Radio frequency

Pulse weapon brings cars to a halt

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A British company has demonstrated a prototype device capable of stopping cars and other vehicles using a blast of electromagnetic waves.

The RF Safe-Stop uses radio frequency pulses to “confuse” a vehicle’s electronic systems, cutting its engine.

E2V is one of several companies trying to bring such a product to market.

It said it believed the primary use would be as a non-lethal weapon for the military to defend sensitive locations from vehicles refusing to stop.

There has also been police interest.

The BBC was given a demonstration of the device at Throckmorton Airfield, in Worcestershire.

Deputy Chief Constable Andy Holt, of the Association of Chief Police Officers (Acpo), who has evaluated the tech, said the machine had “potential, but it’s very early days yet”.

Radio pulse

At one end of a disused runway, E2V assembled a varied collection of second-hand cars and motorbikes in order to test the prototype against a range of vehicles.

In demonstrations seen by the BBC a car drove towards the device at about 15mph (24km/h).

As the vehicle entered the range of the RF Safe-stop, its dashboard warning lights and dials behaved erratically, the engine stopped and the car rolled gently to a halt. Digital audio and video recording devices in the vehicle were also affected.

“It’s a small radar transmitter,” said Andy Wood, product manager for the machine.

“The RF [radio frequency] is pulsed from the unit just as it would be in radar, it couples into the wiring in the car and that disrupts and confuses the electronics in the car causing the engine to stall.”

He did not provide other specifics. However, the Engineer magazine has reported the device uses L- and S-band radio frequencies, and works at a range of up to 50m (164ft).

Some experts the BBC has spoken with suggested that turning off the engine in this manner would not stop vehicles rapidly enough. Others worried about what effect it might have on a car’s electronic brake and steering systems.

But E2V said the risks were lower than with alternative systems.

Acpo suggested the machine’s ability to stop motorbikes “safely” could prove particularly useful.

Mr Holt noted that the tyre deflation devices used by some police forces posed the risk of causing “serious injury” if used against two-wheelers.

E2V added that its device could also be effective against other types of vehicles, including boats.

But because the device works on electronic systems, he acknowledged that it would not work on all older vehicles.

“Certainly if you took a 1960s Land Rover, there’s a good chance you’re not going to stop it,” Mr Wood said.

The firm added that it did not believe the RF Safe-Stop posed any risk to people using a pacemaker.

Nanomechanical FM transmitter is smallest yet.

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Researchers at Columbia University in the US have built the smallest frequency-modulated (FM) radio transmitter ever. Based on a graphene nanomechanical system (NEMS), the device oscillates at a frequency of 100 MHz. It could find use in a variety of applications, including sensing tiny masses and on-chip signal processing. It also represents an important first step towards the development of advanced wireless technology and the design of ultrathin mobile phones, says team co-leader James Hone.

“Our device is much smaller than any other radio-signal source ever made and, importantly, can be put on the same chip that is used for data processing,” he explains.

Graphene is a sheet of carbon atoms arranged in a honeycomb-like lattice that is just one atom thick. Since its discovery in 2004, this “wonder material” has continued to amaze scientists with its growing list of unique electronic and mechanical properties, which include high electrical conductivity and exceptional strength. Indeed, some researchers believe that graphene might even replace silicon as the electronic industry’s material of choice in the future.

Ideal for making NEMS

Graphene is ideal for making NEMS – which are scaled-down versions of the microelectromechanical systems (MEMS) that are routinely employed in vibration-sensing applications. The new device made by Hone and colleagues is a NEMS version of a common electronic component known as a voltage-controlled oscillator (VCO) and generates a frequency-modulated (FM) signal of about 100 MHz. This frequency lies exactly in the middle of the FM radio band (87.7–108 MHz) and the researchers say that they have already succeeded in using low-frequency music signals to modulate the 100 MHz carrier signal from their graphene NEMS and recover the signals again using an ordinary FM receiver.

While graphene NEMS might not replace conventional radio transmitters yet, they will certainly be used in many other wireless signal-processing applications. Although electrical circuits have been continuously shrinking over the last few decades (as described by Moore’s law), there are still some types of devices – especially those involved in creating and processing radio-frequency (RF) signals – that are notoriously difficult to miniaturize, explains team co-leader Kenneth Shepard. Called off-chip components because they cannot be integrated with miniaturized devices, they require a lot of space and electrical power, and their frequency cannot be easily tuned.

Graphene NEMS offer a solution to this problem because they are very small – the active area is only a few microns across – and they can potentially be integrated directly onto conventional CMOS chips. Most importantly, it is easy to tune their frequency thanks to graphene’s exceptional strength.

