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Rapid Prototyping (RP) technologies provide the ability to fabricate initial prototypes from various model materials. Stratasys Fused Deposition Modeling (FDM) is a typical RP process that can fabricate prototypes out of ABS plastic. To predict the mechanical behavior of FDM parts, it is critical to understand the material properties of the raw FDM process material, and the effect that FDM build parameters have on anisotropic material properties. This paper characterizes the properties of ABS parts fabricated by the FDM 1650. Using a Design of Experiment (DOE) approach, the process parameters of FDM, such as raster orientation, air gap, bead width, color, and model temperature were examined. Tensile strengths and compressive strengths of directionally fabricated specimens were measured and compared with injection molded FDM ABS P400 material. For the FDM parts made with a 0.003 inch overlap between roads, the typical tensile strength ranged between 65 and 72 percent of the strength of injection molded ABS P400. The compressive strength ranged from 80 to 90 percent of the injection molded FDM ABS. Several build rules for designing FDM parts were formulated based on experimental results.

Enabling technologies for wireless sensor networks have gained considerable attention in research communities over the past few years. It is highly desirable, even necessary in certain situations, for wireless sensor nodes to be self-powered. With this goal in mind, a vibration based piezoelectric generator has been developed as an enabling technology for wireless sensor networks. The focus of this paper is to discuss the modeling, design, and optimization of a piezoelectric generator based on a two-layer bending element. An analytical model of the generator has been developed and validated. In addition to providing intuitive design insight, the model has been used as the basis for design optimization. Designs of 1 cm 3 in size generated using the model have demonstrated a power output of 375 µW from a vibration source of 2.5 m s −2 at 120 Hz. Furthermore, a 1 cm 3 generator has been used to power a custom designed 1.9 GHz radio transmitter from the same vibration source.

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P ervasive networks of wireless sensor and communication nodes have the potential to significantly impact society and create large market opportunities. For such networks to achieve their full potential, however, we must develop practical solutions for self-powering these autonomous electronic devices.Fixed-energy alternatives, such as batteries and fuel cells, are impractical for wireless devices with an expected lifetime of more than 10 years because the applications and environments in which these devices are deployed usually preclude changing or re-charging of batteries. There are several power-generating options for scavenging ambient environment energy, including solar energy, thermal gradients, and vibration-based devices. However, it's unlikely that any single solution will satisfy all application spaces, as each method has its own constraints: solar methods require sufficient light energy, thermal gradients need sufficient temperature variation, and vibration-based systems need sufficient vibration sources. Vibration sources are generally more ubiquitous, however, and can be readily found in inaccessible locations such as air ducts and building structures.We've modeled, designed, and built small cantilever-based devices using piezoelectric materials that can scavenge power from low-level ambient vibration sources. Given appropriate power conditioning and capacitive storage, the resulting power source is sufficient to support networks of ultra-low-power, peer-to-peer wireless nodes. These devices have a fixed geometry and-to maximize power output-we've individually designed them to operate as close as possible to the frequency of the driving surface on which they're mounted. Here, we describe these devices and present some new designs that can be tuned to the frequency of the host surface, thereby expanding the method's flexibility. We also discuss piezoelectric designs that use new geometries, some of which are microscale (approximately hundreds of microns). Problem overviewWe first analyze the wireless sensor nodes' power requirements, and then investigate the various sources that can fill those demands. Power demandAssuming an average distance between wireless sensor nodes of approximately 10 meters-which means that the radio transmitter should operate at approximately 0 dBm (decibels above or below 1 milliwatt)-the radio transmitter's peak power consumption will be around 2 to 3 mW, depending on its efficiency. Using ultra-low-power techniques, 1 the receiver should consume less than 1 mW. Including the dissipation of the sensors and Given appropriate power conditioning and capacitive storage, devices made from piezoelectric materials can scavenge power from low-level ambient sources to effectively support networks of ultra-low-power, peerto-peer wireless nodes.

Vibration energy scavenging, harvesting ambient vibrations in structures for conversion into usable electricity, provides a potential power source for emerging technologies including wireless sensor networks. Most vibration energy scavenging devices developed to date operate effectively at a single specific frequency dictated by the device's design. However, for this technology to be commercially viable, vibration energy scavengers that generate usable power across a range of driving frequencies must be developed. This paper details the design and testing of a tunable-resonance vibration energy scavenger which uses the novel approach of axially compressing a piezoelectric bimorph to lower its resonance frequency. It was determined that an axial preload can adjust the resonance frequency of a simply supported bimorph to 24% below its unloaded resonance frequency. The power output to a resistive load was found to be 65-90% of the nominal value at frequencies 19-24% below the unloaded resonance frequency. Prototypes were developed that produced 300-400 μW of power at driving frequencies between 200 and 250 Hz. Additionally, piezoelectric coupling coefficient values were increased using this method, with k eff values rising as much as 25% from 0.37 to 0.46. Device damping increased 67% under preload, from 0.0265 to 0.0445, adversely affecting the power output at lower frequencies. A theoretical model modified to include the effects of preload on damping predicted power output to within 0-30% of values obtained experimentally. Optimal load resistance deviated significantly from theory, and merits further investigation.

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Advances in low power VLSI design, along with the potentially low duty cycle of wireless sensor nodes open up the possibility of powering small wireless computing devices from scavenged ambient power. Low level vibrations occurring in typical household, office, and manufacturing environments are considered as a possible power source for wireless sensor nodes. This work focuses on the design of electrostatic vibration-to-electricity converters using MEMS fabrications technology. Detailed models of three different design concepts are developed. The three design concepts are evaluated and compared based on simulations and practical considerations. A formal optimization of the preferred design concept is performed, and a final design is produced using the optimal design parameters. Simulations of the optimized design show that an output power density of 116 μW/cm3 is possible from input vibrations of 2.25 m/s2 at 120 Hz. Test devices have been designed for a Deep Reactive Ion Etching (DRIE) process that etches MEMS structures into the top layer of a Silicon On Insulator (SOI) wafer. The devices are currently being fabricated.