ALTERNATIVE SOURCES OF ELECTRICAL ENERGY BASED ON PIEZOELECTRIC TRANSDUCERS

SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 12 DECEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 60 ALTERNATIVE SOURCES OF ELECTRICAL ENERGY BASED ON PIEZOELECTRIC TRANSDUCERS M.A. Tursunov1, B.T. Eltazarov2, Z.A. Alimova3, R.A. Khudoyberdiyeva4 Tashkent State Technical University1,2,3,4 https://doi.org/10.5281/zenodo.17920577 Abstract. This paper presents an in-depth analysis of the physical principles and practical applications of piezoelectric materials used for converting mechanical energy generated by human footsteps into electrical energy. The study highlights the importance of sustainable energy technologies in modern urban environments, emphasizing that piezoelectric systems can operate independently of fuel, sunlight, or wind. The fundamental properties of non-centrosymmetric crystals, the direct piezoelectric effect, and the mathematical relationships governing charge generation are reviewed to illustrate how mechanical deformation produces measurable electrical signals. Special attention is given to the structural components of a typical piezoelectric harvesting system, including the mechanical input, piezoelectric plate, rectifying circuit, filter capacitor, and energy storage device. This approach ensures efficient accumulation of electrical charges produced during cyclic loading such as walking. The ecological advantages of such systems include zero emissions, the absence of chemical waste, and their ability to function continuously in areas with high pedestrian traffic. The economic feasibility of implementing piezoelectric modules in public spaces—such as transport hubs, sidewalks, shopping centers, and parks—is discussed. Modeling and experimental data indicate that pedestrian flows of several thousand people per day can generate sufficient energy to support low-power devices, including LED lighting, environmental sensors, and smart-city components. Overall, the study demonstrates that piezoelectric technologies have strong potential for integration into distributed and autonomous energy infrastructures. Advances in material science, improved composite structures, and enhanced energy storage systems make piezoelectric harvesting a promising direction for sustainable urban development. Keywords: piezoelectric materials, energy harvesting, mechanical-to-electrical conversion, sustainable energy, urban infrastructure, piezoelectric effect, low-power systems, PZT ceramics, PVDF polymers, smart cities. Introduction Modern energy development trends emphasize the need to minimize environmental impact and transition toward sustainable energy sources. With the continuous growth of electricity consumption and the depletion of non-renewable resources, technologies that allow energy harvesting from the surrounding environment—such as mechanical vibrations, motion, heat, and light-are gaining increasing importance [1, 2]. This push is critical for achieving global climate goals and fostering energy resilience. The piezoelectric effect is one of the most promising areas in the field of small-scale energy harvesting. It enables the direct conversion of mechanical energy, such as human footsteps, machine vibrations, or traffic movements, into electrical energy without the need for combustion, fuel, sunlight, or wind. This intrinsic autonomy makes such systems particularly attractive for integration into urban infrastructure, where mechanical activity is a constant, reliable source of SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 12 DECEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 61 energy [3, 4]. The objective of this study is to explore the physical foundations of the piezoelectric effect, the operating principles and engineering challenges of piezoelectric energy converters, and to evaluate the ecological, economic, and implementation efficiency of using such systems for electricity generation in urban environments. General Overview The piezoelectric effect is the phenomenon of generating an electric charge on the surface of certain crystalline solids when subjected to mechanical deformation [5, 6]. The term “piezoelectricity” originates from the Greek word piezein, meaning “to press” or “to squeeze.” Discovered in 1880 by Jacques and Pierre Curie, the effect has been instrumental in numerous fields, including electronics, sensors, medicine, and, more recently, energy harvesting. The physical essence of the effect lies in the displacement of the centers of positive and negative charges in non-centrosymmetric crystal lattices when stress or strain is applied. This structural asymmetry is fundamental; materials possessing a center of symmetry cannot exhibit piezoelectricity. The applied stress causes a shift in the charge centroids, which creates an electric dipole moment and, consequently, an electric potential, which is the source of electromotive force (e.m.f.) [9]. Direct and Inverse Piezoelectric Effect Two types of piezoelectric phenomena exist:  Direct piezoelectric effect - generation of an electrical charge in response to mechanical deformation. This effect is employed for energy generation and sensing;  Inverse piezoelectric effect - the deformation of a crystal under the influence of an electric field, which is the source of an ultrasonic generator. For energy generation, the direct effect is employed [11]. The linear relationship