Journal of Applied Science and Engineering, Vol. 18, No. 4, pp. 339 344 (2015) DOI: 10.6180/jase.2015.18.4.04 Experimental Study on Electromechanical Performances of Two Kinds of the Integral Arrayed Cymbal Harvesters Chun-Hua Sun*, Jian-Hong Du, Guang-Qing Shang and Hong-Bing Wang Department of Mechanic and Electronic Engineering, Suzhou Vocational University, Suzhou 215104, P.R. China Abstract To expand the use scope of the well-known cymbal, two new integral arrayed cymbal harvesters are proposed. Similar to some cymbals in electrical parallel, the two harvesters are made up some piezoelectric disks sandwiched between two metal endcaps. On the endcap, many dome-shaped cavities corresponding to the PZT disks are evenly stamped. The only difference between the two harvesters is that there are some punched-holes on the metal endcaps of the second one. The experiment for testing electromechanical performances of the two harvesters is done at various frequencies and resistive loads. According to the experimental results, higher open voltage can be excited with the two harvesters at low frequency over a wide range. Moreover, the second one with punched-holes is more available for harvesting energy at lower frequency over a wider range and matches lower resistive load. One piece of the second harvester can obtain the maximum output power of 1.25 mw across 45 k. The simulation via the finite element method shows the validity of the applied experiment scheme. This reveals that the presented harvesters can be used as an alternative of effective tools for harvesting vibration energy under low frequency environment. Key Words: Piezoelectric Effect, Energy Harvesting, Cymbal, Integral Arrayed, Finite Element Analysis 1. Introduction The piezoelectric cymbal transducer is capable of withstanding high force applications while producing usable power and has received the most attention [1]. Based on the positive piezoelectric effect, electromechanical performances of the original cymbal have been investigated by many researchers [2 5]. Further, to enlarge the harvesting energy efficiency and to broaden the applicable scope, some studies took the scheme by arranging some original cymbals along the longitudinal or horizontal direction in electrical series or parallel [6,7]. In addition, high circumferential stresses caused by flexural motion *Corresponding author. E-mail: sunch@jssvc.edu.cn of the metal endcaps can induce loss of mechanical input energy and decrease the energy transmission coefficient when the original cymbal receives external force. A new slotted-cymbal structure was proposed to set free the circumferential stresses and increase the output coefficient [8]. However, due to the limitations of the piezoelectric ceramic manufacturing technique, the sizes of PZT disks are small. That leads to smaller size of the existed cymbal and makes it to be restricted for capturing energy on large scale. In the paper, two new kinds of the integral arrayed cymbal harvesters with many PZT disks sandwiched between two larger metal endcaps were presented for overcoming the above disadvantages. The electromechanical performance containing the output voltage and
340 Chun-Hua Sun et al. power of the two harvesters were evaluated. The simulation was also done for identifying the validity of the experimental scheme. 2. Preparation of Two Kinds of Integral Arrayed Cymbal Harvesters In order to simplify the subsequent arrangement of the original cymbals in series or parallel, an innovative structure, which is named the integral arrayed cymbal harvester, is proposed, as shown in Figure 1. The harvesters are made up some PZT disks sandwiched between two metal endcaps, on which there are evenly punched dome-shaped cavities corresponding to the PZT disks. The arrayed distribution lists as following: 1 is on the center; 6 are on the second circle at 60 degree spacing; 12 are on the third at 30 degree. The diameter of the harvester is 100 mm. The spacing distance between adjacent cavities is set as 20 mm along the horizontal axis. The process flow of the first kind of harvester, as shown in Figure 1(a) is addressed as following: (1) 100 of circular endcap is manufactured via punching from aluminum metal sheet. (2) The dome-shaped cavities are formed on endcaps with the stamping die, as shown in Figure 2. (3) PZT-5A disks arrayed with the same polarized direction are bonded with two endcaps by using conductive adhesive and curing at 80 C for 8 h. The pasted positions of PZT disks are located according to the dome-shaped cavities on the endcaps. (4) The epoxy resin is filled into the gap betweem two endcaps through the filled hole on the boundary of endcaps. The produces are then placed on the air and wait for drying. (5) Two conductive wires are soldered on the edges of the two endcaps. A integral arrayed cymbal harvester is prepared. To ease the phenomenon that the flexural motions of the metal endcaps could introduce high circumferential stresses, the improved one with the evenly holes in metal endcaps is then presented, as shown in Figure 1(b). This structure is inspired by the slotted-cymbal mentioned in Ref. [8]. The holes with diameter of 10 mm are located among the center of three adjacent cavities. The same as the first kind of harvester, the second one with many holes on endcaps is also easily fabricated. The only difference between the twos is the punching holes on the endcaps before stamping. When the alternating force is taken on cavities of the proposed harvesters, PZT disks are excited out electric charges and then output through the two wires. Therefore, the two harvesters can be used to capture ambient vibration and transfer it into electricity. As PZT disks are arrayed along the same polarized Figure 1. Models and goods: (a) The first harvester; (b) The second harvester. Figure 2. The stamp die for forming the metal endcap with dome-shaped cavities.
