Ultraefficient thermoacoustic conversion through a split ring resonator

Microwaves, which have a ∼10-cm wavelength, can penetrate deeper into tissue than photons, heralding exciting deep tissue applications such as modulation or imaging via the thermoacoustic effect. Thermoacoustic conversion efficiency is however very low, even with an exogenous contrast agent. We break this low-conversion limit, using a split ring resonator to effectively collect and confine the microwaves into a submillimeter hot spot for...