Active Ultrasound Electrical Recharging (USer) uses ultrasonic pressure waves to transfer energy through tissue to a receiver and then to a rechargeable battery or capacitor. Power can also be provided to an application for direct use. This project was originally funded by Phase I and Phase II SBIR grants from the National Institutes of Health.
The method can be applied to batteries for implanted medical devices such as drug pumps, sensors, and neurostimulators.
Active USer is similar to the Pitch-Catch Method of Non-Destructive Testing via transmission of ultrasound. A frequency-matched, impedance-matched, transmitter-receiver pair are placed at opposite ends of the medium. The transmitter is activated via a frequency-generator and power source. The receiver converts pressure pulses to electrical power. A charging chip appropriate to the battery determines the charging protocol. Alternatively, the electrical power can be delivered to a mechanical device or sensor.
An important element of an ultrasound power delivery system is a transmitter unit that can orient the piezoelectric transducer providing lateral and angular alignment to optimize transmitter-receiver power transfer.
A key aspect of the implementation is the design of a convenient way to deliver power and also communicate with the implanted medical device (IMD). The design of an external unit must consider, among other things, that some applications require its use on patients for long periods of time (several hours), a time that in turn depends on the power transfer efficiency. The resulting design must be simple to apply and align, user friendly and comfortable.
The functions of a complete external unit are: power transmission, transducer (piezo) positioning and orientation, duplex data transmission with the IMD and an external controller. Telemetry with the IMD can consist of activation and reading of sensors measuring for example: state of charge of a battery or supercapacitor, charging current, temperature, pH, force, and pressure.