Ultra-Wideband Power Amplifier Design Strategy for 5G Sub-6-GHz Applications.

This paper presents a strategy to design ultrawideband power amplifiers with a fractional bandwidth of approximately 200%. It exploits a simple output matching network, which consists of a series transmission line together with a shunt stub, to compensate the output parasitic network of the device. Following this, a multisection transformer is implemented to obtain the optimal load at the intrinsic drain plane. As design examples, several output matching networks were designed for two different size GaN HEMT devices. One of these examples was implemented and characterized, and a drain efficiency from 52% to 70% and an output power between 40 dBm and 42.5 dBm were obtained, over 67% of the 5G sub-6-GHz band (i.e., 0.1 to 4 GHz). The aforementioned results, to the best of the authors' knowledge, represent the state of the art in broadband power amplifiers.

Wideband Doherty Power Amplifier: A Design Approach.

This paper presents a simple method to design wideband Doherty power amplifiers (DPAs) based on the synthesis of a combiner network which can mimic the response of an ideal compensation of the device reactive output equivalent network and exploit the maximum power capabilities of the device. Using the Wolfspeed's CGH40006 and CG2H40025 GaN HEMT devices, two DPAs were designed and simulated to demonstrate the effectiveness of the proposed approach. In both cases, a 1.4 GHz bandwidth was obtained together with an efficiency higher than 44 and 49% at 6 dB OBO. The saturated output power was higher than 41.2 and 47 dBm over the band, for the DPAs using the CGH40006 and CG2H40025 devices, respectively.

Broadband, Ultra-High-Responsive Monolayer MoS2/SnS2 Quantum-Dot-Based Mixed-Dimensional Photodetector.

Atomically thin two-dimensional (2D) materials have gained significant attention from the research community in the fabrication of high-performance optoelectronic devices. Even though there are various techniques to improve the responsivity of the photodetector, the key factor limiting the performance of the photodetectors is constrained photodetection spectral range in the electromagnetic spectrum. In this work, a mixed-dimensional 0D/2D SnS2-QDs/monolayer MoS2 hybrid is fabricated for high-performance and broadband (UV-visible-near-infrared (NIR)) photodetector. Monolayer MoS2 is deposited on SiO2/Si using chemical vapor deposition (CVD), and SnS2-QDs are prepared using a low-cost solution-processing method. The high performance of the fabricated 0D/2D photodetector is ascribed to the band bending and built-in potential created at the junction of SnS2-QDs and MoS2, which enhances the injection and separation efficiency of the photoexcited charge carriers. The mixed-dimensional structure also suppresses the dark current of the photodetector. The decorated SnS2-QDs on monolayer MoS2 not only improve the performance of the device but also extends the spectral range to the UV region. Photoresponsivity of the device for UV, visible, and NIR region is found to be ∼278, ∼ 435, and ∼189 A/W, respectively. Fabricated devices showed maximum responsivity under the visible region attributed to the high absorbance of monolayer MoS2. The response time of the fabricated device is measured as ∼100 ms. These results reveal that the development of a mixed-dimensional (0D/2D) SnS2-QDs/MoS2-based high-performance and broadband photodetector is technologically promising for next-generation optoelectronic applications.

All Single-Mode-Fiber Supercontinuum Source Setup for Monitoring of Multiple Gases Applications.

In this paper, a gas sensing system based on a conventional absorption technique using a single-mode-fiber supercontinuum source (SMF-SC) is presented. The SC source was implemented by channeling pulses from a microchip laser into a one kilometer long single-mode fiber (SMF), obtaining a flat high-spectrum with a bandwidth of up to 350 nm in the region from 1350 to 1700 nm, and high stability in power and wavelength. The supercontinuum radiation was used for simultaneously sensing water vapor and acetylene gas in the regions from 1350 to 1420 nm and 1510 to 1540 nm, respectively. The experimental results show that the absorption peaks of acetylene have a maximum depth of approximately 30 dB and contain about 60 strong lines in the R and P branches, demonstrating a high sensitivity of the sensing setup to acetylene. Finally, to verify the experimental results, the experimental spectra are compared to simulations obtained from the Hitran database. This shows that the implemented system can be used to develop sensors for applications in broadband absorption spectroscopy and as a low-cost absorption spectrophotometer of multiple gases.

Multi-Cell LTE-U/Wi-Fi Coexistence Evaluation Using a Reinforcement Learning Framework.

Cellular broadband Internet of Things (IoT) applications are expected to keep growing year-by-year, generating demands from high throughput services. Since some of these applications are deployed over licensed mobile networks, as long term evolution (LTE), one already common problem is faced: the scarcity of licensed spectrum to cope with the increasing demand for data rate. The LTE-Unlicensed (LTE-U) forum, aiming to tackle this problem, proposed LTE-U to operate in the 5 GHz unlicensed spectrum. However, Wi-Fi is already the consolidated technology operating in this portion of the spectrum, besides the fact that new technologies for unlicensed band need mechanisms to promote fair coexistence with the legacy ones. In this work, we extend the literature by analyzing a multi-cell LTE-U/Wi-Fi coexistence scenario, with a high interference profile and data rates targeting a cellular broadband IoT deployment. Then, we propose a centralized, coordinated reinforcement learning framework to improve LTE-U/Wi-Fi aggregate data rates. The added value of the proposed solution is assessed by a ns-3 simulator, showing improvements not only in the overall system data rate but also in average user data rate, even with the high interference of a multi-cell environment.

