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Measuring the distance between two points has multiple uses. Position can be geometrically calculated from multiple measurements of the distance between reference points and moving sensors. Distance measurement can be done by measuring the time of flight of an ultrasonic signal traveling from an emitter to receiving sensors. However, this requires close synchronization between the emitter and the sensors. This synchronization is usually done using a radio or optical channel, which requires additional hardware and power to operate. On the other hand, for many applications of great interest, low-cost, small, and lightweight sensors with very small batteries are required. Here, an innovative technique to measure the distance between emitter and receiver by using ultrasonic signals in air is proposed. In fact, the amount of the signal attenuation in air depends on the frequency content of the signal itself. The attenuation level that the signal undergoes at different frequencies provides information on the distance between emitter and receiver without the need for any synchronization between them. A mathematical relationship here proposed allows for estimating the distance between emitter and receiver starting from the measurement of the frequency dependent attenuation along the traveled path. The level of attenuation in the air is measured online along the operation of the proposed technique. The simulations showed that the range accuracy increases with the decrease of the ultrasonic transducer diameter. In particular, with a diameter of 0.5 mm, an error of less than ± 2.7 cm (average value 1.1 cm) is reached along two plane sections of the typical room of the office considered (4 × 4 × 3 m3).

Increasing efforts toward the development of positioning techniques testify the growing interest for indoor position-based applications and services. Many applications require accurate indoor positioning or tracking of people and assets, and some market sectors are starting a rapid growth of products based on these technologies. Ultrasonic systems have already been demonstrating their effectiveness and to possess the desired positioning accuracy and refresh rates. In this work, it is shown that a typical signal used in ultrasonic positioning systems to estimate the range between the target and reference points&mdash, namely, the linear chirp&mdash, due to the effects of acoustic diffraction, in some cases, undergoes a shape aberration, depending on the shape and size of the transducer and on the angle under which the transducer is seen by the receiver. In the presence of such signal shape aberrations, even one of the most robust ranging techniques, which is based on cross-correlation, provides results affected by a much greater error than expected. Numerical simulations are carried out for a typical ultrasonic chirp, ultrasonic emitter, and range technique based on cross-correlation and for a typical office room, obtained using the academic acoustic simulation software Field II. Spatial distributions of the ranging error are provided, clearly showing the favorable low error regions. The work demonstrates that particular attention must be paid to the design of the acoustic section of the ultrasonic positioning systems, considering both the shape and size of the ultrasonic emitters and the shape of the acoustic signal used.

The conversion efficiency of an RF energy harvester is studied at 868 MHz as a function of temperature on a printed circuit board charge-pump, based on off-the-shelf diodes and capacitors. Extensive experimental measurements are presented in the temperature range from 25°C to 85°C, showing that the harvested power may significantly degrade with T, in particular at the lower incident power regimes. It is shown that the rectifiers quality, and precisely the temperature dependent rectification ratio of silicon Schottky diodes commonly used for this application, has the strongest impact of the harvester performances.

An experimental study is carried out to assess the effect of temperature on the conversion efficiency of ultrahigh-frequency energy harvesters based on diode-capacitor Dickson charge pumps, frequently used in self-energizing circuits, such as in radio frequency identification tags or in wireless sensor nodes. Using off-the-shelf Schottky diodes often adopted for this application, it is shown that the harvester conversion efficiency at 868 MHz is temperature dependent due to the changing rectification ratio, namely the ratio between the forward and the reverse current flowing through the low barrier height Schottky diodes, which both show a positive derivative with T. The experimental study, supported by SPICE simulations, has shown that a temperature variation might be particularly harmful at the lowest incident power regimes, when even a minimal drop in the conversion efficiency might determine the out-of-servicing of a wirelessly energized circuit.

The growing interest for indoor position-based applications and services, as well as ubiquitous computing and location aware information, have led to increasing efforts toward the development of positioning techniques. Many applications require accurate positioning or tracking of people and assets inside buildings, and some market sectors are waiting for such technologies for starting a fast growth. Ultrasonic systems have already been shown to possess the desired positioning accuracy and refresh rate. However, they still require accurate synchronization between ultrasound emitters and receivers to work properly. Usually, synchronization is carried out through radio frequency (RF) signals, adding system complexity and raising the cost. In this work, this limit is overcome by introducing a novel self-synchronizing indoor positioning technique. Ultrasonic signals travel from emitters placed at fixed reference positions to any number of mobile devices (MD). The travelled distance is computed from the time of flight (TOF), which requires in turn synchronism between emitter and receiver. It is shown that this synchronism can be indirectly estimated from the time difference of arrival (TDOA) of the ultrasonic signals. The obtained positioning information is private, in the sense that the positioning infrastructure is not aware of the number or identity of the MDs that use it. Computer simulations and experimental results obtained in a typical office room are provided.

