Radio-frequency source localization becomes a major challenge for many applications such as beam-steering or MIMO communication. This task is commonly carried out by taking advantage of the adjustable radiation patterns of phased arrays to scan an area. Nevertheless, it can be difficult and expensive to implement in some frequency bands of the last generation of communication systems. Here, we propose an alternative based on a single port compact metamaterial antenna. We use a finite periodic array of sub-wavelength (λ/6) resonators for the design of this antenna. A microstrip line is added to excite the resonator array etched on a grounded low-loss substrate and to use it as a planar antenna. In such antenna system, the coupling between sub-wavelength resonators is able to induce a strong dispersion and leads to several complex radiation patterns over a specific narrow frequency band. We implement numerical methods to estimate the direction of a target antenna by taking benefits of the complex frequency signatures. We experimentally demonstrate that a single port sub-wavelength antenna made of a finite array of metamaterial resonators is able to retrieve the direction of a narrow band (3.6% relative bandwidth) emitting target around 5.5 GHz with a maximum precision of 3˚. Such a compact planar system (λ/3, λ/2 and 2λ/3) can be used to substitute the phased array localization technique in order to provide the necessary angular information in many applications such as mm-Wave communication and can be extended to high frequency regimes by using the corresponding resonators.
Synthetic aperture interferometric radiometer (SAIR) requires lots of antennas, receivers, and correlators to accurately reconstruct the brightness temperature (BT) distribution of the scene. Aiming to reduce the complexity of the hardware requirements in SAIR system while maintaining the image quality, a new optimal sparse reconstruction method is developed in this paper. Different from the existing imaging methods, the proposed method constructs the optimal receiving array with a few elements by evaluating the mutual coherence and the array factor of the sensing matrix in SAIR system, so as to achieve high-quality reconstruction of the BT image. Numerical simulations and experiments demonstrate that the proposed method can reconstruct the BT image by solely using a few receivers with higher image fidelity than the competing methods.
An efficient biochemical sensor for the detection of cholesterol concentration using 1-dimensional photonic crystal (1D-PhC) based cavity structure has been proposed in this paper. The structure comprises a 1-dimensional alternating dielectric photonic crystal designed as (A/B)2/Dd/(A/B)2 for measuring cholesterol concentration in blood, where `A' and `B' represent high and low refractive index materials, respectively. A cavity containing the cholesterol is inserted in the middle of the structure to assess its concentration. The transfer matrix method is used to analyze the reflection characteristics of the proposed multilayer structure. Sensitivity is analyzed by taking the difference in shifted resonant wavelength by infiltrating varying cholesterol concentrations ranging from 200 to 300 mg/dl. After rigorous optimization, it has been observed that the maximum sensitivity of 2.9 nm/(mg/dl) or 325 nm/RIU can be achieved.
We propose a transmission metasurface (TMS) with ultra-high polarization conversion properties and carrying orbital angular momentum (OAM) vortex waves based on Ku-band's unique periodic unit cell structure in Ku-band. The TMS periodic unit cell structure consists of four cascaded metal layers with parallel-stripe double-arrow and three dielectric layers. We theoretically explain the ultra-high polarization conversion properties of the periodic unit cell by introducing the Jones matrix. Meanwhile, the transmission loss of the periodic unit cell is less than 2.92 dB, and a phase shift of 2π is obtained in 17-19 GHz. We design OAM modes of ±1, ±2, and ±3 for 2π full-phase controlled TMSs by combining the multilayer cascade structure with the Pancharatnam-Berry (P-B) phase principle. The processed TMS produced a vortex wave with an OAM mode of +2 and achieved a polarization conversion rate (PCR) of 83.3% under left-hand circular polarization (LHCP) to right-hand circular polarization (RHCP) in agreement with the simulated and measured data. The results show that vortex waves also have the advantages of high efficiency, broadband, and high mode purity. The generated vortex waves are available for fast beam alignment, which is significant for unmanned aerial vehicles (UAVs) and satellite communications in the Ku band.
