On the safety design of radar based railway level crossing surveillance systems

Recent accidents experienced at railway level crossings are pushing researchers to design surveillance systems able to grant safety of passengers and structural integrity of trains at level crossings. The challenge is represented by granting at the same time an appropriate reliability, availability and maintainability degree despite the high safety requirements imposed by the application. The approach proposed in this paper takes into consideration the most common suggested standards used in designing this kind of systems and introduces new general concepts which demystify the use of such standards in actual applications. This paper illustrates the roadmap to be followed in general when designing level crossing monitoring systems, to minimize the risk due to object misdetection occurring on barrier closure when exploiting radar technology

A Closed-Form Representation of Isofrequency Dispersion Curve and Group Velocity for Surface Waves Supported by Anisotropic and Spatially Dispersive Metasurfaces

A general closed-form representation is introduced for representing the isofrequency dispersion curve (IDC) of an anisotropic, spatially, and frequency dispersive metasurface (MTS) constituted by a dense periodic texture of metallic elements printed on a grounded substrate. The formulation is restricted to printed elements isolated from each other (namely, patches and not slots) whose geometry exhibits at least two axes of symmetry. The expression is valid for the dominant TM surface wave (SW) until the limit of the Floquet-Bloch (FB) region and generalizes our previous formulation to arbitrary direction of propagation. This generalization permits a closed-form representation of the IDCs and of the group velocity as a function of two parameters only; these are the equivalent quasi-static capacitances along the symmetry directions of the geometry. The limit of validity of the closed-form representation has been defined and the formulation has been tested by full-wave analysis. The present formulation simplifies the design of MTS antennas and flat transformation optics devices

Low-power UWB transmitter for RFID transponder applications

An UWB low power active transmitter operating in the European UWB band (6-8.5 GHz) is presented, which may find applications in RFID transponders with asymmetric downlink and uplink communication, as well as in others communication devices. It is based on a 7.25 GHz oscillator driven by a base-band pulse generator, and connected to a small size UWB antenna. The oscillator is turned on and off by the base-band pulsed control voltage, according to a modulation scheme, and it consumes power only when the 7.25 GHz pulse is generated. The RF pulse waveform exhibits a peak amplitude of about 2.2 Vpp and a width of about 2 ns. The power spectral density of the single UWB pulse is in accordance with the European UWB mask. A planar compact UWB antenna is also proposed as the load of the transmitter. It shows a return loss lower than -14 dB in the operating frequency band

Hybrid methods based on generalized scattering matrices

A general hybrid technique based on the use of generalized scattering matrices is presented for the electromagnetic analysis of complex antenna and/or scattering problems. The analysis domain is decomposed into separate subdomains, which are independently studied through the most appropriate technique and characterized by a generalized scattering matrix (GSM), where the ports are associated with a proper set of wave objects. Finally, the interactions among the subdomains are described by imposing the proper subdomain connections. Two particular implementations of the general technique are illustrated. In the first one, the wave objects are complex point source (CPS) beams. Thanks to the angular selectivity of the CPS beams, only a small fraction of the beams are involved in the final system, thus, leading to an efficient numerical procedure. In the second one, spherical waves are used as wave objects. This choice offers the advantage of direct interfaceability with the output of spherical near-field measurements or numerical simulations. © 2011 IEEE

A Hybrid PO/Generalized-Scattering-Matrix Approach for Estimating the Reflector Induced Mismatch

4reservedmixedC. Della Giovampaola; E. Martini; A. Toccafondi; S. MaciDELLA GIOVAMPAOLA, Cristian; Martini, Enrica; Toccafondi, Alberto; Maci, Stefan

Reflecting Luneburg Lenses

International audienceThis paper presents the exact closed-form solution for a new planar lens, hereinafter referred to as Reflecting Luneburg Lens (RLL). The proposed structure consists of two stacked parallel plate waveguides of circular shape. The rays generated by a point source located at the periphery of the bottom waveguide propagate along curvilinear paths, whose trajectories result from a variable refractive index profile with azimuthal symmetry. Then, these rays encounter a reflecting boundary and emerge all parallel in the upper uniform waveguide. The behavior of this lens resembles that of a flat Luneburg lens, with the fundamental difference that it works in reflection. The exact refractive index profile is found by solving the non-linear integral equation of ray-congruence trough a truncated Abel transform method. The concept is numerically verified through different implementations of the effective refractive index profile, including a metasurface-based implementation. The proposed lens triggers new possibilities that the normal flat Luneburg lens does not offer, and it is applicable in a large variety of microwave, terahertz and optical devices

Target measurements influence on level crossing detection system safety assessment

The design of critical to safety systems is usually approached through the observation of specific standards which are applicable in the field of interest of the considered application itself. Even if, most of time this kind of design orientation can be satisfactory to address the majority of problems, sometimes it may lead to tricky situations where some crucial aspects can be neglected. This risk is high when new sensors or new system applications are designed because some hidden hazards can be related to the sensor physics or to the specific considered scenario as well. In this paper the authors discuss how the implementation of a peculiar application for level crossing monitoring (LC) based on a specific radar technology can be jeopardized if sharp analysis of the target to be detected is not performed. The possibility to exploit single sensor or multi sensor solutions is proposed discussing the advantages and pitfalls of the different designs in terms of system reliability, availability and safety. Considerations about measurement uncertainty depending on the type and orientation of the object to be detected is presented on an empirical basis as well

Target measurements influence on level crossing detection system safety determination

The design of critical safety systems is usually approached through the investigation about the applicability of specific standards that can be applied in that specific field of interest. Even if very often this design strategy can be satisfactory to address the most part of common problems, sometimes a generalized approach may lead to tricky situations where some crucial aspects can be neglected. This risk is high when new technologies or advanced measurement systems are designed. The main reasons may lay in some hidden hazards related to the sensor physics or to the specific context. In this paper the authors discuss how the implementation of a peculiar system for level crossing monitoring (LC) based on a specific radar technology can be jeopardized if a limiting standard approach is followed. Moreover, a sharp analysis of the target to be detected is performed. Safety systems based on single or multi sensor architectures are analyzed discussing the advantages and pitfalls of the different designs in terms of system RAMS parameters. Considerations about measurement uncertainties due to the type and orientation of the specific item to be detected are presented on an empirical basis as well