Piezo-resistive transducer

Another type of transducer is the pneumatic pressure transducer. It has good robustness, but poor temperature sensitivity, poor dynamic response, and average measurement error. The capillary transducer has fair robustness, fair temperature sensitivity, and fair dynamic response. The total measurement error varies from 0.5 to 3% depending on the quality of the transducer. The pushrod is similar to the capillary transducer, except that it tends to have poor temperature sensitivity and poor total error. The piezo-resistive transducer has good robustness because of its relatively thick diaphragm, good temperature sensitivity, good dynamic response, and low measurement error. A comparison of different pressure transducers is shown in Table 4.1. 

Piezo-resistive pressure transducers offer a number of advantages [82]. The transducer is quite robust because of the relatively thick diaphragm. There is no liquid fill inside the transducer as a result, there is no concern about leakage of mercury. The natural frequency of piezo-resistive transducers is about three orders of magnitude better than strain gauge type transducers. As a result, the dynamic response of piezo-resistive transducers is very good compared to that of strain gauge transducers. 

Strain gauge or piezo-resistive pressure transducers can be bought as versions for absolute and gauge pressure. One disadvantage is the high temperature drift of the zero signal which constrains the measurement range to two pressure decades. 

Figure 7.3 Piezo-resistive absolute pressure transducer (principle).

Brandenberg SJ, Bellana N, Shantz T (2010) Shear wave velocity as function of standard penetration test resistance and vertical effective stress at California bridge sites. Soil Dyn Earthq Eng 30 1026-1035 Brignoli EG, Gotti M, Stokoe KH (1996) Measurement of shear waves in laboratory specimens by means of piezo-electric transducers. Geotech Test J 19(4) 384-397... 

ZnO is a wide band gap semiconductor, which is used for various applications. Based on textured ZnO films one can build highly effective piezo field emitters. On the other hand ZnO is a very effective electron-excited phosphor. ZnO films easily withstand electron fluence more than 1 W/cm. ZnO films doped with Al, Ga, or In have a low resistivity of about 10 " Qcm and a high transparency of about 90%. This is sufficient for applications as a front contact in solar cells, liquid crystal displays etc. Dielectric ZnO films have a high electromechanical coupling factor that allow using ZnO in various surface acoustic wave (SAW) devices such as delay lines, delay-line filters, resonators, transducers and SAW convolvers. 

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