3. Experimental test on the electret electrostatic harvester output performance

In order to further study the performance of electret electrostatic harvester, a prototype of electrostatic harvester with double-ended fixed-beam electret was fabricated and tested experimentally.

The effects of excitation frequency, air gap, load resistance, and other factors on the output characteristics of the electret electrostatic harvester are tested by the experimental method.

#### 3.1. Effect of excitation frequency on the output of electrostatic harvester

The output of the harvester is related to the excitation frequency. In the acceleration peak of 1.5 harmonic excitation, the output voltage and output power with frequency curve are shown in Figures 17 and 18.

gap is 0.15 mm, the peak-to-peak output voltage is 66 V; when the air gap is reduced to

Integrated Power Supply for MEMS Sensor http://dx.doi.org/10.5772/intechopen.74804 41

As shown in Figure 20, as the air gap increases, the output power first increases and then decreases. When the gap is 0.2 mm (optimal air gap), the output power reaches a maximum of 0.08 mW. When the air gap increases to 0.5 mm, the output power is reduced to 0.015 mW.

As shown in Figure 21, as the air gap decreases, the electrostatic force between the upper and lower plates gradually increases, the soft spring effect increases, and the stiffness coefficient of

As shown in Figure 22, as the air gap decreases, the half-power bandwidth gradually increases. When the air gap is 0.5 mm, the bandwidth is 1.8 Hz, and when the air gap is reduced to

the spring decreases. As a result, the resonant frequency shifts from 96.8 to 94.8 Hz.

0.5 mm, the output voltage is reduced to 20.8 V.

Figure 18. Output power with frequency curve.

Figure 17. Output voltage with frequency curve.

0.15 mm, the bandwidth reaches a maximum of 6 Hz.

The experimental results show that when the initial air gap is 0.2 mm and the acceleration peak is 1.5 m/s<sup>2</sup> , the resonant frequency of the electrostatic harvester is 96.2 Hz, the maximum peakto-peak output voltage is 63.6 V, the corresponding half-power bandwidth is 3.2 Hz, and the maximum output power is 0.054 mW.

#### 3.2. Effect of air gap on the output of electrostatic harvester

The air gap is one of the most important parameters of the electret electrostatic harvester, which plays a key role in the output of the electrostatic harvester.

When the external excitation acceleration peak and the electret surface potential are constant, as shown in Figure 19, the output voltage decreases with the increase of air gap. When the air

Figure 17. Output voltage with frequency curve.

3. Experimental test on the electret electrostatic harvester output

3.1. Effect of excitation frequency on the output of electrostatic harvester

In order to further study the performance of electret electrostatic harvester, a prototype of electrostatic harvester with double-ended fixed-beam electret was fabricated and tested experimentally. The effects of excitation frequency, air gap, load resistance, and other factors on the output characteristics of the electret electrostatic harvester are tested by the experimental method.

The output of the harvester is related to the excitation frequency. In the acceleration peak of 1.5 harmonic excitation, the output voltage and output power with frequency curve are shown in

The experimental results show that when the initial air gap is 0.2 mm and the acceleration peak

to-peak output voltage is 63.6 V, the corresponding half-power bandwidth is 3.2 Hz, and the

The air gap is one of the most important parameters of the electret electrostatic harvester,

When the external excitation acceleration peak and the electret surface potential are constant, as shown in Figure 19, the output voltage decreases with the increase of air gap. When the air

, the resonant frequency of the electrostatic harvester is 96.2 Hz, the maximum peak-

performance

40 MEMS Sensors - Design and Application

Figures 17 and 18.

maximum output power is 0.054 mW.

Figure 16. Voltage across the load resistance varies with time.

3.2. Effect of air gap on the output of electrostatic harvester

which plays a key role in the output of the electrostatic harvester.

is 1.5 m/s<sup>2</sup>

Figure 18. Output power with frequency curve.

gap is 0.15 mm, the peak-to-peak output voltage is 66 V; when the air gap is reduced to 0.5 mm, the output voltage is reduced to 20.8 V.

As shown in Figure 20, as the air gap increases, the output power first increases and then decreases. When the gap is 0.2 mm (optimal air gap), the output power reaches a maximum of 0.08 mW. When the air gap increases to 0.5 mm, the output power is reduced to 0.015 mW.

As shown in Figure 21, as the air gap decreases, the electrostatic force between the upper and lower plates gradually increases, the soft spring effect increases, and the stiffness coefficient of the spring decreases. As a result, the resonant frequency shifts from 96.8 to 94.8 Hz.

As shown in Figure 22, as the air gap decreases, the half-power bandwidth gradually increases. When the air gap is 0.5 mm, the bandwidth is 1.8 Hz, and when the air gap is reduced to 0.15 mm, the bandwidth reaches a maximum of 6 Hz.

Figure 21. Output power with frequency curve.

Integrated Power Supply for MEMS Sensor http://dx.doi.org/10.5772/intechopen.74804 43

Figure 22. Half power bandwidth with air gap curve.

Figure 23. The relationship between load resistance and output power.

Figure 19. Output voltage with air gap curve.

Figure 20. Output power with air gap curve.

#### 3.3. Effect of load on electrostatic harvester output

In addition to the excitation frequency and air gap, the output power of the electrostatic harvester is also related to the external load resistance. The best load test method is as follows:


Integrated Power Supply for MEMS Sensor http://dx.doi.org/10.5772/intechopen.74804 43

Figure 21. Output power with frequency curve.