Positioning objects such as appliances inside rooms has become of fundamental importance in the Internet o Things (IoT) and ooin-home automation, as well as in augmented reality (AR). A new positioning system based on a smartphone and radio-frequency identification (RFID) tags applied to the objects to be localized is presented. The 3D positioning of the smartphone is obtained through an ultrasound system while its orientation in space is obtained with the onboard magnetometers and accelerometers. When a certain RFID tag is read through the near-field communication (NFC) interface of the smartphone, from its distance and from the orientation of the smartphone that reads it, the 3D position of the tagged object is obtained. The system architecture is explained and simulation results are presented. Positioning accuracy of about ten centimeters is achieved

Natural disasters and the poor management of civil engineering structures and infrastructures require timely action and new tools such as specially designed structural health monitoring platforms. This paper proposes an innovative platform based on a network of wirelessly connected, low-power, and renewable-energy-fed sensor units. The platform is a multipurpose tool for diagnostics, maintenance, and supervision, capable of simultaneously carrying out damage detection, localization, identification, and &ldquo, multiclass&rdquo, and &ldquo, multi-material&rdquo, level quantification of different types of failures. In addition, it works as a decision support tool for emergency management and post-disaster assessment, here tailored for an Italian theme park. The platform uses innovative algorithms based on the concept of the vibro-acoustic signature of the asset monitored. The vibro-acoustic signatures of the monitored assets are gathered by the microphones and accelerometers of the platform&rsquo, s sensor units. Then, almost simultaneously, they are analyzed using specifically designed wavelet-based and convolutional-neural-network-based algorithms, which are able to extract crucial information about the structural and environmental conditions of both the asset and the areas of the thematic park. In addition, the platform shows escape routes during an emergency, indicating meeting points and helping people to proceed safely along a recognizable escape route to a safe place, as demonstrated by the simulations.

The design and testing phase of photovoltaic (PV) power systems requires time-consuming and expensive field-testing activities for the proper operational evaluation of maximum power point trackers (MPPT), battery chargers, DC/AC inverters. Instead, the use of a PV source emulator that accurately reproduces the electrical characteristic of a PV panel or array is highly desirable for in-lab testing and rapid prototyping. In this paper, we present the development of a low-cost microcontroller-based PV source emulator, which allows testing the static and dynamic performance of PV systems considering different PV module types and variable operating and environmental conditions. The novelty of the simple design adopted resides in using a low-cost current generator and a single MOSFET converter to reproduce, from a fixed current source, the exact amount of current predicted by the PV model for the actual load conditions. The I-V characteristic is calculated in real-time using a single diode exponential model under variable and user-selectable operating conditions. The proposed method has the advantage of reducing noise from high-frequency switching, reducing or eliminating ripple and the demand for output filters, and it does not require expensive DC Power source, providing high accuracy results. The fast response of the system allows the testing of very fast MPPTs algorithms, thus overcoming the main limitations of state-of-art PV source emulators that are unable to respond to the quick variation of the load. Experimental results carried on a hardware prototype of the proposed PV source emulator are reported to validate the concept. As a whole result, an average error of &plusmn, 1% in the reproduction of PV module I‐V characteristics have been obtained and reported.

Schottky-barrier solar cells (SBSCs) represent low-cost candidates for photovoltaics applications. The engineering of the interface between absorber and front electrode is crucial for reducing the dark current, blocking the majority carriers injected into the electrode, and reducing surface recombination. The presence of tailored interfacial layers between the metal electrode and the semiconductor absorber can improve the cell performance. In this work, the interface of a graphene/n-type Si SBSC by introducing a graphene-based derivative (GBD) layer meant to reduce the Schottky-barrier height (SBH) and ease the charge collection are engineered. The chemical vapor deposition (CVD) parameters are tuned to obtain the two graphene films with different structure and electrical properties: few-layer graphene (FLG) working as transparent conductive electrode and GBD layer with electron-blocking and hole-transporting properties. Test SBSCs are fabricated to evaluate the effect of the introduction of GBD as interlayer into the FLG/n-Si junction. The GBD layer reduces the recombination at the interface between graphene and n-Si, and improves the external quantum efficiency (EQE) with optical bias from 50 to 60%. The FLG/GBD/n-Si cell attains a power conversion efficiency (PCE) of ≈5%, which increase to 6.7% after a doping treatment by nitric acid vapor.

