The Effect of Drive Signals on Output Performance of Piezoelectric Pumps

Abstract

The output performance of piezoelectric pumps is not only affected by the structural design but is also related to the drive signal. To study the effect of different drive signals on the output performance of piezoelectric pumps, this paper takes dual-chamber serial piezoelectric pumps as the investigation object, theoretically deduces the effective value of the drive signal and the output performance of the piezoelectric pump, and tests the displacement of piezoelectric vibrator center, the output performance of the piezoelectric pump, and the operating noise within the range of 0–500 Hz, respectively, driven by square waves, sine waves, and triangular waves (the peak-to-peak values of which are all 300 V). The results show that at low frequencies, the piezoelectric vibrator’s center displacement curve matches the drive signal, which is sinusoidal and decreases with frequency. Under the square drive, the piezoelectric pump has the best performance, with a flow of 147.199 mL/min and pressure of 14.42 kPa, but the noise is also the highest. The output performance of the sine wave is better than that of the triangular wave, and the flow rate of the three signals shows a trend of first increasing and then decreasing.

1. Introduction

As the power source of microfluidic systems [1,2], micropumps feature high integration, simple structure, low energy consumption, and resistance to environmental influences. These attributes make micropumps widely used in various fields, including medical drug delivery [3,4], chemical reagent analysis [5], electronic equipment cooling [6,7], and fuel transportation [8,9]. Piezoelectric pumps, driven by the inverse piezoelectric effect, are a specific type of micropump. In 1978, W.J. Spence and colleagues [10] proposed a micro-piezoelectric pump for insulin delivery and designed electronically controlled release valves, pioneering a new research area for piezoelectric pumps. Since then, the theoretical study and practical applications of piezoelectric pumps across various fields have continued to evolve.

Single-chamber piezoelectric pumps typically rely on a single piezoelectric vibrator to pump liquid. They have a simple structure and are easy to manufacture, but their output performance is not ideal. Xiuhua He et al. [11] have significantly enhanced the output flow rate of the piezoelectric pump by incorporating a specially designed flow restrictor within the chamber of the valveless piezoelectric pump to amplify the Coanda effect. Experimental results showed that under a signal drive of 300 V/50 Hz, the maximum output flow rate of the prototype can reach 4.84 mL/min, with an output pressure of up to 1.75 kPa. Yongming Yao et al. [12] machined a Tesla-valve-like channel at the inlet and outlet of a piezoelectric pump to be unidirectionally conductive in order to minimize the liquid reflux phenomenon present in valveless piezoelectric pumps. The optimal parameters of the channel were determined by simulation combined with fabricated test prototypes of various sizes. The experimental results show that the design can achieve a maximum output flow rate of 79.26 mL/min at the optimum parameters with a drive voltage of 350 V_pp (peak-to-peak voltage) and a frequency of 28 Hz.

Lipeng He et al. [13] designed a single-chamber piezoelectric pump using a wheel valve as a check valve structure and explored the impact of the wheel valve’s structural parameters on the pump’s output performance. The experimental results show that the optimal parameters for the wheel-type check valve structure are when the number of valve arms is four, and the length and width are 2.02 mm and 0.8 mm, respectively, resulting in the best output performance of the piezoelectric pump. Jiafeng Ni et al. [14] reported a single-chamber valveless piezoelectric micropump characterized by high flow and high-pressure load, suitable for wearable and portable applications, with a gas output flow rate of 135 mL/min and a maximum output pressure exceeding 40 kPa. Inspired by the changes in the working state of heart valve structures during cardiac pumping, Jiayue et al. [15] designed a piezoelectric pump with valves resembling the shape of heart valves. The uniqueness of this design lies in its ability to switch between two operating modes—valveless and valve-type piezoelectric pumps—by varying the magnitude of the driving voltage. When the driving voltage is below 140 V, the design functions as a valveless piezoelectric pump. When the driving voltage exceeds 140 V, it operates as a valve-type piezoelectric pump, achieving a maximum output flow rate of 44.5 mL/min at a driving voltage of 220 V.

