I may have answered my own question.. Per Wiki:
Medical imaging
Unlike X-rays, terahertz radiation is not ionizing radiation and its low photon energies in general do not damage living tissues and DNA. Some frequencies of terahertz radiation can penetrate several millimeters of tissue with low water content (e.g., fatty tissue) and reflect back. Terahertz radiation can also detect differences in water content and density of a tissue. Such methods could allow effective detection of epithelial cancer with an imaging system that is safe, non-invasive, and painless.
The first images generated using terahertz radiation date from the 1960s; however, in 1995 images generated using terahertz time-domain spectroscopy generated a great deal of interest.
Some frequencies of terahertz radiation can be used for 3D imaging of teeth and may be more accurate than conventional X-ray imaging in dentistry.
I have long suspected that this frequency is causing the hearing problems in the Cuban Embassy staff.
Per wiki:
Security
Terahertz radiation can penetrate fabrics and plastics, so it can be used in surveillance, such as security screening, to uncover concealed weapons on a person, remotely. This is of particular interest because many materials of interest have unique spectral “fingerprints” in the terahertz range. This offers the possibility to combine spectral identification with imaging.
In 2002 the European Space Agency (ESA) Star Tiger team, based at the Rutherford Appleton Laboratory (Oxfordshire, UK), produced the first passive terahertz image of a hand.