A new design method of an ultra-wideband circularly-polarized planar multiple-input-multiple-output (MIMO) antenna is presented in this paper. The proposed MIMO antenna consists of four unit cell antennas, being comprised of a microstrip feed line and a square slotted ground plane. In the proposed unit cell design, a circular stub is protruded from the ground plane strip for achieving circular polarization. The unit cell of the MIMO antenna is optimized by adjusting design parameters. The compact four-port MIMO antenna prototype is designed on the FR4 substrate with the overall dimensions of 45 × 45 × 1.6 mm3. The proposed four-port MIMO antenna design provides an impedance bandwidth (S11 < −10 dB) of 112% (3.1–11 GHz) and a 3 dB axial ratio bandwidth of 36% (4.8–6.9 GHz). The performance of the fabricated MIMO antenna shows good agreement between the EM simulation and measurement results.

A novel flexible radio frequency (RF) sensor is designed to facilitate the accurate testing of various samples used in the biomedical industry at the industrial, scientific and medical (ISM) frequency band. The proposed RF biosensor comprises a liquid channel-loaded interdigitated capacitor, which is integrated on a coplanar waveguide structure. The prototype of the sensor is fabricated on a 0.13 mm thin biodegradable polyethylene terephthalate polyester film to perform the testing of various bio-graded samples by recording the corresponding resonant frequency. It is observed that there is a noticeable change between the measured resonant frequencies of these samples, which primarily occurs due to the difference in their dielectric properties. The designed sensor was used to monitor and investigate the quality of glycerol, which is the most commonly used raw ingredient in the biomedical and food industry. The determination of glucose concentration in base fluids is considered to ease the challenges faced by doctors and biochemists regarding the monitoring of glucose concentration. It is found that the proposed sensor can quantify the glycerol purity up to the minimum specified adulteration level of 2 and 1% corresponding to toxic contaminants diethylene glycol and ethylene glycol, respectively, and the glucose concentration of 0.5 mg/ml.

This paper specifies a concise review of recent research and development in the context of electromagnetic absorbers. An attempt has been made to justify the need for economical and thin microwave absorbers for achieving good absorption characteristics over a wide range of frequencies within a specified band of electromagnetic spectrum. This paper mainly focuses on the challenges encountered while designing a perfect electromagnetic absorber which can absorb electromagnetic radiations of any polarization that may appear from any direction and may occur over a broader bandwidth. The absorbers which are competent enough to withstand all these challenges are capable to suppress the reflection and transmission of unknown electromagnetic radiations efficiently to the lowest possible level. Several prospects of nanotechnology in flexible absorber design are also described to enhance absorber characteristics. This paper also provides a futuristic glimpse on several applications of such absorbers for commercial and military purposes.

A novel multiple-input and multiple-output (MIMO) fractal antenna excited by a coplanar waveguide was investigated in this study. A novel technique was used to improve the isolation of 20 dB between the dual radiating elements by inserting a strip line into the outer edges of the ground plane. A sunflower structure was used to configure the antenna in three steps. At each step, an additional sunflower structure was added with half the size of that used in the previous step to enhance the impedance bandwidth. The measured values of envelop correlation coefficient and total active reflection coefficient indicated that the proposed MIMO antenna has high-diversity performance between radiating elements. Wide dual operating bands of 2–2.9 and 5–10 GHz were obtained, which can support different wireless communications, such as 3G, LTE (2.6 GHz), WLAN (2.4 GHz/5 GHz), WiMAX (2.4 GHz/5GHz), ISM (2.4 GHz/5 GHz), 5G (5–6 GHz), and satellite communications (6–8 GHz). The MIMO fractal antenna with a small size achieved a maximum efficiency of 85% and a peak value gain of 6 dBi, low-channel capacity loss of 0.15–0.4 b/s/Hz, and high isolation between radiating elements is suitable for portable communication devices.

This paper proposes a differential sensor based on a pair of open split ring resonators (OSRR) operating in reflection. The output signal is thus the differential reflection coefficient of both resonators, intimately related to their dielectric loading. Thus, for identical loads in both sensing resonators, the individual reflection coefficients are equal, thereby providing an ideally null output signal. By contrast, when unequal dielectric loads truncate the symmetry, the reflection coefficients are different, resulting in a differential output signal related to the level of asymmetry. In order to ease the measurement of the output signal, a rat-race hybrid coupler is used. The OSRR sensing loads are connected to the coupled ports of the hybrid coupler, whereas the input signal is injected to the Δ-port, and the output signal is collected at the isolated port (Σ-port). By this means, the output signal, i.e. the differential reflection coefficient between both sensing loads, is obtained from the transmission coefficient of a simple two-port structure. For experimental validation purposes, the sensor is applied to the measurement of isopropanol content in aqueous solutions, and for that purpose, the sensitive regions are equipped with microfluidic channels.

