A. Monorchio - Academia.edu (original) (raw)

Papers by A. Monorchio

Microwave and Optical Technology Letters, 1995

A numerical technique is presented that makes use of the finite-element method for the analysis o... more A numerical technique is presented that makes use of the finite-element method for the analysis of the scattering from perfectly conducting cylinders with cauity-backed apertures. The method of solution, based on an application of the equiualence principle, is very flexible and can be easily extended to analyze ruses in which the cylinder is inserted into a complex environment.

Electronics Letters, 2006

A novel approach for obtaining small periodicity frequency selective surface (FSS) screens with e... more A novel approach for obtaining small periodicity frequency selective surface (FSS) screens with enhanced bandwidth performance is proposed. The issue of miniaturising FSS unit cells has gained extreme importance in recent metamaterials applications. To this end several procedures have been suggested in the literature. However, such procedures usually result in a bandwidth degradation as long as miniaturisation is improved. On the contrary, the bandwidth performance of the structures here presented is enhanced as the FSS periodicity gets smaller. Application of such structures to the synthesis of artificial magnetic conductors are also presented.

IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010)

ABSTRACT

2005 IEEE Antennas and Propagation Society International Symposium, 2005

This paper presents a technique to reconstruct the permittivity range profile of a layered medium... more This paper presents a technique to reconstruct the permittivity range profile of a layered medium using noisy backscattering data. Working on an ill-posed problem, inverse scattering normally provides either unstable or oversmoothed results. Our method tries to obtain an accurate reconstruction using a two-step genetic algorithm employing a regularization constraint with an explicit line process and a local deterministic optimization strategy.

2006 IEEE Antennas and Propagation Society International Symposium, 2006

This paper proposes a novel procedure to extract the wide-band propagation channel parameters, th... more This paper proposes a novel procedure to extract the wide-band propagation channel parameters, that employs a RT simulation carried out at different frequencies and followed by a proper processing of the simulated data. In particular, a RT-based tool suitable to be used for accurate and reliable site-planning in the framework of wide-band indoor wireless systems has been implemented, which shows

IEEE Antennas and Propagation Society International Symposium. Digest. Held in conjunction with: USNC/CNC/URSI North American Radio Sci. Meeting (Cat. No.03CH37450)

In this paper, a multilayered dielectric ~tructure backed by a perfectly electric conducting (PEC... more In this paper, a multilayered dielectric ~tructure backed by a perfectly electric conducting (PEC) ground plane is investigated for realizing high-impedance surfaces. There surfaces behave like a perfect mamelic conductor (PMC) at a certain frequency range. The inclusion of an FSS in lhe stmclure provides an additional degree of freedom which c m be exploited to obtain lhe desired frequency and angular performance. All the presented iolution~ are derived by using a genetic algorithm-based synthesis procedure. The genetic algorilhm (CA) resorts 10 an eleclromagnetic S O I Y C~ based on the Melhod of Momcnts (MOM) 10 describe the ~~a t t~r i n g bchavior of thc stillcfllre. In pa'li~lar. lhe CA delemines the permittivity and the thickness of each dielectric layer and the shape md the dimensions of the FSS screen. The synchesized SVUEIY~CS are discussed with panicular reference to Ihe frequency iesponie and to the robustnssi ofthe solulion with respect lo lhe angle of illumination.

IEEE Antennas and Propagation Society International Symposium (IEEE Cat. No.02CH37313)

... paid to the sampling interval A a : the discretization of a continuous spectrum generates fic... more ... paid to the sampling interval A a : the discretization of a continuous spectrum generates fictitious side replicas whose repetition period depends on ALY [1,2]. The ... We calculate 7, using fo=3Oo~z, O ~ , = O , D , = ~ , n=440 and Aa=32kln; n and Aa are obtained according to [1,2 ...

2010 IEEE Antennas and Propagation Society International Symposium, 2010

... Bianchi(1), Nunzia Fontana(1), Simone Genovesi(1), Agostino Monorchio(1), Andrea Vallecchi(2)... more ... Bianchi(1), Nunzia Fontana(1), Simone Genovesi(1), Agostino Monorchio(1), Andrea Vallecchi(2), Matteo Cerretelli(2), Mariano Linari(2), Guido Biffi Gentili(2) (1) Microwave and Radiation Laboratory, Dept. of Information Engineering, University of Pisa, Via Caruso 16, 56122 ...

