1,720,961 research outputs found
A Homogenized Magnetic Metasurface for Misalignment Robustness Enhancement in Wireless Power Transfer
No full textIn this paper, we introduce the adoption of a magnetic metasurface whose response is opportunely controlled as a method to alleviate the misalignment issue in resonant inductive Wireless Power Transfer. In particular, we first present the analytical framework thanks to which the metasurface response can be homogenized, avoiding undesired truncation effects. Then, a numerical set-up is designed to demonstrate the validity of the proposed approach. The results obtained through accurate full-wave simulations show that a homogenized metasurface can outperform a traditional one in terms of misalignment robustness, while maintaining the same efficiency level. This work can pave the way to the adoption in WPT applications of response-controlled metasurfaces with respect to the traditional version
A Radio-frequency High-Q System for Biomedical Sensing Applications
No full textIn this paper, a preliminary analysis of a near-field radiating system for biomedical sensing applications by using a radio-frequency magnetic field is presented. The proposed system, operating at 50 MHz, consists in a resonant helical coil wrapped around on a ferromagnetic core and inductively coupled with an unloaded probe loop. The system design has the main purpose to produce a focused magnetic field distribution, and, consequently, to guarantee a good spatial resolution of the sensing device. In addition, the introduction of the ferromagnetic material allows to improve the device detection sensibility at the operating frequency, by significantly enhancing the nominal helical coil inductance, thus optimizing the coil Q-factor. The main advantages of the proposed non-invasive system, beside the relatively low-complexity instrumentation, also include the possibility to reducing the health risks associated with the present diagnostic techniques, as the X-rays. The preliminary numerical results suggest the feasibility for an innovative near-field clinical device, for non-invasive sensing applications, as malignant inclusions detection; further analysis is therefore encouraged
Sensorized Nozzle for Material Properties Monitoring through Electromagnetic Field
No full textThis paper proposes the use of a circular waveguide operating around the fundamental mode cut-off frequency to be employed as a sensorized nozzle in the food industry or in 3D printers. Specifically, this paper aims to demonstrate the use of a metallic nozzle as a circular waveguide to detect foreign bodies or air bubbles during material sliding in order to guarantee an automatic product quality assessment. As a matter of fact, the presence of undesired inclusions changes the mixture dielectric permittivity, resulting in the waveguide cut-off frequency shift. To validate this theoretical approach, a circular waveguide operating around 2.5 GHz has been numerically designed and a set of materials, different in terms of dielectric properties, are used as waveguide fillers. A correlation between the real part of the material permittivity and the cut-off frequency shift has been observed, hence proving the possibility to detect foreign bodies or air by using the metallic nozzle as a circular waveguide. Therefore, the proposed system can be potentially used for innovative industrial applications, encouraging further analysis
Design of a Conformal and Low-Frequency Metasurface for Magnetic Field Shielding in Wireless Power Transfer Systems
No full textThis paper investigates the use of an arbitrarily conformal and low-frequency metasurface for magnetic field shielding in Wireless Power Transfer (WPT) systems. Firstly, we carry out the metasurface design by employing an analytical approach, which enables the manipulation and customization of its response, despite the finite nature of the array and the near-field excitation. In particular, we are able to set a 180° phase shift between the current flowing in the WPT active RF driver and those in the metasurface unit-cells. In this way, the metasurface, by interacting with the driver, will produce a magnetic field opposite to the inducing one, accomplishing the desired shielding behavior. Then, a numerical set-up is designed to demonstrate the validity of the proposed approach. The results, obtained through accurate full-wave simulations, show that is possible to achieve a maximum level of shielding effectiveness of approximately 8 dB. The study demonstrates the potential application of conformal magnetic metasurfaces for enhancing WPT systems safety, thereby addressing certain constraints associated with existing devices
Near-Field Focusing Conformal Magnetic Metasurface for Wireless Power Transfer