Single-chamber piezoelectric pumps tend to have small output flow rates and output pressures due to the limited number of chambers. The researchers enhanced the output performance of the piezoelectric pump by increasing the number of chambers and connecting them in series, parallel, and series-parallel configurations. Xiaopeng Liu et al. [16] fabricated and tested series-connected piezoelectric pumps with different numbers of chambers and compared them with single-chamber piezoelectric pumps. The results showed that the output flow rates and pressures of the dual-chamber and four-chamber designs were 1.73 times, 2.97 times, and 1.88 times, and 4.5 times those of the single-chamber design, respectively. Taijiang Peng et al. [17] combined the advantages of series and parallel modes by creating a four-chamber hybrid piezoelectric pump with two dual-chamber units connected in parallel and then in series. This design achieved an output flow rate of 1845 mL/min and an output pressure of 32.47 kPa. Abhijeet Vante et al. [18] explored multi-chamber series, parallel, and hybrid connections by adjusting the inlet and outlet connections of each chamber. Their experiments demonstrated that all three modes could effectively reduce flow pulsations during liquid pumping under asynchronous operation. Song Chen et al. [19] designed a dual-chamber piezoelectric pump, driven by a circular double-crystal piezoelectric vibrator, incorporating flow detection functionality. The detection results in both series and parallel modes correlated highly with the actual output flow rate. Mai Yu et al. [20] proposed a novel three-chamber cascaded piezoelectric pump, where the first stage consists of two chambers in parallel and the second stage consists of a single chamber. These two stages are connected in series, allowing the piezoelectric pump to simultaneously leverage the advantages of both series and parallel structures. They experimentally investigated the optimal combination of driving signals for the operation of the three chambers. When the phase difference between the driving signals of the first and second stages is 180°, the maximum output flow rate is achieved at 24.52 mL/min, representing a significant improvement in output performance compared to traditional dual-chamber series piezoelectric pumps.

Currently, researchers are not only studying the structural design of piezoelectric pumps but also investigating the impact of drive signals on their output performance. Although piezoelectric pumps serve as the power source for microfluidic systems, they experience flow pulsations during operation. To address this issue, Lin Lin et al. [21] designed a microfluidic stabilizer and modified the square wave drive signal. Experimental results showed that the modified square wave signal effectively suppressed flow pulsations caused by sudden signal changes. Gürhan Özkayar et al. [22] reduced low-flow pulsations by increasing the number of piezoelectric pumps operating in parallel and adjusting the phase difference of the drive signals according to the number of working chambers. Experiments revealed that using three piezoelectric pumps connected in parallel with a 120° phase difference in the drive signals could eliminate over 90% of flow pulsations. Sun Yeming et al. [23] designed a dual-active-valve piezoelectric pump and developed a specialized power supply capable of independently adjusting the voltage, frequency, and phase of the drive signals. Experimental results demonstrated that controlling the phase difference between the drive signals of the active valves at the inlet and outlet and the piezoelectric vibrators within the pump chamber allowed for changes in fluid transport direction and stable control of output flow and pressure. P. Dhananchezhiyan et al. [24] investigated the effect of changes in driving signal on improving the flow pulsation phenomenon when multiple piezoelectric pumps operate in parallel. By altering the phase difference of the driving signals for each piezoelectric pump, the working sequence of the pumps was changed. The experimental results showed that when the driving voltage was 250 Vpp and the frequency was 30 Hz, the flow pulsation rate of two piezoelectric pumps operating in parallel was reduced by 29% when the phase difference of the driving signals was 180°, compared to the condition with no phase difference. When three piezoelectric pumps operated in parallel with a phase difference of 120°, the flow pulsation rate was reduced to just 8%.

In summary, current research on piezoelectric micropump chamber structures and quantities [25,26], valve structures [27,28], and working modes [29] has become quite abundant. However, most of the existing studies have only used a single driving signal to drive the piezoelectric pump, and there is limited research on the impact of driving signal waveforms on the output performance of piezoelectric pumps. To investigate the influence of driving signals on the output performance of piezoelectric pumps, this study focuses on a dual-chamber serial piezoelectric pump and employs square waves, sine waves, and triangular waves for driving. It explores the vibration characteristics of the piezoelectric vibrator and the output performance and operational noise of the piezoelectric pump under different signal driving conditions. While improving the output performance of the piezoelectric pump, this research also provides some reference for its applications in fields that have specific requirements for output signals and quietness, such as drug delivery and electronic chip cooling.

