## 1 Introduction  
Rapidly developing wireless communication systems have brought the urgency of protecting devices from electromagnetic interference (EMI) [1, 2, 3]. Generally, shielding materials, metal and composite materials, for example, are widely used to isolate unexpected signals and avoid radiating interference signals to free space, which is essential for improving the electromagnetic compatibility (EMC) of devices [1, 4, 5, 6]. However, the fixed physical dimensions and electrical properties of those materials also limit their ability in adapting to increasingly intelligent electronic systems [7]. Therefore, it is imperative to develop the shielding effectiveness (SE) of tunable materials, which could realize the precise control of electromagnetic distribution in time and space [7, 8, 9]. In the GHz band, where the shielding of communication signals is primary, by switching the SE of shielding materials between blocking and transmitting, the space utilization of places like confidential meeting rooms, airport security chambers or military duty rooms can be greatly improved. In the THz band, where effective generation, detection and modulation methods of THz signals are still scarce, the use of low profile, structurally stable and tunable EMI shielding materials can effectively realize the wavefront modulation of terahertz electromagnetic waves [10, 11, 12, 13]. Besides, the flexibility and conformability of the materials are also key factors in practical applications, which are of great significance for foldable displays, micro robots, and wearable devices [2, 14]. At present, the implementation of tunable SE mainly includes the loading of active devices between periodic arrays, the use of electromagnetic characteristics, tunable materials, or the change of structural parameters, and there are few reports on materials having tunable characteristics both in the THz and GHz frequency bands [7, 9, 15, 16, 17]. By loading active devices such as MEMS or PINs, electromagnetic waves can be shielded in a specific frequency range [17, 18, 19]. However, the frequency selectivity of this method is too strong to achieve broadband control, and the array-type point loading method brings more complex near-field effects, limiting the miniaturization and compact application of devices. The most widely used method to achieve tunable SE is to add conductive fillers, such as carbon nanoparticles, to the polymer to obtain a polymer composite shielding material,by changing the aspect ratio, conductivity, permeability or other parameters of the filler through external conditions, the SE could be adjusted [7; 8; 9; 16; 20]. In recent years, with further research on graphene, a two-dimensional material with adjustable electrical properties, a variety of graphene photoelectric modulation units have been born, which can realize the regulation of SE in a wide frequency range [2; 21; 22], especially in the terahertz frequency range [11; 13; 22; 23; 24]. The authors of [25] proposed a broadband SiO\({}_{2}\)-based graphene terahertz modulator, by applying voltage from 0-50 V, it realized the tuning of transmission amplitude for about 15% in the 0.57-0.63 THz band. Based on the supercapacitor structure, a graphene/ionic liquid/graphene sandwich structure was subsequently proposed to realize the photoelectric modulation [26; 27; 28; 29; 30; 31; 32], which could achieve a modulation depth of 50% between 0.1 and 0.4 THz with voltage less than 3 V [27]. However, the ionic liquid also limits the application scenarios of the structure to a certain extent, and has the disadvantages of poor weather resistance and difficulty in conformability, thus finding it hard to meet the urgent needs of flexible electronics. In this paper, we propose the use of solid ionic materials to construct a graphene/ion gel/graphene (GIG) sandwich structure, which has excellent electronic and structural stability.