We propose a mid-infrared device based on thermocouple optical antennas for light sensing and energy harvesting applications. We numerically demonstrate that antennas are able to generate low-power dc signals by beneficing of the thermoelectric properties of the metals that constitute them. We theoretically evaluate the optical-to-electrical conversion efficiency for harvesting applications and finally discuss strategies to increase its performance. Thermocouple optical antennas therefore open the route toward the design of photovoltaic devices.

The multi-resonant response of three-steps tapered dipole nano-antennas, coupled to a resistive and fast micro-bolometer, is investigated for the efficient sensing in the infrared band. The proposed devices are designed to operate at 10.6 μm, regime where the complex refractive index of metals becomes important, in contrast to the visible counterpart, and where a full parametric analysis is performed. By using a particle swarm algorithm (PSO) the geometry was adjusted to match the impedance between the nanoantenna and the micro-bolometer, reducing the return losses by a factor of 650%. This technique is compared to standards matching techniques based on transmission lines, showing better accuracy. Tapered dipoles therefore open the route towards an efficient energy transfer between load elements and resonant nanoantennas.

In this work, a comparison of the microwave absorption properties of Opuntia ficus-indica cladodes, Agave atrovirens branches, and Cocos nucifera L. husk samples was performed. The study was carried out by inserting dry and powdered samples of these organic materials transversely and in the middle of a rectangular waveguide, for which scattering parameters S₂₁ and S₁₁ were measured to estimate the absorption coefficient. These measurements were compared to determine the material that behaves the best as a microwave absorber with a view to develop future low-cost and eco-friendly products by reusing agricultural waste. Specifically, Agave atrovirens sample showed the best performance, having an average value of absorption coefficient of 0.4218, while its maximum was 0.5792 at 9.706 GHz within the range from 8.005 to 13 GHz.

In this letter, we evaluate the conversion efficiency of thermally isolated Seebeck nanoantennas by numerical simulations and discuss their uses and scope for energy harvesting applications. This analysis includes the simple case of titanium-nickel dipoles suspended in air above the substrate by a 200 nm silicon dioxide membrane to isolate the heat dissipation. Results show that substantially thermal gradients are induced along the devices leading to a harvesting efficiency around 10-4 %, 400 % higher than the previously reported Seebeck nanoantennas. In the light of these results, different optimizing strategies should be considered in order to make the Seebeck nanoantennas useful for harvesting applications.

Due to strong inter-band transitions, the optical response of copper exhibits a high light absorbance in the visible region of the spectrum, recovering blue wavelengths and reflecting a reddish color. In this contribution, copper is split into subwavelength thin films, which are separated by silicon dioxide dielectric layers to take advantage of photonic bandgaps, which subtract bands from the reflected light and, thus, give rise to a wide range of reflective colors, including blue. Using numerical simulations, we investigate the photonic bandgaps of SiO2/Cu stacks, enabled by Fabry–Pérot transmission resonances, which demonstrate the color tunability of these structures.

The authors investigate the efficiency of a series of broadband rectennas designed to harvest the free-propagating electromagnetic energy at terahertz frequencies. We analyze by simulations the case of self-complementary square- and Archimedean-spiral antennas coupled to L-shaped self-switching diodes (L-SSDs). First, the geometry (i.e., the width and length of the channel) of the L-SSD was optimized to obtain a remarkable diode-like I–V response. Subsequently, the optimized L-SSD geometry was coupled to both types of spiral antennas and their characteristic impedance was studied. Finally, the energy conversion efficiency was evaluated for both rectenna architectures.