Neftali Nuñez

Bluetooth Low Energy (BLE) is a prominent short-range wireless communication protocol widely extended for communications and sensor systems in consumer electronics and industrial applications, ranging from manufacturing to retail and healthcare. The BLE protocol provides four generic access profile (GAP) roles when it is used in its low-energy version, i.e., ver. 4 and beyond. GAP roles control connections and allow BLE devices to interoperate each other. They are defined by the Bluetooth special interest group (SIG) and are primarily oriented to connect peripherals wirelessly to smartphones, laptops, and desktops. Consequently, the existing GAP roles have characteristics that do not fit well with vehicular communications in cooperative intelligent transport systems (C-ITS), where low-latency communications in high-density environments with stringent security demands are required. This work addresses this gap by developing two new GAP roles, defined at the application layer to meet the specific requirements of vehicular communications, and by providing a service application programming interface (API) for developers of vehicle-to-everything (V2X) applications. We have named this new approach ITS-BLE. These GAP roles are intended to facilitate BLE-based solutions for real-world scenarios on roads, such as detecting road traffic signs or exchanging information at toll booths. We have developed a prototype able to work indistinctly as a unidirectional or bidirectional communication device, depending on the use case. To solve security risks in the exchange of personal data, BLE data packets, here called packet data units (PDU), are encrypted or signed to guarantee either privacy when sharing sensitive data or authenticity when avoiding spoofing, respectively. Measurements taken and their later evaluation demonstrated the feasibility of a V2X BLE network consisting of picocells with a radius of about 200 m.

This paper presents the comparison of two temperature Accelerated Life Tests (ALTs) for space commercial solar cells. The tests are carried out in dark conditions to circumvent the inherent problems of illumination ALTs. In the first ALT the solar cell working conditions were emulated by means of forward bias (that emulates the electric performance under illumination) while in the second ALT, forward bias was used together with reverse bias (that emulates the shadowing at eclipse periods or any other shadowing event such as for example the shadows cast by antennas) in order to reproduce more adequately the real operation conditions of solar cells. Forward to reverse time ratio is 4:1. Furthermore, the high temperatures used in the second ALT (190, 210 and 230 °C) allow a considerable time reduction of the test with respect to the first ALT (150, 165 and 180°C). The evaluation of the Arrhenius activation energy for an illumination power degradation of 10% was 0.88 eV in the forward bias test while 1.06 eV in the forward-reverse test. Reverse bias promotes similar degradation mode than forward one, namely parallel resistance reduction, but probably with a different degradation mechanism that degrades solar cell more intensely, thus reducing reliability which is more than 7 times shorter in the forward-reverse test than in forward one. Despite this reliability reduction, the time for a 90% reliability in the forward-reverse ALT is 32 years of continuous operation assuming a nominal temperature of 80°C which is typical of many GEO missions. The solar cells used in both ALTs were commercial GaInP/Ga(In)As/Ge triple junction and perform very robustly and exhibiting a high reliability for many space applications. It should be noted that these reliability figures are related to the degradation caused exclusively by high temperatures and other stressors like radiation are not considered here.

The lifetime of ultraviolet high-power light-emitting diodes (UV HP-LEDs) is an open issue due to their high current density, high temperature, and UV radiation. This work presents a reliability study and failure analysis of three high-temperature accelerated life tests (ALTs) for 13,500 h with 3 W commercial UV LEDs of 365 nm at a nominal current in two working conditions: continuous mode and cycled mode (30 s on/30 s off). Arrhenius–Weibull parameters were evaluated, and an equation to evaluate the lifetime (B50) at any junction temperature and other relevant lifetime functions is presented. The Arrhenius activation energy was 0.13 eV for the continuous mode and 0.20 eV for the cycled mode. The lifetime at 50% survival and 30% loss of optical power as a failure definition, working at T_a = 40 °C with a multi-fin heat sink in natural convection, was over 4480 h for the continuous mode and 19,814 h for the cycled mode. The need to add forced convection for HP-LED arrays to achieve these high-reliability values is evidenced. The main source of degradation is the semiconductor device, and the second is the encapsulation silicone break.

