Partial Electrode Configuration for Loss and Physical Parameter Determination of Piezoelectric Ceramics
Open Access
- Author:
- Park, Yoonsang
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 06, 2021
- Committee Members:
- Wenwu Cao, Outside Unit & Field Member
Ram Narayanan, Major Field Member
Mehdi Kiani, Major Field Member
Kenji Uchino, Chair & Dissertation Advisor
Kultegin Aydin, Program Head/Chair - Keywords:
- loss
mechanical quality factor
piezoelectric device
piezoelectric ceramics
high-power piezoelectrics - Abstract:
- Piezoelectric devices are driving technology in a number of industries, including sonar transducers used in military-grade underwater systems, compact electronic devices like mobile phones and digital cameras, fuel injectors, and the automobile industry. Especially, piezoelectric energy harvesting devices are to be set on “elimination of batteries”, which are classified as hazardous wastes, but recycled by less than 0.5% of 10s of Billion batteries sold per year in the world. The major problem of piezoelectric devices is that further miniaturization is limited by “heat generation”, owing to the “losses” in piezoelectric materials. Losses are mathematically described as imaginary parts of complex physical parameters of piezoelectric materials (that is, response phase lag to the input drive force) and categorized into three components: dielectric, elastic, and piezoelectric. These three categories of losses are further divided as I-type and E-type losses, depending on mechanical/electrical boundary conditions. The necessity of accurate loss determination of piezoelectric materials is mainly two-fold. First, I-type losses, as input parameters, greatly increase the accuracy of finite element analysis (FEA) computer simulation, which is a powerful tool to investigate desired output performance of piezoelectric devices. Second, E-type losses are helpful in elucidating heat generation mechanism that is known to limit further miniaturization and degrade the performance of high-power piezoelectric devices. Therefore, obtaining accurate values losses are important for both technological and scientific assets. The standard method to determine losses was previously established by Institute for Electrical and Electronics Engineer (IEEE) in 1980s. However, there are several deficits in this method that prevent users from obtaining accurate parameters. For example, IEEE Standard excludes existence of “piezoelectric loss”, which is the key factor for heat generation mechanism. There are even more issues with IEEE Standard on piezoelectricity in k33 mode, such as small capacitance and electric field leakage that hinders researchers from obtaining accurate losses. Furthermore, IEEE Standard does not provide the method to obtain both I-type and E-type loss factors, as well as the method to characterize unpoled piezoelectric materials that take up majority of the volumes of many types of piezoelectric devices. In order to resolve such disadvantages of IEEE Standard, partial electrode (PE) method, which utilizes samples with PE configuration, is proposed in this Ph. D. Dissertation. PE configuration is a plate structure that is composed of electrically excited and measured center part and the mechanically excited side parts. Since the purpose of PE configuration is to characterize properties of the side part, center part is maintained to about 10 % of the length of plate, whereas side parts take up about 90 % of the entire length. This particular characterization methodology is based on mechanical excitation, which is different from electrical excitation method suggested by IEEE Standard. The sample preparation is not significantly laborious compared to the preparation of IEEE Standard samples, since it only has an additional electrode sputtering and one additional poling step. The measurement is done through the center part with capacitance about 200 times larger than IEEE Standard. Therefore, the measurements do not suffer from small capacitance issue. It also enables characterization of both I-type and E-type losses simply by covering the side part with electrode or not, respectively. Moreover, with mechanical excitation, it is possible to characterize unpoled piezoelectric materials, which cannot be electrically excited due to zero piezoelectricity. This thesis is composed of seven chapters. Chapter 1 deals with theoretical backgrounds necessary to understand basics of high-power piezoelectric devices and loss mechanisms. Chapter 2 details deficits of current IEEE Standards for selected vibration modes (k31 and k33 modes) to explain necessity for new characterization method for better accuracy, along with some brief background of standard measurement methods and contributions from other researchers. Chapter 3 proposes PE method to resolve IEEE Standards issues, along with analytical and simulation approaches, Chapter 4 demonstrates error analysis and Chapter 5 show determined losses and physical parameters with PE method, along with brief discissions on materials differences. Chapter 6 represents PE method for characterization of unpoled piezoelectric ceramics and physical explanation related to domain and grain charge configuration for elastic intermediacy of unpoled piezoceramics. Finally, Chapter 7 summarizes the thesis and provide future work.