[{"date_updated":"2022-01-06T07:04:20Z","author":[{"first_name":"Waleed","last_name":"Al-Ashtari","full_name":"Al-Ashtari, Waleed"},{"last_name":"Hunstig","full_name":"Hunstig, Matthias","first_name":"Matthias"},{"first_name":"Tobias","last_name":"Hemsel","id":"210","full_name":"Hemsel, Tobias"},{"first_name":"Walter","last_name":"Sextro","id":"21220","full_name":"Sextro, Walter"}],"date_created":"2019-05-13T13:51:00Z","volume":24,"title":"Increasing the power of piezoelectric energy harvesters by magnetic stiffening","doi":"10.1177/1045389X13483021","issue":"11","year":"2013","citation":{"apa":"Al-Ashtari, W., Hunstig, M., Hemsel, T., &#38; Sextro, W. (2013). Increasing the power of piezoelectric energy harvesters by magnetic stiffening. <i>Journal of Intelligent Material Systems and Structures</i>, <i>24</i>(11), 1332–1342. <a href=\"https://doi.org/10.1177/1045389X13483021\">https://doi.org/10.1177/1045389X13483021</a>","short":"W. Al-Ashtari, M. Hunstig, T. Hemsel, W. Sextro, Journal of Intelligent Material Systems and Structures 24 (2013) 1332–1342.","bibtex":"@article{Al-Ashtari_Hunstig_Hemsel_Sextro_2013, title={Increasing the power of piezoelectric energy harvesters by magnetic stiffening}, volume={24}, DOI={<a href=\"https://doi.org/10.1177/1045389X13483021\">10.1177/1045389X13483021</a>}, number={11}, journal={Journal of Intelligent Material Systems and Structures}, author={Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}, year={2013}, pages={1332–1342} }","mla":"Al-Ashtari, Waleed, et al. “Increasing the Power of Piezoelectric Energy Harvesters by Magnetic Stiffening.” <i>Journal of Intelligent Material Systems and Structures</i>, vol. 24, no. 11, 2013, pp. 1332–42, doi:<a href=\"https://doi.org/10.1177/1045389X13483021\">10.1177/1045389X13483021</a>.","ama":"Al-Ashtari W, Hunstig M, Hemsel T, Sextro W. Increasing the power of piezoelectric energy harvesters by magnetic stiffening. <i>Journal of Intelligent Material Systems and Structures</i>. 2013;24(11):1332-1342. doi:<a href=\"https://doi.org/10.1177/1045389X13483021\">10.1177/1045389X13483021</a>","ieee":"W. Al-Ashtari, M. Hunstig, T. Hemsel, and W. Sextro, “Increasing the power of piezoelectric energy harvesters by magnetic stiffening,” <i>Journal of Intelligent Material Systems and Structures</i>, vol. 24, no. 11, pp. 1332–1342, 2013.","chicago":"Al-Ashtari, Waleed, Matthias Hunstig, Tobias Hemsel, and Walter Sextro. “Increasing the Power of Piezoelectric Energy Harvesters by Magnetic Stiffening.” <i>Journal of Intelligent Material Systems and Structures</i> 24, no. 11 (2013): 1332–42. <a href=\"https://doi.org/10.1177/1045389X13483021\">https://doi.org/10.1177/1045389X13483021</a>."},"page":"1332-1342","intvolume":"        24","_id":"9794","user_id":"55222","department":[{"_id":"151"}],"language":[{"iso":"eng"}],"type":"journal_article","publication":"Journal of Intelligent Material Systems and Structures","abstract":[{"lang":"eng","text":"A piezoelectric cantilever beam with a tip mass at its free end is a common energy harvester configuration. This article introduces a new principle of designing such a harvester that increases the generated power without changing the resonance frequency of the harvester: the attraction force between two permanent magnets is used to add stiffness to the system. This magnetic stiffening counters the effect of the tip mass on the efficient operation frequency. Five set-ups incorporating piezoelectric bimorph cantilevers of the same type in different mechanical configurations are compared theoretically and experimentally to investigate the feasibility of this principle: theoretical and experimental results show that magnetically stiffened harvesters have important advantages over conventional set-ups with and without tip mass. They generate more power while only slightly increasing the deflection in the piezoelectric harvester and they can be tuned across a wide range of excitation frequencies."