Millimeter wave probing of the acoustic phase for concealed object detection

We developed a far infrared technique for detecting objects that are concealed behind a barrier, which is opaque for visible light. The technique makes use of the fact that mechanically coupled objects can be distinguished by their acoustic phase during a driven vibration. The pattern of the acoustic phase is imaged using 70 GHz radiation. The experimental data demonstrate that virtually all objects can be sensed, which includes metals as well as dielectric materials.