Turbomachine components used in aerospace and power plant applications preferably require continuous structural health monitoring at various temperatures. The structural health of pristine and damaged superalloy compressor blades of a gas turbine engine was monitored using real electro-mechanical impedance of deposited thick film piezoelectric transducers at 20 and 200 °C. IVIUM impedance analyzer was implemented in laboratory conditions for damage detection in superalloy blades, while a custom-architected frequency-domain transceiver circuit was used for semi-field circumstances. Recorded electromechanical impedance signals at 20 and 200 °C acquired from two piezoelectric wafer active sensors bonded to an aluminum plate, near and far from the damage, were initially utilized for accuracy and reliability verification of the transceiver at temperatures >20 °C. Damage formation in both the aluminum plate and blades showed a peak shift in the swept frequency along with an increase in the amplitude and number of impedance peaks. The thermal energy at 200 °C, on the other hand, enforces a further subsequent peak shift in the impedance signal to pristine and damaged parts such that the anti-resonance frequency keeps reducing as the temperature increases. The results obtained from the impedance signals of both piezoelectric wafers and piezo-films, revealed that increasing the temperature somewhat decreased the real impedance amplitude and the number of anti-resonance peaks, which is due to an increase in permittivity and capacitance of piezo-sensors. A trend is also presented for artificial intelligence training purposes to distinguish the effect of the temperature versus damage formation in sample turbine compressor blades. Implementation of such a monitoring system provides a distinct advantage to enhance the safety and functionality of critical aerospace components working at high temperatures subjected to crack, wear, hot-corrosion and erosion.

Reducing maintenance costs while increasing the safety and reliability, especially in moving structures, needs a reliable nondestructive analyzer. The aim of this research is to provide a practical solution for this problem, which works based on high-frequency excitation of stationary and moving structures by propagating standing Lamb waves in the range of 1 to 1000 kHz. The proposed solution comprises of a controlled frequency swept signal source, a number of piezoelectric sensors, a portable analyzer, and a rotary mechanism. Measuring the accurate electromechanical impedance (EMI) is made possible by monitoring the applied voltages, currents, and phase differences, accurately. In this study, design and implementation of a low-cost, compact and portable transceiver is explored for periodic structural health monitoring of a proposed rotary structure using EMI technique. The compactness of the proposed system is an essential requirement for rotary structures as compared to bulky, heavy and expensive laboratory-type impedance analyzers. Challenges in design and development of such a system are discussed in this paper, together with mitigations to make the system functional and practical. An experimental study is carried out directly in frequency domain to measure the real and imaginary parts of impedance spectrum of piezo-transducers. Stationary experiments are first carried out on an aluminum plate 5083. Having ensured of the transceiver accuracy, a turbomachine prototype which is able to work at up to 3000 rpm and 300 °C is introduced to perform tests on a rotary structure. Damage detection is investigated for pristine and damaged superalloy blades considering the sensible change in mechanical stiffness of the blades. The proposed transceiver is calibrated with a standard impedance analyzer. The results show that the portable transceiver has the capability to detect structural incipient damages before any catastrophic failure, thus avoiding undesirable shut down during the operation.

This paper presents a conceptual design and control of a novel gasoline direct injector (GDI) using giant magnetostricitve material, Terfenol-D, as an actuation component. Electromagnetic and fluid analyses are accomplished to investigate the influence of some parameters, such as nozzle length, pressure of input fuel, and cone angle of injector's needle. Experimental results obtained from fabricated GDI show good agreement with the numerical results provided by the 3-D finite-element analysis. Furthermore, the fabricated GDI is controlled by fuzzy and PID controllers. It was shown that fuzzy controllers provide faster response with less accuracy compared to the PID controller. Consequently, there is a tradeoff between fast response and steady-state error for selecting the propoer controller.

This article first reviews the position control of piezoelectric actuators, particularly charge-based sensorless control systems, which often include a charge estimator as a key component. The rest of the paper is about charge estimators for piezoelectric actuators. Two of the most recent/effective types of these estimators utilise either a sensing capacitor (type I in this paper) or a sensing resistor (type II); the latter (and the newer) type is broadly known as a digital charge estimator. Some experimental results in the literature show that, with the same loss in excitation voltage, a considerably higher amount of charge can be estimated with a type II estimator in comparison with a type I estimator; therefore, the superiority of type II estimators was acknowledged. In order to re-assess this conclusion, this paper equitably compares type I and II estimators through analytical modelling and experimentation. The results indicate that type II estimators have only a slight advantage in estimating higher amounts of charge, if both type I and II estimators are designed appropriately. At the same time, type II estimators have disadvantages; e.g., the resistance of type II estimators has to be tuned to suit different excitation frequencies. This research concludes that capacitor-based (type I) charge estimators for piezoelectric actuators, with pertinent design and implementation, can be still the prime solution for many charge estimation problems despite claims in the literature in the last decade.