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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 aims to produce a high data capacity and miniaturized flexible chipless RFID tag based on the frequency signature using the Modified Complementary Split Ring Resonator (MCSRR). The proposed 19 bits chipless RFID tag using the frequency shifting technique consists of five slotted overlaying MCSRR with Different Width (MCSRR with DW) structures and the dimension of 48 mm $\times48$ mm. The structure is designed by using a flexible (Polyethylene Terephthalate ) PET substrate with permittivity of 0.2. The operating frequency is between 0.9 GHz and 2.7 GHz. The advancement of slotted overlaying MCSRR with DW structures has successfully miniaturized the chipless RFID tag structure to about $107~{\mathrm {mm}}^{2}$ / bit, $0.02\lambda _{mid}^{2}/\mathrm {bit}$ and 0.09 GHz/bit by maximizing the number of resonators in a limited space and minimizing the frequency separation between the resonators. The omnidirectional tag antenna is incorporated with the proposed MCSRR structure using the retransmission measurement method. The log-periodic antenna with a gain of 5–7 dBi is used for this measurement to improve the range distance between tag and reader system. Based on the retransmission measurement involving the antenna tag, the 19 bits chipless RFID tag which consists of five MCSRR with DW structures can be detected with a maximum range distance of 30 cm and a power transmitted level of 30 dBm.

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.

In this paper, design and realization of tunable multi-band microstrip antenna based on artificial magnetic conductor (AMC) is presented. The involvement of AMC structure on the design of microstrip antenna makes the dimension of antenna to be smaller, hence it is easy to use for portable communication devices. The tunable frequency response of proposed microstrip antenna can be achieved by incorporating external elements, namely varactor diode. Here, the varactor diodes of STMD3001 type are used with the reverse DC bias voltage of 0V, 3V, and 10V. The proposed multi-band microstrip antenna is design using two layers of 1.6mm thick FR4 epoxy dielectric substrate. There is a square patch on the top side of the first layer and 4 identical square patches arranged in a 2×2 array on the top side of the second layer. The results show that the proposed AMC-based microstrip antenna could produce the tunable frequency response in the frequency range of 1.575GHz to 2.75GHz along with the variation of reverse DC bias voltage.

This paper presents the characterization of rectangular s-ring resonator as an electromagnetic wave absorber for C band. The structure consists of copper s-ring patch in the top layer, FR-4 dielectric substrate, and the back is fully copper laminated. The initial dimension has 7 mm × 7 mm with the thickness of FR4 is 1 mm. The characterization observes the changes of each variable from the initial design that affect the shift in resonant frequency and bandwidth. Maximum bandwidth can be achieved at S-Ring length 4.4 mm for 0.0941 GHz.

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°).

Most of electromagnetics (EM) wave absorbers have been realized on some hard substrates. Therefore the use was limited only in the field of planar surfaces, while absorbing EM waves are required with various forms of field. In this paper, based on a principle of artificial magnetic conductor (AMC) used as a metasurface, a thin EM wave absorber composed of octagonal patch array is designed on a dielectric substrate of silicon with the relative permittivity of 5.7 and the thickness of 0.3 mm. The use of thin substrate for the absorber is necessary to have possibility and flexibility in surface of field with a non planar shape. To obtain high absorption rate of proposed wave absorber, resistive elements are incorporated into the patches and connecting to the adjacent patches. The characterization result shows that the reflection coefficient was up to 29.15 dB at the resonant frequency of 2.5 GHz for the value of resistive elements of $2100\ \Omega$ , in which this is much higher than the result without resistive elements.

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.

This paper presents a spiral-shaped printed planar inverted-F antenna (PIFA) for body wearable application. A combination method between planar inverted-F technique and geometry modification is implemented for reducing the physical dimension of proposed antenna. The antenna which is intended to work at the frequency of 920MHz is designed and implemented using a circular shape of FR4 epoxy dielectric substrate with the thickness and diameter of 0.8mm and 18mm, respectively. Prior hardware realization, the parameters of antenna such as reflection coefficient, working bandwidth, gain, and radiation pattern are numerically investigated to achieve the design with optimum performance. Meanwhile from the characterization, the measurement result indicates that the realized antenna has the resonant frequency of 911MHz with −10dB measured working bandwidth of 20MHz and gain of −30.79dBi. This achievement could be beneficial for body wearable application such as implantable antenna.