2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014

A novel approach for the fast evaluation of the performance of a loaded antenna exploiting the sc... more A novel approach for the fast evaluation of the performance of a loaded antenna exploiting the scattering matrix properties is presented. Starting from the scattering matrix calculated by using a generic full-wave solver, it is shown how to obtain the frequency response of the antenna loaded with lumped series/parallel RLC elements, properly applying short/open circuits, without recurring to repetitive and time consuming full-wave simulations. The procedure is also able to evaluate the power dissipated on the resistive elements and hence the overall efficiency of the loaded antenna. As an example of the usefulness and reliability of the proposed approach, this fast solver has been used in conjunction with a genetic algorithm (GA) for synthesizing a loaded wideband antenna with a 20:1 bandwidth.

2014 International Conference on Electromagnetics in Advanced Applications (ICEAA), 2014

2009 IEEE Antennas and Propagation Society International Symposium, 2009

ABSTRACT

ABSTRACT Figure 1: The (a,b) simulation mode, (c,d) SoM B 1 fields and (e,f) worst-case SAR for t... more ABSTRACT Figure 1: The (a,b) simulation mode, (c,d) SoM B 1 fields and (e,f) worst-case SAR for the 60mm array. Figure 2: B 1 field strength vs. array length normalised for (a) transmit power and (b) worst-case 10g SAR. Discussion/Conclusion: SoM B 1 field intensity at the array centre increases as the array length is reduced, even for extremely short loops, due to reduced probe loading. However, shortening the array also increases worst-case 10g SAR, as loop capacitors come into close proximity to the head. Highest B 1 /SAR is given by the 120-210mm arrays; within this range the 120mm array generates highest B 1 /√(power). A 120mm array will now be built, using transformers to decouple neighbouring loops [4]. References: [1] Christ et al, PMB 55(2), 2010; [2] Van de Moortele et al, MRM 54(6), 2005; [3] Collins et al, ISMRM 2007; [4] Avdievich et al, MRM 62(1), 2009. Purpose/Introduction: Several clinical MRI/MRS applications require an ap-propriate design of the RF coil, in order to optimize the RF spatial distribution and sensitivity. As frequency increases, RF fields interact more strongly with the sample, rendering quasi-static approaches [1] less reliable for electromagnetic (EM) characterization. On the other hand, many different numerical methods can be employed, including the Finite-Difference Time-Domain (FDTD) [2,3], the Finite Element Methods (FEM) [4,5] and the Method of Moments (MoM) [6,7]. Those techniques allow EM characterization of low and UHF MR coil, each one having its own advantages and drawbacks. To the best of ourknowledge, a quantitative comparison of the computationperformances of the EM simulation methods is not available in a widefrequency range, making the methods selection difficult and,sometimes, not optimal. Subjects and Methods: The software CST MW uses the Finite Integration Technique (FIT) inthe time domain, this methodology being similar to the tra-ditionalFinite Difference but the integral form of Maxwell's equations is solved, instead of the differential form. Frequency-domain numerical simulations were used with the Method of Moment (MoM), implemented in the FEKO software and a Finite Element Method (FEM) developed by CST MW Studio. The quantitative comparison was made using two prototypes of surface coils, a Figure of Eight (Fo8) at 1.5 T [8] and a Dual Tuned 1H/31P coil, made with two concentric loops of radius 5 cm (1H) and 3.5 cm (31P), operating at 7T. The comparison comprised workbench measurements (S11/S12 parameters), electromagnetic fields, simulation time and allocated memory. Results:

Circuit analysis of frequency selective surfaces is reviewed with the aim to underline range of v... more Circuit analysis of frequency selective surfaces is reviewed with the aim to underline range of validity of different models and their advantages in terms of simplicity and physical insight. The circuit approach is based on an equivalent representation of the FSSs with series or shunt connections of inductances and capacitances. Dense non-resonant periodic surfaces (i.e.: grid or patch arrays) can be analyzed analytically by computing the values of inductors or capacitors via the homogenization theory. As the lattice period increases with respect to the operating wavelength or the element shape becomes resonant, a fully analytical circuital approach fails, in particular, in the presence of thin substrates. However, simple circuit approaches can still be employed by deriving lumped parameters values via a quick pre-processing and then generalizing them. The results are accurate up to the resonant frequency region of the element. By including an additional lumped element it is possible, taking into account the effect of the first high order Floquet harmonic. The multi-mode formulation is also able to catch the highly nonlinear response of FSS screens in the grating lobe region provided that the current profile of the element does not change significantly.

