In this paper we summarize the hardware and software issues of impedance-based structural health moni- toring based on piezoelectric materials. The basic concept of the method is to use high-frequency structural excitations to monitor the local area of a structure for changes in structural impedance that would indicate imminent damage. A brief overview of research work on experimental and theoretical stud- ies on various structures is considered and several research papers on these topics are cited. This paper concludes with a discussion of future research areas and path forward. Piezoelectric materials acting in the "direct" manner pro- duce an electrical charge when stressed mechanically. Con- versely, a mechanical strain is produced when an electrical field is applied. The direct piezoelectric effect has often been used in sensors such as piezoelectric accelerometers. With the converse effect, piezoelectric materials apply local- ized strains and directly influence the dynamic response of the structural elements when either embedded or surface bonded into a structure. Piezoelectric materials have been widely used in structural dynamics applications because they are lightweight, robust, inexpensive, and come in a variety of forms ranging from thin rectangular patches to complex shapes being used in microelectromechanical systems (MEMS) fabrications. The applications of piezoelectric mate- rials in structural dynamics are too numerous to mention and are detailed in the literature (Niezrecki et al., 2001; Chopra, 2002). The purpose of this paper is to explore the importance and effectiveness of impedance-based structural health mon- itoring from both hardware and software standpoints. Imped- ance-based structural health monitoring techniques have been developed as a promising tool for real-time structural dam- age assessment, and are considered as a new non-destructive evaluation (NDE) method. A key aspect of impedance-based structural health monitoring is the use of piezoceramic (PZT) materials as collocated sensors and actuators. The basis of this active sensing technology is the energy transfer between the actuator and its host mechanical system. It has been shown that the electrical impedance of the PZT material can be directly related to the mechanical impedance of a host structural component where the PZT patch is attached. Uti- lizing the same material for both actuation and sensing not only reduces the number of sensors and actuators, but also reduces the electrical wiring and associated hardware. Fur- thermore, the size and weight of the PZT patch are negligible compared to those of the host structures so that its attach- ment to the structure introduces no impact on dynamic char- acteristics of the structure. A typical deployment of a PZT on a structure being monitored is shown in Figure 1. The first part of this paper (Sections 2 and 3) deals with the theoretical background and design considerations of the impedance-based structural health monitoring. The signal processing of the impedance method is outlined in Section 4. In Section 5, experimental studies using the impedance approaches are summarized and related previous works are listed. Section 6 presents a brief comparison of the imped- ance method with other NDE approaches and, finally, sev- eral future issues are outlined in Section 7. 2. Theoretical Background

Overview of Piezoelectric Impedance-Based Health Monitoring and Path Forward

This paper presents experimental evidence on the use of the impedance-based health-monitoring technique on components typical of civil structures. The basic principle behind this technique is to utilize high-frequency structural excitations (typically >30 kHz) through a surface-bonded piezoelectric sensor/actuator to detect changes in structural point impedance due to the presence of damage. Real-time damage detection on composite-reinforced concrete walls was investigated and the capability of this technique to detect imminent damage, well in advance of actual failure, was confirmed. Concepts that directly applied to this technique itself, such as effects of boundary condition changes and the effects of temperature changes, were also investigated. Experimental investigations were carried out on a 1/4-scale bridge element and a pipe joint commonly found in civil structures, to verify robustness of the technique to changes in environmental conditions. Data collected from the tests demonstrate the capabilit...

Impedance-based health monitoring of civil structural components

Piezoelectric nanofibers for energy scavenging applications

Mechanical behavior of high-entropy alloys

Damage detection with spatial wavelets

This paper presents a frequency domain impedance-signature-based technique for health monitoring of an assembled truss structure. Unlike conventional modal analysis approaches, the technique uses piezoceramic (PZT) elements as integrated sensor-actuators for acquisition of signature pattern of the truss. The concept of the localization of sensing/actuation area for damage detection of an assembled structure is presented for the first time. Through a PZT patch bonded to a truss node and the measurement of its electric admittance, which is coupled with the mechanical impedance of the truss, the signature pattern of a truss is monitored. The admittance of a truss in question is compared with that of the original healthy truss. Statistic algorithm is then applied to extract a damage index of the truss based on the signature pattern difference. Experimental proof that over a selected band, the detection range of a bonded PZT sensor on a truss is highly constrained to its immediate neighborhood is presented. This characteristic allows accurate determination of the damage location in a complex real-world structure with a minimum mathematical modeling and numerical computation.

Truss Structure Integrity Identification Using PZT Sensor-Actuator

An active material system may be generalized as an electro-mechanical network because of the incorporation of actuators (electrically driven) and sensors (that convert mechanical energy into electrical energy). An investigation of the coupled electrical and mechanical aspects of an active material system will help reveal some of its most important characteristics, in particular regarding energy conversion and consumption issues. The research performed in the area of the electro-mechanical impedance (EMI) modeling of active material systems is herein summarized. In this paper, a generic EMI model to describe the electro-mechanical network behavior (time domain and frequency domain) of active material systems will be discussed. The focus of the discussion will be on the methodology and basic components of the EMI modeling technique and its application to assist in the design of efficient active control structures. This paper will first introduce the basic concept of the EMI modeling and its general utility in the area of active material systems. The methodology of the EMI modeling technique will be illustrated using an example of PZT actuator-driven mechanical systems. The basic components of the EMI modeling, including the electro-mechanics of induced strain actuators, the dynamic analysis of active material systems, and the electrical power consumption and requirements, will be discussed. Finally, some applications of the EMI modeling approach, including the determination of the optimal actuator locations, modal analysis using collocated PZT actuator - sensors, and the prediction of radiated acoustic power, will be presented.

https://iopscience.iop.org/article/10.1088/0964-1726/5/2/006/pdf

Electro-mechanical impedance modeling of active material systems

Ultra-high temperature multi-component shape memory alloys

This paper presents a new technique for acquiring structural Frequency Response Function (FRF) via measurement of electric impedance of a piezoceramic (PZT) patch bonded to a structure. The PZT patch, when driven by an ac voltage, behaves like an actuator as well as a sensor through its interaction with the host structure. The electric impedance thus obtained carries the information of the structural signature. Through a generic multi-input model governing the electromechanical interaction of PZT actuators with structure, the structural FRF can be extracted from measured electric impedance. Both the point FRF of single location and the transfer FRF between two locations on a structure can be obtained. The concept of measuring the "coupled impedance" of two PZT sensors is presented and used to derive the transfer FRF of the structure. The effect of actuator stiffening to the structure and its removal from the measured FRF is addressed. The technique is proven to be an efficient and low cost approach to acquiring structural FRF. Because of the negligible mass load and stiffening effect of the solid state transducer, the approach is more appropriate for the system identification of light and flexible structures.

Fanping Sun

Papers

Truss Structure Integrity Identification Using PZT Sensor-Actuator

Electro-mechanical impedance modeling of active material systems

Ultra-high temperature multi-component shape memory alloys

Structural frequency response function acquisition via electric impedance measurement of surface-bonded piezoelectric sensor /actuator

On the deformation response and cyclic stability of Ni50Ti35Hf15 high temperature shape memory alloy wires