Robotics: Amoebas have provided the inspiration for new, squishy kinds of robot capable of squeezing into confined spaces
TRAPPED UNDER A PILE OF RUBBLE, you wait for rescue. Then, to add to your troubles, you see a small blob ooze through a nearby crack. Soon afterwards it is followed by the emergency services digging down to find you. This scene is science fiction now, but it might not be for much longer. Traditionally, people have thought of robots as whirring bits of metal, but there are those in the field who ask why that need be so. Instead of trying to build a robot that looks like a human, an insect or even a tank, some roboticists have decided to look to the humble amoeba for inspiration.
America’s Department of Defence has taken the idea seriously enough to provide a $3.3m grant via its research arm, the Defence Advanced Research Projects Agency, to iRobot (a firm best known for its vacuum-cleaning robot, the Roomba). Chris Jones of iRobot says DARPA’s criterion for the robot was that it had to fit through an opening half its full diameter.
The result is the blob-like Chembot, which moves by deforming one side. To achieve this, iRobot’s engineers used a concept called “jamming”, which takes advantage of the fact that some particulate materials are quite stiff when compressed but, given space, flow like liquids. Dr Jones says the phenomenon is much like that observed in a vacuum-packed coffee brick. An unopened brick is stiff and strong because the external air pressure is compressing it. When the foil is cut, however, air gets in, equalising the pressure. The coffee then acts like the pile of particles it is, and the brick can change shape.
The Chembot is a vaguely spherical structure made of soft triangular panels, each of which is filled with particles. The control system, which uses tiny compressors to pump air in and out of the panels, is in the centre. The triangular panels remain stiff until a small amount of air is pumped into them. That lets the particles move around and allows the panel to deform. Increasing the pressure inside a panel on one side of the robot’s base makes it bulge and causes the robot to roll over slightly; many such inflations and deflations make the robot roll along. The deformability also allows the robot to enter any space no smaller than its fully compressed state, more or less regardless of the shape of that space.
Nor is the Chembot the only contender for the artificial-amoeba crown. Dennis Hong, a mechanical engineer at Virginia Tech, has taken a different approach. He has looked at the way amoebas move and tried to replicate it. The Chembot moves by pushing itself along. Real amoebas, however, pull themselves. They extend a pseudopod in the direction they wish to travel, and the rest of the amoeba then flows forward into the pseudopod.
Dr Hong could not exactly duplicate that, but he came up with something similar: the idea of an extended torus, or doughnut shape, which turns itself inside out. For large robots, he accomplishes this with a series of hoses, arranged like ribs, to form the torus. Each hose can be expanded and contracted independently. Doing so in sequence along the length of the torus generates forward motion.
For small robots Dr Hong has used rings made of a polymer that changes shape in response to a specific chemical stimulus. The result is a robot that scuttles along when an appropriate chemical is brushed on one end. Dr Hong will not yet say which chemicals he uses, but the robot moves impressively fast. It can also, like the Chembot, squeeze through openings smaller than its initial diameter.
Search-and-rescue is one obvious application for robots like this. Another is endoscopy – the process by which doctors insert a camera into someone through an orifice to perform an internal examination. At the moment, the camera has to be fitted to the end of a stiff, yet flexible cable. A soft, squishy robot, sufficiently small, could be an alternative. How patients would feel about having an autonomous blob roaming around inside them is another matter.
This article was first published in The Economist in June 2010.
Military technology: Using rubber rather than steel tracks on military vehicles could reduce wear and tear on both soldiers and equipment
RATTLING ALONG in the “washing-machine environment” of an armoured personnel-carrier (APC) on steel tracks can shake the soldiers inside to the point of exhaustion, according to Dan Goure, a military analyst at the Lexington Institute, a think-tank in Arlington, Virginia. And J.G. Brunbech, an APC expert at the Danish Army Material Command in Oksboel, observes that the crew’s limbs are prone to becoming prickly and numb, and their hands get tired, because they must grip the vehicle’s safety handles tightly. The vehicle itself suffers, too. The vibrations cause rapid wear and tear – not to mention outright damage, especially to electronics.