2. Structure Design Working Principle

2.1. Double-Chamber Serial Piezoelectric Pump Structure Design

The exploded view, overall effect diagram, and physical diagram of the dual-chamber serial piezoelectric pump are shown in Figure 1. The pump is mainly composed of top and bottom plates, a chamber plate, piezoelectric vibrators, rubber sealing rings, umbrella valves, an inlet, and an outlet. The front and back sides of the chamber plate each have two annular chambers serving as the two pump chambers. The sealing rubber rings ensure good sealing between the piezoelectric vibrators and the chambers. The umbrella valves inside the chambers provide excellent one-way cutoff performance, preventing backflow of the liquid during the pumping process. The layers of the piezoelectric pump are fastened together using securing bolts. The relevant parameters of the fabricated dual-chamber serial piezoelectric pump prototype are shown in

Table 1. Parameters of the dual-chamber serial piezoelectric pump test prototype.

Parameters	Size and Material
Size of prototypes	58.8 mm × 42.3 mm × 15 mm
Diameter of PZT disk	29 mm
Diameter of copper disk	35 mm
Height of chamber	1.2 mm
Diameter of outlet and inlet	5 mm
Materials of pump body	PMMA
Materials of PZT disk	PZT-5 (origin: Shenzhen, China)
Materials of check valve	rubber

.

2.2. Dual-Chamber Serial Piezoelectric Pump Working Principle

The dual-chamber serial piezoelectric pump is driven by an internal piezoelectric vibrator that oscillates up or down in response to an excitation signal, thereby increasing or decreasing the volume of the pump chamber. This periodic change in volume exerts a corresponding pressure change within the pump chamber, which, in conjunction with the umbrella-shaped valve that opens unidirectionally, regulates the inflow and outflow of fluid into and out of the pump chamber, thus enabling continuous fluid pumping. In the design, the two chambers operate with a phase difference of 180° in their driving signals, meaning that while one chamber is in the water absorbing stage, the other chamber is in the water discharging stage. During the continuous pumping of liquid, the operational process of the dual-chamber series piezoelectric pump consists of three stages: chamber 1 absorbing water; chamber 1 discharging water and chamber 2 absorbing water; and chamber 2 discharging water. The working schematic diagram is shown in Figure 2.

Stage 1: Chamber 1 absorbing water. The piezoelectric vibrator inside chamber 1 moves upwards, making chamber 1 larger and reducing the internal pressure. Under the effect of the internal and external pressure differential, the umbrella valve at the inlet of chamber 1 and the umbrella valve at the outlet are, respectively, in an open and closed state, allowing the liquid to flow into the interior of chamber 1.

Stage 2: Chamber 1 discharging and chamber 2 absorbing. After chamber 1 absorbs water, the internal piezoelectric vibrator moves downward, so that the volume of chamber 1 decreases, the internal pressure increases, and the outlet umbrella valve opens. Simultaneously, inside chamber 2, the piezoelectric vibrator moves downward, so that the chamber 2 volume becomes larger and the internal pressure becomes smaller. Since the outlet umbrella valve of chamber 1 also functions as the inlet umbrella valve of chamber 2, under the effect of external pressure difference, the liquid flows into chamber 2 directly from chamber 1, and the outlet umbrella valve of chamber 2 is in a closed state.

Stage 3: Chamber 2 discharging. The piezoelectric vibrator inside chamber 2 moves upwards, so that the volume of chamber 2 decreases, the internal pressure becomes larger, and the outlet umbrella valve opens under the action of the internal and external pressure difference. At the same time, chamber 1 is in the absorption stage, its internal outlet umbrella valve is closed, i.e., the internal inlet umbrella valve of chamber 2 is in the closed state, and liquid from piezoelectric pump flows out of the internal outlet valve of chamber 2.

3. Theoretical Analysis

The piezoelectric pump in this paper consists of two single chambers connected in series. According to the literature [10,30], for a single chamber working process, when the piezoelectric vibrator’s driving frequency is much lower than the resonance frequency, the displacement of its center can be approximated as a constant $\delta$, and the change in the volume of the piezoelectric vibrator in a single vibration can be expressed as:

$$\delta ={\displaystyle \frac{3d^2{d}_{31}}{8h^2}}U$$

(1)

$$\mathrm{\Delta }V={\displaystyle \frac{\pi d^2}{8}}\delta ={\displaystyle \frac{3\pi d_{31}{d}^4}{64h^2}}U$$

(2)

where $d$ and $h$ are the diameter and thickness of the piezoelectric vibrator, respectively, $d_{31}$ is the piezoelectric constant of the piezoelectric vibrator, and $U$ is the value of the drive signal.

