When Captain Kirk beams down to an alien world, his tricorder quickly analyzes if the atmosphere is safe to breathe. Now, Stanford electrical engineers have taken the latest step toward developing such a device for non-contact thermoacoustic detection of embedded objects in highly dispersive media. They are using microwaves and ultrasound to create a safe and portable way to detect hidden objects. The work grows out of research designed to detect buried plastic explosives, but the researchers said the technology could also provide a new way to detect early stage cancers. The careful manipulation of two scientific principles drives both the military and medical applications. First, all materials expand and contract when stimulated with electromagnetic energy, such as light or microwaves. Second, this expansion and contraction produces ultrasound waves that travel to the surface and can be detected remotely.