Described embodiments include a system and a method. A system includes an electromagnetic structure having a surface and a radiofrequency electromagnetic field source. The field source includes electronically controllable, artificially structured electromagnetic unit cells configured to create quasi-static electromagnetic fields within the electromagnetic structure. Each unit cell is responsive to a control signal. A selector circuit selects a quasi-static electromagnetic field pattern creating a high contrast electric field in a subwavelength electromagnetic cavity and is defined by the surface of the electromagnetic structure and an exterior surface of a perturbing object. The high contrast electric field has a power density that is localized to a volume adjoining the exterior surface of the perturbing object. A field pattern implementation circuit generates the control signal assigning electromagnetic field characteristic to each of the electromagnetic unit cells. The assigned radiofrequency electromagnetic field characteristics collectively creating the selected quasi-static electromagnetic field pattern.