In the past, engineers have tried to reduce these vibrations by fixing rubber pads to the treads. The pads wear out quickly, however, and often get torn or even melted. But now tough, new rubbers have come to the rescue. Moreover, these rubbers are not being used just as pads. Instead, they are crafted into enormous rubber bands that replace the steel tracks completely. The Danes are converting their entire APC fleet to rubber tracks. This will increase the amount of time a soldier can safely spend on board from just one and a half hours to ten hours.
Details of how the new super-rubbers are made are still classified, but the results are not, and they are impressive. Rubber tracks weigh less than half as much as their steel counterparts. That, in turn, allows the weight of the suspension system to be reduced by 25%. All this can cut fuel consumption by as much as 30%, says TACOM, the American army’s Tank-Automotive and Armaments Command.
Rubber tracks also provide more traction, in part because, being lighter, they can be made wider than steel tracks. That means vehicles fitted with them do not get stuck in the mud. The vehicles accelerate faster, too, and drivers say they handle almost as well on paved roads as wheeled vehicles do. On top of this, they are quieter. That has two benefits. One is that crews are often able to talk to each other without resorting to intercoms. The other is that it is harder for the enemy to hear them coming. According to Curt Aspelund, the head of tracks and suspension development at BAE Systems, a British defence firm that is collaborating with TACOM to design a new APC called the Manned Ground Vehicle (MGV), rubber tracks will reduce the distance from which the vehicle can be heard by 40%.
Rubber tracks are more reliable, too. Tracked military vehicles are notorious for breaking down. On average, the segments of a steel track must be repaired or replaced after just 400km (250 miles) of use. Carrying spare segments adds to a vehicle’s weight. Rubber tracks, by contrast, usually last more than 3,000km.
They are also kinder to roads. Traditionally, of course, that did not matter much. The whole point of a tank or an APC is that it is the ultimate off-road vehicle. But the growth of peacekeeping operations, in which showing the flag to the locals is an important tactic, means that road-friendly vehicles are becoming more desirable. The locals will certainly not love you if you chew up their tarmac and make their streets impassable.
As a result of all this, Soucy International of Drummondville, Quebec, one of the firms that makes the tracks, reports booming business. The armed forces of both Canada and Norway have converted almost all their APCs to tracks made by Soucy. Those of several other countries, including Britain, Germany, Italy, the Netherlands, Singapore and Sweden, are following suit or are in the advanced stages of testing the tracks. France plans to start tests next year. And although America has not sent APCs with rubber tracks into action, they form part of Future Combat Systems, the Department of Defence’s main modernisation programme.
At the moment, rubber tracks can support only vehicles weighing less than 20 tonnes. They are not strong enough for 50-tonne battle tanks. But this is changing. The MGV, for example, will weigh 30 tonnes, and Canada has begun a trial of rubber tracks on the Mobile Tactical Vehicle Light (MTVL), a 22-tonne APC. If the MTVL passes muster it will join Canada’s rubber-tracked 20-tonne M113 APCs in Afghanistan. Soucy, meanwhile, is developing rubber tracks for full-sized tanks. Warfare, it seems, is about to get quieter.
This article was first published in The Economist in December 2008.
America’s navy is developing an antenna made of seawater
A BIG AMERICAN WARSHIP bristles with more than 100 large copper antennae that send and receive signals for its weapons, its radar and its voice and data communications. A lot of aerials, then, but still not enough. The navy wants its ships to carry even more of them. Fulfilling that desire has, however, stymied experts for decades. If placed too close together, antennae interfere with each other’s signals. They also get in the way of aircraft and weapons. And, crucially, naval antennae – many of them more than 20 metres tall – make warships more easily visible to enemy radar.
At the American navy’s Space and Naval Warfare Systems Command (known as SPAWAR for short), in San Diego, a team of more than 30 engineers is trying to solve such problems. In 2007 the team’s leader, Daniel Tam, thought of a possible answer, appropriately enough, while taking his morning shower. The sodium and chloride ions in salt water conduct electricity. Could a spout of sea-water, he mused, replace a metal antenna?
