Enhancing Circular Polarization Performance of Low-Profile Patch Antennas for Wearables Using Characteristic Mode Analysis.

A wearable antenna functioning in the 2.4 GHz band for health monitoring and sensing is proposed. It is a circularly polarized (CP) patch antenna made from textiles. Despite its low profile (3.34 mm thickness, 0.027 λ0), an enhanced 3-dB axial ratio (AR) bandwidth is achieved by introducing slit-loaded parasitic elements on top of analysis and observations within the framework of Characteristic Mode Analysis (CMA). In detail, the parasitic elements introduce higher-order modes at high frequencies that may contribute to the 3-dB AR bandwidth enhancement. More importantly, additional slit loading is investigated to preserve the higher-order modes while relaxing strong capacitive coupling invoked by the low-profile structure and the parasitic elements. As a result, unlike conventional multilayer designs, a simple single-substrate, low-profile, and low-cost structure is achieved. While compared to traditional low-profile antennas, a significantly widened CP bandwidth is realized. These merits are important for the future massive application. The realized CP bandwidth is 2.2-2.54 GHz (14.3%), which is 3-5 times that of traditional low-profile designs (thickness < 4 mm, 0.04 λ0). A prototype was fabricated and measured with good results.

Comparison of peak electromagnetic exposures from mobile phones operational in either data mode or voice mode.

The aim of this study is to compare the typical peak ElectroMagnetic (EM) exposures from smart phones during data transmission and voice calls, respectively, in the typical Western-European city of Leuven, Belgium. Since transmission powers towards the outdoor network in an indoor environment are expected to be higher than in an outdoor environment, measurements were executed indoors. The influence of factors like network generation [2G, 3G, and 4G] and choice of mobile operator was also investigated. The most important conclusion of the study is that there is a huge difference between peak exposures generated by the 3 network generations currently active in Leuven. To the average, in many cases the peak exposure for 3G is more than a factor 20 lower than for 2G, and about a factor 5-10 lower than for 4G. These numbers are much higher than expected. There are also systematic differences between peak exposures for data mode and voice mode.

Study of the electromagnetic exposure from mobile phones in a city like environment: The case study of Leuven, Belgium.

A measuring campaign for the assessment of electromagnetic exposure levels from mobile phones in the city center of Leuven, Belgium, has been carried out. The main objective of the assessment is to study the dependency of the exposure of the user by his own mobile phone in terms of location in the city (very close to base stations and at randomly selected locations). The measurements were performed in both public and private areas in 60 outdoor and 60 indoor locations in Leuven. The campaign was focused on GSM 900 mobile communications. The results show that the exposure is considerably higher for indoor environments compared to outdoor environments, and at the randomly chosen locations compared to locations very close to base stations. However, the most important observation is that the average outdoor exposure in Leuven of the user of a mobile phone is about 8 times higher than the average outdoor exposure by base stations. Indoors, this factor rises to about 30.

Study of the correlation between outdoor and indoor electromagnetic exposure near cellular base stations in Leuven, Belgium.

A measuring campaign for the assessment of electromagnetic radiation near base stations in the city center of Leuven, Belgium, has been carried out. The main objective of this assessment is to study the correlation between the outdoor and the indoor exposure produced by cellular base stations and to investigate the changes of electromagnetic exposure within a typical day and over 1 month in the vicinity of these base stations. The study was also carried out as a function of location and time using highly precise measurement equipment. The measurements were performed in both public and private areas in sixty (30 indoor and 30 outdoor) different locations in Leuven. The measurement was focused on mobile communication networks: GSM (Global System for Mobile Communication, 900 MHz and 1800 MHz) and UMTS (Universal Mobile Telecommunications System, 2110 MHz) were the frequency bands of interest. The data at these frequencies were extracted from raw measurements in the 824-2170 MHz frequency band. The results show that all analyzed locations are in compliance with the exposure limits recommended by ICNIRP (International Commission on Non-Ionizing Radiation Protection) and that the (maximum) indoor exposure correlates to the outdoor exposure with a factor of about 0.5.

Nanostripe length dependence of plasmon-induced material deformations.

Following the impact of a single femtosecond light pulse on nickel nanostripes, material deformations-or "nanobumps"-are created. We have studied the dependence of these nanobumps on the length of nanostripes and verified the link with plasmons. More specifically, local electric currents can melt the nanostructures in the hotspots, where hydrodynamic processes give rise to nanobumps. This process is further confirmed by independently simulating local magnetic fields, since these are produced by the same local electric currents.

Interacting plasmonic nanostructures beyond the quasi-static limit: a "circuit" model.

The interaction between individual plasmonic nanoparticles plays a crucial role in tuning and shaping the surface plasmon resonances of a composite structure. Here, we demonstrate that the detailed character of the coupling between plasmonic structures can be captured by a modified "circuit" model. This approach is generally applicable and, as an example here, is applied to a dolmen-like nanostructure consisting of a vertically placed gold monomer slab and two horizontally placed dimer slabs. By utilizing the full-wave eigenmode expansion method (EEM), we extract the eigenmodes and eigenvalues for these constituting elements and reduce their electromagnetic interaction to the structures' mode interactions. Using the reaction concept, we further summarize the mode interactions within a "coupling" matrix. When the driving voltage source imposed by the incident light is identified, an equivalent circuit model can be constructed. Within this model, hybridization of the plasmonic modes in the constituting nanostructure elements is discussed. The proposed circuit model allows the reuse of powerful circuit analysis techniques in the context of plasmonic structures. As an example, we derive an equivalent of Thévenin's theorem in circuit theory for nanostructures. Applying the equivalent Thévenin's theorem, the well-known Fano resonance is easily explained.

Plasmon-enhanced sub-wavelength laser ablation: plasmonic nanojets.

In response to the incident light's electric field, the electron density oscillates in the plasmonic hotspots producing an electric current. Associated Ohmic losses raise the temperature of the material within the plasmonic hotspot above the melting point. A nanojet and nanosphere ejection can then be observed precisely from the plasmonic hotspots.