**1. Introduction**

The rapid progress in communication technology in recent years has been noted by scientists and engineers working in this field. These technological advances have motivated people to utilize them with the purpose to improve their quality of life. A good level of life always strives for ease of communication, among others, by the presence of cellphone abbreviated as hand phone, a type of wireless telephone that is easy to carry everywhere and practical because of its small size so that it is easily inserted into a pocket. A cellular telephone or hand phone is a device that can make and receive phone calls transmitted via electromagnetic waves and can be used

around a large geographical area. Because communication using this cellphone uses electromagnetic waves in the microwave frequency range, the microwave radiating out of the mobile emitter will theoretically affect the human body, especially the head around the ear as shown in **Figure 1**.

Radiation emitted can also affect the function of enzymes and proteins, which is a change in albumin protein that functions in supplying blood flow to the brain. For this reason, we need a microwave absorbent material that can reduce and even eliminate the effect of microwave radiation on human health [1, 2].

 In the electronics field, microwave absorbers are used to reduce the presence of electromagnetic wave interference (EMI) [3, 4]. In general, electronic components that work at high frequencies often experience problems such as frequency signal leakage. EMI will not be present if the electronic device is in an open condition or is not in a closed medium. However, signals travelling in a closed medium will be reflected back to the device. This will cause the energy to increase in phase at certain frequencies due to the appearance of EMI emitted in the form of noise, which then interferes with the performance of these electronic devices. But after the closed media are protected by microwave absorbers, the effect of EMI can be avoided. An illustration of this phenomenon is shown in **Figure 2**.

In the field of defense (military) [5, 6], this microwave absorber is used for coating or painting on defense equipment and facilities such as stealth aircraft, warships (war ship), and for army clothing, especially troops in the guard front. as shown in **Figure 3**.

 In a radar system, microwaves are transmitted continuously in all directions by the transmitter. If there is an object affected by this wave, the signal will be reflected by the object and received back by the recipient. This reflection signal will provide information that there is a close object that will be displayed by the radar screen. Radar (radio detection and ranging) is a microwave system that is useful for detecting and measuring distances and making maps of an object. The radar waves emitted are able to detect the presence of an object. The radar concept is measuring the distance from the sensor to the target. The measure of distance is obtained by measuring the time needed by the radar wave during its propagation from the sensor to the target and back to the sensor again. The measured distance based on the time needed by the electromagnetic waves emanating from the target is then reflected back to the radar sensor. The target is able to reflect electromagnetic

**Figure 1.**  *Use of microwave absorbers for shielding radiation.* 

*Metamaterial: Smart Magnetic Material for Microwave Absorbing Material DOI: http://dx.doi.org/10.5772/intechopen.84471* 

**Figure 2.**  *Use of microwave absorbers to reduce EMI.* 

**Figure 3.**  *Use of microwave absorbers in the defense sector.* 

waves, so that the radar is able to detect the existence of these objects. However, the case is different if the object cannot reflect radar waves, so that the radar is not able to detect the existence of the object. This phenomenon is then developed for certain interests related to the defense system.

Because of the vast utilization of these microwave absorbent materials, it is generally accepted, recognizing that microwave absorbent material is a material that can weaken the energy of electromagnetic waves. These microwave absorbent materials can externally reduce or even eliminate reflections or transmissions from certain objects and can be used internally to reduce oscillations caused by resonance cavities. Besides that, this microwave absorbent can be used to create a reflection free space or anechoic space.

Metamaterial is one of the solutions for the development of microwave absorbent materials. Metamaterials that are developing rapidly are smart magnetic-based materials. Smart magnetics are modified magnetic materials so these materials have a single-phase frequency-dependent permeability and permittivity depending on the type of magnetic material used. Smart magnetic is an advanced magnetic material in the future in the form of new inorganic crystalline materials with permeability and permittivity made from interpenetrating lattices with magnetic field and electric field responses.
