Abstract:Additive manufacturing paves new ways to the efficient exploration of the third space dimension, providing advantages over conventional planar architectures. In particular, volumetric electromagnetic antennas can demonstrate superior characteristics, outperforming their planar counterparts. Here a new approach to the fabrication of electromagnetic devices is developed and applied to antennas, implemented on curved surfaces. Highly directive and broadband antennas are 3D‐printed on hemispherical supports. The a… Show more
“…4). Typical permeability of those constructions are around 3 30 , which does not significantly affect the scattering from the SRRs. This accurate and repeatable positioning was implemented to achieve high experimental precision, which is necessary due to the sensitivity of the coupled micro-Doppler combs to variations in the geometry.…”
The classical Doppler shift originates from the movement of a target's center of mass, but it does not hold information about the internal dynamics of the scattering object. In contrast, micro-Doppler signatures contain data about the micro-motions that arise from internal degrees of freedom within the target (such as rotation and vibration), which can be remotely detected by careful analysis of the scattered field. Here we investigate, both theoretically and experimentally, how coupling between a pair of closely situated targets affects the resulting micro-Doppler signatures. The presented model considers a pair of near-field coupled resonators with dynamically reconfigurable scattering properties. Voltage controlled varactor diodes enable modulating the scattering cross-section of each target independently, mimicking rotational degrees of freedom. As a result, coupled micro-Doppler combs are observed, containing new frequency components that arise from the near field coupling, making it possible to extract information about the internal geometry of the system from far-field measurements. From a practical point of view, micro-Doppler spectroscopy allows remote classification of distant objects, while deep understanding of the coupling effects on such signatures in the low frequency regime can provide valuable insight for radar and sonar systems, as well as optical and stellar radio-interferometry, among many others.
“…4). Typical permeability of those constructions are around 3 30 , which does not significantly affect the scattering from the SRRs. This accurate and repeatable positioning was implemented to achieve high experimental precision, which is necessary due to the sensitivity of the coupled micro-Doppler combs to variations in the geometry.…”
The classical Doppler shift originates from the movement of a target's center of mass, but it does not hold information about the internal dynamics of the scattering object. In contrast, micro-Doppler signatures contain data about the micro-motions that arise from internal degrees of freedom within the target (such as rotation and vibration), which can be remotely detected by careful analysis of the scattered field. Here we investigate, both theoretically and experimentally, how coupling between a pair of closely situated targets affects the resulting micro-Doppler signatures. The presented model considers a pair of near-field coupled resonators with dynamically reconfigurable scattering properties. Voltage controlled varactor diodes enable modulating the scattering cross-section of each target independently, mimicking rotational degrees of freedom. As a result, coupled micro-Doppler combs are observed, containing new frequency components that arise from the near field coupling, making it possible to extract information about the internal geometry of the system from far-field measurements. From a practical point of view, micro-Doppler spectroscopy allows remote classification of distant objects, while deep understanding of the coupling effects on such signatures in the low frequency regime can provide valuable insight for radar and sonar systems, as well as optical and stellar radio-interferometry, among many others.
“…Continuous shape variation of the cavity configuration allows permittivity retrieval. Additive manufacturing techniques and selective surface metallization can allow creating complex geometries 6,22 and, as the result, can allow more accurate parametric retrieval on expense of computational and post-processing simplicity.…”
Material susceptibilities govern interactions between electromagnetic waves and matter. They are of a crucial importance for basic understanding of natural phenomena and for tailoring practical applications. Here we present a new calibration-free method for relative complex permittivity retrieval, which allows use of inexpensive and accessible equipment, and simplifies the measurement process. This method combines the advantages of resonant and non-resonant techniques, which allow the extraction of material parameters of liquids and solids in a broad frequency range, where material's loss tangent is less than 0.5. The essence of the method is based on excitation of magnetic dipole resonance in a spherical sample with variable dimensions. The size-dependent resonant frequencies and the quality factors of magnetic dipolar modes are mapped on real and imaginary parts of permittivity by employing Mie theory. Samples are comprised of liquid solutions, enclosed in stretchable covers, which allows changing the dimensions continuously. This approach enables the tuning of the magnetic dipolar resonance over a wide frequency range, effectively making resonance retrieval method broadband. The technique can be extended to powders and solid materials, depending on their physical parameters, such as granularity and processability.
“…The diameter of the shell is d = 55 mm. The parameters of the plastic were taken from 29 . Figure 3 ( a ) Numerical |S 11 | spectra of the ceramic tag in free space and within the roly-poly holder.…”
Radio frequency identification (RFID) is a mature technology that allows contactless data readout via a wireless communication link. While numerous passive RFID tags are available on the market, accurate alignment between tags and readers is required in a vast majority of cases to mitigate polarization mismatches. We show that enhancing electromagnetic designs with additional mechanical degrees of freedom allows bypassing fundamental limitations and approach ideal performances. Here, we demonstrate a new miniature tag, accessible from any direction and immune to rotations in space. Our tag is made of a high permittivity ceramic resonator, inductively coupled to a metal ring, which contains an RFID chip. The structure is placed inside a spherical plastic holder. In this architecture, the ceramic resonator serves several functions. First, it allows reducing the device footprint without significant bandwidth degradation. Second, it acts as a bob, aligning the electromagnetic structure parallel to the ground, regardless of its initial orientation in space. The bob is designed to slide inside the plastic holder. This roly-poly effect relaxes the constraint on a mutual tag-reader orientation, including the polarization mismatch, and provides next to perfect long-range operation. Being only 55 mm in diameter, our device can be interrogated from a 12 m distance, regardless of the tag’s orientation in space. Introducing mechanical degrees of freedom into electromagnetic designs allows obtaining new functionalities, contributing to applications where a mutual orientation between transvers is required.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
