Piezoelectric Charge Constant Research Articles

Development and Field Test of Integrated Electronics Piezoelectric Accelerometer Based on Lead-Free Piezoelectric Ceramic for Centrifugal Pump Monitoring.

In this study, an Integrated Electronics Piezoelectric (IEPE)-type accelerometer based on an environmentally friendly lead-free piezoceramic was fabricated, and its field applicability was verified using a cooling pump owned by the Korea Atomic Energy Research Institute (KAERI). As an environmentally friendly piezoelectric material, 0.96(K,Na)NbO3-0.03(Bi,Na,K,Li)ZrO3-0.01BiScO3 (0.96KNN-0.03BNKLZ-0.01BS) piezoceramic with an optimized piezoelectric charge constant (d33) was introduced. It was manufactured in a ring shape using a solid-state reaction method for application to a compression mode accelerometer. The fabricated ceramic ring has a high piezoelectric constant d33 of ~373 pC/N and a Curie temperature TC of ~330 °C. It was found that the electrical and physical characteristics of the 0.96KNN-0.03BNKLZ-0.01BS piezoceramic were comparable to those of a Pb(Zr,Ti)O3 (PZT) ring ceramic. As a result of a vibration test of the IEPE accelerometer fabricated using the lead-free piezoelectric ceramic, the resonant frequency fr = 20.0 kHz and voltage sensitivity Sv = 101.1 mV/g were confirmed. The fabricated IEPE accelerometer sensor showed an excellent performance equivalent to or superior to that of a commercial IEPE accelerometer sensor based on PZT for general industrial use. A field test was carried out to verify the applicability of the fabricated sensor in an actual industrial environment. The test was conducted by simultaneously installing the developed sensor and a commercial PZT-based sensor in the ball bearing housing location of a centrifugal pump. The centrifugal pump was operated at 1180 RPM, and the generated vibration signals were collected and analyzed. The test results confirmed that the developed eco-friendly lead-free sensor has comparable vibration measurement capability to that of commercial PZT-based sensors.

The Investigation of the Effect of La3+, Eu3+, and Sm3+ Ions on Photoluminescence and Piezoelectric Behavior of RE1.90Y0.10Zr2O7 (RE: Eu, Sm and Y: La, Sm, Eu) Pyrochlore-Based Multifunctional Smart Advanced Materials.

A series of compounds with the general formula RE1.90Y0.10Zr2O7 (where RE includes Eu, Sm and Y includes La, Sm, Eu) were synthesized using a solid-state reaction method. These compounds were analyzed through differential thermal analysis (DTA), thermogravimetric analysis (TG), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). Additionally, their dielectric constant, loss tangent, piezoelectric charge constant, and Curie temperature were measured using an LCR meter, d33 meter, and TG/DTA. X-ray diffraction results indicated that all samples crystallize in a cubic pyrochlore structure. Photoluminescence studies revealed that Eu3+ ions predominantly contribute to the emission, whether as activators or co-activators. Among the phosphors, Eu1.90La0.10Zr2O7 exhibited a significantly longer afterglow compared to Sm1.90Eu0.10Zr2O7 and Eu1.90Sm0.10Zr2O7. Conversely, Sm1.90Eu0.10Zr2O7 demonstrated luminescence intensity that was 20 times greater than that of Eu1.90La0.10Zr2O7 and Eu1.90Sm0.10Zr2O7. Furthermore, all samples with characteristic Eu3+ emissions also exhibited piezoelectric properties. Curie temperature (Tc) of Eu1.90La0.10Zr2O7, Sm1.90Eu0.10Zr2O7, and Eu1.90Sm0.10Zr2O7 are 770°C, 830°C, and 845°C, respectively. Therefore, Sm3+ ion improves piezoelectric properties and Curie temperature when doping into the Eu2Zr2O7 host crystal.

