Optimizing Piezoelectric Bimorphs for Energy Harvesting from Body Motion: Finger Movement in Computer Mouse Clicking

Abstract

Electrical devices are integral to daily life, but limited battery life remains a significant issue. A proposed solution is to convert dissipated energy from human motion into electricity using piezoelectric materials. This study investigates lead–zirconate–titanate (PZT) piezoelectric materials in bimorph configuration, conducts performance tests to understand their characteristics and determine the optimal load resistance, and develops an energy-harvesting prototype. Performance tests adjusted input parameters and varied load resistance and input magnitude to optimize power gained from the PZT bimorph. A suitable human movement for the application of the bimorph is a mouse-clicking motion by fingers. A prototype was created by integrating the bimorph into a computer mouse to capture energy from clicks. The results showed that the deformation rate of the PZTs, input magnitude, and resistance load were key factors in optimization. The bimorph configuration produced 0.34 mW of power and 5.5 V at an optimum load of 5072 Ω, requiring less effort to generate electricity. For the computer mouse energy harvester case, it yielded a total average power of approximately 38.4 μW per click with a click frequency of 4 Hz. This power could be used to support IoT devices such as human sensors (e.g., CO₂, temperature, and pulse sensors) and smart home sensors, enabling comprehensive health and environmental monitoring. In conclusion, input specifications, magnitude, and load resistance are essential for optimizing piezoelectric energy harvesters.

1. Introduction

Nowadays, many electronic devices are an important part of our daily life, serving as essential tools for communication, productivity, and entertainment. However, despite the advancement in micro-electromechanical system (MEMS) technologies that fabricate very low power consumption electronic devices, the issue of limited battery lifetime persists [1]. An alternative power source that overcomes this problem is desired to replace or at least extend the lifetime of the conventional battery. This motivation inspires many researchers to make these alternative power sources a reality.

A promising alternative for power sources involves converting energy from human activities into electrical power. The state-of-the-art output power harvested from human motion is in the range from 1 μW to 7 W [2]. There are two main methods that stand out for harvesting energy dissipating from human motion: electromagnetic and piezoelectric. Electromagnetic devices convert biomechanical energy from human activities into electrical power and have higher power output compared to piezoelectric energy harvesters. However, among the various methodologies explored by researchers, the utilization of piezoelectric materials to harvest biomechanical energy stands out over the usage of electromagnetic due to their compact size and lightweight nature, making them suitable for integration into wearable and portable devices [3,4].

Recent research on piezoelectric materials highlights their energy harvesting and diverse applications [5,6,7,8,9]. High-performance composites with PZT fillers excel in ammonia detection. Core–shell-structured smart textiles enable self-powered NO₂ sensing. Piezoelectric textiles with Sm-doped PMN-PT ceramics are effective for humidity detection and wearable biomonitoring. Zinc oxide nanorods offer multifunctional uses in gas sensing and piezoelectric nanogenerators. These advancements showcase the potential of piezoelectric materials in developing efficient, self-powered devices for various applications.

Piezoelectric materials can be categorized into lead–zirconate–titanate (PZT), which requires higher input force, and polyvinylidene fluoride (PVDF), which necessitates bending of piezoelectric films. This study was structured into lower and upper body movements. Lower body movements, such as knee joint, ankle, and heel strike, relate to the gait cycle. A knee-joint energy harvester with a bimorph–plectra mechanism was designed to bend the bimorph during knee motion, converting low-frequency rotation to its resonant frequency, achieving a maximum power output of 3.5 mW at 80 kΩ [10]. An enhanced version with a magnetic plucking mechanism increased power output to 5.8 mW and extended the device’s lifetime to over 7.3 h (approximately 3.8 × 10⁵ plucking excitations) [11]. Heel strikes also proved suitable for energy harvesting. Attaching piezoelectric material to the shoe sole generates energy through force excitation and sole bending. Liu [1] reported that PVDF yielded a maximum power of 15 nW at 6 km/h, while PZT produced 1.4 mW. PVDF is more flexible and easier to integrate but generates lower power output compared to PZT.

