13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- Side frame ⊗ Coil entering the page Coil leaving the page Coil housing Cantilever beam Directions of magnetic field ⊙ Figure 2 Schematics of (a) the piezoelectric energy harvesting modules and (b) the electromagnetic energy harvesting module. According to Hayt et al.[17] and Fu et al.[9], the theoretical optimum load resistances of the electromagnetic and piezoelectric modules for maximum power output are ( )2 2 2 LEO o c o R R f L π = + , (9) 1 10 LPO rf p R f C π = . (10) where Ro and Lo are the internal resistance and inductance of the coil, respectively, fc is the angular frequency of vibration of the cantilever beam, rf f is the resonant frequency of the top or bottom frames, and Cp is the clamped capacitance of a piezoelectric plate. 3. Experimental Method During the experiments, the VEH was firmly fixed on an electric shaker (HSB-01, HUASHEN) by bolting connection, as shown in Fig. 3. A function generator (AFG 3022B, TEKTRONIX) was used to supply sinusoidal excitation signal to a power amplifier, through which the signal was power amplified and transferred to the shaker to generate harmonic excitation for the test. Excitation frequency and amplitude can be controlled by adjusting the function generator and the power amplifier. The input signal to the shaker was monitored by digital oscilloscope (TDS 2014, TEKTRONIX). To measure the power generation capability, a resistive load RL was directly connected to the VEH prototype; the root mean square (rms) voltage Vrms across the load was measured; the average power by RL was calculated by 2 / a rms L P V R = . In addition, the excitation acceleration of the electric shaker was measured by a strain gauge accelerometer (LC0801, LANCE) and the resonant frequency of first bending mode was measured by Polytec Scanning Vibrometer PSV-300. Signal Generator Power Amplifier Electric Shaker Digital Oscilloscope VEH Prototype Fixture Accelerometer Digital Multimeter Resistor Digital Oscilloscope Polytec Scanning Vibrometer Figure 3 Schematic diagram of the experimental setup.
RkJQdWJsaXNoZXIy MjM0NDE=