Using embedded energy-harvesting nanodevices for neural data communications in the human body

Implanted biomedical devices are an important part of the diagnosis and treatment of human illnesses. Such devices need electrical power for operation, transmission systems for data communications and a high level of bio-compatibility to reduce the possibility of inflammation. Powering by battery is widely used but requires removal of the device from the body for battery renewal. Wireless electromagnetic (EM) systems are also in common use but are subject to tissue absorption and potential tissue heating. It would be preferable to use some form of energy-harvesting for power and a more biocompatible method for data communications. This Thesis proposes the use of ultrasound as a method of providing in-body energy harvesting for an implanted device at a shallow depth of tissue. The medical use of ultrasound for imaging is widespread, well understood and has recommended safety levels. Arrays of devices containing piezoelectric nanowires can convert incident ultrasound energy into electrical pulses. These pulses can stimulate a nerve to generate a stream of modulated signals along the nerve and deliver data packets to a more deeply embedded receiver. The maximum bit rate is 200 bit/s, limited by the rate at which nerves can generate electrical signals. The proposed modulation is simple on-off keying (OOK) to create a stream of logic “ones" and “zeroes". The send and receive timing is asynchronous and the direction of transmission is one-way so no re-sending of faulty packets can be supported. We model a specific scenario of a stimulus system on the vagus nerve in the neck sending modulated data pulses to an embedded, multi-reservoir drug-delivery system in the brain. The drug-delivery system could use cerebrospinal glucose as a source for energy harvesting. Forward error correction is analysed as a potential method to improve transmission performance. The overall energy-harvesting and communications system is simple, biocompatible and safe.