Transportation systems are gradually changing. Innovative solutions are provided by automotive industries, construction firms, computer-aided pavement management systems, sensor-based structural health monitoring (SHM) systems, and international regulations. This calls for efforts and studies aiming at finding a trade-off between the ever-growing request of innovation (smart cities), and the never-ending depletion of resources and energy. Energy savings in road infrastructures can be pursued through: 1) construction process optimization; 2) traffic management improvement; 3) vehicle optimization; 4) recycling and reuse of construction materials; 5) innovative materials; 6) energy harvesting; 7) smart roads; 8) maintenance and rehabilitation optimization through SHMmethods and technologies. Theobjective of the study is to set up an innovative SHM method aiming at achieving energysavings in transportation in terms of Pavement Management System (PMS) optimization.The new method here setup was implemented through an experimental investigation. Amicrophone was placed on different road pavements, impulse loads were produced by aLight weight Deflectometer, LWD, and vibro-acoustic signals were recorded and analyzedin the pursuit of assessing the structural condition of the pavement. Using this knowledge toimprove the management process of transportation infrastructures, it is expected that safer,more resilient, and less energy-consuming assets will be provided.

The Authorities that are responsible for the design and management of infrastructures have an increasing need of information and support in order to optimize their work, save money, time, and, sometimes (e.g., in case of disastrous events), lives. Technological development is leading to new possibilities, in terms of new technologies increasingly available, widespread, reliable and inexpensive and that can be applied to make smart cities safer and more efficient. Hence, new methods and devices may be thought out in order to respond to these requests and to help Authorities during the structural health assessment/monitoring (SHA/SHM) of infrastructures and also during the emergency management. To this end, in this paper a new SMA/SHM method is proposed and validated through experimental investigations. The new proposed method is based on the vibro-acoustic response of a transportation infrastructure and pertains to its SHA/SHM. The method builds on using the road traffic noise as source of vibrations and sounds. Microphones are placed in different positions (in drilled holes and/or on the upper surface: receiver), and vibro-acoustic signals are recorded. The spectra of these signals are expected to represent the vibro-acoustic signature of the road pavement under investigation. From the analysis of this signature, information about the presence and the severity of cracks into the layers of the road section can be derived. In the pursuit of the method validation, non-destructive on-site tests, aimed at classifying the level of damage through high-speed devices/methods (i.e., visual detection of surface distress, moduli estimation through the light falling weight deflectometer (LWD), laser detection of roughness), were carried out. Road pavements in different structural conditions were investigated. From the analysis of the gathered acoustic signatures, the identification and localization of cracks into the pavements under investigation was carried out. These results are going to be used to set up a preliminary database of acoustic signature of different road pavements. Further applications of the new method are expected for a large number of road infrastructures, aiming at enriching the abovementioned database and improving predictive algorithms. Based on the proposed method, it is expected: i) to make available an estimation of the level of integrity of a road pavement to use in the management of transportation infrastructure for better, safer, and more economical smart cities and roads; ii) to provide a fast, inexpensive, and useful tool for the authorities that are responsible for the management of road infrastructures and other civil infrastructures in smart cities; iii) to provide a tool for delivering essential services to citizens.

A SPICE model of a complete photovoltaic (PV) system, including a detailed model of photovoltaic cells, a modified cascaded multilevel inverter, and energy storage elements, is presented. The simulation of the system as a whole allows evaluating readily the effects on its performances of the variation of the component parameters, as well as of the external load, the solar irradiation, and the cell temperature. The global conversion efficiency and the total harmonic distortion (THD) of the output waveform are in particular analysed. The role and sizing criteria of a storage element, such as a capacitor, placed at the PV module output are also analysed for various operating conditions. Experimental tests have been carried out on a custom designed prototype photovoltaic system and compared to those obtained with the simulation model.

In recent years, the increasing usage of tablet PCs and smartphones has made obsolete the traditional keyboard and mouse as input devices, replaced by multi-touch or stylus-based input solutions that are perceived as being more user-friendly. Over the past 30 years, has been shown in literature and by patents, several solutions based on different types of interaction, from optics to acoustics. Our objective is to make surfaces, also wide, which have not been designed for use as a touch-screen, in particular with the new operating systems that widely use the intuitive features of the touch-methodology, usable. The goal of the work is to realize an autonomous stylus, at low cost, capable of generating flexural waves in any surface, which can be detected with a sensors system, also simple and low-cost, with an appropriate accuracy, in order to detect the position of the stylus, both to be used as pointer, either to be used as an input device for natural writing or drawing.

In this paper we report the design, fabrication process, and characterization of a 64-elements capacitive micromachined ultrasonic transducer (cMUT), 3 MHz center frequency, 100% fractional bandwidth. Using this transducer, we developed a linear probe for application in medical echographic imaging. The probe was fully characterized and tested with a commercial echographic scanner to obtain first images from phantoms and in vivo human body. The results, which quickly follow similar results obtained by other researchers, clearly show the great potentiality of this new emerging technology. The cMUT probe works better than the standard piezoelectric probe as far as the axial resolution is concerned, but it suffers from low sensitivity. At present this can be a limit, especially for in depth operation. But we are strongly confident that significant improvements can be obtained in the very near future to overcome this limitation, with a better transducer design, the use of an acoustic lens, and using well matched, front-end electronics between the transducer and the echographic system.

