Abstract – The paper presents general aspects of a new unconventional micromotor: the [604065]

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Abstract – The paper presents general aspects of a new unconventional micromotor: the
magnetostrictive motor.
Are presented : theoretical aspects, functional principle, and the main electromechanical aspects.

Index Terms – Magnetostriction, magnetostrictive motor, magnetostrictive actuator, micromechanical contact.

I. INTRODUCTION

The magnetostriction is defined as the dependence of the state of strain (dimensions) of a
ferromagnetic sample on the direction and extent of its magnetization.
In discussing the effect of a unidirectional stress it is convenient to divide materials into two
classes [1], which have:
– Positive magnetostriction – where the magnetization is increased by tension and the material
expan ds when magnetized;
– Negative magnetostriction – where the magnetization is decreased by tension and the
material contracts when magnetized.
The main equations of the magnetostrictive effects are [1], [2], [3]:
nT
mn j mj mn ni jH
ij i
H BH
TddTsS

(1)
where:
S
– the longitudinal deformation tensor;
T
– the mechanical stress tensor;
sH
– the electromechanic compliance tensor to a constant magnetic intensity field;
d
– the magnetostriction ratio tensor;

– the magnetic permeability tensor to a constant mechanical stress.
Among the magnetostrictive applications (there are many magnetostriction effects:
longitudinal, volume effects, radial, Young modulus variation, etc.) [1], [2], [3], [4]: sensors,
actuators, harvesting microgenerators, an interesting application is represented by the
magnetostriction motor [5], [6], [7], [8].
A general functio nally algorithm of the magnetostrictive motor is presented in Fig. 1, and in Fig.
2 a simple sketch of the functional structure.
Short Introduction on the Magnetostrictive Motor
*Mircea Ignat, **Alexandru Dalea
National Institute for Research and Development in Electrical Engineering (INCDIE ICPE -CA), Splaiul
Unirii, No. 313, District 3, 030138, Bucharest, Romania, *mircea.ignat@icpe -ca.ro

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Fig. 1. The functional mode

Fig. 2. A simple functional structure
Magnetostrictive actuator
Magnetostrictive core (terfenol)
Vibration working condition of
the magnetostrictive core.
The coupling beetwen the
magnetostrictive core and the
microcontact element
The friction transmission
The movement of the rotor.
Bearing
Spindle
Disk-rotor

Micromechanical
contact

Magnetostrictive
actuator

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The magnetostrictive actuat or (which is fed with AC voltage) generates the mechanical vibrations which
are transmitted to a disk rotor through the micromechanical contact. In this way a mechanical torque
appears.

II. A MECHANICAL ANALYSIS

In Fig. 3 is presented the micromechanical contact structure where the main guide mark is the
flexible friction element, and in Fig. 4 are presented the components of the active force (
P ) of
the magnetostrictive actuator, where
 is the angle between the a ctuator and the disk rotor
plane. For a good efficiency of this motor , is necessary to mount the actuator inclined to a
certain angle.

Fig. 3. The micromechanical contact structure
The active force , which is generated by m agnetostrictive actuator , has the form :
) sin(0   T PP

Magnetostrictive
rod

Micromechanic
coupling element
Flexible friction
element

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Fig. 4. The force system of the magnetostrictive actuator

The static model of the disk rotor is presente d in Fig. 5.

Fig. 5. The static micromechanical model of the rotor
The equations of the static representation are:
02 1 mr rl rl F F F
(3)
(Ox)
02 1xl xlF F (4)
(Oy)
f myF F (5)
(Oz)
02 1 mz zl zl F F F (6)

where:
rlF1
,
xlF1 ,
zlF1 – the components of the upper microbearing;
rlF2
,
xlF2 ,
zlF2 – the components of the lower microbearing;
fF
– the main friction force;
r – the radius where is realized the micromechanical contact.

r

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III. THE MICROMECHANICAL EQUIVALENT SCHEME

The diagram of the equivalent micromechanic contact is presented in Fig. 6, and in Table 1 the
elastic and damping (or viscous) ratios of the equivalent diagram descri bed [7], [8].

