A method of diagnosing internal characteristics of a device includes applying a strong magnetic field to the device. The method can include reducing the strong magnetic field at a location of one or more sensors. At least one of the one or more sensors is proximate to the device. The method can include measuring induced magnetic fields around the device. The method can include measuring induced or intrinsic electrical current flow. The method can include measuring intrinsic magnetic properties. The induced magnetic fields can include diagnostic information on properties of the device and how the properties change over time. The device may be, for example, a battery, a capacitor, a supercapacitor, or a fuel cell. The presented measurement of magnetic susceptibility can be performed on materials, solutions, chemical substances, or tissue samples.

An implantable susceptometry marker (1001) for use in surgical guidance comprising one or more ferromagnetic elements (1004a, 1004b, 1004c); and at least one diamagnetic element (1003); wherein the one or more ferromagnetic elements are formed of at least one ferromagnetic material having an initial relative permeability of at least about 10,000 and a saturation induction Bs of less than about 1.5 T, and the at least one diamagnetic element is formed of at least one diamagnetic material having a bulk susceptibility of at least about 0.1610.sup.4; and wherein the total volume of diamagnetic material in the marker is about 100-10,000 times greater than the total volume of ferromagnetic material.

An implantable susceptometry marker (1001) for use in surgical guidance comprising one or more ferromagnetic elements (1004a, 1004b, 1004c); and at least one diamagnetic element (1003); wherein the one or more ferromagnetic elements are formed of at least one ferromagnetic material having an initial relative permeability of at least about 10,000 and a saturation induction Bs of less than about 1.5 T, and the at least one diamagnetic element is formed of at least one diamagnetic material having a bulk susceptibility of at least about 0.1610.sup.4; and wherein the total volume of diamagnetic material in the marker is about 100-10,000 times greater than the total volume of ferromagnetic material.