How can we limit magnetic fields outside the coil ?

Do you provide a certificate proving there are no magnetic leaks...

 Ambrell recommends outside agencies that can plot the magnetic fields radiated from the induction coil. A typical Faraday cage would then need to be installed to eliminate any magnetic fields around the induction coil. Once the cage is installed, one would need to run the tests again to prove that the stray magnetic fields have been controlled. The testing agency will then provide a certificate for your particular application.