Experimental Study on Electromechanical Performances of Two Kinds of the Integral Arrayed Cymbal Harvesters 341 direction during the process of fabricating the harvesters, the harvesters are similar to many original cymbal harvesters in electrical parallel. Owing to the advantages of the original cymbal, the harvesters also possess the following characteristics: more easily manufactured for saving processing time, more suitable for scavenging large-scale vibration. The following will test the electromechanical properties of the two harvesters. 3. Experimental Results and Discussion Figure 3 shows the picture of the experimental setup. The sinusoidal vibration, which is generated by a signal generator (VC2002), is amplified by the power amplifier (GF100). It drives the electrical vibration exciter (JZQ- 10) to supply vibration for the vibrating rod and provides the exciting force for the piezoelectric harvester. The output voltage from the harvesters was monitored with Tektronix digital oscilloscope (TDS 2022B). This vibrator has the capability of providing a frequency range of 1 10 khz, which can be driven at various voltages and frequencies using the function generator and a high-power amplifier to produce a cyclic force of the required magnitude and frequency. All experiments were performed on an isolated bench to avoid any interference from the surrounding environment. The two harvesters were experimented under high vibration level with pre-stress conditions controlled by a metal block. Figures 4 5 shows the output voltages from the two harvesters with various gains of the vibration source at 50 k resistive load. In the experimental setup, the number of vibration source s gain represents the size of the dynamic force on the harvester. Obviously, from the two above figures, the results can be drawn that the output voltages increase with the gains by two harvesters. This trend can be explained as follows: with increasing the gain of vibration source, the forces on the harvesters increase. Thus the deformation of the PZT disk is drastically increased to excite the bigger electric charge. Furthermore, the output voltage by the second harvester increases more rapidly than the first one. 6 V output voltage is increasing by the second harvester when one gain increases, while 5 V by the first harvester. There is about 20% increasing of the output voltage with the second harvester than the first one. This is due to easier deformation of the metal endcaps because the hollowed areas release the circumferential stresses around the dome-shaped cavities and increase the energy transmission coefficient. Therefore, it is prone for the second harvester to convert strain energy into electrical energy. Figures 6 7 show the results of the two harvesters as a function of the output voltage with various frequencies. Figure 4. Output voltage at different gains by the first harvester. Figure 3. The experimental setup: (1) Vibration source (shaker); (2) Pre-stress block, and (3) Current amplifier. Figure 5. Output voltage at different gains by the second harvester.
342 Chun-Hua Sun et al. The adopted experimental frequency range is 0 50 Hz. From Figures 6 7, the conclusions can be drawn as follows: 1) More than 10V open voltage can be stimulated over a wide frequency range with the two harvesters. So, the bandwidths have been effectively improved if the bandwidth is defined to be the half of the maximum open voltage. 2) Open voltage by the second harvester can more rapidly up to 10 V at 5.5 Hz, while 9 Hz by the first harvester. 3) The average open voltage is 14.7 V via the second harvester, which is larger than 14.3 V by the first harvester. That is, the two harvesters are capable for scavenging energy at low frequency of 0 50 Hz. The second one is improved for validating to harvest higher voltage from ambient energy over a wider frequency range than the first one. The voltage and power for various external resistive loads with the two harvesters are measured at the frequency of 10 Hz, as shown in Figure 8 9. Some remarkable phenomena can be found as follows: 1) valid voltage increases with the resistive loads in both cases, 2) a maximum power of 1.25 mw can be harvested across 45 k resistive load with the second harvester, larger than 0.85 mw via the first one. 3) Comparison of Figures 8 and 9 shows that the output voltage and power of the second harvester are larger than those of the first one. It indicates that the second harvester is preferred because of the higher harvested electric power and the lower matching resistive load. 4. Simulation and Comparison To identify the validity of the experiment results, one quarter finite element model of the first harvester is constructed according to the axisymmetric characteristic, as shown in Figure 10. The unit of SOLID45 is used to mesh the endcaps and the binder, and SOLID5 is used for PZT disks. The units are meshed by using HyperMesh and then transferred into ANSYS. The total contract force, which is equal to the weight of the metal block, is accepted to act evenly on the cavities of one endcap along the axis direction, as shown in Figure 1. The transit analysis are then done after applying the Figure 6. Voltage at different frequencies by the first harvester. Figure 8. Voltage and electric power at various resistors by the first harvester. Figure 7. Voltage at different frequencies by the second harvester. Figure 9. Voltage and electric power at various resistors by the second harvester.