Ultrasound (US) probes in the MHz range used in the medical field must comply with specific rules. Traditionally, calibrated hydrophones measure the pressure of the US field within a given volume but this procedure is time consuming. More recently, the Schlieren system has been demonstrated a fast and accurate technique for the quantification of the ultrasonic field characteristics (beam width and average acoustic intensity in function of the gray level). However, a relationship between the video gray level and the peak pressure was not determined, and only a small number of medical probes could be studied in real time due to a limited field of view. In this paper, the realization of an experimental set-up based on the Schlieren effect, allowing real time imaging, and a quantitative tomographic reconstruction of the US field of a wide range of medical probes, driven with continuous waves, is reported. We also investigated the relationship between pressure measurements and tomographic luminance values, in order to calibrate our Schlieren system. The results demonstrate that this new Schlieren system of compact dimension, 40 cm x 100 cm x 40 cm, is a time efficient method to characterize several medical probes in the frequency range 1-40 MHz. A non-linear relationship between the gray level of the tomographic reconstruction and the peak pressure was experimentally found. Once the system has been calibrated, it allows the quantitative reconstruction of tomographic views at any depth. Our future work is to quantify the video of the US field in real time and to obtain a 3D visualization.

The mechanical effects of the metal layer on the membranes of capacitive micromachined ultrasonic transducers (CMUTs) are analyzed in this paper by means of finite element simulations. The influence of electrode size and thickness on the electrostatic behavior of the single CMUT cell, including diaphragm displacement, cell capacitance, and collapse voltage, is explored. The effect on device sensitivity is investigated through the transformation factor of the cell, that is computed by FEM and compared with the parallel plate model prediction. It is found that for a non-negligible electrode thickness, as in the majority of fabricated devices, both the static and dynamic performance of the cell can be affected in a significant way. Thus, the effects of membrane metallization must be taken into account in CMUT design and optimization.

Spatial resolution in modern ultrasound imaging systems is limited by the high cost of large aperture transducer arrays, which require a large number of transducer elements and electronic channels. A new technique to enhance the spatial resolution of pulse-echo imaging systems is presented. The method attempts to build an image that could be obtained with a transducer array aperture larger than that physically available. We consider two images of the same object obtained with two different apertures, the full aperture and a subaperture, of the same transducer. A suitable artificial neural network (ANN) is trained to reproduce the relationship between the image obtained with the transducer full aperture and the image obtained with a subaperture. The inputs of the neural network are portions of the image obtained with the subaperture (low resolution image), and the target outputs are the corresponding portions of the image produced by the full aperture (high resolution image). After the network is trained, it can produce images with almost the same resolution of the full aperture transducer, but using a reduced number of real transducer elements. All computations are carried out on envelope-detected decimated images; for this reason, the computational cost is low and the method is suitable for real-time applications. The proposed method was applied to experimental data obtained with the ultrasound synthetic aperture focusing technique (SAFT), giving quite promising results. Real-time implementation on a modern, full-digital echographic system is currently being developed.

In this letter, a 1.8-mm × 1.8-mm capacitive micromachined ultrasonic transducer (CMUT) element is experimentally characterized by means of optical measurements. Optical displacement measurements provide information on the resonant behavior of the single membranes and also allow us to investigate the dispersion in the frequency spectrum of adjacent membranes. In addition, higher order mode shapes are observed, showing that either symmetrical or asymmetrical modes are excited in CMUT membranes. Laser interferometry vibration maps, combined with quantitative displacement measurements, provide information about the quality and repeatability of the fabrication process, which is a basic requirement for 2-D array fabrication for ultrasound imaging.

A new, simple extrapolation technique to enhance the lateral resolution of pulse-echo imaging systems is presented. The method attempts to build an image that could be obtained with a transducer aperture larger than that physically available, extrapolating the information contained in the image to be enhanced. The extrapolation process requires small hardware modifications of the standard echographic systems. The computational cost is very low compared with Fourier-based deconvolution approaches. The obtained computer simulations give very interesting and promising results.

In this work, the radial symmetric vibration modes of thin piezoceramic rings have been analyzed by means of a previously proposed theoretical model. Both the resonance frequencies and the effective electromechanical coupling factor (k/sub eff/), as a function of the aspect ratio G between the inner and outer radii of the ring, were computed. The results have shown that the disk structure (G/spl rarr/0) has only one radial symmetrical mode (with its harmonics), but, for the ring structure (G/spl rarr/1), two different modes are clearly distinguished: the ring mode, which has no harmonics, and a width-like mode, with its harmonics. Moreover, the results show that the ring structure can be assumed to be definitely reached for G>0.6. An analysis of the material coupling factor in the ring geometry is reported as well.