Although toroidal transformers emit minimal stray magnetic fields by their nature, a certain amount will always be present as with all magnetic devices. For the vast majority of applications, toroidal emissions are far too low to affect circuit operation, but there are some applications that are especially sensitive.
These include wideband, high-gain instrumentation and preamplification, high-end audio, and high-resolution CRT circuits. In this case, magnetic shielding can be applied around the toroid in the form of a high-permeability metal band. This can be Silicon Steel for the majority of cases or Mu Metal for sensitive applications. For extremely sensitive circuits, total encapsulation in a steel can or case may be the only option. There are ways to reduce emissions by design (before any protection is added to the transformer), so if your circuit is prone to magnetic interference, please include this information in specifications when requesting a quotation.
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