between the electric displacement (D) and mechanical stress (σ) is expressed аs: Di = dij σj (1) where (dij) is the piezoelectric coefficient that characterizes the material’s ability to convert mechanical energy into electrical energy. A higher coefficient indicates a more efficient material. Additionally, the elastic and dielectric coupling is represented as: Sj=sjkE σk+ dij Ei (2) where, (Sj) is the mechanical strain, (sjkE) is the elastic compliance at a constant electric field, and ( Ei) is the electric field strength [12,13]. These equations describe the conversion of mechanical energy into electric potential, allowing for the calculation of output voltage and power during cyclic loading typical of human walking or traffic vibration. Electromechanical Coupling Coefficient (k) Beyond the (dij) coefficient, the overall efficiency of energy conversion is quantified by the electromechanical coupling coefficient (k). This is a critical metric defined as: k2 = 𝐶𝑜𝑛𝑣𝑒𝑟𝑡𝑒𝑑𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙𝐸𝑛𝑒𝑟𝑔𝑦 𝐼𝑛𝑝𝑢𝑡𝑀𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙𝐸𝑛𝑒𝑟𝑔𝑦 (3) A higher k value indicates a more efficient and desirable material for energy harvesting applications. These equations describe how mechanical energy can be converted into electric potential, allowing calculation of output voltage and power during cyclic loading typical of human walking. Classic materials for piezoelectric transducers include the natural mineral quartz (SiO₂), a naturally occurring mineral with a low coefficient but high stability; the synthetic ferroelectrics SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 12 DECEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 62 barium titanate (BaTiO₃) and lead zirconate titanate (PZT); and PVDF polymers and its copolymers (polyvinylidene fluoride). PZT Dilemma: PZT offers superior piezoelectric coefficients (d33 often >300 pC/N) due to its Morphotropic Phase Boundary (MPB), making it the industry standard. However, its high lead content poses significant environmental and public health concerns, driving the search for lead-free alternatives. Lead-Free Alternatives: Research focuses on materials like Potassium Sodium Niobate (KNN) and modified (BaTiO₃) ceramics, aiming to achieve PZT-like performance without toxicity. Polymeric and Flexible Materials: Polymers such as polyvinylidene fluoride (PVDF) and its copolymers (PVDF-TrFE) are gaining importance. They offer low d33 but high flexibility, robustness, and biocompatibility, making them ideal for integration into clothing, wearable devices, or flexible pavements. Nanogenerators (PENGs): The use of piezoelectric nanostructures (e.g., ZnO nanowires) provides extremely high surface-to-volume ratios, enhancing charge generation from minute, lowamplitude movements. Energy efficiency is ultimately determined not only by the material's intrinsic properties but also by its geometry, thickness, frequency of action, and the resistance of the external circuit [15]. Principle of Operation and System Structure When a person walks, periodic mechanical pressure acts upon a piezoelectric element, causing it to deform and generate an electric potential. The resulting charge is rectified and stored in an electrical accumulator or capacitor. Under optimal conditions, a single piezoelectric plate can generate 2–12 V with energy yields of 10⁻³–10⁻² J per step. When applied across large pedestrian areas, the cumulative effect becomes substantial [16]. Figure 1. Basic structure of a piezoelectric energy harvesting system: 1. Mechanical input (pressure from walking); 2. Piezoelectric plate; 3. Rectifier (diode bridge); 4. Filter capacitor; 5. Energy storage (battery or supercapacitor); 6. Energy consumer (lighting, sensors, monitoring systems). The primary engineering hurdle is the frequency mismatch. Human motion is low frequency (1–5 Hz), whereas the high-efficiency resonance of most ceramics occurs in the kHz range. To bridge this gap, PEH systems employ: SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 12 DECEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 63  Mechanical Frequency Up-Conversion: Using non-linear mechanical interfaces, such as cantilever beams with proof masses or magnetic plucking mechanisms, to convert a single low-frequency input into multiple high-frequency oscillations in the piezo-element.  Power Management Circuits (PMC): To maximize power transfer, the raw, variable AC output must be efficiently converted and regulated. Advanced PMCs use synchronous rectification and Maximum Power Point Tracking (MPPT) algorithms to dynamically match the electrical impedance of the harvesting circuit to the piezoelectric source, minimizing power loss and maximizing energy stored. Ecological and Economic Feasibility Environmental Benefits The key advantage of piezoelectric energy systems is their absolute environmental cleanliness. The conversion process requires no combustion of fuels, emits no greenhouse gases, and produces no waste. Unlike solar or wind systems, piezoelectric devices operate independently of weather or daylight conditions, relying solely on mechanical activity. Implementation of piezoelectric technologies in urban environments allows:  Reduction in dependency on centralized power grids;  Create an ecologically clean zone in the city;  Improvement of energy efficiency in public spaces;  Utilization of energy that would otherwise