Fig. 6. The equivalent scheme of the micromechanical contact

TABLE I. The elastic and damping ratio of equivalent diagram.

Together with the equation (2) is possible to
describe the dynamic behaviour in
micromechanical contact (and the transmission
of the vibrations):

y m m m Pykdtdycdtydm 22

(7)

022
 ykdtdycdtydmc c c
(8)
022
 ykdtdycdtydmmc mc mc
(9)

The solution of the first equation is [9], [10]:
Guide mark Spring
rate Damping
rate Mass
The
magnetostrictive
rod
mk
mc
mm
The microme –
chanical
coupling
ck
cc
cm
The contact
element
mck
mcc
mcm

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) sin( ) sin cos(0 1 1 m m mtp
m t ytp Btp A eymm   
(10)

and it can be generalize d also for equations ( 8) and ( 9)

The micromechanical pressure on the contact has an ellip soidal distribution [10], [11].

Fig. 7. The contact pressure distribution

The analytical relation of the x, y distribution is [10]:

(11)
IV. DESIGN ASPECTS
The main element of the magnetostrictive motor is the actuator.
The structure of the magneto strictive actuator has the following elements (see Fig. 8):
The magnetostrictive rod ( by Terfenol [1], [2], [3], [14]);
The permanent magnet necessa ry for the magnetic bias [1], [2], [3];
The coil ;
The ferromagnetic circuit.
The design of magnetic circuit includes [2], [3], [5], [6]:
the magnetic reluctance:

]/[WbAlHR
iii
i
(12)

where:
]/[mAHi – the magnetic intensity field on the magnetic segment i ,
][mli – the length of
the magnetic segment,
][Wbi – the magnetic flux.
– the magnetic reactance (because of the AC worki ng condition of the actuator):

22
22
0 22
22
1 123),(by
axpby
ax
abPyxpy 

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]/[2
2WbAGpX
if f
i (13)
where :
]/[kgWpf – the speci fic losses on the i subdomain,
][kgGf – the mass of subdomain
(segment ) i,
f2 , with
][Hzf – frequency.

Fig. 8. The magnetostrictive actuator

The flux is:

][2WbNU
i
(14)

where
][VU – voltage, N – the number of turns in coil.
In Fig. 9 is shown the characteristic of flux vs. turns, for an actuator which was realised to the
Microelectromechanical Department of INCDIE.

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Fig. 9. The characteristic flux vs. the number of turns
An important parameter of the actuator is:

ll
s
(15)

where
ll, – are the initial length of the magnetostric tive rod and the expansion of the rod to the
magnetic stress [3], [14], with:
1000 ppm <
s < 4000 ppm ;
20 m < l < 400 m.
The mechanical properties of the Terfenol D ( Tb0,27Dy0,75Fe2) are showed in Table 2 [3], [14].
TABLE 2. Mechani cal properties of Terfenol D.
Density 9250 kg/m3
Young modulus 23-35 GPa
Mechanical traction 28 MPa
Mechanical
compression 700 MPa
Relative permeability 3-10

The permanent magnets are in general ALNiCo magnets.
The force of the actuator is:

02
2AnFB
(16)

where A is the rod section.
A material ratio in design is magnetostrictive ratio (for specific coupling module 33):

T Hsdk
33 332
332
33
(17)

Specific ratios of Terfenol (Tb0,27Dy0,75Fe2) (see the rod in Fig. 10):

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%.67, 6,9, 8,3],1[ 3,4], [40],[100
339
330 3311
3300
1010



kdsTH
AmPaMPamkA
TH


(18)

Fig. 10. The magnetostrictive rod

The force valuation is possible with the relation:

AT Fact 0
(19)

with
A – the section of the magnetostrictive rod.

Fig. 11. The estimation of characteristic force

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V. SOME STRUCTURES OF THE MAGNETOSTRICTIVE MOTOR

Fig. 12. The motor with a single actuator

There are two main divisions of the magnetostrictive motors:
With single or many actuators which drive the rotor (Fig. 12);
With many actuators with phase difference which drive the spindle of the motor (Fig. 13, 14).

