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Robert L. Fox

Bio: Robert L. Fox is an academic researcher from Langley Research Center. The author has contributed to research in topics: Induction heating & Particle. The author has an hindex of 7, co-authored 16 publications receiving 807 citations.

Papers
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Proceedings ArticleDOI
12 Jun 2000
TL;DR: In this article, a planar composite piezoceramic actuator is presented, which uses interdigitated electrodes for poling and subsequent actuation of an internal layer of machined piezoelectric fibers.
Abstract: The design, manufacture, and testing of a low-cost, flexible, planar composite piezoceramic actuator device will be presented. The actuator uses interdigitated electrodes for poling and subsequent actuation of an internal layer of machined piezoceramic fibers. The fiber sheets are formed from monolithic piezoceramic wafers and conventional computer controlled wafer-dicing methods. The fabrication and use of fiber sheets allows precise handing and alignment of piezoceramic fibers during subsequent phases of actuator assembly. Test show that the actuator is capable of producing large, directional in-plane strains; on order of 2000 parts-per-million under a 4000 V peak-to-peak applied voltage cycle. Preliminary endurance testing indicates that the device is relatively durable, with no reductions in free-strain performance up to 90 million electrical cycles.

561 citations

Patent
25 Jul 1997
TL;DR: In this article, the authors proposed a method for mounting a pre-stressed electroactive material to a support layer, such that large displacement actuators or sensors can be used.
Abstract: The present invention relates to the mounting of pre-stressed electroactive material in such a manner that large displacement actuators or sensors result. The invention comprises mounting the pre-stressed electroactive material to a support layer. This combination of a pre-stressed electroactive material and support layer may in turn be attached to a mounting surface. The pre-stressed electroactive material may be a ferroelectric, pyroelectric, piezoelectric, or magnetostrictive material. The size, stiffness, mass, and material of the support layer is selected to result in the electroactive device having dynamic response properties, environmental capability characteristics, and the required resilience optimized for a given application. The capacity to connect the support layer to a surface expands the arenas in which the pre-stressed electroactive device may be used. Application for which the invention may be used include actuators, sensors, or as a component in a pumps, switches, relays, pressure transducers and acoustic devices.

102 citations

Patent
12 May 1993
TL;DR: An induction heating device includes a handle having a hollow interior and two opposite ends, a wrist connected to one end of the handle, a U-shaped pole piece having two spaced apart ends, and a tank circuit including an induction coil wrapped around the pole piece and a capacitor connected to the induction coil as mentioned in this paper.
Abstract: An induction heating device includes a handle having a hollow interior and two opposite ends, a wrist connected to one end of the handle, a U-shaped pole piece having two spaced apart ends, a tank circuit including an induction coil wrapped around the pole piece and a capacitor connected to the induction coil, a head connected to the wrist and including a housing for receiving the U-shaped pole piece, the two spaced apart ends of the pole piece extending outwardly beyond the housing, and a power source connected to the tank circuit. When the tank circuit is energized and a susceptor is placed in juxtaposition to the ends of the U-shaped pole piece, the susceptor is heated by induction heating due to a magnetic flux passing between the two ends of the pole piece.

29 citations

Proceedings ArticleDOI
09 Jul 1999
TL;DR: The concept of using piezoelectric actuators in devices that alter the way in which an airfoil interacts with its environment is not new. as discussed by the authors describes the characteristics and performances of these high displacement actuators and the devices that incorporate these actuators to create the synthetic jets.
Abstract: The concept of using piezoelectric actuators in devices that alter the way in which an airfoil interacts with its environment is not new. In fact, several notable research institutions, federal laboratories and industrial partners are actively pursuing this type of research. The main driving force for this activity is increased fuel economy, lighter aircraft and the elimination of hydraulically actuated control surfaces. Several years ago, researchers at NASA developed a process that uniformly prestressed the piezoelectric actuators resulting increased movement at low frequencies. The key to this increased motion was the ability to develop an evenly prestressed actuator that behaved like a leaf spring. In order to take full advantage of this piezoelectric wafer, the fixturing and drive electronics had to be developed. This is a critical issue for all piezoelectric systems. This paper describes the characteristics and performances of these high displacement actuators and the devices that incorporate these actuators to create the synthetic jets. It is envisioned that these devices will play a critical role in the future of aeronautics.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

