Most airline passengers agree that few things are more annoying than removing their shoes for security x-rays, but researchers might have found a way to speed the footwear check. MIT electrical engineer Markus Zahn and research assistant Jason Sears are developing a shoe-bomb detector embedded in a floor pad. When a passenger steps onto the pad, a series of electrodes generates a low-energy electromagnetic field a few centimeters high that penetrates the soles of the shoes. In less than a second, sensors in the device measure the changes in the field due to the footwear; that “signature” is compared to database-stored signatures for explosives and other dangerous substances. Working with Jentek Sensors in Waltham, MA, the MIT researchers hope to market the technology within two years.