**3. The idea of the composite rod in the wideband actuator and energy harvester**

Bearing in mind the justifiability of limiting the use of solid Terfenol-D in the construction of magnetostrictive resonators, two solutions are presented below, namely the use of a GMM composite core and—in Chapter 4—a core consisting of a neodymium magnet and Terfenol-D.

#### **3.1. The preparation of GMM composite**

to be effective. For this purpose, Smart Ultrasonic Resonant Power System (SURPS), a system for simultaneous power and data transmission, was developed. It ensured transmission through various media (solid, liquid) and with various transmitter-receiver configurations [17].

**Figure 8.** Prototyping of multi-DOF wireless sensors platform: Main communication station and Multi-DOF software [17].

**Figure 7.** Energy harvesting sources and their power requirements: (A) mechanical impact, (B) low-frequency mechanical

resonance and (C) energy transmission by ultrasonic vibration [17].

64 Actuators

Referring to price of Terfenol-D which is a relatively expensive material, a device which would not require this material would be adequately cheaper. The brittleness of pure Terfenol-D can be replaced with a composite material [7].

A prospective application area for Terfenol-D, which is a typical representative of the GMM group, is (electric) energy harvesting from, for example, mechanical vibration systems [18, 19]. However, some of the applications of this material are restricted due to eddy current loss at a high frequency. In addition, it has some drawbacks, such as intrinsic brittleness accompanied by maximizing the fraction of the brittle, Laves phase. The magnetostrictive composite materials have been developed as an alternative way to overcome both the eddy current loss and intrinsic brittleness since 1990.

The main advantages of magnetostrictive composites based on a nonmagnetic polymer matrix and containing Terfenol-D powder particles are as follows:


Therefore, the main goal of this research was to investigate the magnetostriction of a fieldstructural composite with Terfenol-D particles. The composite should replace the solid Terfenol-D rods in an actuator or a damper. It was decided to closely examine the effect of the (perpendicular, parallel, without polarization) direction of composite polarization and different frequencies of magnetic field stimulation. The results were compared with those obtained for solid Terfenol-D samples with the same geometry.

In the study, a magnetostrictive composite was used (hereafter referred to as GMMc). It was prepared in the Department of Mechanics, Materials Science and Engineering at Wroclaw University of Science and Technology. The composite was made by combining an epoxy resin and Terfenol-D powder (GMM material).


Specimens presented in this work contain 70% of Terfenol-D particles volume fraction, and they have different polarization directions. For each case, the particles and resin were homogeneously mixed together and deaerated. Moreover, one of the samples was polarized perpendicular, and others were polarized parallel to the main axis of the specimen. This effect was obtained by using permanent magnets and coil during a composite curing process, respectively.

The container with the mixture was placed between two magnets or inside a coil and after that it was placed on an MTS hydraulic pulsator, where samples were pressed with a force of 10 kN for 4 h until the preliminary resin binding started. This process allowed to reduce the excess of epoxy resin from samples and to obtain a high volume fraction of Terfenol-D particles. The schemes of these processes for perpendicular and parallel polarized specimens are shown in **Figure 9A** and **Figure 9B**, respectively. Additionally, one of the specimens was cured without any source of a magnetic field.

After 24 h preliminarily cured specimens were placed in an oven at 70°C for another 24 h to ensure the full cure of the epoxy resin. Samples produced in this way contain a small portion of pores, which confirms the good connection of powders with resin. The polymer material provides a good magnetic insulation of the Terfenol-D powder grains and prevents its oxidation.

The experiments methodology involving the quasi-static measurements of the magnetostriction of the produced composites and the measurements made for different magnetic field

**Figure 10.** 3D magnetic vector fields around perpendicular (A) and parallel (B) premagnetized Terfenol-D composites [22].

**Figure 9.** Schema of perpendicular (A) parallel (B) polarization to the main axis of the sample during curing process.

