Development of Self-Generating Wireless Temperature Sensor Network Utilizing Pb-Free Energy-Harvesting Technology to Prevent Fire Caused by Using Lithium-Ion Batteries in Power Plants

Article information

Int J Fire Sci Eng. 2022;36(1):50-61
Publication date (electronic) : 2022 March 31
doi : https://doi.org/10.7731/KIFSE.4aa296c1
1Graduate School of Industry, Pukyong National University, 45 Yongso-ro, Nam-gu, Busan, 48513, Republic of Korea
2Division of Architectural and Fire Protection Engineering, Pukyong National University, 45 Yongso-ro, Nam-gu, Busan, 48513, Republic of Korea
Corresponding Author, TEL: +82-51-629-7830, FAX: +82-51-629-7078, E-Mail: jchoi@pknu.ac.kr
Received 2022 March 10; Revised 2022 March 10; Accepted 2022 March 10.

Abstract

A recent battery fire accident in a power plant has drawn attention to fire safety management. The lithium-ion battery, the most widely used among secondary batteries, has a high energy density with a high risk of ignition, owing to shock, overheating, discharging, and overcurrent. Installing batteries in a hazardous area inside a power plant increases the risk of a fire. Therefore, there is a need to construct a facility capable of monitoring the state of the managed area without using a battery. Therefore, the aim of this study is to develop a self-powered wireless temperature sensor network using Pb-free piezoelectric energy-harvesting technology. The developed harvester consisted of a Pb-free piezoelectric element produced using Ba0.9Ca0.1Ti0.93Zr0.07O3 + 0 .3 m ol % CuO (BCTZ0.3C) ceramic. When the Pb-free piezoelectric energy harvester was operated for 15 s, power to stably operate the wireless sensor network could be obtained, sufficient to transmit the temperature measured once every 1.2 s to the wireless transmitter.

1. Introduction

1.1 Background and purpose of the study

Energy harvesting is the process of collecting unused ambient energy (for example, sunlight, wind, temperature changes, vibration, or pressure) and transforming it into usable electrical energy by storing it in a small wireless device, which can be classified as a different energy source from the existing energy sources [1,2]. Thermoelectric energy harvesting uses the Seebeck effect to convert temperature gradients into electrical energy. The Seebeck effect converts the temperature difference into electrical energy at the junction between two different materials. This effect has been applied in heating and cooling applications and electrical energy-generating devices [3,4]. Piezoelectric energy harvesting uses the piezoelectric effect to convert mechanical energy into electrical energy.

However, the smart factory that will lead the innovation of the fourth industrial revolution requires a lowvibration or nonvibration environment, unlike the existing industrial environment. In the future industrial environment, vibration, which is the energy source of the current piezoelectric energy- harvesting technology, is expected to decrease gradually. Therefore, it is necessary to develop piezoelectric harvesting technology applicable to the smart factory based on indirect vibration (induced vibration) rather than direct vibration [5]. Electromagnetic piezoelectric harvesting technology is a power generation technology produced through indirect vibration. Electromagnetic piezoelectric harvesting technology is a core technology for the industrialization of piezoelectric harvesting technology in a low-vibration or nonvibration industrial environment. With the spread of smart factories, the existing production line system is gradually converted to a module production system. As a solution to the independent power supply problem to the Internet of Things sensors to achieve a module production system, extensive research on piezoelectric harvesting technology using the rotational force that inevitably exists in the production line is required [6-8].

Recently, fire occurrences have been increasing, owing to the absence of a safety platform for the facility standards of energy storage systems. Battery fires emit significant amounts of toxic smoke and combustion gases and generate high heat, with concerns about fragmentation caused by the explosion, deterioration of structures, and damage by the spreading fire to surrounding facilities. Furthermore, it is difficult to determine the exact cause of battery explosions and fires. When a fire occurs, the damage is significant compared to the area lost, raising concerns about combustion expansion in unprotected, exposed power generation facilities or buildings. The lithium-ion battery, the most widely used among secondary batteries, has a high energy density with a high risk of ignition due to shock, overheating, discharging, and overcurrent. Under certain extreme environmental conditions in power plants, the installation and use of lithium- ion batteries may have additional risks, requiring the development of technology to analyze the cause of the accident and monitor the status.

The aim of this study is to develop a wireless sensor network capable of real-time monitoring and overcoming environmental limitations by applying energy-harvesting technology.

