Andrea Michel

Design and performance analysis of a planar antenna for near-field UHF-RFID desktop readers

A near-field UHF (865-928MHz) RFID desktop reader antenna is designed by means of a traveling wave antenna. Since the detection of a tagged item in an arbitrary position and orientation is desirable, a meandered coplanar waveguide (CPW) line is properly designed, getting an homogeneous magnetic field amplitude. The main parameters of the RFID reader antenna (reflection coefficient, gain, effective isotropic field factor) are presented and discussed. Furthermore, the simulated and measured H-field distribution are compared, resulting in a good agreement. Finally, the overall RFID system performance is evaluated in terms of tag detection, considering short-range and long-range commercial RFID tags.

Dual-Band UHF-RFID/WLAN Circularly Polarized Antenna for Portable RFID Readers

A compact, low-profile, two-port dual-band circularly polarized (CP) antenna for portable RFID readers is presented. The radiating element for the UHF-RFID band (902-928 MHz) has been realized through a circular array of four inverted-F meandered monopoles, where the array elements are excited with a 90 ° phase offset (sequential rotation feeding technique) through a microstrip feeding network. In order to also provide the portable reader with a wireless web access, a miniaturized CP patch has been added for the WLAN IEEE 802.11b,g radio link, by exploiting the available space between the four array elements, without increasing the overall antenna volume. The meandered monopoles and the patch are both etched on the same layer of an FR4 substrate, so getting a significant antenna compactness (60 mm×60 mm×7 mm). The patch loading effect on the monopoles can be compensated by adjusting the meandered monopole length. Reflection coefficient, port isolation, axial ratio and radiation patterns are evaluated by numerical simulations and compared with measurements on an antenna prototype.

UHF-RFID Desktop Reader Antennas: Performance Analysis in the Near-Field Region

In this letter, a metric is proposed to qualitatively predict the achievable reading performance of a near-field (NF) UHF-RFID (865-928 MHz) desktop reader antenna, through a numerical analysis. Specifically, since the typical far-field antenna parameters (gain, radiation pattern, axial ratio) are not effective in the near-field region, the normalized power density is here proposed as a near-field antenna performance parameter. For a given NF antenna, the mean value of the normalized power density is evaluated on an area parallel to the antenna surface, at a set of different distances. Then, its decay rate is studied as a function of the distance from the antenna surface, which is useful to compare reading range performance of different antenna layouts. Additionally, the probability density function of the normalized power density at a given distance from the antenna surface is considered to investigate the field uniformity characteristics, the latter being important to guarantee tag reading independently on its location with respect to the reader antenna. The proposed analysis is applied to a set of NF UHF-RFID printed antennas, and conclusions are validated through a set of experimental tests.

Modular antenna for reactive and radiative near-field regions of UHF-RFID desktop readers

A general and reconfigurable antenna scheme for RFID desktop readers operating in the UHF band is here proposed. To maximize the electromagnetic field in a confined volume within the antenna near-field region (namely, in both the reactive and radiative near-field regions), a travelling wave antenna is combined with a low-gain resonating antenna, which share the surface of the desktop reader antenna. The travelling wave antenna allows for covering the reactive near-field region, with almost uniform electric and magnetic fields up to a few cm from the antenna surface. The low-gain resonating antenna is used to cover the radiative near-field region, up to a few tens of cm from the antenna surface, yet radiating a relatively low field in the antenna far-field region as required by antennas for desktop readers. In such a way, a satisfactory tag readability is expected independently on the material of the item the tag is attached to and the effect of the mutual coupling among stacked tags. The suggested modular configuration can be realized by using different technologies for the travelling wave antenna (microstrip, coplanar waveguide, slotline, etc.), as well as different layouts for the resonating antenna. Above degrees of freedom allow the antenna designer to easily meet the specifications on antenna size and RFID read range. The antenna modules used to realize the reader antenna can be combined through either a shunt or series feeding connection; as an alternative, a few switches and variable power splitters could be added to implement a reconfigurable desktop reader antenna.

Integration of Slot Antennas in Commercial Photovoltaic Panels for Stand-Alone Communication Systems

The integration of slot antennas in a class of commercial photovoltaic (PV) panels is addressed. The basic idea is to exploit the room available between adjacent solar cells, also taking advantage of the presence of the cover glass layer that gives a valuable miniaturization effect. As test cases, two antenna designs are presented for stand-alone communication systems operating in the GSM/UMTS (1710-2170 MHz) and WiMAX (3300-3800 MHz) frequency bands, respectively. At early design stage, antenna design has been performed by resorting to a simplified numerical model; afterwards, the effects on the antenna performance of nearby solar cells and DC bus wires have been numerically evaluated. The impedance tuning of the final antenna design has been carried out through a measurement campaign with slot antenna prototypes attached to real PV panels.

Accuracy of a Multiprobe Conformal Sensor in Estimating the Dielectric Constant in Deep Biological Tissues

A theoretical analysis is presented on the accuracy of a novel method to extract the dielectric constant of deep tissues. The method exploits the variations of the electric fields on the surface of a multilayer dielectric scattering model and their dependence on dielectric properties of the deep tissues. The dielectric constant at a specific depth is expressed as a linear combination of the surface electric field samples. Critical parameters that affect the accuracy are determined through a numerical study, and basic guidelines for sensor design optimization are provided, using an emulation of a human torso. It is concluded that accuracies with errors <;3% can be achieved, demonstrating the efficacy of the method and proposed representation.

A modular antenna for UHF RFID near-field desktop reader

The combination of a near-field coupling antenna placed in the central area of a UHF RFID desktop reader with a low-gain resonating antenna allocated at the reader border is here proposed to obtain a confined detection volume within the antenna near-field region (including both the reactive and radiative near field regions). The antenna layout consists of a spiral Travelling Wave Antenna (TWA) which series-feeds an array of two circularly-polarized miniaturized patches. The spiral TWA geometry allows for exciting an almost homogeneous field on the antenna surface, making the tag detection on the reader antenna (near-field reactive region) almost independent on tag location and orientation. The low-gain patch array is used to extend the read range up to the radiative near-field region. Good results in terms of read range and RSSI (Received Signal Strength Indicator) distribution have been checked experimentally, also for a stacked tag configuration.

Reconfigurable Modular Antenna for NF UHF RFID Smart Point Readers

In this paper, a reconfigurable modular antenna is presented for smart point readers employed in near-field (NF) radio-frequency identification applications at the ultrahigh frequency European Telecommunications Standards Institute band (865–868 MHz). The antenna comprises two modules sharing the same

Energy-Based Considerations for Ungrounded Wearable UHF Antenna Design

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Antennas for UHF-RFID printer-encoders

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