Upper body movements occur not only during walking but also in daily activities such as handshaking, arm or elbow movements, and finger bending. Handshaking involves relatively high amplitude and frequency. To capture this energy, a frame with a sliding free mass and two PZT sheets was attached to the hand, generating an average output power of 47 μW [12]. For energy harvesting from arm and elbow swings, a PZT beam with a magnet was fixed above a rotor. As the rotor rotated, the beam oscillated, producing electricity. The maximum output power of this device, when attached to the upper arm during running, was 42 μW [13]. Reviews highlight piezoelectric materials as excellent for capturing lost energy from human motion due to their small size and light weight. Although the generated power may seem lower than by other methods, it is sufficient for low-power devices such as IoT devices, for example, human sensors (e.g., CO₂, temperature, and pulse sensors). The power consumption of IoT devices is approximately 10 μW [14,15,16,17,18,19]. Then, for example, this power could be used to continuously monitor a person’s vital signs, such as heart rate and temperature, while also tracking indoor air quality to provide comprehensive health and environmental monitoring.

Despite advancements in energy harvesting, there is still limited research on capturing energy from upper body movements, especially finger bending. This research focuses on energy harvesting from finger bending, motivated by the potential of PZT to harvest energy from body motions. Using PZT to harvest energy from finger clicking on a mouse is appropriate, as this motion is small and occurs frequently. PZT ceramic is particularly effective at converting mechanical strain from bending into electrical energy. Finger bending during mouse clicking is an ideal activity for PZT-based energy harvesting because it involves small bending motions that occur frequently throughout the day. For instance, professional software developers perform between 3000 to 5000 mouse clicks daily [20], making it a prime opportunity for energy harvesting.

To design piezoelectric bimorphs for energy harvesting from mouse clicks, a commercial PZT ceramic was selected because it can generate more power output compared to PVDF. However, PZT ceramic has limited deflection and is fragile. Additionally, the PZT ceramic data sheet presents its characteristics when used as sensors or actuators. Therefore, an experimental setup for the PZT ceramic was established to study its characteristics and determine the optimum load resistance for maximizing the harvested energy. The optimized parameters and optimum load resistance were then used to design a mouse model for harvesting energy from finger bending. Following this, experiments on the mouse model were conducted to investigate its performance.

Therefore, the objective of this research is to apply a piezoelectric energy harvester to a computer mouse, capturing energy from finger movements during mouse clicking. To achieve this, this study focuses on optimizing energy harvesting by analyzing the characteristics of piezoelectric bimorphs and determining the optimal load resistance. The experimentation involves characterizing a bender-type piezo energy harvesting (PEH) structure, with several key advantages: simulating the dynamic press load similar to mouse clicks with adjustable load levels, scaling up the PEH model with controlled deflection using beam theory to ensure reliability, and including a stopper to control the piezo deflection within yield limits. Additionally, the experiment setup can be adapted to other PEH beam designs to investigate their performance. Ultimately, this research aims to develop an application of the mouse click model to harvest energy for IoT devices.

This paper is organized into the following sections: In Section 2, the design of the piezoelectric bimorph system and the relevant parameters for investigating its characteristics are described in detail. Section 3 presents the experimental method and the power output from the system, as well as the determination of the optimum load resistance for maximizing the harvested energy. Section 4 discusses the application of the piezoelectric energy harvester with a mouse for finger bending, along with the tested results. Section 5 and Section 6 present the applications and implications, and future directions and research opportunities, respectively. Finally, the conclusion is presented in Section 7.

2. Description of Piezoelectric Bimorph Experimental Design

Piezoelectric bimorphs consist of two PZT layers adhered together with a passive support layer in between. They bend when a voltage difference is applied and generate electricity when bent. This bidirectional property allows for them to act as both actuators and energy harvesters [21]. For energy harvester applications, bimorphs generate positive voltage when bent in one direction and negative voltage when bent in the opposite direction. This behavior shows that bimorphs function as an alternating current (AC) source. The bimorphs used in this study are model PB4NB2W from Thorlabs, as shown in Figure 1a [22]. They feature three soldered wires (red, white, and green) connected to the top, middle, and bottom layers, respectively, as shown in Figure 1b [23]. For energy harvesting, bending the bimorphs creates tensile force in the top layer and compressive force in the bottom layer, generating a voltage difference. The greatest voltage is obtained across the red and green wires [24,25,26]. These PZT bimorphs are fragile, with a maximum displacement of approximately 450 μm. Also, the data sheet of the piezo presents its characteristics when used as sensors or actuators. Thus, the characteristics for energy harvesting need to be verified. The experimental setup designed to handle these requirements is described in the following section.