}],"status":"public"},{"department":[{"_id":"151"}],"user_id":"55222","_id":"9795","language":[{"iso":"eng"}],"keyword":["Energy harvesting","Cantilever array","Bandwidth","Power increase"],"publication":"Sensors and Actuators A: Physical","type":"journal_article","status":"public","abstract":[{"text":"Power and bandwidth of piezoelectric harvesters can be increased by using multiple piezoelectric elements in one harvester. In this contribution, a novel energy harvesting cantilever array with magnetic tuning including three piezoelectric bimorphs is investigated theoretically and experimentally, with a good agreement between model and experiment. Other than harvester designs proposed before, this array is easy to manufacture and insensitive to manufacturing tolerances because its optimum operation frequency can be re-adjusted after fabrication. Using the superposition principle, the Butterworth-Van Dyke model and a mechanical lumped parameters model, the generated voltage and current are determined analytically. Formulas for calculating the power generated by array harvesters with an arbitrary number of piezoelectric elements connected in series or in parallel are derived. It is shown that optimum harvester design must take both the connected load and the operating frequency into account. Strategies for connecting multiple bimorphs to increase the maximum generated power and/or enhance the bandwidth compared to a single bimorph harvester are investigated. For bandwidth enhancement it is essential that individual rectifiers are used for the bimorphs. An example with three bimorphs shows that, depending on the chosen tuning strategy, the power is increased by about 340\\% or the bandwidth is increased by about 500\\%, compared to one single bimorph.","lang":"eng"}],"volume":200,"date_created":"2019-05-13T13:51:59Z","author":[{"full_name":"Al-Ashtari, Waleed","last_name":"Al-Ashtari","first_name":"Waleed"},{"full_name":"Hunstig, Matthias","last_name":"Hunstig","first_name":"Matthias"},{"first_name":"Tobias","last_name":"Hemsel","full_name":"Hemsel, Tobias","id":"210"},{"first_name":"Walter","full_name":"Sextro, Walter","id":"21220","last_name":"Sextro"}],"date_updated":"2022-01-06T07:04:20Z","doi":"10.1016/j.sna.2013.01.008","title":"Enhanced energy harvesting using multiple piezoelectric elements: Theory and experiments","page":"138 - 146","intvolume":"       200","citation":{"chicago":"Al-Ashtari, Waleed, Matthias Hunstig, Tobias Hemsel, and Walter Sextro. “Enhanced Energy Harvesting Using Multiple Piezoelectric Elements: Theory and Experiments.” <i>Sensors and Actuators A: Physical</i> 200 (2013): 138–46. <a href=\"https://doi.org/10.1016/j.sna.2013.01.008\">https://doi.org/10.1016/j.sna.2013.01.008</a>.","ieee":"W. Al-Ashtari, M. Hunstig, T. Hemsel, and W. Sextro, “Enhanced energy harvesting using multiple piezoelectric elements: Theory and experiments,” <i>Sensors and Actuators A: Physical</i>, vol. 200, pp. 138–146, 2013.","ama":"Al-Ashtari W, Hunstig M, Hemsel T, Sextro W. Enhanced energy harvesting using multiple piezoelectric elements: Theory and experiments. <i>Sensors and Actuators A: Physical</i>. 