Electromagnetic device design and flexible electronics fabrication are combined to demonstrate mechanically tunable metamaterials operating at terahertz frequencies. Each metamaterial comprises a planar array of resonators on a highly elastic polydimethylsiloxane substrate. The resonance of the metamaterials is controllable through substrate deformation. Applying a stretching force to the substrate changes the inter-cell capacitance and hence the resonance frequency of the resonators. In the experiment, greater than 8% of the tuning range is achieved with good repeatability over several stretching-relaxing cycles. This study promises applications in remote strain sensing and other controllable metamaterial-based devices.

We study single-term exponential-type bounds (also known as Chernoff-type bounds) on the Gaussian error function. This type of bound is analytically the simplest such that the performance metrics in most fading channel models can be expressed in a concise closed form. We derive the conditions for a general single-term exponential function to be an upper or lower bound on the Gaussian error function. We prove that there exists no tighter single-term exponential upper bound beyond the Chernoff bound employing a factor of one-half. Regarding the lower bound, we prove that the single-term exponential lower bound of this letter outperforms previous work. Numerical results show that the tightness of our lower bound is comparable to that of previous work employing eight exponential terms.

Two-dimensional (2D) materials play more and more important roles these days, due to their broad applications in many areas. Herein, we propose an optically-pumped terahertz (THz) modulator, based on Si-grown MoS2 nanosheets. The broadband modulation effect has been proved by THz time domain spectroscopy and numerical simulation. The modulation depth of this Si-grown MoS2 nanosheet can reach over 75% under the low pumping power of 0.24 W cm(-2), much deeper than that of bare silicon. By theoretical models and simulation, it is proved that the broadband modulation effect can be described as a free carrier absorption for THz waves in the Drude form. Importantly, by a catalyst mechanism in the Si-grown MoS2, it is concluded that the MoS2-Si heterostructure enables the MoS2 to catalyze more carriers generated on the Si surface. This novel 2D material has a high effective modulation on THz waves under a low pumping power density, which affords it a promising potential in THz applications.

With the booming microwave and terahertz technology for communication, detection, and healthcare, the consequently increasingly complicated electromagnetic environment is in urgent need of high-performance microwave and terahertz absorption materials. However, it is still a huge challenge to achieve consecutively strong absorption in both microwave and terahertz regimes. Herein, an ultra-broadband and highly efficient absorber for both microwave and terahertz bands based on the monolithic three-dimensional cross-linked Fe3O4/graphene material (3DFG) is first reported. The 3DFG shows an incredible wide qualified absorption bandwidth (with reflection loss less than −10 dB) from 3.4 GHz to 2.5 THz, which is the best result in this area by far. Furthermore, the remarkable absorption performance can be maintained under oblique incidence, different compressive strains, and even after 200 compression/release cycles. The designed highly porous structure for minimizing surface reflection combined with the micro–macro integrated high lossy framework results in the excellent absorptivity, as verified by the terahertz time-domain spectroscopy technique. With these, the 3DFG achieves an unprecedentedly average absorption intensity of 38.0 dB, which is the maximum value among the broadband absorbers. In addition, its specific average microwave and terahertz absorption value is over 2 orders of magnitude higher than other kinds of reported materials. The results provide new insights for developing novel ultra-broadband absorbers with stronger reflection loss and wider absorption bandwidth.

terahertz imaging, [9][10][11] terahertz detection, [12][13][14] and so on, terahertz related circuits and electronic components have been widely applied to current technologies. The fast-growing applications for terahertz waves have led to an urgent demand for terahertz shielding materials in order to effectively reduce the interference of terahertz wave signals, improve their transmission environment, and ensure that the delicate electronic instruments work as normal. Moreover, terahertz stealth materials also play a very important role in the fields of national security and information protection, which may help to avoid significant losses to individuals, enterprises, and even countries. Therefore, high-performance terahertz shielding/stealth materials have the potential for wide applications. [15] Traditional terahertz shielding materials are mainly composed of reflective materials because they reflect the incident terahertz wave by simply increasing conductivity. [16,17] For example, it is reported that a terahertz-shielding membrane prepared by a pyrolysis process for commercial polyimide has a very high reflectivity of more than 90%. [18] However, reflective shielding materials have two fatal flaws. First, reflective shielding materials cannot completely eliminate the interference of terahertz waves, because the reflected terahertz wave still adversely affects other sophisticated electronic elements inside the shielded devices. [19] Second, reflective shielding materials usually have a large density. The reflective Strong terahertz-response material which exhibits both excellent terahertz shielding and stealth performance is promising in practical applications of terahertz technology. Here, ultralight graphene foam (GF) and multiwalled carbon nanotubes/multiwalled graphene foam (MGF) have been first demonstrated to achieve both superior terahertz shielding and stealth performance due to the dominant absorption loss with negligible reflection. The terahertz shielding effectiveness values of GF and MGF, both 3 mm thick, reach up to 74 and 61 dB. Meanwhile, their average terahertz reflection loss values are achieved up to 23 and 30 dB, respectively, which are the best results in existing broadband terahertz shielding/stealth materials. Importantly, their qualified absorption bandwidths (reflection loss value larger than 10 dB) cover the entire measured frequency band of 0.1-1.6 THz. Furthermore, the quantitative relationships between the terahertz shielding effectiveness, reflection loss, and material parameters are accurately established, which should facilitate the material design for terahertz shielding and stealth. Comprehensively considering the important indicators of density, bandwidth, and intensity, the specific average terahertz shielding coefficient and the specific average terahertz absorption performance are achieved up to 1.1 × 10 5 and 3.6 × 10 4 dB cm 3 g −1 , respectively, which is over thousands of times larger than other kinds of materials reported previously. Shielding/Stealth MaterialsThe...