A non-invasive glucose sensor using defective ground structure (DGS) coplanar waveguide (CPW) transmission line is proposed for the first time. The device operates as a microwave resonantor, which is affected by glucose concentration. The size of the fabricated DGS sensor is 22mm×12mm with a sample holder realized by three-dimension (3D) printing technology. Experiments demonstrate that the frequency sensitivity is about 1.852×10 ^-5 GHz/(mg/dL) and the amplitude sensitivity is close to 6.54×10 ^-4 dB/(mg/dL). On this basis, the array structure is repeated 5 times to expand the sensing area, leading to a frequency sensitivity of 3.9×10 ^-6 GHz/(mg/dL) and an amplitude sensitivity of 5×10 ^-3 dB/(mg/dL). The array DGS sensor sacrifices frequency sensitivity, but improves the amplitude sensitivity by a factor of 7.65 compared to the single-structure device. The proposed sensor may have a good application prospect for human health monitoring in future.

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°.

A 2-D MEMS wind sensor based on Δ 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 Δ 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]

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.

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.

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°.