The output flow rate and output pressure values for single chambers operating individually are:

$$Q_{one}=\mathrm{\Delta }Vf\eta ={\displaystyle \frac{3\pi d_{31}{d}^4}{64h^2}}Uf\eta$$

(3)

$$P_{one}={\displaystyle \frac{12\pi Y_{11}^D}{4.5\pi Y_{11}^D{g}_{31}{d}_{31}+1}}{\displaystyle \frac{h}{d^2}}U$$

(4)

where $f$ is the driving signal frequency, $\eta$ is the efficiency coefficient of the umbrella valve, $Y_{11}$ is the piezoelectric vibrator elasticity model, $g_{31}$ piezoelectric constant.

Assuming that the two chambers in the design have the same output performance when working individually, the output pressure and output flow rate of a dual-chamber piezoelectric pump in series are

$$P_{all}=n{P}_{\mathrm{one}}$$

(5)

$$Q_{all}=C_{v}A\sqrt{{\displaystyle \frac{2n{P}_{one}}{\rho }}}=\sqrt{n}Q$$

(6)

where $n$ is the number of chamber, $C_v$ is the flow coefficient, $A$ is the flow area, and $\rho$ is the liquid density.

The square, sine, and triangle wave signals used to drive the piezoelectric pump are all periodic signals, and the three periodic signal functions are Taylor expanded as follows:

$$f_{squ}(t)={\displaystyle \frac{4U_m}{\pi }}(\sin \omega t+{\displaystyle \frac{1}{3}}\sin 3\omega t+{\displaystyle \frac{1}{5}}\sin 5\omega t+\cdots +{\displaystyle \frac{1}{2n}}\sin 2i\omega t)={\displaystyle \frac{4U_m}{\pi }}{\displaystyle \sum _{i=1}^{\infty }\frac{1}{2n-1}\sin \left[\left(2i-1\right)\omega t\right]}$$

(7)

$$f_{\sin }(t)=U_m\sin \omega t$$

(8)

$$f_{tri}(t)={\displaystyle \frac{8U_m}{{\pi }^2}}\left[\sin \omega t-{\displaystyle \frac{1}{9}}\sin 3\omega t+{\displaystyle \frac{1}{25}}\sin 5\omega t-\cdots \right]={\displaystyle \frac{8U_m}{{\pi }^2}}{\displaystyle \sum _{i=1}^{\infty }\frac{{(-1)}^{i-1}}{{(2i-1)}^2}\sin \left[\left(2i-1\right)\omega t\right]}$$

(9)

where $U_m$ is the maximum value of the voltage signal.

For periodic signals, the RMS value is calculated as

$$f(t)=U_0+{\displaystyle \sum _{i+1}^{\infty }{U}_{mi}\sin (i\omega t+{\phi }_i})$$

(10)

$$U_r=\sqrt{{\displaystyle \frac{1}{T}}{\displaystyle {\int }_0^T{\left[f(t)\right]}^{2}dt}}$$

(11)

where $U_0$ is the first term of the signal after expansion; $U$ is the signal RMS value; $T$ is the signal period; $f(t)$ is the periodic signal function; $U_{mi}$ is the ith component peak voltage; $\omega$ is the signal angular frequency; ${\phi }_i$ is the initial phase of the ith component; and $t$ is the time.

Using the calculation, when the peak voltage and frequency remain the same, the square wave, sinusoidal wave, and triangular wave, the three kinds of signals, have an effective ratio of $\sqrt{2}$:1:$\sqrt{2}$/2. When the piezoelectric vibrator is in the working process, the energy from the drive signals is converted into piezoelectric vibrator mechanical energy and thermal energy, but when the piezoelectric vibrator is operating at a low frequency, the heat production is lower; and the energy can be approximated to be used for all the fluid drive. Therefore, when using the three drive signals to drive the piezoelectric pump, the piezoelectric vibrator center displacement and the piezoelectric pump output flow and output pressure, the relationship between the drive signals should also be the same as the ratio of the RMS value of the drive signal, namely, $\sqrt{2}$:1:$\sqrt{2}$/2.

