Pietro Burrascano

Coded waveforms for optimised air-coupled ultrasonic nondestructive evaluation

This paper investigates various types of coded waveforms that could be used for air-coupled ultrasound, using a pulse compression approach to signal processing. These are needed because of the low signal-to-noise ratios that are found in many air-coupled ultrasonic nondestructive evaluation measurements, due to the large acoustic mismatch between air and many solid materials. The various waveforms, including both swept-frequency signals and those with binary modulation, are described, and their performance in the presence of noise is compared. It is shown that the optimum choice of modulation signal depends on the bandwidth available and the type of measurement being made.

Exploiting Pseudorandom Sequences to Enhance Noise Immunity for Air-Coupled Ultrasonic Nondestructive Testing

The application of a pulse-compression procedure based on pseudorandom m-sequences to air-coupled ultrasonic nondestructive testing is presented. The signal-to-noise ratio enhancement assured by this technique is theoretically analyzed and experimentally verified, particularly focusing on the positive effect of the procedure to reduce quantization noise. The possibility of faithfully reconstructing signals whose amplitudes are lower than the quantization step of the analog-to-digital converter (ADC) board is analyzed theoretically and experimentally verified.

Skyrmion based microwave detectors and harvesting

Magnetic skyrmions are topologically protected states that are very promising for the design of the next generation of ultra-low-power electronic devices. In this letter, we propose a magnetic tunnel junction based spin-transfer torque diode with a magnetic skyrmion as ground state and a perpendicular polarizer patterned as nano-contact for a local injection of the current. The key result is the possibility to achieve sensitivities (i.e., detection voltage over input microwave power) larger than 2000 V/W for optimized contact diameters. We also pointed out that large enough voltage controlled magnetocrystalline anisotropy could significantly improve the sensitivity. Our results can be very useful for the identification of a class of spin-torque diodes with a non-uniform ground state and to understand the fundamental physics of the skyrmion dynamical properties.

Ultrasonic Nondestructive Evaluation Systems: Industrial Application Issues

This book deals with a number of fundamental issues related to the practical implementation of ultrasonic NDT techniques in an industrial environment. The book discusses advanced academic research results and their application to industrial procedures. The text covers the choice and generation of the signals energizing the system to probe position optimization, from quality assessment evaluation to tomographic inversion. With a focus to deepen a number of fundamental aspects involved in the specific objective of designing and developing an ultrasonic imaging system for nondestructive testing, aimed to automatically classify the entire production of an industrial production line, targeted to the field of precision mechanics. The contents of this book is the result of the common effort of six University Research Groups that focused their research activities for two years on this specific objective, working in direct conjunction with primary industrial firms, in a research project funded by the Italian government as a Strategic Research Project.

Numerical modeling for the localization and the assessment of electromagnetic field sources

In this work, we present a possible approach to electromagnetic source localization using a hybrid blind separation-minimum search inversion algorithm. The total electrical field versus time, emitted by the working antennas located at different and unknown geographical positions, is used, via a suitable blind signal processing technique based on neural networks, to reconstruct each separate contribute. When the emitted electric signals have been separated for each emitting antenna, the unknown locations of the antennas are determined with a minimum-search numerical technique.

Exploiting Non-Linear Chirp and sparse deconvolution to enhance the performance of pulse-compression ultrasonic NDT

A pulse-compression procedure based on Non-Linear Chirp for Ultrasonic Non Destructive Testing is presented. Non-Linear Chirp signals can be tailored to reproduce any desired continuous spectrum. Here, such capability is exploited to take into account the features of the specific hardware set-up in use, and particularly to adapt the excitation signal to the probes. An application of the proposed procedure to Air-Coupled Ultrasound Imaging is also presented. In order to enhance the imaging resolution, L1-norm Total Variation deconvolution is exploited and compared with standard L2-norm Wiener deconvolution. Although the usage of Air-Coupled probes entails a high attenuation of the ultrasonic signals due to transmission in air and reflections at the air-sample interface, the experimental results show that the combination of Pulse Compression technique and of advanced signal processing guarantees the effectiveness of the inspection.

Galois sequences in the non-destructive evaluation of metallic materials

A new eddy currents non-destructive evaluation technique for the investigation of deep defects is presented. The method joins the favourable features of the pulsed eddy currents approach with the peculiar properties of the Galois sequences to extend the detection area down to large depths. The proposed method has been successfully tested on a benchmark; the experimental results have been compared with the standard pulsed method and with numerical simulations. The comparisons confirmed the accuracy of the method and its effectiveness in allowing a significant improvement in deep defect detection.

Numerical Identification Procedure for a Phenomenological Vector Hysteresis Model

This paper presents an identification procedure for a phenomenological vector hysteresis model, called the Della Torre, Pinzaglia and Cardelli Model, introduced as a general hysteresis vector model for magnetic materials. The identification of the distribution function is approached by using the classical deterministic inverse problem theory and a suitable regularization procedure. A discussion on the presented method and an identification process for a sample of commercial Fe-Si magnetic steel are provided.

Noise-Like Sequences to Resonant Excite the Writing of a Universal Memory Based on Spin-Transfer-Torque MRAM

The effects of a noise-like weak signal in the resonant switching of the magnetization driven by spin transfer torque have been systematically studied by means of micromagnetic simulations in both in-plane spin valves and out-of-plane magnetic tunnel junctions. The use of a noise-like resonant excitation allows the overpassing of some critical points compared to the traditional microwave assisted switching. In particular, the application of binary spreading sequences (BSS) does not require the precise knowledge of the resonant frequency and of the optimum relative phase, allowing the use of the same resonant excitation for all the devices in a matrix of memory cells, even if small variations of the physical and geometrical parameters are present. In addition, we also found that in spin valves the switching probabilities close to 100% can be achieved with a smaller current pulse, and in magnetic tunnel junctions a significant energy saving can be obtained.

A pruning technique maximizing generalization

The paper proposes an estimator of the relevance of each weight connection on generalization which relies on a probabilistic description of the training phase: based on the above estimator, a pruning technique is derived.