Pyroelectric Flow Sensors

Pyroelectric Flow Sensors, Fig. 1 A capillary flow meter with external heater and transducers is depicted at the top with the corresponding temperature profile along the capillary for zero (upper) and nonzero (lower) gas flow... 

Pyroelectric flow sensors are a kind of thermal flow sensor. They can be classified according to the thermal transfer mechanism, i.e.,... 

Pyroelectric Flow Sensors, Table 1 The advantages and disadvantages of different film deposition teehniqnes ... 

A 200 pm thick, 30 mm diameter, Z-cut, single-crystal LiTaOs wafer, unpolished on both sides, was used to fabricate the pyroelectric flow sensor. The wafer was first degreased by immersing in trichloroethane, acetone, and isopropyl alcohol for 10 min each, and then it was rinsed in deionized (DI) water and blown dry with nitrogen. After cleaning, nichrome (NiCr) and gold films were sequentially deposited on the front surface of the wafer. This was done in a cryopumped electron-beam evaporator at a pressure of about 10 Pa without breaking vacuum between the NiCr and Au evaporations. The last step minimized contamination of the devices. 

Pyroelectric Flow Sensors, Fig. 3 Layer of (a) a two-electrode element pyroelectric flow sensor and (b) a six-electrode one and (c) the equivalent circuit of the pyroelectric electrode... 

The two-electrode element, 3.8 mm x 3.8 mm X 0.2 mm in size, is shown in Fig. 3. The device was mounted on a ceramic carrier with one end of the heater connected to the NiCr common on the other side of the LiTa03 chip. The assembled tmit was then inserted into a standard 1/4 Union Tee. For completeness, the equivalent circuit of the pyroelectric flow sensors electrode is shown in Fig. 3. 

Pyroelectric Flow Sensors, Fig. 4 Diagram of the measurement system... 

Also, multifunctional pyroelectric flow sensors have also appeared. As we know, any change in the temperature induces charges on the surface of the material, inducing an electric field, which generates transverse strain and bending deformation (see Fig. 3). A typical example is used for flow sensor and valving purposes. 

During recent years, the study of micro- and nanoscale fluids has shown significant opportunities for high detectivity of elementary devices with small size. For pyroelectric flow sensors, it is highly desirable to develop theoretical models, experimental methods for pyroelectric element preparation and sensor fabrication, and higher sensitivity with excellent mechanical properties. 

Pyroelectric Flow Sensors, Figure 2 Schematic diagram of a pyroelectric detector eiement Eletrode Heater Eletrode Eletrodes Heater Eletrodes... 

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