4. Experimental Setup

The experimental setup shown in Figure 3 was used to test the displacement of the piezoelectric vibrator and the output of the piezoelectric pump under different drive signals, using water as the working medium. A specialized piezoelectric ceramic driver (XMT, E00.D3, Harbin, China) capable of outputting square, sine, and triangular waveforms in the range of 0–300 V_pp and 0–20 KHz was used to drive the piezoelectric pump. The voltage of the drive signal was fixed at 300 V_pp and increased gradually in 5 Hz increments. A laser displacement sensor with 0.001 μm accuracy (Keyence, LK-G5000, Osaka, Japan) was used to measure the center displacement of the piezoelectric vibrator in the range of 0–500 Hz. Simultaneously, the output flow rate and output pressure of the piezoelectric pump are measured with a timer, a precision balance with an accuracy of 0.001 g, and a pressure gauge with an accuracy of 0.01 KPa within a set time of 60 s. The noise generated by the piezoelectric pump under various drive signals is measured with a sound level meter with an accuracy of 0.1 dB.

Considering the structure and working conditions of the piezoelectric pump, its service life is equivalent to the fatigue life of the piezoelectric transducer. Using the method described in the author’s literature [31], the fatigue life of the PZT-5 piezoelectric transducer ceramic material used in the piezoelectric pump in this paper was calculated based on the fatigue damage accumulation hypothesis, resulting in approximately 4580 h (with a safety factor of 1.20), which also represents the service life of the piezoelectric pump. Under environmental conditions of room temperature between 15 to 25 °C and air humidity below 60%, with an excitation voltage of 0–400 Hz and 0–125 V, the actual measured service life of the PZT-5 piezoelectric vibrator (manufactured in China) used in the piezoelectric pump was found to range from 3450 to 5150 h.

5. Results and Discussion

5.1. Piezoelectric Vibrator Center Displacement Results and Discussion

The results of the center displacement of the piezoelectric vibrator with a frequency in the range of 0–500 Hz when the piezoelectric vibrator is driven by a square wave, a sine wave, and a triangle wave, respectively, with the value of the driving signal voltage fixed at 300 V_pp are shown in Figure 4. From Figure 4, it can be seen that with a constant voltage value, the center displacement of the piezoelectric vibrator decreases with increasing frequency under the driving of all three signals. The reason is that the piezoelectric vibrator has inherent mechanical damping. As the drive frequency increases, the vibration speed of the piezoelectric vibrator also increases, causing the damping to increase as well, leading to greater energy loss and reduced displacement during high-frequency vibrations. The displacement at the center of the piezoelectric vibrator is largest when driven by a square wave, varying from 7.098 μm to 33.34 μm, followed by a sine wave, varying from 6.264 μm to 30.028 μm, and when driven by a triangular wave, the displacement has the smallest range of variation, in the range of 4.05 μm to 23.069 μm. At 5 Hz, the square wave drive piezoelectric vibrator center displacement is 33.434 μm, with 30.028 μm for the sine wave and 23.069 μm for the triangular wave. At 500 Hz, the corresponding values are 7.098 μm for the square wave, 6.264 μm for the sine wave, and 4.05 μm for the triangular wave. The reason for these differences is found in Equation (1): when the material parameters and structural parameters of the piezoelectric vibrator are determined, the displacement of the center of the piezoelectric vibrator is only related to the magnitude of the voltage. From the theoretical derivation, it can be seen that under the same peak-to-peak value, the RMS value of the square wave signal is the largest, the sine wave is the second largest, and the triangular wave is the smallest, so when the piezoelectric pump is driven by three kinds of signals, the displacement of the piezoelectric vibrator center will be presented as the maximum displacement of the square wave drive, the sinusoidal wave is in the middle, and the triangular wave is the minimum.

During the experimental process, it was observed that the displacement variation curve of the center of the piezoelectric vibrator shifted with increasing frequency. Figure 5 shows the displacement variation curves of the piezoelectric vibrator’s center when the driving signal frequencies are set to 5 Hz, 25 Hz, and 50 Hz. As shown in Figure 5, the displacement curve of the center of the piezoelectric vibrator coincides with the waveform of the driving signal under low-frequency driving. The main reason for this is that at low-frequency drive, the piezoelectric material has sufficient time to complete the transformation from electric field to mechanical strain, allowing the displacement variation of the piezoelectric material to accurately follow the waveform of the driving signal.