2013;200:138-146. doi:<a href=\"https://doi.org/10.1016/j.sna.2013.01.008\">10.1016/j.sna.2013.01.008</a>","short":"W. Al-Ashtari, M. Hunstig, T. Hemsel, W. Sextro, Sensors and Actuators A: Physical 200 (2013) 138–146.","bibtex":"@article{Al-Ashtari_Hunstig_Hemsel_Sextro_2013, title={Enhanced energy harvesting using multiple piezoelectric elements: Theory and experiments}, volume={200}, DOI={<a href=\"https://doi.org/10.1016/j.sna.2013.01.008\">10.1016/j.sna.2013.01.008</a>}, journal={Sensors and Actuators A: Physical}, author={Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}, year={2013}, pages={138–146} }","mla":"Al-Ashtari, Waleed, et al. “Enhanced Energy Harvesting Using Multiple Piezoelectric Elements: Theory and Experiments.” <i>Sensors and Actuators A: Physical</i>, vol. 200, 2013, pp. 138–46, doi:<a href=\"https://doi.org/10.1016/j.sna.2013.01.008\">10.1016/j.sna.2013.01.008</a>.","apa":"Al-Ashtari, W., Hunstig, M., Hemsel, T., &#38; Sextro, W. (2013). Enhanced energy harvesting using multiple piezoelectric elements: Theory and experiments. <i>Sensors and Actuators A: Physical</i>, <i>200</i>, 138–146. <a href=\"https://doi.org/10.1016/j.sna.2013.01.008\">https://doi.org/10.1016/j.sna.2013.01.008</a>"},"year":"2013"},{"title":"Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems","date_updated":"2022-01-06T07:04:20Z","date_created":"2019-05-13T13:53:25Z","author":[{"first_name":"Waleed","full_name":"Al-Ashtari, Waleed","last_name":"Al-Ashtari"},{"last_name":"Hunstig","full_name":"Hunstig, Matthias","first_name":"Matthias"},{"first_name":"Tobias","full_name":"Hemsel, Tobias","id":"210","last_name":"Hemsel"},{"last_name":"Sextro","id":"21220","full_name":"Sextro, Walter","first_name":"Walter"}],"place":"Hannover, Germany","year":"2013","page":"159-161","citation":{"apa":"Al-Ashtari, W., Hunstig, M., Hemsel, T., &#38; Sextro, W. (2013). Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems. In <i>Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013</i> (pp. 159–161). Hannover, Germany.","bibtex":"@inproceedings{Al-Ashtari_Hunstig_Hemsel_Sextro_2013, place={Hannover, Germany}, series={Berichte aus dem IDS}, title={Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems}, number={05/2013}, booktitle={Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013}, author={Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}, year={2013}, pages={159–161}, collection={Berichte aus dem IDS} }","short":"W. Al-Ashtari, M. Hunstig, T. Hemsel, W. Sextro, in: Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013, Hannover, Germany, 2013, pp. 159–161.","mla":"Al-Ashtari, Waleed, et al. “Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems.” <i>Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013</i>, no. 05/2013, 2013, pp. 159–61.","ama":"Al-Ashtari W, Hunstig M, Hemsel T, Sextro W. Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems. In: <i>Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013</i>. Berichte aus dem IDS. Hannover, Germany; 2013:159-161.","chicago":"Al-Ashtari, Waleed, Matthias Hunstig, Tobias Hemsel, and Walter Sextro. “Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems.” In <i>Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013</i>, 159–61. Berichte Aus Dem IDS. Hannover, Germany, 2013.","ieee":"W. Al-Ashtari, M. Hunstig, T. Hemsel, and W. Sextro, “Characteristics of Piezoelectric Energy Harvesters in Autonomous Systems,” in <i>Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013</i>, 2013, no. 05/2013, pp. 159–161."