2016年10月26日星期三

Wirelessly Powered Drone Technology Demonstrated

 Scientists have demonstrated an efficient method for wirelessly transferring power to a drone while it is flying. The technology could in theory allow flying drones to stay airborne indefinitely simply by hovering over a ground support vehicle to recharge—potentially opening up new industrial applications.
The technology uses inductive coupling, a concept initially demonstrated by inventor Nikola Tesla over a century ago. Two copper coils are tuned into one another electronically, which enables the wireless exchange of power at a certain frequency.
To demonstrate the technology, engineers from Imperial College London removed the battery from an off-the-shelf mini-drone and demonstrated that they could wirelessly transfer power to it to keep it aloft. They believe their demonstration is the first to show how wireless charging via inductive coupling can be carried out efficiently with a flying object such as a drone.
To achieve the feat, after removing the battery from the 12 cm-diameter quadcopter drone, the researchers altered its electronics and made a copper foil ring to act as a receiving antenna encircling the drone's casing. On the ground, a transmitter device made out of a circuit board was connected to the electronics and a power source, creating a magnetic field.
The drone's electronics were calibrated at the frequency of the magnetic field. When it flew into the magnetic field, an alternating-current voltage was induced in the receiving antenna, and the drone's electronics converted it efficiently into a direct-current voltage to power it.
The technology is still in its experimental stage, the researchers say, as the drone can currently fly only 10 cm above the magnetic field transmission source. The team estimates they are one year away from a commercially feasible product.
The use of small drones for commercial purposes—for surveillance, reconnaissance missions and search-and-rescue operations—is growing rapidly. However, the distance that a drone can travel and the duration it can stay in the air are limited by the availability of power and recharging requirements. Wireless power-transfer technology may solve this, the team says.
"Imagine using a drone to wirelessly transmit power to sensors on things such as bridges to monitor their structural integrity," says Paul Mitcheson, professor in the Department of Electrical and Electronic Engineering. "This would cut out humans having to reach these difficult-to-access places to recharge them."
The technology could potentially allow flying drones to stay airborne indefinitely simply by hovering over a ground support vehicle to recharge. Image credit: Imperial College London.

2016年10月13日星期四

New Process for Copper Nanowires

Cell phones and Apple watches could last longer due to a new method to create copper nanowires.
A team of Lawrence Livermore National Laboratory (LLNL) scientists has developed a process for purifying copper nanowires with a near-100% yield. The research shows how the method can yield large quantities of long, uniform, high-purity copper nanowires that meet the requirements of nanoelectronic applications—and provide an avenue for purifying industrial-scale synthesis of copper nanowires, a key step for commercialization.
Functional nanomaterials are notoriously difficult to produce in large volumes with highly controlled composition, shapes and sizes. This difficulty has limited adoption of nanomaterials in many manufacturing technologies.
The most common approach to create nanowires not only yields nanowires but also other low-aspect ratio shapes, such as nanoparticles and nanorods. These undesired byproducts are almost always produced due to difficulties in controlling the non-instantaneous nucleation of the seed particles as well as seed types, which cause the particles to grow in multiple pathways.
The key to the process developed at LLNL is the use of a hydrophobic surfactant in an aqueous solution, together with an immiscible water organic solvent system, to create a hydrophobic-distinct interface, allowing nanowires to cross over spontaneously due to their different crystal structure and total surface area from those of nanoparticles. The resulting copper nanowires carry no byproducts that would affect their shape and purity.
"The principles developed from this particular case of copper nanowires may be applied to a variety of nanowire applications," says LLNL staff scientist Fang Qian. "This purification method will open up new possibilities in producing high-quality nanomaterials with low cost and in large quantities."
The researchers say they envision using purified nanomaterials in a potentially wide variety of new fabrication approaches, including additive manufacturing.
illustration of the separation process from a mixture of various copper nanocrystal shapes

An illustration of the separation process from a mixture of various copper nanocrystal shapes (two tubes on the left) to pure nanowires and nanoparticles (two tubes on the right).