About this Article
Written by: Tim Furnish
Written on: September 3rd, 2007
Tags: electrical engineering, energy & sustainability
Thumbnail by: Charles Beichman/CalTech
About the Author
In the fall of 2007, Timothy Allen Furnish was a mechanical engineering student at the University of Southern California Viterbi School of Engineering. His interests in engineering include learning new ways to solve mechanical problems and learning about new technology.
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Volume IX Issue IV > Motion Sensors
Motion sensors are found everywhere today. This technology has helped accommodate our busy schedules by making our daily activities more efficient and convenient. These sensors were introduced by the demand for detection of enemy aircraft during World War II and were ultimately developed to apply to everyday life. With the demand of useful tools to make our lives more expedient, motion sensors were developed in areas such as public restrooms, grocery store doors, and security systems. This technology will continue to grow and contribute to the modern age, and will one day be found everywhere from fully automated restrooms to inside human bones.


Ildar Sagdejev/Wikimedia Commons
Figure 1: Motion sensors in a public doorway.
When shopping at a local store, I noticed that there were two sets of exit doors -- one was automatic and the other manual. As I was exiting, I chose the automatic door without even thinking about it, as did many other people. When faced with an automatic door and a manual door, which one do you choose? It is a sign of the times that people prefer an automatic door to a manual one; the convenience that technology has to offer has changed the way we think and act (see Fig. 1). In this modern age, we are becoming more dependent on and accustomed to automatic features. But what makes these automatic features work? How can we expect doors to just open for us? The answer has to do with motion sensors. This article will discuss two types of motion sensors that people may experience every day but often overlook: radar and infrared.

A Brief History

The increased demand for detection and monitoring during World War II generated technological advances in motion sensing. Radar, which had been invented decades earlier but had not yet been fully developed, was now being used to counter the advantage provided by aircraft by enabling its detection [1]. Although the development of radar systems was a great achievement, its applications were limited to military use. One of the first applications of motion sensing outside the military was developed by Samuel Bagno in the mid 1940s. Using his knowledge of radar and newly developed electrical components, Bagno began doing research on an ultrasonic alarm, which worked similarly to radar. His ultrasonic alarm created "a web of ultrasonic waves inside a room" and detected the motion of a person [2]. The detector "spins its web by establishing a pattern in the way that waves bounce off inanimate objects in the room and return to a receiver." Movement shifts created disturbances in the pattern and triggered an alarm. The invention of the ultrasonic alarm generated a demand for other non-military applications of this technology, especially infrared technology. Although infrared detection had been invented in the mid 1800s, its applications were limited to astronomy [3]. Around the same time that the ultrasonic sensors were being developed, new materials used for infrared sensing were being researched and applied [4]. Both radar and infrared motion sensing are widely used today.