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F—direction of force during curing process, H—direction of magnetic field during curing process [22].

The magnetic field strength acting on the magnetostrictive composite was dependent on the strength of the current in the coil. The magnetic field was generated by an adjustable power supply unit (0–30 V, 20 A). The magnetic field strength range H was limited by the magnetic circuit and amounted to 0 ÷ 168 kA/m. The measurement was conducted with the use of the Hall's sensor (placed inside the coil), for both positive and negative H values to check the evenness of the phenomenon in the composite samples. Sample displacement *∆λ* was measured using the innovative method of fiber Bragg grating (FBG) sensors. In this way, the influence of the electromagnetic field on the results was eliminated. The FBG method is described in more detail in [24]. The strain sensors were placed directly on the specimens, as shown in **Figure 11**. One of the sensors was placed along the main axis of the specimen while the other one was attached to the sample circumference. The aim of such a sensor arrangement was to

frequencies is shown later.

#### **3.2. Experimental determination of GMMc parameters**

To determine if the polarization applied during the curing process to the manufactured composites made any changes in the magnetization of specimens, the magnetic scans of their surfaces were made (**Figure 10A** and **Figure 10B**). The scans were obtained with the use of the innovative system of Magscanner described in [23]. The results show clearly that there is a difference between the manufactured specimens with different types of polarization. The magnetization layout along its main axis for the parallel polarized specimen (**Figure 10A**) is even as evident, as the one contrasted with the parallel polarized specimen (**Figure 10B**). This confirms that polarized samples preserved the direction of the desired magnetization.

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(perpendicular, parallel, without polarization) direction of composite polarization and different frequencies of magnetic field stimulation. The results were compared with those obtained

In the study, a magnetostrictive composite was used (hereafter referred to as GMMc). It was prepared in the Department of Mechanics, Materials Science and Engineering at Wroclaw University of Science and Technology. The composite was made by combining an epoxy resin

• The next step was the addition of a properly measured amount of Terfenol-D powder with a grain size of 0–300 μm (according to the manufacturer, Gansu Tianxing Rare Earth

Specimens presented in this work contain 70% of Terfenol-D particles volume fraction, and they have different polarization directions. For each case, the particles and resin were homogeneously mixed together and deaerated. Moreover, one of the samples was polarized perpendicular, and others were polarized parallel to the main axis of the specimen. This effect was obtained by using permanent magnets and coil during a composite curing process,

The container with the mixture was placed between two magnets or inside a coil and after that it was placed on an MTS hydraulic pulsator, where samples were pressed with a force of 10 kN for 4 h until the preliminary resin binding started. This process allowed to reduce the excess of epoxy resin from samples and to obtain a high volume fraction of Terfenol-D particles. The schemes of these processes for perpendicular and parallel polarized specimens are shown in **Figure 9A** and **Figure 9B**, respectively. Additionally, one of the specimens was

After 24 h preliminarily cured specimens were placed in an oven at 70°C for another 24 h to ensure the full cure of the epoxy resin. Samples produced in this way contain a small portion of pores, which confirms the good connection of powders with resin. The polymer material provides a good magnetic insulation of the Terfenol-D powder grains and prevents its

To determine if the polarization applied during the curing process to the manufactured composites made any changes in the magnetization of specimens, the magnetic scans of their surfaces were made (**Figure 10A** and **Figure 10B**). The scans were obtained with the use of the innovative system of Magscanner described in [23]. The results show clearly that there is a difference between the manufactured specimens with different types of polarization. The magnetization layout along its main axis for the parallel polarized specimen (**Figure 10A**) is even as evident, as the one contrasted with the parallel polarized specimen (**Figure 10B**). This

confirms that polarized samples preserved the direction of the desired magnetization.

for solid Terfenol-D samples with the same geometry.

• The first step was introduction of a hardener to the epoxy resin.

and Terfenol-D powder (GMM material).

