Application Cases

Experiment Name: Numerical Analysis and Experimental Testing of Impact-Type Piezoelectric Energy Harvesters

Research Direction: The application of wireless sensor networks in ecological environment monitoring and human health monitoring holds significant importance and promising prospects. However, how to achieve sustainable power supply for these networks remains a major challenge. Due to the widespread distribution of sensor nodes, using cable transmission is costly, while battery-powered solutions suffer from various drawbacks (e.g., lack of sustainability and environmental pollution). Wind energy, as one of the world's abundant and widely distributed natural resources, is an ideal source of energy. Utilizing energy harvesters to capture energy for powering wireless sensor networks can effectively address the issue of continuous power supply for sensors. Integrating energy harvesters with wireless sensor networks to form self-powered monitoring networks for ecological environment monitoring, climate monitoring, natural disaster monitoring, and human health monitoring is of great significance for protecting and improving the human living environment.

Experimental Objective: To theoretically validate the base-excited impact-type piezoelectric energy harvester, investigate the effects of the piezoelectric beam's vibration characteristics and power generation performance, and analyze the motion state and output characteristics of the piezoelectric beam after colliding with the impact beam. Experimental verification is conducted on parameters such as excitation acceleration, external resistance, and excitation frequency.

Testing Equipment: Impact-type piezoelectric energy harvester prototype, vibration exciter, vibration control console, power amplifier, NI data acquisition card, accelerometer, variable resistor (0–1 MΩ), laptop, clamps, and connecting wires.

Experimental Procedure: First, the impact-type piezoelectric energy harvester prototype is fixed on the aluminum baseplate of the vibration exciter using clamps. The NI data acquisition card and variable resistor are connected, and the accelerometer is attached to the aluminum baseplate using a permanent magnet. The output terminal of the NI data acquisition card is connected to the laptop via a USB interface. The vibration control console, laptop, power amplifier, and accelerometer are connected to form a closed loop.

During the experiment, the power is first turned on, and the variable resistor is adjusted. The base excitation signal, such as the frequency and acceleration required by the vibration exciter, is set using the computer software accompanying the vibration control console. The base excitation signal is then amplified by the power amplifier and transmitted to the vibration exciter, which outputs the signal. The impact beam of the energy harvester undergoes mechanical vibration. When the impact beam collides with the piezoelectric beam, the piezoelectric beam outputs a voltage signal. The NI data acquisition card collects the voltage signal and transmits the data to the laptop via a USB cable. A pre-designed program in the data acquisition software is used to display and record the real-time voltage signals. Using the control variable method, relevant parameters in the experiment are adjusted to obtain real-time voltage signals of the energy harvester under different conditions, which are recorded and saved. Data analysis software is used to process the experimental data. Finally, the equipment switches and the main power supply are turned off, and the experimental platform is tidied up.

To ensure smooth progress of the experiment and obtain reliable data, the following precautions must be taken before conducting experimental tests:
(1) The piezoelectric patch is fragile; waterproof soft tape is wrapped around the clamped end of the piezoelectric beam to prevent the piezoelectric patch from breaking due to clamping.
(2) Ensure the experiment is completed in one go to prevent significant errors caused by other factors.
(3) Maintain consistency of experimental parameters when repeating experiments.

Experimental Results: The voltage time-domain diagrams of the energy harvester at different excitation frequencies are shown in Figure 2.14. Under conditions of 4g acceleration, no mass block at the free end of the piezoelectric beam, and an impact beam thickness of 0.2 mm, the output performance of the energy harvester was tested at excitation frequencies of 6 Hz, 6.6 Hz, 9.2 Hz, 12 Hz, 13.4 Hz, and 13.8 Hz. By analyzing the voltage output of the energy harvester under single-frequency excitation, it was found that the collision positions between the impact beam and the piezoelectric beam are not identical in each cycle, leading to slight differences in the signals of each cycle, but the overall characteristics remain consistent. As the excitation frequency increases, the number of collisions between the impact beam and the piezoelectric beam per second increases, and the decay period of the free vibration of the piezoelectric beam decreases. At an excitation frequency of 13.8 Hz, the time-domain diagram exhibits smooth periodic characteristics, indicating that no collision occurs between the impact beam and the piezoelectric beam at this frequency. This is because the excitation frequency of 13.8 Hz is far from the natural frequency of the impact beam, resulting in reduced vibration amplitude and displacement insufficient to reach the collision distance. Consequently, no kinetic energy is transferred to the piezoelectric beam, and the vibration displacement of the piezoelectric beam is close to zero.

The output performance of the base-excited impact-type piezoelectric energy harvester under different excitation accelerations was further tested through sweep frequency experiments, as shown in Figure 2.15. Under conditions of no mass block at the free end of the piezoelectric beam and the impact position at the front end of the piezoelectric beam, the voltage output of the energy harvester was tested at excitation frequencies ranging from 6 Hz to 14 Hz under accelerations of 2g, 3g, 4g, and 5g. The figure clearly shows that as the excitation acceleration increases, the output voltage of the energy harvester also increases. As the excitation frequency increases, the voltage output of the energy harvester gradually rises, reaching its first peak at an excitation frequency of 6.5 Hz. Subsequently, as the excitation frequency further increases, the output voltage gradually decreases, reaching a minimum before rising again. The second peak occurs at an excitation frequency of 13.6 Hz, after which the output voltage rapidly decreases and approaches zero. This is because, as the excitation frequency increases, the vibration displacement of the impact beam becomes smaller than the collision distance between the impact beam and the piezoelectric beam, preventing further collisions. The sweep frequency response more intuitively demonstrates the output performance and vibration characteristics of the energy harvester in the frequency range of 6–14 Hz.

Power Amplifier Recommendation: ATA-3090C

Figure: ATA-3090C Power Amplifier Specifications

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