Elena Autizi

Highly directional planar ultra wide band antenna for radar applications

We describe a novel planar highly directive ultra wide band (UWB) antenna based on a disc monopole fed by a 50-Ohm microstrip line. The key feature of the proposed antenna is a careful engineering of the ground plane that permits to increase directionality for radar applications. We demonstrate through numerical simulations and measurements in anechoic chamber that the designed antenna exhibits low return loss, high directivity and good time-domain properties in the band of interest between 6 and 8 GHz.

Compact UWB-MIMO antenna array with a novel decoupling structure

In this paper, a compact planar Ultra-Wideband (UWB) Multiple-input Multiple-output (MIMO) antenna array is proposed. This UWB-MIMO antenna array consists of two identical monopole antenna elements with a novel decoupling structure etched on the ground plane. The antenna performs very well over the UWB frequency range of 3.1-10.6 GHz. The decoupling structure improves the isolation between the antennas over the complete frequency band which can only be achieved otherwise by increasing the separation between the antenna elements. The analysis of antenna performance with and without stub is provided to demonstrate the significance of adding the decoupling stub to the design. The proposed compact and cost efficient antenna array system measures 27 × 47 mm2 only.

A Novel Configuration for Phase-Matched Second-Harmonic Generation in LiNbO

We present a feasibility study of a novel technique for continuously phase-matched second-harmonic generation in proton-exchanged lithium niobate waveguides. We demonstrate that a periodic variation of the nonlinear coefficient along the transverse direction with respect to the propagation one permits for efficient conversions. Comparison with the conventional first-order quasi-phase-matching interactions are then presented in front of unavoidable imperfections of real devices whenever Czochralski off-center technique is exploited in the fabrication process

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The monitoring of the acoustic emissions (AEs) due to rock fracturing allows the detection of the rockfall precursor signals, leading to a strong improvement of the real time assessment of the induced risk. A network of piezoelectric sensors (PZTs) provides reliable AE data, as testified by a series of applications in non-destructive testing, but PZTs are strongly affected by lightings and electromagnetic interference. In order to avoid such PZT drawbacks and limitations and therefore to allow the rock fracturing monitoring in unstable slopes, two FOS architectures (referred to as fibre coil sensor and ferrule top cantilever) have been recently proposed in previous works from the same authors. In this paper, the two sensors are tested in a more realistic scenario, by monitoring AE in a rock block in which crack is induced by highly expansive mortar; complementary activities, mainly aimed at the recognition of the type of expected signals and optimisation of the sensor array in the framework of the monitoring system, are also described here.

Waveguides

A simple, yet effective, setup for the simultaneous interrogation of multiple ferrule-top-cantilever sensors for acoustic sensing is here presented and experimentally tested with two ferrule-top-cantilever sensors; results confirm the feasibility of the approach.

Rockfall precursor detection based on rock fracturing monitoring by means of optical fibre sensors

An unconventional optical diffraction technique is exploited to characterize periodically poled lithium niobate crystals grown by the off-center Czochralski technique. The method, based on maps of the diffracted intensity in the reciprocal space, pointed out that a modulation in the refractive index occurs with a periodicity close to that measured by the chemical etching procedure. In this case, therefore, the linear optical properties of domains with opposite polarization are different.

Interrogation of multiple ferrule-top-cantilever sensors for acoustic emission sensing

A novel method to perform 3D vector measurement of intense and static magnetic elds is presented. The technique is based on the recently introduced distributed magnetic- eld ber optic sensor, which exploits Faraday rotation of polarization in standard single-mode bers. In the present case, the ber is arranged in several concatenated short coils, and the component of the magnetic eld parallel to the ber axis is measured by the distributed sensor. We show that by analyzing amplitude and spatial phase of the Faraday rotation measured along a coil, the 2D vector component of the magnetic eld parallel to the coil plane can be calculated. By arranging two close coils on orthogonal planes, a 3D reconstruction of the magnetic eld is achieved. Measurement uncertainty of few percents has been experimentally demonstrated over coils of just two loops; better accuracy can be obtained by increasing the number of ber loops.

Refractive Index Modulation in Periodically Poled Lithium Niobate Crystals

Optimization of an interferometric fiber optic sensor for ultrasonic acoustic detection in rockfall monitoring is addressed. The optimized sensor employs a polyimide coated fiber and improved design with an almost doubled acoustic sensitivity.

A novel quasi-distributed fiber optic sensor for 3D vector measurement of static magnetic fields

The work focuses on periodically poled lithium niobate crystals grown by the off-center Czochralski technique and exhibiting an appreciable second harmonic generation efficiency. Several samples have been characterized through experimental measurements of domains periods in order to find out the real period values and drifts of the border domains positions. By means of the nonlinear bidirectional beam propagation method (NL Bi-BPM), the governing equations describing the interaction between the wave at fundamental frequency and the wave at second harmonic have been integrated and the theoretical SHG efficiency was numerically determined. In order to take into account the border domain effects, the normalized efficiency was used to rescale the calculated value furnishing the real SHG efficiency. As an interesting result an efficiency of 0.5% in forward QPM SHG has been predicted for a reference structure of 0.5 mm length.