BACKGROUND: New technology that will be used by law enforcement and the military can look through walls. It is available now, and is being tested by a handful of police departments, before it could move into widespread use.
HOW IT WORKS: The Xaver800 technology provides 'Through the Wall' vision, allowing the user to rapidly and reliably observe one or more people in a room and monitor their movements, while positioned outside the room's walls. The system uses sound waves at a particular frequency -- ultra-wide radio waves, which pass through wood and concrete -- to capture images, much like ultrasound imaging captures the image of a fetus through the mother's skin. Sensors detect the reflected waves. That mechanical motion is translated into electrical signals. Then the computer software algorithms process the signals and create a 3-D image of the people or objects concealed by solid barriers made of cement, plaster, brick, concrete and wood. The system operates on very low power signals; the total energy transmitted is less than that emitted by a standard cellphone.
WHAT ARE RADIO WAVES? Like visible light, radio waves are a part of the electromagnetic spectrum, only with much longer wavelengths. They can be as long as a football field, or as short as a football. This wide range makes them ideal for transmitting information, because different frequencies can be assigned to specific devices. We use radio waves not just in AM, FM, and police and fire department radios, but also in television, radar, cellphones, baby monitors, TV remote controls, and garage door openers, to name just a few. Each type of device has its own frequency range to avoid overlap with others.
SOUND SCIENCE: Sound waves are pressure waves: the result of a vibrating object that creates a disturbance in the surrounding air. The vibrations disturb the molecules that make up the air. The air molecules push closer together as the object moves one way -- an effect known as compression -- and then create a space between themselves and the vibrating object as it moves the other way, called rarefaction. The motion disturbs the neighboring molecules in turn, creating an outward ripple effect, much like a stone cast in a quiet pond will cause waves to ripple outward from the spot where the stone hit. So sound waves travel in repeating patterns of compressions and rarefactions. The distance between compressions determines the wavelength. Objects that vibrate very quickly create short wavelengths because there is very little space between the compressions, creating a high-pitched sound. Objects that vibrate very slowly create long wavelengths because the compressions are spaced further apart. This creates a low-pitched sound. Frequency measures how many crests, or compressions, occur within one second. A sound wave's amplitude, or range of movement, determines its volume.
The Institute of Electrical and Electronics Engineers, Inc., contributed to the information contained in the TV portion of this report.