A compact planar ultra-wideband (UWB) antenna with WiMAX and WLAN notched band is presented in this paper. The presented antenna consists of a rectangular patch and slotted partial ground plane and fed by a microstrip feed line. The volumetric size of the antenna is 30 mm × 22 mm × 1.6 mm. Method of moment-based simulation technology is used to simulate and analyze the characteristics of the antenna. To generate two notch bands at WiMAX and WLAN, a pair of parasitic resonator is placed beneath the radiating patch. The presented antenna achieves an operating band (VSWR ≤2) ranging from 2.98 to 12 GHz with an average gain of 3.95 dBi along with considerable efficiency and symmetric radiation patterns. Moreover, the antenna exhibits two notch bands at 3.5 and 5.45 GHz and is able to avoid possible interference with pre-existing narrow band services. The proposed antenna is low cost and low profile and is modeled to be used as a transceiver in UWB communication applications.

In this paper, a flexible CPW fed ultrawide band (UWB) antenna with mu-negative (MNG) metamaterial is designed, fabricated, and tested for wearable applications. Initially, a UWB antenna of size 50 mm × 43 mm is fabricated on two different substrates, viz. flexible FR4 and semi-flexible Rogers RT/duroid 5880. A metamaterial structure fabricated on flexible FR4 shows a magnetic resonance from 7.2 GHz to 9.2 GHz with maximum stop band attenuation (−49 dB) and high MNG value (−2121.6) at 7.87 GHz. Then a (3 × 3) array of designed MNG metasurface is used as ground plane with flexible UWB antenna, which improves its overall gain and radiation pattern. The performance of the flexible antenna with/without metamaterial at various distances from flat and cylindrical three-layered human phantom of skin, fat, and muscle is studied. Further, the bending characteristics at different angles and performance over thin metallic sheet is also evaluated. Additionally, the peak specific absorption rate value averaged over 1 g of tissue at three chosen frequencies from UWB range (3, 5, 10 GHz) with/without metamaterial using 0.3 and 0.1 W of input power is also analyzed. The simulated and measured results are in good agreement which confirms that the designed antenna is a good candidate for wearable applications.

In this paper, a differential microfluidic sensor and comparator based on a pair of microstrip lines loaded with dumbbell-shaped defected ground structure resonators is applied to the characterization of electrolyte concentration in samples of horse urine. Since variations in the total electrolyte content in urine may be indicative of certain pathologies, the interest is to use the device as a comparator, in order to determine changes in the electrolyte concentration as compared to a reference level. To validate the approach, we have made differential measurements of a set of urine samples with different electrolyte concentrations (which have been previously obtained by means of electrochemical methods). The obtained results correlate with the nominal electrolyte concentrations of the samples, thereby pointing out the potential of the approach as a low-cost pre-screening method (or complementary diagnosis system) to detect potential pathologies or diseases in horses and other animals.

The paper presents a new coplanar waveguide (CPW)-fed rectangular patch antenna with a square-shaped ground plane that can be employed in modern advanced navigation systems. For realizing broad impedance bandwidth in the proposed antenna, a wide slot is introduced in the square ground plane and the rectangular patch is shifted toward the left edge of the ground surface. In addition, by means of introducing square-shaped stubs near the left and right edge of the ground plane, the circular polarization is achieved at L1, L2, and L5 satellite bands. As per the simulation results, the proposed antenna provides a wide impedance bandwidth (S11<−10 dB) of 123% (1.12–4.72 GHz) and 3 dB axial ratio bandwidth of 11% (1.15–1.29 GHz) and 18% (1.5–1.8 GHz) suitable for multipurpose wireless applications. The designed single feed circularly polarized antenna is low profile, small size, light weight and easily integrable with other high-frequency communication devices. To validate radiation performance of the proposed structure, the antenna is fabricated and integrated with the commercially available Global Positioning System (GPS) receiver and it is found that the measured values are in close agreement with the desired results.

A high selective dual band and miniaturized electromagnetic band gap (EBG) unit cell is presented in this paper. The analysis and characterization of the new cell are explained. The modified compact EBG unit cell is based on cutting two inverted U-shaped slots inside the typical mushroom-like EBG. The modified EBG has a 70% size reduction. The dual-band functionality of the structure is confirmed by applying it in a dual-notch ultra-wideband antenna (3.1–10.6 GHz), and the notch frequencies are 5.2 and 5.8 GHz. The dual-band functionality has advantages of a highly selective bandpass between them. The antenna can suppress interference frequencies in less than 100 MHz bandwidth without affecting the antenna performance in the whole bandwidth. Presented results are addressed in terms of circuit modeling, 3D full-wave simulations, and measurements.