After a trip to a hardware store, Mr Tam discovered that indeed it could. With an $80 water pump, a $15 rubber hose and a $20 electrical device called a current probe that was easily plugged into a hand-held radio, he produced a spout roughly four metres tall from the waters of San Diego Bay. With this he could send and receive a clear signal. Over the intervening years his invention, dubbed the “pee antenna” by incredulous colleagues, has been tweaked and improved to the point where it can transmit over a distance of more than 50km (30 miles).
To make a seawater antenna, the current probe (an electrical coil roughly the size and shape of a large doughnut) is attached to a radio’s antenna jack. When salt water is squirted through the hole in the middle of the probe, signals are transferred to the water stream by electromagnetic induction. The aerial can be adjusted to the frequency of those signals by lengthening or shortening the spout. To fashion antennae for short-wave radio, for example, spouts between 18 and 24 metres high are about right. To increase bandwidth, and thus transmit more data, such as a video, all you need do is thicken the spout. And the system is economical. The probe consumes less electricity than three incandescent desk lamps.
A warship’s metal antennae, which often weigh more than 3½ tonnes apiece, can be damaged in storms or combat. Seawater antennae, whose components weigh next to nothing and are easily stowable, could provide handy backups – and, eventually, more than backups. Not all of a ship’s antennae are used at once, so the spouts could be adjusted continuously to obtain the types needed at a given moment. According to SPAWAR, ten such antennae could replace 80 copper ones.
Fewer antennae mean fewer things for enemy radar to reflect from. Seawater is in any case less reflective of radar waves than metal. And if a ship needed to be particularly stealthy (which would mean keeping its transmissions to a minimum), her captain could simply switch the water spouts off altogether.
One disadvantage of water spouts is that they can be torn apart by the wind. SPAWAR’s researchers have, however, found that their antennae work just as well if encased in a plastic tube. The tube can be sealed at the top so that the water goes up the middle, bounces off the top and then trickles down the inside of the tube’s wall to the bottom, where it may be recycled.
That innovation also means that SPAWAR’s invention need not be restricted to the navy. The closed-tube design allows saline aerials to be deployed on land, too. Indeed, one has already been tested successfully by a group of marines. It worked, as expected, with brine made from fresh water and a few pinches of salt. But if salt is not to hand, never fear. It also worked fine when the spout was fed with Gatorade.
This article was first published in The Economist in January 2011.
How to stop echoes giving you away
IN GREEK MYTHOLOGY, Echo was a mountain nymph who lost her voice and was condemned to repeat only the words of others. Now science is poised to silence the sprite completely. A group of physicists, led by Steven Cummer of Duke University in North Carolina, has devised plans for a cloak that would shield objects from sound, preventing its reflection. Such a device could be used to hide submarines.
Sonar, the technique employed to detect subs, uses a transmitter to emit a pulse of sound – usually a distinctive “ping” – and a receiver to listen for its reflection. That reflection indicates the presence of an object and the time that elapses between the sound’s being emitted and its being detected indicates how far away it is. A second ping allows the object’s direction, speed and location to be calculated.
Dr Cummer, however, has devised a plan to surround a submarine with a shell that directs sound waves to flow around it as though the vessel were not there. The proposal relies on two properties of the material used to make the shield – its density and its “bulk modulus”, a measure of its springiness. It should be possible to tailor these so that sound waves are bent such that no echo results. The design would also avoid absorbing sound, ensuring no acoustic “shadows” were cast.
Dr Cummer’s method, reported in the current issue of Physical Review Letters, is akin to an existing design for an invisibility cloak that would work for light waves, proposed by Sir John Pendry of Imperial College, London. (Sir John is also one of the authors of the new paper.) Yet the acoustic version has a distinct advantage over its optical counterpart. Making an invisibility cloak would be tricky because the device would work only at certain wavelengths. An aeroplane shrouded in such kit might be invisible to the human eye, for example, but would be picked up readily by radar, which works at radio wavelengths.
