A handheld through-the-wall surveillance system is being developed for use by law enforcement and military personnel. The system utilizes high-power ultrasonic transducers to detect and locate stationary or moving persons inside metallic and nonmetallic walled enclosures. Design details are presented with proof-of-concept data and analyses. The sensor system is being designed to operate as a handheld monitor with a near real-time user display of the location, in range and azimuth, of each detected individual. Preliminary test data include wall penetration/sensitivity, locating accuracy, and probability of detection. Applications of this technology include detecting and locating unconscious, sleeping, tightly bound, or otherwise stationary persons, as well as moving persons, inside a closed room. The sensor should also prove useful in border patrol applications for inspecting truck trailers and shipping containers at points of entry.
INTRODUCTIONThis paper describes an ongoing effort to develop a handheld device for through-the-wall surveillance (TWS) of moving and stationary persons inside walled enclosures. Here, TWS refers to detecting and locating persons through walls or other barriers to visual surveillance. The objective of our efforts is to demonstrate that a low-cost (under $1000 in production quantities) ultrasonic monitor can accurately locate and track multiple stationary and moving persons inside a closed room, and do so through metallic and nonmetallic walls on a single, easily understood display.The ability to locate and track multiple stationary and moving persons behind a wall would be of great value to many kinds of law enforcement (LE) officers and security personnel for counterterrorism, drug enforcement, and for military and special operations. Law enforcement applications for such a monitor include hostage situations, SWAT-team scenarios, drugenforcement forced entries, and inspections at national points of entry. Such a capability could provide life-saving information, particularly in scenarios in which LE personnel must enter rooms that may harbor armed and dangerous persons.Detecting stationary persons is a greater challenge than detecting moving persons. Meeting this challenge is essential, however, for TWS to support military and civilian counterterrorism efforts for which hostages may be unconscious or otherwise immobile. Overlooking a stationary person with only a TWS motion detector might make a life-or-death difference to law enforcement officers and others.The system will use high peak-power ultrasonic transducers operating at 30-40 kHz to transmit and receive modulated acoustic pulses through a variety of wall and window materials including wood, metal, drywall, concrete, glass, and composites. The device will employ signal processing algorithms similar to those being developed concurrently for Jaycor's Prisoner Health Status Monitor (PHSM). These algorithms allow determination of an individual's respiration rate and, in some instances, heart rate. The TWS sensor detects respiratio...