Jaakko Palosaari

Combined electrical and electromechanical simulations of a piezoelectric cymbal harvester for energy harvesting from walking

In this article, simulation combining real-life mechanical input energy with electromechanical and electrical behavior of piezoelectric energy harvester and electronics is demonstrated. A finite element method model for a piezoelectric cymbal harvester is developed and compared to measurements from an actual prototype. The measurements were taken using a piston imitating a measured walking pressure profile, which was also used in the simulations as an arbitrary input signal. The finite element method model was used to calculate the electrical power of the prototype under a resistive load. These results were then compared to the measured results, which showed that the error in the generated power between the model and the actual prototype was below 7% for stroke displacements below 1.3 mm. Such accurate modeling of full chain from mechanical to electrical energy will be an essential tool in optimization of the mechanics, electronics, and materials of the future energy harvesting devices.

A Game Changer: A Multifunctional Perovskite Exhibiting Giant Ferroelectricity and Narrow Bandgap with Potential Application in a Truly Monolithic Multienergy Harvester or Sensor

An ABO3 -type perovskite solid-solution, (K0.5 Na0.5 )NbO3 (KNN) doped with 2 mol% Ba(Ni0.5 Nb0.5 )O3-δ (BNNO) is reported. Such a composition yields a much narrower bandgap (≈1.6 eV) compared to the parental composition-pure KNN-and other widely used piezoelectric and pyroelectric materials (e.g., Pb(Zr,Ti)O3 , BaTiO3 ). Meanwhile, it exhibits the same large piezoelectric coefficient as that of KNN (≈100 pC N-1 ) and a much larger pyroelectric coefficient (≈130 µC m-2 K-1 ) compared to the previously reported narrow-bandgap material (KNbO3 )1-x -BNNOx . The unique combination of these excellent ferroelectric and optical properties opens the door to the development of multisource energy harvesting or multifunctional sensing devices for the simultaneous and efficient conversion of solar, thermal, and kinetic energies into electricity in a single material. Individual and comprehensive characterizations of the optical, ferroelectric, piezoelectric, pyroelectric, and photovoltaic properties are investigated with single and coexisting energy sources. No degrading interaction between ferroelectric and photovoltaic behaviors is observed. This composition may fundamentally change the working principles of state-of-the-art hybrid energy harvesters and sensors, and thus significantly increases the unit-volume energy conversion efficiency and reliability of energy harvesters in ambient environments.

Piezoelectric circular diaphragm with mechanically induced pre-stress for energy harvesting

This paper presents the results of a piezoelectric circular diaphragm harvester utilising a unique measurement setup with tailored input force (walk profile), adjustable mechanical pre-stress, and simultaneous measurement of the harvested energy output and input force pressure. The harvester, incorporating the pre-stressing mechanism, consisted of a 191 ?m thick PZ-5A piezoelectric disc (? 34.5 mm) and a 100 ?m thick steel plate (? 45.5 mm). Its performance was measured with pressure cycles at a frequency of 0.96 Hz. Harvested energy was measured as a function of the pre-stressing state, the applied force, and the pressure profile. The optimal bending pre-stress was found to improve the efficiency of harvesting by ?141% compared to the case without pre-stress. The maximum obtained efficiency was 14.7%, and the maximum average power density of 6.06 mW cm?3 was measured for a unimorph diaphragm energy harvester. The results show that the pre-stressing technique is an effective method to improve the efficiency and generated power in this type of piezoelectric harvester, potentially enabling it to power different portable devices and sensors in future applications.

Fully printed memristors for a self-sustainable recorder of mechanical energy

Memristors have attracted significant interest in recent years because of their role as a missing electronic component and unique functionality that has not previously existed. Since the first discoveries of the existence of memristive materials, various different fabrication processes for memristors have been presented. Here, a simple additive fabrication process is demonstrated where memristors were deposited on a polymer substrate by conventional inkjet printing. The memristor structure was printed on a 125 μm thick polyethylene terephthalate (PET) substrate by sandwiching a thin layer of TiO x between two silver nanoparticle ink electrodes. Current–voltage (IV) characterization measurements were performed and they showed clear memristive behavior when voltage pulse amplitude varied between −1.5 V and 1.5 V. The corresponding resistance change is approximately between 150 Ω and 75 kΩ. In order to demonstrate the switching scheme in practical application, printed memristors and a printed voltage doubler were connected with a piezoelectric element. The element was subjected to impact-type excitation thus producing an electric charge that was able to switch the memristor between high and low resistive states. These results pave the way for an exploitation of cost-efficient, self-sufficient, all-printable memory elements for wide utilization in future electronics applications.

End cap profile optimization of a piezoelectric Cymbal actuator for quasi-static operation by using a genetic algorithm

This article describes how an extrinsically amplified Cymbal-type piezoelectric actuator is optimized for displacement generation by using genetic algorithms in combination with COMSOL Multiphysics finite element method modeling software. The research was focused on optimizing the shape of the end cap profile in a quasi-static operation scheme in order to keep the number of parameters and calculation times at a reasonable level. In contrast to conventional linear end cap profiles, a genetic algorithm tends to generate more complex shapes and especially a corrugated structure in the vicinity of the output point of force and displacement. Modeling showed that about 26.9% higher displacement could be produced with a complex shape derived by the algorithm compared with a linear end cap profile. Moreover, about the same level of displacement as achieved with a wagon wheel transducer was obtained simply by profile optimization without material removal, which could, however, improve performance even further. The developed genetic algorithm proved to be a feasible tool for complex multi-parameter optimization, utilizable in a wide range of shape and structure optimizations for future electromechanical components.

Characteristics of thin film piezoelectric ultrasonic transducer array by chemical solution deposition

In this paper, thin film piezoelectric ultrasonic transducers with a two electrode design and various different membrane sizes were manufactured and characterized. The transducers were fabricated on a silicon wafer by chemical solution deposition (CSD) where PZT was deposited with a total thickness of ~2 ¿m. Afterwards, cavities were wet etched underneath the piezoelectric layer creating bending membranes with a total thickness of ~13 ¿m and cavity sizes from 0.056 mm2 to 0.181 mm2. Then the transducers were poled and their electromechanical properties were measured with laser vibrometer. The membranes resonance frequencies and quality factors were measured at ~780-2000 kHz and 70-135, respectively, and effective d33 coefficients from 100-290 nm/V.