The hertz (symbol Hz) is the unit of frequency in the International System of Units (SI) and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves.
One of the unit's most common uses is in the description of sine waves and musical tones, particularly those used in radio and other audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven.
The hertz is equivalent to cycles per second. In defining the second, the International Committee for Weights and Measures declared that "the standard to be employed is the transition between the hyperfine levels F = 4, M = 0 and F = 3, M = 0 of the ground state 2S1/2 of the cesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9 192 631 770 hertz" thereby effectively defining the hertz and the second simultaneously.
The Active Denial System (ADS) is a non-lethal, directed-energy weapon developed by the U.S. military, designed for area denial, perimeter security and crowd control. Informally, the weapon is also called the heat ray since it works by heating the surface of targets, such as the skin of targeted human subjects. Raytheon is currently marketing a reduced-range version of this technology. The ADS was deployed in 2010 with the United States military in the Afghanistan War, but was withdrawn without seeing combat. On August 20, 2010, the Los Angeles Sheriff's Department announced its intent to use this technology on prisoners in the Pitchess Detention Center in Los Angeles, stating its intent to use it in "operational evaluation" in situations such as breaking up prisoner fights. The ADS is currently only a vehicle-mounted weapon, though U.S. Marines and police are both working on portable versions. ADS was developed under the sponsorship of the DoD Non-Lethal Weapons Program with the Air Force Research Laboratory as the lead agency. There are reports that Russia and China are developing their own versions of the Active Denial System.