Phase (deg) Magnitude (dB) 20 20 40 180 135 90 45 10' 0 ġ(t) 하 R www Mechanical Deformation Piezo Charge Amplifer 10 10 Frequency (rad's) v(t) Figure 2: Frequency response function of a microphone Figure 3: A simple model for piezoelectric sensor 3. Figure 3 is a simple circuit modeling a piezoelectric sensor. Mechanical deformation of the sensor induces charge q(t), which is first modeled as a current source. The capacitance C models the piezoelectric material, and the resistance R represents impedance of a charge amplifier with output voltage v(t). Usually, C is fixed for a sensor, but R is adjustable from the amplifier. The frequency response function from q(t) to v(t) is Answer the following questions. G(w)= = jRw 1+jRCw (6) (a) Consider the case when C = 1 Farad and R = 0.5 Ohm. (The numbers are chosen to ease calculations. In practical applications, C is much smaller and R is much bigger.) If the input deformation induces electric charge = q(t) cost+2 sin 3t (7) predict the voltage output v(t) in time domain. (b) For the output voltage v(t) in part (a), calculate and plot its frequency spectrum. (c) For the same sensor with C = 1 Farad, what should be the resistance R to ensure that the output voltage v(t) is proportional to the induced charge q(t) in (7)?

A test was undertaken to find the dynamic properties of a SDOF system. The measured transient response recorded is shown in Figure QA2a. If the stiffness of the system is 1,000 N/m estimate: i) the damping ratio, ii) the undamped natural frequency, and iii) the mass of the system. Displacement (m) 0.08 0.06 0.04 0.02 O -0.02 -0.04 -0.06 -0.08 Figure QA2a 0.5 Time (s) 1.5 2

It's not a graded assignement, but a question in past paper.

Do not answer in image format