**2. Review of EH methods capable of supplying wireless harvesting nodes**

Currently, there is a trend to create autonomous power supply systems for low-power consumer electronic devices (including the so-called toward zero-power information and communication technology (ICT)) or a variety of sensor systems and monitoring systems (e.g., structural health monitoring (SHM)), e.g., [6]. It is assumed that even the use of batteries in these cases is not an optimal solution, e.g., due to the troublesome replacement of batteries and their recycling.

The development of the physics of cross-field phenomena, in which one field (e.g., mechanical, thermal, magnetic) enables energy to be obtained in a different form (e.g., electricity), progresses very quickly and is supported by achievements in the field of material engineering. This results in the fact that there are an increasing number of materials usually called smart, which can be effectively used to build harvester.

The number of physical phenomena that produce electric current is significant, e.g., [29–32]. You can include here:

• Piezoelectric effect

*A Guide to Small-Scale Energy Harvesting Techniques*

personnel carriers, tanks, and airplanes.

piezoelectric and magnetostriction transducers are used for this purpose. There are many ways of wireless power transmission (WPT) using various couplings, e.g., inductive (most popular today since the pioneering work of N. Tesla), capacitive coupling, microwaves, optical coupling, and sound waves, including ultrasound. This last opportunity has been known for over 40 years. In 1970, the first paper [7] appeared, indicating the possibility of using ultrasounds not only for medical or engineering research but also as an energy carrier in transmission through solid bodies. The ease with which ultrasound passes through the solids was then observed. In 1998, using the given idea, a special heart stimulation electrode was patented for arrhythmia [8]. The biomedical application of ultrasound for energy transmission is intensively developed. Particularly noteworthy here is, for example, work [9], which shows the way of powering, using ultrasound, an actuator placed in the human body. The idea of this type of power lies in the fact that in the receiver, the energy of ultrasonic waves and vibrations caused by them are not converted back to the electrical voltage at all, but through the arrangement of vibrating elements—they directly supply the actuator. Other interesting studies in this area are described in [10, 11]. Much attention is devoted to energy conversion efficiency using piezoelectric transducers. The most frequently cited are works [12–14]. The last of them showed efficiency at the level of 50% in the transmission of ultrasound in the air at a distance of 70–80 m. Equally spectacular achievements are the Dutch team [15, 16]. Another interesting example is the transmission of data with the help of ultrasound over the plane [17, 18]. It should be noted that very intensively developed activities are aimed at mastering the effective transfer of energy and information through thick metal barriers, mainly using piezoelectric harvester. These works, initiated in the United States by Saulnier in 2006 [19], gained interest in the navy due to the possibility of sending energy and information through the thick walls of submarines. Particularly significant results were published in the dissertation of Lawry [20] and in a dozen or so publications after its defense, e.g., [21, 22]. The last two indicate that the state of knowledge allows the use of such relays on submarines today. The continuous supply of approximately 50 W of electricity, along with 12.4 Mbps of data through 2.5-inch (over 6 cm) metal walls, is an ideal system for use in submarines that require avoiding leakage and high safety. In [23], it is also pointed out that the system can also be used in ships, unmanned vehicles, armored

Another large American project funded by the National Aeronautics and Space Administration (NASA) is research conducted by the team of Sherrit from the Jet Propulsion Laboratory. The research, begun already in 1998, concerned the possibility of generating and reading ultrasound signals using piezoelectric actuators and generators [23]. In 2005–2008 this technique was constantly improved. In 2005, the theoretical basis for energy transmission by flexible materials of thickness over 1.5 cm [24] using piezoelectric actuators was described and then—to improve efficiency—using special graphite "patches" attached with thin layers on both sides of the wall [25]. Obtained results were promising, and it was decided to do the first trials with use of mentioned above technology in the vehicles of the NASA. The team's many years of work have been summarized in a comprehensive publication on the physical basis of ultrasonic harvesting [26] with the use of piezoelectric receivers and transmitters. Recently, a team led by Sherrit has developed a method for feeding the stepper motor through the metal wall of the vessel [27]. Thanks to the uniform power transmission, it is possible to continuously control the motor by the generated ultrasonic waves. Interestingly, this wave is not converted here to electricity and again to the mechanical energy of the engine, but the vibrating elements cause the motor to move directly by picking up ultrasonic waves. A broader literature analysis

in the field of power transfer using ultrasound was carried out in [28].

**36**


EH can also be realized using double cross fields, for example, first heat and then electric current. The interdisciplinary nature of the issue, which is energy harvesting (physics of cross effects, material engineering, mechanics, electronics), stimulates the development of science and the economy. It should be emphasized that, despite numerous works undertaken mainly in the last decade in the research centers of the most developed countries, the subject of EH and the various smart materials used for this purpose is still very topical in terms of science and application. Leading economies and research centers allocate significant resources to basic and applied research in the field of EH.

Due to scientific goals and interests, further work was focused on the use of methods increasing the parameters of harvester, mainly energy conversion efficiency, using the acquired experience in the field of magnetomechanical cross effects, smart materials, strength of materials and mechanical structures, and measurement methods. The extent of the subject matter required the imposition of restrictions. Therefore, magnetostrictive harvesters using GMM-type materials were recognized as key. Thanks to their application, instruments that were able to recover energy from sources not yet explored such as mechanical impact were obtained. An important limitation of the magnetic core harvester is its size and weight. Installing piezoelectric harvesters is a lot simpler than a magnetic core harvester that requires a complicated mechanical construction, premagnetization,

#### *A Guide to Small-Scale Energy Harvesting Techniques*

**Figure 2.**

*Determining the dominant issues taken from energy harvesting.*

and prestress. However, the current-voltage performance of magnetostrictive harvester is an order of magnitude larger than other types of harvester. That is why this type of harvester was considered to be particularly interesting. Further designs will include further miniaturization of the instruments. Current and future interests in this area are characterized by the graph presented in **Figure 2**. The following examples of implemented harvesting technologies are only briefly presented, the broader discussion of which will take place later.

