We designed, fabricated, and characterized metamaterial-based RF-microelectromechanical system (RF-MEMS) strain sensors that incorporate multiple split ring resonators (SRRs) in a compact nested architecture to measure strain telemetrically. We also showed biocompatibility of these strain sensors in an animal model. With these devices, our bioimplantable wireless metamaterial sensors are intended, to enable clinicians, to quantitatively evaluate the progression of long-bone fracture healing by monitoring the strain on the implantable fracture fixation hardware in real time. In operation, the transmission spectrum of the metamaterial sensor attached to the implantable fixture is changed when an external load is applied to the fixture, and from this change, the strain is recorded remotely. By employing telemetric characterizations, we reduced the operating frequency and enhanced the sensitivity of our novel nested SRR architecture compared to the conventional SRR structure. The nested SRR structure exhibited a higher sensitivity of 1.09 kHz/kgf operating at lower frequency compared to the classical SRR that demonstrated a sensitivity of 0.72 kHz/kgf. Using soft tissue medium, we achieved the best sensitivity level of 4.00 kHz/kgf with our nested SRR sensor. Ultimately, the laboratory characterization and in vivo biocompatibility studies support further development and characterization of a fracture healing system based on implantable nested SRR.

We present telemetric sensing of surface strains on different industrial materials using split-ring-resonator based metamaterials. For wireless strain sensing, we utilize metamaterial array architectures for high sensitivity and low nonlinearity-errors in strain sensing. In this work, telemetric strain measurements in three test materials of cast polyamide, derlin and polyamide are performed by observing operating frequency shift under mechanical deformation and these data are compared with commercially-available wired strain gauges. We demonstrate that hard material (cast polyamide) showed low slope in frequency shift vs. applied load (corresponding to high Young's modulus), while soft material (polyamide) exhibited high slope (low Young's modulus).

We present circular architecture bioimplant strain sensors that facilitate a strong resonance frequency shift with mechanical deformation. The clinical application area of these sensors is for in vivo assessment of bone fractures. Using a rectangular geometry, we obtain a resonance shift of 330 MHz for a single device and 170 MHz for its triplet configuration (with three side-by-side resonators on chip) under an applied load of 3,920 N. Using the same device parameters with a circular isotropic architecture, we achieve a resonance frequency shift of 500 MHz for the single device and 260 MHz for its triplet configuration, demonstrating substantially increased sensitivity.