Nuts and Volts - November 2010

TECH KNOWLEDGEY

EVENTS, ADVANCES, AND NEWS

2010

■ BY JEFF ECKERT

ADVANCED TECHNOLOGY

NEW APPROACH TO SOLAR

We've become pretty much accustomed to the steady flow of ho-hum incremental improvements in solar technology, but engineers at Stanford University ( www.stanford.edu) claim to have come up with a process that can more than double the efficiency of solar cell technology and even make it price competitive with petroleum. Called photon enhanced thermionic emission (PETE), it is uniquely able to simultaneously tap into the sun's light and heat.

Most photovoltaic cells use a silicon semiconducting material to convert photons into juice, but they use only a portion of the light spectrum and discard the rest in the form of heat. Unfortunately, such cells become less efficient (and physically degraded) at higher temperatures, so you generally can't boost their output via concentrating devices such as parabolic dishes. (In 2008, IBM demonstrated a system that focused 2,300 equivalent suns on a one sq cm cell to generate 70W, but it required a "liquid metal" cooling system to keep the temperature in check.) In contrast, a PETE device doesn't really hit its peak output until it gets past about 200°C (392°F), so there's no reason why you can't couple one with a thermal conversion system to double the overall output. The new photovoltaic is based on coating a

■ A small PETE device glows inside a vacuum test chamber.

different semiconductor material (in this case, gallium nitride) with a layer of cesium to produce a substance that can handle the high temperatures. The nice touch is that, if properly designed, a PETE system can be retrofitted to existing thermal systems for a relatively inexpensive conversion. According to Prof. Nick Melosh, "This is really a conceptual breakthrough, a new energy conversion process, not just a new material or a slightly different tweak. It is actually something fundamentally different about how you can harvest energy." The materials used in the devices are cheap and readily available, so we're not talking about something that's exotic and cost prohibitive. The only apparent catch is that you probably won't want something sizzling on your rooftop at temperatures as high as 800°C (1,500°C), so the devices will probably be exiled to such places as the Mojave Desert. ▲

US ARMY DEVELOPING SNAKEBOTS

The desktop prototype may not look like much, but the US Army Research Lab ( www.arl.army.mil) is expanding on snakebot technology developed at Carnegie Mellon's Robotics Institute that may allow the use of systems instead of soldiers for dangerous search-and-rescue missions, IED disposal, and cargo and checkpoint inspections. The incarnation is the Robotic Tentacle Manipulator, described as an "arrangement of the bases of several snakes in a circular array that functions like a team using multiple parts of their bodies to manipulate an object, scan a room, or handle improvised explosive devices." An interesting aspect is that the system is scalable and therefore can be built as a subsystem to larger platforms such as the iRobot Warrior which is designed to traverse rough terrain and even climb stairs. It is also extensible in that, by varying the number of links on each tentacle, you can adjust its reach and its ability to crawl, swim, climb, or otherwise move through narrow spaces. Plus, fitted with a camera, it can simultaneously send images back to the operator. In fact, the subsystem can be equipped with an array of sensors, including LADAR, allowing it to generate 3D images. It even features touch sensitivity which allows it to balance objects and detect applied forces. Researchers are hoping that the manipulator will soon solve the "opening a door problem" — a challenge posed by the variety of knobs, handles, levers, bars, etc., used on doors. Summarizing, an Army rep observed, "This is a distributed intelligence framework that permits advanced manipulation algorithms to run on a complex but affordable hardware platform." ▲