Piezoelectric Ceramic Wafer Research Articles

Electromechanical Impedance Temperature Compensation and Bolt Loosening Monitoring Based on Modified Unet and Multitask Learning

Bolts are frequently subjected to loosening due to time varying external loads during service. The electromechanical impedance (EMI) technique based on piezoelectric ceramic wafers (PZT) is sensitive to the initial bolt preload looseness. However, the change in environmental temperature has a great effect on EMI monitoring. Deep convolutional neural network (CNN) is a promising technique for EMI monitoring. Nevertheless, it is difficult to train a deep CNN with limited training data to accurately identify damages under a wide range of temperature variations. To this end, this study proposes a multitask CNN for identifying bolts loosening. The network consists of a temperature compensation subnetwork to compensate for the temperature effect, and a lightweight damage identification subnetwork to identify bolt loosening states. The temperature compensation subnetwork is a modified Unet, and both the impedance and temperature are used as its input. The damage identification subnetwork is connected in series behind the temperature compensation subnetwork. A multiloss function is proposed in which a TV regularizer is used. Experimental results show that the validation accuracy of the multitask network is 97.71% when the network is trained by only about 30 samples from each loosening state. Moreover, the generalization abilities of the proposed multitask model to unexpected temperatures and bolt torques are investigated. The model is interpreted by the integrated gradients method, and is also compared with single-task damage identification CNNs. It is proved that the multitask network trained by limited samples can achieve accurate damage identification in temperature varying environments.

Ceramic-Based Piezoelectric Material for Energy Harvesting Using Hybrid Excitation.

This paper analyzes the energy efficiency of a Micro Fiber Composite (MFC) piezoelectric system. It is based on a smart Lead Zirconate Titanate material that consists of a monolithic PZT (piezoelectric ceramic) wafer, which is a ceramic-based piezoelectric material. An experimental test rig consisting of a wind tunnel and a developed measurement system was used to conduct the experiment. The developed test rig allowed changing the air velocity around the tested bluff body and the frequency of forced vibrations as well as recording the output voltage signal and linear acceleration of the tested object. The mechanical vibrations and the air flow were used to find the optimal performance of the piezoelectric energy harvesting system. The performance of the proposed piezoelectric wind energy harvester was tested for the same design, but of different masses. The geometry of the hybrid bluff body is a combination of cuboid and cylindrical shapes. The results of testing five bluff bodies for a range of wind tunnel air flow velocities from 4 to 15 m/s with additional vibration excitation frequencies from 0 to 10 Hz are presented. The conducted tests revealed the areas of the highest voltage output under specific excitation conditions that enable supplying low-power sensors with harvested energy.

Influence of different ultrasonic transducers on the precision of fastening force measurement

In the assembly process of aero-engines, the accurate measurement of bolt fastening force is particularly important, which is related to the normal operation of the entire system. Ultrasonic non-destructive testing has been applied to bolt fastening force measurement and has a broad application background. The core device of the ultrasonic transducer is a piezoelectric ceramic wafer, and the normal operation of the wafer is affected by the power frequency and external stress. For the same type of bolt with the same nominal diameter, the ultrasonic transducer wafers of different diameters will cause the transducer wafers to be subjected to different external stresses. According to the acoustoelastic effect, the relationship between the variation of time of flight (TOF) and bolt fastening force of different types of ultrasonic transducers is established. Then the measurement errors of various models are calculated and analyzed. The experimental results show that when the nominal diameter of the bolt is close to the diameter of the wafer of the ultrasonic transducer, the fastening force measurement accuracy of the bolt is the highest. When small or large size transducer is used, the measurement accuracy will be reduced due to energy and external stress. When a transducer with a higher center frequency is used to measure the fastening force of the bolt rod, the accuracy of the model established due to the faster attenuation of the sound wave is reduced, and the accuracy of the measurement result is reduced. Therefore, in order to ensure the accuracy of the fastening force measurement in the aerospace field, when selecting an ultrasonic transducer, the impact of the transducer size and center frequency should be fully considered.

Experiment Research on Power Generation Performance of Double Piezoelectric Vibration Energy Harvester

In order to collect the vibration energy in the environment, the cantilever double piezoelectric vibration energy harvester is designed to collect the mechanical vibration energy of the motor. The output voltage of the upper and lower piezoelectric ceramic wafer of the bimorph piezoelectric vibrator and the output voltage of the cantilever suspension length at different rotational speeds of the motor are investigated. At last the experimental results are verified.

