In this letter, a reconfigurable radiation pattern antenna for multiple-input-multiple-output (MIMO) applications on mobile devices is proposed. The operating frequency band of the antenna is ...5.15-5.35 GHz for a wireless local area network (WLAN) 802.11a service. Each antenna is composed of a loop-and-dipole structure, as well as two switches for the reconfigurable radiation pattern, to generate a beam in three different directions. The proposed antenna is designed to have an orthogonally directional radiation pattern with high isolation and a low-correlation coefficient in the MIMO environment.
The need to support various recognition applications on energy-constrained mobile computing devices has steadily grown. Exploiting common characteristics of recognition algorithms, a very ...energy-efficient multiplier that can support a runtime trade-off between computational accuracy and energy consumption is proposed. Compared to a precise multiplier, the proposed multiplier consumes 11.6×–3.2× less energy per multiplication while achieving 82–99% of the computational accuracy with negligible negative impact on recognition accuracy for three different recognition applications.
Research on smart environments saturated with ubiquitous computing devices is rapidly advancing while raising serious privacy issues. According to recent studies, privacy concerns significantly ...hinder widespread adoption of smart home technologies. Previous work has shown that it is possible to infer the activities of daily living within environments equipped with wireless sensors by monitoring radio fingerprints and traffic patterns. Since data encryption cannot prevent privacy invasions exploiting transmission pattern analysis and statistical inference, various methods based on fake data generation for concealing traffic patterns have been studied. In this paper, we describe an energy-efficient, light-weight, low-latency algorithm for creating dummy activities that are semantically similar to the observed phenomena. By using these cloaking activities, the amount of fake data transmissions can be flexibly controlled to support a trade-off between energy efficiency and privacy protection. According to the experiments using real data collected from a smart home environment, our proposed method can extend the lifetime of the network by more than 2× compared to the previous methods in the literature. Furthermore, the activity cloaking method supports low latency transmission of real data while also significantly reducing the accuracy of the wireless snooping attacks.
Current work principally provides an idea on controlling the Er3+: NIR (near-infrared) emission characteristics by changing a glass constituent and finding a suitable glass host favorable to design a ...novel C-optical band (1.53–1.565 μm) amplifier. By melting and rapid quench route, six transparent Er3+ (1 mol%)-doped B2O3-rich glasses having different single and mixed alkali ions were fabricated, and optical and fluorescence (visible and NIR) traits including Er3+ ion upper-levels 4S3/2 and 4I13/2 decay dynamics were inspected for such samples. At 1.4–1.65 μm wavelength range, an intense and wide NIR luminescence band centered at 1.532 μm (Er3+: 4I13/2 → 4I15/2 transition) has been obtained by a 980 nm laser diode pumping (4I15/2 → 4I11/2). NIR fluorescence Δλeff (effective bandwidth) varied depending on added single or mixed alkali ions, and a maximum Δλeff ∼74.66 nm was acquired for Er3+: Li ions constituting glass. For the 4I13/2 → 4I15/2 transition, σemi (stimulated emission cross-section) was evaluated using both Füchtbauer–Ladenburg and McCumber's theories. In all glasses, comparably, higher gain bandwidth (= 5.384 × 10−26 cm3) and peak σemiM (= 1.692 × 10−20 cm2) values have been attained for 4I13/2 → 4I15/2 transition in Li ions containing sample, and also this glass possesses the largest σabs (absorption cross-section) (= 1.459 × 10−20 cm2) for 4I15/2 → 4I13/2 transition. Further, at distinctive P (population inversion) values, gain spectra were computed, and all samples show C-optical band amplification beginning from P = 50%. All analyzed NIR fluorescence results indicate that Li ions having glass could be a potential gain medium for fiber amplifiers.
Display omitted
•Absorption and Vis-NIR emission features of Tm3+-doped borate glasses are analyzed.•J–O parameters, radiative parameters, and emission cross-sections are evaluated.•All Tm3+-doped ...glasses CIE (x, y) values represent the purplish-blue light region.•σmaxem & Δλeff of 3H4→3F4 transition are 1.832 × 10–21 cm2 & 121 nm for Tm3+: Li glass.
For six 1 mol% Tm3+-doped B2O3-BaO-ZnO-LiF glasses containing single and mixed alkali oxides (fabricated by melt-cast approach), optical absorption, and visible and near-infrared (NIR) fluorescence features including visible luminescence decay times were explored. Optical band gaps, Urbach energy, and two-photon absorption coefficients were evaluated for all studied glasses. Judd–Ofelt (J–O) analysis from absorption spectra was performed to compute Tm3+: 4f–4f transitions J–O parameters Ωλ (λ = 2, 4, 6), and utilizing Ω2, Ω4 and Ω6 values radiative transition probabilities (AR), branching ratios (βR), and radiative lifetimes (τR) for all Tm3+ ion’s excited levels were assessed. For obtained intense blue emission band (454 nm) upon 358 nm excitation, various parameters considered in developing visible laser systems were calculated. Tm3+: Na ions having sample exhibits high AR, highest peak emission cross-section (σmaxem) (=5.89 × 10–21 cm2) and gain bandwidth(σmaxem × Δλeff) (=9.69 × 10–27 cm3) for 1D2→3F4 luminescence transition in all glasses for a favorable blue lasing process. All emission decay curves of the 1D2 upper level showed nonexponential nature. Commission Internationale de l'éclairage (CIE) coordinates, color purity, and luminous efficiency of radiation were derived from visible fluorescence spectra, and attained CIE (x,y) coordinates values reflect the purplish-blue light region. Under direct optical pumping of 3H6→3H4 transition using 808 nm laser diode, NIR fluorescence spectra exhibit a wideband within 1.3–1.6 μm spectral range peaked at 1.46 μm (3H4→3F4 transition). NIR emissions effective bandwidth (Δλeff) was varied relying on different alkali oxides. Δλeff ~ 121 nm was deduced for Tm3+: Li ions comprising glass with large σmaxem (=1.832 × 10–21 cm2), high(σmaxem × Δλeff) (=2.22 × 10–26 cm3), and optical gain (=12.608 × 10–25 cm2s) for 3H4→3F4 emission transition and its gain profile wraps the entire S-optical communication band range for efficient broadband amplification purpose in wavelength-division multiplexing systems.