2.1. Piezoelectric Displacement Control

Since the PZT bimorph is very fragile and has a maximum piezoelectric displacement of approximately 450 µm, a piezo–beam structure with fixed end supports, shown in the schematic in Figure 2, was designed to study its characteristics. The long beam allows for varying and controlling the deflection, which can be easily measured and adjusted. Additionally, a bolt stopper at the midpoint of the base limits the maximum deflection range and can be adjusted by changing the height of the bolt. To accurately control the small displacement, the piezoelectric bimorph was glued to one end of a two-millimeter-thick aluminum beam. This structural design enabled precise control of the piezoelectric displacement through the beam deflection [27].

The aluminum beam was attached to the piezoelectric bimorph as a fixed-end beam, which was deflected by a single-point load at the beam’s midpoint. A schematic of the beam is shown in Figure 3. The beam deflection was calculated to set the stopper, preventing the piezoelectric deflection from exceeding the limit.

To set the stopper position, the deflection of the beam at any position x was then calculated:

$$\delta (x)={\displaystyle \frac{F{x}^2}{48EI}}\left(3L-4x\right); 0\le x\le {\displaystyle \frac{L}{2}}$$

(1)

where δ is deflection at position x from the left side, E is modulus of elasticity, and I is area moment of inertia.

Firstly, the deflection of the beam at the position of the bimorph was designated to be 450 µm. Then, the unknown parameter, $F/EI$, could be determined. The dimensions of the piezoelectric bimorph and aluminum beam are shown in Figure 4. Essentially, the value of δ and x are 0.45 and 28 mm, respectively, and were applied to Equation (1).

$${\displaystyle \frac{F}{EI}}=43.39\times {10}^{-6} {\mathrm{m}\mathrm{m}}^{-2}$$

Next, the deflection at the beam’s midpoint was determined by applying the value of $F/EI$ and $x=L/2$ to Equation (1) as well, resulting in the following:

$${\delta }_{midpoint}=3.489 \mathrm{m}\mathrm{m}$$

Finally, the height-adjustment bolt at the beam’s midpoint was adjusted to match the deflection at the midpoint, ${\delta }_{midpoint}$, to obtain the maximum piezoelectric displacement. To attain the other values of piezoelectric displacement, the same method was used to calculate the beam deflection value.

2.2. Power Optimization of the Piezoelectric Bimorph

The power gained from the piezoelectric bimorph was affected by electrical and mechanical parameters in the system. Both parameters were investigated in this section to design further experiments.

2.2.1. Electrical Parameters

A circuit diagram used in this study is shown in Figure 5. To convert the AC signal from the bimorph to the direct current (DC) signal before supply the load, a full-wave rectifier circuit, containing four diodes with a forward voltage of 0.7 V, was connected to the piezoelectric bimorph and then connected to an external load.

Once the piezoelectric was excited, voltage across the variable resistor $\left(V_R\right)$ was measured using Analog Discovery 2. Then, the energy generation of this resistor at time $t_j$ was calculated:

$$\begin{gathered} E_R\left(t_j\right)=\sum _{k=1}^j{P}_R\left(t_k\right)\Delta t \\ =\sum _{k=1}^j{\displaystyle \frac{V_R^2}{R_L}}\left(t_k\right)\Delta t \end{gathered}$$

(2)

where $P_R$ is the power of the external loads, $∆t$ is the sampling time, $V_R$ is the voltage across the load, $R_L$ is the variable resistor, and $E_R\left(t_j\right)$ is the energy dissipated in variable resistor at the time $t_j$.

Whenever the average power appears, it is calculated as follows:

$$P_{avg}={\displaystyle \frac{\left|E\left(t_2\right)-E\left(t_1\right)\right|}{t_2-t_1}}$$

(3)

where $E\left(t_1\right)$ and $E\left(t_2\right)$ are the energy at times $t_1$ and $t_2$, respectively.

The optimized power is achieved through the variation in load resistance. Within this process, there exists a singular value of load resistance that yields the highest output power, referred to as the optimum load resistance [28].