Functional Materials Co., Ltd.).

cured without any source of a magnetic field.

**3.2. Experimental determination of GMMc parameters**

respectively.

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oxidation.

**Figure 9.** Schema of perpendicular (A) parallel (B) polarization to the main axis of the sample during curing process. F—direction of force during curing process, H—direction of magnetic field during curing process [22].

**Figure 10.** 3D magnetic vector fields around perpendicular (A) and parallel (B) premagnetized Terfenol-D composites [22].

The experiments methodology involving the quasi-static measurements of the magnetostriction of the produced composites and the measurements made for different magnetic field frequencies is shown later.

The magnetic field strength acting on the magnetostrictive composite was dependent on the strength of the current in the coil. The magnetic field was generated by an adjustable power supply unit (0–30 V, 20 A). The magnetic field strength range H was limited by the magnetic circuit and amounted to 0 ÷ 168 kA/m. The measurement was conducted with the use of the Hall's sensor (placed inside the coil), for both positive and negative H values to check the evenness of the phenomenon in the composite samples. Sample displacement *∆λ* was measured using the innovative method of fiber Bragg grating (FBG) sensors. In this way, the influence of the electromagnetic field on the results was eliminated. The FBG method is described in more detail in [24]. The strain sensors were placed directly on the specimens, as shown in **Figure 11**. One of the sensors was placed along the main axis of the specimen while the other one was attached to the sample circumference. The aim of such a sensor arrangement was to

**4.1. Coupling of NdFeB magnets and Terfenol-D in the resonator core**

speed of a defined value for moving aluminum frame

and 8 highly independent functional units;

for data transfer between Heron modules;

• Capacitors by EPCOS Company of 2.2uF.

speed linear motor is shown in **Figure 14**.

the main testing system;

• PZT sensor used to measure force signal in the place of mounting;

• Laser switch by Balluff Company used to trigger the start of acquisition;

prestress.

response is presented below:

dpi resolution;

energy;

The idea of the Top Core Coil Magnet (TCCM) actuators and reversible harvesters appeared in the Department of Mechanics, Materials Science and Engineering laboratories. The basic model of unique TCCM system is shown in **Figure 13**. The model called TCCM is a construction combining four major elements: Top whose role was to transfer shock to the core, Coil, Magnet and Core which determines the processing energy of impact (obtained from the Top part) into electricity. The TCCM harvester is the simplest form of the implementation of the harvester based on the core placed in the coil with a fairly large number of coils in the magnetic field of the NdFeB magnet. Low rigidity and low resonance frequency at the moment of impact describe the system without the

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The range of measurement and devices used to perform the testing of actuator/harvester

• IXFN20N200, MOSFET by IXYS, a fast transistor for linear motor was used to provide the

• Encoder strip coupled with a reader by Sharp Company, path measurement system of 720

• Hi-speed, Hi-power linear motor-dumper up to 20 N hammer used to provide impact

• (TMS320C6701 DSP) Hunt Engineering Heron System by Texas Instruments, with GFLOPS performance at a clock rate of 167 MHz, used for high-performance DSP programming. It possesses the operational flexibility of high-speed controllers and the numerical capability of array processors. The processor has 32 general-purpose registers of 32-bit word length

• The Heron HEPC8 Module Carrier Board is a PCI form factor module carrier board supporting up to four Heron modules which can be multiplied. HEPC8 provides 32-bit first-in, first-out (FIFO) buffers between each module slot and the other module slots on the board

• PicoPower Evaluate System v0.8 2010, PicoPower Processor Development Platform by the Institute of Material Science and Applied Mechanics of WrUST, designed in the Institute as

The scheme of the test stand for the shock test TCCM harvesting system based on a high-

**Figure 11.** Arrangement of the strain sensors on a sample: 1—Sensors, 2—Specimen, 3—Glue [22].

**Figure 12.** Comparison of magnetostrictive dependence from magnetic field intensity H, at frequency f = 5 Hz, for composite specimens and solid Terfenol-D [22].

check whether the volumetric magnetostriction occurs in the material apart from the linear magnetostriction.

