Performance of parallel FDTD method for shared- and distributed-memory architectures: Application tobioelectromagnetics.

This work provides an in-depth computational performance study of the parallel finite-difference time-domain (FDTD) method. The parallelization is done at various levels including: shared- (OpenMP) and distributed- (MPI) memory paradigms and vectorization on three different architectures: Intel's Knights Landing, Skylake and ARM's Cavium ThunderX2. This study contributes to prove, in a systematic manner, the well-established claim within the Computational Electromagnetic community, that the main factor limiting FDTD performance, in realistic problems, is the memory bandwidth. Consequently a memory bandwidth threshold can be assessed depending on the problem size in order to attain optimal performance. Finally, the results of this study have been used to optimize the workload balancing of simulation of a bioelectromagnetic problem consisting in the exposure of a human model to a reverberation chamber-like environment.

Experimental and numeric investigation about electromagnetic interference between implantable cardiac pacemaker and magnetic fields at power line frequency.

The present contribute describes the investigation about the implantable pacemaker (PM) immunity against high level magnetic interfering fields at 50 Hz that a pacemaker wearer could find in his working environment. To this purpose, a test bench has been set up based on a Helmholtz coil for producing extremely low frequency (ELF) magnetic fields and a heart simulator rightly fed by electric signals that simulate atrium and ventricle signals. A widely diffused PM has been tested, under different operation modes and configurations, for both continuous interfering waves (CW) and variously pulsed interfering waves (PW). Pertaining the obtained results, high levels of CW field, only in unipolar mode, produce a behaviour called 'asynchronous mode' (not dangerous). For PW fields, under particular and rare conditions, the complete inhibition occurred (the most dangerous effect for PM wearer). In order to validate experimental results, a numerical 3-D model has been developed to simulate the whole bench system formed by Helmholtz coil, human trunk, pacemaker case and its electric leads. In this model the electromagnetic problem is solved by reconstructing the inhomogeneous bench system associating the relative values of conductivity to each cubic cell in which the whole system is discretized. Application of Maxwell's equations in their integral form has allowed to obtain a 3-D electrical network, whose solution gives the current density distribution inside the heart simulator.

A realistic model for the analysis of heart magnetic stimulation.

The aim of the paper is the development of an accurate numerical model to compute the current density flowing through the heart of a virtual human body, and induced by an external electric or magnetic excitation. The model has been experimentally validated and then applied to investigate the main characteristics of the heart magnetic stimulation. This has been carried out by comparing the current density induced in the cardiac region by an external magnetic pulse with the corresponding quantity due to the more traditional electric source. Magnetic stimulation is studied because it offers some advantages: in fact, compared with the electrical stimulation, this technique is contactless and might allow the stimulation of a dressed patient. The design constraint of the whole system is represented by the current density, whose waveform and intensity are a compromise between the strength of the magnetic induction field and the pulse rise time.