Log-periodic Nanoantennas Research Articles

Design of a wideband microstrip nanoantenna array

This paper presents the design of a logarithmic array of microstrip nano-antennas at terahertz frequencies. For applications in which small antennas are required, microstrip antennas are preferred. However, they have a narrow bandwidth. To overcome this problem in microstrip antennas, a log-periodic nanoantenna design is presented which exhibits a wide bandwidth and ultra-compact design. This antenna is smaller in size compared to log-periodic antennas in microwave bands and comparable and better radiation characteristics. The proposed Log-periodic microstrip nanoantenna array consists of seven patch elements on a dielectric layer and are fed directly by a feed line through the branch lines connected to each of the elements. Scaling factor, τ = 0.95 is considered for this design and inset feed is used. In this structure, the substrate has a relative dielectric constant of er = 4.4 and a thickness of h = 800 nm. For good performance at high frequencies, gold is used for the design of the antenna. The considered operating frequency is 3.3 THz corresponding to a wavelength of 91 µm. Good impedance matching and a wide bandwidth of 800 GHz is obtained.

Photoluminescence-Driven Broadband Transmitting Directional Optical Nanoantennas.

Optical nanoantennas mediate near and far optical fields. Operating a directional nanoantenna in transmitting mode is challenging because the antenna needs to be driven by a nanosized optical frequency generator, which must work at the antenna's resonance frequency and be precisely attached to the antenna's feed with correct polarization. Quantum emitters have been used as optical nanogenerators, but their precise positioning relative to the nanoantenna is technically challenging, setting up a barrier to the practical implementation. One unique source to drive nanoantenna is the photoluminescence from the material of the nanoantenna because the high operational frequency of the antenna reaches the regime for the electronic transitions in matter. Here, we exploit plasmon-modulated photoluminescence (PMPL) as an effective optical source to drive directional nanoantennas. We experimentally realize two technically challenging theoretical proposals, namely, an optical nanospectrometer based on Yagi-Uda nanoantennas and tunable broadband directional emission from log-periodic nanoantennas. Using photoluminescence from the nanoantenna as an optical source promotes practical implementation of transmitting optical nanoantennas.

Analysis of a log periodic nano-antenna for multi-resonant broadband field enhancement and the Purcell factor

Broadband nano-antennas play a central role in many areas of science and technology. However, a more intuitive understanding for rational design of nano-antennas with broadband response is desirable. A log periodic nano-antenna was studied in the paper. The finite-difference time-domain method was used to explore the spectral characteristics of the log periodic nano-antenna by the excitation mode of reception and emission. The effects of geometry on field enhancement and the Purcell factor were systematically described and investigated. The field enhancement of the nano-antenna can be tuned by geometric parameters such as the outer radius, the tooth angle, and the ratio of the radial sizes of successive teeth, which provide control over both the spectral resonance position and the field enhancement peak amplitude. The Purcell factor mainly depends on the outer radius, the tooth angle, and the bow angle. In addition, multi-resonant field enhancement was analyzed in detail by conformal transformation. Furthermore, a careful comparison of the characteristics of a bowtie nano-antenna demonstrated that the log periodic nano-antenna has considerable potential for multi-resonant field enhancement and improvement of the Purcell factor. The results provide a promising prospect for designing and optimizing the log periodic nano-antenna in a broad range of wavelengths.

Plasmonic Nanoantennas for Multispectral Surface-Enhanced Spectroscopies

Plasmonic nanoantennas provide new routes for efficiently detecting, analyzing, and monitoring single biomolecules via fluorescence, Raman, and infrared absorption spectroscopies. The development of efficient biosensors for multispectral spectroscopy remains nevertheless limited by the narrowband responses of plasmonic devices, as they are generally designed to operate in a specific bandwidth, matching with the absorption, scattering, or emission frequency of target biomolecules under investigation. Therefore, performing biosensing from visible to infrared frequencies systematically requires designing and fabricating multiple plasmonic nanoantenna configurations and prevents the development of nanoscale integrated sensors for multispectral probing of random chemical species. Here, we propose to overcome these limitations by using broadband log-periodic nanoantennas designed to generate significant electromagnetic intensity enhancements from the visible to the mid-IR wavelength regions. We demonstrate simu...

Design of optical wide-band log-periodic nanoantennas using surface integral equation techniques

In this paper we propose the design of plasmonic nanoantennas for optical applications with high directivity patterns in a wide bandwidth. The design is supported by surface integral equation (SIE) formulations solved by the method of moments (MoM). Although not widely used until now in optics, this solution brings important advantages compared with usual volumetric approaches. We will demonstrate through numerical computations that almost frequency independent directivity patterns can be obtained over a large bandwidth for judiciously designed log-periodic nanoantennas.