Displacement Investigation of KNN-Bitumen-Based Piezoceramics in Asphalt Concrete

Piezoelectric material has excellent characteristics of electromechanical coupling so that it could be widely applied in structural health monitoring field. Nondestructive testing of piezoelectric technique becomes a research focus on piezoelectric field. Asphalt concrete produces cumulative damage under the multiple repeated vehicle load and natural situation, so it is suited material and structure for nondestructive application. In this study, a test system was established by driving power of piezoceramic, laser displacement sensor, computer, and piezo-embedded asphalt concrete. Displacement, hysteresis, creeps, and dynamic behavior of KNN piezoceramic element embedded in asphalt concrete were tested. The results indicate that displacement output attained 0.4 μm to 0.7 μm when the loads were from 0 N to 150 N. The hysteresis was not obvious when the load was from 0 N to 100 N, aside from higher loads. The creep phenomenon can be divided into two parts: uptrend and balance. The more serious the asphalt binder ageing is, the larger the displacement is, when piezo-asphalt concrete has already been in serious ageing.

Artificial Cochlear Hair Cells Using Active Piezoelectric Materials

The inner hair cells (IHC’s) and outer hair cells (OHC’s) in the cochlea are vital components in the process of hearing. The IHC’s are responsible for converting sound-induced vibration into electrical signals. The OHC’s produce forces that amplify these vibrations and therefore enhance the electrical signals produced by the IHC’s. The resulting “cochlear amplifier” produces a nonlinear amplification which gives the ear its ability to detect sound pressure levels ranging from 20 μPa to 20 Pa (0 to 120 dB). This paper presents the modeling and testing of an artificial hair cell (AHC) piezoelectric sensor inspired by the hair cells found in the mammalian ear. The sensor is a bimorph cantilever beam consisting of a sensing piezoceramic element and an actuating piezoceramic element bonded to a brass substrate. The sensing element is used to detect the mechanical motion of the beam. Output feedback control can be used to send a voltage signal to the actuating element and alter the frequency response of the beam. A control law, which modifies the linear damping term of the first mode and introduces cubic damping, is used to create a closed-loop system perched at a Hopf bifurcation. The result is a system that produces a nonlinear amplification of the beam’s mechanical response in a manner which mimics the nonlinear behavior of the mammalian cochlea. This active sensor is studied under base acceleration and the initial test results are compared to a finite element model. Simulations of the closed-loop system are examined for the system with a single mode and for the system with multiple modes.

Parameter Optimization of a Vibration-Based Energy Harvester With an RL Electric Circuit

An alternative circuit to improve the performance of a vibration-based energy harvester is proposed. The harvesting device considered consists of a piezoceramic element operating in the {33} direction. In normal operating conditions, piezoceramics experience small deflection and hence the small signal linear constitutive law of piezoelectricity is adopted for the scope of this work. Typically, vibration-based energy harvesters are designed to operate at the resonance or antiresonance frequencies. This condition might be tolerable in many cases, but is often difficult to realize in real-life applications. In this work, the authors propose adding an inductor to the harvesting circuit. It is shown that the addition of this simple electric element modifies the performance remarkably in a qualitative and quantitative manner. The maximum power values obtained at the resonance and antiresonance frequencies can be achieved at any frequency ratio if optimal electric elements are used. This allows for harvesting a constant optimal power everywhere in the frequency domain. Further investigation reveals the existence of a singularity at low damping ratios (below a bifurcation damping ratio). In that case, the optimization scheme yields a negative value for the optimal inductance between the resonance and antiresonance frequencies. However, this singularity is not experienced at a high damping ratio (beyond a bifurcation damping ratio). Moreover, for high damping ratios, it is shown that the proposed circuit is superior to a circuit that does not deploy an inductor.

Stresses in a Thin Piezoelectric Element Bonded to a Half-Space

In this paper, a thin piezoceramic element is considered which is bonded to an elastic or a rigid half-space. Such a model may be an approximation of the interaction between piezoceramic elements and elastic structures like beams and plates. For an elastic half-space, the determination of the shear stress in the bonding layer leads to a singular integral equation. A half-space which is very stiff may be modeled as a rigid substrate. For this case, displacement functions are introduced. Hamilton’s principle for electromechanical systems allows the use of Lagrange multipliers to incorporate the condition of a stress free upper surface of the piezoceramic element. The stresses in the bonding layer and in the piezoceramic element are estimated by this method and compared with Finite Element results. Though the singularity near the ends of the piezoceramic element cannot be modeled by both methods, stress concentrations can clearly be seen for the shear stress as well as for the normal stress. As infinite stresses due to the singularity do not occur in reality, the results allow an estimation of the bonding stresses except in the near vicinity of the edges. The knowledge of these stresses is important to prevent failure due to delamination.