Wireless power recovery for Internet of Things devices using pre-charged CMUTs

Capacitive micromachined ultrasonic transducers (CMUTs) are currently used in diagnostic ultrasound imaging systems, and are also attractive solutions for therapeutic and tracking applications in the body. Most CMUTs require a voltage bias for operation with high sensitivity and efficiency; this requirement can be inconvenient for some applications, such as catheter- and capsule-based endoscopy, while being prohibitive for others, such as wirelessly-powered millimeter-sized nodes for the Internet of Things. The use of pre-charged CMUTs, which can operate without a voltage bias, holds the potential to open up an entire class of previously inaccessible applications for CMUTs that are incompatible, due to issues of size, complexity, or safety, with a voltage bias. Pre-charging can also greatly increase the safety and simplicity of system-level design for applications that are compatible with a voltage bias, but that do not require tuning of the bias in the course of operation.