Normative data for calcaneal broadband ultrasound attenuation among children and adolescents from Colombia: the FUPRECOL Study.

UNLABELLED: Quantitative ultrasound (QUS) has been found to be a safe and reliable method for evaluating bone mineral density (BMD). Using calcaneal QUS techniques, the current study contributes to remedying this gap in the literature by establishing normative data among children and adolescents from Colombia. INTRODUCTION: Minimal data on BMD changes are available from populations in developing countries. BMD reference values for children and adolescents have not been published for a Latin-American population. The aim of this study was to establish a normal reference range of calcaneal broadband ultrasound attenuation (BUA) in Colombian children and adolescents with ages ranging from 9 to 17.9 years. METHODS: A sample of 1001 healthy Colombian youth (boys n = 445 and girls n = 556), children, and adolescents (9-17.9 years old) participated in the study. A calcaneus QUS parameter (BUA) was obtained for boys and girls, stratified by age group. Furthermore, height, weight, fat mass percentage, and body mass index were measured. Centile smoothed curves for the third, tenth, 25th, 50th, 75th, 90th, and 97th percentiles were calculated using the LMS method (L [curve Box-Cox], M [curve median], and S [curve coefficient of variation]). RESULTS: Mean (± SD) values for the participants' anthropometric data were 12.9 ± 2.3 years of age, 45.2 ± 11.5 kg weight, 1.51 ± 0.1 m height, 19.5 ± 3.1 kg/m(2) BMI, and 69.5 ± 17.1 dB/MHz BUA. Overall, all variables were significantly higher in boys except in BMI and body fat percentage. Girls generally had higher mean calcaneal BUA (dB/MHz) values than the boys, except in the age ranges 16 and 17.9, p > 0.05. In addition, the BUA (dB/MHz) increased with age throughout childhood and adolescence and reached a plateau by age 15-17.9 for girls. CONCLUSIONS: For the first time, our results provide sex- and age-specific BUA reference values for Colombian children and adolescents aged 9-17.9 years. A more specific set of reference values is useful for clinicians and researchers and informs clinical practice to monitor bone mineral status.

Effects of Pilates-Interventional Program on Calcaneus-Bone Density Parameters of Adult Women / Efectos de un Programa de Intervención de Pilates Sobre Parámetros de Densidad Ósea en el Calcáneo de Mujeres Adultas

Physical exercise has a positive influence on bone tissue and therefore, is recommended in order to prevent the bone mass loss during the aging process. Similarly, normally practice of exercise potentially prevents the incidence of osteoporosis and bone fractures in adult women. In order to evaluate the differences of a Pilates-Interventional Program on parameters of bone density (right and left calcaneus) for six months, a total of 22 women (48.18±9.59) participated in the study. Bone mineral density (BMD) was estimated by the broadband ultrasonic attenuation (BUA) and the speed of sound signals (SOS), through "Sahara" sound device. The BUA showed significant difference in the right and the left leg (both, P< 0.01), the SOS of the right leg (P<0.05), whereas the BMD was not proved to be statistically significant at the end of the treatment. In conclusion, the bone mineral density by BUA increased, while the speed of sound of the right leg decreased. Thus, our findings might imply a better level of bone strength after a specific intervention focused on the Pilates method.

El ejercicio físico tiene una influencia positiva en el tejido óseo y por consiguiente, es recomendado a la hora de prevenir pérdida de masa ósea durante el envejecimiento. Igualmente, la práctica regular de ejercicio previene la osteoporosis y fractura de huesos en población adulta y mayor. Con el fin de evaluar las diferencias de parámetros en la densidad ósea (huesos calcáneos derecho e izquierdo) tras un programa de intervención Pilates de 6 meses, un total de 22 mujeres (48,18±9,59) participaron en el estudio. La densidad mineral ósea (DMO) fue estimada mediante la atenuación ultrasónica de banda ancha (AUBA) y la velocidad de las señales del sonido (VSS) a través del dispositivo de sonido "Sahara". La AUBA mostró diferencias significativas en ambos calcáneos (P<0,01), la VSS obtuvo diferencias significativas en el calcáneo derecho (P<0,5) y la DMO no mostró significancia alguna tras el programa de intervención. En conclusión, el calcáneo incrementó mediante medición AUBA mientras que VSS fue significativo en el calcáneo derecho. Nuestros resultados podrían implicar un mejor nivel de fuerza del calcáneo después de una intervención específica con Pilates.