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In this work, wearable resistive gas sensors based on hybrid graphene/zinc oxide (ZnO) nanocomposites were fabricated on a flexible cotton fabric and employed to monitor odorless and colorless carbon monoxide (CO). Dip-coating and chemical bath deposition (CBD) was used to deposit the graphene layer and grow the ZnO nanorods, respectively. The films were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-Ray diffraction (XRD) to investigate their morphological structures, elemental composition, and crystal phase, respectively. Those characterizations were also confirming the growth of ZnO nanorods on the already-deposited graphene layer on fabrics. From the gas sensor measurements at room temperature, it was revealed that these graphene/ZnO nanocomposites were highly sensitive and selective towards CO gas at low concentration down to 10 ppm. The shortest response and recovery times of the sensors were measured to be 280 s and 45 s, respectively. Moreover, in comparison to bare graphene sensors, the surface modification by ZnO nanorods could obviously enhance the sensing response by up to 40% (i.e., doubled sensitivity). These flexible hybrid sensors are therefore expected to be a promising alternative for the existing rigid CO sensors in the market by offering unique nanostructures, low-cost fabrication, high flexibility, and good sensing performances.

This paper deals with an experimental approach for investigating characteristics of an electromagnetic (EM) wave absorber made of artificial magnetic conductor (AMC) structure. An array of ring resonators in symmetrical shape used as the basis of AMC structure is designed to absorb the incoming EM waves at a certain operating frequency. The proposed design of wave absorber made of ring resonator-based AMC structure is deployed on a Flame Retardant (FR) 4 Epoxy dielectric substrate with the thickness of 1.6 mm. The shape and dimension of ring resonator are optimized to work at the certain operating frequency using a unit cell with proper boundary conditions. To investigate the absorptivity rate of proposed wave absorber, resistive elements are incorporated into the ring resonator. Here, the experimental measurement aims to verify the realized wave absorber with the proposed design and to measure the absorptivity characteristics of realized wave absorber. The measured results for the realized wave absorber which takes the dimension of 220 mm × 220 mm have the absorptivity rate, in terms of reflection coefficient (S 11 ), of –16.65 dB and –25.72 dB for the wave absorber without and with resistors, respectively. These results are comparable to the simulated ones with the S 11 values of –18.01 dB and –23.41 dB for the design without and with resistors, respectively.

This paper presents an implementation of a dual-band wearable reflector composed of an artificial magnetic conductor (AMC) structure and its characterization through experimental measurement. The proposed wearable reflector, which is meant for wireless communications, comprises 3x3 AMC unit cells. Each unit cell comprises a square patch and a square ring patch with gaps placed in a concentrically organized pattern. An RT/Duroid® RO3003 dielectric substrate with a thickness of 0.5 mm is employed for the design and implementation. Meanwhile, a printed dipole antenna as an inseparable part of the wearable reflector is also deployed on the same dielectric substrate. This configuration, i.e., a printed dipole antenna and a wearable reflector, is expectable to operate at two different frequency bands or dual-band, covering the required frequencies of wireless communications while maintaining its compact size and simple configuration. Experimental characterization is applied to validate the proposed design, in which the results demonstrate the ability of configuration to work at two frequency responses, namely 2.45 GHz band, and 3.35 GHz band.

In this paper, the design of dual-band wearable reflector based on Artificial Magnetic Conductor (AMC) structure is presented for Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) applications. The AMC structure used to construct the dual-band wearable reflector is configured by a 3×3 unit cell whereby each unit is the combination of a rectangular patch and an L-patch with a gap. Meanwhile, to characterize the property of dual-band wearable reflector, a printed dipole antenna with slots is applied in varied distances to the reflector. The configuration of AMC-based dual-band reflector and printed dipole antenna which is designed on a 0.5mm thick Rogers RO3003 dielectric substrate is expected to produce two different resonant frequencies to cover the desired frequency bands while maintaining its small size and simple structure. Parametric studies are conducted upon the physical parameters of the dual-band wearable reflector and the printed dipole antenna to obtain an optimum design of the configuration. The characterization results show that the proposed configurations are operable at two frequency bands, i.e., 2.45GHz and 3.35GHz, suitable for WLAN and WiMAX applications, respectively.

In absorbent applications, the technology of surface textured is often used to reduce the material thickness thus allowing the realization of thinner materials. In order to obtain high absorption rate of electromagnetics (EM) wave absorber at the desired frequency, a metal patch upon the wave absorber can be made in a specific shape. In this paper, a characterization of EM wave absorber composed of ring resonator structure is carried out by incorporating resistors between the ring resonator structures on two types of boundary condition, namely perfect electric conductor (PEC) and perfect magnetic conductor (PMC) to represent an infinite double periodic arrangement, and the radiation boundary to analyze the performance of proposed EM wave absorber in an actual condition. By using an FR4 epoxy dielectric substrate with the thickness of 1.6 mm, the proposed EM wave absorber is constructed by two-dimensional array of unit cells. Meanwhile, each unit cell has the dimension of 22 mm × 22 mm and is composed of a couple of ring resonator structures in a symmetrical configuration. Based on parametric studies, the resistor value required to be incorporated into the structure is in the range of 1 kΩ to 6 kΩ. The characterization result shows that the absorption rate of proposed EM wave absorber is −23.41 dB on the PEC and PMC boundaries with the resistor value of 6 kΩ, and −18.3 dB on the radiation boundary with the resistor value of 5.6 kΩ at the frequency of 2.45 GHz.

