Martino Aldrigo

A tunable microwave slot antenna based on graphene

The paper presents the experimental and modeling results of a microwave slot antenna in a coplanar configuration based on graphene. The antennas are fabricated on a 4 in. high-resistivity Si wafer, with a ∼300 nm SiO2 layer grown through thermal oxidation. A CVD grown graphene layer is transferred on the SiO2. The paper shows that the reflection parameter of the antenna can be tuned by a DC voltage. 2D radiation patterns at various frequencies in the X band (8–12 GHz) are then presented using as antenna backside a microwave absorbent and a metalized surface. Although the radiation efficiency is lower than a metallic antenna, the graphene antenna is a wideband antenna while the metal antennas with the same geometry and working at the same frequencies are narrowband.

Towards a terahertz direct receiver based on graphene up to 10 THz

We present a study for a THz receiver based on graphene. First, the dipole and the bowtie THz antennas on graphene are designed, and followed by the on-wafer fabrication of a graphene diode matched to the antenna. Finally the responsivity of the receiver up to 10 THz is computed. Our results show that the antenna and the diode behaviors exhibit new properties (e.g., the antennas are acting as high reactive impedance surfaces, the diode is rectifying only due to its geometrical shape). These new properties are due to the physical properties of graphene having the carrier transport described by Dirac equation.

Smart antennas based on graphene

We report two configurations of smart graphene antennas, in which either the radiation pattern of the antenna or the backscattering of the periodic metallic arrays is controlled by DC biases that induce metal-insulator reversible transitions of graphene monolayers. Such a transition from a high surface resistance (no bias) to a low surface resistance state (finite bias voltage) causes the radiation pattern of metallic antennas backed with graphene to change dramatically, from omnidirectional to broadside. Moreover, reflectarrays enhance the backscattered field due to the same metal-dielectric transition.

Carbon nanotube-based electromagnetic band gap resonator for CH4 gas detection

In this paper, we present the experimental results obtained in the microwave frequency range using an electromagnetic band gap (EMBG) resonator covered with carbon nanotubes (CNTs) and dedicated to CH4 gas detection. The multi-walled CNTs layer is decorated with gold nanoislands (with sizes between 2 nm and 20 nm) and deposited over the EMBG resonator. The microwave measurements of the CNT-based EMBG resonator in air (no gas) and kept for 60 min inside the chamber filled with CH4 demonstrate a shift in the resonance frequency of about 139 MHz and a phase shift of about 9.63°. A very good sensitivity of about 4.58% was obtained from scattering parameters measurements. A new device for CH4 detection was then fabricated and tested.

Graphene as a high impedance surface for ultra-wideband electromagnetic waves

The metals are regularly used as reflectors of electromagnetic fields emitted by antennas ranging from microwaves up to THz. To enhance the reflection and thus the gain of the antenna, metallic high impedance surfaces (HIS) are used. HIS is a planar array of continuous metallic periodic cell surfaces able to suppress surface waves, which cause multipath interference and backward radiation in a narrow bandwidth near the cell resonance. Also, the image currents are reduced, and therefore the antenna can be placed near the HIS. We demonstrate that graphene is acting as a HIS surface in a very large bandwidth, from microwave to THz, suppressing the radiation leakages better than a metal.

Extraordinary tunability of high-frequency devices using Hf0.3Zr0.7O2 ferroelectric at very low applied voltages

This paper presents the applications of the Hf0.3Zr0.7O2 ferroelectric with a thickness of 10 nm for tuning high-frequency devices such as filters, phase shifters, and phased antenna arrays in the X band when the low bias voltages in the range −3 V–+3 V are applied. In this respect, we show that a bandpass filter shifts its central frequency located at 10 GHz with 3 GHz, a phase shifter produces a phase difference of about 60 degrees in the X band, while the antenna array formed by two patched antennas is steering its lobe with ±32° at 10 GHz. These results open the way for the tunability of high frequency devices for very low power applications, which represent one of the most challenging issues in applied physics.

MoS2 thin films as electrically tunable materials for microwave applications

In this paper, we show that a MoS2 thin film formed from a mixture of pristine MoS2 monolayers and few-layer flakes deposited on a coplanar waveguide (CPW) is acting as an electrically tunable microwave material. In this respect, we have seen that up to 30 GHz, the transmission and reflection parameters of the CPW depend on the applied voltage. We have extracted from the measurements an equivalent circuit and have observed that the surface resistance is dependent on the DC applied voltage, as in the case of other two-dimensional materials such as graphene. So, the device is acting as a tunable matching network via an applied DC voltage.

Graphene rectenna for efficient energy harvesting at terahertz frequencies

In this paper, we propose a graphene rectenna that encompasses two distinct functions in a single device, namely, antenna and rectifier, which till now were two separate components. In this way, the rectenna realizes an efficient energy harvesting technique due to the absence of impedance mismatch between antenna and diode. In particular, we have obtained a maximum conversion efficiency of 58.43% at 897 GHz for the graphene rectenna on n-doped GaAs, which is a very good value, close to the performance of an RF harvesting system. A comparison with a classical metallic antenna with an HfO2-based metal-insulator-metal diode is also provided.

Switching microwaves via semiconductor-isolator reversible transition in a thin-film of MoS2

In this paper, we show that a thin-film of MoS2 is able to switch microwave signals due to a reversible semiconductor-insulator transition displaying an ON/OFF ratio greater than 104. This switching occurs in the range of 4–16 GHz, which encompasses the C, X, and K bands. In this respect, the current-voltage dependence and the microwave properties of the MoS2 thin-film are investigated. An integrated microwave switch device and a single pole double throw switch circuit are then implemented based on this unique property.

Infrared nano-rectennas exploiting on-demand laser sources

In this paper we propose an in-depth investigation on energy harvesting solutions from THz to DC, deploying a dedicated laser source in the infrared (IR) region. Planar bow-tie nano-antennas with misaligned monopoles are arranged in both an array and a multi-element architecture, and combined with tunnel diodes for rectification. A highly directive IR laser is adopted as the 84-THz source, and the receiving antennas are arranged in such a way to cover an area comparable to that illuminated by the laser beam. A theoretical estimation of the overall system performance in terms of achievable DC power is provided by means of an accurate circuit/electromagnetic co-simulation.