2.2.2. Mechanical Parameters

The performance of the piezo–beam structure described in Section 2.1 was evaluated by applying an external pressing force to the beam’s midpoint, as shown in Figure 6, to study the behavior of the piezoelectric bimorph. Two types of force were used: high-speed pressing, which rapidly pushed the beam’s midpoint downward causing quick piezoelectric displacement changes, and low-speed pressing, which bent the beam more slowly, resulting in gradual deformation. Both forces pushed the beam downward to the height-adjustment bolt and were held until the voltage output of the bimorph consistently reached zero. As shown in Figure 7a, the higher deformation rate produced a voltage peak of up to 2.5 V, while the slower rate generated only 0.45 V over a longer period. Using Equation (2), the energy generated was calculated and is shown in Figure 7b. The faster deformation rate produced up to 2.2 μJ of energy, whereas the slower rate generated only 0.45 μJ. These results indicate that the deformation rate is crucial for maximizing energy and power output in energy harvesting applications.

From the investigation in both electrical and mechanical parameters, it can be concluded that the energy and power output is affected by the external load resistance and deformation rate of the bimorph. The effect of both parameters are studied experimentally in Section 3 to maximize the power.

3. Performance Evaluation of Piezoelectric Bimorph

The setup configuration for the performance test of the piezoelectric bimorph is shown in Figure 8. In the experimental setup, the bimorph was attached to an aluminum beam to consistently control its deformation rate. The setup involved bending the beam to a specific deflection range by adjusting the height of a bolt, followed by rapidly releasing the beam using a linear solenoid. By allowing the aluminum beam to vibrate freely after releasing the linear solenoid, the deformation rate of the bimorph was kept consistent. This setup ensured the experiment could be repeated reliably.

The piezoelectric bimorph experiment was divided into two parts: the first part aimed to estimate the optimum load resistance for the tested piezo model, and the second part was to measure the output voltage and power from various piezoelectric displacements.

The setup of the piezoelectric bimorph experiment and the wiring diagram are shown in Figure 9. In the first part of the experiment, a linear solenoid initially enforced and controlled the beam deflection at the midpoint to 3 mm, then released to let the beam vibrate freely. The voltages across the variable resistor were measured using Analog Discovery 2 as a scope during the vibration, and then the power was calculated to define the optimum load resistance.

After the optimum load resistance was identified in the first part, the second part of the experiment was conducted to examine the relationship between the input piezoelectric displacement and the output power. This time, the resistor was fixed at its optimum value while the beam initial displacement was varied from 0 mm to 3 mm instead.

Figure 10 shows the result example of the time dependence of the voltage across the 9520 Ω resistor. It was found that the highest voltage occurred at the first peak and was decaying over time because of the free vibration of the beam. Note that the voltage only appeared on the positive side due to the rectifier circuit. From the voltage response, the total energy and average power were calculated by Equations (2) and (3). Next, the variable resistor was varied from 500 Ω to 15 kΩ to find the optimum load resistance. The relationship between load resistance, peak output voltage, and average power is shown in Figure 11. The result showed that the highest average power was around 0.32 mW when the optimum load resistance was approximately 5072 Ω.

The average power of the piezoelectric bimorph with the optimal load of 5072 Ω was then calculated at various piezoelectric displacements. Figure 12 presents the relationship between piezoelectric displacement, the average power, and the peak voltage. It could be observed that the highest average and peak voltage in the experiment were 0.34 mW and 5.5 V, respectively. Both average power and peak voltage tended to increase linearly as the piezoelectric displacement was increased. However, the last two data points in the graph appear to saturate due to the bimorph reaching its limit, which is around 450 µm. Consequently, the bimorph would not be able to generate additional power and could potentially crack if bent beyond this limit.

The power obtained from the experiment appears to be lower than for the 5.8 mW reported for the knee rotating device mentioned in Section 1. This notable difference could be due to variations in the number and size of the bimorphs used in the respective devices. However, when compared to the power generated by a piezoelectric bimorph of similar size in a cantilever beam model represented in [29], the average power from both experiments seems to be comparable. This suggests that the experiment setup and methodology yield consistent outcomes regarding the relationship between input and output of piezoelectric bimorphs, as observed in the existing literature.

4. Feasibility Design of Piezoelectric Bimorph Applications

After understanding the piezoelectric bimorph characteristics, this section utilizes the findings from Section 2 and Section 3 regarding power generation from various inputs parameters to explore energy harvesting from actual movement. The finger movement when clicking was inspired by [30]; therefore, the computer mouse was selected for this study because of the frequency and rapidity of the mouse clicking movement. The first prototype underwent testing to assess the power output relative to the input, following a similar approach as in Section 3. Finally, the results were examined, and potential future directions are discussed.