1.2 Previous research trends

Piezoelectric energy-harvesting technology utilizes the piezoelectric effect. In the piezoelectric effect, an electric field is generated when a physical force (strain) is applied to the piezoelectric element, and lead zirconate titanate (PZT) material-based ceramics are generally used. In line with the worldwide trend of reducing the use of leadcontaining products according to the RoHS of the European Union, several studies have been conducted to develop Pb-free materials with properties comparable to those of conventional lead-based piezoelectric materials [12-15].

Piezoelectric materials have been used in many applications, such as electronic and microelectronic devices. Piezoelectric materials have several advantages, owing to their high energy conversion, reliability, and performance. Furthermore, piezoelectric energy harvesting is an attractive technique for transforming mechanical energy into electrical energy at low vibration frequencies with low environmental impact.

The efficiency of piezoelectric energy harvesting is significantly influenced by the performance of the energy conversion material. The first property required for piezoelectric energy conversion materials is piezoelectric performance. When the electromechanical coupling factor, k, of the piezoelectric material is increased from 0.5 to 0.9, the energy conversion efficiency increases from 25% to 81% [16]. Some previous studies aimed to improve energy conversion efficiency [17,18]. The second property required is impact resistance and flexibility. Because piezoelectric energy harvesting collects energy from shocks and continuous vibrations from railways or roadways, durability must be ensured. Therefore, many studies have been conducted to enhance the flexibility of the material [19-21]. The third property is ecofriendliness and harmlessness to the human body. The most widely used piezoelectric material is PZT. As this material contains lead, it is harmful to the human body, brittle, and susceptible to damage.

The aim of this study is to manufacture Pb-free piezoelectric ceramic materials to examine Pb-free piezoelectric materials and develop a wireless sensor network suitable for extreme environments using such materials.

2. Pb-free Piezoelectric Energy-Harvesting Composition

Piezoelectric energy-harvesting technology requires convergence research encompassing materials, machinery, and electricity through material optimization to develop piezoelectric compositions. These piezoelectric materials are expected to have excellent properties, mechanical optimization to efficiently convert energy in the surrounding environment, and electrical optimization to apply high-efficiency electric circuit techniques for maximum power delivery. In this study, such convergence research was conducted to develop a piezoelectric energy harvester with a high power density.

First, material optimization was performed by developing composition for Pb-free piezoelectric ceramics to replace Pb-based piezoelectric ceramics. This optimization was conducted to develop Pb-free Ba1-xCaxTi1-yZryO3 (BCTZ) piezoelectric ceramic compositions based on barium, calcium, titanium, and zirconium oxides to replace the existing PZT-based piezoelectric material containing lead.

The cantilever-type piezoelectric energy harvester generally uses a bending vibration mode for electromechanical energy conversion. It is essential to increase the energy conversion efficiency (η) through material optimization to improve the performance of a piezoelectric harvester that obtains electrical energy from ambient vibration. The energy conversion efficiency of the piezoelectric material is expressed by Eq. (1). The energy conversion efficiency of piezoelectric ceramics is expressed as the electromechanical coupling factor (kp) and the mechanical quality factor (Qm). Piezoelectric ceramics must have high kp and Qm values to obtain high values at the resonant frequency [22].

(1) η=(12kp21-kp2)÷(1Qm+12×kp21-kp2)

A solid solution is utilized at the A and B sites of BaTiO3 (generally, A = Ca, Sr, La; B = Nb, Ta, Zr) to improve the piezoelectric and dielectric properties. Several studies on Ca2+ and Zr4+ doping have been conducted, and a high piezoelectric coefficient (d33 = 620 pC/N) has been reported for Ba0.9Ca0.1Ti0.93Zr0.07O3. Most of such studies focused on increasing the piezoelectric charge coefficient (d) in the same composition, as sintering temperature control and dopant substitution change the microstructure of Ba0.9Ca0.1Ti0.93Zr0.07O3 [23].

It was intended to develop a lead-free piezoelectric composition with a 20k-class energy conversion coefficient (d × g) value to develop lead-free piezoelectric materials for energy harvesting by developing a composition near Ba0.9Ca0.1Ti0.93Zr0.07O3. This is followed by adding a dopant and altering the sintering and poling conditions. (Figure 1)

Figure 1.

BCTZ phase diagram.

