The skin effect describes how alternating electromagnetic fields and high-frequency currents cannot penetrate deeply into conductive materials, instead confining themselves to a thin outer layer or "skin." 1. Why Current Crowds the Outer Skin of a Wire
When direct current (DC) flows through a wire, it spreads out evenly across the entire cross-section. But when alternating current (AC) flows, the current constantly reverses direction, creating an alternating magnetic field inside and around the wire. - *Opposing eddy currents:* This changing magnetic field induces tiny swirling loops of current (eddy currents) within the conductor itself. - *Core cancellation:* At the center of the wire, these induced eddy currents directly oppose the main current, choking it off. - *Surface reinforcement:* Near the outer surface, the eddy currents align with the main current, reinforcing it. - *Frequency scaling:* The faster the signal alternates (higher frequency), the more violently the changing magnetic fields fight current flow in the core. At radio frequencies (RF), virtually the entire electrical signal travels within a microscopic rim along the metal’s exterior. 2. Why Faraday Cage Envelopes Block Cell Phone Signals A Faraday pouch works on the exact same electromagnetic interaction: - *Mobile signals are high-frequency RF:* Modern cellular, Wi-Fi, Bluetooth, and GPS signals oscillate at gigahertz frequencies (billions of cycles per second). - *Inducing surface currents:* When an incoming electromagnetic wave strikes the conductive metallic lining of the envelope, it pushes the free electrons inside the metal, setting up oscillating surface currents. - *Field reflection and cancellation:* Because the skin depth at gigahertz frequencies is a tiny fraction of a millimeter (often just a few micrometers), the electromagnetic wave cannot penetrate into the interior. The surface currents act like a mirror, generating an opposing field that reflects the incoming wave away and seals the interior off completely. 3. Why Submarines Use VLF Instead of HF, VHF, or Microwaves Seawater is salt water—a dense soup of dissolved sodium and chloride ions that behaves as an electrical conductor. - *The ocean acts like a giant wire core:* Just as a copper conductor attenuates high-frequency electromagnetic fields, conductive seawater rapidly absorbs and dissipates radio waves as heat via the skin effect. - *High frequencies vanish immediately:* At microwave, UHF, or VHF frequencies, the skin depth of seawater is measured in millimeters to centimeters. A cell signal or standard radio broadcast cannot penetrate past the first splash of sea spray. At HF, it penetrates only a few inches to a foot. - *Low frequencies penetrate deeper:* Skin depth is inversely related to frequency—the lower the frequency, the deeper an electromagnetic wave penetrates into a conductor. Very Low Frequency (VLF, 3 kHz to 30 kHz) signals have skin depths that allow waves to penetrate tens of feet into seawater (typically 30 to 60 feet / 10 to 20 meters). Extremely Low Frequency (ELF, below 300 Hz) can reach several hundred feet, though at data rates as slow as a few characters per minute. Submarines ascend to shallow periscope or antenna depth because even VLF waves weaken exponentially. Operating just under the surface allows the submarine to trail a wire antenna within the top 30 to 50 feet of the water column to capture the signal without exposing the hull above the waterline. On Sat, Oct 3, 2026 at 2:48 PM Donovan Balli via BVARC <[email protected]> wrote: > Newsletters are also available at the BVARC Beacon Archive at > https://bvarc.org/newsletters.php. > > Donovan Balli > KG5BDZ > _______________________________________________ > Brazos Valley Amateur Radio Club (BVARC) > > 🌐 Website: https://bvarc.org > 🤝 Get Involved: https://bvarc.org > 💡 Suggestions: https://bvarc.org/home/suggestions > 👥 Member Roster: https://bvarc.org/roster.php > > Unsubscribe or Change Settings: > https://bvarc.org/home/club-listserver/ > _______________________________________________ > -- Best Regards, Mark
_______________________________________________ Brazos Valley Amateur Radio Club (BVARC) 🌐 Website: https://bvarc.org 🤝 Get Involved: https://bvarc.org 💡 Suggestions: https://bvarc.org/home/suggestions 👥 Member Roster: https://bvarc.org/roster.php Unsubscribe or Change Settings: https://bvarc.org/home/club-listserver/ _______________________________________________