The reflector has a role in enhancing the return loss of antenna becoming a selective frequency. In this paper, an artificial magnetic conductor (AMC) based reflector composed of slotted square rings is proposed and characterized using a printed dipole antenna. The used of AMC layer which has high surface impedance is expected to reduce the distance between the antenna and the reflector yielding a compact device. The configuration of AMC reflector and printed dipole antenna is designed each on an RO3003 dielectric substrate with the relative permittivity of 3.0 and the thickness of 0.5 mm. The configuration is intended to be used for wireless communication at the Industrial, Scientific, and Medical (ISM) band frequency of 2.4 GHz. The proposed reflector is constructed by a 3×3 unit cell of AMC structure where each unit cell is composed of slotted square rings configured concentrically. Meanwhile, the characterization is carried out by varying the parameters of AMC reflector and printed dipole antenna. The result shows the configuration with the distance between the antenna and the reflector of λ/23, or around 5 mm, could produce a significant value of reflection coefficient (S 11 ) among others. This configuration could achieve the S 11 value up to –24 dB at the frequency of 1.98 GHz.

In this paper, the absorption characteristics of tunable electromagnetics (EM) wave absorber developed using artificial magnetic conductor (AMC) is investigated by incorporating varactor diode into the structure. The proposed wave absorber configured by 5×5 cells of AMC structure is designed on an FR4 epoxy dielectric substrate with the thickness of 1.6 mm. Each cell which is composed of a square patch has the dimension of 20.8 mm × 20.8 mm, hence the total dimension of AMC-based wave absorber is 104 mm × 104 mm. To gain a tunable frequency response with the optimum absorptivity, a varactor diode with varied DC bias voltage is incorporated midway along the square patch in parallel to the incident wave. The equivalent circuit of varactor diode is used to characterize the performance of proposed tunable AMC-based wave absorber. Prior characterizing the effect of varactor diode incorporation, parametric studies upon the characteristic of AMC-based wave absorber is investigated by incorporating some passive elements such as resistor and capacitor. The characterization results show that the frequency response of tunable AMC-based wave absorber can be tuned from the frequency of 1.55 GHz to 2.51 GHz which corresponds to the DC bias voltages variation of varactor diode from 10V to 0V.

This paper deals with the experimental characterization of thin tunable absorber developed based on artificial magnetic conductor (AMC). To produce the tunable frequency response, the varactor diodes with varied reverse DC bias voltage are incorporated into the AMC structure of proposed absorber. By using an equivalent circuit of varactor diode, the performance of AMC-based thin tunable absorber is characterized through a simulation software. To improve the absorptivity, a resistor with the value of 470Ω is also incorporated into the AMC structure in parallel to each varactor diode. A 1.6mm thick FR4 epoxy dielectric substrate with the dimension of 104mm × 104mm is used for deploying the design as well as for the realization. The experimental characterization which is performed using a horn antenna shows that the realized absorber has a tunable frequency response from the frequency of 2.26GHz with the reflection coefficient (S 11 ) value of -21.5dB at the reverse DC bias voltage of 0V to the frequency of 3.01GHz with the S 11 value of -19.75dB at the reverse DC bias voltage of 10V. This performance is comparable to the simulation result for the proposed absorber with the varactor diode and 470Ω resistor incorporation.

A pattern reconfigurable antenna offers diverse pattern configurations and beam steering to cater the congested signal environment problem while maintaining the performances and operating frequency, as well as increasing the signal and data security. The pattern reconfigurable antenna using EBG structure is presented in this paper for beam-steering configurations. Most of the previous works proposed the PIN diode on the radiating patches, which caused the degradation of its performances. In this work, the structure offers good efficiency as the RF switches are not embedded to the radiating patches. A dual-band slotted pattern reconfigurable antenna using EBG structure is designed and analyzed. The EBG patches are located at the right and left of the radiating edge of the antenna. The EBG is designed so that its surface wave of band gap covers the radiation of the antenna. As a result, the surface waves excited by the patch antenna are prohibited from propagating by the EBG and caused the radiation pattern to be tilted to another side. The operating frequency of the proposed antenna is 2.45 GHz and 5.8 GHz for the dual-band antenna. The proposed antenna is capable of having beam shifting at three different angles (0°, +26°, and −26°).

Wearable communication systems required high performance, compact and flexible antenna devices. In this paper, a flexible artificial magnetic conductor (AMC) reflector is designed using square patch array for wearable antenna application at the Industrial, Scientific and Medical (ISM) frequency of 2.45 GHz. The proposed AMC reflector is composed of 3 × 3 squares patches with concentric slots to gain the wide bandwidth response. A flexible dielectric material of RO3003@ from Rogers Corporation with the relative permittivity of 3.0 and the thickness of 0.5 mm is used as a dielectric substrate for the reflector deployment as well as for the wearable antenna. The characterization results show that the integration of flexible AMC reflector with a wearable antenna has improved radiation characteristic and gain of the antenna. The results indicate that the proposed flexible AMC reflector has the feasibility for performance enhancement of wearable antenna especially in wireless body area network (WBAN) communications.

In this paper, the development of thin electromagnetic (EM) wave absorber and its characteristic measurement are presented. The absorber is developed based on a textured surface structure of octagonal patch array which is loaded with surface resistor. The octagonal patch is employed as a unit cell which is intended to operate whereby at the resonance frequency of resistively textured surface. Each unit cell which has the substrate width of 14.4mm consists of an octagonal shape of patch with the width of 5.178mm. Here, the surface resistor are incorporated midway in between the adjacent patches to reduce the amount of backscatter from the absorber. The textured surface structure of octagonal patch array is deployed on a single-sided 3.2mm thick FR4 Epoxy dielectric substrate. From the result of experimental characterization, it shows that the reflection characteristic of absorber with 453Ω of surface resistor loading upon the incident wave is up to 34dB at frequency of 2.78GHz where this is 10dB better than the absorber without surface resistor loading.