A typical acceptor-doped ion, Cu2+, is used to improve the output properties of the piezoelectric material and reduce the sintering temperature. CuO is a sintering material that effectively reduces the sintering temperature improves the dense microstructure of piezoelectric materials. The developed composition has been used to manufacture a beam-shaped piezoelectric element for application to a piezoelectric energy harvester. In addition, a piezoelectric energy harvester was designed using the manufactured piezoelectric element. Based on physical phenomenon analysis, a piezoelectric harvester with a mechanically optimized structure was designed and manufactured based on mechanical performance verification through structural and fatigue analyses.

3. Pb-free Piezoelectric Element

3.1 Method for manufacturing Pb-free piezoelectric element

Pb-free Ba0.9Ca0.1Ti0.93Zr0.07O3 + 0.3 mol % CuO (BCTZ0.3C) ceramics was manufactured using the conventional solid-state reaction method. Powders, such as BaCO3 (99.0%), CaCO3 (99.0%), TiO2 (99.0%), ZrO3 (99.0%), and CuO (99.9%), were weighed and mixed by ball milling in alcohol for 24 h. After drying, the mixture was calcined in an alumina crucible at 1,250 °C for 2 h. The calcined powder was milled again for 12 h. The dried powder was mixed with 2% polyvinyl alcohol and manufactured in a bulk form under 100 MPa pressure. The green disk was sintered in the air at 1,300-1,450 °C for 4 h, and the sintered bulk surface was polished and refined before measurements.

The calcined powder was remixed with a plasticizer (B- 73225, FERRO, USA) and polyvinyl butyral polymer for 24 h to prepare a slurry with a ceramic-to-polymer weight ratio of 2:1. The slurry was then defoamed in a vacuum for 30 min to remove air bubbles. Using the finished slurry, green sheets each with a thickness of approximately 30 μm, were manufactured using a tape-casting process. A square sample of 30 mm × 40 mm was prepared by cutting the fabricated green sheets with a cutter (DC-5, DH). Next, the sheets were laminated layer by layer, with 10 sheets laminated under a pressure of 10 kg/cm2 at 60 °C for 10 min. The specimen was slowly heated at 600 °C using an electric furnace (AJ-MLBF2, AJEON) to remove organic additives from the laminated sheet, and heating was maintained at the same temperature for 3 h. An electric field was applied to the sintered thick film to undergo the poling process by applying 2 kV/mm for 2 h. The piezoelectric charge constant, d33 (pC/N), was measured using a d33 meter (PM100, Piezotest). A BCTZ0.3C thick film was attached to the top and bottom of a stainless steel substrate (SUS304), and the power generation characteristics were determined using an oscilloscope (DPO4054B, Tektronix).

3.2 Development of Pb-free piezoelectric element

Figure 2 shows BCTZ0.3C bulk samples arranged according to the sintering temperature variation. For the optimal design of the piezoelectric energy harvester composition, a bulk sample with the highest piezoelectric and dielectric properties was prepared. Bulk samples were prepared by increasing the sintering temperature from 1,300 to 1,450 °C in 50 ℃ intervals. The surface color gradually darkened as the sintering temperature increased.

Figure 2.

BCTZ0.3C bulk samples according to changes in sintering temperature.

Figure 3 shows the surface images of the BCTZ0.3C bulk sample with variations in sintering temperature captured using field emission-scanning electron microscopy (FE-SEM) equipment. In the bulk sample sintered at 1,350 °C, various grains of approximately 5 to 10 μm were observed. As the sintering temperature increased to 1,500 °C, an increase from 20 to 40 μm was observed. For the bulk sample sintered at 1,500 °C, the piezoelectric and dielectric properties could not be measured because the surface melted, owing to the high sintering temperature.

Figure 3.

Surface FE-SEM images of BCTZ0.3C bulk samples according to changes in sintering temperature.

Figure 4 shows the X-ray diffraction (XRD) analysis values for different sintering temperatures in determining the optimal composition of the BCTZ0.3C bulk sample, a Pb-free piezoelectric material. Rhombohedral crystals having a perovskite structure without a secondary phase were observed in BCTZ0.3C with changing sintering temperature. As the sintering temperature increased from 1,300 to 1,450 °C, the 110 peak intensity increased relatively. As observed through FE-SEM, the peak intensity appeared to be significantly influenced by grain size. In the sample sintered at 1,500 °C, the 110 intensity decreased, and the 200 intensity increased. This phenomenon was observed when melting proceeded, and the grain size increased significantly.

