_Compmunication_  
**Reconfigurable Terahertz Moire Frequency Selective Surface Based on Additive Manufacturing Technology**  
**[PERSON] 1, [PERSON] 1,2, [PERSON] 1,3, [PERSON] 2, [PERSON] 2, [PERSON] 4 and [PERSON] 1,* 2023**  
**Abstract: We designed and fabricated a terahertz (THz) frequency selective surface (FSS) based on two distinct additive manufacturing technologies, namely, printable electronics (PE) and three-dimensional (3D) printing. Silver nanoparticle ink was printed on a polyethylene terephthalate (PET) substrate utilizing a large-scale roll-to-roll industrial PE technique with a flexographic printed unit, while the 3D-printed THz FSS was fabricated based on a powder bed fusion-selective laser melting system. The filtering characteristics of both types of FSS were verified through calculation, simulation, and experiments. Furthermore, the rotational tuning approach was applied to two identical FSS to form reconfigurable FSS which could be defined as Moire FSS. Based on the numerical results obtained, our proposed technique which used a PE-based Moire FSS achieves a 58% modulation depth at 0.25 THz, while experimental verification found a modulation depth of 41% at 0.22 THz, confirming that its adoption is simple and cost-effective. To the best of our knowledge, this is the first demonstration of a Moire reconfigurable printed FSS operating in the THz region. **  
**Keywords: terahertz frequency selective surface; printable electronics; 3D printing; moire interference**  
**1. Introduction**  
Terahertz (THz) waves, with frequencies ranging from 0.1 to 10 THz and wavelengths from 0.03 to 3 mm, have potential applications in various domains, including communications, spectroscopy, imaging, security, and medical diagnostics [1, 2, 3]. For each of these applications, it is critical to control the wavefront, and this can be done through generation and detection processes, or by inserting a filter, modulator, an absorber, etc., inside the THz path [4, 5]. The frequency selective surface (FSS) is a two-dimensional frequency filter with transmission and reflection characteristics that can be designed to have high-pass, low-pass, band-pass, or band-stop characteristics [6]. Compared to metasurfaces (MS), which have sub-wavelength structures, one of the characteristics of standard FSS structures is that their unit cell size is about half that of the operational wavelength [7]. In addition to filtering properties, THz FSSs also have been reported as polarization converters [8] and absorbers [9], among other applications [10, 11, 12]. Notwithstanding this great variety of the features characterizing them, the parameters of these FSSs remain passive, and can consequently only be used for specific intended applications. A tunability technique may also be used to control the peak transmission amplitude of an FSS, resulting in the formation of a reconfigurable amplitude modulator at a certain frequency. The key materials that have been identified as potential candidates for developing THz reconfigurable modulators include semiconductors [13, 14], liquid crystal [15, 16], graphene [17], vanadium dioxide films [18], etc. To date, multiple tunability approaches, such as photoinduced [18], mechanical [19], electrical [20], electrical [21], and rotational [22] methods, have been used to produce modulators with active control. Impressively, over the last ten years, the performance of the THz modulator has improved dramatically, with modulation speeds increasing from the kilohertz (kHz) to the gigahertz (GHz) [23] and modulation depths have been recorded at up to 80% [18], 90% [24], and 93% [15]. So far, the vast majority of reconfigurable THz modulators have required costly facilities such as clean rooms and multiple production steps, making them ill-suited for large-scale production.