We propose an original and detailed investigation of a moving dielectric half-space with oblique plane wave incidence, by using the Finite Difference Time Domain (FDTD) method. In our FDTD program, movements are implemented by changing positions of the interfaces at different time instants, through the classical FDTD time loop. With this ``brute-force'' approach, time is implicitly absolute, and Voigt-Lorentz transformations are not implemented. This technique is suitable for non-relativistic electromagnetic problems with moving bodies, thus for most encountered electromagnetic problems. We analyze the transmitted and reflected waves, for different speeds, different refractive indices, and different incidence angles. Based on the obtained results, we derive several analytical formulas for the reflection coefficients, transmission coefficients, Doppler frequency shifts, and angles of transmission and reflection. These formulas are validated by full-wave electromagnetic simulations and are in agreement with the literature. The electric field distribution obtained at time instants is also studied.
A multi-band microstrip patch antenna consisting of an elliptical shape patch with four triangular-shaped arms mounted on a Rogers AD255C substrate with coaxial feed technique to cover 1720 MHz for 2G, 2120 MHz for 3G, 2372 MHz for 4G, and 3536 MHz for Sub-6 GHz 5G wireless communication applications is proposed in this paper. The antenna is designed by exciting a dominant & its orthogonal as well as higher order TMzmn0 modes based on cavity model-circular patch theory and then reshaped to an elliptical shape to get the resonance at desired bands. A Characteristics Mode Analysis (CMA) is used for computing electromagnetic resonance frequencies in conducting bodies. A radiating characteristic of the proposed antenna structure is analyzed and verified using CMA technique for target applications frequencies. The CMA demonstrates that the proposed antenna resonates at 1728 MHz, 2127 MHz, 2358 MHz, and 3436 MHz, making them suitable for use as multi-band antenna for 2G, 3G, 4G, and Sub-6 GHz 5G applications respectively after proper feeding. A simulated bandwidth at -10 dB return loss is 23 MHz (1707-1730 MHz) for 2G, 34 MHz (2104-2138 MHz) for 3G, 18 MHz (2364-2382 MHz) for 4G, and 67 MHz (3499-3566 MHz) for Sub-6 GHz 5G applications. The simulated peak gains are 6.29 dBi, 7.08 dBi, 4.51 dBi & 6.18 dBi which are validated by measured results at the respective resonant frequencies. An overall dimension of the proposed antenna is 100×100×3.175 mm3. The proposed antenna was simulated by CST Studio Suite 2020. Measurement was done for the fabricated antenna which shows good agreement with simulated ones. The proposed multi-band antenna with low complexity & easy design offers a quasi-omnidirectional radiation pattern and performance improvement.
The magnetically mediated thermoacoustic imaging with magnetic nanoparticles (MNPs), which is excited by nonuniform pulsed envelope magnetic field, is constructed here, and the results of the magnetic susceptibility distribution of nanoparticles are extracted. In this paper, the theoretical model of the nonuniform magnetic field based on space-time separation is solved, and the Rosensweig model is used to obtain the heat generation of MNPs under the excitation of the pulsed envelope magnetic field. To solve the inverse problem, the heat source distribution is calculated by the time inversion method according to the sound pressure propagation formula under adiabatic conditions. After filtering out the effect of the non-uniform magnetic field, the magnetic susceptibility distribution can be obtained. The reconstruction results from simulation and experiment are consistent with the original distribution of MNPs and the distribution of the magnetic susceptibility. This method is expected to be applied to the precise diagnosis and treatment of tumors and provide a new idea for the precise localization and distribution image reconstruction of nanoparticles in vivo.
Quantum-based systems are an emerging topic of research due to their potential for increasing performance in a variety of classical systems. In radar and communication systems, quantum technologies have been explored in an effort to increase the correlation performance in the low signal-to-noise ratio (SNR) regime. While this increase has been shown both mathematically and in the laboratory using bipartite states, systems utilizing multi-partite squeezing and entanglement may lead to an even further performance increase. We investigate this by analyzing the correlation coefficient for a tripartite system electric field measurement to determine how it compares to the bipartite systems in the current literature for the same transmit powers. This is done by defining a tripartite wave function in terms of the mean photon number per mode then determining the covariance matrix from this wave function. This work is important in understanding how alternative states of light can be used for quantum radar applications.
