Vivaldi Antennas for Contactless Sensing of Implant Deflections and Stiffness for Orthopaedic Applications

Abstract

The implementation of novel coaxial dipole antennas has been shown to be a satisfactory diagnostic platform for the prediction of orthopaedic bone fracture healing outcomes. These techniques require mechanical deflection of implanted metallic hardware (i.e., rods and plates), which, when loaded, produce measurable changes in the resonant frequency of the adjacent antenna. Despite promising initial results, the coiled coaxial antenna design is limited by large antenna sizes and nonlinearity in the resonant frequency data. The purpose of this study was to develop two Vivaldi antennas (a.k.a., "standard" and "miniaturized") to address these challenges. Antenna behaviors were first computationally modeled prior to prototype fabrication. In subsequent benchtop tests, metallic plate segments were displaced from the prototype antennas via precision linear actuator while measuring resultant change in resonant frequency. Close agreement was observed between computational and benchtop results, where antennas were highly sensitive to small displacements of the metallic hardware, with sensitivity decreasing nonlinearly with increasing distance. Greater sensitivity was observed for the miniaturized design for both stainless steel and titanium implants. Additionally, these data demonstrated that by taking resonant frequency data during implant displacement and then again during antenna displacement from the same sample, via linear actuators, that "antenna calibration procedures" could be used to enable a direct clinically relevant quantification of fracture stiffness from the raw resonant frequency data. These improvements mitigate diagnostic challenges associated with nonlinear resonant frequency response seen in previous antenna designs.INDEX TERMS Antenna for orthopaedic application, antenna resonant frequency, computational electromagnetic simulations, electromagnetic sensor, external sensing of object displacement / deflection / stiffness, monitoring and predicting bone fracture healing, near electromagnetic field, resonant frequency measurements, Vivaldi antenna.

Theoretical and experimental sensing of bone healing by microwave approach

“…This is used especially to detect metal plate and plate deflection results from mechanical effects 12 . A high sensing of diagnostic of orthopedic bone fracture healing has also been realized by using two vivaldi antennas which has advantageous with respect to coiled coaxial antennas due to their large sizes and low linearity around resonant frequency 22 . The detection of bone fracture also carried out by using helical antenna without any connection to the related bone.…”

“…12 A high sensing of diagnostic of orthopedic bone fracture healing has also been realized by using two vivaldi antennas which has advantageous with respect to coiled coaxial antennas due to their large sizes and low linearity around resonant frequency. 22 The detection of bone fracture also carried out by using helical antenna without any connection to the related bone. The observation of the statement of bone is realized according to the scattering parameters on finger type bone.…”