Fig. 13. The motor with many phas e difference actuators

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Fig. 14. The diagram of the drive of the motor with phase difference

Fig. 15. The functional motor

VI. REFERENCES

[1] R. M. Bozorth, “Ferromagnetism”, D. Van Nostrand Company, Inc.Princeton, New Jersey London,
Melbourne, 1 951;
[2] D. Bushko, J. Goldie, “High Performance Magnetostrictive Actuators”, IEEE AES Systems Magazine,
November 1991, pp. 251-267;
[3] F. Claeyssen, N. Lhermet, R. Le Letty, “State of art in the field of magnetostrictive actuators”, JASA,
89(3), 1991, pp . 1231 -1239;
[4] W. Lei, Y. Fuh Gwo, “Structural Vibration Energy Harvesting by Magnetostrictive Materials (MsM)”,
The Proceedings of 4th China -Japan -US Symposium on Stru ctural Control and Monitoring, O ct. 16 -17,
2006, pp. 26-34.
[5] J. M. Vranish , D. P. Naik, “ Magnetostrictive Direct Drive Rotary Motor Development, NASA Goddard
Space Flight Center, Greenbelt, MD 20771 ;
[6] J. B. Restorff , J. P. Teter, R43, Naval Surface Warfare Center, Silver Spring, MD 20903 -5000 ;
[7] F. Claeyssen, N . Lhernict, R . Le Lett y, “Design and Construction of a Resonant Magnetostrictive
Motor” , Cedrat Recherche, ZEST 4301, F38943 Meplan Cedes, France Philippe Bouchillous, Magsoft ;
[8] I. Romaniuc, I. NiŃan, M. RaŃa et al ., “Magnetostrictive Vibromotor with Reversible Rotation ”,
Patent application A/01425/2011a;
[9] A. H. Church, ”Mechanical Vibrations”, John Wiley a nd Sons, New York, London, 1957;
[10] R. Voinea, D. Voiculescu , F. Simion , “Introducere in mecanica solidului cu aplicatii in inginerie” Ed.
Academiei, Bucuresti, 1989;
[11] R. Holm , “Electric Contacts. Theory and Applications”, Springer Verlag, 1967;
[12] K. Sezawa , “Vibration theory”, Gendai Kogaku Sha.Co.Ltd, Tokyo, 1972;
[13] K. Ragulskis, R. Bansevičius, R. Barauskas, G. Kulvietis , “Vibromotos for precision microrobots”,
Hemisphere Publishing Corporation, 1990.
[14] M. Ignat, Gh. Amza , “Some experimental aspects regarding Terfenol -D applications” , The Vth
Magnetic Materia ls and Superconductors MMS’96, Cluj -Napoca, 12 -13 September 1996;
[15] M. Ignat, G. Zarnescu, I. Puflea, Al. Catanescu, L.Paslaru, V. Stoica, ”Actuatori electromagnetici”, Ed.
Electra, 2008, pp. 22-50;

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[16] M. Ignat, I.Ardelean, G. Zarnescu, S. Soltan, “Mi cro-actionari neconventionale”, Ed. Electra, 2006,
pp.22 -54.

VI. BIOGRAPHIES

Mircea Ignat was born in Bucharest on March 4, 1953. He graduated at 1977 and he received Ph.D.
degrees in electrical engineering from Bucharest Polyte chnic University in 1999.
His employment experience included the National Research Electrical Engineering Institute, Dep. of
Electrical Micromachines Research and he is the head of Electromechanics Department.
The research preoccupation include: the synchro nous generators and the hi gh speed electric machines.
Is member of IEEE.
Alexandru Dalea was born in Bucharest on 14th of M arch1987, and he is a student at the Polyte chnic
University of Bucharest , Electrical Engineering Faculty.
The research preoccupation include: the unconventiona l applications of the piezoelectric and
magnetostrictive effects.