Metamaterial elements/arrays exhibit a sensitive response to fluids yet with a small footprint, therefore, they have been an attractive choice to realize various sensing devices when integrated with ...microfluidic technology. Micro-channels made from inexpensive biocompatible materials avoid any contamination from environment and require only microliter-nanoliter sample for sensing. Simple design, easy fabrication process, light weight prototype, and instant measurements are advantages as compared to conventional (optical, electrochemical and biological) sensing systems. Inkjet-printed flexible sensors find their utilization in rapidly growing wearable electronics and health-monitoring flexible devices. Adequate sensitivity and repeatability of these low profile microfluidic sensors make them a potential candidate for point-of-care testing which novice patients can use reliably. Aside from degraded sensitivity and lack of selectivity in all practical microwave chemical sensors, they require an instrument, such as vector network analyzer for measurements and not readily available as a self-sustained portable sensor. This review article presents state-of-the-art metamaterial inspired microfluidic bio/chemical sensors (passive devices ranging from gigahertz to terahertz range) with an emphasis on metamaterial sensing circuit and microfluidic detection. We also highlight challenges and strategies to cope these issues which set future directions.
In this paper, a complementary split-ring resonator (CSRR)-loaded patch is proposed as a microfluidic ethanol chemical sensor. The primary objective of this chemical sensor is to detect ethanol's ...concentration. First, two tightly coupled concentric CSRRs loaded on a patch are realized on a Rogers RT/Duroid 5870 substrate, and then a microfluidic channel engraved on polydimethylsiloxane (PDMS) is integrated for ethanol chemical sensor applications. The resonant frequency of the structure before loading the microfluidic channel is 4.72 GHz. After loading the microfluidic channel, the 550 MHz shift in the resonant frequency is ascribed to the dielectric perturbation phenomenon when the ethanol concentration is varied from 0% to 100%. In order to assess the sensitivity range of our proposed sensor, various concentrations of ethanol are tested and analyzed. Our proposed sensor exhibits repeatability and successfully detects 10% ethanol as verified by the measurement set-up. It has created headway to a miniaturized, non-contact, low-cost, reliable, reusable, and easily fabricated design using extremely small liquid volumes.
A polarization-independent ultrawideband metamaterial absorber is proposed for X-band applications. High absorptivity over an ultrawide spectrum is achieved by the combination of an artificial ...impedance surface (AIS) and a resistor-capacitor (RC) layer. In addition, the unique hexagonal shape of an AIS and RC layer enables polarization insensitivity. A circuit analysis is introduced based on a transmission-line model and shows good agreement with the full-wave analysis. Fabrication tolerance issues are considered with parametric studies in the electromagnetic simulation. The proposed absorber is fabricated on low-cost FR4 substrates, and its absorption performance is experimentally demonstrated at different angles and polarizations of incident electric fields.
In this paper, a wide incidence angle-insensitive metamaterial absorber is proposed using eight-circular-sector (ECS). Under normal incidence, the proposed absorber shows high absorptivity at ...different polarizations due to its symmetric geometry. Under oblique incidence, zero-reflection conditions for transverse electric (TE) and transverse magnetic (TM) polarization are different. Nevertheless, the proposed absorber shows high absorptivity under oblique incidence of both TE and TM polarization due to ECS. The performance of the proposed absorber was demonstrated with full-wave simulation and measurements. The simulated absorptivity at the specular angles exceed 90% and the frequency variation is less than 0.7% at approximately 9.26 GHz up to a 70° incidence angle in both TM and TE polarization. We built the proposed absorber on a printed-circuit board with 20 × 20 unit cells, and we demonstrated its performance experimentally in free space. The measured absorptivity at 9.26 GHz for the specular angles is close to 98% for all polarization angles under normal incidence. As the incidence angle is varied from 0° to 70°, the measured absorptivity at 9.26 GHz for the specular angles remain above 92% in both TE and TM polarization.
Inkjet printing is an advanced printing technology that has been used to develop conducting layers, interconnects and other features on a variety of substrates. It is an additive manufacturing ...process that offers cost-effective, lightweight designs and simplifies the fabrication process with little effort. There is hardly sufficient research on tactile sensors and inkjet printing. Advancements in materials science and inkjet printing greatly facilitate the realization of sophisticated tactile sensors. Starting from the concept of capacitive sensing, a brief comparison of printing techniques, the essential requirements of inkjet-printing and the attractive features of state-of-the art inkjet-printed tactile sensors developed on diverse substrates (paper, polymer, glass and textile) are presented in this comprehensive review. Recent trends in inkjet-printed wearable/flexible and foldable tactile sensors are evaluated, paving the way for future research.
