  We numerically demonstrate two types of metasurface absorbers to efficiently
absorb digital signals. First, we show that the digital waveforms used in this
study contain not only a fundamental wave but also nonnegligible harmonic
waves, which limits the absorption performance of a conventional metasurface
absorber operating in only a single, finite frequency band. The first type of
the proposed absorbers is designed using two kinds of unit cells, each of which
absorbs either a fundamental frequency or third harmonic of an incident digital
waveform. This dual-band metasurface absorber exhibits absorption performance
exceeding that of the conventional metasurface absorber and more strongly
dissipates the energy of a digital waveform. In addition, the second type of
absorber exploits the concept of nonlinear analogous circuits to convert an
incoming wave to a different waveform, specifically, a triangular waveform that
has a larger magnitude at a fundamental frequency. Therefore, the incoming
waveform is more effectively absorbed by this waveform-conversion metasurface
absorber as well. Although still there remain some issues to put these digital
signal absorbers into practice, including experimental validation, our results
contribute to mitigating electromagnetic interference issues caused by digital
noise and realising physically smaller, lighter digital signal processing
products for the next generation.
