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netic field suffers a torque (T) that causes the magnetization
to line up with the external field [31].
T = V.M × B (1)
Where V is the volume of the object, M is the magnetization,
and B is the flux density.
Equation (2) describes the force (F) exerted in the presence
of a uniform spatial gradient of the magnetic field. The mobil-
ity of a magnetic microrobot using these equations is based
on the premise that the microrobot may be approximated as a
polar and also that non-zero magnetic spatial gradients have
a minor effect on the direction and strength of the magnetic
field in the microrobot’s workspace [32].
F = ?(M.B) (2)
Where ? is the gradient operator.
The electromagnetic actuation (EMA) system was capable
of creating magnetic fields with various properties, including
controllable uniform gradient magnetism, spinning, and an
alternating magnetic field [33, 34]. Different types of coils
have been suggested by researchers to actuate the microrobot
magnetically. A novel EMA system is comprised of stationary
and rotational Helmholtz with Maxwell coil pairs. A uniform
magnetic flux density is generated by the Helmholtz coils,
while a uniform gradient magnet flux is generated by the
Maxwell coils [35]. A pair of Helmholtz and Maxwell electric
coils make up an EMA system, which is used to fabricate a
microrobot [36].
In [37] the authors have proposed a system consisting of
three pairs of stationary Helmholtz coils, one pair of stationary amount of onboard energy storage [23, 29]. Magnetic mi-
Maxwell coils, and one rotating pair of rotating Maxwell
coils. The rotating magnetic fields consisted of three pairs of
square-shaped Helmholtz coils, which gave the microrobot
locomotion and drilling motion. One Maxwell coil pair with
a circular shape was developed [38]. A magnetic actuation
system that is based on rectangular coils is called RectMag3D.
It can control a microrobot in three dimensions with five
degrees of freedom of motion [39]. For a smaller volume and
less power consumption, an EMA system has been developed
using 2-pairs of Helmholtz coils and a pair of Maxwell coils
[40]. Helmholtz and Maxwell’s coils are also used in an
EMA system designed for the microrobot’s five degrees of
freedom locomotion [41]. The magnetic field created by the
source coil is employed for propulsion in wireless power
transfer technology, and the Lorentz force is used to generate
torque [42].
Another type of coil has been suggested. Two pairs of uni-
form saddle coils, a pair of Helmholtz coils, a pair of Maxwell
coils, and a pair of gradient saddle coils compose the EMA
system [27]. For rotating permanent magnets, a novel actua-
tion technology generates less heat while providing the same
Bresam & Al-Mumen
Fig. 3. Different shapes of coils (a) circular coils (b) square
coils (c) saddle coils
level of control for untethered microscale objects by using
a grid [43]. An untethered magnetic microrobot was acti-
vated for navigation using a novel alternating electromagnetic
field production technology that was developed and optimized
for use with inverted microscopes [44]. Three circular coils
placed at the points of an equilateral triangle form a triad of
electromagnetic coils that could control a magnetic micro-
robot’s 2D motions within a sizable working area [45]. Fig.
3 illustrates the different shapes of coils. Fig. 3(a) shows the
circular type and the structural simplicity of these circular
coils. This combination has also been employed by numer-
ous researchers to actuate magnetic robots [46]. Fig. 3(b)
shows the square-type, high magnetic field peaks generate
at the corners of a square-shaped coil’s magnetic field [47].
and Fig. 3(c) shows the saddle type, there have been devel-
opments in uniform saddle coils (USCs) and gradient saddle
coils (GSCs) [48].
In comparison with other external actuation methods, the
external magnetic field-based control approach has the sub-
stantial advantages of wireless connectivity and high effi-
ciency in order to perform motion control of the microrobot
at a limited scale. The basic advantages of magnetic actuation
include transparency and safety for biological tissues. Mi-
crorobots can also wirelessly receive actuation power from
an external magnetic manipulation device with a constrained
crorobots have recently started to provide novel prospects in
targeted therapeutic administration because of their compact
size and capacity to reach challenging locations with minimal
surgical intervention [49, 50]. Magnetic fields have the ability
to penetrate dense biological tissues, hence magnetic thrust
microrobots offer enormous potential for in vivo minimally in-
vasive surgery [51]. Moreover, the magnetic field can reduce
chemotherapy’s negative risks by lowering drug concentration
in other organs [52]. Magnetic soft microrobots have a variety
of uses due to their exceptional flexibility, movement diver-
sity, and remote controllability [53]. These advantages have
provided very good results for magnetic actuation, which is a