Mikko Leinonen

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.

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.

A piezoelectric active mirror suspension system embedded into low-temperature cofired ceramic

Low-temperature cofired ceramic (LTCC) has proven to be a cost-effective, flexible technology for producing complicated structures such as sensors, actuators, and microsystems. This paper presents a piezoelectric active mirror suspension system embedded into LTCC. In the structure, the LTCC was used as a package, for the passive layers of piezoelectric monomorphs, as support for the mirrors, and as a substrate for the conductors. The active mirror structure, 17 mm in diameter, was made by compiling 20 LTCC layers using common LTCC processing techniques. Each sample contained a laser-micromachined bulk lead zirconate titanate (PZT) structure which formed a monomorph with the LTCC during the firing process. A mirror substrate (diameter 4 mm) was mounted in the middle of the monomorph arms for evaluation of the positioning performance, where each of the three arms had independent signal electrodes and a common ground electrode. Electrical and electromechanical properties were investigated with an LCR meter, network analyzer, and laser vibrometer for the different arms and the mirror. The active mirror structure exhibited more than 1 μm dc displacement for mirror leveling and also allowed small changes in mirror angle up to 0.06°. The first bending resonance frequency of the structure with the mirror was detected at 11.31 kHz with 4.0 μm displacement; 13.02 kHz and 2.7 μm were obtained without the mirror. The structure exhibited characteristics feasible for further utilization in tunable Fabry-Perot filter applications, allowing the mounting of active mirrors on both sides with distance and angle control.

Piezoelectric active mirror suspension embedded into Low Temperature Co-fired Ceramic

Low Temperature Co-fired Ceramic (LTCC) has proven to be a cost effective and flexible technology for producing complicated structures: sensors, actuators and microsystems. In this paper, piezoelectric active mirror suspension embedded into LTCC is presented. In the structure the LTCC was used as a package, passive layers of piezoelectric monomorphs, support for the mirrors and substrate for conductors. Active mirror structure, 17 mm in diameter, was made by compiling 20 layers using standard LTCC processing techniques. Each sample contained a laser micromachined bulk PZT structure which formed a monomorph with LTCC during the firing process. A mirror substrate (Ø 4mm) was mounted in the middle of the monomorph arms for evaluation of positioning performance where each of the three arms had independent signal electrodes and a common ground electrode. Electrical and electromechanical properties were investigated with LCR meter, network analyser and laser vibrometer for different arms and the mirror. Active mirror structure exhibited over 1 µm DC displacement for mirror leveling allowing also small changes in mirror angle up to 0.06°. First bending resonance frequency of the structure with the mirror was detected at 11.31 kHz with 4.0 µm displacement while 13.02 kHz and 2.7 µm was obtained without the mirror. The structure exhibited feasible characteristics for further utilization as tunable Fabry-Perot filter applications, allowing mounting of two active mirrors on both sides with distance and angle control.

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.