Figure 6 shows the displacement variation curves of the piezoelectric vibrator’s center at 100 Hz, 150 Hz, and 200 Hz, while Figure 7 shows these curves at 240 Hz, 250 Hz, and 280 Hz. From Figure 6 and Figure 7, it can be observed that as the driving frequency continuously increases, the displacement variation curves of the piezoelectric vibrator’s center, when driven by square wave and triangular wave signals, gradually become similar to those when driven by sine wave signals. Specifically, from Figure 7, it can be seen that at 240 Hz, the displacement variation curve of the piezoelectric vibrator’s center driven by a triangular wave signal transforms into a sinusoidal curve. At 280 Hz, the displacement variation curve driven by a square wave signal also transforms into a sinusoidal curve.

Figure 8 shows the displacement variation curves of the center of the piezoelectric vibrator at 300 Hz, 400 Hz, and 500 Hz. From Figure 8, it can be observed that when the piezoelectric pump operates under high-frequency conditions and is driven by square wave, sine wave, and triangular wave signals, the displacement variation curves of the piezoelectric vibrator’s center all exhibit sinusoidal changes. According to the Fourier series expansion of the square wave and triangular wave signal functions in Equations (7) and (9), both square waves and triangular waves contain odd harmonics. The mechanical and electrical characteristics of the piezoelectric vibrator can be approximated as an RLC circuit. Under high-frequency drive, the higher-order harmonics present in square and triangular waves are attenuated, leaving only the sinusoidal components of the fundamental frequency. This results in the displacement variation curve of the piezoelectric vibrator’s center approximating a sinusoidal wave under high-frequency drive.

5.2. Piezoelectric Pump Output Performance Results and Discussion

Figure 9 illustrates the relationship between the output flow rate of a two-chamber series piezoelectric pump and increasing frequency. From Figure 9, it can be seen that the trend of the output flow rate with increasing frequency is very similar for all three waveforms. The flow rate increases continuously with frequency until there is a significant decrease after 400 Hz. This decrease is due to the opening and closing delay of the umbrella valve inside the piezoelectric pump chamber compared to the high-frequency vibration of the piezoelectric vibrator, resulting in incomplete closure. Under the square wave drive, the maximum output flow rate is 147.199 mL/min at 320 Hz. With the sine wave drive, the maximum output flow rate is 97.265 mL/min at 310 Hz. For the triangular wave drive, the maximum output flow rate occurs at 310 Hz and is 66.685 mL/min. From the overall change curves, it is evident that, regardless of the low- or high-frequency drive, the output flow rate is highest under the square wave drive, intermediate under the sine wave drive, and lowest under the triangular wave drive. The combination of Equations (3) and (6) shows that the output characteristics of the piezoelectric pumps are dependent on both voltage and frequency. When the frequency is the same, under the same peak voltage, the effective voltage values of the three waveforms are arranged from the largest to the smallest in the following order: square, sine, and triangle. The experimental results are in accordance with the theoretical derivation.

Figure 10 shows the curve of output pressure of the piezoelectric pump as it varies with increasing frequency. From Figure 10, it can be observed that when driven by the three types of signals, the trend of output pressure increasing with frequency is generally consistent; all show an increase in output pressure with rising frequency, followed by a decline at high frequencies. Under the square wave drive, the piezoelectric pump achieves its maximum output pressure of 14.42 KPa at 280 Hz. For the sine wave drive, the maximum output pressure occurs at 285 Hz and is 11.91 KPa, while for the triangular wave drive, the maximum output pressure also occurs at 285 Hz and reaches 10.26 KPa.

Table 2. Performance comparison of the proposed dual-chamber serial piezoelectric pump with previous studies.

Ref.	Valve Types	Chamber Numbers	Connection Type	Drive Signal Waveform	Voltage	Frequency	Flow Rate	Pressure
Yao et al. [12] 2021	Valveless	One	—	Sine wave	350 Vpp	28 Hz	79.26 mL/min	—
Zhou et al. [15] 2022	Cardiac Valve-like Structure	One	—	Sine wave	220 V	7 Hz	—	199 mm H2O
						11 Hz	44.5 mL/min	—
Liu et al. [16] 2022	Cantilever valve	Two	Serial	—	170 V	120 Hz	65.5 mL/min	—
						100 Hz	—	59.1 kPa
Yu et al. [20] 2020	Cantilever valve	Three	Parallelserial	Sine wave	220 Vpp	70 Hz	24.52 mL/min	—
This work	Umbrella valve	Two	Serial	Square wave	300 Vpp	320 Hz	147.199 mL/min	—
						280 Hz	—	14.42 kPa
				Sine wave	300 Vpp	310 Hz	97.265 mL/min	—
						285 Hz	—	11.91 kPa
				Triangle wave	300 Vpp	310 Hz	66.685 mL/min	—
						285 Hz	—	10.26 kPa

shows the comparison of the output performance of the dual-chamber serial piezoelectric pump proposed in this paper with previous piezoelectric pump works.

