Our goal was to demonstrate a robust strain energy harvesting system for powering an embedded wireless sensor network without batteries.
A composite material specimen was laminated with unidirectional aligned piezoelectric fibers (PZT5A, 250 um, overall 13x10x.38 mm). The fibers were embedded within a resin matrix for damage tolerance
(Advanced Cerametrics, Lambertville, NJ). A foil strain gauge (Micro-Measurements, Raleigh, NC) was bonded to the piezoelectric fiber and shunt calibrated. The specimen was loaded in three point cyclic
bending (75 to 300 με peak) using an electrodynamic actuator operating at 60,120, and 180 Hz.
Strain energy was stored by rectifying piezoelectric fiber output into a capacitor bank. When the capacitor voltage reached a preset threshold, charge was transferred to an integrated, embeddable wireless sensor node (StrainLink, MicroStrain, Inc., Williston, VT). Nodes include: 16 bit A/D converter w/programmable gain and filter, 5 single ended or 3 differential sensor inputs, microcontroller w/16 bit
address, on-board EEPROM, and 418 MHz FSK RF transmitter. Transmission range was 1/3 mile (LOS, 1/4 wavelength antennas, 12 milliamps at +3 VDC). The RF receiver included EEPROM, XML output,
and Ethernet connectivity. Received data from network nodes are parsed according to their individual addresses.
The times required to accumulate sufficient charge to accomplish data transmission was evaluated. For peak strains of 150 με, the time to transmit was 30 to 160 seconds (for 180 to 60 Hz tests).