Optical Nanoantennas for Energy Harvesting

In the last decade, the increasing demand for renewable energy has been leading to the development of new devices, which overcome the disadvantages of the traditional photovoltaic conversion and exploit the thermal radiation created by the Sun, that is transferred in the form of electromagnetic waves into free space and finally absorbed by the surface of the Earth [1-2]. These new devices, called nanoantennas, have only recently been considered thanks to the development of electron beam lithography and similar techniques. Nanoantennas operate at nanometers wavelengths and their dimensions range from a few hundred nanometres to a few microns. They exhibit potential advantages in terms of polarization, tunability, and rapid time response. Furthermore, the nanoscale dimensions, combined with the high electric field enhancement in the antenna gap, enable a small device footprint, making it compact enough to be monolithically integrated with electronics and auxiliary optics [3]. Similar to traditional RF antennas, nanoantennas capture the incident visible or infrared electromagnetic wave causing an AC current onto the antenna surface, such that it oscillates at the same frequency of that of the wave. The movement of the electrons produces an alternating current in the antenna circuit. A proper rectifier coupled with nanoantenna is used in order to produce a DC power [3]. This rectifier contains one or more diodes whose power loss and fast response can influence the whole device efficiency. This circuit is known as rectenna and the typical block diagram and the equivalent circuit are shown in figure 1-2 [3-4]. Infrared nanoantennas are also coupled to a metallic thermocouple. The rectification mechanism is based on the Seebeck effect, a thermoelectric voltage generation due to the infrared irradiation induced currents in the antenna. Figure 3 shows the electric equivalent circuit of the antenna-coupled thermocouples [5]. The purpose of this contribution is to critically compare advantages and disadvantages of new optical nanoantennas for energy harvesting, focusing on the state of the art and its perspectives. Nanoantennas for visible radiation reveal better upper bound limits in terms of efficiency and available power density, table 1 [4]. Infrared nanoantennas can work even in the absence of solar radiation, but the efficiency is still very low. Some technological issues have to be taken into account before these commercial devices are put on the market. They mainly regard the circuits between the antenna and the load. Nonetheless, they show a greater efficiency than traditional PV solar cells and could be an alternative to the latter in the energy harvesting process in the next future

Fabrication and Photoelectrochemical Behavior of Ordered CIGS Nanowire Arrays for Application in Solar Cells

In this work, we report some preliminary results concerning the fabrication of quaternary copper, indium, gallium, and selenium CIGS nanowires that were grown inside the channels of an anodic alumina membrane by one-step potentiostatic deposition at different applied potentials and room temperature. A tunable nanowire composition was achieved through a manipulation of the applied potential and electrolyte composition. X-ray diffraction analysis showed that nanowires, whose chemical composition was determined by energy-dispersive spectroscopy analysis, were amorphous. A composition of Cu0.203In0.153Ga0.131Se0.513, very close to the stoichiometric value, was obtained. These nanostructures were also characterized by photoelectrochemical measurements: They showed a cathodic photocurrent and an optical gap of 1.55 eV

Dependence of Terahertz Emission and Detection in Photoconductive Antennas on Laser Parameters

In this study, we employ a standard Terahertz time-domain spectroscopy (THz-TDS) setup based on two photoconductive antennas (PCAs) for THz radiation generation and detection. The characterization of the emission and detection performance as a function of the input pulse wavelength and bandwidth is performed

Thrust Vector Controller Comparison for a Finless Rocket

The paper focuses on comparing applicability, tuning, and performance of different controllers implemented and tested on a finless rocket during its boost phase. The objective was to evaluate the advantages and disadvantages of each controller, such that the most appropriate one would then be developed and implemented in real-time in the finless rocket. The compared controllers were Linear Quadratic Regulator (LQR), Linear Quadratic Gaussian (LQG), and Proportional Integral Derivative (PID). To control the attitude of the rocket, emphasis is given to the Thrust Vector Control (TVC) component (sub-system) through the gimballing of the rocket engine. The launcher is commanded through the control input thrust gimbal angle δ , while the output parameter is expressed in terms of the pitch angle θ . After deriving a linearized state–space model, rocket stability is addressed before controller implementation and testing. The comparative study showed that both LQR and LQG track pitch angle changes rapidly, thus providing efficient closed-loop dynamic tracking. Tuning of the LQR controller, through the Q and R weighting matrices, illustrates how variations directly affect performance of the closed-loop system by varying the values of the feedback gain (K). The LQG controller provides a more realistic profile because, in general, not all variables are measurable and available for feedback. However, disturbances affecting the system are better handled and reduced with the PID controller, thus overcoming steady-state errors due to aerodynamic and model uncertainty. Overall controller performance is evaluated in terms of overshoot, settling and rise time, and steady-state error