AC poling of high Qm and low acoustic impedance Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 single crystals produced by a solid-state crystal growth

The AC poling cycle dependence of Mn-doped Pb(Mg1/3Nb2/3)O3-0.3Pb(Zr.Ti)O3 (PMN-0.3PZT) single crystals (SC) produced via the solid-state crystal growth (SSCG) method was investigated. The piezoelectric strain and charge constants, d 33 ＝ 1130 pC/N, g 33 = 42.7 × 10−3 Vm/N, and mechanical quality factor Q m = 800 were obtained under conditions of 1 Hz, bipolar sine wave, 7.5 kV cm−1 electric field, and 6000 cycles. In contrast to the conventional Bridgman process SC, the low-density and high Q m SSCG SC necessitates a substantial number of AC cycles due to the presence of pores within the SC. In addition, the ACP SC showed a 13 °C increase in the phase change temperature T rt compared to the DC-poled SC. This information on ACP SSCG SCs with improved thermal stability, low acoustic impedance, and enhanced receiving efficiency attributable to high g 33 offers new insight into high-frequency ultrasonic devices.

Temperature dependence of piezoelectric properties of the binary Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals prepared by continuous feeding Bridgeman method

We have confirmed that the temperature dependence of the dielectric constant and piezoelectric charge constant of length-extensional mode d 31 of AC poled (ACP) Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals (SC) is 15 °C higher than that of DC poled (DCP) SC. The ACP SC, grown by the continuous feeding Bridgman process exhibited a d 31 of −2500 pC N−1 at 88 °C and maintained over −700 pC N−1 up to 105 °C. In comparison, the DCP SC showed a d 31 of −1500 pC N−1 at 88 °C and only maintained −700 pC N−1 up to 90 °C. In addition, low frequency constant N 31 of 560 Hz·m at 25 °C and 390 Hz·m at 88 °C of the ACP SC showed 25% and 37% lower than those of DCP SC. The ACP SC outperforms DCP SC not only in piezoelectric properties at room temperature but also heat resistance and this information is important for future ultrasound devices design.

Comprehensive analysis of ferroelectric, piezoelectric, mechanical, and nonlinear optical properties of imidazolium d-camphorsulfonate single crystals

Single crystals of imidazolium d-camphorsulfonate (D-ImCS) are synthesized through the slow evaporation solution method. Powder X-ray diffraction reveals that the grown crystals have crystallized in the monoclinic phase with non-centrosymmetric space group P21. UV–visible spectroscopy measurements showed that D-ImCS crystals only absorb in the UV region. Photoluminescence studies indicated emissions in the blue and violet regions. The functional groups present in the crystal were identified through FTIR analysis. The soft nature of the crystal was identified using Vicker's microhardness testing. Dielectric analysis reveals the transition temperature Tc= 365.7 K. The piezoelectric charge constant (d22) is determined to be ±8 pC N−1. The polarization hysteresis loop demonstrates the ferroelectric nature. The presence of NLO property is demonstrated through SHG. Density Functional Theory (DFT) utilizing Gaussian 16 W software provided the optimized structure, UV–visible absorbance, FTIR spectra, frontier molecular orbitals, density of states, molecular electrostatic potential, atomic charge distribution, natural population analysis and non-linear optical properties (NLO). This computational approach complements and validates experimental findings, resulting in a thorough knowledge of D-ImCS behavior and properties.

Field-assisted sintering of barium titanate and 45S5 bioactive glass for biomedical applications

The development of electrically active biomaterials, which create electrical cues on demand to foster cellular stimulation, remains a challenge. Here, we utilized a Field-assisted sintering approach to densify barium titanate and 45S5 bioactive glass to create a piezoelectric and potentially bioactive composite. By using Field-assisted sintering, we aimed to fabricate dense piezoelectric specimens, preserving a low degree of crystallization of the bioactive glass to keep bioactivity as high as possible. Therefore, we have varied the compositions of the materials and processed them at different sintering temperatures. This enabled us to produce dense test specimens in the 94 %–98 % relative density range. The samples were successfully polarized, and piezoelectric charge constants d33 were determined for the composites. The content of bioactive glass and the sintering temperature influence the charge constant d33. It is in the range of 0.8–3.4 pC/N for the composites, approximately in the order of magnitude assigned to natural tissues such as bone. X-ray diffraction was used to analyze the composition of the processed samples and to investigate the influence of an additional thermal post-treatment. Altogether, we established a process window for field-assisted sintering, allowing the fabrication of a piezoelectric and potentially bioactive biomaterial for tissue engineering.

