Flow following sensor particles are a promising route to obtaining spatially resolved measurements in chemical and biochemical reactors. Their practical deployment, however, is limited by challenges in miniaturisation, power supply and packaging. In this work, the authors present a millimeter-scale Lagrangian sensor platform that integrates an inertial measurement unit (IMU) and a low-power microcontroller unit (MCU) on a high-density interconnect (HDI) printed circuit board (PCB). The work describes the evolution from a first demonstrator towards a reduced footprint design intended for spherical encapsulation.
The main contribution is a quantitative system level feasibility boundary that links miniaturised sensor node design, duty cycled energy demand, candidate energy input routes and spherical packaging constraints at the targeted millimeter scale. The baseline power demand of the current duty cycled implementation is analysed, including a cycle based charge and energy budget, and this demand is related to two experimentally investigated energy input routes: photovoltaic harvesting under controlled optical illumination and resonant inductive power transfer at 13.56 megahertz. The harvesting experiments are performed on dedicated evaluation platforms and are used to quantify the candidate energy input routes.
The results show that the platform concept, compact HDI integration, low-power duty cycling, optical data transmission and a glass based encapsulation route are technically feasible at the targeted size. At the same time, neither harvesting route yet closes the gap to robust energy autonomous operation under realistic reactor conditions. Photovoltaic powering appears strongly constrained by alignment, optical access and geometric coupling, while inductive transfer remains highly sensitive to orientation, field distribution and RF to DC conversion efficiency. The presented measurements therefore define both the current feasibility range and the remaining engineering requirements for future energy autonomous sensor spheres.
The collaborative research was carried out at the Institute of Microsystems Technology and the Institute of Mathematics at Hamburg University of Technology within project A08 of the Collaborative Research Centre CRC 1615 (SMART Reactors).
Anton Geläschus, Lukas Rennpferdt, Vamika Rathi, Muhammad Daniyal Hussain, Daniel Ruprecht, Hoc Khiem Trieu (2026). Millimeter-Scale Lagrangian Sensor Spheres for Local State Monitoring in SMART Reactors: Towards Energy-Autonomous Operation.Ind. Eng. Chem. Res. 65 (38): 20528–20545.
