There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

http://www.nanoscience.gatech.edu/paper/2012/12_NE_04.pdf

Flexible triboelectric generator

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.

/pdf/energy-harvesting-vibration-sources-for-microsystems-46t885pwdp.pdf

Energy harvesting vibration sources for microsystems applications

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.

/pdf/a-review-of-power-harvesting-using-piezoelectric-materials-k69swwfj1u.pdf

A review of power harvesting using piezoelectric materials (2003–2006)

The process of acquiring the energy surround- ing a system and converting it into usable electrical energy is termed power harvesting. In the last few years, there has been a surge of research in the area of power harvesting. This increase in research has been brought on by the mod- ern advances in wireless technology and low-power electron- ics such as microelectromechanical systems. The advances have allowed numerous doors to open for power harvesting systems in practical real-world applications. The use of pie- zoelectric materials to capitalize on the ambient vibrations surrounding a system is one method that has seen a dramat- ic rise in use for power harvesting. Piezoelectric materials have a crystalline structure that provides them with the ability to transform mechanical strain energy into electrical charge and, vice versa, to convert an applied electrical potential into mechanical strain. This property provides these materials with the ability to absorb mechanical energy from their surround- ings, usually ambient vibration, and transform it into electrical energy that can be used to power other devices. While piezo- electric materials are the major method of harvesting energy, other methods do exist; for example, one of the conventional methods is the use of electromagnetic devices. In this paper we discuss the research that has been performed in the area of power harvesting and the future goals that must be achieved for power harvesting systems to find their way into everyday use. and replacement of the battery can become a tedious task. In the case of wireless sensors, these devices can be placed in very remote locations such as structural sensors on a bridge or global positioning system (GPS) tracking devices on ani- mals in the wild. When the battery is extinguished of all its power, the sensor must be retrieved and the battery re- placed. Because of the remote placement of these devices, obtaining the sensor simply to replace the battery can be- come a very expensive task or even impossible. For in- stance, in civil infrastructure applications it is often desirable to embed the sensor, making battery replacement unfeasible. If ambient energy in the surrounding medium could be ob- tained, then it could be used to replace or charge the battery. One method is to use piezoelectric materials to obtain ener- gy lost due to vibrations of the host structure. This captured energy could then be used to prolong the life of the power supply or in the ideal case provide endless energy for the electronic devices lifespan. For these reasons, the amount of research devoted to power harvesting has been rapidly in- creasing. In this paper we review and detail some of the top- ics in power harvesting that have been receiving the most research, including energy harvesting from mechanical vi- bration, biological systems, and the effects of power har- vesting on the vibration of a structure.

A Review of Power Harvesting from Vibration using

The process of acquiring the energy surrounding a system and converting it into usable electrical energy is termed power harvesting. In the last few years, there has been a surge of research in the area of power harvesting. This increase in research has been brought on by the modern advances in wireless technology and low-power electronics such as microelectromechanical systems. The advances have allowed numerous doors to open for power harvesting systems in practical real-world applications. The use of piezoelectric materials to capitalize on the ambient vibrations surrounding a system is one method that has seen a dramatic rise in use for power harvesting. Piezoelectric materials have a crystalline structure that provides them with the ability to transform mechanical strain energy into electrical charge and, vice versa, to convert an applied electrical potential into mechanical strain. This property provides these materials with the ability to absorb mechanical energy from their surroundings, usually ambient vibration, and transform it into electrical energy that can be used to power other devices. While piezoelectric materials are the major method of harvesting energy, other methods do exist; for example, one of the conventional methods is the use of electromagnetic devices. In this paper we discuss the research that has been performed in the area of power harvesting, and the future goals that must be achieved for power harvesting systems to find their way into everyday use.

A Review of Power Harvesting from Vibration using Piezoelectric Materials

Piezoelectric materials (PZT) can be used as mechanisms to transfer mechanical energy, usually ambient vibration, into electrical energy that can be stored and used to power other devices. With the recent advances in wireless and micro-electro-mechanical-systems (MEMS) technology, sensors can be placed in exotic and remote locations. As these devices are wireless it becomes necessary that they have their own power supply. The power supply in most cases is the conventional battery; however, problems can occur when using batteries because of their finite life span. Because most sensors are being developed so that they can be placed in remote locations such as structural sensors on a bridge or global positioning service (GPS) tracking devices on animals in the wild, obtaining the sensor simply to replace the battery can become a very expensive task. Fur- thermore, in the case of sensors located on civil structures, it is often advantageous to embed them, making access impossible. Therefore, if a method of obtaining the untapped energy surrounding these sensors was implemented, significant life could be added to the power supply. One method is to use PZT materials to obtain ambient energy surrounding the test specimen. This captured energy could then be used to prolong the power supply or in the ideal case provide endless energy for the sensors lifespan. The goal of this study is to develop a model of the PZT power harvesting device. This model would simplify the design procedure necessary for determining the appropriate size and vibration levels necessary for sufficient energy to be produced and supplied to the electronic devices. An experimental verification of the model is also performed to ensure its accuracy.

Estimation of Electric Charge Output for Piezoelectric Energy Harvesting

Piezoelectric materials can be used as a means of transforming ambient vibrations into electrical energy that can then be stored and used to power other devices. With the recent surge of microscale devices, piezoelectric power generation can provide a convenient alternative to traditional power sources used to operate certain types of sensors/actuators, telemetry, and MEMS devices. However, the energy produced by these materials is in many cases far too small to directly power an electrical device. Therefore, much of the research into power harvesting has focused on methods of accumulating the energy until a sufficient amount is present, allowing the intended electronics to be powered. In a recent study by Sodano et al. (2004a) the ability to take the energy generated through the vibration of a piezoelectric material was shown to be capable of recharging a discharged nickel metal hydride battery. In the present study, three types of piezoelectric devices are investigated and experimentally tested to deter...

Henry A. Sodano

Papers

A review of power harvesting using piezoelectric materials (2003–2006)

A Review of Power Harvesting from Vibration using

A Review of Power Harvesting from Vibration using Piezoelectric Materials

Estimation of Electric Charge Output for Piezoelectric Energy Harvesting

Comparison of piezoelectric energy harvesting devices for recharging batteries