},"quality_controlled":"1","issue":"05/2013","keyword":["Energy harvesting","harvester modeling","load dependence","generated voltage"],"language":[{"iso":"eng"}],"_id":"9796","department":[{"_id":"151"}],"series_title":"Berichte aus dem IDS","user_id":"55222","abstract":[{"lang":"eng","text":"A basic autonomous system powered by a piezoelectric harvester contains three components apart from the harvester: a fullwave rectifier, a reservoir capacitor and an electronic device performing the primary task of the system. In this contribution, a model describing the operation of such a system is derived. It is found that in steady-state operation, the piezoelectric harvester experiences two alternating load conditions due to the rectification process. These alternating load conditions can have a significant effect on the operation of the harvester and must be considered in the design of autonomous systems. The results also show that such an autonomous system works efficiently if it is connected to a high impedance load and excited by a frequency matching the anti-resonance frequency of the piezoelectric harvester."}],"status":"public","publication":"Proceedings of 10th International Workshop on Piezoelectric Materials and Applications and 8th Energy Harvesting Workshop, Hannover, Germany, 14.-17.7.2013","type":"conference"},{"_id":"9801","series_title":"HNI-Verlagsschriftenreihe","user_id":"55222","department":[{"_id":"151"}],"language":[{"iso":"eng"}],"type":"conference","publication":"9. Paderborner Workshop Entwurf mechatronischer Systeme","editor":[{"last_name":"Gausemeier","full_name":"Gausemeier, Jürgen","first_name":"Jürgen"},{"first_name":"Roman","full_name":"Dumitrescu, Roman","last_name":"Dumitrescu"},{"first_name":"Franz","full_name":" Rammig, Franz","last_name":" Rammig"},{"full_name":"Schäfer, Wilhelm","last_name":"Schäfer","first_name":"Wilhelm"},{"full_name":"Trächtler, Ansgar","last_name":"Trächtler","first_name":"Ansgar"}],"status":"public","date_updated":"2022-01-06T07:04:21Z","publisher":"Heinz Nixdorf Institut, Universität Paderborn","date_created":"2019-05-13T14:02:10Z","author":[{"first_name":"Matthias","full_name":"Hunstig, Matthias","last_name":"Hunstig"},{"first_name":"Waleed","full_name":"Al-Ashtari, Waleed","last_name":"Al-Ashtari"},{"first_name":"Tobias","last_name":"Hemsel","full_name":"Hemsel, Tobias","id":"210"},{"first_name":"Walter","last_name":"Sextro","full_name":"Sextro, Walter","id":"21220"}],"title":"Leistungs- und Bandbreitensteigerung von Energy-Harvesting-Generatoren für Energieautarke Systeme","place":"Paderborn","year":"2013","citation":{"short":"M. Hunstig, W. Al-Ashtari, T. Hemsel, W. Sextro, in: J. Gausemeier, R. Dumitrescu, F.  Rammig, W. Schäfer, A. Trächtler (Eds.), 9. Paderborner Workshop Entwurf Mechatronischer Systeme, Heinz Nixdorf Institut, Universität Paderborn, Paderborn, 2013, pp. 359–372.","bibtex":"@inproceedings{Hunstig_Al-Ashtari_Hemsel_Sextro_2013, place={Paderborn}, series={HNI-Verlagsschriftenreihe}, title={Leistungs- und Bandbreitensteigerung von Energy-Harvesting-Generatoren für Energieautarke Systeme}, booktitle={9. Paderborner Workshop Entwurf mechatronischer Systeme}, publisher={Heinz Nixdorf Institut, Universität Paderborn}, author={Hunstig, Matthias and Al-Ashtari, Waleed and Hemsel, Tobias and Sextro, Walter}, editor={Gausemeier, Jürgen and Dumitrescu, Roman and  Rammig, Franz and Schäfer, Wilhelm and Trächtler, AnsgarEditors}, year={2013}, pages={359–372}, collection={HNI-Verlagsschriftenreihe} }","mla":"Hunstig, Matthias, et al. “Leistungs- Und Bandbreitensteigerung von Energy-Harvesting-Generatoren Für Energieautarke Systeme.” <i>9. Paderborner Workshop Entwurf Mechatronischer Systeme</i>, edited by Jürgen Gausemeier et al., Heinz Nixdorf Institut, Universität Paderborn, 2013, pp. 359–72.","apa":"Hunstig, M., Al-Ashtari, W., Hemsel, T., &#38; Sextro, W. (2013). Leistungs- und Bandbreitensteigerung von Energy-Harvesting-Generatoren für Energieautarke Systeme. In J. Gausemeier, R. Dumitrescu, F.  