Second-order semi-aplanatic freeform optics as a limit case of the SMS 3D design method.

Second-order semi-aplanatism provides better imaging quality along a line of the object plane close to a point than conventional aplanatic optics, which is of interest in applications with high aspect ratio sensors. Designing an optic with second-order semi-aplanatism requires the use of freeform surfaces, and can be done as a limit case of the SMS 3D design method applied to stigmatically image 3 collinear object points. The algorithm for this specific design problem is described and a lens example with 3 freeform surfaces is designed and analyzed.

A Universal Testbed for IoT Wireless Technologies: Abstracting Latency, Error Rate and Stability from the IoT Protocol and Hardware Platform.

IoT applications rely strongly on the performance of wireless communication networks. There is a wide variety of wireless IoT technologies and choosing one over another depends on the specific use case requirements-be they technical, implementation-related or functional factors. Among the technical factors, latency, error rate and stability are the main parameters that affect communication reliability. In this work, we present the design, development and validation of a Universal Testbed to experimentally measure these parameters, abstracting them from the wireless IoT technology protocols and hardware platforms. The Testbed setup, which is based on a Raspberry Pi 4, only requires the IoT device under test to have digital inputs. We evaluate the Testbed's accuracy with a temporal characterisation-accumulated response delay-showing an error less than 290 µs, leading to a relative error around 3% for the latencies of most IoT wireless technologies, the latencies of which are usually on the order of tens of milliseconds. Finally, we validate the Testbed's performance by comparing the latency, error and stability measurements with those expected for the most common IoT wireless technologies: 6LoWPAN, LoRaWAN, Sigfox, Zigbee, Wi-Fi, BLE and NB-IoT.

The Smart Meter Challenge: Feasibility of Autonomous Indoor IoT Devices Depending on Its Energy Harvesting Source and IoT Wireless Technology.

Most smart meters are connected and powered by the electric mains, requiring the service interruption and qualified personnel for their installation. Wireless technologies and energy harvesting techniques have been proved as alternatives for communications and power supply, respectively. In this work, we analyse the energy consumption of the most used IoT wireless technologies nowadays: Sigfox, LoRaWAN, NB-IoT, Wi-Fi, BLE. Smart meters' energy consumption accounts for metering, standby and communication processes. Experimental measurements show that communication consumption may vary upon the specific characteristics of each wireless communication technology-payload, connection establishment, transmission time. Results show that the selection of a specific technology will depend on the application requirements (message payload, metering period) and location constraints (communication range, infrastructure availability). Besides, we compare the performance of the most suitable energy harvesting (EH) techniques for smart meters: photovoltaic (PV), radiofrequency (RF) and magnetic induction (MIEH). Thus, EH technique selection will depend on the availability of each source at the smart meter's location. The most appropriate combination of IoT wireless technology and EH technique must be selected accordingly to the very use case requirements and constraints.

Smart Metering for Challenging Scenarios: A Low-Cost, Self-Powered and Non-Intrusive IoT Device.

In this work, a novel current metering device was presented. This device was intended to bring current metering capabilities to a wide variety of scenarios: Developing countries, rural areas, or any situation with technological constraints. The device was designed to provide a straightforward installation with no intrusion in the electrical panels. This was achieved by applying energy harvesting techniques and wireless communication technology for data transmission. The device was able to exploit the magnetic field inducted around a wire carrying electricity as energy harvesting, thus acquiring the power it needed to work. Since very low power was harvested, an efficient treatment for the incoming power and a minimal power consumption system were essential. Although exploiting the magnetic fields inducted around a wire has been used for years, the combination of this technology for both energy harvesting and current metering in an end-user device was off-center. To work in a wide variety of scenarios, it used Sigfox for communications as this brought wide coverage and out-of-the-box functioning. The theoretical design of the device was validated by verification assessments for the joint performance of the individual parts compounding the device, including metering capabilities and wireless communication test-bench. Finally, the metering device was tested under three distinct real-world scenarios that demonstrated the viability of the system. Results show that, depending on the metering period and the average current value in the mains line, the device could work forever acquiring and sending electricity consumption data. Perpetual working was achieved with an average current of 3.1 A to meter every 15 min, and an average current of 5 A for a 5-min metering period.

Free-form optics for Fresnel-lens-based photovoltaic concentrators.

The Concentrated Photovoltaics (CPV) promise relies upon the use of high-efficiency triple-junction solar cells (with proven efficiencies of over 44%) and upon high-performance optics that allow for high concentration concurrent with relaxed manufacturing tolerances (all key elements for low-cost mass production). Additionally, uniform illumination is highly desirable for efficiency and reliability reasons. All of these features have to be achieved with inexpensive optics containing only a few (in general no more than 2) optical elements. In this paper we show that the degrees of freedom using free-forms allow the introduction of multiple functionalities required for CPV with just 2 optical elements, one of which is a Fresnel lens.

SMS-based optimization strategy for ultra-compact SWIR telephoto lens design.

A new optical design strategy for rotational aspheres using very few parameters is presented. It consists of using the SMS method to design the aspheres embedded in a system with additional simpler surfaces (such as spheres, parabolas or other conics) and optimizing the free-parameters. Although the SMS surfaces are designed using only meridian rays, skew rays have proven to be well controlled within the optimization. In the end, the SMS surfaces are expanded using Forbes series and then a second optimization process is carried out with these SMS surfaces as a starting point. The method has been applied to a telephoto lens design in the SWIR band, achieving ultra-compact designs with an excellent performance.

