An engineer in Sensor Company has recently received a job order from POSB to fab
ID: 2080699 • Letter: A
Question
An engineer in Sensor Company has recently received a job order from POSB to fabricate an accurate thermal-radiation sensor, which can be used for building up an automatic control door system in POSB main office. With regard to this job order, a business manager in Sensor Company decided to provide a pyroelectric sensor made of a Perovskite ceramic material.
(a) State clearly the principle of “Pyroelectric effects”.
(b)Before fabricating the pyroelectric sensor, a testing engineer in USC Sensor Company measured the pyroelectric coefficient of the Perovskite ceramic material to estimate the D.C. sensing
performance. He put the material with cubic geometry of 2 2 cm3 in front of a heating body, which produces a 4.91 m of wavelength, and he observed a 3 mA of current change in a unit time. Find the pyroelecric coefficient of this material.
(c) The pyroelectric sensor made of the material tested in part (b) was installed in the main door of POSB office. One day, when a customer stood in front of the main door, it was successfully opened, because the pyroelectric sensor provided an enough D.C. voltage of 7.77 mV to the automatic door system. If the relative dielectric constant of the pyroelectric material, r , is
2.11011 and the ambient temperature is a 27 °C, what is the body temperature of the customer? (0 8.851012 [F/m])
(d) In order to estimate the A.C. output characteristics of the pyroelectric sensor material described in part (b), the sensor was connected to a basic operating circuit as shown in Fig. Q4. Find the resonant frequency, f0 , and the surface temperature, T, of the pyroelectric sensor if the sensor
+V Pyroelectric Sensor R I Output Voltage out Fig. Q3. A basic operating circuit of pyroelectric sensor.Explanation / Answer
a) Principle of Pyroelectric effet
IT is the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes.