Acceleration-waveform-sending wireless sensor node powered by piezoelectric vibration energy harvester

Abstract

We have developed a wireless sensor node (WSN) powered by a piezoelectric vibration energy harvester that enables transmission of three-axis acceleration waveform data. Unlike a conventional WSN, which sends a single point representing the root mean square acceleration value, the proposed WSN allows the frequency, vibrational modes, and displacement of the target structure to be obtained. Therefore, this waveform-sending scenario is highly suitable for structural health monitoring applications. We used a power gating technique to reduce the standby energy consumption significantly and thus realize the waveform-sending concept. The overall dimensions and mass of the WSN are 3×3×3 cm 3 and 26 g, respectively. The overall dimensions of the harvester are 5.6×2×2.1 cm 3 . The WSN measures the threeaxis acceleration of the structure's vibration for 1.2 s at a sampling rate of 3,200 samples every 5 min, transmits the data, and then goes into standby mode. Because of the power gating technique, the energy consumption per cycle is as low as 108 mJ. We evaluated the WSN under both harmonic and random vibration conditions. For harmonic vibrations, the acceleration magnitude applied using a shaker was 1 m/s 2 at the harvester's resonance. For random vibrations, a power spectral density (PSD) of 0.1 (m/s 2 ) 2 /Hz and a frequency range of 10-100 Hz were set. The WSN operated successfully using only energy generated by the harvester and the transmitted waveforms matched the waveforms measured by a high-precision acceleration pick-up. Here, we report the WSN design methodology and the detailed charging characteristics of the energy storage capacitor.

Wireless sensor node powered by piezoelectric vibration energy harvester for vibrational mode identification and structural health monitoring

“…Therefore, this study applies our practical WSN [7] to structural health monitoring and validates the excellent classification performance from the transmitted waveform data. A normal intact beam and four beams that contain notches at four different locations were prepared.…”

“…The energy consumption per transmission cycle was as low as 108 mJ [7]. As reported in our previous study [7], it is very difficult to predict the power based on the theory alone because the nonlinear piezoelectricity [8−10], the diode voltage drops [11], and the unique charging properties [7] of the specific EDLC must be considered within the analysis. Furthermore, the random nature of the vibration makes the analysis more complex.…”

“…The WSN connected to the piezoelectric VEH was then mounted near the tip of the beam. The WSN was described in detail in our original work [7], and the lengthy description has thus been omitted here. The dimensions and mass of the WSN are 30×30×30 mm 3 and 26 g, respectively.…”

“…To meet this demand, WSNs powered by VEHs that can transmit waveform data have been developed recently [3]− [7]. Rubes et al [3] developed a WSN powered by an electromagnetic VEH that can transmit the structural vibration waveform data measured by a macro fiber composite (MFC) sensor attached to the structure.…”

“…These studies used large and heavy harvesters to realize the self-powered WSNs and the energy consumption per transmission was relatively high for these devices. Recently, the authors [7] developed a WSN powered by a miniature piezoelectric VEH that can transmit three-axis acceleration waveform data with low power consumption. This practical WSN allows us to classify or predict the conditions of structures or machinery more accurately because more features can be extracted and used to perform AI analysis from the three-axis acceleration waveforms when compared with the data from a uniaxial acceleration waveform.…”