Evaluating the probability of failure of a product during the warranty is key to estimating the cost of its entire life cycle. Photovoltaic (PV) modules are the most reliable elements of a PV system, and their high reliability translates into long warranty periods (typically 25 to 30 years). The number of PV modules that fail during warranty and when they failed is an important issue to estimate the life cycle cost of PV modules. In this paper, we propose a coupled degradation‐warranty model for PV modules. The proposed model is aimed to assess the probability of failure over time covered by warranty based on degradation data. This allows us to estimate the time of PV modules failure covered by the warranty. Although the warranty model has been applied to some forms of degradation and sales functions, our method can be applied to any real application. This allows the key parameters of the warranty to be obtained in a simple way. The required degradation parameters to fulfill warranty depend on the allowable ratio of warranted elements. However, the main conclusion of the influence of degradation rates on warranty is that it is not possible to fulfill 25 years of warranty if degradation rates are larger than 0.8%/year. The required degradation rates values, for 25 years of warranty, will be lower than 0.5%/year if the allowed warranted element is in the range of 1%.

Development of contaminant detection systems in various natural and industrial environments has been favored in recent years thanks to the evolution of processors and sensors. Our group works specifically on contaminant detection systems in inland waters: immediate and continuous detection is a fundamental requirement in this type of sensing. Regarding the sensors, the proposed system is based on fluorescence, since it offers a method in which there is no contact with water, which means less wear on the components and a great saving in cleaning and maintenance. On the other hand, the spectrum processing is of great importance, since it is used both in the generation of a library of fluorescence spectra taken in the laboratory and in the continuous analysis of the samples and in the comparison algorithm for identification. The validity of the system is based on the last process that is carried out in a very short time. This article describes a system to process spectra in a more accelerated way.

A temperature accelerated life test on Upright Metamorphic Ga_0.37In_0.63P/Ga_0.83In_0.17As/Ge triple‐junction solar cells has been carried out. The acceleration has been accomplished by subjecting the solar cells to temperatures (125, 145 and 165°C) significantly higher than the nominal working temperature inside a concentrator (90°C), while the nominal photo‐current (500×) has been emulated by injecting current in darkness. The failure distributions have been fitted to an Arrhenius–Weibull model resulting in an activation energy of 1.39 eV. Accordingly, a 72 years warranty time for those solar cells for a place like Tucson (AZ, USA), was determined. After the ALT, an intense characterization campaign has been carried out in order to determine the failure origin. We have detected that temperature soak alone is enough to degrade the cell performance by increasing the leakage currents, the series resistance, and the recombination currents. When solar cells were also forward biased an increase of series resistance together with a reduction of short circuit current is detected. The failure analysis shows that: a) several metallization sub‐products concentrate in several regions of front metal grid where they poison the silver, resulting in a two times reduction of the metal sheet resistance; b) the metal/cap layer interface is greatly degraded and there is also a deterioration of the cap layer crystalline quality producing a huge increase of the specific front contact resistance, c) the decrease of short circuit current is mainly due to the GaInP top subcell degradation.

Qualification standards are one the driving forces for the commercialization and production of the Concentrator Photovoltaic (CPV) technology. After several years of preparation the Committee Draft of IEC 62787 has been finally submitted. The new standard IEC 62787 (Concentrator photovoltaic (CPV) solar cells and cell-on-carrier (CoC) assemblies – Qualification) fills the gap between the IEC TS 62789:2014 (Photovoltaic concentrator cell documentation) and the IEC 62108 Ed 2 (Concentrator photovoltaic (CPV) modules and assemblies - Design qualification and type approval). In the present article, apart from analyzing the objective, main guidelines, the innovative characteristics, and the life estimation from several tests of the qualification standard is also explained.