March 09, 2009 | 12:41:44 PM
Today's Tasers stun their targets for just a few seconds. A new technique using ultra-short electric pulses could allow tomorrow's electroshock weapons to immobilize people for as long as fifteen minutes –- and may one day also be used to destroy tumors.
As I note in my latest New Scientist story, existing Tasers use an electric pulse that lasts a few microseconds, and delivers around .07 Joules of energy. This is sufficiently intense to disrupt nerve cell membranes, effectively paralyzing the neuromuscular system however tough you are. The microsecond pulses are repeated over a five-second cycle. According to Steve Tuttle of Taser International, the effects wear off almost immediately once the cycle finishes; he describes tests in which subjects have been able to carry out a task, such as pushing a specific button, immediately after being Tasered. [Others disagree, and point to all those times when coroners have ruled that the shock weapons contributed to someone's death. -- ed.]
Short-term incapacitation meets police requirements, allowing a suspect to be incapacitated for long enough to make a quick arrest. The U.S. military is looking at a longer keeping people stunned for much longer, however. The Joint Nonlethal Weapons Directorate is looking at a new generation of electroshock weapon that might knock the target down for fifteen minutes with a single ultra-short pulse.
Research is being carried out by the Frank Reidy Research Center for Bioelectrics at Old Dominion University. The Center's mission is to "to increase scientific knowledge and understanding of how electromagnetic fields and ionized gases interact with biological cells." A significant amount of their funding is military; the Center notes that their largest award was $5 million from Air Force Office of Scientific Research.
The key to the technology lies in using short pulses, which can have very different effects than the longer ones. When an electric field is applied to a cell, a charge starts to build up on the cell membranes. After a few microseconds, the charge is so high that holes (or "pores") start to form in the cell wall, an effect called electroporation. This allows material (in particular calcium ions) to pass through, affecting the function of the cell. With shorter pulses there is not enough time to affect the cell. But electroporation can affect the structures within the cell such as the nucleus, known as organelles.
"Because the organelles are much smaller than the cell itself... they reach their maximum charge much more quickly," Center founder Karl H. Schoenbach explains in an article. " Ending the pulse after the organelles are charged up, within a few hundred nanoseconds but before large pores appear in the cell’s own membrane, lets you focus the electric field’s effects on the organelles, such as the nucleus, while leaving the cell membrane relatively untouched. That, in turn, lets you do the complex and varied things medical science is interested in, such as killing tumor cells or triggering an immune system response."
So on the one hand ultra-short pulses can be used to selectively destroy cancerous cells. But they can also produce much more effective stunning effects.
A paper from the Center on Neuromuscular disruption with ultrashort electrical pulses compares 450-nanosecond pulses with multi-microsecond Taser pulses and found that the shorter pulses were more effective for suppressing voluntary movement, and used less energy. Another study found that even shorter, 60-nanosecond pulses could stun rats.
But the most significant is a paper which found that it was possible to incapacitate cells for a prolonged period -- "our study provides experimental evidence that even a single 60-ns pulse at 12 kV/cm can cause a profound and long-lasting (minutes) reduction of the cell membrane resistance (Rm), accompanied by the loss of the membrane potential." The paper says that cells could be prevented from functioning for fifteen minutes. These are early days, but researchers have suggested that a single ultrashort shock could leaving the target immobilized for "tens of minutes" using far less energy than a Taser pulse.
Obviously there are concerns over what other effects ultrashort pulses might have on the body.
"We have been advised by contacts who track the development of this type of technology that the medical and biological effects of such ultra-short electrical shocks in such a weapon are presently unknown," says Angela Wright of Amnesty International. "Stringent testing, before deployment, of the medical effects of such a weapon should take place."
"Studies are being conducted to examine the ion transport mechanisms and the effects on long term cell viability," says David B. Law of the JNLWD. He says that plans for tests on live animals are under way, but declined to comment on when human tests might happen -- if ever.
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