An indirect method to measure the variation of elastic constant c33 of piezoelectric ceramics shunted to circuit under thickness mode

Academic interest in the use of piezoelectric shunt damping technology in the field of vibration and noise control has been on the rise in recent years. The experimental observation of the variation of elastic constants of piezoelectric materials shunted to different circuits is a fundamental problem of this technology. The existing methods to measure the elastic constants of piezoelectric ceramics are either unsuited or complicated for such a purpose. In this paper, a modified resonator measurement method is proposed to indirectly measure the variation of elastic constant c33 of piezoelectric ceramics shunted to circuit under thickness mode. The main idea is transforming the change of c33 into the change of the electrical resonant frequency of a single-oscillator model which is easier to be observed. Mason equivalent circuit and ANSYS finite element simulation are employed for the analysis of the admittance and resonant frequency of the proposed system. Based on the proposed method, the variation of the elastic constant c33 has been investigated when the piezoelectric ceramic wafer (PZT-5H) is shunted to a resistor, a capacitor, and a resistor connected in series with an inductor respectively. The variations of the resonant frequency measured in the experiment are highly consistent with those of c33. Besides, the measurement of variation of mechanical loss factor with a shunt resistor is also discussed in this paper.

Simulation Analysis on Cymbal Transducer

The resonance frequency of the cymbal transducer ranges from 2kHz to 40kHz and its effective electromechanical coupling factor is around 20%. Finite element analysis has been performed to ascertain how the transducer’s makeup affect the transducer’s performance parameters. Two-dimensional axisymmetric model of the cymbal transducer was founded by finite element software-ANSYS, the application of the element type was discussed and the FEM models were built up under the far field condition. Eight groups of cymbal transducers of resonance frequency around 3kHz with different structural dimensions were designed. It was better for choosing the cymbal transducer of the 8mm cavity coping diameter, 20.8mm cavity bottom diameter and 26.8mm piezoelectric ceramic wafer diameter than others for reducing distortion degree of the signal and improving communication turnover in the researched cymbal transducers. It was appropriate for choosing the cymbal transducer of the 8mm cavity coping diameter, 22.4mm cavity bottom diameter and 26.4mm piezoelectric ceramic wafer diameter in order to improve the free-field voltage sensitivity and transmission efficient.

Measurement of elastic constants of limited-size piezoelectric ceramic sample by ultrasonic method

Measurement of material elastic constants for limited-size samples by ultrasonic method is described and validated. Based on acoustic microscope technology, the material elastic constants are determined by longitudinal wave and leak surface wave velocities simultaneously measured by developed ultrasonic system with a line-focus PVDF transducer. In this paper, the elastic constants of limited-size Cr 2O 3 doping on 0.2 PZN–0.8 PZT piezoelectric ceramic wafer sample are determined and the measurement errors are analyzed. The experimental results show this ultrasonic system can be used for measurement of material elastic constants for limited-size samples with high measurement precision, and the relative errors for Poisson’s ratio and Young’s module measurements are, respectively, less than 1% and 3%. It can satisfy the requirement of engineering and science research. Furthermore, it is suitable to measure elastic constants of both isotropic and anisotropic materials by ultrasonic method with help of developed ultrasonic system.

Performance evaluation of lightweight piezo-composite actuators

This paper is concerned with the performance evaluation and comparison for several kinds of lightweight piezo-composite actuator (LIPCA) device system. LIPCA device system is composed of a piezoelectric ceramic wafer layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low coefficient of thermal expansion (CTE) and base layers with high CTE. To investigate the effect of lay-up structure of the LIPCA on the actuating performance, five kinds of actuator with different lay-up stacking sequence have been designed, manufactured, and tested. The performance of each actuator was evaluated using an actuator test system consisted of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system. From the comparison of the performance of the LIPCA prototypes, it was found that the actuator with higher coefficient of unimorph actuator can generate larger actuating displacement.

