**5. Construction of high-power wideband actuator**

#### **5.1. Design of classic magnetostrictive actuator dedicated for mechanical vibrations in selected frequency range**

and provides easy access to the core of the device. Two plates, top and bottom, made of ferromagnetic material are the main elements of the actuator housing. They are intended to spread the magnetic field uniformly and to prevent the excessive loss of the magnetic field inside the coil. Thus, the authors decided to use square plates which allowed to preserve symmetry.

Development of Resonators with Reversible Magnetostrictive Effect for Applications…

http://dx.doi.org/10.5772/intechopen.78572

75

In addition, four middle elements with a cylindrical shape made of a ferromagnetic material were used. The shape of these connectors was conditioned by the fact that in the case of parts with sharp edges, the concentration of the magnetic field appears on those edges. Therefore, it impedes the free flow of the magnetic field and may cause disturbances in the propagation of the magnetic field around the coil. The cylindrical shape of the connectors allows a more uniform distribution of the magnetic field and limits losses. Additionally, the number of connecting elements was chosen in such a way that they ensure a secure and stable connection between the two plates of the housing, while preserving as many open spaces as possible. This solution results in a sufficiently large heat radiation area for the cooling of the coil. Due to the fact that the actuator will work in applications where different displacement values will be required, it was necessary to increase the external dimensions of the actuator, including its

housing. However, it should be noted that the construction is compact and simple.

• ensure the electric and magnetic safety of the user and the whole construction,

• provide easy access and allow for the replacement of the sample,

following requirements:

materials,

is shown in **Figure 20**.

• provide a compact and simple construction,

• provide easy control of the entire system.

During the design process of the actuator system, the authors decided that it should meet the

• allow to control the value of pre-stress on both solid and magnetostrictive composite

• ensure an easy installation procedure on the test rig or in the case of potential applications,

Among the components of the actuator, one can find a sleeve made of bronze which was located at the top of the housing. The reason for the usage of such an element is to reduce the potential friction that could occur between the upper rod of the actuator and the upper plate during system operation. It should be noted that although the elements which ensure the alignment of magnetostrictive material are used, even a small deviation from the vertical position of the sample could cause friction between the active element and the top of the housing. This might cause a high reduction of the parameters of the actuator and, what is more, it would influence the ability to control the device with the use of a feedback loop. In addition, the interior of the housing is protected by the elastic ring (which is not shown) whose main task is to ensure the prestress, that can be adjusted by lowering the connecting rods. The possibility to adjust prestress is very important due to its influence on the obtained magnetostriction value. A real construction of the actuator

During the process of selecting the geometry of the actuator, the authors decided to use knowhow gathered during previously performed computer simulations. To achieve the goal, they did not restrict the maximum value of the displacements obtained during test in any way. The only limitation was the maximum value of the magnetic field used to stimulate the material. It was assumed that the actuator together with the system will operate most of the time at a specific value of DC power, which necessitated the use of open housing design. This solution was chosen due to the fact that when the system is DC powered for a longer time, the electromagnet coil generates a lot of heat. The heat should be dissipated as soon as possible. The main component of the system was the magnetostrictive composite material with Terfenol-D powder which was obtained in the way described in the previous part. The visualization of the parametric model of the actuator is presented in **Figure 19**. It can be observed that its structure is not very complex; however, it allows to obtain high values of the magnetic field

**Figure 19.** Construction of the basic type of magnetostrictive actuator for acoustical frequency band applications (A), magnetic core structure (B), simulations of magnetic field around magnetostrictive core and actuator body (C). Components define: 1-front cover, 2-rod centering alignment, 3-magnetic core, 4-back cover, 5-outer NdFeB ring, 6- GMM(c) rod, 7-alignment tip, 8-coil [22].

and provides easy access to the core of the device. Two plates, top and bottom, made of ferromagnetic material are the main elements of the actuator housing. They are intended to spread the magnetic field uniformly and to prevent the excessive loss of the magnetic field inside the coil. Thus, the authors decided to use square plates which allowed to preserve symmetry.

In addition, four middle elements with a cylindrical shape made of a ferromagnetic material were used. The shape of these connectors was conditioned by the fact that in the case of parts with sharp edges, the concentration of the magnetic field appears on those edges. Therefore, it impedes the free flow of the magnetic field and may cause disturbances in the propagation of the magnetic field around the coil. The cylindrical shape of the connectors allows a more uniform distribution of the magnetic field and limits losses. Additionally, the number of connecting elements was chosen in such a way that they ensure a secure and stable connection between the two plates of the housing, while preserving as many open spaces as possible. This solution results in a sufficiently large heat radiation area for the cooling of the coil. Due to the fact that the actuator will work in applications where different displacement values will be required, it was necessary to increase the external dimensions of the actuator, including its housing. However, it should be noted that the construction is compact and simple.

