Abstract
Abstract In the quest to realize analog signal processing using subwavelength metasurfaces, in this paper, we present the first demonstration of programmable time-modulated metasurface processors based on the key properties of spatial Fourier transformation. Exploiting space-time coding strategy enables local, independent, and real-time engineering of not only amplitude but also phase profile of the contributing reflective digital meta-atoms at both central and harmonic frequencies. Several illustrative examples are demonstrated to show that the proposed multifunctional calculus metasurface is capable of implementing a large class of useful mathematical operators, including 1st- and 2nd-order spatial differentiation, 1st-order spatial integration, and integro-differential equation solving accompanied by frequency conversions. Unlike the recent proposals based on the Green’s function (GF) method, the designed time-modulated signal processor effectively operates for input signals containing wide spatial frequency bandwidths with an acceptable gain level. Proof-of-principle simulations are also reported to demonstrate the successful realization of image processing functions like edge detection. This time-varying wave-based computing system can set the direction for future developments of programmable metasurfaces with highly promising applications in ultrafast equation solving, real-time and continuous signal processing, and imaging.
Highlights
The history of analog computation comes from several electronic and mechanical computing machines developed to implement simple mathematical operations [1]
Motivated by the recent renewed interest in wave-based analog signal processing, different proposals within two separate categories have been investigated in one of which the mathematical operators are directly realized in the realspace coordinate using a specially designed structure (Green’s function (GF) approach in the literature) [4,5,6,7,8,9,10,11,12,13,14] and in the other group, the transfer functions associated with the operator of choice are realized in the spatial Fourier domain governed by graded-index lenses [15,16,17,18]
The main idea of this paper is to transform the energy of the incident signal into the high-order harmonics so that the required spatial amplitude variation dictated by the transfer function of choice is imitated by the positiondependent equivalent amplitude of the meta-atoms at one specific harmonic
Summary
The history of analog computation comes from several electronic and mechanical computing machines developed to implement simple mathematical operations [1]. Relying on a decade of fruitful development and the recent breakthrough in the seemingly unrelated field of metamaterials, Silva et al [3] brought the analog computations back to the competition as “computational metamaterials” to overcome the speed and energy limitations as well as data conversion loss of digital techniques In this way, different mathematical operations (spatial differentiation, integration, or convolution) can be realized as electromagnetic (EM) waves propagate through the metamaterial layer. To the best of our knowledge, it is the first time that realization of multiple analog signal processing functions by using a single programmable architecture at the microwave frequencies is reported
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