No full textThis paper proposes a conformal magnetic metasurface whose response can be opportunely controlled to obtain an efficient near-field focusing for resonant inductive Wireless Power Transfer applications. In particular, an analytical model is employed, allowing a proper control of the metasurface response so that a the magnetic near-field focusing can be achieved. A numerical Wireless Power Transfer set-up, working at 13.56 MHz, is designed to demonstrate the validity of the proposed approach. The results obtained through full-wave simulations prove that the magnetic field can be focused in the desired spatial spot, although the low frequency herein employed and overcoming the effects of metasurface conformal shape. In addition, the power transfer efficiency has been tested by positioning the receiver in two distinct spatial regions, respectively coaxial to and far from the focalized location. The results demonstrate that the WPT efficiency is effectively enhanced only when the receiver is positioned above the magnetic field focalized spot. Several WPT technologies, including charging pads, biomedical implants, and automotive applications, may advantageously exploit these features to precisely power multiple receivers, to achieve reconfigurability, and to realize conformal devices
A Dual-Band Metasurface for Functional and Anatomical 1.5 T MRI
No full textIn this work, a dual-band passive metasurface, excited by an RF coil and able to homogenize the magnetic field distribution for 1.5 T magnetic resonance imaging is presented. In particular, the metasurface is composed by a 5×5 passive array, covering a 15 cm x 15 cm area. Each unit-cell consists of two concentric spiral coils resonating at different Larmor frequencies: the internal coil at 64 MHz and the external one at 17 MHz, respectively. The two frequencies have been chosen to simultaneously combine the anatomical (1H, 64 MHz) and functional 23Na, 17 MHz) imaging for 1.5 T MRI scanners within the same hardware system. To validate the theoretical approach, we performed preliminary numerical full-wave simulations with and without the metasurface presence. Specifically, we compared the magnetic field distributions in terms of uniformity within the Field of View for the two configurations and at different distances from the radiating system. A superior magnetic field uniformity and, thus, a high signal-to-noise ratio, has been observed in the presence of the metasurface for both the frequencies. Therefore, these preliminary results demonstrated the possibility to use the proposed system for both anatomical and functional 1.5 T MRI
Arbitrarily Conformal Metasurfaces for Enhanced Wireless Power Transfer Systems
No full textIn this paper, design guidelines and unique features of arbitrarily conformal metasurfaces for Wireless Power Transfer (WPT) systems are discussed. In particular, we demonstrate the flexibility of conformal metasurfaces in achieving different behaviors by proposing two different applicative test cases: 1) magnetic field shielding in the region behind an RF coil, as typically required in automotive WPT scenarios, and 2) wireless power transmission with a magnetic field distribution spatially focused by the metasurface, eventually useful for electromagnetic exposure and interferences reduction. In general, the metasurface design is performed by following an analytical method that allows controlling and tailoring its response even though the array is finite, conformal and near-field excited. For both the implementations, the analytical design was corroborated by accurate full-wave simulations and experimental measurements carried out at 13.56 MHz. In particular, the possibility to obtain a 8 dB shielding effectiveness of an RF coil magnetic field at distances larger than twice of its diameter was proved. Conversely, in the second implementation, the conformal metasurface was capable to guarantee a measured power transfer efficiency of 8% for a receiver placed in correspondence of the 4 cm diameter focusing spot, while drastically reducing the magnetic field everywhere else. The results demonstrated the excellent potentialities of conformal magnetic metasurfaces for WPT applications in ensuring the electromagnetic safety for operators while simultaneously achieving enhanced performance
Implementation of a microwave sensor for the non-destructive detection of plant water stress
No full textIn this paper, the preliminary results from a measurement campaign of a novel sensor for plants hydric stress monitoring are presented. The proposed microwave sensing system, working at a frequency of about 250 MHz, consists in a microstrip self-resonant spiral coil inductively coupled to an external concentric planar probe loop. The microwave sensing configuration is the result of an optimization procedure aimed at maximizing the spiral coil Q-factor, required to obtain high sensitivity. The experiments have been conducted on 22 maize plants (Zea mays L.) randomly divided into two water treatments: T25 (applying 25% of the irrigation requirements) and T100 (full watering). In particular, plant responses to soil water depletion were detected by monitoring the amplitude and frequency shift variation of the external planar probe input impedance acquired by the sensor. In accordance with the theoretical expectations, we detected an upshift in the inner spiral resonant frequency and a rise in the probe loop input impedance amplitude as irrigation water decreased. The obtained experimental results encourage future research, especially envisioning applications in precision agriculture. Indeed, the sensor might be employed to detect and real-time monitor the health status of maize plants, optimizing the resource deployment strategy accordingly
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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