An Overview of Indoor Localization System for Human Activity Recognition (HAR) in Healthcare.

The number of older people needing healthcare is a growing global phenomenon. The assistance in long-term care comprises a complex of medical, nursing, rehabilitation, and social assistance services. The cost is substantial, but technology can help reduce spending by ensuring efficient health services and improving the quality of life. Advances in artificial intelligence, wireless communication systems, and nanotechnology allow the creation of intelligent home care systems avoiding hospitalization with evident cost containment. They are capable of ensuring functions of recognition of activities, monitoring of vital functions, and tracking. However, it is essential to also have information on location in order to be able to promptly intervene in case of unforeseen events or assist people in carrying out activities in order to avoid incorrect behavior. In addition, the automatic detection of physical activities performed by human subjects is identified as human activity recognition (HAR). This work presents an overview of the positioning system as part of an integrated HAR system. Lastly, this study contains each technology's concepts, features, accuracy, advantages, and limitations. With this work, we want to highlight the relationship between HAR and the indoor positioning system (IPS), which is poorly documented in the literature.

Twisted Bands with Degenerate Points of Photonic Hypercrystals in Infrared Region.

Photonic hypercrystals (PHCs) are materials combining hyperbolic metamaterials (HMMs) with widely used photonic crystals. We found that finite-sized Type-I HMMs can support unique electromagnetic modes, which could be utilized in two-dimensional photonic crystals to achieve PHCs with twisted bands in the infrared region. Numerical investigation of the PHCs showed that the twisted bands have degenerate points that can support all-angle self-collimation effects. The behaviors of light beams change dramatically in such bands, which provides an effective method in controlling light propagation and can be applied as switching. The effect of the filling factor and the permittivity of the dielectric medium of the HMM on the twisted bands were studied. Furthermore, by considering the nonlinear effect of the dielectric layers, an all-optical switch working on the PHC twisted bands is proposed, which has low switching power and high extinction ratio (19.75 dB), superior to conventional HMM switches that require type transformation of metamaterial.

High-speed amplitude modulator with a high modulation index based on a plasmonic resonant tunable metasurface.

High-speed optical amplitude modulation is important for optical communication systems and sensors. Moreover, nano-optical modulators are important for developing optical-communication-aided high-speed parallel-operation processors and micro-biomedical sensors for inside-blood-capillary examinations or microsurgery operations. In this paper, we have designed a plasmonic resonant tunable metasurface with barium titanate (BTO) as a nanoscale optical modulator with a high modulation index and high speed. The BTO operated well in the VIS and near-IR ranges, enabling tunable optical devices with zero dispersion and high speed. The results obtained by rigorous finite-element method simulations have shown that the hypothesized device has good potential for fast modulation in related applications, e.g., modulators in nano-optical systems, nano-optical switches and nanosensors.

Single step synthesis of highly conductive room-temperature stable cation-substituted mayenite electride target and thin film.

Novel approaches to synthesize efficient inorganic electride [Ca24Al28O64]4+(e-)4 (thereafter, C12A7:e-) at ambient pressure under nitrogen atmosphere, are actively sought out to reduce the cost of massive formation of nanosized powder as well as compact large size target production. It led to a new era in low cost industrial applications of this abundant material as Transparent Conducting Oxides (TCOs) and as a catalyst. Therefore, the present study about C12A7:e- electride is directed towards challenges of cation doping in C12A7:e- to enhance the conductivity and form target to deposit thin film. Our investigation for cation doping on structural and electrical properties of Sn- and Si-doped C12A7:e- (Si-C12A7:e, and Sn-C12A7:e-) reduced graphene oxide (rGO) composite shows the maximum achieved conductivities of 5.79 S·cm-1 and 1.75 S·cm-1 respectively. On the other hand when both samples melted, then rGO free Sn-C12A7:e- and Si-C12A7:e- were obtained, with conductivities ~280 S.cm-1 and 300 S·cm-1, respectively. Iodometry based measured electron concentration of rGO free Sn-C12A7:e- and Si-C12A7:e-, 3 inch electride targets were ~2.22 × 1021 cm-3, with relative 97 ± 0.5% density, and ~2.23 × 1021 cm-3 with relative 99 ± 0.5% density, respectively. Theoretical conductivity was already reported excluding any associated experimental support. Hence the above results manifested feasibility of this sol-gel method for different elements doping to further boost up the electrical properties.