During the design process of the actuator system, the authors decided that it should meet the following requirements:

• provide a compact and simple construction,

**5. Construction of high-power wideband actuator**

**in selected frequency range**

74 Actuators

GMM(c) rod, 7-alignment tip, 8-coil [22].

**5.1. Design of classic magnetostrictive actuator dedicated for mechanical vibrations** 

During the process of selecting the geometry of the actuator, the authors decided to use knowhow gathered during previously performed computer simulations. To achieve the goal, they did not restrict the maximum value of the displacements obtained during test in any way. The only limitation was the maximum value of the magnetic field used to stimulate the material. It was assumed that the actuator together with the system will operate most of the time at a specific value of DC power, which necessitated the use of open housing design. This solution was chosen due to the fact that when the system is DC powered for a longer time, the electromagnet coil generates a lot of heat. The heat should be dissipated as soon as possible. The main component of the system was the magnetostrictive composite material with Terfenol-D powder which was obtained in the way described in the previous part. The visualization of the parametric model of the actuator is presented in **Figure 19**. It can be observed that its structure is not very complex; however, it allows to obtain high values of the magnetic field

**Figure 19.** Construction of the basic type of magnetostrictive actuator for acoustical frequency band applications (A), magnetic core structure (B), simulations of magnetic field around magnetostrictive core and actuator body (C). Components define: 1-front cover, 2-rod centering alignment, 3-magnetic core, 4-back cover, 5-outer NdFeB ring, 6-


Among the components of the actuator, one can find a sleeve made of bronze which was located at the top of the housing. The reason for the usage of such an element is to reduce the potential friction that could occur between the upper rod of the actuator and the upper plate during system operation. It should be noted that although the elements which ensure the alignment of magnetostrictive material are used, even a small deviation from the vertical position of the sample could cause friction between the active element and the top of the housing. This might cause a high reduction of the parameters of the actuator and, what is more, it would influence the ability to control the device with the use of a feedback loop. In addition, the interior of the housing is protected by the elastic ring (which is not shown) whose main task is to ensure the prestress, that can be adjusted by lowering the connecting rods. The possibility to adjust prestress is very important due to its influence on the obtained magnetostriction value. A real construction of the actuator is shown in **Figure 20**.

#### **5.2. High power actuators with magnetostriction feedback**

Based on results described in the previous part of this chapter, a specific coil was chosen for the new type of actuator (**Figure 21**). This coil allows a relatively long time of work at a constant DC current level, and at the same time ensures the slowest growth of temperature. Due to the characteristics of the GMM material, the system test can be performed for a small value of the magnetic field which should be approximately 200 kA/m. Because of the predicted specification of the working characteristic of the system, it was decided that the system responsible for the preliminary magnetization of the sample will affect only the initial increase in the magnetic moment of the material. Therefore, the control of the system allows to increase the current value, which causes the deformation of the material only in one direction, regardless of the phase of the magnetic field generated in the coil.

In addition, due to the necessity to measure the deformation of the actuator core made of a GMM, it was decided to implement the Fiber Bragg grating sensor. This solution allowed to increase the accuracy thanks to which it was possible to control the actuator and neutralize the effect of the electromagnetic field on the control of the device. It significantly helped during the preparation of the control algorithm. The use of fiber optic sensors forced additional changes in the design of the actuator which allowed to mount fibers directly into its core. At the same time, it was easier to measure the deformation of the sample.

The goal of testing was to obtain the quasi-static and cyclic properties of the actuator and check the possibility of using the feedback loop control of the actuator. The use of cyclic tests means that during the test there is an alternating deformation of the composite core inside the actuator which is caused by stimulating the magnitude of the magnetic field in the frequency range from 1 to 20 Hz. For each test, a change of deformation of the composite core, at the corresponding values of the magnetic field, was recorded. The obtained data allowed to determine the maximum value of magnetostriction, depending on the method of stimulation. The study consisted of determining changes in the magnetic field with the use of a triaxial Hall probe and the deformation of the sample with a Fiber Bragg grating sensors. Additionally, during

the investigations the value of the prestress applied to the composite core was changed. This solution was proposed to check whether the value of prestress affects the value of obtained magnetostriction. In addition, during the study, it was checked whether the proposed deformation control algorithm of the magnetostrictive core was valid and able to control the system working in the feedback loop. In such a system, the controlled value is the value of magnetostriction. **Figure 22** shows the schema of the experimental system of the actuator feedback loop. The same values of the pre-stress showed that it does not change the value of the magnetostriction of the composite material regardless of the test method (quasi-static or cyclic). In the following figures, a comparison of the performance of the actuator in the case of the application of the feedback loop system and without such a system is presented. The subsequent