4.1. An Application of a Piezoelectric Bimorph Energy Harvester: Computer Mouse Clicking

The piezoelectric bimorph has a maximum displacement of approximately 450 μm, which may seem small compared to many human movements. However, there is one motion that involves such a small amount of body movement and is becoming increasingly common: clicking a computer mouse. The computer mouse is clicked when a finger pushes the mouse button down rapidly and then releases it. This motion relates to the performance test in Section 3 that pushed and released the bending bimorph. So, the idea of harvesting energy from the mouses is to integrate the bimorph into the button. The piezoelectric materials then bend due to the clicking force, causing electricity generation. Office workers perform this action hundreds of times a day. Additionally, for individuals who play computer games, the number of clicks can range up to several thousand per day. Importantly, the displacement of the computer mouse switch is sufficient for triggering the displacement of the bimorph with minimal force effort. All these factors make the act of clicking a computer mouse an interesting motion to investigate.

To attach the bimorph into a mouse button, all components of the mouse needed to be separated to observe the possible options. In this study, an OKER M149, which is shown in Figure 13, was selected as an example of a typical mouse because of its large size, providing more space for the bimorph. There are three switches inside the OKER mouse, which are the H-7.3 model. The dimension of the H-7.3 switch is shown in Figure 14. Two horizontal switches are for the left and right mouse button, and one is a middle switch laying under a scroll wheel.

Section 2 and Section 3 demonstrate that the performance of the piezoelectric bimorph depends on the deformation rate and piezoelectric displacement. Therefore, the prototype should be designed to fix the piezoelectric bimorph to a metal beam with low stiffness. This design choice aims to decrease the deformation rate and reaction force, improving the bimorph’s performance and actual usability, respectively. A 0.3 mm thick stainless-steel plate was selected to function as a cantilever support, as shown in Figure 15. This plate was installed using a nut and bolt with a 3D-printed part. Although the beam type attached to the bimorph in the prototype differs from that in Section 3, the bimorph’s performance depends on the piezoelectric displacement. The deflection of the stainless steel and the bimorph was calculated using the same approach as shown in Section 2.

Consider the stainless-steel beam attached to the piezoelectric bimorph as a cantilever beam deflected by a single-point load at the beam’s tip. A schematic of the beam is shown in Figure 16.

The deflection of the cantilever beam at any position x was then calculated:

$$\delta (x)={\displaystyle \frac{F{x}^2}{6EI}}\left(3L-x\right); 0\le x\le L$$

(4)

where δ is deflection at position x from the left side, E is modulus of elasticity, and I is area moment of inertia.

The deflection at the beam’s tip was set to be 400 μm, within the range of the mouse switch. The piezoelectric displacement was then calculated using Equation (4). The piezoelectric displacement in this design was approximately 314 μm, which did not exceed its limit but also did not achieve the highest possible performance.

The piezoelectric bimorph was designed to harvest energy from the clicking motion. And for this mouse’s model, the bimorph was expected to be attached above the right click switch to avoid the scroll wheel encoder. A piezoelectric bimorph energy harvester structure, as shown in Figure 17, contained a cantilever beam substrate made of a 0.3 mm thickness stainless-steel sheet. This beam would bend when the mouse was clicked, and the bimorph attached to the beam then bent along it. The beam was fixed on the 3D-printed part designed to fit inside the mouse. Its tip was positioned directly on the H-7.3 switch, as the clicking range of this switch shown in Figure 14 is around 400 μm. The bimorph was then bent to the displacement of 314 μm, with the expectation that electricity would be generated in nearly the same amount as observed in Section 3.

4.2. Performance Test of the Mouse Clicking Energy Harvester Device

This experiment aimed to determine the average power per click. The setup and wiring diagram of the experiment are shown in Figure 18. The optimum load resistance of this experiment was expected to be around 5072 Ω, like the previous bimorph performance test. Nonetheless, the test was conducted with various resistances to confirm the optimum load resistance. The procedure involved clicking the right mouse button five times consecutively. The total energy and average power of each click were then calculated using Equations (2) and (3), respectively. Finally, the total energy and average power per click were determined as the average of these five clicks.

Figure 19 presents the time dependence of the voltage across the 5080 Ω resistance for five clicks. It was found that each click comprised two distinct peaks. The first peak occurred when the bimorph was pushed down with the click, while the second peak occurred upon releasing the mouse button. The highest value of the first peak was around 3.4 V, whereas the lowest was 2.5 V. These variations were attributed to the deformation rate of piezoelectric materials, as discussed in Section 2. In other words, the faster the click, the higher the generated voltage.