Figure 4.

XRD graph for intensity of BCTZ0.3C bulk sample with changes in sintering temperature.

X-ray photoelectron spectroscopy (XPS) was performed to analyze the components of the BCTZ0.3C bulk sample sintered at 1,450 °C (Figure 5). Based on the component analysis results, Ba, Ti, Ca, and Zr components included in the experiment were detected, and the secondary phase of CuO was not observed.

Figure 5.

XPS component analysis graph of BCTZ0.3C sample sintered at 1,450 °C.

Figure 6 shows the variation of the piezoelectric and dielectric properties of the BCTZ0.3C bulk sample with sintering temperature. As the sintering temperature increased, the density increased at all temperatures. The piezoelectric voltage constant (g33) also improved, owing to the increased piezoelectric charge constant (d33) and a relative decreased dielectric constant. The piezoelectric voltage constant was expressed as g33 = d33/dielectric constant. The dielectric constant tended to decrease when the sintering temperature increased above 1,400 °C, increasing the piezoelectric voltage constant (g33).

Figure 6.

Graph of piezoelectric and dielectric properties of BCTZ0.3C bulk sample with changes in sintering temperature.

The conversion efficiency (η) values exceeded 82% at all sintering temperatures, and the conversion constant (kp) tended to increase with increasing temperature. However, the quality factor (Qm) value decreased sharply, resulting in low conversion efficiency (η).

The piezoelectric conversion constant (d33 × g33) increased as the sintering temperature increased, and the piezoelectric voltage constant (g33) and piezoelectric charge constant (d33) increased to 15.7 k in the BCTZ0.3C bulk sample sintered at 1,450 °C. Based on the energy density equation {u = 1/2 (d33 × g33)(F/A)2}, the BCTZ0.3C sample sintered at 1,450 °C had the highest energy density. The FE-SEM analysis showed that as the grain size increased, the dielectric constant tended to decrease, and the piezoelectric charge constant (d33) increased, increasing the power conversion constant (d33 × g33). This trend appeared to be closely associated with the phenomenon in which the power conversion constant (d33 × g33) was high when the 110 intensity value was the highest as the sintering temperature increased to 1,450 °C based on the XRD result analysis. Table 1 lists the piezoelectric and dielectric properties for different sintering temperatures. The BCTZ0.3C specimen sintered at 1,450 °C had a high piezoelectric charge constant (d33) value of 526 pC/N, a kp value of 49.3%, and a high power conversion constant (d33 × g33) of 15,780 × 10-15 m2/N, which was a power-generating element in this study.

Piezoelectric and Dielectric Properties of BCTZ Bulk for Different Sintering Temperatures

3.3 Evaluation of Pb-free piezoelectric energy- arvesting characteristics

A unimorph cantilever-type piezoelectric energy harvester was manufactured using a BCTZ0.3C thick film. Each piezoelectric thick film (size = 1.9 cm × 1.6 cm × 0.025 cm) was attached to SUS304 (size = 4.0 cm × 9.0 cm × 0.020 cm). The operating performance of the energy harvester was determined based on the physical parameters of the piezoelectric harvester (length, mass, area, thickness, and position of the piezoelectric ceramic and SUS304). The piezoelectric cantilever beam was designed to be tuned to a low resonant frequency. The frequency was modeled using a lateral load concentrated at the tip and batch parameters, where E is Young's modulus, L is the length of the beam, I is the moment of inertia, and m is the mass of the tip.

(2) fr=12π3EIL3m

The variation in the output voltage of the BCTZ0.3C thick film with sintering temperature was analyzed. For the 7.52 Hz resonant frequency generated under the vibration conditions, the output voltages increased to 2.65, 3.8, 5.3, and 6.2 V as the sintering temperatures increased to 1,300, 1,350, 1,400, and 1,450 °C, respectively.

The output power, which varied with the sintering temperature of the BCTZ0.3C thick film and depended on load resistances of 100 Ω to 100 kΩ, was measured at a resonant frequency of 7.52 Hz (displacement = 1.5 cm at 1.0 m/s2). The peak voltage (V) applied to the load resistor (R) was measured and calculated using the equation, P = V2/R, to determine the power (P) output from the energy harvester (Figure 7). The output power (mW) steadily increased as the sintering temperature increased from 1,300 to 1,450 ℃. The output power of BCTZ0.3C sintered at 1,300 °C was 4.0 mW (power density = 52.63 mW/cm3), and that sintered at 1450 °C was 8.2 mW (power density = 107.9 mW/cm3).