2014 IEEE RFID Technology and Applications Conference (RFID-TA), 2014

A periodic surface printed on a grounded dielectric slab is employed as a chipless RFID tag in or... more A periodic surface printed on a grounded dielectric slab is employed as a chipless RFID tag in order to realize a phase-only encoding. The variation of the length of a single loop in the unit cell is addressed to verify the possibility of encoding the information by exploiting the difference between the TE and TM phase response of the tag.

IEEE Antennas and Propagation Society Symposium, 2004., 2004

A novel procedure to calculatte the induced current densit on large gently undulated surfaces has... more A novel procedure to calculatte the induced current densit on large gently undulated surfaces has been presented. The method is based on the use of high-frequency derived basis functions, which also accounts for the undulation of the surface. By employing these basis functions in an integral equation procedure, electrically large problems can be handled in a computationally efficient and numerically rigorous manner, considering, at the same time, the random characteristics of the surface undulations.

ABSTRACT The evaluation of the local Specific Absorption Rate (local SAR) is a major concern in h... more ABSTRACT The evaluation of the local Specific Absorption Rate (local SAR) is a major concern in high field Magnetic Resonance (MR) systems. The investigation here presented is focused on the estimation of the Specific Absorption Rate in human head excited by a 7T surface coil. The aim of our work is to evaluate the maximum local SAR of the sample inside the scanner under realistic condition of use. The proposed methodology can be adopted to avoid the over-exposure of the body during the MR exam.

Microwave and Optical Technology Letters, 1994

A perturbatwe solution is described for determining the field scattered by a peeectly conducting ... more A perturbatwe solution is described for determining the field scattered by a peeectly conducting wedge with a crack or gap in one of its faces. The wedge is illuminated by a plane wave perpendicularly incident on its edge. 17ze gap aperture is modeled by an equivalent sueace impedance strip. Numerical results are presented to demonstrate the applicability of this perturbatwe technique.

Microwave and Optical Technology Letters, 2010

was taken as the power-handling capacity of the phase shifter, and the results are shown in Table... more was taken as the power-handling capacity of the phase shifter, and the results are shown in Table 1. As the PIN diodes used in our design had an instantaneous power-handling capacity of 34 dBm, the expected power-handling capacity of the phase shifter was 50.41 dBm. Table 1 shows that the peak powers of the phase shifter at 9, 9.5, and 10 GHz are all over 50.5 dBm, which is about 45 times of the power-handling capacity of the PIN diodes. 5. CONCLUSIONS The design of a 3-bit phase shifter with small size and high power-handling capacity based on using a single CRLH-TL unit cell has been presented. The phase shifter has a compact size and can provide a phase-shift range from 0 to 157.5 at a step 22.5 and operate in the frequency band from 9 to 10 GHz. Simulation and measurement results have shown that the phase shifter has low insertion losses of less than 1.3 dB and a low return loss of less than À15 dB across the operating frequency band. The maximum phase shift error is only þ4.5. It can handle the power 45 times higher than that handled by the PIN diodes used as switches in our design. 0 /18) of the AMC screen has been manufactured and tested. Measurements confirmed a remarkable improvement in spiral cross polarization discrimination (XPD) in correspondence of the two AMC resonances. The dual-band behavior of the AMC could be exploited in applications where multifrequency operation is required. The low profile structure is characterized by an overall thickness of 1.

IEICE Transactions on Electronics, 2007

A major step in the numerical solution of electromagnetic scattering problems involves the comput... more A major step in the numerical solution of electromagnetic scattering problems involves the computation of the convolution based reaction integrals. In this paper a procedure based on the analytical Fourier transform is introduced which allows us to calculate the convolution-based reaction integrals in the spectral domain without evaluating any convolution products directly. A numerical evaluation of the computational cost is presented to show the efficiency of the method when handling electrically large problems.