Magnetic Field Converter

1 T is equivalent to 10,000 Gauss. Earth's field is only 0.00005 T (0.5 G). Even a strong permanent magnet (neodymium) is about 1 T at close range. MRI machines at 3 T are so powerful that they can attract ferromagnetic objects (IV poles, wheelchairs) across a room with potentially fatal force. Superconducting magnets are required for fields above ~2-3 T because normal conductors would melt from resistive heating.

The record continuous magnetic field as of 2023 is 45.5 T, achieved at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida. This uses a hybrid magnet combining a resistive outer magnet (33 MW power!) and a superconducting inner coil. Pulsed fields (millisecond duration) have reached over 100 T. Single-turn coil experiments have briefly reached ~2,800 T before destroying themselves.

MRI uses three types of magnetic fields: (1) the static B₀ field (1.5-7 T) to align proton spins; (2) radiofrequency B₁ pulses at the Larmor frequency (ω = γB₀, where γ = 42.577 MHz/T for protons) to flip spins; (3) gradient fields (10-80 mT/m) to spatially encode the signal. The received signal from relaxing protons is Fourier-transformed to create images with millimeter resolution.

Magnetars are neutron stars with surface magnetic fields of 10⁸-10¹¹ T (10¹²-10¹⁵ G). These extreme fields cause starquakes (sudden crust fractures) that release enormous bursts of gamma rays. The December 2004 magnetar SGR 1806-20 flare released more energy in 0.2 seconds than the Sun emits in 250,000 years. The field energy density B²/(2μ₀) ~ 10²⁰ J/m³ is comparable to nuclear energy densities.

Magnetic susceptibility χ = M/H relates a material's magnetization to the applied H-field. Diamagnetic materials (χ < 0, e.g., water χ = −9.1 × 10⁻⁶, bismuth χ = −1.7 × 10⁻⁴) weakly repel fields. Paramagnetic materials (χ > 0, e.g., aluminum χ = 2.2 × 10⁻⁵) weakly attract. Ferromagnetic materials (iron, nickel, cobalt) have χ up to 10⁵ and retain magnetization — they form permanent magnets.

The Zeeman effect is the splitting of atomic spectral lines in a magnetic field. The energy shift is ΔE = gμ_B × B × m_J, where g is the Landé g-factor, μ_B = 9.274 × 10⁻²⁴ J/T is the Bohr magneton, and m_J is the magnetic quantum number. At 1 T, the splitting is ~2μ_B ≈ 1.16 × 10⁻⁴ eV ≈ 28 GHz. This is the basis of atomic clocks, NMR, ESR, and Zeeman slower devices for cooling atoms.

Earth's field is measured by: fluxgate magnetometers (measure all three components, ~0.1 nT resolution); proton precession magnetometers (measure field magnitude from proton Larmor frequency, ~0.1 nT); optically pumped magnetometers (cesium or rubidium vapor, ~0.001 nT); SQUID magnetometers (superconducting quantum interference device, ~10⁻¹⁵ T sensitivity for medical MEG imaging). Satellite missions (Swarm, CHAMP) map the global field.

Yes, with mu-metal (μr ≈ 20,000-100,000), a high-permeability alloy of iron-nickel. The magnetic field is channeled through the high-permeability material rather than through the shielded space. Multiple nested shields achieve attenuation factors of 10,000 or more. Superconductors provide perfect diamagnetic shielding (Meissner effect) — the field is completely expelled from the superconductor interior.

A charged particle in a magnetic field undergoes circular motion at the cyclotron frequency f_c = qB/(2πm). For a proton at 1 T: f_c = 1.602 × 10⁻¹⁹ × 1 / (2π × 1.673 × 10⁻²⁷) = 15.24 MHz. For an electron: 27.99 GHz/T. This frequency is used in cyclotrons, magnetrons (microwave ovens), and the electron cyclotron resonance (ECR) ion sources used in particle accelerators and semiconductor processing.