United States patent. Patent no. US 9,060,743 B2, Munro et al.

A system for monitoring strain as an indicator of biological conditions, such as spinal fusion, glucose levels, spinal load ing, and heart rate. The system includes an inter-digitated capacitor sensor, and RF transmitter, and an associated antenna, all of which are microminiature or microscopic in size and can be implanted in a biological host Such as a human or animal. An inductively coupled power Supply is also employed to avoid the need for implantation of chemical batteries. Power is provided to the sensor and transmitter, and data is transmitted from the sensor, when an external receiv ing device, such as a handheld RFID type receiver, is placed proximate the location of the implanted sensor, transmitter and inductively coupled power Supply. The implanted sensor, transmitter and inductively coupled power Supply can be left in place permanently or removed when desired