Paul K. Wright

Bio: Paul K. Wright is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Energy harvesting & Wireless sensor network. The author has an hindex of 55, co-authored 325 publications receiving 18046 citations. Previous affiliations of Paul K. Wright include New York University & University of California.

A study of low level vibrations as a power source for wireless sensor nodes

Abstract: 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. A broad review of potential power scavenging technologies and conventional energy sources is first presented. Low-level vibrations occurring in common household and office environments as a potential power source are studied in depth. The goal of this paper is not to suggest that the conversion of vibrations is the best or most versatile method to scavenge ambient power, but to study its potential as a viable power source for applications where vibrations are present. Different conversion mechanisms are investigated and evaluated leading to specific optimized designs for both capacitive MicroElectroMechancial Systems (MEMS) and piezoelectric converters. Simulations show that the potential power density from piezoelectric conversion is significantly higher. Experiments using an off-the-shelf PZT piezoelectric bimorph verify the accuracy of the models for piezoelectric converters. A power density of 70 @mW/cm^3 has been demonstrated with the PZT bimorph. Simulations show that an optimized design would be capable of 250 @mW/cm^3 from a vibration source with an acceleration amplitude of 2.5 m/s^2 at 120 Hz.

Anisotropic material properties of fused deposition modeling ABS

Abstract: 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.

A piezoelectric vibration based generator for wireless electronics

Abstract: 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 cm3 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 cm3 generator has been used to power a custom designed 1.9 GHz radio transmitter from the same vibration source.

Improving power output for vibration-based energy scavengers

Abstract: Pervasive 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. 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. In this paper, 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).

Energy Scavenging for Wireless Sensor Networks: with Special Focus on Vibrations

Abstract: 1 Introduction.- 1. Energy Storage.- 2. Power Distribution.- 3. Power scavenging.- 4. Summary of potential power sources.- 5. Overview of Vibration-to-Electricity Conversion Research.- 2 Vibration Sources and Conversion Model.- 1. Types of Vibrations Considered.- 2. Characteristics of Vibrations Measured.- 3. Generic Vibration-to-Electricity Conversion Model.- 4. Efficiency of Vibration-to-Electricity Conversion.- 3 Comparison of Methods.- 1. Electromagnetic (Inductive) Power Conversion.- 2. Electrostatic (Capacitive) Power Conversion.- 3. Piezoelectric Power Conversion.- 4. Comparison of Energy Density of Converters.- 5. Summary of Conversion Mechanisms.- 4 Piezoelectric Converter Design.- 1. Basic Design Configuration.- 2. Material Selection.- 3. Analytical Model for Piezoelectric Generators.- 4. Discussion of Analytical Model for Piezoelectric Generators.- 5. Initial Prototype and Model Verification.- 6. Design Optimization.- 7. Analytical Model Adjusted for a Capacitive Load.- 8. Discussion of Analytical Model Changes for Capacitive Load.- 9. Optimization for a Capacitive Load.- 10. Conclusions.- 5 Piezoelectric Converter Test Results.- 1. Implementation of Optimized Converters.- 2. Resistive load tests.- 3. Discussion of resistive load tests.- 4. Capacitive load tests.- 5. Discussion of capacitive load test.- 6. Results from testing with a custom designed RF transceiver.- 7. Discussion of results from custom RF transceiver test.- 8. Results from test of complete wireless sensor node.- 9. Discussion of results from complete wireless sensor node.- 10. Conclusions.- 6 Electrostatic Converter Design.- 1. Explanation of concept and principle of operation.- 2. Electrostatic Conversion Model.- 3. Exploration of design concepts and device specific models.- 4. Comparison of design concepts.- 5. Design Optimization.- 6. Flexure design.- 7. Discussion of design and conclusions.- 7 Fabrication of Electrostatic Converters.- 1. Choice of process and wafer technology.- 2. Basic process flow.- 3. Specific processes used.- 4. Conclusions.- 8 Electrostatic Converter Test Results.- 1. Macro-scale prototype and results.- 2. Results from fluidic self-assembly process prototypes.- 3. Results from integrated process prototypes.- 4. Results from simplified custom process prototypes.- 5. Discussion of Results and Conclusions.- 9 Conclusions.- 1. Justification for focus on vibrations as a power source.- 2. Piezoelectric vibration to electricity converters.- 3. Design considerations for piezoelectric converters.- 4. Electrostatic vibration to electricity converters.- 5. Design considerations for electrostatic converters.- 6. Summary of conclusions.- 7. Recommendations for future work.- Acknowledgments.- Appendix A: Analytical Model of a Piezoelectric Generator.- 1. Geometric terms for bimorph mounted as a cantilever.- 2. Basic dynamic model of piezoelectric generator.- 3. Expressions of interest from basic dynamic model.- 4. Alterations to the basic dynamic model.- Appendix B: Analytical Model of an Electrostatic Generator.- 1. Derivation of electrical and geometric expressions.- 2. Derivation of mechanical dynamics and electrostatic forces.- 3. Simulation of the in-plane gap closing converter.- References.