Mn-doped 0.67BiFeO3-0.33BaTiO3 ceramic sensor for high-temperature structural health monitoring

Real-time monitoring of structural health status is very important for supersonic aircraft, since the long-term operation in harsh service environments, such as high temperatures, can cause potential damage. Structural health monitoring (SHM) based on lamb wave has been approved to be a critical technique for the reliable operation of supersonic aircraft, but is limited by the operating temperature of conventional piezoelectric sensors, which makes it difficult to meet the high-temperature monitoring requirements. The BiFeO3–BaTiO3 ceramics exhibit excellent piezoelectric properties and high Curie temperature (Tc), making them promising for high-temperature SHM of supersonic aircraft. Here, we fabricated a piezoelectric sensor using 0.67BiFeO3-0.33BaTiO3-0.25%molMnO2 (BF33BTMN-025) ceramic, which exhibits a piezoelectric charge constant (d33) of 135 pC/N at room temperature and a Tc of 448 °C. The BF33BTMN-025 ceramic sensor operates effectively at temperatures up to 200 °C and maintains stable damage monitoring sensitivity as well. Compared with Pb(Zr, Ti)O3 (PZT), BaTiO3 (BTO) and other piezoelectric sensors commonly used in SHM field, the BF33BTMN-025 ceramic sensor has a higher operating temperature and a comparable sensitivity. Our work demonstrates that the BF33BTMN-025 ceramic sensor can be employed as piezoelectric sensor for high-temperature SHM, which has a wide application potential in the field of real-time monitoring of supersonic aircraft.

Investigation of the structural and piezoelectric characteristics of (1-x)Pb(Zr, Ti)O3-xPb(Zn0.4Ni0.6)1/3Nb2/3O3 ceramics with R-PC-T multistructure

The structural and various electrical properties of (1-x)Pb(Zr1-zTiz)O3-xPb(Zn0.4Ni0.6)1/3Nb2/3O3 [(1-x)P(Z1-zTz)-xPZNN] piezoceramics have been systematically investigated to ascertain the compositions that manifest a rhombohedral-pseudocubic-tetragonal (R-PC-T) multistructure. Rietveld refinement results indicate that the pseudocubic (PC) structure observed in the (1-x)P(Z1-zTz)-xPZNN piezoceramics closely resembles the Pm3m cubic structure. Nonetheless, the PC structure cannot be classified as cubic, given that piezoceramics exhibiting the PC structure also demonstrate ferroelectric and piezoelectric properties. The R-PC-T multistructure was detected in (1-x)P(Z1-zTz)-xPZNN piezoceramics for compositions where 0.335 ≤ x ≤ 0.44, across various z values. Compositions exhibiting the R-PC-T multistructure are identified as particularly promising. Notably, the piezoceramic with the composition 0.58 P(Z0.41T0.59)-0.42PZNN (x = 0.42 and z = 0.59) displayed remarkable piezoelectric properties, including a high piezoelectric charge constant, d33, of 825 pC/N, a coupling coefficient, kp, of 0.7, and a strain of 0.185% at 3.0 kV/mm, alongside a high Curie temperature (TC) of 240 °C.

Tuning the Piezoelectric Performance of K0.5Na0.5NbO3 through Li Doping: Insights from Structural, Elastic and Electronic Analyses.

The structural, elastic, piezoelectric, and electronic properties of Li-doped K0.5Na0.5NbO3 (K0.5-xNa0.5-yLix+yNbO3, KNN-L) are calculated. The properties of KNN-L are related to the Li-doping content and the replaced K or Na atoms. The bulk modulus, the shear modulus, and Young's modulus of KNN-L are mostly higher than those of KNN, and the hardness value increases. The Poisson ratio of KNN-L is lower than that of most KNN, and the ductility is reduced. All doped structures are direct band gap semiconductors. K0.5Na0.375Li0.125NbO3 has the largest piezoelectric charge constant, d33 = 44.72 pC/N, in the respective structures, which is 1.5 fold that of K0.5Na0.5NbO3 (29.15 pC/N). The excellent piezoelectric performance of Li-doping KNN-L was analyzed from the insights of elastic and electronic properties.

