Metamaterial based electromagnetically induced transparency (EIT) analogue have attracted as an alternative way to realize exotic EIT applications such as slow light devices and biosensors. Researches on metamaterial EIT analogues have recently focused on the realization of active system to control the EIT-like spectral properties via various external stimuli, including optical, mechanical, and thermal methods. Graphene based EIT metamaterials have been also reported through the numerical analysis as an electrically controlled active system, but there are no experimental reports in terahertz regime due to insufficient electrical mobility and conductance variation range of practical graphene sheets to realize active EIT analogues. In our previous study, we had reported a new concept of metamaterial analogue to achieve EIT-like phenomena, in which cut-wire (CW) pair and pseudo complementary cut-wire (CCW) were orthogonally combined with each other, generating EIT-like properties by funneling terahertz waves through the pseudo-CCW hole in broad reflection resonance of CW pair. Since this extraordinary transmission could be easily suppressed with resistive conductors along the pseudo-CCW structure, we designed the ion-gel gated graphene lines on the center of meta-atom structures to control the funneling of terahertz waves. Controlling the electromagnetic funneling provided switchable EIT-like spectral properties of the proposed metamaterials and we numerically confirmed that the graphene lines successfully acted as switching materials, even if the lines were formed with practically achievable graphene films. Finally, we verified that the fabricated EIT metamaterials experimentally showed 54.9% of modulation depth and 1ps of group delay change at the transmission peak in terahertz range.
In the past decade, there have been many studies on metamaterial based chemical and biological sensors due to their exotic resonance properties in microwave ranges. However, in spite of their non-destructive and highly sensitive properties, they have suffered from the use of bulky and expensive external measurement systems like a network analyzer for measuring resonance properties in the microwave regime. In this study, to increase accessibility of the metamaterial-based sensors, we propose a novel wireless chemical sensor system based on energy harvesting metamaterials at the microwave frequencies. The proposed metamaterial chemical sensor consists of a single split ring resonator and rectifier circuit to harvest the energy at the specific frequency, so that the chemical composition of the specific solution can be distinguished by the proposed metamaterial sensor by using the resonance property between the source antenna and the metamaterial which induces the variation in the energy harvesting rate of our sensor system. In our experimental setup, we used a 2.4 GHz Wi-Fi system as a source antenna. To verify the chemical sensitivity of the proposed sensor intuitively, we adopted a light emitting diode as an indicator of which luminescence is proportional to the energy harvesting rate determined by the ratio of ethanol and water in their binary mixture. With these results, it can be expected that our metamaterial-based wireless sensor can pave the way to the miniaturized wireless sensor systems and can be applied to not only for the chemical fluidic sensors but also for other dynamic environment sensing systems.