dissipate as mechanical loss. The electricity generated can be used to power LED lighting, information panels, environmental sensors, or motion detection systems, aligning with the concept of Smart Cities. Economic Efficiency and Implementation Potential Economic feasibility depends on the balance between installation costs and the value of energy produced or saved. Although initial investments in piezoelectric systems may be relatively high, however their operational lifespan exceeds 10–15 years with negligible maintenance costs. Piezoelectric modules can be integrated into pedestrian crossings, transport terminals, shopping centers, parks, and public squares, where high foot traffic provides a consistent source of mechanical energy. Simulation and experimental data indicate that in a public area of 10 m² with a daily pedestrian flow of 10,000 people, energy generation can reach 2–4 kWh per day, sufficient to power streetlights or charge low-power electronic systems [16]. Figure 2. Economic and ecological model of a piezoelectric system: • Input: Mechanical energy from pedestrian steps; • Process: Conversion of mechanical energy to electrical energy; SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 12 DECEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 64 • Output: Power supply for local systems; • Effect: Energy savings, reduced CO₂ emissions, reduced operating costs, and the creation of environmentally friendly "Smart Cities." According to modeling and calculations, assuming 10,000 people per day walking across a 10 m² surface, it is possible to generate 2–4 kWh per day, which is sufficient to provide pedestrian crossing lighting or charge low-power devices. Conclusion Piezoelectric technologies hold significant potential for integration into distributed smallscale energy systems. They enable the efficient use of previously wasted mechanical energy and its conversion into an environmentally friendly source of electricity. The mаin advantages of these systems include environmental sustainability, autonomy, long operational life, and the ability to integrate seamlessly into existing urban infrastructure. Аdvances in piezoelectric material science, improved structural composites, and energy storage systems make such solutions promising for implementing the concept of sustainable development and energy independence of power supply systems in urban infrastructure. REFERENCES 1. Priya, S., & Inman, D. J. (Eds.). (2009). Energy Harvesting Technologies. Springer Science & Business Media. DOI: 10.1007/978-0-387-76464-1 2. Erturk, A., & Inman, D. J. (2011). Piezoelectric Energy Harvesting. John Wiley & Sons. ISBN: 978-0-470-68254-8 3. Beeby, S. P., Tudor, M. J., & White, N. M. (2006). “Energy harvesting vibration sources for microsystems applications.” Measurement Science and Technology, 17(12), R175–R195. 4. Anton, S. R., & Sodano, H. A. (2007). “A review of power harvesting using piezoelectric materials (2003–2006).” Smart Materials and Structures, 16(3), R1–R21. 5. Kim, H. S., Kim, J.-H., & Kim, J. (2011). “A review of piezoelectric energy harvesting based on vibration.” International Journal of Precision Engineering and Manufacturing, 12(6), 1129–1141. 6. Elvin, N. G., & Erturk, A. (2013). Advances in Energy Harvesting Methods. Springer. 7. Sriramdas, R., & Reddy, P. D. (2017). “Piezoelectric energy harvesting systems: Review and application.” International Journal of Engineering and Technology (IJET), 9(3), 2062–2072. 8. Bowen, C. R., Kim, H. A., Weaver, P. M., & Dunn, S. (2014). “Piezoelectric and ferroelectric materials and structures for energy harvesting applications.” Energy & Environmental Science, 7(1), 25–44. 9. Mateu, L., & Moll, F. (2005). “Optimum piezoelectric bending beam structures for energy harvesting using shoe inserts.” Journal of Intelligent Material Systems and Structures, 16(10), 835–845. 10. Saha, C. R., O'Donnell, T., Wang, N., & McCloskey, P. (2008). “Electromagnetic generator for harvesting energy from human motion.” Sensors and Actuators A: Physical, 147(1), 248– 253. 11. Ferrari, M., Ferrari, V., Guizzetti, M., Marioli, D., & Taroni, A. (2008). “Piezoelectric multifrequency energy converter for power harvesting in autonomous microsystems.” Sensors and Actuators A: Physical, 142(1), 329–335. 12. Kaur, G., Singh, M., & Singh, P. (2020). “A review on piezoelectric energy harvesting technologies and its applications.” Journal of Physics: Conference Series, 1706(1), 012134. SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 12 DECEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 65 13. Wang, Z. L. (2017). Nanogenerators for Self-Powered Devices and Systems. Georgia Institute of Technology. 14. Dagdeviren, C., et al. (2014). “Conformal piezoelectric energy harvesting and storage from motions of the heart, lung, and diaphragm.” Proceedings of the National Academy of Sciences, 111(5), 1927–1932. 15. Roundy, S., Wright, P. K., & Rabaey, J. (2003). Energy Scavenging for Wireless Sensor Networks with Special Focus on Vibrations. Kluwer Academic Publishers. 16. Tursunov, M. A., Eltazarov, B. T., Khudoyberdiyeva, R. A. (2025). Obtaining Alternative Electrical Energy Using Piezoelectric Transducers. In Proceedings of the Republican Scientific and Practical Conference “Digital Industry and Automation: Innovative Solutions in Technological Processes and Production Management Systems” (pp. 651–654). Qarshi: Intellekt Publishing House.