femtoteslas

Femtotesla (symbol fT) is the SI unit of magnetic flux density, equal to 10^-15 tesla. It is used to describe extremely weak magnetic fields encountered in advanced physics experiments and biomagnetism. To put the scale in perspective, 1 microtesla (1 μT = 10^-6 T) is about one billion femtoteslas, illustrating the vast range of magnetic field strengths studied in science. In conversions, 1 fT = 10^-15 T = 10^-6 nT = 0.001 pT.

Measuring fields at the femtotesla level requires specialized instrumentation and careful noise control. Techniques such as superconducting quantum interference devices (SQUIDs) and high-sensitivity atomic or optical magnetometers are routinely used. Experiments often operate in magnetically shielded rooms to minimize environmental interference and to reach the needed sensitivity.

Applications of femtotesla-scale measurements include biomagnetism, most notably magnetoencephalography (MEG), which records magnetic fields produced by neural activity with sensors responsive to tens of femtotesla. Fetal magnetocardiography and other biomagnetic diagnostics likewise rely on fT-scale sensitivity. In physics and materials science, fT-level measurements enable studies of extremely weak magnetic effects, fundamental symmetries, and subtle magnetic phenomena in novel materials.

Overall, the femtotesla represents a practical scale for describing extraordinarily small magnetic fields detected by state-of-the-art instrumentation in research and clinical contexts.