Magnetic retention device

An apparatus, comprising:

• an external component of a medical device, including:
• a first permanent magnet;
• and
• a second permanent magnet, wherein
• the external component is configured to enable the first permanent magnet to be moved for purposes of adjustment relative to the second permanent magnet, which adjustment adjusts a strength of a magnetic field resulting from the first and second permanent magnets, and
• at least one of:
• (i) the apparatus is configured such that the first permanent magnet can be moved from a location where the first permanent magnet is within the second permanent magnet to a location at least substantially outside the second permanent magnet so as to decrease the strength of the magnetic field;
• or
• (ii) the apparatus further comprises a third permanent magnet and a fourth permanent magnet, wherein
• the magnetic field also results from the third and fourth permanent magnets,
• the third permanent magnet is movable relative to the fourth permanent magnet and the second permanent magnet so as to adjust the strength of the magnetic field,
• the first permanent magnet is movable relative to the fourth permanent magnet so as to adjust the strength of the magnetic field resulting from the first, second, third and fourth permanent magnets,
• the first and third permanent magnets are arrayed in a first circular path,
• the second and fourth permanent magnets are arrayed in a second circular path encompassing or encompassed by the first circular path, and
• the first and third permanent magnets move along the first circular path and thus relative to the second and fourth permanent magnets so as to adjust the strength of the magnetic field resulting from the first, second, third and fourth permanent magnets.