The average power of these five peaks was calculated. Subsequently, the same experimental method was performed, but with variation in resistance, to confirm that the optimum load resistance of the bimorph in this system remains consistent. The relationship between load resistance, average power, and peak voltage is shown in

Table 1. Average power and peak voltage generated by the piezoelectric bimorph as a function of load resistance.

Resistance (Ω)	Average Power (mW)	Peak Voltage (V)
2000	0.075	1.80
3250	0.144	2.40
5080	0.202	3.40
6000	0.086	4.10
8000	0.080	4.70

. It can be observed that the peak voltage increased continuously with increasing resistance, while the average power also rose steadily until reaching the optimum load resistance of 5080 Ω, with the highest average power recorded at 0.2 mW. Beyond this point, the average power dropped significantly as the resistance increased. As a result, the optimum resistance was confirmed to be the same as found in Section 3. At this optimum resistance, a total energy generation of 9.6 μJ per click was recorded. The time per one click is approximately 48 ms. Therefore, with the click frequency of 4 Hz, the total average power is approximately 38.4 μW. (Note: According to Refs. [25,31,32], during normal walking at a frequency of 1 Hz, a piezoelectric (PZT) under the heel-strike center can generate around 8.4 mW, while other designs might harvest approximately 1 mW during walking).

This experiment revealed a similarity in the trend of the relationship between resistance, average power, and peak voltage observed in both the piezoelectric bimorph on an aluminum beam and the mouse clicking performance test. Additionally, the findings indicate that the optimum load resistance remained consistent across both experiments. However, it was noted that the highest average power and peak voltage were lower by approximately 23% and 29%, respectively, compared to the bimorph on an aluminum beam test at the same piezoelectric displacement. One possible explanation for this difference is that the clicking speed may not be as fast as the beam free vibration. Moreover, while the electricity was generated along the beam’s vibration in the bimorph test, the clicking action only produced two peaks of electricity. Consequently, the mouse clicking energy harvester generated lower electricity over a longer duration, resulting in lower voltage and power output. Additionally, integrating a piezoelectric bimorph energy harvester into a mouse increases the stiffness of the mouse clicking mechanism and decreases operational comfort because of the higher clicking force required. This extra force can introduce a slight delay between the user’s intention to click and the actual registration of the click. This delay can affect the perceived sensitivity and responsiveness of the mouse. However, other structural designs and experimental setups may deliver entirely different results. Thus, the approach outlined in this study should be replicated in other experimental setups to further explore the performance of piezoelectric material energy harvesters.

The proposed piezoelectric bimorphs face several limitations. They are fragile due to the brittleness of PZT materials, requiring careful handling and protection. Their power output is generally lower than in other methods like electromagnetic systems, limiting them to low-power applications. Material fatigue from repeated mechanical stress can reduce efficiency and reliability. Additionally, environmental factors such as temperature and humidity can affect performance. Integrating bimorphs into devices like computer mice poses challenges in maintaining user experience and functionality, complicating design and manufacturing. Addressing these issues is crucial for enhancing the practical applicability of the energy harvesting system.

There are other ways to improve the efficiency of energy collection in the computer mouse prototype. For example, increasing the number of piezoelectric elements can significantly enhance the energy output. Additionally, replacing the stainless-steel beam structure attached to the piezo with a more flexible or softer material can reduce resistance force and increase the voltage output of the piezo. These modifications can collectively boost the energy harvesting efficiency, making the system more viable for practical applications.

In summary, this section focuses on the design and testing of a piezoelectric bimorph integrated into a computer mouse button for energy harvesting from mouse clicking. Leveraging insights from previous experiments, the piezoelectric bimorph’s suitability for capturing energy from small, repetitive motions such as mouse clicking is explored. The section details the design process, including the selection of the mouse model, placement of the bimorph, and structural considerations. Subsequent performance testing assesses the average power per click, revealing a consistent relationship between load resistance, average power, and peak voltage. Comparisons with previous experiments highlight similar trends, while demonstrating differences in output due to variations in motion dynamics. The findings emphasize the potential for energy harvesting not only from the finger clicking on the mouse motion but also other daily activities such as heel strike or arm swinging during walking. Additionally, the power management and storage system presented in [33,34], although not discussed in this study, is suggested for further exploration. Implementing such a system could make these energy-harvesting methods more practical and enable them to charge a battery effectively. The harvested energy in this case could be utilized to support various IoT devices, such as human sensors (e.g., temperature and pulse sensors) and smart home sensors (e.g., CO₂ and air quality monitors). This application enables continuous health and environmental monitoring, providing real-time feedback to improve indoor air quality and track vital signs, enhancing overall well-being.

