Experimental demonstration of nonlinear waveform‐dependent metasurface absorber with pulsed signals

Abstract

The absorbing performance of a nonlinear waveform-dependent metasurface with pulsed signals is demonstrated. The metasurface is a periodic structure containing diodes, capacitors and resistors. These enable us to first rectify a high-power incoming signal to a static field, then store the energy during the illumination and dissipate it before the next pulse comes in. The incident pulses contain a finite width of spectrum of around 4.2 GHz. By using the nonlinear metasurface, absorption that depends on both the power and the duty cycle of the incoming signals is measured. These measurements demonstrate the first waveform-dependent absorbing metasurface.Introduction: A surface current propagates on a conducting surface and, with sufficiently high power, can disrupt electronic devices deployed there, leading to microwave interference issues. One difficulty lies in handling different levels of signals simultaneously. This is because widely used linear materials, such as lossy materials [1], Salisbury screens [2] or high-impedance metasurfaces [3, 4], either simply absorb or reflect any incoming signals, including low-power signals used for wireless communications. Therefore, it is important to decouple the high-power surface impedance from its low-power response by introducing nonlinearity. Such an idea was proposed in [5], where circuit-based nonlinear metasurfaces absorbed high-power pulsed sine waves, while allowing transmission of low power continuous waves. Interestingly, these structures exhibited waveform dependence, which distinguishes even the same frequency in accordance with the waveform, i.e. pulsed or continuous signals. Moreover, the absorbing performance was demonstrated with a Gaussian pulse including a finite width of frequency spectrum. Such a pulse is assumed to be a more realistic threat to modern electronics. However, this demonstration was limited to only numerical simulations. Therefore, in this Letter, we experimentally investigate the absorbing performance of the nonlinear metasurface with short pulses containing a finite width of frequency spectrum.

Time-Domain Filtering of Metasurfaces

“…In addition, these metasurfaces can be potentially exploited for converting a simple sine wave to a different waveform. Although the following study provides numerical simulation results only, similar effects are expected to be obtained experimentally as demonstrated earlier 26 27 28 29 . In realistic measurements, however, there might appear some minor difference in the operating frequencies of metasurfaces due to the presence of solder and parasitic components in diodes, which makes it slightly difficult to analyse the time filtering effects demonstrated below.…”

“…Such a capability of metamaterials and metasurfaces is known to be further extended by introducing nonlinear media or nonlinear circuits as they gave us a flexible tunability to vary electromagnetic properties 22 23 24 25 . Especially, recently developed metasurfaces that consisted of several circuit elements including schottky diodes exhibited new electromagnetic characteristics named waveform selectivity 26 27 28 29 . These waveform-selective metasurfaces allowed us to distinguish different waves even at the same frequency in response to their waveforms or pulse widths.…”

Waveform-selective metasurfaces with free-space wave pulses at the same frequency

“…[18][19][20][21] In these structures, first an incoming wave induced electric charges on periodically metalized patches, generating strong electric field across the gaps. Within the gaps diodes rectified the incoming signal and converted the frequency component to an infinite set of components, but most of the energy was at zero frequency.…”

Waveform Selectivity at the Same Frequency

“…Importantly, such new electromagnetic properties and applications were widely exploited in other disciplines such as acoustics 12 13 14 15 , thermodynamics 16 and vibration engineering 17 18 . Moreover, a recent study on metasurface absorbers containing circuit elements such as diodes and capacitors demonstrated a new property called waveform dependence 19 20 . Interestingly these metasurfaces absorbed only short sine wave pulses, while transmitting continuous waves (CWs) even at the same frequency.…”