23 citations


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Journal ArticleDOI
TL;DR: A comprehensive review of existing piezoelectric generators is presented in this paper, including impact coupled, resonant and human-based devices, including large scale discrete devices and wafer-scale integrated versions.
Abstract: This paper reviews the state-of-the art in vibration energy harvesting for wireless, self-powered microsystems. Vibration-powered generators are typically, although not exclusively, inertial spring and mass systems. The characteristic equations for inertial-based generators are presented, along with the specific damping equations that relate to the three main transduction mechanisms employed to extract energy from the system. These transduction mechanisms are: piezoelectric, electromagnetic and electrostatic. Piezoelectric generators employ active materials that generate a charge when mechanically stressed. A comprehensive review of existing piezoelectric generators is presented, including impact coupled, resonant and human-based devices. Electromagnetic generators employ electromagnetic induction arising from the relative motion between a magnetic flux gradient and a conductor. Electromagnetic generators presented in the literature are reviewed including large scale discrete devices and wafer-scale integrated versions. Electrostatic generators utilize the relative movement between electrically isolated charged capacitor plates to generate energy. The work done against the electrostatic force between the plates provides the harvested energy. Electrostatic-based generators are reviewed under the classifications of in-plane overlap varying, in-plane gap closing and out-of-plane gap closing; the Coulomb force parametric generator and electret-based generators are also covered. The coupling factor of each transduction mechanism is discussed and all the devices presented in the literature are summarized in tables classified by transduction type; conclusions are drawn as to the suitability of the various techniques.

2,834 citations

Journal ArticleDOI
TL;DR: The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans as mentioned in this paper, and the use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement.
Abstract: The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. Current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of a disposable nature to allow the device to function over extended periods of time. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. A number of sources of harvestable ambient energy exist, including waste heat, vibration, electromagnetic waves, wind, flowing water, and solar energy. While each of these sources of energy can be effectively used to power remote sensors, the structural and biological communities have placed an emphasis on scavenging vibrational energy with piezoelectric materials. This article will review recent literature in the field of power harvesting and present the current state of power harvesting in its drive to create completely self-powered devices.

2,438 citations

Patent
09 Jul 2007
TL;DR: In this paper, the authors proposed a method for fabricating electromechanical devices including one or more electroactive polymers and compliant electrodes that conform to the shape of a polymer.
Abstract: The present invention relates to electroactive polymers that are pre-strained to improve conversion from electrical to mechanical energy. When a voltage is applied to electrodes contacting a pre-strained polymer, the polymer deflects. This deflection may be used to do mechanical work. The pre-strain improves the mechanical response of an electroactive polymer. The present invention also relates to actuators including an electroactive polymer and mechanical coupling to convert deflection of the polymer into mechanical work. The present invention further relates to compliant electrodes that conform to the shape of a polymer. The present invention provides methods for fabricating electromechanical devices including one or more electroactive polymers.

855 citations

Patent
20 Jul 2000
TL;DR: In this article, the authors present methods for fabricating electromechanical devices including one or more electroactive polymers, and compliant electrodes that conform to the shape of a polymer included in a transducer.
Abstract: The present invention relates to transducers, their use and fabrication. The transducers convert between mechanical and electrical energy. Some transducers of the present invention include a pre-strained polymer. The pre-strain improves the conversion between electrical and mechanical energy. The present invention also relates to devices including an electroactive polymer to convert between electrical and mechanical energy. The present invention further relates to compliant electrodes that conform to the shape of a polymer included in a transducer. The present invention provides methods for fabricating electromechanical devices including one or more electroactive polymers.

716 citations