Luis Hernan was always curious about how wireless technologies like radio are transmitted through the air. So after finishing up his studies in architecture, computer science, and design, Hernan decided to research these invisible signals through a PhD at Newcastle University. Hernan set up a system that turned the wireless signals around him into colourful, ghostlike images using long-exposure photography, allowing people to see the strength of the signals around them. (Photo by Luis Hernan)

A team of female cadets takes part in a tug-of-war competition at Budyonny Military Academy of the Signal Corps in St Petersburg, Russia on March 7, 2021. (Photo by Peter Kovalev/TASS/Profimedia)

Vietnamese female commissioned officers of the signal force march during a parade marking their 70th National Day at Ba Dinh square in Hanoi, Vietnam September 2, 2015. (Photo by Reuters/Kham)

A Russian ground staff member signals to the pilot of a Sukhoi Su-25 fighter jet at the Hmeymim air base near Latakia, Syria, in this handout photograph released by Russia's Defence Ministry October 22, 2015. (Photo by Reuters/Ministry of Defence of the Russian Federation)

Tara West signals to her partner Natalie Cook during the Bronze final match during the Australian Beach Volleyball Championships at Glenelg Beach on March 13, 2011 in Adelaide, Australia.

The cruise ship Viking Sky as it drifts after sending a Mayday signal because of engine failure in windy conditions near Hustadvika, off the west coast of Norway, Saturday March 23, 2019. The Viking Sky is forced to evacuate its estimated 1,300 passengers. (Photo by Odd Roar Lange/NTB Scanpix via AP Photo)

Passengers brave the strong winds as they wait for a bus, in Hong Kong, Monday, September 15, 2014. The Hong Kong Observatory issued the number 8 southeast storm signal, as Typhoon Kalmaegi edges closer to Hong Kong. (Photo by Kin Cheung/AP Photo)

Julian Ryerson of Borussia Dortmund during the Bundesliga match between Borussia Dortmund and 1. FC Union Berlin at Signal Iduna Park on April 8, 2023 in Dortmund, Germany. (Photo by Alexandre Simoes/Borussia Dortmund via Getty Images)