Enhanced soft piezoelectric properties of Sb2O3 doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 materials

In this paper, we have studied the soft piezoelectric properties of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 doped with Sb2O3. The optimal piezoelectric charge constant and dielectric permittivity of the calcined and sintered 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 were determined by varying the Sb2O3 content. The mol% of Sb2O3 was set to 0, 0.05, 0.1, 0.15, and 0.2, and the doped ceramics were sintered at a temperature of 1475 °C. The piezoelectric charge constant d33, electromechanical coupling coefficient kp, and dielectric permittivity εr of the doped ceramics increased with the increasing Sb2O3 content, whereas their Curie temperature Tc slightly decreased. At 0.1 mol% of Sb2O3, the highest piezoelectric charge constant, electromechanical coupling coefficient, and dielectric permittivity values were obtained. Although the Curie temperature was slightly lowered, the dielectric permittivity improved. 0.5BZT-0.5BCT doped with Sb2O3 exhibited a high remnant polarization Pr even when a weak coercive electric field Ec was applied, resulting in an easy polarization. It can be seen that the improved electrical properties and the behavior of the P-E hysteresis loop through the dopant addition of Sb2O3 are close to the soft piezoelectric characteristics. Thus, the synthesized lead-free and Sb2O3-doped ceramics, with excellent piezoelectric properties and depolarization behaviors, are expected to replace lead-based ceramics and will be useful in energy converters, such as piezoelectric transformers.

Parametric estimation analysis of compressive stress effects on piezoelectric properties of PZT ceramic

ABSTRACT In this study, the frequency and capacitance of piezoelectric materials due to compressive stress were analyzed, and the overall material properties (compliance matrix, piezoelectric charge constant and dielectric constant) of piezoelectric ceramics were optimized using parametric estimation methods. The piezoelectric ceramic used for optimization was KICET-PZT8, and the compressive stress was applied from a stress-free condition up to 50 MPa. As a result, with increasing compressive stress, the values of s 11 E , − s 12 E and s 66 E tended to increase, while − s 13 E and s 33 E increased and then decreased at 20 MPa or higher. − d 31 and d 33 showed the maximum values at 40 MPa of compressive stress, with the values reaching 147 pC/N and 375 pC/N, respectively. These values were analyzed to have increased by 117% and 115%, respectively, compared to the stress-free condition. Additionally, the dielectric constant ( ε 33 T ) was found to increase linearly with the applied compressive stress. The understanding of the changes in piezoelectric properties under various compressive stresses derived from this study is expected to be applicable in various ways for the design and application of piezoelectric devices using compressive stresses, including BLT.

Study of temperature and frequency dependant dielectric, impedance, AC resistivity, modulus spectroscopy and electromechanical coupling properties of [BaNd0.1Ti0.8Nb0.1O3](1-x)[Na0.5Bi0.5TiO3]x relaxor ferroelectric ceramics

[BaNd0.1Ti0.8Nb0.1O3](1-x)[Na0.5Bi0.5TiO3]x ceramics with x = 0.25, 0.40, 0.60, 0.65 & 0.70 were prepared through solid-state sintering route. In the present study, temperature and frequency dependant dielectric, Impedance, AC resistivity, modulus spectroscopy and electromechanical coupling properties carried out. These materials showed modulus resonance and anti-resonance i.e. electromechanical coupling (M″ vs. frequency). From these modulus resonance and anti-resonance studies piezoelectric charge constant (d33) was obtained. The values of the piezoelectric charge constant (d33) are 3.34 nm V−1, 6.26 nm V−1, 11.58 nm V−1, 14.10 nm V−1 & 10.70 nm V−1 for x = 0.25, 0.40, 0.60, 0.65 & 0.70, respectively. In the present study, the modulus electromechanical was studied in jig with spring which applies constant stress on the ceramic sample. The higher value of electromechanical coupling conversion in the present study may be attributed to this constant applied stress, higher temperature and polarized oxygen vacancies at the crystal lattice at these elevated temperatures (773 K & 873 K).