Figure 7.

Comparison of variation in output power through impedance matching of BCTZ0.3C thick film with sintering.

The output power (P) and BCTZ0.3C thick film size were calculated as power density = P/Volume to obtain the power density. As a parameter that improves the output power, the d33 value increased as the 110 peak intensity of the BCTZ0.3C sample increased, following an increase in the sintering temperature. The variation in the piezoelectric conversion constant (d33 × g33) of the BCTZ0.3C composition with the sintering temperature is closely associated with the output (mW) of the piezoelectric energy harvester manufactured in this study.

Figure 8 shows the variations in the output power (mW) and piezoelectric conversion constant (d33 × g33) with the sintering temperature of the BCTZ0.3C thick film. The piezoelectric conversion constant (d33 × g33) and the output power (mW) increased, exhibiting a similar tendency. In the piezoelectric energy harvester produced using the BCTZ0.3C thick film, the increase in the piezoelectric conversion constant (d33 × g33) was a factor that improved the power generation close to the output power (mW). Therefore, the piezoelectric energy harvester manufactured in this study must have a high piezoelectric conversion constant (d33 × g33) value to achieve improved output power (mW). The piezoelectric harvester produced in this study used BCTZ0.3C sintered at 1,450 °C as the power source of the self-powered wireless sensor network.

Figure 8.

Variations in output power and piezoelectric conversion constant (d33 × g33) value of BCTZ0.3C thick film with sintering temperature.

4. Development of Self-powered Wireless Temperature Sensor Network

4.1 Development of self-powered wireless sensor network

A unimorph-type piezoelectric energy harvester manufactured with a BCTZ0.3C thick film sintered at 1,450 °C was used to develop a real-time sensing system by supplying power generated under vibration conditions to a wireless sensor network and wirelessly transmitting temperature data to a laptop computer. A wave generator and an exciter were used to simulate vibration conditions in a laboratory environment. Electricity was continuously supplied where vibration was applied to the piezoelectric energy harvester at 7.52 Hz, supplying the power required to operate the temperature sensor and wireless transmitter.

An energy harvester was fabricated using the BCTZ0.3C thick film sintered at 1,450 °C to operate the selfgenerated wireless sensor network. After converting the alternating-current (AC) voltage generated by the energy harvester to a direct- current voltage using a rectifier, the capacitor was charged with the necessary power to provide stable electricity to the wireless sensor network. The voltage of the supplied power was constantly reduced using a step-down converter, and information regarding the ambient temperature was transmitted to the wireless transmitter connected to the computer by supplying power to the temperature sensor and wireless transmitter.

Figure 9 shows the voltage used when the temperature sensor and wireless transmitter were operated by the electricity stored in the capacitor (capacity = 150 μF) using the output voltage of the energy harvester manufactured with the BCTZ0.3C thick film sintered at 1,450 °C. In the energy harvester, vibration (7.52 Hz) was charged to the capacitor by 7 V for 2.8 s, supplying sufficient power to operate the wireless sensor network. Power was supplied to the temperature sensor wireless transmitter (eZ430-RF2500T, Texas Instruments, USA) for real-time monitoring by measuring the ambient temperature every 1.2 s with sufficient power supplied. The measurable temperature ranged from −40 to 85 °C. Furthermore, the voltage was continuously charged up to 17 V, despite the stable power supply to the wireless sensor network.

Figure 9.

Graph of wireless sensor network operation using voltage generated from BCTZ0.3C.

4.2 Wireless temperature sensor network using Pb-free piezoelectric energy harvester

Figure 10 shows the temperature measurement results obtained using the electricity charged by the voltage generated by operating the piezoelectric energy harvester under vibration for 15 s. The energy harvester manufactured using the BCTZ0.3C thick film sintered at 1,450 °C could supply sufficient power for 15 s under vibration conditions, and it was measured from the lowest temperature (29 °C) to the highest temperature (30.2 °C). Although it was measured in a laboratory environment with constant vibrations, electricity could be supplied through the selfdeveloped Pb-free piezoelectric energy harvester.

Figure 10.

Graph of temperature measured by supplying power to wireless sensor network.

