Power and Energy Harvesting on Vibration
Nowadays, wireless sensors are improved exponentially in terms of power usage. In today technologies, data transmission with using wireless network over 10 meters dominate most of the power consumption in devices . Battery powered wireless sensor networks are limited by the battery capacity so that, it provides finite power supply. Eventually, these network systems need regular maintenance and charging batteries. Therefore, energy harvesting methods are devised to provide portable power supply and reducing dependency finite power supplies. Thanks to energy harvesters reduce maintenance cost and eliminated power supply changing and charging .
Energy harvesting technologies have different types which depend on systems environment’s conditions. In this paper review of vibration energy harvesters. For example, the vibrations of a ship’s engine and the forces created by the waves hitting the front of the ship energies can be extracted by vibration energy harvesters . Also, vibration energy generated by vehicles vibration when passing on pothole or hull can be harvested.
Vibrational harvesters have three main types, which are electromagnetic, electrostatic and piezoelectric. Electromagnetic methods can harvest energy surprisingly but when reduced the size their performance decrease sharply . Inversely, electrostatic can be applicable small size but their power performance is not satisfying. Piezoelectric energy harvesters are in the middle of these two methods, so they can produce satisfactory power within different size scales. Piezoelectric energy harvesters use piezoelectric materials to convert either mechanical stress or strain to induces a charge on the material. However, piezoelectric materials charged asymmetrically over their structure and generating current is not enough for the working network sensor nodes so that, converting to stable direct current(DC) and more power extracting implementation are necessary for the operating electronic modules. This converting can be performed by energy harvesting circuits which are self-powered and pre-biased, for extraction power.
If we examine from the self-powered side, the simplest way of extracting the real power on piezoelectric transducer connect a resistive load parallel to output as shown in Fig. 1. Maximum power extraction occurs when using an optimal resistor. However wireless sensors need DC to operate, thus store the harvested energy in capacitor or battery necessary. Also, the piezoelectric material output voltage is sinusoidal so that, the output voltage must be rectified. The bridge rectifier is the simplest way of the rectification. It can implement using passive diodes and connected directly storage module as shown Fig. 2. After that, on storage devices can supply DC on a resistive load. Another energy harvested circuits approach is switched resistive load.
Piezoelectric energy harvesters can be used as velocity damped resonant generators (VHRGs). Optimal damping of VHRGs happened when load resistance and piezo capacitance are opposite ratios each other. In other words, when resistive load decrease, increase current flow but most of the power dissipated in circuits. Also, piezoelectric damping level is depended on the velocity of vibrating mass so that it is difficult to control and non-constant thus, this method is not suitable . On another hand, Piezoelectric energy harvesters can be used like as Coulomb damped resonant generators (CDRGs).
These methods use the extreme point of the charging on the structure so that is easier than VHRGs to control . In Fig. 3 shows the demonstration of CDRG, connection load resistance and switch series to the harvester. When peak voltage occurs on the harvester, switch closeand maximum current flow on the resistor. When applied rectifier, storage devices and buck converter for smooth charging to storage devices on this method as Fig. 4,maximum generated power increase 8/pi times to simple resistive load .
Resonant charge transfer (also named as charge flipping) is one of the power extraction techniques use a switch for flip charging between piezoelectric capacitance and storage device as shown Fig.5. In other words, when the piezoelectric capacitor charged fully, close the switch and all load energies transferred the storage devices then open switch. Another method which is synchronized switch harvester on inductor (SSHI) shown as Fig.6 is one of the high-efficiency technique in self-powered energy harvesting circuits, uses a switch for flip charging to increase charges. This method’s circuits work as like that when the piezoelectric beam reaches maximum voltage on it, switch close for flipping the capacitor energy to inductor after that, voltage inverted across on the piezoelectric material . Also, diode rectifier converts output voltage for the charge storage capacitor. On the other hand, switch implementation and control circuits also consume power so that choosing components for the switch implementation should be m
inimized power consuming for reach good efficiency. SSHI circuits also have different types which are parallel and series SSHI circuits. Difference between them is the type of the inductor connection (parallel or series). Synchronized charge extraction is another most efficient circuit that also uses switches to charge flipping shown in Fig. 7. Shuai Pang’s article which is “Optimization Analysis of Interfaces circuits in piezoelectric energy harvesting circuits”, simulation result for self-powered energy harvesting circuits shown as Fig.8. Simulation results under 2 Hz sinusoidal signal show four circuits’ output power based on resistive load parameter . When resistive load increasing SSHI circuits output power bigger than others. Moreover, wireless sensor modules total load resistance usually is between 10^5 to 10^7 ohm so that best choice is P-SSHI for the self-powered sys
tems. Also Fig. 9. shows another scientific simulation result with different components for switching circuits for the four different self-powered systems and results support the previous simulation result, higher energy can be extracted with SSHI .