Sleep monitoring is vital as sleep plays an important role in recovering physical and mental health. To have a sound sleep, one has to avoid bad sleep positions associated with personal health ...conditions. However, most of the existing sleep trackers merely show quantitative information about sleep patterns and duration at each sleep stage, overlooking the importance of sleep positions upon sleep quality. To accurately keep track of sleep positions, we propose a wearable sleep position tracking system consisting of two wristbands and one chest-band. We suggest a two-level classifier specialized for sleep motion based on Dynamic State Transition (DST)-framework. The DST-framework is designed to process the spatiotemporal sleep motion data collected via accelerometer/gyro sensing and classify twelve sleep position (SP) motions from four sleep positions. Our experimental results demonstrate that the proposed system effectively and accurately classify twelve SP motions for tracking sleep positions, and hence, serves as a key building block for comprehensive sleep care applications related to sleep positions.
As wearable devices are powered by batteries, they need to consume as little energy as possible. To address this challenge, in this article, we propose a synergistic technique for energy-efficient ...approximate speech signal processing (ASSP) for wearable devices. More specifically, to enable the efficient trade-off between energy consumption and sound quality, we synergistically integrate an approximate multiplier and a successive approximate register analog-to-digital converter using our enhanced conversion algorithm. The proposed ASSP technique provides ~40% lower energy consumption with ~5% higher sound quality than a traditional one that optimizes only the bit width of SSP.
Measuring the compressive behaviour of sheet materials is an important process for understanding the material behaviour and numerical simulation of metal forming. The application of side force on ...both surfaces of a specimen in the thickness direction is an effective way to prevent buckling when conducting compressive tests. However, the side effects of side forces (such as the biaxial stress state and non-uniform deformation) make it difficult to interpret the measured data and derive the intrinsic compressive behaviour. It is even more difficult for materials with tension–compression asymmetry such as steels that undergo transformation-induced plasticity. In this study, a novel design for a sheet compression tester was developed with freely movable anti-buckling bars on both sides of the specimen to prevent buckling during in-plane compressive loading. Tensile and compressive tests under side force were conducted for low-carbon steel using the digital image correlation method. The raw tensile and compressive stress–strain data of the low-carbon steel showed apparent flow stress asymmetry of tension and compression, originating from the biaxial and thickness effects. A finite element method-based data correction procedure was suggested and validated for the low-carbon steel. The third generation advanced high strength steels showed intrinsic tension–compression asymmetry at room temperature whereas the asymmetry was significantly reduced at 175 °C.
In this letter, we propose a broadband reconfigurable antenna for aircraft communication that covers the VHF/UHF/L-bands (30-300/300-400/960-1220 MHz). The proposed antenna structure is a modified ...biconical unipole antenna. The antenna is frequency-reconfigurable using a p-i-n diode switch. In the on state, the antenna operates as a V-type traveling antenna and covers 30-300 and 960-1150 MHz. In the off state, the antenna operates as a unipole antenna and covers 300-400 and 1150-1220 MHz. The maximum power dissipation of the proposed antenna is 18 W. The proposed antenna has VSWR <; 2.5 for all bands. Antenna gain is less than 1.8 dBi at 30-400 MHz and 2.5 dBi at 960-1220 MHz.
In smart environments, target tracking is an essential service used by numerous applications from activity recognition to personalized infotaintment. The target tracking relies on sensors with known ...locations to estimate and keep track of the path taken by the target, and hence, it is crucial to have an accurate map of such sensors. However, the need for manually entering their locations after deployment and expecting them to remain fixed, significantly limits the usability of target tracking. To remedy this drawback, we present a self-configuring and device-free localization protocol based on genetic algorithms that autonomously identifies the geographic topology of a network of ultrasonic range sensors as well as automatically detects any change in the established network structure in less than a minute and generates a new map within seconds. The proposed protocol significantly reduces hardware and deployment costs thanks to the use of low-cost off-the-shelf sensors with no manual configuration. Experiments on two real testbeds of different sizes show that the proposed protocol achieves an error of 7.16~17.53 cm in topology mapping, while also tracking a mobile target with an average error of 11.71~18.43 cm and detecting displacements of 1.41~3.16 m in approximately 30 s.
PDF
