Split-Ring Resonator Sensor Penetration Depth Assessment Using In Vivo Microwave Reflectivity and Ultrasound Measurements for Lower Extremity Trauma Rehabilitation

Design of a novel dual-polarized microwave sensor for human bone fracture detection using reactive impedance surfaces

This paper presents a novel miniaturized dual-polarized transceiver sensor system for detecting fractures in human bone tissues. The system features a patch antenna and a Reactive Impedance Surface (RIS) layer that reduces its size by 30% compared to conventional designs, resulting in enhanced fracture detection accuracy. Additionally, the system includes a dielectric plano-concave lens that adapts to the human body and improves impedance matching for optimal performance. The lens contains via holes filled with a lossy dielectric material similar to human fat tissue, which concentrates electromagnetic (EM) power and increases penetration depth for more effective crack detection. To detect fractures, two identical sensors are placed opposite each other on the tissue and moved simultaneously. The amount of EM power collected by the receiver sensor is measured using S-parameters; the transmission coefficient (S₂₁) phases and contrast between the crack and surrounding tissue are used to construct images of fractured bones. Full-wave simulations and experimental measurements on a semi-solid human arm mimicking phantom demonstrate the proposed dual-polarized sensor's ability to detect the location and orientation of narrow cracks in the millimeter range. The system exhibits reliable performance across different human bodies.

Effect of Fe/Fe3O4 Nanoparticles Stray Field on the Microwave Magnetoresistance of a CoFeB/Ta/CoFeB Synthetic Ferrimagnet

The effect of the stray field of Fe/Fe₃O₄ nanoparticles on the angular dependence of the microwave absorption derivative in CoFeB/Ta/CoFeB synthetic ferrimagnetic structures and CoFeB films with perpendicular anisotropy is analyzed, and its application for sensor technology is proposed. The effective field of the "platform-particles" system controlled by the magnetic dipole interaction of the CoFeB-Fe/Fe₃O₄ system decreased to zero in areas where the platform was magnetostatically coupled with nanoparticles. Micromagnetic modeling demonstrated the distribution of magnetization and resistance in local areas of CoFeB/Ta/CoFeB structures under the nanoparticles. The microwave absorption derivative can be used as an indicator of local magnetization switching of the giant magnetoresistance (GMR) structure under scattering fields of NPs or magnetically labeled cells. The limiting sensitivity of the detection method was 2.4 × 10⁷ nanoparticles, which covered the spin-valve surface. We have proposed to combine the advantages of a GMR sensor with wireless technology of microwave reading of magnetoresistance for the detection of magnetically labeled cells.

MAS: Standalone Microwave Resonator to Assess Muscle Quality

Microwave-based sensing for tissue analysis is recently gaining interest due to advantages such as non-ionizing radiation and non-invasiveness. We have developed a set of transmission sensors for microwave-based real-time sensing to quantify muscle mass and quality. In connection, we verified the sensors by 3D simulations, tested them in a laboratory on a homogeneous three-layer tissue model, and collected pilot clinical data in 20 patients and 25 healthy volunteers. This report focuses on initial sensor designs for the Muscle Analyzer System (MAS), their simulation, laboratory trials and clinical trials followed by developing three new sensors and their performance comparison. In the clinical studies, correlation studies were done to compare MAS performance with other clinical standards, specifically the skeletal muscle index, for muscle mass quantification. The results showed limited signal penetration depth for the Split Ring Resonator (SRR) sensor. New sensors were designed incorporating Substrate Integrated Waveguides (SIW) and a bandstop filter to overcome this problem. The sensors were validated through 3D simulations in which they showed increased penetration depth through tissue when compared to the SRR. The second-generation sensors offer higher penetration depth which will improve clinical data collection and validation. The bandstop filter is fabricated and studied in a group of volunteers, showing more reliable data that warrants further continuation of this development.

Head-compliant microstrip split ring resonator for non-invasive healing monitoring after craniosynostosis-based surgery

A soft and highly directive, proximity-coupled split-ring resonator fabricated with a liquid alloy, copper and polydimethylsiloxane (PDMS) is presented. The same was designed for sensing osteogenesis of calvarial bone. As dielectric properties of bone grafts in ossifying calvarial defects should change during the osteogenesis process, devices like this could monitor the gradual transformation of the defect into bone by differentiating changes in the dielectric properties as shifts in the resonance frequency. Computational Software Technology (CST) Microwave Studio®-based simulation results on computational head models were in good agreement with laboratory results on head phantom models, which also included the comparison with an in-vivo measurement on the human head. A discussion based on an inductive reasoning regarding dynamics' considerations is provided as well. Since the skin elasticity of newborn children is high, stretching and crumpling could be significant. In addition, due to typical head curvatures in newborn children, bending should not be a significant issue, and can provide higher energy focus in the defect area and improve conformability. The present concept could support the development of soft, cheap and portable follow-up monitoring systems to use in outpatient hospital and home care settings for post-operative monitoring of bone healing after reconstructive surgical procedures.