You place a disc's center over a small joint, run the full session, and the relief comes up short. With a pancake coil, that's usually a placement miss. With a donut coil, the placement itself is the miss: you've aimed the field's weak spot at the joint. Two discs can share the same outer size and housing and still deliver very different fields. The coil wound inside sets the field's shape. A pancake concentrates its strength at the center. A donut spreads its strength into a ring and leaves a dip in the middle. A cross-section of a donut coil…

When you place a disc on a knee for a 40-minute session and the patient feels less relief than expected, the instinct is to blame the device. Placement is the more likely culprit. A brochure can list peak Gauss without saying where the field is strongest. That value alone doesn't tell you where to place the disc. Two discs of the same outer size can deliver very different fields. A pancake coil peaks at the center; a donut coil peaks in a ring around the center. A cross-section of a pancake coil drawn beneath a field-strength curve. The spiral winding…

A smaller peak Gauss value can induce more in tissue. Faraday's law explains why. Two PEMF devices sit side by side on a shelf. One brochure says 7,000 Gauss. The other says 1,500 Gauss. The bigger value looks like the obvious winner. Faraday's law explains why it sometimes isn't. Tissue inside the body doesn't respond to the strength of a magnetic field. It responds to how fast that field is changing. A short, sharp pulse from a lower-peak device can induce more electrical activity in tissue than a tall, slow pulse from a higher-peak device. A magnetic-field-versus-time chart comparing two…