Land mines are explosive devices that are triggered to explode by pressure or a tripwire. All landmines, metal or plastic, are filled with explosives with electrical properties that can be detected with the right technology.
In the past, soldiers would probe the ground with a stick or bayonet to locate landmines. Dogs can be trained to sniff out vapors from the explosive ingredients inside the landmine, and some scientists are hoping to develop an electronic sensor version of a dog's nose.
More recently, metal detectors and ground-penetrating radar have been used to locate mines. GPR devices focus radar waves just below the ground's surface, and buried objects shine in the radar image. Once a landmine is detected, the device shoots chemical agents into the ground to solidify the trigger and the soil around it, either temporarily so soldiers can cross the ground or permanently so the mine can be removed and destroyed.
However, GPR devices can be less efficient at finding the smaller plastic mines that have become more prevalent. They can also confuse ground clutter -- rocks, sticks, or scraps of metal -- with potential land mines. A half-filled soda can may have the same resonance as a plastic land mine. Combining metal detection and GPR with other emerging detection technologies -- including the use of sound waves, infrared detection, and a new technique that looks at contrasts between the nitrogen concentration between explosives and the soil -- could be the most efficient system for detecting landmines.