Additive Manufacturing of Piezoelectric Niobium-Doped Lead Zirconate Titanate (PZT-N) by Binder Jetting

Binder jetting is an emerging indirect additive manufacturing technique for ceramic materials, which could be employed to produce application-oriented designed components impossible to achieve with traditional processes and featuring enhanced performances. In our study, niobium-doped lead zirconate titanate (PZT-N) powder, usually processed through the standard press-and-sinter route, was employed as the raw material. First, the powder was characterized in terms of granulometry and flowability to assess its suitability for the printing process. Then, shaping by binder jetting was studied, and the effect of three levels of binder saturation (75–90–105%) on the green bodies was assessed. Finally, the microstructure of the sintered samples was studied using SEM, to investigate the effect of thermal treatments on the grain size distribution and residual porosity (~40%). The piezoelectric properties were measured and compared to those of conventionally processed material. The piezoelectric charge and voltage constants (d33 and g33) were evaluated to determine the possible use of printed parts as porous piezoelectric components to be exploited in hydrophones in the direct mode.

A study on Sm2O3-doped Ba(Zr0.02Ti0.98)O3 ceramics for sensor applications

ABSTRACT Ba(Zr0.02Ti0.98)O3 (BZT) samples with various weight percentages of Sm2O3 (0.02–0.06) were synthesized and calcined at 1100°C for 4 h. Circular pellets were prepared using calcined powders and sintered at 1450°C for 2 h. The sintered and poled samples were used for the measurement of various electrical properties. Maximum piezoelectric charge constant (d 33) of 372 pC/N obtained for 0.02 wt.% Sm2O3-doped BZT. Dielectric constant (K = 15,855) at 100 Hz was found maximum for this composition at Curie temperature (T c) of 125°C. Scanning electron microscopy (SEM) study revealed a decrease in grain size with an increase in Sm2O3 content. Largely, a lower concentration of Sm2O3-doped BZT compositions with higher d 33 could be suitable for vibration sensor and accelerometer applications.

3D Printing and processing of miniaturized transducers with near-pristine piezoelectric ceramics for localized cavitation

The performance of ultrasonic transducers is largely determined by the piezoelectric properties and geometries of their active elements. Due to the brittle nature of piezoceramics, existing processing tools for piezoelectric elements only achieve simple geometries, including flat disks, cylinders, cubes and rings. While advances in additive manufacturing give rise to free-form fabrication of piezoceramics, the resultant transducers suffer from high porosity, weak piezoelectric responses, and limited geometrical flexibility. We introduce optimized piezoceramic printing and processing strategies to produce highly responsive piezoelectric microtransducers that operate at ultrasonic frequencies. The 3D printed dense piezoelectric elements achieve high piezoelectric coefficients and complex architectures. The resulting piezoelectric charge constant, d33, and coupling factor, kt, of the 3D printed piezoceramic reach 583 pC/N and 0.57, approaching the properties of pristine ceramics. The integrated printing of transducer packaging materials and 3D printed piezoceramics with microarchitectures create opportunities for miniaturized piezoelectric ultrasound transducers capable of acoustic focusing and localized cavitation within millimeter-sized channels, leading to miniaturized ultrasonic devices that enable a wide range of biomedical applications.

Effect of Contents on the Electrical and Piezoelectric Properties of (1 - x)(Bi, Na)TiO3-x(Ba, Sr)TiO3 Lead-Free Piezoelectric Ceramics.

In this study, the composition of lead-free piezoelectric ceramics (1 - x)(Bi0.5Na0.5)TiO3-x(Ba0.5Sr0.5)TiO3 with excellent piezoelectric properties was investigated. Crystal analysis and electrical and piezoelectric properties were analyzed according to the content of the BST composition. A phase change from rhombohedral to tetragonal structure was observed in 0.12 BST, and the densest and most uniform microstructure was confirmed in this composition. The dielectric constant increased from 905 to 1692 as the composition of BST increased to 0.12 BST. Afterward, as the composition of BST increased, the permittivity tended to decrease. Additionally, at 0.12 BST, Pr was the highest at 23.34 μC/cm2. The piezoelectric charge constant (d33) and the electromechanical coupling coefficient (kp) were 152 pC/N and 0.37, respectively, and showed the highest values at 0.12 BST. Curie temperature (Tm) was analyzed 242 °C at 0.12 BST, the optimal composition. It was confirmed that the characteristics of 0.12 BST were excellent in all conditions. Therefore, it was confirmed that 0.12 BST is the optimal composition for (1 - x)BNT-xBST piezoelectric ceramics.