Rammig, W. Schäfer, &#38; A. Trächtler (Eds.), <i>9. Paderborner Workshop Entwurf mechatronischer Systeme</i> (pp. 359–372). Paderborn: Heinz Nixdorf Institut, Universität Paderborn.","ieee":"M. Hunstig, W. Al-Ashtari, T. Hemsel, and W. Sextro, “Leistungs- und Bandbreitensteigerung von Energy-Harvesting-Generatoren für Energieautarke Systeme,” in <i>9. Paderborner Workshop Entwurf mechatronischer Systeme</i>, 2013, pp. 359–372.","chicago":"Hunstig, Matthias, Waleed Al-Ashtari, Tobias Hemsel, and Walter Sextro. “Leistungs- Und Bandbreitensteigerung von Energy-Harvesting-Generatoren Für Energieautarke Systeme.” In <i>9. Paderborner Workshop Entwurf Mechatronischer Systeme</i>, edited by Jürgen Gausemeier, Roman Dumitrescu, Franz  Rammig, Wilhelm Schäfer, and Ansgar Trächtler, 359–72. HNI-Verlagsschriftenreihe. Paderborn: Heinz Nixdorf Institut, Universität Paderborn, 2013.","ama":"Hunstig M, Al-Ashtari W, Hemsel T, Sextro W. Leistungs- und Bandbreitensteigerung von Energy-Harvesting-Generatoren für Energieautarke Systeme. In: Gausemeier J, Dumitrescu R,  Rammig F, Schäfer W, Trächtler A, eds. <i>9. Paderborner Workshop Entwurf Mechatronischer Systeme</i>. HNI-Verlagsschriftenreihe. Paderborn: Heinz Nixdorf Institut, Universität Paderborn; 2013:359-372."},"page":"359-372"},{"title":"Model based enhancement of an autonomous system with a piezoelectric harvester","author":[{"first_name":"Waleed","full_name":"Al-Ashtari, Waleed","last_name":"Al-Ashtari"}],"date_created":"2019-05-13T13:47:14Z","publisher":"Shaker","date_updated":"2023-09-15T12:29:42Z","citation":{"chicago":"Al-Ashtari, Waleed. <i>Model Based Enhancement of an Autonomous System with a Piezoelectric Harvester</i>. Shaker, 2013.","ieee":"W. Al-Ashtari, <i>Model based enhancement of an autonomous system with a piezoelectric harvester</i>. Shaker, 2013.","ama":"Al-Ashtari W. <i>Model Based Enhancement of an Autonomous System with a Piezoelectric Harvester</i>. Shaker; 2013.","bibtex":"@book{Al-Ashtari_2013, title={Model based enhancement of an autonomous system with a piezoelectric harvester}, publisher={Shaker}, author={Al-Ashtari, Waleed}, year={2013} }","mla":"Al-Ashtari, Waleed. <i>Model Based Enhancement of an Autonomous System with a Piezoelectric Harvester</i>. Shaker, 2013.","short":"W. Al-Ashtari, Model Based Enhancement of an Autonomous System with a Piezoelectric Harvester, Shaker, 2013.","apa":"Al-Ashtari, W. (2013). <i>Model based enhancement of an autonomous system with a piezoelectric harvester</i>. Shaker."},"year":"2013","language":[{"iso":"eng"}],"user_id":"210","department":[{"_id":"151"}],"_id":"9792","status":"public","abstract":[{"text":"''Energy Harvester`` wandeln Umgebungsenergie in nützliche elektrische Energie. Zur Berechnung der elektromechanischen Charakteristik eines piezoelektrischen ''Energy Harvesters\" wird ein auf Materialeigenschaften, Geometrie und Randbedingungen basierendes analytisches Modell vorgestellt. Dieses dient als Basis für ein weiteres Modell, welches den Betrieb eines autonomen Systems beschreibt. Die theoretischen Arbeiten werden mit Laborversuchen validiert. Es zeigt sich, dass der piezoelektrische Harvester im eingeschwungenen Zustand durch den Gleichrichtungsvorgang zwei abwechselnde Lastzustände erfährt. Dies führt zu nichtlinearem Verhalten des Harvesters, besonders wenn die angeschlossene Last eine geringe Impedanz hat. Desweiteren zeigen die Ergebnisse, dass ein solches autonomes System effizient arbeitet, wenn es an eine Last mit hoher Impedanz angeschlossen ist und bei einer der Antiresonanzfrequenz des piezoelektrischen Harvesters