A parallel plate waveguide forms a volume coil used for magnetic resonance imaging and spectroscopy. The waveguide includes a first conductor arranged on a first side of the waveguide and a second conductor arranged on a second side of the waveguide. Excitation of the first conductor and the second conductor creates a transverse electromagnetic field between the first conductor and the second conductor which causes a target within the volume coil to emit radio frequency signals used for producing an image of the target.

A topologically-protected traveling-wave amplifier includes resonators arranged in a two-dimensional array defining a periphery including a first edge. An output line is coupled to an output resonator disposed along the first edge spaced from an input resonator coupled to an output line. A synthetic gauge field generator associated with the resonators provides a topologically-protected edge state corresponding to propagation along the periphery in a propagation direction from the input resonator along the first edge to the output resonator. A parametric driving element creates pairs of photons in the edge state and amplifies a signal propagating along the first edge in the propagation direction. A signal incident from the input line propagates in the propagation direction along the first edge while being amplified and is detected at the output line as an amplified signal. A signal incident from the output line is attenuated before emerging at the input resonator.