Roberto Mendes Finzi Neto

A low-cost electromechanical impedance-based SHM architecture for multiplexed piezoceramic actuators

The electromechanical impedance (EMI) method has been regarded as a promising tool for structural health monitoring (SHM) in real time. Usually, massive, high-cost, single-channel impedance analyzers are used to process the time domain data, aiming at obtaining the complex, frequency-dependent, EMI functions, from which features related to the presence, position, and extent of damage can be extracted. However, for large structures, it is desirable to deploy an array of piezoelectric transducers over the area to be monitored and interrogate these transducers successively so as to increase the probability of successful detection of damage in an early phase. In this context, a miniaturized, low-cost, highly expandable SHM architecture for monitoring an array of multiplexed piezoelectric transducers is proposed. Each logical block of the proposed architecture is presented in detail. The proposed architecture does not use costly fast Fourier transform analyzers/algorithms nor requires a digital computer for processing. A personal computer is only necessary for user interfacing. It has been verified that the system can work for frequencies ranging from 0 to 400 kHz with high accuracy and stability. A prototype using inexpensive integrated circuits and a digital signal processor was built and tested for two different types of structures: an aluminum beam and an aircraft aluminum panel. Simulated damages were introduced to each structure and the detection performance of the prototype was tested. The actual prototype uses a universal serial bus connection to communicate with a personal computer; however, a WiFi® connection is also available.

A high-power-factor half-bridge doubler boost converter without commutation losses

This paper proposes a high-power-factor half-bridge doubler boost converter without commutation losses, which provides high output voltages, i.e., from 600 to 900 V. The voltages across the semiconductor devices are low and approximately equal to the output voltage, as doubled output voltages and reduced high-frequency ripple can be achieved. A detailed mathematical analysis concerning its operation is presented, and simulation and experimental results describe the converter performance.

Probabilistic Neural Network and Fuzzy Cluster Analysis Methods Applied to Impedance-Based SHM for Damage Classification

Impedance-based structural health monitoring technique is performed by measuring the variation of the electromechanical impedance of the structure caused by the presence of damage. The impedance signals are collected from patches of piezoelectric material bonded on the surface of the structure (or embedded). Through these piezoceramic sensor-actuators, the electromechanical impedance, which is directly related to the mechanical impedance of the structure, is obtained. Based on the variation of the impedance signals, the presence of damage can be detected. A particular damage metric is used to quantify the damage. Distinguishing damage groups from a universe containing different types of damage is a major challenge in structural health monitoring. There are several types of failures that can occur in a given structure, such as cracks, fissures, loss of mechanical components (e.g., rivets), corrosion, and wear. It is important to characterize each type of damage from the impedance signals considered. In the present paper, probabilistic neural network and fuzzy cluster analysis methods are used for identification, localization, and classification of two types of damage, namely, cracks and rivet losses. The results show that probabilistic neural network and fuzzy cluster analysis methods are useful for identification, localization, and classification of these types of damage.

A soft-switched current-controlled converter for induction machine drives

The paper proposes a current controlled inverter operating in zero voltage switching (ZVS) mode for an induction machine drive. Operation with no voltage stress in the DC link bus is achieved. Together with the soft switching operation, a fixed frequency bang-bang current control technique is also implemented to allow for an accurate shaping of sinusoidal currents to feed the motor. As a result, a ripple free torque profile in steady state operation is achieved. With the soft switching technique it is possible to operate conventional IGBTs at 40 kHz. A detailed analysis of the circuit operation is presented. The feasibility of the proposed scheme is experimentally verified on a prototype.

Architecture of a remote impedance-based structural health monitoring system for aircraft applications

The essence of structural health monitoring (SHM) is to develop systems based on nondestructive inspection (NDI) technologies for continuous monitoring, inspection and detection of structural damages. A new architecture of a remote SHM system based on Electromechanical Impedance (EMI) measures is described in the present contribution. The proposed environment is employed to automatically monitor the structural integrity of aircrafts and is composed by sensor networks, a signal conditioning system, a data acquisition hardware and a data processing system. The obtained results allow the accomplishment of structural condition-based maintenance strategies, in opposite to those based only on the usage time of the equipment. This approach increases the operational capacity of the structure without compromising the security of the flights. As the environment continually checks for the first signs of damage, possibly reducing or eliminating scheduled aircraft inspections, it could significantly decrease maintenance and repair expenses. Furthermore, the usage of this system allows the creation of a historical database of the aircrafts structural integrity, making possible the incremental development of a Damage Prognosis System (DPS). This work presents the proposed architecture and a set of experiments that were conducted in a representative aircraft structure (aircraft window) to demonstrate the effectiveness of the proposed system.