entsprechenden Frequenz angeregt wird.Das Modell des autonomen Systems wird auf ein System mit mehreren piezoelektrischen Wandlern erweitert. Zur praktischen Implementierung eines solchen Systems wird eine Technik zur Frequenzeinstellung eingeführt, da die optimalen Betriebsfrequenzen der einzelnen Wandler aufeinander abgestimmt werden müssen. Die Einstellung erfolgt, indem die Entfernung zwischen zwei Permanentmagneten und damit deren Anziehungskraft, welche die Steifigkeit des Harvesters beeinflusst, angepasst wird. Diese Technik zur Frequenzeinstellung wird modelliert und experimentell validiert. Die Ergebnisse zeigen, dass die Frequenzeinstellung mittels Permanentmagneten eine einfache und zugleich effektive Lösung für das Problem der Frequenzanpassung piezoelektrischer ''Energy Harvester\" darstellt. \r\nEnergy harvesters convert ambient energy into useful electrical energy. An analytical model for calculating the electromechanical characteristics of a piezoelectric harvester based on the material properties, geometry and boundary conditions is presented. This model is the basis for a further model which describes the operation of an autonomous system powered by a piezoelectric harvester. This theoretical work is validated by corresponding laboratory experiments. It is found that, in steady-state operation, the piezoelectric harvester experiences two alternating load conditions due to the rectification process. These load conditions make the system behave nonlinearly, especially if the connected electrical load is of low impedance. Furthermore, the results show that such an autonomous system works efficiently if it is connected to a high impedance load and excited at a frequency matching the anti-resonance frequency of the piezoelectric harvester.The model of an autonomous system is extended to describe a system with multiple piezoelectric transducers. For implementing such a system, the optimum operation frequencies of the individual transducers must be adjusted. Therefore, a frequency tuning method is introduced. The tuning is accomplished by adjusting the distance between two permanent magnets and thus changing the attracting force between them in order to affect the structural stiffness of the harvester. This tuning method is modeled and validated experimentally. The results show that frequency tuning using permanent magnets is a simple and effective solution for the frequency adjustment of piezoelectric energy harvesters.","lang":"eng"}],"type":"dissertation"},{"title":"Frequency tuning of piezoelectric energy harvesters by magnetic force","date_created":"2019-05-13T13:16:33Z","author":[{"first_name":"Waleed","full_name":"Al-Ashtari, Waleed","last_name":"Al-Ashtari"},{"first_name":"Matthias","full_name":"Hunstig, Matthias","last_name":"Hunstig"},{"last_name":"Hemsel","id":"210","full_name":"Hemsel, Tobias","first_name":"Tobias"},{"last_name":"Sextro","full_name":"Sextro, Walter","id":"21220","first_name":"Walter"}],"volume":21,"date_updated":"2022-01-06T07:04:20Z","citation":{"chicago":"Al-Ashtari, Waleed, Matthias Hunstig, Tobias Hemsel, and Walter Sextro. “Frequency Tuning of Piezoelectric Energy Harvesters by Magnetic Force.” <i>Smart Materials and Structures</i> 21, no. 3 (2012): 035019.","ieee":"W. Al-Ashtari, M. Hunstig, T. Hemsel, and W. Sextro, “Frequency tuning of piezoelectric energy harvesters by magnetic force,” <i>Smart Materials and Structures</i>, vol. 21, no. 3, p. 035019, 2012.","ama":"Al-Ashtari W, Hunstig M, Hemsel T, Sextro W. Frequency tuning of piezoelectric energy harvesters by magnetic force. <i>Smart Materials and Structures</i>. 