An acoustic cloak, however, would work for a wider range of wavelengths, making it far harder to spot. That is possible because light and sound are rather different sorts of waves. As Einstein observed, light in a vacuum travels at the greatest speed possible, around 300m metres a second. Even when it is slowed by air and water, its progress usually remains close to this limit. That means light must obey the rules of Einstein’s special theory of relativity. When light is bent by an invisibility cloak, certain components of the wave are allowed to stretch the laws of physics and travel faster than the nominal speed of light, but only under strict conditions. The energy and the information that the wave carries, for example, cannot exceed the speed of light. The effect is to narrow the range of wavelengths that can be bent by an optical shroud.
Sound, meanwhile, travels at a sedate 300 metres a second. Because this is a million times shy of the relativistic limit, the behaviour of sound waves is not restricted in the same way. Under non-relativistic conditions, many different wavelengths can be bent simultaneously by the same acoustic shield, making it far more effective at concealing an object.
It was unrequited love that made the Echo of Greek mythology fade away until only her voice remained. Although Dr Cummer and his colleagues are still some way from transforming their design into a working device, they reckon precisely engineered materials may soon erase her final utterances.
This article was first published in The Economist in January 2008.
Nanotechnology: Cotton fibres coated with carbon nanotubes could be used to make clothing that glows, or detects bleeding
MANY SCIENCE-FICTION STORIES portray a time when warring generals monitor their forces on computer displays that are linked to special suits worn by their soldiers. Information about any injuries are sent to the command station immediately, so the generals can tell that, say, Sergeant Johnson has a fractured ankle or that Corporal Caley has lost 1.2 litres of blood. Such a day may not be too far off. Researchers have been able to produce cotton fibres capable of detecting blood and of signalling its presence electrically.
Intelligent textiles have a lot of appeal. For both soldiers and doctors, clothing that adapts to changing conditions could provide adjustable levels of protection from such things as microbes, chemicals and radiation. Commercial manufacturers see huge potential in clothes that glow, do not wrinkle or overcome body odour. Materials can already be made to do some of these things, but they are too bulky, rigid or complicated for practical use. So the aim is to manufacture a light material that can be easily woven but is also highly durable and, in order to transmit information, can conduct electricity.
A team of researchers led by Nicholas Kotov, a chemical engineer at the University of Michigan, has come up with a way in which this might be done by coating cotton threads with carbon nanotubes. These tubes are cylindrical carbon molecules with a unique honeycomb-like arrangement of atoms. They are regarded as among the most versatile nanomaterials available because of their mechanical strength and electrical properties.
Nanotube composites are often made into solid structures or sheets, although flexible versions, such as electrically conductive films and electronic inks, can be prepared from dilute nanotube solutions. Some electronic devices, such as field-emission displays in some flat panels, are made from nanotube yarns. But the weaving of these yarns, which may be only one-thousandth of a millimetre thick, is complicated and expensive. Creating garments with electrical properties has not been considered practical.
However, Dr Kotov and his colleagues have reported in Nano Letters a simple process for coating standard cotton threads with carbon nanotubes. Being much thicker than nanotube yarns, such threads can be woven more easily. The researchers dispersed carbon nanotubes in a dilute solution of a mixture of Nafion, a commercial synthetic polymer, and ethanol. They then repeatedly dipped cotton threads, 1.5mm in diameter, into the solution, letting them dry between each dip. This allowed the nanotubes to cover individual cotton strands and to adhere strongly to the surface of the cellulose fibres in the strands. The process also encouraged the nanotubes to arrange themselves along the axis of the cotton fibres, which increased electrical connectivity. After several dips, Dr Kotov found that the cotton threads were conductive enough that they could be used to wire up a light-emitting diode.
In a further test the researchers added molecules of a material that reacts with human serum albumin, an essential component of human blood, to the dipping solution. Then they immersed more cotton threads. This time they ran an electrical current through the thread while exposing it to different concentrations of albumin. They found that the threads’ electrical conductivity varied according to the level of albumin. The researchers propose that such material could be used to detect bleeding if suitably woven into military clothing – just as the science-fiction writers predicted.
This article was first published in The Economist in March 2009.