5. Conclusion

This study focused on developing a Pb-free BCTZ0.3C ceramic to develop a Pb-free piezoelectric element for replacing the Pb-based piezoelectric element. A piezoelectric energy-harvesting system was developed using the BCTZ0.3C ceramic, which was used to develop a wireless temperature sensor network. The piezoelectric energy harvester developed in this study can achieve self-generation and supply sufficient power to operate the temperature sensor and wireless transmitter. The main conclusions of this study are as follows.

(1) A comparison of the composition characteristics of BCTZ0.3C piezoelectric energy with sintering temperature changes showed that the grain size and the peak intensity in the 110 direction increased with increasing temperature. This phenomenon increased the piezoelectric conversion constant (d33 × g33), increasing the output voltage of the piezoelectric energy harvester.

(2) The piezoelectric conversion constant (d33 × g33) of the BCTZ0.3C sintered at 1,450 °C was 15.8k, and the power generation property was 8.2 mW (power density = 107.9 mW/cm3).

(3) Power to stably operate the wireless sensor network could be obtained by operating the piezoelectric energy harvester in a vibrating environment for 15 s.

(4) The power generated by the piezoelectric energy harvester could supply sufficient power to transmit the temperature measured once every 1.2 s to the wireless transmitter.

An independent power-monitoring system based on this Pb-free piezoelectric energy harvesting can be applied to an actual power plant. Furthermore, it is expected to be applicable as an energy source for fire detection and alarm systems. In other words, by arranging an optimized harvester around the power line cable of the power plant using this technology, it is possible to supply power to the temperature and gas sensors necessary to prepare for fire and hazardous gas exposure. By utilizing the AC magnetic field of the power line cable installed in the power plant, continuous power can be supplied to the wireless sensor and data transmission system.

Furthermore, as the installation and utilization of lithium-ion batteries under extreme environmental conditions in nuclear power plants may pose additional risks, the application of energy harvesting technology equipped with firefighting technology is expected to overcome environmental limitations and prevent battery explosions and fire outbreaks.

Notes

Author Contributions

Conceptualization, J.-W.J. and J.-H.C.; methodology, J.-W.J. and J.-H.C.; software, J.-W.J.; validation, J.-W.J.; formal analysis, J.-W.J. and J.-H.C.; investigation, J.-W.J.; resources, J.-W.J.; data curation, J.-W.J. and J.-H.C.; writing―original draft preparation, J.-W.J.; writing―review and editing, J.-H.C.; visualization, J.-W.J.; supervision, J.-H.C.; project administration, J.-H.C.; All the authors have read and agreed to the published version of the manuscript.

Conflict of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This paper has been reconstructed according to the submission guidelines of the International Journal of Fire Science and Engineering based on the first author’s thesis for the award of a Master’s degree in Engineering (Jang, 2015)[24].

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Article information Continued

Figure 1.

BCTZ phase diagram.

Figure 2.

BCTZ0.3C bulk samples according to changes in sintering temperature.

Figure 3.

Surface FE-SEM images of BCTZ0.3C bulk samples according to changes in sintering temperature.

Figure 4.

XRD graph for intensity of BCTZ0.3C bulk sample with changes in sintering temperature.

Figure 5.

XPS component analysis graph of BCTZ0.3C sample sintered at 1,450 °C.

Figure 6.

Graph of piezoelectric and dielectric properties of BCTZ0.3C bulk sample with changes in sintering temperature.

Figure 7.

Comparison of variation in output power through impedance matching of BCTZ0.3C thick film with sintering.

Figure 8.

Variations in output power and piezoelectric conversion constant (d33 × g33) value of BCTZ0.3C thick film with sintering temperature.

Figure 9.

Graph of wireless sensor network operation using voltage generated from BCTZ0.3C.

Figure 10.

Graph of temperature measured by supplying power to wireless sensor network.

Table 1.

Piezoelectric and Dielectric Properties of BCTZ Bulk for Different Sintering Temperatures

Sintering temperature [°C] Dielectric constant Density [g/cm3] d33 [pC/N] g33 [10-3 Vm/N] kp [%] d33 × g33 [10-15 m2/N] Efficiency [ŋ]
1300 2500.4 1.37 265 10.6 46.8 2809 0.88
1350 3016.6 1.40 530 17.6 41.6 9322 0.89
1400 1734.3 1.54 456 26.3 44.6 11990 0.85
1450 1976.2 1.48 526 30.0 49.3 15780 0.84