2012;21(3):035019.","apa":"Al-Ashtari, W., Hunstig, M., Hemsel, T., &#38; Sextro, W. (2012). Frequency tuning of piezoelectric energy harvesters by magnetic force. <i>Smart Materials and Structures</i>, <i>21</i>(3), 035019.","short":"W. Al-Ashtari, M. Hunstig, T. Hemsel, W. Sextro, Smart Materials and Structures 21 (2012) 035019.","bibtex":"@article{Al-Ashtari_Hunstig_Hemsel_Sextro_2012, title={Frequency tuning of piezoelectric energy harvesters by magnetic force}, volume={21}, number={3}, journal={Smart Materials and Structures}, author={Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}, year={2012}, pages={035019} }","mla":"Al-Ashtari, Waleed, et al. “Frequency Tuning of Piezoelectric Energy Harvesters by Magnetic Force.” <i>Smart Materials and Structures</i>, vol. 21, no. 3, 2012, p. 035019."},"page":"035019","intvolume":"        21","year":"2012","issue":"3","quality_controlled":"1","language":[{"iso":"eng"}],"user_id":"55222","department":[{"_id":"151"}],"_id":"9781","status":"public","abstract":[{"lang":"eng","text":"A piezoelectric energy harvester is an electromechanical device that converts ambient mechanical vibration into electric power. Most existing vibration energy harvesting devices operate effectively at a single frequency only, dictated by the design of the device. This frequency must match the frequency of the host structure vibration. However, real world structural vibrations rarely have a specific constant frequency. Therefore, piezoelectric harvesters that generate usable power across a range of exciting frequencies are required to make this technology commercially viable. Currently known harvester tuning techniques have many limitations, in particular they miss the ability to work during harvester operation and most often cannot perform a precise tuning. This paper describes the design and testing of a vibration energy harvester with tunable resonance frequency, wherein the tuning is accomplished by changing the attraction force between two permanent magnets by adjusting the distance between the magnets. This tuning technique allows the natural frequency to be manipulated before and during operation of the harvester. Furthermore the paper presents a physical description of the frequency tuning effect. The experimental results achieved with a piezoelectric bimorph fit the calculated results very well. The calculation and experimental results show that using this tuning technique the natural frequency of the harvester can be varied efficiently within a wide range: in the test setup, the natural frequency of the piezoelectric bimorph could be increased by more than 70\\%."}],"type":"journal_article","publication":"Smart Materials and Structures"},{"doi":"10.1177/1045389X11430742","title":"Analytical determination of characteristic frequencies and equivalent circuit parameters of a piezoelectric bimorph","volume":23,"author":[{"first_name":"Waleed","last_name":"Al-Ashtari","full_name":"Al-Ashtari, Waleed"},{"first_name":"Matthias","last_name":"Hunstig","full_name":"Hunstig, Matthias"},{"last_name":"Hemsel","id":"210","full_name":"Hemsel, Tobias","first_name":"Tobias"},{"id":"21220","full_name":"Sextro, Walter","last_name":"Sextro","first_name":"Walter"}],"date_created":"2019-05-13T13:17:37Z","date_updated":"2022-01-06T07:04:20Z","intvolume":"        23","page":"15-23","citation":{"ama":"Al-Ashtari W, Hunstig M, Hemsel T, Sextro W. Analytical determination of characteristic frequencies and equivalent circuit parameters of a piezoelectric bimorph. <i>Journal of Intelligent Material Systems and Structures</i>. 