Battery-powered implants have been clinically approved to provide neural stimulation for symptomatic relief from Parkinson’s and epilepsy. However, the limited life span of batteries requires replacement by surgical procedure. Wired implants are also of limited long-term use as the penetration of wires through the skin poses infection risks. A power supply remedy in the form of a wireless, battery-free implantable neural stimulator activated by an externally applied magnetic field has been engineered at Rice University.
The device is the size of a grain of rice and is covered with a magnetoelectric material composed of iron, boron, silicon and carbon, vibrates at a molecular level when exposed to a magnetic field. A piezoelectric crystal forms 
A sample of the bi-layered magnetoelectric film atop a bed of uncooked rice. Source: Jeff Fitlow/Rice Universitya second layer that converts mechanical stress directly into an electric voltage that produces an electrical voltage in response to an applied magnetic field. The frequency of the vibrations is too low to affect nearby cells and the miniature magnetically powered neural stimulator operates up to clinically relevant frequencies in excess of 100 Hz.
The devices were implanted below the skin of rodents, which frequented areas of their enclosures where a magnetic field activated the stimulator, providing a small voltage to the reward center of their brains.
Component miniaturization and designing a modulated biphasic signal that could stimulate neurons without harming them were major challenges tackled by the researchers. The successful realization of small size and wireless capabilities suggests that the neurostimulators can be implanted anywhere in the body through a minimally invasive procedure.
