Design, Characterization, and Optimization of a Waveguide-Based RF/MW Exposure System for Studying Nonthermal Effects on Skeletal Muscle Contraction

A waveguide-based exposure system for studying in vitro nonthermal radio-frequency/microwave (RF/MW) effects on skeletal muscle contraction in the frequency range of 0.75-1.12 GHz was designed, characterized, and optimized. The design includes a vertical organ bath (OB) placed inside the waveguide for suspending an intact skeletal muscle from the hind limb of the mouse, i.e., flexor digitorum brevis, in an oxygenated Tyrode solution during the RF/MW exposures. Muscle contraction is stimulated by an electric field generated between two platinum electrodes and continuously measured before, during, and after RF/MW exposure by a force transducer. A temperature feedback system that controls the perfusion rate of the Tyrode solution works in conjunction with the outer water jacket of the OB to maintain the temperature of the solution to within plusmn0.2degC. Characterization and optimization of the RF/MW exposure setup were accomplished by a detailed numerical computation of the RF/MW fields and specific absorption rate (SAR) inside the inner chamber of the OB, where the muscle is suspended, using the finite-difference time-domain (FDTD) method. Analysis of the computed RF/MW fields within and immediately surrounding the skeletal muscle showed that the RF/MW fields and SAR exhibit the level of homogeneity required for performing well-controlled RF/MW exposure experiments