Solid state switching and signal conditioning system for Structural Health Monitoring based on piezoelectric sensors actuators

The Structural Health Monitoring - SHM method based on electrical impedance has been developed as a promising tool for structure failure identification in real time and is considered a novel non-destructive evaluation method. The piezoelectric - PZT impedance can be directly associated to the structures mechanical impedance where de PZT is bonded. Assuming that the mechanical PZT properties do not change over the monitoring time, the electrical PZT impedance can be used for monitoring structural health. The use of each PZT as both sensor and actuator reduces the total number of sensor and wires connecting them to the switching circuit. The technique consists in obtaining Frequency Response Functions - FRF, with the related signal modification, periodically. Modifications in the FRF of each PZT would indicate structural changes and, therefore, a possible failure. The required number of PZTs will be determined by the dimensions of the monitored structure and the precision required for locating a possible failure. To obtain the FRF of the entire monitored structure it is used a switching and signal conditioning system that continuously activate and deactivate each PZT. This paper proposes a solid state, low power, small sized and low signal distortion switching system. The system is quite modular and each module can manage 16 PZTs. It is possible to expand the sensing net by interconnecting a non limited number of modules. Descriptions of the working principles, circuits used and experimental results are presented.

Fault Detection in a Rotating Machine by Using the Electromechanical Impedance Method

Shaft crack detection is a very serious problem and machines that are suspected of having a crack should be carefully and continuously monitored. The importance attributed to this problem is addressed to the serious consequences when cracks are not early identified in rotating systems. Although there are no statistical studies that account for the exact dimension of the damage caused by cracks in rotating shafts, estimations reveal that approximately

System for Structural Health Monitoring based on piezoelectric sensors/actuators

1 billion were expended in repairs, exchanges, loss of production, etc., in electrical industries, nuclear, and conventional, since the 1970s. Significant research effort has been directed in recent years to online monitoring techniques, i.e., based on vibration signals measured during rotor operation. However, most of these techniques are able to only detect deep cracks. In this context, the aim of this paper relies on the detection of incipient faults in rotating shafts by using the so-called electromechanical impedance method. Basically, this structural health monitoring technique—SHM monitors changes in the electric impedance of piezoelectric transducers bonded to (or embedded into) the host structure, through specific mathematic equations, the so-called damage metrics, to detect damage. This is possible since that the electrical impedance of the transducer is directly related to the mechanical impedance of the structure. Previously, successful experimental tests were performed in a horizontal rotor supported by roller bearings in which PZT patches were bonded along the rotor shaft. Although successful, the use of rigid PZT patches seems to be disadvantageous. Aiming at overcoming the drawbacks previously faced, in this contribution flexible transducers (MFC—macro fiber composites) are bonded along the shaft. A small mass was added on the shaft to simulate a fault condition (small structural modification). The technique was validated for the rotor under operation.

Damage Detection Integrating ISHM and LWSHM Techniques

The Structural Health Monitoring - SHM method based on electrical impedance has been developed as a promising tool for structure failure identification in real time and is considered a novel non-destructive evaluation method. The piezoelectric - PZT impedance can be directly associated to the structures mechanical impedance where de PZT is bonded. Assuming that the mechanical PZT properties do not change over the monitoring time, the electrical PZT impedance can be used for monitoring structural health. The use of each PZT as both sensor and actuator reduces the total number of sensor and wires connecting them to the switching circuit. The technique consists in obtaining Frequency Response Functions - FRF, with the related signal modification, periodically. Modifications in the FRF of each PZT would indicate structural changes and, therefore, a possible failure. The required number of PZTs will be determined by the dimensions of the monitored structure and the precision required for locating a possible failure. To obtain the FRF of the entire monitored structure it is used a switching and signal conditioning system that continuously activate and deactivate each PZT. This paper proposes a solid state, low power, small sized and low signal distortion switching system. The system is quite modular and each module can manage 16 PZTs. It is possible to expand the sensing net by interconnecting a non limited number of modules. Descriptions of the working principles, circuits used and experimental results are presented.

Real-time structural health monitoring of fatigue crack on aluminum beam using an impedance-based portable device

Currently, structural health monitoring (SHM) represents one of the main areas of interest in engineering, being applied both for maintenance cost reduction and operational safety. In this contribution, a hybrid SHM system is proposed as a complementary methodology for the damage diagnosis of a typical aeronautical material panel (aeronautical aluminum plate 2024-T3), through the integration of two SHM techniques, namely the electromechanical impedance technique and the Lamb waves. For the diagnosis, a damage metric extracted from the impedance signatures of the structure was used in conjunction with an algorithm for localization of the damage by considering Lamb waves. In addition, temperature compensation techniques were systematically employed to avoid false diagnoses and a statistical model was developed to establish threshold indices according to a predefined confidence level. Thus, this work presents an evaluation of the sensitivity of the proposed techniques, considering a success rate. Finally, the results show the great potential for the integration of the two techniques together with statistical approach.