One-Step Electrodeposition of CZTS for Solar Cell Absorber Layer

CZTS thin films were obtained by one-step electrochemical deposition from aqueous solution at room temperature. Films were deposited on two different substrates, ITO on PET, and electropolished Mo. Differently from previous studies focusing exclusively on the formation of kesterite (Cu4ZnSnS4), here, the synthesis of a phase with this exact composition was not considered as the unique objective. Really, starting from different baths, amorphous semiconducting layers containing copper–zinc–tin–sulphur with atomic fraction Cu0.592Zn0.124Sn0.063S0.221 and Cu0.415Zn0.061Sn0.349S0.175, were potentiostatically deposited. Due to the amorphous nature, it was not possible to detect if one or more phases were formed. By photoelectrochemical measurements, we evaluated optical gap values between 1.5 eV, similar to that assigned to kesterite, and 1.0 eV. Reproducibility and adhesion to the substrate were solved by changing S with Se. Preliminary results showed that an amorphous p-type layer, having atomic fraction Cu0.434Zn0.036Sn0.138Se0.392 and an optical gap of 1.33 eV, can be obtained by one-step electrochemical deposition

Microwave gas sensor based on graphene aerogel for breath analysis

Exhaled breath can be used for early detection and diagnosis of diseases, monitoring metabolic activity, and precision medicine. In this work, we design and simulate a microwave sensor in which thin graphene aerogels are integrated into rectangular microwave waveguides. Graphene aerogels are ideal sensing platforms for gases and volatile compounds as they combine extremely high surface-to-volume ratio and good electrical conductivity at RF and microwave frequencies. The latter is modified by exposure to different gases, and -when integrated into a waveguide- these changes result in significant shifts in transmission and reflection scattering parameters. We model the aerogel as a graphene grid with hexagonal openings of size 22.86×10.16×0.1 mm3, characterized by an air volume equal to about 90 % of its entire volume. This grid is used as a building block for modeling thicker samples (up to 9 mm), To simulate the variation in the dynamic conductivity of the graphene sheets as a consequence of the absorption of gaseous molecules, a sweep of the chemical potential from 0.0 e V to 0.5 e V with steps of 0.1 e V was used. The results show a significant variation of the waveguide transmission scattering parameters resulting from the gas-induced modification of the graphene conductivity, and hence the potential of the proposed sensor design for breath analysis

Investigation of the JPA-Bandwidth Improvement in the Performance of the QTMS Radar

Josephson parametric amplifier (JPA) engineering is a significant component in the quantum two-mode squeezed radar (QTMS) to enhance, for instance, radar performance and the detection range or bandwidth. We simulated a proposal of using engineered JPA (EJPA) to enhance the performance of a QTMS radar. We defined the signal-to-noise ratio (SNR) and detection range equations of the QTMS radar. The engineered JPA led to a remarkable improvement in the quantum radar performance, i.e., a large enhancement in SNR of about 6 dB more than the conventional QTMS radar (with respect to the latest version of the QTMS radar and not to the classical radar), a substantial improvement in the probability of detection through far fewer channels. The important point in this work was that we expressed the importance of choosing suitable detectors for the QTMS radars. Finally, we simulated the transmission of the signal to the target in the QTMS radar and obtained a huge increase in the QTMS radar range, up to 482 m in the current study

Strategies and Techniques for Powering Wireless Sensor Nodes through Energy Harvesting and Wireless Power Transfer

