Radioplasmonics: Plasmonic Transducers in the Radiofrequency Regime for Resonant Thermo-acoustic Imaging in Deep Tissues

In this work, we introduce a radically new approach for achieving doubly resonant light-to-sound conversion with radiofrequency waves, namely, electromagnetic waves in the range of 1-100 MHz. By taking the profit from recently published metamaterials exhibiting plasma-like responses in the radio range, we introduce the concept of "radioplasmonics" that deals with localized surface plasmons in the radio regime. In analogy with conventional plasmonics, radioplasmonics can be exploited to design microtransducers that effectively convert radio-waves into heat through resonant electromagnetic absorption. Then, by tuning the Young's modulus of the transducers, we can achieve resonant acoustic vibrations in the same range of frequencies as the plasmonic resonances. In this way, plasmonic heating is converted into resonant thermo-acoustic expansion and its consequent generation of pressure waves. The latter can then be used for ultrasound imaging. We show that, in this double resonance framework, the intensity of the generated acoustic waves is above the current detection level under realistic conditions. The importance of using the radio range is related to its ability to deeply penetrate water and biological tissues. Hence, the proposed approach paves the way to the first total-body thermo-acoustic imaging able to reach a single-cell resolution.