Inspired by music-playing harmonicas that create tones via oscillations of reeds when subjected to air blow, this paper entails a concept for microwind power generation using flow-induced self-excited oscillations of a piezoelectric beam embedded within a cavity. Specifically, when the volumetric flow rate of air past the beam exceeds a certain threshold, the energy pumped into the structure via nonlinear pressure forces offsets the system’s intrinsic damping setting the beam into self-sustained limit-cycle oscillations. The vibratory energy is then converted into electricity through principles of piezoelectricity. Experimental and theoretical results are presented demonstrating the feasibility of the proposed concept.

In this work, inspired by music playing harmonicas, we conduct a conceptual investigation of a coupled aero-electromechanical system for wind energy harvesting. The system consists of a piezoelectric cantilever unimorph structure embedded within an air chamber to mimic the vibration of the reeds in a harmonica when subjected to air flow. In principle, when wind blows into the air chamber, the air pressure in the chamber increases and bends the cantilever beam opening an air path between the chamber and the environment. When the volumetric flow rate of air past the cantilever is large enough, the energy pumped into the structure via the nonlinear pressure forces offset the intrinsic damping in the system setting the beam into self-sustained limit-cycle oscillations. These oscillations induce a periodic strain in the piezoelectric layer which produces a voltage difference that can be channeled into an electric load. Unlike traditional vibratory energy harvesters where the excitation frequency needs to match the resonant frequency of the device for efficient energy extraction, the nonlinearly coupled aero-elasto dynamics of this device guarantees autonomous vibration of the cantilever beam near its natural frequency as long as the volumetric flow rate is larger than a certain threshold. Experimental results are presented to demonstrate the ability of this device to harvest wind energy under normal wind conditions.

Human activities alter disturbance regimes and spatio-temporal distribution of soil resources that can affect plant invasion outcomes. The objective of this study was to test whether fire history and cattle activity alter soil resource gradients, thereby affecting patterns of annual brome invasion. Six paired burned and unburned transect lines (1-kilometer in length) were established in the northeast Mojave Desert along the boundaries of four independent wildfires. At 100-meter transect increment points, we measured the distance to the two nearest cowpats and then established two random points and measured the density, height, biomass, and seed production of red brome, soil moisture and inorganic N. Cattle activity was 29% greater along burned transects compared to unburned transects. Red brome height, density, and seed production were 11% to 34% greater along burned transects than unburned transects (P < 0.05). Red brome height, biomass, density, and seed production were 2- to10-fold greater next to cowpats compared to random points (P < 0.05), likely due to increased soil moisture and inorganic N. Post-fire conditions and cowpats increased soil inorganic N, which was strongly correlated with red brome density, height, biomass and seed production (R2 = 0.60-0.85). Transgenerational legacy effects were evident as seeds from red brome next to cowpats had 27% higher germination than seeds collected from random points. The results suggest that positive responses of red brome to increases in inorganic N related to fire and cattle activity could significantly reinforce fine fuel infill that drives invasive grass-fire cycles in deserts of North America.

We present and validate a nonlinear aero-electro-mechanical model that describes the response of a scalable self-excited wind energy harvester. Similar to music-playing harmonica that create tones via oscillations of reeds when subjected to air blow, the proposed device uses flow-induced self-excited oscillations of a piezoelectric beam embedded within a cavity to generate electric power. Specifically, when the volumetric flow rate of air past the beam exceeds a certain threshold, the energy pumped into the structure via nonlinear pressure forces offsets the intrinsic damping in the system setting the beam into self-sustained limit-cycle oscillations. The vibratory energy is then converted into electricity through principles of piezoelectricity.

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