Pietro Giannelli

An Integrated Acousto/Ultrasonic Structural Health Monitoring System for Composite Pressure Vessels

This paper describes the implementation of a structural health monitoring (SHM) method for mechanical components and structures in composite materials with a focus on carbon-fiber-overwrapped pressure vessels (COPVs) used in the aerospace industry. Two flex arrays of polyvinylidene fluoride (PVDF) interdigital transducers have been designed, realized, and mounted on the COPV to generate guided Lamb waves (mode A0) for damage assessment. We developed a custom electronic instrument capable of performing two functions using the same transducers: passive-mode detection of impacts and active-mode damage assessment using Lamb waves. The impact detection is based on an accurate evaluation of the time of arrival and was successfully tested with low-velocity impacts (7 and 30 J). Damage detection and progression is based on the calculation of a damage index matrix which compares a set of signals acquired from the transducers with a baseline. This paper also investigates the advantage of tuning the active-mode frequency to obtain the maximum transducer response in the presence of structural variations of the specimen, and therefore, the highest sensitivity to damage.

A Novel Differential Time-of-Arrival Estimation Technique for Impact Localization on Carbon Fiber Laminate Sheets

Composite material structures are commonly used in many industrial sectors (aerospace, automotive, transportation), and can operate in harsh environments where impacts with other parts or debris may cause critical safety and functionality issues. This work presents a method for improving the accuracy of impact position determination using acoustic source triangulation schemes based on the data collected by piezoelectric sensors attached to the structure. A novel approach is used to estimate the Differential Time-of-Arrival (DToA) between the impact response signals collected by a triplet of sensors, overcoming the limitations of classical methods that rely on amplitude thresholds calibrated for a specific sensor type. An experimental evaluation of the proposed technique was performed with specially made circular piezopolymer (PVDF) sensors designed for Structural Health Monitoring (SHM) applications, and compared with commercial piezoelectric SHM sensors of similar dimensions. Test impacts at low energies from 35 mJ to 600 mJ were generated in a laboratory by free-falling metal spheres on a 500 mm × 500 mm × 1.25 mm quasi-isotropic Carbon Fiber Reinforced Polymer (CFRP) laminate plate. From the analysis of many impact signals, the resulting localization error was improved for all types of sensors and, in particular, for the circular PVDF sensor an average error of 20.3 mm and a standard deviation of 8.9 mm was obtained.

Multifunctional Piezopolymer Film Transducer for Structural Health Monitoring Applications

This paper describes the design of a multifunctional transducer for structural health monitoring (SHM) applications that integrates an interdigital piezoelectric transducer, used for Lamb wave generation and reception, a circular piezoelectric sensor, used for the detection and localization of low-velocity impacts, and a resistance temperature detector (RTD) in a single device. The three elements were fabricated on the same metallized piezoelectric polyvinylidene fluoride (PVDF) film using a laser etching process. Characterization of the resulting device proved the advantages of having different transducers on the same device, providing information useful to implement advanced SHM algorithms. Testing of the RTD highlighted some criticalities of the metallized PVDF film that prevented accurate temperature measurements due to spurious behavior under strain.

The ZetaBoost: A step-up DC/DC topology derived from the Zeta converter

This work investigates a step-up topology derived from the Zeta converter: the ZetaBoost. A ZetaBoost converter design for consumer applications is presented and its steady-state performances are compared to a classical Boost converter with the support of computer simulations and measurements. The results presented include the efficiency and output voltage ripple.

A survey of electromagnetic characteristics of soils in the Donbass region (Ukraine) for evaluation of the applicability of GPR and MD for landmine detection

In order to design holographic and impulse GPRs, as well as metal detector (MD) sensors for humanitarian demining in the Donbass conflict zone, we have compiled a listing of the AP and AT mines that have been confirmed in use in Donbass, and their dimensions and construction. Just as importantly, we have attempted, from existing literature (since it is an active war zone), to characterize the specific soils in this region in order to understand the physical property contrasts between mine casings/components and the soils in which they may be buried, as well as the propagation characteristics of radar signals in these soils. We conclude that MD should be generally effective for locating Donbass mines, and GPRs operating near the frequency of 2GHz should provide sufficient penetration for detection and, simultaneously, sufficient resolution to assist with discrimination of mines from clutter. As is common in GPR applications, the main limiting factor may be soil moisture content, so operations may be restricted to dry periods or seasons. Field measurements are scheduled to confirm the values from the literature.

Multichannel airborne ultrasonic ranging system based on the Piccolo C2000 MCU

The combination of different characteristics of airborne ultrasonic transducers for ranging applications opens up new applications for autonomous navigation systems in robotics. The features of a Piccolo C2000 MCU are suitable for the design of a ranging system with four channels. Each channel has different operating range and accuracy depending on the transducer characteristics and the implemented ranging technique. This paper presents the system architecture and the experimental results obtained with transducers operating at 40kHz, 100kHz and 300kHz.

Analysis of Errors in the Estimation of Impact Positions in Plate-Like Structure through the Triangulation Formula by Piezoelectric Sensors Monitoring

The structural health monitoring (SHM) of critical structures is a complex task that involves the use of different sensors that are also aimed at the identification of the location of the impact point using ultrasonic sensors. For the evaluation of the impact position, reference is often made to the well-known triangulation method. This method requires the estimation of the differential time of arrival (DToA) and the group velocity of the Lamb waves propagating into a plate-like structure: the uncertainty of these two parameters is taken into consideration as main cause of localization error. The work proposes a simple laboratory procedure based on a set-up with a pair of sensors that are symmetrically placed with respect to the impact point, to estimate the uncertainty of the DToA and the propagation velocity estimates. According to a theoretical analysis of the error for the impact position, the experimental uncertainties of DToA and the propagation velocity are used to estimate the overall limit of the SHM system for the impact positioning. Because the error for the DToA estimate depends also on the adopted signal processing, three common methods are selected and compared: the threshold, the correlation method, and a likelihood algorithm. Finally, the analysis of the positioning error using multisensory configuration is reported as useful for the design of the SHM system.

A reduced output ripple step-up DC-DC converter for automotive LED lighting

This works presents the design and test of a switching power supply intended for powering LED tail lights in automotive applications. The design is proposed as an alternative to an existing Boost reference design, and is based on a different step-up topology, the ZetaBoost, with the objective of reducing the output ripple, and therefore ease the compliance with automotive electromagnetic interference regulations.