Micro capacitance detection circuit for MEMS capacitive sensor

With the development of micro-electr o-mechanical system(MEMS) technolog y,the MEMS-based capacitive sensor has been widely applied in the field of ele ctron components.However,the capacitance of the micromachined sensor is so sma ll that the detection of the smaller value change of the capacitance is a great challenge.Based on the principle of charging and discharging of the capacitor,a kind of pulse width modulated differential circuit is introduced in this paper.For subsequent amplification,a modified amplifier is presented.The different ial circuit converts the weak capacitance change to the change of the pulse widt h of the output voltage,and the linear relationship can be obtained.And the mo dified amplifier implements the processes of amplification and filtering synchro nously,and a large DC output voltage can be obtained by the lo w-pass filter.T he designed circuits have advantages as simplified circuit,high voltage stabili ty,perfect linearity and resolution.Besides,it is feasible to be integrated w ith the sensor to largely reduce the transmission error and interference.

Design and test of a capacitance detection circuit based on a transimpedance amplifier

This paper presents a transimpedance amplifier （TIA） capacitance detection circuit aimed at detecting micro-capacitance, which is caused by ultrasonic stimulation applied to the capacitive micro-machined ultrasonic transducer （CMUT）. In the capacitance interface, a TIA is adopted to amplify the received signal with a center frequency of 400 kHz, and finally detect ultrasound pressure. The circuit has a strong anti-stray property and this paper also studies the calculation of compensation capacity in detail. To ensure high resolution, noise analysis is conducted. After optimization, the detected minimum ultrasound pressure is 2.1 Pa, which is two orders of magni- tude higher than the former. The test results showed that the circuit was sensitive to changes in ultrasound pressure and the distance between the CMUT and stumbling block, which also successfully demonstrates the functionality of the developed TIA of the analog-front-end receiver.

Broken and fine powder detection method of fuses

Since powder and cotton wool may cause mechanical test fail,and the accuracy of ray detection method is not very ideal,this paper introduces the tiny capacitance detection method for broken gunpowder,in which the medium type capacitive sensor’s capacitance changes when the gunpowder core diameter changes.The detection is based on the relationship between non-electric quantity and electric quantity.Simulation results show that the designed system works well with easy installation and low power consumption.Therefore,it is suitable for broken gunpowder detection.

Simultaneous laser-induced fluorescence and contactless-conductivity detection for microfluidic chip

A combined detection system involving simultaneous LIF and contacfless-conductometric measurements at the same place of the microfluidic chip was described. The LIF measurement was designed according to the confocal principle and a moveable contactless-conduetivity detector was used in C^4D. Both measurements were mutually independent and advantageous in analyses of mixtures. Various experimental parameters affecting the response were examined and optimized. The performances were demonstrated by simultaneous detection of Rhodamine B. And the results showed that the combined detection system could be used sensitively and reliably.

Oxidating liquid metal interface integrated capacitive pressure detection

The characteristics of real-time monitoring and flexible integration based on passive capacitive detection are becoming the preferred sensing strategy for wearable devices.However,the currently designed capacitive sensors mostly focused on the bionic microstructures to improve sensitivity and measurement accuracy,while ignoring the inherent mechanical wear and resistance of multilayer structures.In this paper,an integrated monolithic capacitive pressure detection based on room temperature liquid metal is designed and fabricated,avoiding the tightness problem of the multi-layer structure.The oxidized paste-like liquid metal owning superior interfacial wetting properties can stably adhere to the surface of the porous framework.The gas-filled porous framework endows the capacitive sensor with a mechanical response of 0.0557 g with a response and recovery time of 1.26 and 0.63 s under a load condition of 150 Pa,and steadily maintained in 1600 cycle tests.Finally,the capacitive sensor is employed to detect human physiological signals and force shock responses,which could clearly distinguish different action signals,providing a new platform for the subsequent development and design of integrated capacitive sensors.

Design of soil moisture distribution sensor based on high-frequency capacitance

In order to obtain accurate real-time soil moisture data and the spatial distribution of soil moisture,the soil moisture measurement methods based on high-frequency capacitance edge field effect were analyzed,the structure of probe was studied,and a multi-channel soil moisture sensor was designed.Moreover,with the established two-dimensional trace planar capacitance probe model and the method of the finite element analysis,relationship between the structure of sensor probe and electric field intensity was studied and capacitance of the probe trace amount planar capacitance model was analyzed,the most optimal structure of sensor probe was determined.Design parameters of the probe which can achieve optimal sensitivity and detection range are:outer diameter 40 mm and inner diameter 38.4 mm for the probe copper ring electrode,axial length 20 mm and axial spacing 10 mm.The sensor is suitable for measuring the moisture of different type of soil.Moreover,the features of the profile soil moisture sensor were experimentally explored.The measurement accuracy reached±1.31%with better stability and consistency.Sensor probes can be assembled according to the measurement depth and used to measure soil moisture of different crop root zone.