In addition, changes in the value of the magnetic field during the same test were presented in **Figure 12**.

#### **4. Designing of magnetostrictive core for solid-type resonators**

In this chapter, the problem of cores built with neodymium magnets and Terfenol-D and impulse power supply for the microcontroller is discussed.

#### **4.1. Coupling of NdFeB magnets and Terfenol-D in the resonator core**

The idea of the Top Core Coil Magnet (TCCM) actuators and reversible harvesters appeared in the Department of Mechanics, Materials Science and Engineering laboratories. The basic model of unique TCCM system is shown in **Figure 13**. The model called TCCM is a construction combining four major elements: Top whose role was to transfer shock to the core, Coil, Magnet and Core which determines the processing energy of impact (obtained from the Top part) into electricity. The TCCM harvester is the simplest form of the implementation of the harvester based on the core placed in the coil with a fairly large number of coils in the magnetic field of the NdFeB magnet. Low rigidity and low resonance frequency at the moment of impact describe the system without the prestress.

The range of measurement and devices used to perform the testing of actuator/harvester response is presented below:


check whether the volumetric magnetostriction occurs in the material apart from the linear

**Figure 12.** Comparison of magnetostrictive dependence from magnetic field intensity H, at frequency f = 5 Hz, for

In addition, changes in the value of the magnetic field during the same test were presented

In this chapter, the problem of cores built with neodymium magnets and Terfenol-D and

**4. Designing of magnetostrictive core for solid-type resonators**

**Figure 11.** Arrangement of the strain sensors on a sample: 1—Sensors, 2—Specimen, 3—Glue [22].

impulse power supply for the microcontroller is discussed.

magnetostriction.

composite specimens and solid Terfenol-D [22].

in **Figure 12**.

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The scheme of the test stand for the shock test TCCM harvesting system based on a highspeed linear motor is shown in **Figure 14**.

**Figure 13.** Scheme of the magnetostrictive core used as reversible effect resonator in energy harvesting devices [16].

The TCCM device was fixed with a PZT sensor in the horizontal orientation on a nonmagnetic, hard surface. In the main axis of the device, at the distance of 80mm was the aluminum hammer. Its speed accelerates to a defined value due to the fast linear motor transistor MOSFET. The speed of hammer was measured with an encoder strip coupled with a reader. The energy of impact was controlled by weights attached to a linear motor moving element. The maximum weight that could be used to accumulate energy is 2 kg. Due to the small size of a harvester, a beater load of 0.5 kg was used. The high reproducibility of the hammer speed and run-off place of the transistor MOSFET were obtained for that test stand, which resulted in the stability of impact energy *Ek* .

**Figure 14.** The schema of test stand to determine magnetostrictive core parameters (A): (1) linear motor, (2) movable trolley of a linear motor, (3) piezoelectric force sensor, (4) inductor, (5) NdFeB magnets used for constant magnetic field generation around the inductor, (6) base plate with the inductor position regulation. View of the test stand (B) [16].

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**Figure 15.** The current coil measurement for bulk Terfenol-D and its FFT plot.

The shock force was applied to the TCCM device and, as a result, the impulse response of system was registered, as shown in **Figure 15**. Upon the analysis of this signal, the waveform was divided into phases. The first phase occurs before the strike, where the increase in voltage is present as a result of the motion of ferromagnetic hammer in the neodymium magnet's magnetic field. After the strike moment, wave motion passing through the top and the core to the neodymium magnet occurs and creates a string change of the magnetic field of the system, which causes the induction of the voltage resulting from the mechanical resonance frequency of the TCCM harvester.

