Thermocapacitive Flow Sensor

Thermocapacitive Flow Sensor Thermoelectric Flow Sensors... 

Thermocapacitive Flow Sensor, Fig. 1 Simplified case of convective heat transfer... 

The thermocapacitive flow sensor is a velocime-ter used to measure the rate of fluid flow. In a thermocapacitive flow sensor, there is a heater and sensing capacitor, which has a dielectric material with a temperature-dependent dielectric constant. The heater is located close to the capacitor. If electric power is supplied to the heater, it causes the temperature of the capacitor to rise. The dielectric constant of the capacitor increases with temperature, resulting in an increase in the capacitance. When the fluid flows through the capacitor, the temperature of the capacitor will decrease due to the convective heat transfer from the capacitor to the fluid. Thus the capacitance will also be reduced. Through measuring the capacitive value, the flow velocity can be obtained by a calibration relationship between the flow rate and the capacitance. 

The measurement of flow rate is one of main subjects in experimental fluid mechanics. However, the thermocapacitive flow sensor may have electronic and semiconductor components, such as a capacitor, an n-channel MOS transistor, an oscillation circuit, and a microfabrication. Therefore, the thermocapacitive flow sensor is a multidisciplinary tool and some of its electronic and semiconductor components need to be explained. 

Thermocapacitive Flow Sensor, Fig. 2 n-charmel MOS structure and wiring, (a) n-channel MOS structure (b) diagram showing how the MOS is wired to obtain the current between source and drain... 

Thermocapacitive Flow Sensor, Fig. 9 Relationship between output voltage and gas flow velocity for heater power at 45 and 57 mW, respectively (Reproduced from IEEE Electron Device Letters with permission of IEEE)... 

Thermocapacitive Flow Sensor, Fig. 11 Oscillation frequency as a function of heater power without gas flow (Reproduced fi-om Sens Actuators A with permission from Elsevier)... 

To date, the thermocapacitive flow sensor has only been demonstrated in the semiconductor field for measuring the gas flow rate. Many microfluidic chips and most BioMEMS chips work with a liquid medium. Possible future work includes applications of the thermocapacitive flow sensor in a liquid medium, where electrical insulation would be required. 

Kwok CY, Lin KM, Huang RS (1996) A silicon thermocapacitive flow sensor with frequency modulated output. Sens Actuators A 57 35-39... 

In this essay, we focus on the thermocapacitive flow sensor. The advantages of the thermocapacitive flow... 

The function of the thermocapacitive flow sensor strongly depends on the sensing material and the quality of its fabrication. Two dielectric materials have so far been used for... 

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