**Figure 21.** The high power actuator: model components (A): (1) – upper rod (actuator), (2) – Bronze sleeve, (3) – bolts, (4) – upper housing plate, (5) – coil with composite core, (6) – connection elements, (7) – bottom housing plate and (8) – bottom rod , the higher frequency version (low induction coil) (B), version with FBG and magnetic sensors for regulators

Development of Resonators with Reversible Magnetostrictive Effect for Applications…

http://dx.doi.org/10.5772/intechopen.78572

77

numbers in the graphs correspond to the following steps during the test:

of vibrations applications (C) [25].

**Figure 20.** Photo of prototype GMM actuator during laser examinations of true tip displacement under programmed magnetic field stimulations: (1) – assembled actuator, (2) – Rigid stand, (3) – tip and (4) – Keyence LK series – laser sensor.

Development of Resonators with Reversible Magnetostrictive Effect for Applications… http://dx.doi.org/10.5772/intechopen.78572 77

**Figure 21.** The high power actuator: model components (A): (1) – upper rod (actuator), (2) – Bronze sleeve, (3) – bolts, (4) – upper housing plate, (5) – coil with composite core, (6) – connection elements, (7) – bottom housing plate and (8) – bottom rod , the higher frequency version (low induction coil) (B), version with FBG and magnetic sensors for regulators of vibrations applications (C) [25].

the investigations the value of the prestress applied to the composite core was changed. This solution was proposed to check whether the value of prestress affects the value of obtained magnetostriction. In addition, during the study, it was checked whether the proposed deformation control algorithm of the magnetostrictive core was valid and able to control the system working in the feedback loop. In such a system, the controlled value is the value of magnetostriction. **Figure 22** shows the schema of the experimental system of the actuator feedback loop.

The same values of the pre-stress showed that it does not change the value of the magnetostriction of the composite material regardless of the test method (quasi-static or cyclic). In the following figures, a comparison of the performance of the actuator in the case of the application of the feedback loop system and without such a system is presented. The subsequent numbers in the graphs correspond to the following steps during the test:

**5.2. High power actuators with magnetostriction feedback**

76 Actuators

tion, regardless of the phase of the magnetic field generated in the coil.

the same time, it was easier to measure the deformation of the sample.

Based on results described in the previous part of this chapter, a specific coil was chosen for the new type of actuator (**Figure 21**). This coil allows a relatively long time of work at a constant DC current level, and at the same time ensures the slowest growth of temperature. Due to the characteristics of the GMM material, the system test can be performed for a small value of the magnetic field which should be approximately 200 kA/m. Because of the predicted specification of the working characteristic of the system, it was decided that the system responsible for the preliminary magnetization of the sample will affect only the initial increase in the magnetic moment of the material. Therefore, the control of the system allows to increase the current value, which causes the deformation of the material only in one direc-

In addition, due to the necessity to measure the deformation of the actuator core made of a GMM, it was decided to implement the Fiber Bragg grating sensor. This solution allowed to increase the accuracy thanks to which it was possible to control the actuator and neutralize the effect of the electromagnetic field on the control of the device. It significantly helped during the preparation of the control algorithm. The use of fiber optic sensors forced additional changes in the design of the actuator which allowed to mount fibers directly into its core. At

The goal of testing was to obtain the quasi-static and cyclic properties of the actuator and check the possibility of using the feedback loop control of the actuator. The use of cyclic tests means that during the test there is an alternating deformation of the composite core inside the actuator which is caused by stimulating the magnitude of the magnetic field in the frequency range from 1 to 20 Hz. For each test, a change of deformation of the composite core, at the corresponding values of the magnetic field, was recorded. The obtained data allowed to determine the maximum value of magnetostriction, depending on the method of stimulation. The study consisted of determining changes in the magnetic field with the use of a triaxial Hall probe and the deformation of the sample with a Fiber Bragg grating sensors. Additionally, during

**Figure 20.** Photo of prototype GMM actuator during laser examinations of true tip displacement under programmed magnetic field stimulations: (1) – assembled actuator, (2) – Rigid stand, (3) – tip and (4) – Keyence LK series – laser sensor.