Adjusting the tension

The Columbia researchers made their devices by contacting graphene sheets to source and drain electrodes and freely suspending the sheets over metal gates. In this configuration, the graphene functions like the skin of a drum. A DC gate voltage pulls the graphene down towards the gate and this adjusts the tension and, therefore, the mechanical resonance frequency, explains Hone. A radio-frequency signal on the gate drives sheet vibrations. “Finally, we apply a DC bias across the graphene and when the graphene vibrates it acts as a transistor whose gate capacitance is constantly changing – and it is this that creates an RF source–drain current,” he says.

The team studied the vibrational properties of the device at room temperature in a vacuum chamber. “To make an oscillator, we first adjust the signal gain to just above unity (using a variable amplifier) and the phase to zero (using a phase shifter) at the resonance frequency,” says Hone. “We then connect the output to the gate. This creates a closed loop that amplifies random thermal vibrations and makes the device oscillate.”

The researchers say they are now busy looking at how to put their devices directly onto integrated circuits that already contain all the necessary drive and readout circuitry. They also hope to improve the performance of their oscillators and reduce device noise.

Wireless bio-absorbable circuits could kill bacteria.

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Remote-controlled, dissolvable electronic implants have been created that could help attack microbes, provide pain relief and stimulate bone growth.

The spread of bacteria resistant to antibiotics – popularly called superbugs – is threatening to put the clock back 100 years to the time when routine, minor surgery was life-threatening. Some medical experts are warning that otherwise straightforward operations could soon become deadly unless new ways to fend off these infections are found.

Bacteria often evolve clever ways of evading chemical assaults, but they will always struggle to resist the old-fashioned way of killing them: heating them up. It takes only a relatively mild warming to kill bugs without discomfort or harm to tissues. So imagine if little electric heaters could be implanted into wounds and powered wirelessly to fry bacteria during healing before dissolving harmlessly into body fluids once their job is done.

This is just one potential application of the bio-absorbable electronic circuits made by John Rogers of the University of Illinois at Urbana-Champaign and his co-workers. The idea itself is not new: Rogers and others have previously reported biodegradable flexible circuits and electronic devices that can be safely laid directly onto skin. But their success in making their circuits wireless could prove crucial to many potential applications, especially in medicine.

The hope is that radio waves can be used both for remote control of the circuits – to turn them on and off, say, and to provide the power to run them, so that there’s no need for implanted batteries. This kind of radio-frequency (RF) wireless technology is becoming ever more widespread, in food packaging, livestock labelling, tagging of goods in shops for security and in dustbins to monitor recycling, for example.

To make RF circuits, you need semiconductors and metals. Those don’t sound like the kinds of materials our bodies will dissolve, but Rogers and colleagues used layers of non-toxic substances so thin that they disintegrate in water or body fluids. For the metal parts, they used films of magnesium at least half as thin as the average human hair. Magnesium is not only harmless but in fact an essential nutrient: our bodies typically contain about 25g (0.9oz) of it already. For semiconductors, they used silicon membranes 300 nanometres (millionths of a millimetre) thick, which also dissolve in water. They used magnesium oxide as an insulating material when required.

Power scavenger

One of the simplest but most important components of an RF circuit is an antenna, which picks up the radio waves. Rogers and colleagues made these from long strips of magnesium foil deposited onto thin films of silk. Being non-toxic, biodegradable, strong and relatively cheap, silk makes the ideal base for such devices. These antennae, typically about four inches long, dissolve completely in water in about two hours. Although being buried beneath radio wave-absorbing body tissue would hamper performance, they should still receive enough signal for low power applications the researchers are considering.

The researchers have also made a variety of standard circuit components: capacitors, resistors, and crucially, diodes and transistors. Transistors are particularly complex structures, requiring delicately patterned films of a semiconductor like silicon doped with other elements and sandwiched with metal electrodes and insulating layers. Using silicon membranes, along with magnesium and its oxide, Rogers’ team made versions that dissolve within hours.

One of the first full circuits that they have made is an RF “power scavenger”, which can convert up to 15% of the radio waves it absorbs at a particular frequency into electrical power. Their prototype, measuring about 10cm (4in) by 4cm (1.6 in), can pick up enough power to run a small commercial light-emitting diode. The team can control the rate at which these devices dissolve by fine-tuning the molecular structure of the silk sheets on which they are laid down or between which they are sandwiched. This way, they can make devices that last for a week or two – about the length of time needed to ward off bacteria from a healing wound.

As well as deterring bacteria, Rogers says that implantable, bio-absorbable RF electronics could be used to stimulate nerves for pain relief, and to stimulate bone re-growth, a process long proven to work when electrodes are placed on the skin or directly on the bone. Conceivably they could also be used to precisely control drug release from implanted reservoirs.

Source: BBC