Helmholtz coils for EMI immunity testing: stretching the uniform field area

Helmholtz coils are used to establish known, uniform magnetic fields for calibrating magnetic field sensors, for EMI immunity testing, for magnetic bioeffects research, etc. But in the past, it has been assumed that only very small devices could be tested. The paper provides information leading to an understanding of the size of the uniform field region and how to trade off field uniformity for increased size of the device under test. Graphs and a table are provided to assist the helmholtz coil user in this task