**Figure 23** presents the result of the deformation of the material in the actuator when the feedback loop system was off. The actuator was loaded with the weight of 20 kg. It is clear that under the influence of the applied load the value of the received magnetostriction decreased so did the active rod. Such a rod which can be used, for example, for control in various applications, did not keep its position. Moreover, in the case of the system without the feedback loop, the value of the magnetic field did not change during the experiment, as it is shown in

Development of Resonators with Reversible Magnetostrictive Effect for Applications…

http://dx.doi.org/10.5772/intechopen.78572

79

The results show changes in the magnetic field recorder shown by each of the three Hall sensors placed inside the actuator coil. The measurement direction of the Hall sensors are as follows: X direction along the main axis of the sample, Z direction toward the sample and Y

Moreover, it is shown that it is possible to actively control the displacement of an actuator which is based on the magnetostrictive composite core with a feedback loop system. The control of such a system is based on the changes of the intensity value of the magnetic field around the composite core. In addition, through the use of fiber optics strain sensors, the measuring system made it possible to simplify the control of the deformation of the material. Certainly, it is still necessary to further develop this system to improve its parameters; how-

**Table 1** summarizes the most important parameters of the high power actuator.

ever, at this stage one may say that it can be used in many different applications.

1. Maximum DC current with forced cooling 10 A continuous, up to 80°C 2. Maximum real power 400 W, 30% duty cycle 3. Static displacement of tip as a unit step More than 50 μm, 1 kN load 4. Static impedance 3.8 Ω with terminal connections

5. The range of permissible loading force 5 kN, only compression

6. Useful frequency range 0–500 Hz

**Table 1.** The main operational parameters of the actuator (**Figure 21C**).

**Figure 24.** Frequency response of the high power actuator with FBG magnetostriction feedback.

The frequency response of the high power actuator is shown in the **Figure 24**.

**Figure 23A**. This response of the actuator can be predicted.

direction on the outside of the sample (**Figure 23B**).

**Figure 22.** Schema of high power GMMc vibration exciter core that can be controlled using PID controller.

**Figure 23.** Deformation of the magnetostrictive rod with a feedback loop system (A), tri-axial magnetic field measurement using hall sensors attached to the sample: (1) – Sample, (2) – Sensors (B) [25].

loop, the value of the magnetic field did not change during the experiment, as it is shown in **Figure 23A**. This response of the actuator can be predicted.

The results show changes in the magnetic field recorder shown by each of the three Hall sensors placed inside the actuator coil. The measurement direction of the Hall sensors are as follows: X direction along the main axis of the sample, Z direction toward the sample and Y direction on the outside of the sample (**Figure 23B**).

**Table 1** summarizes the most important parameters of the high power actuator.

The frequency response of the high power actuator is shown in the **Figure 24**.

Moreover, it is shown that it is possible to actively control the displacement of an actuator which is based on the magnetostrictive composite core with a feedback loop system. The control of such a system is based on the changes of the intensity value of the magnetic field around the composite core. In addition, through the use of fiber optics strain sensors, the measuring system made it possible to simplify the control of the deformation of the material. Certainly, it is still necessary to further develop this system to improve its parameters; however, at this stage one may say that it can be used in many different applications.


**Table 1.** The main operational parameters of the actuator (**Figure 21C**).

**Figure 23.** Deformation of the magnetostrictive rod with a feedback loop system (A), tri-axial magnetic field measurement

**Figure 22.** Schema of high power GMMc vibration exciter core that can be controlled using PID controller.

using hall sensors attached to the sample: (1) – Sample, (2) – Sensors (B) [25].

**1.** start of the measurement and application of magnetic field,

**Figure 23** presents the result of the deformation of the material in the actuator when the feedback loop system was off. The actuator was loaded with the weight of 20 kg. It is clear that under the influence of the applied load the value of the received magnetostriction decreased so did the active rod. Such a rod which can be used, for example, for control in various applications, did not keep its position. Moreover, in the case of the system without the feedback

**2.** loading of the actuator (load 200 N) (blue dashed line),

**3.** unloading of the actuator (red-dashed line).

78 Actuators

**Figure 24.** Frequency response of the high power actuator with FBG magnetostriction feedback.
