How are people with orthopedic implants made from titanium and platinum not detected by metal detectors? According to my understanding,  the magnetic field created by the metal detector is  inducing eddy currents through a nearby metal, then that eddy current creates its own magnetic field which can be translated by electric circuit into a sound that indicating that there is a nearby metal. My question is it possible that people with orthopedic implants made from metals (mentioned in the title) don't get detected by metal detector?
 A: Metallic implants can be detected by metal detectors. In practice, often they aren't, which is a desired property in many cases (like airport security).
A metal detector's sensitivity is limited, and it will only detect objects that are large or close enough. Implant sizes vary considerably. In addition to that, implants are covered by body tissue. This has two effects, both detrimental to detection:

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*the spacing between a hand-held detector and the object is increased, and

*because of tissue electric conductivity, the penetration depth of the probing RF field is reduced.

These effects combine to most implants usually not being detected, as this report on the website of the US' NIH describes:
Prosthetic metal implants and airport metal detectors
Implants could be made more difficult to detect by applying some composite structure, which blocks the eddy currents, in the same way as transformer cores are made of laminated steel sheets. However, this would compromise the implant material's inherent strength, and drive up cost, so I think it's unlikely that this is done in practice.
