In this work, lead-free (Na_0.475K_0.475Li_0.05)NbO₃ + x wt.% ZnO (NKLN, x = 0 to 0.3) piezoelectric ceramics with high piezoelectric g-coefficients were prepared by conventional solid-state synthesis method. By adding different concentrations of ZnO dopants, we aimed to improve the material properties and enhance their piezoelectric properties. The effects of the ZnO addition on the microstructure, dielectric, piezoelectric and ferroelectric properties of the proposed samples are investigated. Adding ZnO reduced the dielectric constant and improved the g-value of the samples. The properties of the samples without ZnO doping were g₃₃ = 31 mV·m/N, g₁₅ = 34 mV·m/N, k_p = 0.39, Q_m = 92, ε_r = 458, d₃₃ = 127 pC/N and dielectric loss = 3.4%. With the preferable ZnO doping of 1 wt.%, the piezoelectric properties improved to g₃₃ = 40 mV·m/N, g₁₅ = 44 mV·m/N, k_p = 0.44, Q_m = 89, ε_r = 406, d₃₃ = 139 pC/N and dielectric loss = 2.4%. Finally, ring-shaped shear mode piezoelectric accelerometers were fabricated using the optimum ZnO-doped samples. The simulated resonant frequency using ANSYS 2024 R1 software was approximately 23 kHz, while the actual measured resonant frequency of the devices was 19 kHz. The sensitivity was approximately 7.08 mV/g. This piezoelectric accelerometer suits applications requiring lower sensitivity and higher resonant frequencies, such as monitoring high-frequency vibrations in high-speed machinery, robotic arms or scientific research and engineering fields involving high-frequency vibration testing.

A single-structure three-axis MEMS accelerometer often suffers from cross-axis interference, which leads to inaccurate sensitivity and makes it difficult to reliably assess the health condition of the measured object. In addition, achieving high sensitivity often comes at the cost of reduced bandwidth. Because few previous studies have addressed the cross-axis interference of such structures, this study presents the development and optimization of a structural three-axis MEMS piezoelectric accelerometer. A mathematical model was first established, followed by simulation and structural optimization to enhance sensitivity and minimize cross-axis interference while keeping the bandwidth nearly unchanged. This study proposes, for the first time, an improved structure that evolves the L-shaped accelerometer into a composite configuration consisting of a W-shaped cantilever and an additional four-bar proof mass, in order to enhance bandwidth and significantly reduce cross-axis interference. Generally, an increase in sensitivity leads to a reduction in bandwidth; however, by modifying the geometry of the proof mass, the proposed accelerometer achieves a substantial improvement in sensitivity while avoiding a significant loss of bandwidth. The implementation of a triaxial accelerometer can generally be achieved in three ways: using three single-axis accelerometers, realizing three axes through circuitry, or achieving three axes through structural design. Using three single-axis accelerometers results in large volume, heavy weight, and high cost. Circuit-based three-axis implementation cannot detect multi-axis forces simultaneously, whereas structural three-axis design is difficult to realize. This study focuses on designing a triaxial accelerometer based on a structural approach, optimizing it with reference to the most successful examples reported in the literature and progressively addressing the drawbacks of previous structures. First, trapezoidal beams are used instead of rectangular cantilever beams to increase bandwidth. Next, two additional cantilever beams are added to transfer the Z-axis sensitivity detection points to reduce cross-axis interference. Finally, the shape of the proof mass is designed to enhance the sensitivities along all three axes. The optimized accelerometer exhibits resonant frequencies of approximately 12.6 kHz, 31.6 kHz, and 11.8 kHz along the X-, Y-, and Z-axes, with corresponding sensitivities of 6.11, 5.44, and 8.85 mV/g, and cross-axis interference reduced to below 15%. The results demonstrate the achievement of a highly accurate and reliable three-axis MEMS piezoelectric accelerometer through structural design and optimization. The proposed design concept may also be beneficial for other piezoelectric-based sensor applications.