5.3. Sound Results and Discussion

The sound generated by the piezoelectric pump under different signal drives was measured using a decibel meter, as shown in Figure 11. From Figure 11, it can be observed that when driven by a square wave, the operational noise of the piezoelectric pump is relatively high and changes little with increasing frequency. When driven by sine and triangular waves, the noise produced by the piezoelectric pump is slightly greater than that under the sine wave drive; however, both exhibit a similar trend, indicating that the noise generated by the piezoelectric pump does not increase with frequency. The main reason for this is that square wave signals contain a large number of high-frequency harmonic components, which cause the piezoelectric vibrator to produce more intense mechanical vibrations during the operation of the piezoelectric pump, resulting in maximum noise. Although triangular waves also have higher-order harmonic components, their amplitude is relatively small, and the signal energy primarily resides in the funda-mental frequency. In contrast, sine wave signals concentrate all their energy at the fundamental frequency. When driving the piezoelectric pump, the mechanical response of the piezoelectric vibrator is smoother under these two signals, producing similar levels of noise that are both lower than that produced under the square wave drive.

5.4. Comparison of the Performance of Three Signal Drivers

Figure 12 and Figure 13 show the comparison of the center displacement of the piezoelectric vibrator and the output capability of the piezoelectric pump when they are driven by square wave and sine wave signals, and triangular wave and sine wave signals, respectively. Ideally, the ratio of center displacement and output power of the piezoelectric vibrator under the square wave drive to that under the sine wave drive is 1.414, and the ratio of sinusoidal drive to triangular drive is 0.707. However, as shown in Figure 12, the actual ratio of the square wave drive to the sine wave drive fluctuates, with the total range mostly between 1.1 and 1.8. Similarly, as shown in Figure 13, the actual ratio of the sine drive to the triangle drive also fluctuates, with an overall range between 0.5 and 0.89. The main reason is that when the piezoelectric pump is driven with different signals, the center displacement and output power of the piezoelectric vibrator are affected by several factors. These factors include the nonlinear response of the piezoelectric vibrator, the motion state of the umbrella valves inside the piezoelectric pump, and the spectral characteristics of the drive signals. These influences cause a deviation from the theoretical effective value ratio of the drive signals to the actual ratio of the center displacement to the output power of the piezoelectric pump.

6. Conclusions

The influence of drive signals on the output performance of a piezoelectric pump is discussed in this paper. A dual-chamber serial piezoelectric pump was designed and used as the research subject to study the relationship between the center displacement of the piezoelectric vibrator and the frequency of the drive signal, as well as the relationship between the output characteristics of the piezoelectric pump and the frequency of the drive signal, when driven by square wave, sine wave, and triangular wave signals at the same peak voltage. The experimental results show the following:

• Among the three driving signals, the square wave yields the largest displacement of the piezoelectric vibrator’s center, the sine wave produces an intermediate displacement, and the triangular wave results in the smallest displacement. The displacement of the piezoelectric vibrator’s center decreases with increasing frequency for all three waveform drives. At low frequencies, the displacement curve matches the waveform of the drive signal, but as the frequency increases, the displacement curves for both the square and triangular wave drives gradually shift towards a sinusoidal pattern.
• The square wave drive provides the best performance, followed by the sine wave, and the triangular wave provides the lowest performance in terms of the output performance of the piezoelectric pump. The output flow rate and pressure of the piezoelectric pump under all three drive signals first increase with frequency and then decrease.
• The piezoelectric pump generates the highest noise level when driven by a square wave, while the noise levels are similar under the sine wave and triangular wave drives.
• The ratio of the center displacements of the piezoelectric vibrator and the output performance of the piezoelectric pump is not equal to the ratio of the effective values of the respective drive signals when the piezoelectric pump is operated with different drive signals.
• Under the driving voltage of a sine wave, not exceeding 125 V and at 0–400 Hz, the actual measured service life of the PZT-5 piezoelectric vibrator used in piezoelectric pump was found to range from 3450 to 5150 h. In future work, we will conduct calculations and experimental tests on the service life of the piezoelectric pump under square wave and triangular wave driving voltages.