Embodiments of the present invention provide devices (tags), systems, and methods to determine structural integrity and other states of materials-of-interest, such as dental fillings, implants, and root canal posts, to name a few, in a non-invasive and contactless way； and using comparatively safe and/or low energy electromagnetic radiation, such as radio waves. Negligible-sized backscatter-tags with sensors are implanted in such materials-of-interest. Using backscatter imaging technology, the structural integrity and other states of the materials-of-interest may be monitored； which may allow non-invasive and contactless detection of problems such as cracking, bending, excessive pressure, improper temperature, and/or the like. Additionally, initially unknown locations of the implanted negligible-sized backscatter-tags with sensors may be readily determined upon a given scanning (reading) session； and thus mapped to provide an effective image of the material-of-interest.