2012;23(1):15-23. doi:<a href=\"https://doi.org/10.1177/1045389X11430742\">10.1177/1045389X11430742</a>","ieee":"W. Al-Ashtari, M. Hunstig, T. Hemsel, and W. Sextro, “Analytical determination of characteristic frequencies and equivalent circuit parameters of a piezoelectric bimorph,” <i>Journal of Intelligent Material Systems and Structures</i>, vol. 23, no. 1, pp. 15–23, 2012.","chicago":"Al-Ashtari, Waleed, Matthias Hunstig, Tobias Hemsel, and Walter Sextro. “Analytical Determination of Characteristic Frequencies and Equivalent Circuit Parameters of a Piezoelectric Bimorph.” <i>Journal of Intelligent Material Systems and Structures</i> 23, no. 1 (2012): 15–23. <a href=\"https://doi.org/10.1177/1045389X11430742\">https://doi.org/10.1177/1045389X11430742</a>.","apa":"Al-Ashtari, W., Hunstig, M., Hemsel, T., &#38; Sextro, W. (2012). Analytical determination of characteristic frequencies and equivalent circuit parameters of a piezoelectric bimorph. <i>Journal of Intelligent Material Systems and Structures</i>, <i>23</i>(1), 15–23. <a href=\"https://doi.org/10.1177/1045389X11430742\">https://doi.org/10.1177/1045389X11430742</a>","short":"W. Al-Ashtari, M. Hunstig, T. Hemsel, W. Sextro, Journal of Intelligent Material Systems and Structures 23 (2012) 15–23.","mla":"Al-Ashtari, Waleed, et al. “Analytical Determination of Characteristic Frequencies and Equivalent Circuit Parameters of a Piezoelectric Bimorph.” <i>Journal of Intelligent Material Systems and Structures</i>, vol. 23, no. 1, 2012, pp. 15–23, doi:<a href=\"https://doi.org/10.1177/1045389X11430742\">10.1177/1045389X11430742</a>.","bibtex":"@article{Al-Ashtari_Hunstig_Hemsel_Sextro_2012, title={Analytical determination of characteristic frequencies and equivalent circuit parameters of a piezoelectric bimorph}, volume={23}, DOI={<a href=\"https://doi.org/10.1177/1045389X11430742\">10.1177/1045389X11430742</a>}, number={1}, journal={Journal of Intelligent Material Systems and Structures}, author={Al-Ashtari, Waleed and Hunstig, Matthias and Hemsel, Tobias and Sextro, Walter}, year={2012}, pages={15–23} }"},"year":"2012","issue":"1","quality_controlled":"1","language":[{"iso":"eng"}],"department":[{"_id":"151"}],"user_id":"55222","_id":"9782","status":"public","abstract":[{"lang":"eng","text":"Piezoelectric structures are nowadays used in many different applications. A better understanding of the influence of material properties and geometrical design on the performance of these structures helps to develop piezoelectric structures specifically designed for their application. Different equivalent circuits have been introduced in the literature to investigate the behaviour of piezoelectric transducers. The model parameters are usually determined from measurements covering the characteristic frequencies of the piezoelectric transducer. This article introduces an analytical technique for calculating the mechanical and electrical equivalent system parameters and characteristic frequencies based on material properties and geometry for a cantilever bimorph structure. The model is validated by measurements using a cantilever bimorph and fits the experimental results better than previous models. The model gives a full set of piezoelectric transducer parameters and is therefore well suited for further theoretical investigations of piezoelectric transducers for different applications. The results also show that even small manufacturing tolerances have a considerable effect on the system parameters and characteristic frequencies. This might lead to intolerable deviations, especially in dynamic applications and should be avoided by careful design and production."}],"publication":"Journal of Intelligent Material Systems and Structures","type":"journal_article"}]