**2.6 Impact of excitation signal amplitude symmetry on micropump performance**

To compensate for the influence of piezoelectric load and to balance the signal, we introduced a solution based on fine-tuning of duty cycle setting. By prolonging the time of first and shortening the time of the second half-cycle, an amplitudesymmetric signal can be synthesized despite piezoelectric load. The effectiveness of the solution was demonstrated on PZT sample P-5H. The microcontroller code for module was modified to enable adjustment of 16 different signal/pause signal ratios from 20 to 80% in the frequency range from 90 to 150 Hz by 10 Hz increments. The power supply voltage for control module was set to 9 and 10 V, respectively. The

## *Influence of Piezoelectric Actuator Properties on Design of Micropump Driving Modules DOI: http://dx.doi.org/10.5772/intechopen.103789*

module was programmed to a chosen excitation frequency and for each duty cycle setting, amplitude of positive half-cycle V<sup>+</sup> , of negative half-cycle V<sup>−</sup> and power supply current *I*CC were measured. **Figure 15** shows the degree of signal asymmetry *S*ASIM as a function of the power supply voltage and duty cycle at excitation frequencies from 70 to 150 Hz. We observed that duty cycle of equalization DCeq+ at 9 V and 10 V of power supply voltage ranged between 30 and 38% and between 40 and 43%, respectively.

**Figure 16** shows the driving signal amplitude as a function of duty cycle DC<sup>+</sup> , frequency *f* ranging from 70 to 150 Hz and power supply voltages of 9 and 10 V. From **Figure 16**, it follows that the maximum amplitude (120 to 130 V) is achieved only in the interval up to 100 Hz (curves 125 and 120 in **Figure 16**, left), while this limit moves up to 110 Hz at higher power supply voltage (10 V, curves 130, 125 and 120 in

#### **Figure 15.**

*The degree of signal asymmetry SASIM as a function of duty cycle DC+ at excitation frequencies f ranging from 70 to 150 Hz at 9 V (left) and 10 V (right) power supply voltage.*

#### **Figure 16.**

*Micropump driving signal amplitude in V as a function of operating frequency and duty cycle DC+ for power supply voltage of 9 V (left) and 10 V (right).*

#### **Figure 17.**

*Power supply current in mA as a function of operating frequency and duty cycle DC+ for power supply voltage of 9 V (left) and 10 V (right).*

**Figure 16**, right). A higher excitation frequency (Δ*f* = +10%) affects the flow rate and backpressure performance of piezoelectric micropumps.

**Figure 17** shows the power supply current as a function of the power supply voltage and the duty cycle DC+ at various frequencies ranging from 70 to 150 Hz. From **Figure 17**, it follows that the power supply current is not affected by module operating frequency, which is also supported by the theory of switching power supplies but increases almost linearly with duty cycle DC+ setting.

The upper limit of duty cycle setting, which keeps the power supply current below 70 mA is 75% and 62% for 9 V and 10 V of power supply voltage, respectively.

Signals of varying degrees of amplitude asymmetry were synthesized by varying the duty cycle setting. Backpressure and flowrate performance of the micropump was shown to be the highest at the duty cycle of equalization DCeq+ = 40%. To compensate for piezoelectric load and to provide amplitude symmetric driving signal, a solution by fine-tuning of duty cycle setting was proposed.

Duty cycle of equalization DCeq+ at 9 V power supply voltage ranged between 30 and 38% while at 10 V power supply voltage shifted toward 43%.