Only the top and coil materials have an influence on the resonant frequency. The wave that passes through the material inside the coil either circulates repeatedly in the steam-coremagnet system or comes out of the harvester if the magnet has contact with the other surface, Development of Resonators with Reversible Magnetostrictive Effect for Applications… http://dx.doi.org/10.5772/intechopen.78572 71

**Figure 14.** The schema of test stand to determine magnetostrictive core parameters (A): (1) linear motor, (2) movable trolley of a linear motor, (3) piezoelectric force sensor, (4) inductor, (5) NdFeB magnets used for constant magnetic field generation around the inductor, (6) base plate with the inductor position regulation. View of the test stand (B) [16].

**Figure 15.** The current coil measurement for bulk Terfenol-D and its FFT plot.

The TCCM device was fixed with a PZT sensor in the horizontal orientation on a nonmagnetic, hard surface. In the main axis of the device, at the distance of 80mm was the aluminum hammer. Its speed accelerates to a defined value due to the fast linear motor transistor MOSFET. The speed of hammer was measured with an encoder strip coupled with a reader. The energy of impact was controlled by weights attached to a linear motor moving element. The maximum weight that could be used to accumulate energy is 2 kg. Due to the small size of a harvester, a beater load of 0.5 kg was used. The high reproducibility of the hammer speed and run-off place of the transistor MOSFET were obtained for that test stand, which resulted

**Figure 13.** Scheme of the magnetostrictive core used as reversible effect resonator in energy harvesting devices [16].

The shock force was applied to the TCCM device and, as a result, the impulse response of system was registered, as shown in **Figure 15**. Upon the analysis of this signal, the waveform was divided into phases. The first phase occurs before the strike, where the increase in voltage is present as a result of the motion of ferromagnetic hammer in the neodymium magnet's magnetic field. After the strike moment, wave motion passing through the top and the core to the neodymium magnet occurs and creates a string change of the magnetic field of the system, which causes the induction of the voltage resulting from the mechanical resonance frequency

Only the top and coil materials have an influence on the resonant frequency. The wave that passes through the material inside the coil either circulates repeatedly in the steam-coremagnet system or comes out of the harvester if the magnet has contact with the other surface,

.

in the stability of impact energy *Ek*

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of the TCCM harvester.

As the practical application of the pulse power supply (PPS), the acquisition of lifespan of an ATMEL microcontroller based on the primary node was chosen. The ATMEGA48V system was used as a low-power processor. It is one of the most common microcontrollers in industrial applications. It could be started at a voltage level of only 1.8 V. It was powered by a DC of 1.8− 5.5 V, as an AC/DC system transducer on the rectifier used Schottky diodes. The signal acquisition and the control of the test parameters of the harvesting device, the AC/DC recti-

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In **Figure 18**, the current consumption by the system capacitors -μC type recorded as a reduction in voltage on measuring resistor Rsense = 4.7 Ω is presented. In the first phase, there is a very strong increase in current due to the initial charge on C1 and C2 capacitors (**Figure 17**), which are very heavy load on the signal generated by the harvesting device, followed by a decline in current consumption, given that it has not yet started μC. The "life time" algorithm of the program allows the microprocessor to send more than 50 pulses in a voltage range from Umax = 5 V to Umin = 1.8 V, which can be described as about 3 ms of μC life. By selecting various sources of the mechanical extortion obtained values of the microprocessor, one can cause pulses to rise up to 200 and the life time to extend to 8 ms. Based on the results, it can be found that an energy harvesting device (EHD) was developed. EHD is able to supply a popular microcontroller which realizes its code throughout the life of 3 ms from small impact

**Figure 18.** Life time span of microcontroller\circuit powered from energy harvesting device induced at low impact

energy Ek = 0.25 J [16].

fier, a microprocessor and a base station were provided by a dedicated system.

energy Ek = 0.25 J. The core of this device was made of Terfenol-D powder.