Figure 22. Half power bandwidth with air gap curve.

3.3. Effect of load on electrostatic harvester output

1. Keeping the acceleration peak of 1.5 m/s<sup>2</sup>

Figure 20. Output power with air gap curve.

Figure 19. Output voltage with air gap curve.

42 MEMS Sensors - Design and Application

In addition to the excitation frequency and air gap, the output power of the electrostatic harvester is also related to the external load resistance. The best load test method is as follows:

2. The external load resistance must be connected in series with the oscilloscope during the test. 3. Measuring the output voltage corresponding to different resistances sequentially at the resonance point and plotting the recorded data with Matla (shown in Figure 23).

, the air gap is 0.2 mm.

Figure 23. The relationship between load resistance and output power.

As shown in Figure 23, as the external load resistance increases, the output power first increases and then decreases. There is a maximum output power of 0.08 mW; the corresponding optimal load is 40 MΩ.

[2] Li P, Gao S, Shi Y, Liu J. Effects of package on performance of MEMS piezoresistive

Integrated Power Supply for MEMS Sensor http://dx.doi.org/10.5772/intechopen.74804 45

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[16] Mitcheson PD, Green TC, Yeatman EM. Power processing circuits for electromagnetic, electrostatic and piezoelectric inertial energy scavengers. Microsystem Technologies.

[17] Cheng S, Wang N, Arnold DP. Modeling of magnetic vibrational energy harvesters using equivalent circuit representations. Journal of Micromechanics and Microengineering.

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#### 4. Conclusion

Based on the analysis of the basic theory of the electret electrostatic harvester, the basic equations and equivalent analysis model of electret electrostatic harvester are established. Through the experimental tests of electrets electrostatic harvester, it can be seen that the output performance of electret electrostatic harvester is influenced by the parameters, such as excitation frequency, air gap between electrets, and electrode and load resistance and so on. Thus, when designing the electret electrostatic harvester, the influence of some important parameters on the output performance of electrostatic harvester should be considered as much as possible. On the other hand, some microscale effect also should be considered when the MEMS device and the electrostatic energy harvester are integrated design and fabrication. Electrostatic harvesting requires a constant voltage or constant charge condition; it seems that a separate power supply is needed. And it seems contrary to the idea of energy harvesting. However, with the electret material, the material itself can also provide a constant voltage to avoid the use of additional power, which provides an effective way for electrostatic harvesting. Therefore, the electret electrostatic harvesting structure is a kind of ideal energy harvesting method using ambient vibration and can be easily integrated with the MEMS system because of its compatibility with MEMS technology.

## Author details

Hai-peng Liu<sup>1</sup> \*, Lei Jin<sup>2</sup> , Shi-qiao Gao<sup>1</sup> and Shao-hua Niu2

\*Address all correspondence to: lhp@bit.edu.cn

1 State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing, China

2 School of Mechatronical Engineering, Beijing Institute of Technology, Beijing, China

#### References

[1] Li P, Gao S, Cai H. Design, fabrication and performances of MEMS piezoelectric energy harvester. International Journal of Applied Electromagnetics and Mechanics [J]. 2015;47(1): 125-139


As shown in Figure 23, as the external load resistance increases, the output power first increases and then decreases. There is a maximum output power of 0.08 mW; the corresponding optimal

Based on the analysis of the basic theory of the electret electrostatic harvester, the basic equations and equivalent analysis model of electret electrostatic harvester are established. Through the experimental tests of electrets electrostatic harvester, it can be seen that the output performance of electret electrostatic harvester is influenced by the parameters, such as excitation frequency, air gap between electrets, and electrode and load resistance and so on. Thus, when designing the electret electrostatic harvester, the influence of some important parameters on the output performance of electrostatic harvester should be considered as much as possible. On the other hand, some microscale effect also should be considered when the MEMS device and the electrostatic energy harvester are integrated design and fabrication. Electrostatic harvesting requires a constant voltage or constant charge condition; it seems that a separate power supply is needed. And it seems contrary to the idea of energy harvesting. However, with the electret material, the material itself can also provide a constant voltage to avoid the use of additional power, which provides an effective way for electrostatic harvesting. Therefore, the electret electrostatic harvesting structure is a kind of ideal energy harvesting method using ambient vibration and can be easily integrated with the MEMS system because

, Shi-qiao Gao<sup>1</sup> and Shao-hua Niu2

1 State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology,

[1] Li P, Gao S, Cai H. Design, fabrication and performances of MEMS piezoelectric energy harvester. International Journal of Applied Electromagnetics and Mechanics [J]. 2015;47(1):

2 School of Mechatronical Engineering, Beijing Institute of Technology, Beijing, China

load is 40 MΩ.

44 MEMS Sensors - Design and Application

4. Conclusion

Author details

Hai-peng Liu<sup>1</sup>

Beijing, China

References

125-139

of its compatibility with MEMS technology.

\*, Lei Jin<sup>2</sup>

\*Address all correspondence to: lhp@bit.edu.cn


[18] Maurath D, Becker PF, Spreemann D. Efficient energy harvesting with electromagnetic energy transducers using active low-voltage rectification and maximum power point tracking. IEEE Journal of Solid-State Circuits. 2012;47(6):1369-1380

**Section 2**

**BioMEMS**


**Section 2**