Experimental Study on Electromechanical Performances of Two Kinds of the Integral Arrayed Cymbal Harvesters 343 Figure 10. One quarter model of the harvester. boundary conditions. The result from simulation is shown in Figure 6. Comparison of the simulation and experiment results for the first harvester shows that the trends of the simulation and experiment data are consistent. This confirms the validity of the applied experiment scheme. Meanwhile, the experimental data appear fluctuations and most are smaller than the simulation data. The deviation between simulation and experiment may be due to the difference of material properties, such as PZT and epoxy resin. 5. Conclusions This paper develops two kinds of integral arrayed cymbal harvesters. The larger metal endcaps, on which many dome-shaped cavities are evenly stamped, are adopted foreffectively scavenging large scale vibration. The structures are similar to some original cymbals in electrical parallel. For releasing high circumferential stresses around the cavities, the second one is improved by punching holes on the metal endcaps. The performance of the two kinds of harvesters including output voltage and power was tested at low frequency condition. Experimental results show that the output voltage increases with gain, frequency and resistive load with two harvesters. This indicates that two kinds of the integral arrayed cymbal harvesters are capable for harvesting energy over a wide range of low frequency on a large area. The second harvester with punched-hole on metal endcap is more easily excited to deform and generate higher electrical power at lower matched resistive load. The maximum output power of 1.25 mw at 10 Hz and 45 k can be obtained by one piece of the second one, which is 0.5 times than the first one. And the power via resistive load varies in line with the general law and there has a maximum. Comparison of the simulation and experiment for the first harvester shows that both trends are consistent. This confirms the validity of the applied experiment. Based on the results of this study, it can be conjectured that both of the integral arrayed cymbal harvesters can provide an effective alternative for harvesting waste vibration. And the second one with punched-holes is more effective. The further work is to analyze the stress distribution of the two harvesters and optimize their structures. Acknowledgements This research was supported by the National Natural Science Foundation of China (No. 51175359) and the 4th 333 Engineering Research Funding Project of Jiangsu Province (BRA2014086). The authors are very thankful to Dr. Jian Yu, Function Material Research Lab, Tongji University, China, for providing the harvester samples. References [1] Newnham, R. E., et al., U.S, Patent 4999819, 1991, 3. [2] Kim, H. W., Priya, S. and Uchino, K., Modeling of Piezoelectric Energy Harvesting Using Cymbal Transducers, Jpn. J. Appl. Phys., Vol. 45, No. 7, pp. 5836 5840 (2006). doi: 10.1143/JJAP.45.5836 [3] Zhao, H. D., Yu, J. and Ling, J. M., Finite Element Analysis of Cymbal Piezoelectric Transducers for Harvesting Energy from Asphalt Pavement, Journal of the Ceramic Society of Japan, Vol. 118, No. 10, pp. 909 915 (2010). doi: 10.2109/jcersj2.118.909 [4] Guo, Z. Y., Ye, M., Cheng, B. and Cao, B. G., Influence of Shape Parameters on Electricity Generation by Cymbal Transducer, Mechanical Science and Technology for Aerospace Engineering, Vol. 26, No. 11, pp. 1454 1457 (2007). [5] Sun, C. H., Tao, Y. Y., Wang, H. B., Xu, H., Zhi, Z. R. and Zhang, Y. P., Piezoelectric Effect of Cymbal Transducer under Action of Alternating Force, Modern Manufacturing Engineering, No. 12, pp. 91 94 (2010). [6] Xing, J. X., Study on Cymbal Transducer and its Array, Master Dissertation, Harbin Engineering University (2006). [7] Wen, S., Zhang, T. M., Liang, L., Huang, P. S. and Xie, Z. Y., Vibration Analysis on Cymbal Transducer Stack, Journal of Vibration Measurement & Diag-
344 Chun-Hua Sun et al. nosis, Vol. 31, No. 3, pp. 295 299 (2011). [8]Yuan,J.B.,Shan,X.B,Xie,T.andChen,W.S., Energy Harvesting with a Slotted-cymbal Transducer, Journal of Zhejiang University SCIENCE A, Vol. 10, No. 8, pp. 1187 1190 (2009). doi: 10.1631/jzus.A0920183 Manuscript Received: Apr. 17, 2015 Accepted: Sep. 21, 2015