Justin R. Farmer
Virginia Tech
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Justin R. Farmer.
48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | 2007
Mohammed F. Daqaq; Jamil M. Renno; Justin R. Farmer; Daniel J. Inman
The authors present a comprehensive study of the effects of damping and electromechanical coupling on the power optimality of a vibration-based energy harvester. The harvester under consideration utilizes a piezoceramic element operating in the {33} mode to scavenge mechanical energy emanating from a sinusoidal-base excitation. Under typical operating conditions, the piezoceramic element is subjected to small strains and low electric fields, which allows for the adaptation of the linear small-signal constitutive law to model its behavior. To optimize the harvested power, previous researches neglected the role of mechanical damping. This lead to results suggesting that the optimal-harvesting frequencies are not effected by mechanical damping. However, in this paper, exact expressions for the optimal frequency ratios that account for damping are derived. The results show that mechanical damping affects the optimal frequency ratios and optimal harvested power qualitatively and quantitatively. The effects of the electromechanical coupling coefficient is also explored. It is observed that there is an optimal value of the coupling coefficient beyond which the harvested power decreases. This result breaks the taboo suggesting that larger electromechanical coupling culminates in more efficient energy harvesting devices. Additionally, it is shown that at the optimal frequencies, and optimal load resistance, increasing the electromechanical coupling saturates the harvested power
Proceedings of SPIE | 2012
Valery F. Godinez-Azcuaga; Justin R. Farmer; Paul Ziehl; Victor Giurgiutiu; Antonio Nanni; Daniel J. Inman
This paper discusses the development status of a self-powered wireless sensor node for steel and concrete bridges monitoring and prognosis. By the end of the third year in this four-year cross-disciplinary project, the 4-channel acoustic emission wireless node, developed by Mistras Group Inc, has already been deployed in concrete structures by the University of Miami. Also, extensive testing is underway with the node powered by structural vibration and wind energy harvesting modules developed by Virginia Tech. The development of diagnosis tools and models for bridge prognosis, which will be discussed in the paper, continues and the diagnosis tools are expected to be programmed in the nodes AVR during the 4th year of the project. The impact of this development extends beyond the area of bridge health monitoring into several fields, such as offshore oil platforms, composite components on military ships and race boats, combat deployable bridges and wind turbine blades. Some of these applications will also be discussed. This project was awarded to a joint venture formed by Mistras Group Inc, Virginia Tech, University of South Carolina and University of Miami by the National Institute of Standards and Technology through its Technology Innovation Program Grant #70NANB9H007.
Proceedings of SPIE | 2012
M. Amin Karami; Justin R. Farmer; Daniel J. Inman
A nonlinear piezoelectric wind energy harvester is proposed which has a low startup wind speed and is not restricted to a specific wind speed. By using the piezoelectric transduction mechanism, the gearbox is eliminated from the system and the start up speed is improved. Permanent magnets are placed in the blade part of the windmill. The interactions between the rotating magnets, positioned on the blades, and the tip magnets mounted on the piezoelectric beams directly and parametrically excite the beams. The nonlinear magnetic force makes the vibrations of the beams nonlinear and can make the beams bi-stable. This phenomenon is utilized to enhance the power output and to improve the robustness of the power production. Two designs are presented which incorporate parametric and ordinary excitations to generate electric power. The performance of each design is examined through experimental investigations. An analytic model is developed which is verified by the experimental results and explains the nonlinear phenomena captured by the experimental investigations.
Key Engineering Materials | 2007
Daniel J. Inman; Justin R. Farmer; Benjamin L. Grisso
Autonomous, wireless structural health monitoring is one of the key goals of the damage monitoring industry. One of the main roadblocks to achieving autonomous sensing is removing all wiring to and from the sensor. Removing external connections requires that the sensor have its own power source in order to be able to broadcast/telemetry information. Furthermore if the sensor is to be autonomous in any way, it must contain some sort of computing and requires additional power to run computational algorithms. The obvious choice for wireless power is a battery. However, batteries often need periodical replacement. The work presented here focuses on using ambient energy to power an autonomous sensor system and recharge batteries and capacitors used to run an active sensing system. In particular, we examine methods of harvesting energy to run sensor systems from ambient vibration energy using piezoelectric elements.
21st Biennial Conference on Mechanical Vibration and Noise, presented at - 2007 ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, IDETC/CIE2007 | 2007
Jamil M. Renno; Mohammed F. Daqaq; Justin R. Farmer; Daniel J. Inman
An alternative circuit to improve the performance of a vibration-based energy harvester is proposed. The harvesting device considered consists of a piezoceramic element operating in the {33} direction. In normal operating conditions, piezoceramics experience small deflection and hence the small signal linear constitutive law of piezoelectricity is adopted for the scope of this work. Typically, vibration-based energy harvesters are designed to operate at the resonance or antiresonance frequencies. This condition might be tolerable in many cases, but is often difficult to realize in real-life applications. In this work, the authors propose adding an inductor to the harvesting circuit. It is shown that the addition of this simple electric element modifies the performance remarkably in a qualitative and quantitative manner. The maximum power values obtained at the resonance and antiresonance frequencies can be achieved at any frequency ratio if optimal electric elements are used. This allows for harvesting a constant optimal power everywhere in the frequency domain. Further investigation reveals the existence of a singularity at low damping ratios (below a bifurcation damping ratio). In that case, the optimization scheme yields a negative value for the optimal inductance between the resonance and antiresonance frequencies. However, this singularity is not experienced at a high damping ratio (beyond a bifurcation damping ratio). Moreover, for high damping ratios, it is shown that the proposed circuit is superior to a circuit that does not deploy an inductor.Copyright
ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2011 | 2011
M. Amin Karami; Justin R. Farmer; Scott Bressers; Shashank Priya; Daniel J. Inman
A nonlinear piezoelectric wind energy harvester is proposed which operates at low wind speeds and is not sensitive to the speed of the gusts. The piezoelectric transduction mechanism is used instead of DC generators to eliminate the gearbox in the windmill and thus reduces the friction. The reduced friction facilitates operation of the windmill at low wind speeds. Permanent magnets have been placed in the blade part of the windmill. The magnets axially repel another set of magnets which are positioned at the tip of the piezoelectric beams. As a result, when the rotating magnets pass over the piezoelectric beams they excite the beams and affect the type of their vibrations. The nature of excitations in the proposed design is therefore both parametric excitations and ordinary excitations. The nonlinear magnetic axial force makes the vibrations of the beams nonlinear and can make the beams bi-stable. This phenomenon is utilized to enhance the power output and to improve the robustness of the power production. Two designs are presented which incorporate parametric and ordinary excitations to generate electric power. The performance of each design is examined through experimental investigations.© 2011 ASME
Renewable Energy | 2013
M. Amin Karami; Justin R. Farmer; Daniel J. Inman
47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference<BR> 14th AIAA/ASME/AHS Adaptive Structures Conference<BR> 7th | 2006
David A. Neal; Justin R. Farmer; Daniel J. Inman
8th International Conference on Structural Dynamics, EURODYN 2011 | 2011
Jozue Vieira Filho; Fabricio Guimarães Baptista; Justin R. Farmer; Daniel J. Inman
Wind Energy | 2014
B. S. Joyce; Justin R. Farmer; Daniel J. Inman