5. Applications and Implications

The integration of piezoelectric energy harvesting within a computer mouse represents a significant advancement in the quest for sustainable energy solutions in low-power IoT devices. By converting mechanical energy from frequent mouse clicks into electrical energy, this technology not only provides a continuous and reliable power source for embedded sensors and communication modules but also reduces dependency on traditional batteries, which are a major contributor to electronic waste. This aligns with global sustainability goals, particularly in reducing the carbon footprint associated with the production, use, and disposal of batteries [35,36].

Beyond the application in a computer mouse, the principles of piezoelectric energy harvesting have broader implications for a wide range of devices that experience similar high-frequency, low-amplitude mechanical motions. Devices such as keyboards, trackpads, and wearable fitness devices are subjected to constant mechanical interactions that can be effectively harnessed for energy generation. Embedding piezoelectric harvesters into these devices could significantly enhance their energy efficiency and autonomy, leading to reduced energy consumption and longer operational lifespans. This not only offers environmental benefits but also economic advantages, as it could lower the overall cost of ownership by reducing the need for frequent battery replacements [35].

Moreover, the development of hybrid energy systems that combine piezoelectric, solar, and thermoelectric sources represents a crucial step forward in optimizing energy capture. Such systems can ensure a more reliable and consistent energy supply, particularly in environments with variable conditions. By leveraging multiple energy sources, these hybrid systems can extend the operational capabilities of devices, making them more versatile and resilient in a range of applications. This research, by focusing on the simple yet ubiquitous action of mouse clicking, not only demonstrates the feasibility of piezoelectric energy harvesting but also lays the foundation for its broader adoption in everyday technology, potentially transforming how we power and interact with our devices [35,36].

6. Future Directions and Research Opportunities

Building on this study, future research should focus on optimizing piezoelectric materials to enhance efficiency and durability, particularly for applications involving repetitive, low-amplitude motions like mouse clicks. Developing advanced composites that improve energy conversion rates while withstanding continuous mechanical stress is crucial for extending device lifespan [35,36].

Another important direction involves hybrid energy systems that integrate piezoelectric harvesting with other renewable sources, like solar and thermoelectric energy. These systems can ensure a consistent and reliable power supply across varying conditions, making IoT devices more autonomous and versatile [35].

Long-term durability testing is essential to ensure the reliability of these systems under continuous use. Understanding material wear and fatigue under constant stress will guide improvements in material selection and device design [36]. Finally, a thorough assessment of the commercial viability of this technology—including cost-effective manufacturing and market demand—will be critical for transitioning from research prototypes to real-world applications, realizing the full potential of self-powered devices in everyday technology [35,36].

7. Conclusions

This study aims to investigate and analyze methods for harvesting energy from human motion through the utilization of piezoelectric materials. Subsequently, the objective is to develop and construct a measurement system to quantify the harvested energy.

In the experimental setup to determine the optimal load resistance, the piezoelectric bimorph attached to an aluminum beam was tested for performance. By varying the load resistance and controlling the beam deflection, the optimal load resistance was identified as around 5072 Ω. This setup achieved a maximum power output of 0.34 mW and a peak voltage of 5.5 V. This study highlighted that power output increased with piezoelectric displacement, but reached a saturation point due to the material’s limits.

The practical application of the bimorph was tested by integrating it into a computer mouse button to harvest energy from mouse clicks. The bimorph’s placement within the mouse allowed for it to bend with each click, generating electricity. Performance tests revealed that the optimum load resistance for this setup was 5080 Ω, with each click generating an average power of 0.2 mW or the total average power of approximately 38.4 μW per click with a click frequency of 4 Hz. The voltage response showed two distinct peaks per click, corresponding to the pressing and releasing actions. The findings indicate that piezoelectric bimorphs are a possible solution for energy harvesting from human motion, providing a promising alternative to extend the lifetime of batteries in low-power electronic devices. The harvested energy in this case could be utilized to support various IoT devices.