https://www.dhs.gov/publication/st-pointer-factsheet
In 2014, the U.S. Department of Homeland Security partnered with the NASA Jet Propulsion Laboratory (JPL) to develop the Precision Outdoor & Indoor Navigation & Tracking for Emergency Responders (POINTER) technology. "POINTER is a precision positioning sensor that locates first responders via" "low-frequency magnetoquasistatic fields that can transmit signals through any building materials."
"That differentiates it from Ultra-Wide Band, GPS, radio frequency identification systems and sensor fusion methods, all of which rely on radio position location and suffer reduced performance in non-line-of-sight and indoor environments."
Excerpts below from https://www.dhs.gov/science-and-technology/how-pointer-works
"What are Magnetoquasistatic (MQS) fields?"
"MQS fields are magnetic fields with very slow temporal variations that appear static and can penetrate through most natural materials just like the Earth’s magnetic field. As a result, they can be used in a broad array of sensor applications."
"What are some examples of how MQS fields are currently used?"
"MQS fields can be beneficial in applications where information or sensing is needed when a clear line-of-sight (LoS) is not available. This includes position sensing in buildings or homes—like with POINTER—as well as in wireless communications and power transfer technologies currently being used to power smart phones in similar environments."
https://engineering.purdue.edu/~shreyas/SparcLab/static/pdfs/j/MN_TBME_Magnetic.pdf
(Note: Please refer to Figure 1).
Efficient Communication and Powering for Smart Contact Lens with Resonant Magneto-Quasistatic Coupling
https://arxiv.org/abs/2406.08220
An electromagnetic field near an antenna corresponds to a quasi-static electric field and a quasi-static magnetic field (non-propagating).
A propagating waveform may be generated at a distance of 1 to 3 wavelengths*.
Electromagnetic waves travelling away from an antenna can be compared to water ripples created by a droplet, where we initially have spherical waves which, as they spread, become plane waves.
Close to the antenna, surface currents create evanescent waves which influence strongly the electric and magnetic fields, inhibiting them from propagating. As a result, in this region, they can be considered as quasi-static. They vary slowly with time.
Also, the electric and magnetic fields can exist independently of each other in the near field; in other words, they are decoupled. We have a quasi-static electric field and a quasi-static magnetic field.
Moreover, one type of field can be disproportionately larger than the other in different subregions.
Further away from the antenna, they are released from this inhibition and they start propagating together. The two regions found closer and further away from the antenna are termed respectively "near-field" and "far-field".
*More details in the Wikipedia article "Near and far field".
Reference: https://www.mvg-world.com/static/drop3.mp4