where P is the power and V is the voltage drop across the load resistance R. The resulting power
(with a chirp input from 0-250Hz) is shown in Figure 9 and the voltage and current found are
shown in Figure 10. The data presented uses a chirp signal rather than the random signal shown
previously because a chirp signal allows the voltage produced at different frequencies to be
visualized more easily. As can be seen in the Figure, the maximum instantaneous power is
identified as 2mW, which occurs at the resonance of the test plate. Three PZT plates were tested
with the same configuration, and all produce a maximum power in the range of 1.5-2mW, and an
average power of 0.14-0.2mW. These measurements were made with the magnitude of the chirp
signal matching that of the signal measured from the automobile compressor. In addition, these
measurements were made without a capacitor, which points out that this power would be
immediately available for powering other devices. This estimation however does not account for
the efficiencies of circuit components, such as a capacitor, diode, and voltage regulator. This
estimated power certainly would not be sufficient to operate commonly available sensors,
actuators or telemetry devices in many field applications, not to mention that it would require a
certain period of time to charge the circuit, if a capacitor or battery is used.