If we examine another side which is pre-biased technique is increase electrical damping with the transferred small amount of charge. This circuit is also used synchronous switching system shown in Fig. 10, switches work like rectifier in this circuit. When piezoelectric material inducing this circuit supply voltage for the reduce power losses. In other words, When the piezoelectric beam reaches opposite maximum point pre-biased voltage (Vcc) and piezoelectric beam charge transfer onto a storage device and repeats that each side of bending or stress . Switches control the current flow based on piezoelectric charge way so, it acts as a rectifier. If optimal voltage control occurs, peak voltage flow the piezoelectric material is not clamped by diodes so that, this method can extract more energy than SSHI circuits method . However, this circuit has six switches, seven diodes, three inductors, battery and buck control shown in Fig. 10. Therefore, this circuit occurs power losses on components.
Thanks to Single Supply Pre-Biasing (SSPB) which needs fewer components than pre-biased circuits shown in Fig. 11, so that it is the more efficient implementation of pre-biased methods . In this method pre-biased supply and storage device is same so that, extractedpower goes to the same storage battery. Switches work same as original pre-biased circuit, Battery supply piezoelectric material’s charge so that S1 – S4 and S2 – S3 is dependent each other and work opposite. This switching bridge named by H-bridge.
Implementation of the SSPB can be separate four sub-circuits without piezoelectric beam. One of the subcircuits is peak detection circuit, it detects beams maximum charging moment for the decision the controlling switches status. H-bridge circuits change the current flow to providing one direction current flow the storage device. The control circuits works are deciding switching circuits status by using peak detector information. Last sub-circuits is energy storage circuit, it provides supply pre-biased voltage and storage extracted energy into the battery. In Fig. 11 shows all sub-circuits working diagram . Because there are so many components, they have to be chosen so that the choices are the least energy to consume. A.D.T Elliot research in “Power electronic interfaces for piezoelectric energy harvesters” shows that SSPB is %18 efficient than the second best method which is SSHI .
In conclusion, Piezoelectric is best choice other vibration energy harvesting methods (electromagnetic, electrostatic) for the wireless sensor powering. Piezoelectric methods have a lot of different approaches for harvesting circuits but when we categorized two main sides which are self-powered and pre-biased, two implementations are best to own category. These are SSHI and SSPB, SSPB is much more complex than SSHI but it total power extraction is more than SSHI. Overall, for self-powered wireless sensors modules based on vibration is can be using SSPB methods for best extraction power.
 J. Rabaey, J. Ammer, T. Karalar, S. Li, B. Otis, M. Sheets, and T. Tuan, “Picoradios for wireless sensor networks: The next challenge in ultra-low-power design,” in Proceedings of the International Solid-State Circuits Conference, vol. 1, San Francisco, CA, February 2002, pp. 200–201.
 P. D. Mitcheson, E. M. Yeatman, G. K. Rao, A. S. Holmes, and T. C. Green, “Energy harvesting from human and machine motion for wireless electronic devices,” Proceedings of the IEEE, vol. 96, no. 9, pp. 1475–1486, September 2008.
 Elliott, A. D. T. (2015). Power electronic interfaces for piezoelectric energy harvesters. (Doctoral Dissertation). Imperial College London. Retrieved from http://hdl.handle.net/10044/1/39965
 W. S. N. Trimmer, “Microrobots and micromechanical systems,” Sensors and Actuators, vol. 19, pp. 267–287, 1989.
 P. D. Mitcheson, T. C. Green, E. M. Yeatman, and A. S. Holmes, “Architectures for vibration-driven micropower generators,” Microelectromechanical Systems, vol. 13, no. 3, pp. 429–440, June 2004.
 L. M. Miller, P. D. Mitcheson, E. Halvorsen, and P. K. Wright, “Coulomb-damped resonant generators using piezoelectric transduction,” Applied Physics Letters, vol. 100, 2012.
 J. Dicken, P. D. Mitcheson, I. Stoianov, and E. M. Yeatman, “Power-extraction circuits for piezoelectric energy harvesters in miniature and low-power applications,” IEEE Transactions on Power Electronics, vol. 27, pp. 4514–4529, 2012.
 S. Pang, W. Li, and J. Kan, “Optimization Analysis of Interface Circuits in Piezoelectric Energy Harvesting Systems,” J. Power Technol., vol. 96, no. 1, pp. 1–7, 2016.
 Qiu J, Jiang H, Ji H, et al. (2009) Comparison between four piezoelectric energy harvesting circuits. Frontiers of Mechanical Engineering in China 4(2): 153–159.
 J. Dicken, P. D. Mitcheson, I. Stoianov, and E. M. Yeatman, “Increased power output from piezoelectric energy harvesters by pre-biasing,” in PowerMEMS 2009, Washington DC, USA, December 2009, pp. 75–78.