An application of the SMS method for imaging designs.

The Simultaneous Multiple Surface (SMS) method in planar geometry (2D) is applied to imaging designs, generating lenses that compare well with aplanatic designs. When the merit function utilizes image quality over the entire field (not just paraxial), the SMS strategy is superior. In fact, the traditional aplanatic approach is actually a particular case of the SMS strategy.

High-efficiency free-form condenser overcoming rotational symmetry limitations.

Conventional condensers using rotational symmetric devices perform far from their theoretical limits when transferring optical power from sources such as arc lamps or halogen bulbs to the rectangular entrance of homogenizing prisms (target). We present a free-form condenser design (calculated with the SMS method) that overcomes the limitations inherent to rotational devices and can send to the target 1.8 times the power sent by an equivalent elliptical condenser for a 4:1 target aspect ratio and 1.5 times for 16:9 target and for practical values of target etendue.

On the analysis of rotational symmetric microstructured surfaces.

A previous paper [2] presented an analysis of a class of microstructured optical surfaces in two dimensions, in which a classification of the microstructures was obtained (regular and anomalous) and a concept of 2D ideal microstructures was introduced. In this paper the study of those microstructured optical surfaces is extended to three dimensions with rotational symmetry. As a starting point, non-microstructured rotational optical systems in the First Order Approximation are also classified as point-spot type and ring-spot type, with remarkable perfect particular cases. This classification is also extended to the case in which ideal microstructured rotational surfaces are used, for both regular and anomalous type. The case of perfect ring-spot type system with an odd number of rotational, anomalous, ideal microstructures enables the definition of an anomalous aplanatic system that has direct application for mixing spatially and angularly the light emitted by several sources.

Analysis of microstructured surfaces in two dimensions.

A certain class of microstructured surfaces in 2D geometry is studied on the basis of an approximation of infinitesimal microstructure elements. The macroprofile of the surfaces is then treated as a new type of optical surface with a deflection law that differs from the law of reflection and Snell's law. We discuss the propagation of wavefronts by general microstructured surfaces and the discontinuity of the eikonal function at the microstructure. Naturally, a classification of the microstructures is obtained (regular and anomalous), and the concept of 2D ideal microstructures is also introduced, since they are used for coupling two macroscopic extended bundles.

Hamilton-Jacobi equation in momentum space.

The application of the Hamilton-Jacobi equation to isotropic optical materials leads to the well-known eikonal equation which provides the surfaces normal to the ray trajectories. The symmetry between the coordinates x=(x(1),x(2),x(3)) and the momenta p=(p(1),p(2),p(3)) in the Hamiltonian formulation of Geometrical Optics establishes a dual Hamilton-Jacobi equation for "wavefronts" in the momentum space. This equation is also an eikonal equation when the refractive index distribution has spherical symmetry. In this case, another spherical symmetric refractive index distribution may exist such that the ray trajectories in the coordinates and momentum space are exchanged (examples of this case are given: Maxwell fish-eye, Eaton lens and Luneburg lens). The relationship between the wavefronts in the coordinate and momentum space is also analyzed. Curved orthogonal coordinates are considered as well.

Delayed neurobehavioral development in children born to pregnant women with mild hypothyroxinemia during the first month of gestation: the importance of early iodine supplementation.

BACKGROUND: Maternal hypothyroxinemia, due to gestational iodine deficiency, causes neurological dysfunctions in the progeny. Our aim was to determine the effects of delayed iodine supplementation (200 microg KI per day) to mildly hypothyroxinemic pregnant women at the beginning of gestation (i.e., having circulating free thyroxine [FT(4)] within the 0th-10th percentile interval and normal thyrotropin [TSH]) on the neurobehavioral development of their children. METHODS: Using the Brunet-Lézine scale, we evaluated the neurocognitive performance at 18 months of age in three groups of children. Group 1 included children of women with FT(4) above the 20th percentile at 4-6 gestational weeks and at full-term. Group 2 included children of mildly hypothyroxinemic women diagnosed during the first 12-14 gestational weeks and with FT(4) above the 20th percentile at full-term. Group 3 included children born to mildly hypothyroxinemic women at full-term, without iodine supplementation during gestation. Women of all groups were iodine supplemented from the day of enrollment until the end of lactation. RESULTS: Before iodine supplementation, 33.0% of the women (114 out of 345) were hypothyroxinemic, with FT(4) below normal in 28 of them (8.1%). None were found to be hypothyroxinemic at full-term after supplementation. The mean (+/-SD) developmental quotient of children was 101.8 +/- 9.7 in group 1 (n = 13) vs. 87.5 +/- 8.9 in group 3 (n = 19; p < 0.001) and 92.2 +/- 5.4 in group 2 (n = 12; p < 0.05). The difference between groups 2 and 3 was not statistically significant. Delayed neurobehavioral performance was observed in 36.8% and 25.0% of children in groups 3 and 2, respectively, compared with no children in group 1. Differences (p < 0.001) were found on gross and fine motor coordination and socialization quotients. No statistically significant differences were found on language quotients. CONCLUSIONS: A delay of 6-10 weeks in iodine supplementation of hypothyroxinemic mothers at the beginning of gestation increases the risk of neurodevelopmental delay in the progeny. Public health programs should address the growing problem of iodine deficiency among women of gestational age in developing and industrialized nations.