Sonic weapon

Sonic and ultrasonic weapons (USW) are weapons of various types that use sound to injure, incapacitate, or kill an opponent. Some sonic weapons are currently in limited use or in research and development by military and police forces. Others exist only in the realm of science fiction. Some of these weapons have been described as sonic bullets, sonic grenades, sonic mines, or sonic cannons. Some make a focused beam of sound or ultrasound; some make an area field of sound.

Conventional sound
Sound recordings have been used as a weapon to confuse the enemy in battle, as part of psychological warfare, and as a means of torture. Culturally inappropriate music has also been used to discourage teenagers from loitering in civilian settings. For example, the metro trains in Melbourne used to broadcast classical music over the stations' loudspeakers to discourage mischief.

Usage and deployment
Extremely high-power sound waves can disrupt and/or destroy the eardrums of a target and cause severe pain or disorientation. This is usually sufficient to incapacitate a person. Less powerful sound waves can cause humans to experience nausea or discomfort. The use of these frequencies to incapacitate persons has occurred both in counter-terrorist and crowd control settings.

The possibility of a device that produces frequency that causes vibration of the eyeballs — and therefore distortion of vision — was apparently confirmed by the work of engineer Vic Tandy while attempting to demystify a “haunting” in his laboratory in Coventry. This “spook” was characterised by a feeling of unease and vague glimpses of a grey apparition. Some detective work implicated a newly installed extractor fan that, Tandy found, was generating infrasound of 18.9 Hz, 0.3 Hz, and 9 Hz.

A long-range acoustic device has been used by the crew of the cruise ship Seabourn Spirit to deter pirates who chased and attacked the ship. More commonly this device and others of similar design have been used to disperse protesters and rioters in crowd control efforts. A similar system is called a "magnetic acoustic device". 'mobile' sonic devices have been used in Grimsby, Hull and Lancashire to deter teenagers from lingering around shops in target areas. The device works by emitting an ultra-high frequency blast (around 19–20 kHz) that teenagers or people under approximately 20 are susceptible to and find uncomfortable. Age-related hearing loss apparently prevents the ultra-high pitch sound from causing a nuisance to those in their late twenties and above, though this is wholly dependent on a young person's exposure to high sound pressure levels.

High-amplitude sound of a specific pattern at a frequency close to the sensitivity peak of human hearing (2-3 kHz) is used as a burglar deterrent.

Some police forces have used sound cannons against protesters, for example during the G20 summit in Pittsburgh.

Demonstrated infrasonic weapon
The U.S. Department of Defense (DOD) has demonstrated phased arrays of infrasonic emitters. The weapon usually consists of a device that generates sound at about 7 Hz. The output from the device is routed (by pipes) to an array of open emitters. At this frequency, armor and concrete walls and other common building materials allow sound waves to pass through, providing little defense. This presents logistic problems regarding operation of infrasonic weaponry without exposing operating personnel to the potentially damaging effects.

Physicist and researcher Jürgen Altmann, however, has suggested that infrasound "does not have the alleged drastic effects on humans" in his paper "Acoustic Weapons."  While many sources make reference to military research into infrasonic weapons beginning with the work of Dr. Vladimir Gavreau, it is unclear as to whether or not these devices have potential use in conflict.

Research
Some common bio-effects of electromagnetic or other non-lethal weapons include effects to the human central nervous system resulting in physical pain, breathing difficulty, vertigo, nausea, disorientation, or other systemic discomfort. Interference with breathing poses the most significant and potentially lethal results. Light and repetitive visual signals can induce epileptic seizures (see Bucha effect). Vection and motion sickness can also occur. Cavitation, which affects gas nuclei in human tissue, and heating can result from exposure to ultrasound and can cause damage to tissue and organs.

Studies have found that exposure to high intensity ultrasound at frequencies from 700 kHz to 3.6 MHz can cause lung and intestinal damage in mice. Heart rate patterns following vibroacoustic stimulation has resulted in serious negative consequences such as atrial flutter and bradycardia.

The extra-aural (unrelated to hearing) bioeffects on various internal organs and the central nervous system included auditory shifts, vibrotactile sensitivity change, muscle contraction, cardiovascular function change, central nervous system effects, vestibular (inner ear) effects, and chest wall/lung tissue effects. Researchers found that low frequency sonar exposure could result in significant cavitations, hypothermia, and tissue shearing. No follow on experiments were recommended. Tests performed on mice show the threshold for both lung and liver damage occurs at about 184 dB. Damage increases rapidly as intensity is increased. The American Institute of Ultrasound in Medicine (AIUM)has stated that there have been no proven biological effects associated with an unfocused sound beam with intensities below 100 mW/cm² SPTA or focused sound beams below an intensity level of 1mW/cm² SPTA.

Noise-induced neurologic disturbances in humans exposed to continuous low frequency tones for durations longer than 15 minutes has involved in some cases the development of immediate and long-term problems affecting brain tissue. The symptoms resembled those of individuals who had suffered minor head injuries. One theory for a causal mechanism is that the prolonged sound exposure resulted in enough mechanical strain to brain tissue to induce an encephalopathy.