Facile synthesis of a cationic-doped [Ca24Al28O64]4+(4e-) composite via a rapid citrate sol-gel method.

One of the greatest challenges in the enhancement of the electrical properties of conductive mayenite [Ca24Al28O64]4+(4e-) (hereinafter C12A7:e-) is the design of a more suitable/simple synthesis strategy that can be employed to obtain the required properties such as excellent stable electrical conductivity, a high electron concentration, outstanding mobility, and an exceptionally large surface area. Therefore, to synthesize C12A7:e- in the metallic state, we proposed a facile, direct synthesis strategy based on an optimized sol-gel combustion method under a nitrogen gas environment using the low-cost precursors Ca(NO3)2·4H2O and Al(NO3)3·9H2O. Using this developed strategy, we successfully synthesized moderately conductive nanoscale C12A7:e- powder, but with unexpected carbon components (reduced graphene oxide (rGO) and/or graphene oxide (GO)). The synthesized C12A7:e- composite at room temperature has an electrical conductivity of about 21 S cm-1, a high electron concentration of approximately 1.5 × 1021 cm-3, and a maximum specific surface area of 265 m2 g-1. Probably, the synthesized rGO was coated on nanocage C12A7:e- particles. In general, the C12A7:e- electride is sensitive to the environment (especially to oxygen and moisture) and protected by an rGO coating on C12A7:e- particles, which also enhances the mobility and keeps the conductivity of C12A7:e- electride stable over a long period. Doped mayenite electride exhibits a conductivity that is strongly dependent on the substitution level. The conductivity of gallium-doped mayenite electride increases with the doping level and has a maximum value of 270 S cm-1, which for the first time has been reported for the stable C12A7:e- electride. In the case of Si-substituted calcium aluminate, the conductivity has a maximum value of 222 S cm-1 at room temperature.

Plasmonic waveguide design for the enhanced forward stimulated brillouin scattering in diamond.

We propose a scheme of metal/dielectric/metal waveguide for the enhanced forward stimulated Brillouin scattering (FSBS) in diamond that is mediated by gap surface plasmons. Numerical results based on finite-element method show that the maximum Brillouin gain in the small gap (~100 nm) can exceed 106 W-1 m-1, which is three orders of magnitude higher than that in diamond-only waveguides. It is found that the radiation pressure that exists at the boundaries of metal and diamond plays a dominant role in contributing to the enhanced forward stimulated Brillouin gain, although electrostrictive forces interfere destructively. Detailed study shows that high FSBS gain can still be obtained regardless of the photoelastic property of the dielectric material in the proposed plasmonic waveguide. The strong photon-phonon coupling in this gap-surface-plasmon waveguide may make our design useful in the development of phonon laser, RF wave generation and optomechanical information processing in quantum system.

Facile metal-free reduction-based synthesis of pristine and cation-doped conductive mayenite.

In the present study we synthesized conductive nanoscale [Ca24Al28O64]4+(4e-) (hereafter denoted as C12A7:e-) material, and reduced graphene oxide (rGO) was produced, which was unexpected; graphene oxide was removed after melting the sample. The conductivity of C12A7:e- composites synthesized at 1550 °C was 1.25 S cm-1, and the electron concentration was 5.5 × 1019 cm-3. The estimated BET specific surface area of the highly conductive sample was 20 m2 g-1. Pristine C12A7:e- electride was obtained by melting the composite powder, but the nano size of C12A7:e- particles could not be preserved; the value of conductivity was ∼28 S cm-1, electron concentration was ∼1.9 × 1021 cm-3, and mass density was 93%. For C12A7-x V x :e-, where x = 0.25 to 1, the conductivity improved to a maximum value of 40 S cm-1, and the electron density improved to ∼2.2 × 1021 cm-3; this enhancement in conductivity was also proposed by a theoretical study but lacked any associated experimental support.