A novel pattern reconfigurable antenna is proposed to achieve two different radiation patterns by controlling the bias voltage of switches. Initially, the proposed antenna operates as a top-loaded ...monopole antenna fed by a co-planar waveguide (CPW). When the slot from the CPW is disturbed by switching on PIN diodes, it operates as a slot antenna. Therefore, when the switch turns on, the maximum radiation intensity occurs at the normal to the aperture surface defined as the boresight direction, which is similar to a slot antenna. When the switch turns off, the maximum radiation intensity occurs at right angles to the boresight direction, which is similar to a monopole antenna. The pattern reconfigurable capability is successfully demonstrated at 2.3 GHz by full-wave simulation and measurement.
Owing to the rapid growth in wireless data traffic, millimeter-wave (mm-wave) communications have shown tremendous promise and are considered an attractive technique in fifth-generation (5G) wireless ...communication systems. However, to design robust communication systems, it is important to understand the channel dynamics with respect to space and time at these frequencies. Millimeter-wave signals are highly susceptible to blocking, and they have communication limitations owing to their poor signal attenuation compared with microwave signals. Therefore, by employing highly directional antennas, co-channel interference to or from other systems can be alleviated using line-of-sight (LOS) propagation. Because of the ability to shape, switch, or scan the propagating beam, phased arrays play an important role in advanced wireless communication systems. Beam-switching, beam-scanning, and multibeam arrays can be realized at mm-wave frequencies using analog or digital system architectures. This review article presents state-of-the-art phased arrays for mm-wave mobile terminals (MSs) and base stations (BSs), with an emphasis on beamforming arrays. We also discuss challenges and strategies used to address unfavorable path loss and blockage issues related to mm-wave applications, which sets future directions.
Origami technology is promising for the development of antennas operating in the microwave and terahertz regime. This study summarizes recent advances in origami antennas and their construction ...regarding frequency, patterns, and polarization switching capabilities for the microwave frequency band. However, there are some challenges of origami antennas related to stability, robustness, and self-deployment, which should be addressed to design more practical deployable origami antennas in the microwave frequency band. In this review, we explained the design principle of various reconfigurable origami antenna. The dielectric and conductive materials of previous origami antennas are discussed and provided the promission materials to satisfy both easy transformation and high robustness for origami antennas. In addition, various actuators are discussed to pave the way for the practical application. Origami technology has also been employed for nanoscale antennas working in the terahertz and optical regime for several applications, including single molecule detection and artificial light harvesting. Although DNA molecules provide a scaffold for the origami antennas at nanoscale size, various issues require attention for development of more advanced nanoscale origami antennas in the terahertz regime. The most pressing issues are the high cost of DNA and the probability of high error rates in self-assembly fabrication.
Origami inspired antennas from microwave to terahertz regime. Display omitted
•This study summarizes the-state-of-the-arts of origami antennas from micro to nanoscale (terahertz regime)•We explored the opportunities and practical challenges for material selection and design of origami antennas•Potential solutions for the practical challenges are presented for future perspectives•A guideline is provided for the researchers to explore the origami technology for radiation applications
In this paper, we propose an angle- and polarization-insensitive metamaterial absorber. We design a metamaterial unit cell that is based on a split ring cross resonator (SRCR). We observe that the ...absorption frequency and absorption ratio are insensitive to incident angles when a via array surrounds the SRR. We demonstrate the effect of the via array using full-wave simulations by comparing the absorptivity of the SRCR with and without the via array. Because of the symmetric geometry, we also realize polarization insensitivity. We build the proposed absorber on a printed-circuit-board with 30 × 30 unit cells, and we demonstrate its performance experimentally in free space. Under normal incidence, the fabricated absorber shows 99.6% absorptivity at 11.3 GHz for all polarization angles, while for oblique incidence, the fabricated absorber maintains an absorptivity higher than 90% for incident angles up to 70° and 60° for transverse magnetic (TM) and transverse electric (TE) modes, respectively.
In this paper, a radio frequency (RF)-power-modulated active metamaterial loaded with a nonlinear Schottky diode is presented. Its operating mode is a function of the incident power level. It is ...switched by a change in the operating state (i.e., on/off) of the Schottky diode, which is directly triggered by a change in the incident power level. For instance, when a low-power RF radiation is incident on the proposed metamaterial, the Schottky diode is turned off, and the metamaterial passes a 2 GHz signal in the pass-band mode. By contrast, when a high RF power is incident, the diode is turned on, and the metamaterial reflects all frequencies in the reflection mode. The proposed active metamaterial was analysed by performing numerical simulations for both low- and high-power modes, and the proposed concept was successfully demonstrated by circuit analysis, full-wave simulation, and experimental results.
PDF