Designing for piezoelectric ceramic wafers bonded on structures using force transfer criteria

Piezoelectric ceramic wafers embedded or surface mounted are able to generate transverse forces to control structural shape and vibration. These actuators are excited by applying an electric field through the thickness of the piezoelectric ceramic wafer. The proper design of their dimensions such as wafer thickness, and applied actuation voltage will enhance the system reliability, and guarantee the optimal control authority. This paper shows that the force transfer from the piezoelectric ceramic wafer to the structure, rather than the shear stress transfer in bond lines, becomes a key issue in the design when the length relative to the thickness of the piezoelectric ceramic wafer is large. It should be noted at this point that the shear stress distribution in the bond lines may influence the durability of the piezoelectric ceramic actuation system and, therefore, should also be considered when designing the system as a whole. This aspect of design is not discussed here. The force transfer is basically determined by the force transfer efficiency and block force in association with the wafer thickness. Therefore, this paper presents a design window for piezoelectric ceramic wafers bonded onto structures that is based on the relations between the force transfer and the wafer thickness, and also accounting for the applied actuation voltage and dielectric breakdown voltage of the piezoelectric material. The design window clearly describes the upper bound of the force transfer and the maximum value that can be achieved. It is also used to find an appropriate wafer thickness and actuation voltage when a minimum value of force transfer is required. In addition, an analytical model is developed in order to express the relation between the force transfer and the wafer thickness. This model is compared to the results from finite-element analysis. Limitations of the analytical model are described.

Thin-layer composite unimorph ferroelectric driver and sensor properties

Tests were conducted on 13 different configurations of a new class of piezoelectric devices called THUNDER (thin layer composite unimorph ferroelectric driver and sensor). These configurations consisted of a combination of 1, 3, 5, 7, and 9 layers of 25.4 micron thick aluminium as a backing material, with and without a top layer of 25.4 micrometer aluminum. All of these configurations used the same piezoelectric ceramic wafer (PZT-5A) with dimensions of 5.08 x 3.81 x 0.018 cm. The above configurations were tested at two stages of the manufacturing process: before and after repoling. The parameters measured included frequency, driving voltage. displacement, capacitance, and radius of curvature. An optic sensor recorded the displacement at a fixed voltage(100 - 400 V peak to peak) over a predetermined frequency range (1 - 1000 Hz). These displacement measurements were performed using a computer that controlled the process of activating and measuring the displacement of the device. A parameter alpha was defined which can be used to predict the which configuration will produce the most displacement for a free standing device.

The Accelograph: a new neuromuscular transmission monitor.

A new neuromuscular transmission monitor based on measurement of acceleration is presented. The monitor consists of an acceleration transducer, i.e. a piezo-electric ceramic wafer with an electrode on each side, and a stimulation and computing unit. The transducer can be fastened to the thumb, and when the finger is moved in response to nerve stimulation a voltage difference develops between the two electrodes. The voltage is then measured and registered in the computing unit. The acceleration transducer does not require preload, but merely that the muscle on which the measurement is being made can move freely. The accelograph is therefore easy to set up and operate. In daily clinical practice it has proved possible, using this new apparatus, to achieve reliable evaluation of the degree of non-depolarizing neuromuscular blockade in less than 2 min.

Measurement of acceleration: a new method of monitoring neuromuscular function.

A new method for monitoring neuromuscular function based on measurement of acceleration is presented. The rationale behind the method is Newton's second law, stating that the acceleration is directly proportional to the force. For measurement of acceleration, a piezo-electric ceramic wafer was used. When this piezo electrode was fixed to the thumb, an electrical signal proportional to the acceleration was produced whenever the thumb moved in response to nerve stimulation. The electrical signal was registered and analysed in a Myograph 2000 neuromuscular transmission monitor. In 35 patients anaesthetized with halothane, train-of-four ratios measured with the accelerometer (ACT-TOF) were compared with simultaneous mechanical train-of-four ratios (FDT-TOF). Control ACT-TOF ratios were significantly higher than control FDT-TOF ratios: 116 +/- 12 and 98 +/- 4 (mean +/- s.d.), respectively. In five patients not given any relaxant during the anaesthetic procedure (20-60 min), both responses were remarkably constant. In 30 patients given vecuronium, a close linear relationship was found during recovery between ACT-TOF and FDT-TOF ratios. It is concluded that the method fulfils the basic requirements for a simple and reliable clinical monitoring tool.