The Minelab Excalibur II is designed for hardcore fans who would like to take a metal detector on their snorkel or (much more most likely) scuba dive. VLF detectors are the most common variety of metal detectors utilised today. They function by transmitting and getting electromagnetic fields at many frequencies. https://angelomwchv.isblog.net/the-basic-principles-of-types-of-metal-detector-sensor-44399300