In the field of low-power technique, the definition of harvester as the power supply of a single microprocessor was adopted, which after powering wirelessly sends data in accordance with its operating algorithm (program code) to the receiving and processing unit. A single harvesting system is a node in a larger structure managed from a central site. Individual configurations of harvester can make it easier to tune the harvesting power for specific phenomena that trigger its operation.

## **2.1 Harvester as an electric generator**

The obtained power in laboratory harvesters became bigger; hence these devices were treated as (source) an electric generator. Due to the physical phenomenon used for the EH effect, construction, the principle of work, the conditions in which the harvester works, and characteristics of the source, harvesters can be divided, as follows:


**39**

**Figure 3.**

*Energy Harvester Based on Magnetomechanical Effect as a Power Source for Multi-node Wireless…*

The pulse supply differs from the voltage-variable frequency of the occurrence of force and the instantaneous value of the generated current. Voltage supply is characterized by frequencies similar to the electricity in the electrical network (50/60 Hz). The generation of the voltage in the impulse supply occurs rarely and for a very short time, but the amplitude is very large. Due to the characteristics of

The essence of EH is to create new concepts of current generators, using cross effects, including more often magnetomechanical phenomena. It is assumed that

*Configurations of electrical circuits due to energy recovery from a specific source and converter: (a) solar, (b)* 

*temperature differences, (c) piezoelectric transducer, and (d) magnetic transducer.*

• Current sources (Faraday generator, magnetostrictive harvesters)

**2.2 Types of electrical circuits due to the type of energy source**

*DOI: http://dx.doi.org/10.5772/intechopen.85987*

the harvester circuits, they can be divided into:

• Voltage sources (Piezo patch type)

• Impulse (e.g., solid-state harvesters, e.g., top core coil magnet (TCCM)

*Energy Harvester Based on Magnetomechanical Effect as a Power Source for Multi-node Wireless… DOI: http://dx.doi.org/10.5772/intechopen.85987*

The pulse supply differs from the voltage-variable frequency of the occurrence of force and the instantaneous value of the generated current. Voltage supply is characterized by frequencies similar to the electricity in the electrical network (50/60 Hz). The generation of the voltage in the impulse supply occurs rarely and for a very short time, but the amplitude is very large. Due to the characteristics of the harvester circuits, they can be divided into:


*A Guide to Small-Scale Energy Harvesting Techniques*

and prestress. However, the current-voltage performance of magnetostrictive harvester is an order of magnitude larger than other types of harvester. That is why this type of harvester was considered to be particularly interesting. Further designs will include further miniaturization of the instruments. Current and future interests in this area are characterized by the graph presented in **Figure 2**. The following examples of implemented harvesting technologies are only briefly presented, the

the harvesting power for specific phenomena that trigger its operation.

In the field of low-power technique, the definition of harvester as the power supply of a single microprocessor was adopted, which after powering wirelessly sends data in accordance with its operating algorithm (program code) to the receiving and processing unit. A single harvesting system is a node in a larger structure managed from a central site. Individual configurations of harvester can make it easier to tune

The obtained power in laboratory harvesters became bigger; hence these devices

were treated as (source) an electric generator. Due to the physical phenomenon used for the EH effect, construction, the principle of work, the conditions in which the harvester works, and characteristics of the source, harvesters can be divided, as

• Constant voltage (e.g., harvesters based on a thermoelectric effect)

• Variable voltage (e.g., harvesters based on the Faraday effect, e.g., as Piezo

• Impulse (e.g., solid-state harvesters, e.g., top core coil magnet (TCCM)

broader discussion of which will take place later.

*Determining the dominant issues taken from energy harvesting.*

**2.1 Harvester as an electric generator**

**38**

follows:

**Figure 2.**

patch)

#### **2.2 Types of electrical circuits due to the type of energy source**

The essence of EH is to create new concepts of current generators, using cross effects, including more often magnetomechanical phenomena. It is assumed that

**Figure 3.**

*Configurations of electrical circuits due to energy recovery from a specific source and converter: (a) solar, (b) temperature differences, (c) piezoelectric transducer, and (d) magnetic transducer.*

even for small power and efficiency, it can be a valuable power source. The development of the technology of constructing harvester, with similar electrical parameters as chemical cells, may reduce the production of the latter for ecological reasons. As harvesters acquire energy in a nonparasitic manner, i.e., they process energy considered as a by-product ("junk") process, they increase the efficiency of the system as a whole.

Both electricity and electric voltage must have the parameters necessary to supply both the sensors themselves and the built-in processor with the transmitter adapted to it, as well as the communication unit. Another problem is the conversion and conditioning of the voltage/current from the generator (**Figure 3**) [33, 34]. Designing electrical circuits for harvester requires knowledge of the device's operating characteristics.

Only harvesters based on a thermoelectric or photovoltaic effect generate DC current. Harvesters recovering energy from vibration, magnetostrictive, and piezoelectric, as well as based on the Faraday effect, are on the other hand alternating current sources. Harvesters powered by impact impulse are a special case [35]. The generation of electricity in pulsed power takes place for a very short time, but the current amplitude is very high. Harvesters "powered" by mechanical shock generate a variable voltage waveform and are characterized by a strong current pulse, and in the generated signal, there are frequencies related to magnetic resonance of the core-coil system magnetostrictive core.
