on the ceramic substrate by using a typical lift-off technology. The sensor output was measured and compared with the theoretical model. A high measurement accuracy has been achieved from 0 to 40 m/s with a speed error less than ±0.5m/s and a direction error of less than ±2°. [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]

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]

In this paper, the effect of insulation trenches on micromachined silicon thermal wind sensors is explored. The sensor is composed of a central heater and four thermistors. It measures wind speed and direction through detecting the airflow-induced temperature difference on the chip surface. Three different forms of insulation trenches are designed and fabricated to explore their effects on the performance of wind sensors. The experimental results show that when the sensors work in constant voltage mode, the center and arch trenches enhance the performance, while the arch trenches have the most significant effect on the sensitivity improvement. Moreover, all the three kinds of insulation trenches reduce the power consumption for the sensors operated in constant temperature difference mode. The insulation trench design in this paper can provide a valuable reference for the design and fabrication of micromachined silicon thermal wind sensors. [ABSTRACT FROM PUBLISHER]

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]

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]

In this paper, we report a novel and low-cost method to improve the sensitivity of a low-power 2D microelectromechanical systems thermal wind sensor by using HF wet etching. After wet etching, the thickness of the glass substrate decreases, so that the sensor’s thermal vias become more exposed to the wind. As a result, the conductive heat transfer is weakened and the convective heat transfer is enhanced in sensor operation. Finite-element method simulations verify this analysis. Moreover, the sensor chips with different lengths of silicon vias above the substrate are successfully fabricated and tested. Measurement results show that the wet etching has no influence on the metal film sensing and heating elements of the sensor. Besides, before and after wet etching for 7 and 14 min, at the wind speed of 5 m/s, the measured sensitivities of the sensor with a total power consumption of 24.5 mW are 77.2, 98.6, and 164.1 mK/(m/s). Measurement results also show that the improved sensitivity of the sensor chip can provide a more accurate measurement in wind speed but has little effect on the wind direction measurement. Instead, the accuracy of wind direction measurement is mainly related to the structural and thermal symmetries of the wind sensor. After compensation, the proposed thermal wind sensor can detect the wind direction in a full range of 360° with an mean error of 2.3° and a maximum error of 6°. [ABSTRACT FROM PUBLISHER]

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, the wind sensor operating on temperature-balanced mode is investigated. The temperature of four modules is kept as a constant higher than that in the center of the chip. Hence, the wind speed and direction can be characterized by the heating power of the modules. The wind sensor is fabricated on the ceramic substrate, and Ti/Pt is used as heating and sensing resistors. The experiment demonstrates that the power of four modules increases with the wind speed according the King’s law. The total power consumption is about 250 mW@20m/s and 320 mW@40m/s The calibrated results show that the speed varies from 0.2 m/s to 40 m/s with the error of 1 m/s and the direction spans from 0° to 360° with the error of 5°. [ABSTRACT FROM PUBLISHER]