Apparatus and method for harvesting energy from the environment and/or
other external sources and converting it to useful electrical energy. The
harvester does not contain a permanent magnet or other local field source
but instead relies on the earth's magnetic field of another source of a
magnetic field that is external to the sensing device. One advantage of
these new harvesters is that they can be made smaller and lighter than
energy harvesters that contain a magnet and/or an inertial mass. A small
implantable stimulator(s) includes at least one passive
magnetostrictive/electro-active (PME) magnetic-field sensor for
delivering electrical stimulation to surrounding tissue. The PME is
charged utilizing a changing magnetic field from an external alternating
magnetic field source at a frequency particular to the PME. The small
stimulator provides means of stimulating a nerve, tissue or internal
organ with direct electrical current, such as relatively low-level direct
current for temporary or as needed therapy. The field source may be a
hand-held device or a small antenna affixed to the wearer's skin,
clothing or accessories. The stimulator may be configured to be small
enough to be implanted through a surgical needle. Open- and closed-loop
systems are disclosed with measurement of current flow and therapy
through PME sensor function.