CAREER: Developing a compact wireless multi-modal detector array for remote sensing and imaging

Wireless and batteryless sensors are particularly useful for long-term monitoring of physiological parameters inside confined body cavities. Traditionally, a batteryless sensor is implemented as a passive resonator whose resonance frequency is responsive to physiological variation. When the embedded sensor is sufficiently close to the body surface, its resonance frequency can be directly estimated from radio frequency signals backscattered from the sensor.

However, when the penetration depth is much larger than the passive sensor’s own dimension, backscattered signals can be too small to detect. In addition, a passive sensor has limited temporal resolution because repetitive averaging of backscattered signals is required to achieve a reasonable measurement accuracy. To overcome these limitations, this CAREER project will develop a generally applicable circuit that can significantly improve the remote detectability and temporal resolution of batteryless sensors.

Using a very compact circuit design, this Self-oscillation Encoding Telemeter (SET) can utilize wireless power to self-oscillate and encode input signals over a wide frequency range. When the SET is utilized to simultaneously encode neuronal voltages and magnetic resonance images (MRI), it can provide correlated information between electrophysiology and imaging, revealing novel insights into the neuronal origin of MRI signal dynamics.

Besides its immediate impact on neuroscience research, the SET can improve the sensing capability for many other types of input signals including pH, pressure, humidity, temperature, and strain. Owing to its novel concept, concise design, and broad impacts, the SET sensor will be used as an excellent vehicle to inspire scientific interest of K-12 students, and to educate STEM students (including those from underrepresented groups).

It will also serve the national interest with potential transformation of this wireless sensing technology into many advanced sensor systems.

To significantly improve the remote detectability of batteryless sensors, Self-oscillation Encoding Telemeters (SETs) will be developed to encode various types of input signals over a wide frequency range. This project features three novel methods to retrieve multiplexed input signals. (1) When input signals with distinct frequency characteristics are encoded by the same SET sensor, they can be resolved by their different separations from the carrier wave. (2) When multiple SETs are concatenated into an array, each sensor will be wirelessly activated to have a unique oscillation frequency, so that input signals encoded by individual SETs can be identified by their sideband patterns. (3) When input signals of similar frequency characteristics are encoded by the same SET, they can be consecutively encoded by cyclically switching the pumping frequency at a faster speed, enabling selective activation of each encoding mode.

These three novel methods will be implemented towards four research goals. Based on the sideband separation technique described in method #1, aim 1 will decode electrophysiology (slow) and MRI (fast) signals that are simultaneously encoded and broadcasted by the SET sensor. Based on the frequency-division multiplexing concept described in method #2, aim 2 will develop a planar SETs array and signal processing algorithms to retrieve encoded images from individual sensors, enabling high-resolution mapping of micro vessel distribution along the brain surface.

Meanwhile, aim 3 will develop an insertion catheter aligned with a linear SETs array, revealing the underlying correlation between MRI and neuronal signals across multiple brain layers. Utilizing the time-division multiplexing concept described in method #3, aim 4 will consecutively encode multiple quasistatic sensing signals while continuously encoding high-frequency imaging signals at the same time.

Collectively, advances from these endeavors will make the batteryless sensors useful for a range of applications from biomedicine to structural monitoring and environmental sensing.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.