**Figure 16.** Photo series of mechanical impact correlated with velocity and pulse output voltage graphs.

**Figure 17.** Supply current and voltage measurement scheme for detect life time span of powered μC [16].

but it is not transferred to this coil. The crucial effect in the operation of the top-coil-magnet system is the mechanical resonance effect of that system under impact. In **Figure 16**, the hammer impact chart of the TCCM harvester with correlated photos is shown.

In the TCCM type of Energy Harvester construction the calibration of prestess cores is not as critical as in vibrations exciter device. The prestress is obtained in the first phase of impact where the main maximum useable signal occurs. The significant increase in current and voltage occurs at the moment of the resonance frequency of the system. The value of this voltage depends on the number of turns in the coil when the same impact energy is applied.

#### **4.2. Practical aspect of pulse power supply**

The idea of a working harvesting device was not to supply continuous power for the microcontroller, but to provide a strong enough current pulse to quickly charge a high-capacity capacitor, see **Figure 17**. These capacitors were chosen in such a way that the processor voltage did not exceed 5.5 V. The role of the capacitor is very important, and hence, special capacitors which are able to capture the impulse current within a few dozen μF must be used.

As the practical application of the pulse power supply (PPS), the acquisition of lifespan of an ATMEL microcontroller based on the primary node was chosen. The ATMEGA48V system was used as a low-power processor. It is one of the most common microcontrollers in industrial applications. It could be started at a voltage level of only 1.8 V. It was powered by a DC of 1.8− 5.5 V, as an AC/DC system transducer on the rectifier used Schottky diodes. The signal acquisition and the control of the test parameters of the harvesting device, the AC/DC rectifier, a microprocessor and a base station were provided by a dedicated system.

In **Figure 18**, the current consumption by the system capacitors -μC type recorded as a reduction in voltage on measuring resistor Rsense = 4.7 Ω is presented. In the first phase, there is a very strong increase in current due to the initial charge on C1 and C2 capacitors (**Figure 17**), which are very heavy load on the signal generated by the harvesting device, followed by a decline in current consumption, given that it has not yet started μC. The "life time" algorithm of the program allows the microprocessor to send more than 50 pulses in a voltage range from Umax = 5 V to Umin = 1.8 V, which can be described as about 3 ms of μC life. By selecting various sources of the mechanical extortion obtained values of the microprocessor, one can cause pulses to rise up to 200 and the life time to extend to 8 ms. Based on the results, it can be found that an energy harvesting device (EHD) was developed. EHD is able to supply a popular microcontroller which realizes its code throughout the life of 3 ms from small impact energy Ek = 0.25 J. The core of this device was made of Terfenol-D powder.

but it is not transferred to this coil. The crucial effect in the operation of the top-coil-magnet system is the mechanical resonance effect of that system under impact. In **Figure 16**, the ham-

In the TCCM type of Energy Harvester construction the calibration of prestess cores is not as critical as in vibrations exciter device. The prestress is obtained in the first phase of impact where the main maximum useable signal occurs. The significant increase in current and voltage occurs at the moment of the resonance frequency of the system. The value of this voltage

The idea of a working harvesting device was not to supply continuous power for the microcontroller, but to provide a strong enough current pulse to quickly charge a high-capacity capacitor, see **Figure 17**. These capacitors were chosen in such a way that the processor voltage did not exceed 5.5 V. The role of the capacitor is very important, and hence, special capacitors which are able to capture the impulse current within a few dozen μF must be used.

depends on the number of turns in the coil when the same impact energy is applied.

mer impact chart of the TCCM harvester with correlated photos is shown.

**Figure 17.** Supply current and voltage measurement scheme for detect life time span of powered μC [16].

**Figure 16.** Photo series of mechanical impact correlated with velocity and pulse output voltage graphs.

**4.2. Practical aspect of pulse power supply**

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**Figure 18.** Life time span of microcontroller\circuit powered from energy harvesting device induced at low impact energy Ek = 0.25 J [16].