Two-step simulation of piezoelectric properties of porous PZT according to porosity

ABSTRACT Porous piezoelectric materials have been widely used in hydrophone applications owing to their excellent hydrostatic charge constant (dh) and voltage constant (gh). However, owing to the difficulty in sample manufacturing, the evaluation of the overall piezoelectric properties for reliable device design using simulations is challenging. Herein, a two-step simulation was performed to accurately determine the overall properties of the porous PZT. First, the piezoelectric charge constant was calculated by displacement calculations using the electrostrictive effect. Second, using the calculated piezoelectric charge constant and impedance spectrum obtained from the experiment, the initial value for optimizing the properties was selected, and the overall properties were obtained using the parametric estimation technique. These parametric estimation simulation procedures were performed with the samples of radial and thickness modes based on the IEEE standards. Finally, the piezoelectric properties obtained were compared and verified with the experimental values. Therefore, the overall piezoelectric properties include mechanical, frequency and dielectric properties according to the porosity were obtained with reliable results.

Physical properties of Sm2O3 added Pb(Ni1/3Nb2/3) O3–Pb(Zr0.32Ti0.68)O3 system ceramics for piezoelectric speaker application

In this article, to develop the composition ceramics for the application of single-layer piezoelectric speaker, Pb(Ni1/3Nb2/3)0.5(Zr0.32Ti0.68)0.5O3 co-doped with Ta2O5 and Sm2O3 were manufactured and then their dielectric and piezoelectric properties were investigated. At the 0.4 wt% Ta2O5 and 0.0 wt% Sm2O3 added composition ceramics, excellent physical properties were also appeared, respectively: the dielectric constant (ε r) of 6778, piezoelectric charge constant (d33) of 1027 [pC/N], electromechanical coefficient (k p) of 0.67 and curie temperature of 155 [°C]. These values were suitable for the device application such as ultrasonic tooth cleaner and piezoelectric speakers.

Hammer Impact-Driven Power Generator Using Buzzer-Type Piezoelectric Energy Converter for Wind Power Generator Applications

A novel hammer-impact-driven power generator that uses a buzzer-type piezoelectric energy converter (BPEC) for wind-power-generator applications was designed, and the dynamic motions and output characteristics were analyzed. As the active material, Sm0.025-Pb0.9625[(Mg1/3Nb2/3)0.71Ti0.29]O3 (Sm-PMN-PT)ceramic was used; this material has a high piezoelectric charge constant of 1100 pC/N and an electromechanical coupling factor of 58%. A rotational impeller triggered an impact between one end of the bar-type hammer, and, thereby, impact energy transferred to the BPECs. The manufactured power generator was tested from 50 RPM to 250 RPM, using the handmade evaluation system; it was able to operate with small impact force and greatly improved output performance as rotation speed increased. The maximum output of the generator was 10.4 W at a load resistance of 500 Ω and rotation speed of 250 RPM. For improvement of the output characteristics, the generators were arranged such that they could operate simultaneously. Moreover, the proposed model was applied to a Savonius–Darrieus turbine, and the output performance was evaluated at various wind conditions in a wind tunnel.

Developing a face-shear lead-free piezoelectric transducer through anti-parallel co-poling and its application to an omnidirectional piezoelectric transducer

Face-shear deformation was observed in various square piezoelectric transducers prepared using the anti-parallel co-poling method, which led to uniform polarization and the generation and receipt of pure fundamental shear horizontal (SH0) waves without any Lamb wave. The amplitude of the SH0 wave was found to be proportional to the piezoelectric charge constant (d33) of the piezoceramic, suggesting that the d33 value can be used as a figure of merit for piezoelectric transducers with strong SH0 waves. The amplitude of the SH0 wave associated with the square piezoelectric transducer is large at 0° and 90° but almost zero at 45°; therefore, a piezoelectric transducer with good omnidirectional properties needs to be developed. A ring-type omnidirectional piezoelectric transducer was produced using eight trapezoidal piezoceramics. The minimum amplitude of the SH0 wave generated and received by the ring type-transducer exceeded 70% of the maximum amplitude. Hence, this ring-type transducer is highly omnidirectional and can be used for nondestructive testing and structural health-monitoring applications.