Software survey: VOSviewer, a computer program for bibliometric mapping.

Abstract: We present VOSviewer, a freely available computer program that we have developed for constructing and viewing bibliometric maps. Unlike most computer programs that are used for bibliometric mapping, VOSviewer pays special attention to the graphical representation of bibliometric maps. The functionality of VOSviewer is especially useful for displaying large bibliometric maps in an easy-to-interpret way. The paper consists of three parts. In the first part, an overview of VOSviewer’s functionality for displaying bibliometric maps is provided. In the second part, the technical implementation of specific parts of the program is discussed. Finally, in the third part, VOSviewer’s ability to handle large maps is demonstrated by using the program to construct and display a co-citation map of 5,000 major scientific journals.

Multiferroic and magnetoelectric materials

Abstract: A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few 'multiferroic' materials that exhibit both of these properties, but the 'magnetoelectric' coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, there has been a recent resurgence of interest driven by long-term technological aspirations.

Wireless sensor network survey

Abstract: A wireless sensor network (WSN) has important applications such as remote environmental monitoring and target tracking. This has been enabled by the availability, particularly in recent years, of sensors that are smaller, cheaper, and intelligent. These sensors are equipped with wireless interfaces with which they can communicate with one another to form a network. The design of a WSN depends significantly on the application, and it must consider factors such as the environment, the application's design objectives, cost, hardware, and system constraints. The goal of our survey is to present a comprehensive review of the recent literature since the publication of [I.F. Akyildiz, W. Su, Y. Sankarasubramaniam, E. Cayirci, A survey on sensor networks, IEEE Communications Magazine, 2002]. Following a top-down approach, we give an overview of several new applications and then review the literature on various aspects of WSNs. We classify the problems into three different categories: (1) internal platform and underlying operating system, (2) communication protocol stack, and (3) network services, provisioning, and deployment. We review the major development in these three categories and outline new challenges.

Nitrogen cycles: past, present, and future

Abstract: This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.

Epidemiology of Invasive Candidiasis: a Persistent Public Health Problem

Abstract: Invasive candidiasis (IC) is a leading cause of mycosis-associated mortality in the United States. We examined data from the National Center for Health Statistics and reviewed recent literature in order to update the epidemiology of IC. IC-associated mortality has remained stable, at approximately 0.4 deaths per 100,000 population, since 1997, while mortality associated with invasive aspergillosis has continued to decline. Candida albicans remains the predominant cause of IC, accounting for over half of all cases, but Candida glabrata has emerged as the second most common cause of IC in the United States, and several less common Candida species may be emerging, some of which can exhibit resistance to triazoles and/or amphotericin B. Crude and attributable rates of mortality due to IC remain unacceptably high and unchanged for the past 2 decades. Nonpharmacologic preventive strategies should be emphasized, including hand hygiene; appropriate use, placement, and care of central venous catheters; and prudent use of antimicrobial therapy. Given that delays in appropriate antifungal therapy are associated with increased mortality, improved use of early empirical, preemptive, and prophylactic therapies should also help reduce IC-associated mortality. Several studies have now identified important variables that can be used to predict risk of IC and to help guide preventive strategies such as antifungal prophylaxis and early empirical therapy. However, improved non-culture-based diagnostics are needed to expand the potential for preemptive (or early directed) therapy. Further research to improve diagnostic, preventive, and therapeutic strategies is necessary to reduce the considerable morbidity and mortality associated with IC.