Not a sound idea

2019-03-08 03:14:10

By Jeff Hecht ATTEMPTS to build weapons that incapacitate people by harnessing the power of very low-frequency sound waves are destined to fail, says a German physicist. Some weapons developers have claimed that infrasound, frequencies too low to hear, can cause debilitating effects such as nausea and diarrhoea. But Jürgen Altmann of Ruhr-University Bochum has studied the scientific literature and is convinced that the weapons will never work. He presented his findings this week to a joint meeting of European and American acoustical societies in Berlin. “All these effects of infrasound do not really exist,” he says. William Arkin, a writer and consultant based in South Pomfret, Vermont, has obtained documents describing infrasound research that came from the Pentagon under the Freedom of Information Act. The papers claim high-power infrasound could leave troops “incapacitated by nausea”. Police also believe infrasound weapons would have advantages over chemicals such as tear gas. “It is environmentally benign, can be switched on and off, and can be controlled much better,” says Sid Heal of the Los Angeles County Sheriff’s department. The idea that low-frequency vibrations make you ill may have started because some people feel queasy during earthquakes. Nikola Tesla, the inventor of transformers and generators, reportedly duplicated the effect with a vibrating chair almost a century ago. But those observations were based on mechanical vibrations in solids, which couple energy to the human body much more efficiently than sound waves can transfer energy from the air. Altmann says that experiments in which people or animals have been subjected to airborne infrasound suggest the weapons won’t work. “I found no hard evidence for vomiting or uncontrolled defecation, even at levels of 170 decibels or more,” Altmann says. And while air transmits infrasound very well, he points out that the wavelengths are so long—17 metres or more—that it spreads out too rapidly to form a controllable beam. Altmann blames rumour and misunderstanding for the stories surrounding infrasound. “You can’t hear it, so you’re inclined to believe what people say about it,” he says. Heal, who works with the US Army on its infrasound weapons programme, admits that the research has been refocused. As well as attempting to create prototype weapons, researchers are trying to develop a better understanding of how infrasound might affect the human body,