**3. Piezoelectric pump with multiple chambers**

The output performance of the piezoelectric pump can be improved by increasing the number of chambers. When the pump chambers are connected in series, the pressure of the piezoelectric pump increases; when the pump chambers are parallel, the flow rate of the piezoelectric pump increases.

## **3.1 Piezoelectric pump with single actuator and double chamber**

As shown in **Figure 12**, the piezoelectric pump with single actuator and double chamber (PPSADC) includes a piezoelectric bimorph vibrator, two chambers (chamber A and B), four check valves and a pump body. Chamber A has inlet 1 and outlet 1, and chamber B has inlet 2 and outlet 2. The chamber A and chamber B of the piezoelectric pump can be connected in series or in parallel, which can improve the applicable range of the pressure and flow. **Figure 12(a)** shows the series connection of chambers A and B. In the process of working, the fluid enters the chamber B from the inlet 2, and the outlet 2 is connected with the inlet 1, and the liquid enters the chamber A through the inlet 1, so that chamber B and chamber A are in series, which can make the piezoelectric pump obtain high pressure. **Figure 12(b)** shows the parallel connection of chamber A and B. In the process of working, the fluid enters the chamber A and B from the inlet 1 and 2, and flows out from the outlet 1 and 2, so that the chamber A and B form a parallel connection, which can obtain a large flow rate.

**Figure 13** is the three-dimensional structure of PPSADC with the overall dimension of 41 mm × 41 mm × 25 mm. **Figure 14** is the prototype of PPSADC. Chamber A and chamber B are symmetrical. The upper and lower O-rings are used to seal the chambers, which realizes the flexible support of the piezoelectric vibrator. The flexible support can amplify the displacement of the piezoelectric vibrator. The structure of check valve is umbrella valve. The material of pump body is PMMA. The series and parallel switching of chamber A and chamber B is realized through the connection transformation of rubber tube.

**Figure 15** shows the relationship between the output flow rate and the driving voltage when the driving frequency is 100 Hz. It can be seen from the **Figure 15** that the output flow increases with the increase of the driving voltage. When the driving

#### **Figure 12.**

*The structure and working principle of PPSADC. (a) Serial connection. (b) Parallel connection [15].*

voltage is increased to 250 Vpp, the output flow rate of the two chambers in series and in parallel is 17 ml/min and 32 ml/min respectively. The PPSADC can achieve high energy conversion efficiency.

#### **3.2 Piezoelectric pump with five actuators and five chambers**

**Figure 16** is the structure of piezoelectric pump with five actuators and five chambers (PPFAFC). Five piezoelectric actuators and five chambers constitute five pumps in series, which improves the output pressure. Ai (i = 1, 2, 3, 4, 5) represents five piezoelectric actuators; Cj (j = 1, 2, 3, 4, 5) represents five chambers; Vk (k = 1, 2, 3, 4, 5, 6) represents 6 check valves (**Figure 16**).

*Design, Characterisation and Prospect of Piezoelectric Microfluidic Technology DOI: http://dx.doi.org/10.5772/intechopen.98559*

**Figure 13.** *The 3-D structure of PPSADC [15].*

**Figure 14.** *The prototype of PPSADC [15].*

**Figure 17** shows the working principle of PPFAFC. PPFAFC is driven by an AC voltage signal, and the driving voltage of the adjacent piezoelectric vibrator has a phase angle of 180°. As shown in **Figure 14(a)**, during the suction process, A1/A3/A5 bends outwards of the cavity and A2/A4 bends into the cavity. Then the volume of the chamber C1/C3/C5 increases, and the volume of the chamber C2/C4 decrease, valve V1/V3/V5 opens, valve V2/V4 closes; as shown in **Figure 14(b)**, during the discharge process, A2/A4 bends outwards of the chamber and A1/A3/A5 bends towards the chamber, then the volume of the C2/ C4 increases, the volume of C1/C3/C5 decreases, the valve V2/V4 opens, and the valve V1/V3/V5 closes. When it is driven by an AC voltage signal, the suction and discharge processes are alternately performed to achieve continuous fluid output (**Figure 17**).

**Figure 15.** *The relationship between flow rate and driving voltage [15].*

**Figure 16.** *The structure of PPFAFC [16].*

**Figure 15** shows the three-dimensional structure and prototype of PPFAFC. A prototype of PPFAFC was designed, manufactured and assembled. The performance of PPFAFC is tested. The pump body is made of PMMA and sealed by O-ring. It was driven by five piezoelectric actuators. PPFAFC can achieve high output performance at low voltage, where it can meet the needs of different applications (**Figure 18**).

As shown in **Figure 19**, when the driving voltage is 180 Vpp, the relationship between the output flow rate and backpressure of PPFAFC and the driving frequency is analyzed. It can be seen from **Figure 19** that the output flow rate increases with the increase of the driving frequency. When the driving frequency increases to 400 Hz, the flow rate increases to 279.2 ml/min. When the driving frequency is 90 Hz, the maximum output pressure of 10.8 kPa is obtained. PPFAFC owns high output performance.

#### **3.3 Piezoelectric pump with five actuators and ten chambers**

**Figures 20** and **21** show the three-dimensional structure and working principle of piezoelectric pump with five actuators and ten chambers (PPFATC). PPFATC is composed of five groups of single vibrator double chamber piezoelectric pumps in

*Design, Characterisation and Prospect of Piezoelectric Microfluidic Technology DOI: http://dx.doi.org/10.5772/intechopen.98559*

**Figure 17.** *Working principle of PPFAFC. (a) Suction. (b) Discharge [16].*

#### **Figure 18.**

*The three-dimensional structure and prototype of PPFAFC [16].*

series, forming two group of five-chambers mechanisms. When PPFATC is connected in parallel, two groups of five-chambers mechanisms are formed in parallel, which can make the outlet obtain continuous fluid output without fluctuation;

#### **Figure 19.**

*The relationship between flow rate and backpressure and excitation frequency [16].*

#### **Figure 20.**

*The structure and working principle of PPFATC in parallel connection [17].*

**Figure 21.**

when PPFATC is connected in series, two groups of five-chambers mechanisms are formed in series, namely ten chambers in series, which can make the output pressure increase. In the working process, the phase of the driving voltage signal of the adjacent piezoelectric vibrator is 180 degrees, that is, the vibration direction of the adjacent piezoelectric vibrator is opposite in the working process. Combined with the function of check valve, the continuous one-way fluid output of PPFATC is formed under the driving of AC voltage signal.

**Figure 22** is the three-dimensional structure and prototype of the PPFATC. A prototype of the PPFATC is fabricated, and then carried out its output performance test and water cooling test with the PPFATC as the power source, as shown

*The structure and working principle of PPFATC in serial connection [17].*

*Design, Characterisation and Prospect of Piezoelectric Microfluidic Technology DOI: http://dx.doi.org/10.5772/intechopen.98559*

**Figure 22.** *The three-dimensional structure and prototype of PPFATC [17].*

#### **Figure 23.**

*The experimental platform of PPFATC and chip water-cooling system [17].*

in **Figure 23**. The experiment shows that when the driving voltage is 60 Vpp, the maximum flow rate of the PPFATC in parallel is 251.1 ml/min and the maximum output pressure is 60.2 kPa. In series, the PPFATC can achieve 186.2 ml/min and

109.9 kPa, respectively. The water cooling system with PPFATC can obtain good cooling performance under low driving voltage. When the driving voltage is 60 Vpp, the PPFATC can reduce the chip temperature from 107.8–51°C.
