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Piezoelectric materials exhibit high electromechanical coupling that allows them to both generate an electrical signal when strained and, conversely, to produce a strain under an applied electric field. This coupling has led to the use of these materials for a variety of sensing and actuation purposes. One unique application of these materials is their use as self-sensing actuators where both the sensing and actuation functions are performed by a single patch of material. Since the actuation and sensing voltages both exist simultaneously in the piezoelectric material, a specially designed electric circuit, referred to as a bridge circuit, is required to realize the concept. Configuration of the material in this manner is advantageous for control systems due to the enhanced stability associated when collocated control is applied. While certain advantages result from this type of system, precise equilibrium of the bridge circuit is required to achieve stability. This equilibrium is easy to achieve in theory, but difficult in practice due to the thermal dependence of the piezoelectric material's dielectric constant. This study will investigate a novel method of accounting for these changes through the use of thermal switches to passively adjust the bridge circuit and maintain a balanced state. The proposed concept will be theoretically modeled and simulated in a vibration control application to identify the thermal range for stability with and without the array of switches. It will be shown that, through the use of nine thermal switches, the stable operating range can be increased by 95 °C while maintaining vibration control performance.

C ORROSION is an extremely costly problem for industries and business sectors throughout the world and results in severe economic impact. In 1998, Congress funded the Department of Transportation and the Federal Highway Administration to estimate the total cost of corrosion on theU.S. economy and provide corrosion prevention guidelines. The final results of the survey estimated the extrapolated total direct corrosion cost to be $278 billion per year, which is 3.14%of the gross domestic product in theUnited States [1]. In 1996, the U.S. spent $1.7 billion on commercial aircraft maintenance and lost $0.3 billion due to corrosion downtime [2]. The “find it and fix it” maintenance practices of the airline industry are costly and, in some cases, inadequate. The present note will focus on identifying a detection method for the galvanic type of corrosion that plagues aircraft. Many techniques exist for detecting corrosion in aircraft; however, these methods are typically inadequate due to the intrinsic human error present and are difficult and time-intensive to implement. Two general categories of corrosion monitoring techniques exist, nondestructive evaluation (NDE) and structural health monitoring (SHM). NDEmethods include techniques such as visual, eddy current, ultrasonics, electrochemical impedance spectroscopy, color visual imaging, radiography, and infrared imaging [3]. The second class of detection is SHM and is typically superior due to the automated nature of the sensing system. Examples of SHM systems used in aircraft include the monitoring of pH and humidity, acoustic emissions, ion concentration, and chemical potential detectors. The present study will provide results on a series of tests performed using piezoelectric-based impedance techniques, which are a newer and less developed method of performing SHM. These methods use the electromechanical coupling present in piezoelectric materials to determinewhen structural changes have occurred.When the piezoelectric material is bonded to the structure, its electrical impedance is coupled to themechanical impedance (a function of the mass, stiffness, and damping) of the structure, providing a means for characterizing it. As damage occurs or progresses, the electrical impedance measured from the piezoelectric materials shifts, which can be quantified using statistical methods, providing a method of measuring the damage present. For a detailed review of the impedance method and it application see Park et al. [4] However, the ability to use this technique to measure the small changes associated with the onset of corrosion has not been identified. This note will experimentally evaluate the use of piezoelectric materials in conjunction with the piezoelectric-based impedance method to detect, locate, and quantify precrack surface corrosion damage. The impedance variations caused by changes in corrosion location, pit depth, and surface coverage will be correlated to the damage metric, which is calculated from the measured impedance signatures.

With the recent advances in wireless technology and low power electronics the idea of capturing the ambient energy surrounding a system and using it to provide electrical power to devices that do not rely on external power supplies has received a significant amount of attention. Much of this attention has been aimed at the use of piezoelectric materials to capture ambient vibrations. However, the energy generated by such materials is far too small to directly power most of the electronic devices. Therefore, in the present study a Seebeck heat pump is used to convert the ambient thermal gradient generated by solar radiation and waste heat into usable electrical energy. To increase the amount of thermal radiation captured by the power harvesting device, the hot side of the thermoelectric generator is placed in a small greenhouse, while the cold side is secured against a thermal sink, such as a highway bridge. The power generated by the thermoelectric device is shown to be substantially greater than that produced by piezoelectric materials and the ability to recharge a discharged battery is demonstrated. This research focuses on the use of thermal electric generators in a passive configuration where only conduction is used to remove heat from the device. The majority of previous studies have implemented convective heat transfer to increase power output and have only reported gross energy production. The results show that thermal electric materials when used in a passive fashion can form effective power sources with the ability to quickly recharge discharged batteries.

Self-sensing actuation allows a single piezoelectric (PZT) element to be simultaneously used as both a sensor and an actuator. A specially designed electric circuit, referred to as a bridge circuit, is required to realize the concept. However, precise equilibrium of the bridge circuit is extremely difficult to obtain because of the continuous changes in environmental conditions. In this study, the effects of an unbalanced bridge circuit are analytically and experimentally evaluated in an attempt to quantify the variations in the PZT capacitance in terms of performances in vibration testing and control. Once the dynamic characteristics of self-sensing actuation are identified and understood, methods for improving the system’s performance are developed by utilizing capacitors in series and in parallel with the PZT patch. The analytical and experimental results clearly indicate that the new design scheme increases the stability of the system. However, the increase in stability comes at the cost of the increase in the power required for the control system.

Corrosion begins as moisture penetrates the protective barrier of a surface, starting an electrochemical process which over time leads to surface pitting. The combined action of mechanical stresses and corrosion induced pitting reduces structural integrity as the pits enlarge to form nucleation sites for surface cracks, which propagate into through-the-thickness cracks. In most cases, the total mass loss due to corrosion within the structure is small; however, significant reductions in mechanical strength and fatigue life can occur in the corroded material leading to advanced crack growth rates or fast fracture. Since the structural damage due to localized corrosion pitting is small and the crack growth rates may be large, traditional inspections methods and "find it and fix it" maintenance approaches may lead to catastrophic mechanical failures. Therefore, precise structural health monitoring of pre-crack surface corrosion is paramount to understanding and predicting the effect corrosion has on the fatigue life and integrity of a structure. In this study, the impedance method was experimentally tested to detect and quantify the onset and growth of pre-crack surface corrosion in beam and plate like structures. Experimental results indicate the method is an effective detection and tracking tool for corrosion induced structural damage in plates and beams. Additionally, impedance based monitoring of the corrosive effect on the piezoelectric sensors may serve as a useful tool for predicting corrosion growth rates on the surface of structures.