The continuous development of the internet of things (IoT) infrastructure and applications is paving the way for advanced and innovative ideas and solutions, some of which are pushing the limits of state-of-the-art technology. The increasing demand for Wireless Sensor Nodes (WSNs) able to collect and transmit data through wireless communication channels, while often positioned in locations that are difficult to access, is driving research into innovative solutions involving energy harvesting (EH) and wireless power transfer (WPT) to eventually allow battery-free sensor nodes. Due to the pervasiveness of radio frequency (RF) energy, RF EH and WPT are key technologies with the potential to power IoT devices and smart sensing architectures involving nodes that need to be wireless, maintenance free, and sufficiently low in cost to promote their use almost anywhere. This paper presents a state-of-the-art, ultra-low power 2.5 W highly integrated mixed-signal system on chip (SoC), for multi-source energy harvesting and wireless power transfer. It introduces a novel architecture that integrates an ultra-low power intelligent power management, an RF to DC converter with very low power sensitivity and high power conversion efficiency (PCE), an Amplitude-Shift-Keying/Frequency-Shift-Keying (ASK/FSK) receiver and digital circuitry to achieve the advantage to cope, in a versatile way and with minimal use of external components, with the wide variety of energy sources and use cases. Diverse methods for powering wireless Sensor Nodes through energy harvesting and wireless power transfer are implemented providing related system architectures and experimental results

Microwave gas sensor based on graphene aerogels

— In this article, the experimental demonstration of a novel microwave gas sensor based on graphene aerogel is presented. This device makes use of a highly porous structure of the aerogel in combination with the modulation of graphene AC conductivity upon exposure to vacuum and ambient air. As a proof of concept, we integrate the graphene aerogel into rectangular waveguides and measure its scattering parameters by a Vector network Analyzer (VNA). The aerogel is characterized by a combination of scanning electron microscopy and four-probe DC measurements. The aerogel is integrated into WR-90 waveguides by custom-designed support and wave propagation is tested over the 8-12 GHz frequency range (Xband). By exposing the aerogel to either air or a moderate vacuum, clear shifts in the waveguide scattering parameters are observed. In particular, changes of ≈ 3 dB and ≈ 1 dB in the transmission and reflection parameters of the waveguide are obtained, respectively. Moreover, the sensor exhibits excellent reproducibility when exposed to alternating cycles of air and vacuum, proving that the shifts in microwave transmission and reflection are caused by changes in the conductivity of the graphene aerogel due to the absorption and desorption of gas molecules. These proof-of-concept results pave the way for the development of a new class of gas sensors for applications such as breath analysis

A versatile ultrasound system for in vitro experiments

Objective One of the most difficult tasks to achieve with the available instrumentations used to study the interaction between ultrasound (US) and cellular model systems is to design an experiment, where only the effects of one physical parameter at a time is evaluated, while all the others are kept constant. The set-ups are usually custom-made, often by means of clinical instrument intended for a different therapeutic purpose. Furthermore, the results are not strictly comparable with others obtained with techniques considered standard in molecular and cellular biology at this time, because there is the need to use non-standard devices to contain biological samples. Sterility, as well as temperature, is not well controlled and reproducibility is usually a major concern. In our study we show the effects of ultrasound treatments on different cellular systems. The experiments are performed with a versatile bench-top US apparatus to be adapted for several in vitro experiments and that allows easy and robust reproducibility using standard set-ups for the cell samples. Methods One main feature of our bench-top US system is that it has been designed in order to use standard plasticware commonly used in molecular biology labs, ensuring the temperature control and sterility conditions needed in the field. We present a set-up where the simultaneous use of a set of transducers operating at different frequencies on the same plate, allows the comparison of the deposition of the same acoustic pressure, whilst evaluating the effect of frequency alone on the readout of the cell experiments. The apparatus modular design also allows the use of a set of transducers operating at the same frequency, in experiments where the throughput is a relevant factor. We demonstrate that it is possible to define the position of the target within all the achievable areas of the acoustic field with sub-millimetric accuracy. Tests for several applications based on biologic effects by ultrasound have been carried out by varying the acoustic parameters such as power, frequency range, sonication time and duty cycle, all controlled within robust protocols executed in automation. Results The resulting data proves that it is possible to perform in vitro experiments for different purposes (i.e. drug delivery, cellular sonoporation, nanoparticles or microbubbles swelling, tissue regeneration, neuronal cell stimulation etc.) keeping the relevant physical parameters of sonication constant, for instance acoustic pressure, but varying the others parameters (i.e. frequency, pulse length or duty cycle etc) one at the time. Conclusions We show that with our apparatus it is possible to obtain robust and reproducible results on cellular experiments, using all the standard devices that are commonly available in biological labs. The improvement on the side of reproducibility and portability of the experiments allows a straightforward comparison between our results and those obtained with other techniques