Waveform Selectivity at the Same Frequency

Abstract

Electromagnetic properties depend on the composition of materials, i.e. either angstrom scales of molecules or, for metamaterials, subwavelength periodic structures. Each material behaves differently in accordance with the frequency of an incoming electromagnetic wave due to the frequency dispersion or the resonance of the periodic structures. This indicates that if the frequency is fixed, the material always responds in the same manner unless it has nonlinearity. However, such nonlinearity is controlled by the magnitude of the incoming wave or other bias. Therefore, it is difficult to distinguish different incoming waves at the same frequency. Here we present a new concept of circuit-based metasurfaces to selectively absorb or transmit specific types of waveforms even at the same frequency. The metasurfaces, integrated with schottky diodes as well as either capacitors or inductors, selectively absorb short or long pulses, respectively. The two types of circuit elements are then combined to absorb or transmit specific waveforms in between. This waveform selectivity gives us another degree of freedom to control electromagnetic waves in various fields including wireless communications, as our simulation reveals that the metasurfaces are capable of varying bit error rates in response to different waveforms.

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

“…18 This is because although there is the dependence of the operating (resonant) frequency on the incident angle, both of a surface wave and normal wave induce electric charges in patches almost similarly, which are rectified and used for waveform selectivity. Note that capacitor, inductor, and resistor chips do not directly interact with incoming waves, since they are deployed inside diode bridges and only respond to rectified electric charges.…”

“…Within the diode bridge some other circuit components were deployed, which determined the type and behavior of the waveform-selective metasurface. Although details are fully described in other publications, 18 in short use of a capacitor in parallel with a resistor leads to absorption of a short pulse ( Fig. 2(c)), while use of an inductor in series with a resistor results in absorption of a long pulse ( Fig.…”

“…Simulations were carried out by a co-simulation method, 14,18,19 which integrated an EM simulator HFSS (version 15.0) with a circuit simulator Designer (version 8.0). In this method, waveform-selective metasurfaces were first simulated in the EM simulator and used in the circuit simulator as circuit models including scattering parameters.…”

“…Another side of the waveguide was connected to an adapter, which received incoming signals from a network analyzer (Keysight Technology N5222A) via a coaxial cable. Although our previous study used a different measurement setup that consisted of a signal generator, power meters, power sensors, etc., 14,18,19 this new measurement setup allowed us to readily sweep frequency so that finer frequency steps could be used, which was useful to see more details of the waveform selectivity. In these measurements, calibration was performed with an electronic calibration module (N4691-60006) between the cable and adapter for the sake of simplicity.…”

“…[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.…”