Feb. 12, 2007 — It's a problem that plagues New York club bouncers and nuclear reactor security guards alike: How do you let the right people in, but keep the wrong people out?
The solution is easier at nuclear reactors and may involve biometric security devices such as fingerprint or iris scanners. But not every door needs the security of a nuclear reactor. Now researchers have invented an inexpensive, sensor-riddled door that recognizes the person passing through without the need of a key or a card or the inconvenience of stopping to scan a finger or an eye.
The Wisdom Door, created by students at Duke University in Durham, N.C., could not only provide security but could also be rigged to control home electronics, so that when the person passes through the door, a room automatically lights up, plays music, or switches to a television channel all according to personal preference.
"Anything that is electronic can be controlled. When you wake up in the morning, it could automatically start the coffee maker for you," said Kareem Lee, the Wisdom Door's project manager.
Nine sensors work together to make the door a walk-through security device. Above the doorway is an ultrasonic sensor that constantly beams a signal downward. When a person passes underneath, the signal bounces off his head and travels back to the sensor.
The delay in the "echo" signal allows the computer to calculate the distance between the top of the doorway and the head and produce a number for the person's height.
Four infrared signals in the doorframe determine a person's width and girth. The sensors are positioned two on each side of the frame, with two sensors on the outside of the frame and two on the inside. When a person walks through the door, they break the infrared beams at a specific location. The computer subtracts the distance of the breaks from the total width of the door to come up with the person's width.
The same sensors also capture the delay in time between when the person breaks through the two front sensors until they cross through the two back sensors. The difference is used to calculate the person's girth.