In this work, we have designed and fabricated a non-invasive flexible biosensor with a simple and printable structure for blood glucose monitoring. The proposed sensor has been experimentally proven to monitor blood sugar levels through frequency shifts. A cylindrical design with a coplanar waveguide (CPW) feeding technique has been proposed. A targeted frequency of 2.4 GHz with the best S11 at -22.623 dB and a bandwidth of 323 MHz was obtained. However, after propagating through the finger phantom, the signal is sensitive to the blood glucose levels with a significant frequency shift. The biosensor worked well at 1.55-1.88 GHz, representing a finger, without a phantom in the ISM band of 2.4 GHz. There is a bit of shifted frequency during the biosensor measurement with less than a 1.41% error. The overall size of the biosensor is 50.66 mm x 60.31 mm. The biosensor uses a flexible Dupont Pyralux substrate; thus, the index finger is easy to insert. 25 volunteers were involved in this experimental blood glucose. For this, we use an invasive device to measure the volunteers' blood glucose levels. The invasive measurement results obtained are used as a reference for the blood sugar levels of each sample. The test results using a cylindrical biosensor show a frequency shift at 7.5 MHz for every mg/dl of blood sugar levels, with a sensitivity of 0.43 1/(mg/dL). This frequency shift can be used to observe changes in the concentration of sugar levels in the blood. This flexible sensor is a good alternative biosensor for measuring blood glucose levels due to its low cost and printable structure.
We study three comb-line antennas to increase the bandwidth for a 3 dB axial ratio criterion. Each antenna comprises linear radiation elements with loops and a coplanar feedline above the ground plane. First, we analyze a reference antenna with a straight feedline using the method of moments. Next, the straight feedline is transformed into a round one for a sequential rotation technique. It is found that the antenna has an increased bandwidth of 30%, which is three times as wide as that of the reference antenna. Last, we propose a novel antenna with a straight feedline. It is revealed that the antenna shows a 3 dB gain drop bandwidth of 29% (40% for the axial ratio bandwidth). The simulated results are validated by experimental work.
In this manuscript, a miniaturized Multi-Input Multi-Output (MIMO) antenna with dual-notch characteristics is designed for Ultra-Wideband (UWB) indoor positioning system. The proposed UWB MIMO antenna has a compact size of 35*35 mm2 with four orthogonally placed antenna elements on the print circuit board (PCB) with FR4. Each radiating element utilizes the combination of a rectangle and an irregular pentagon, and etches two inverted L-shaped slits to generate two notches in WLAN (5.00 GHz-5.82 GHz) and X-band (7.11 GHz-8.20 GHz). On the grounding planes, the rectangle grounding units are modified into L-shaped branches, on which stepped open-circuit slots and right-angled triangle truncations are etched to broaden the impedance bandwidth. Furthermore, three equidistant rectangular decoupling slits are etched to improve the isolation. The measured results are in good agreement with the simulated ones, which shows an impedance bandwidth of 116.68% (2.96-11.25 GHz) with isolation better than 17 dB. The antenna also has excellent characteristics of good radiation characteristics, total active reflection coefficient (TARC), diversity gain (DG>9.99), low envelope correlation coefficient (ECC<0.005) and channel capacity loss (CCL<0.4 bits/sec/Hz), which can be used in portable UWB-MIMO indoor positioning system.
A new technique to reduce the mutual coupling between closely-spaced, single-layered patch antenna elements is presented. The proposed design comprises an integrated novel decoupling structure to generate an out-of-phase decoupling signal to effectively lower the coupling between the elements. In addition, coplanar L-probes and interdigital filter shaped slits on the ground plane are incorporated to further improve the isolation. The realized isolation level is about 28 dB at the frequency of operation. This is a significant achievement for a single-layered low-profile structure, wherein the center-to-center element spacing is only around 0.25λ0, and more importantly, no shorting vias are used.
On the basis of artificial magnetic conductors (AMCs), a dual-band MIMO antenna is suggested. For WBAN and WLAN applications, the frequency ranges supported by this antenna system are 2.36-2.51 GHz and 5.03-6.12 GHz. The proposed dual-band MIMO antenna is made up of two vertically positioned dipole antenna elements. A simple double circle-based AMC array is suggested to decrease radiation exposure to people while increasing forward gain. The antenna and the 3×3 AMC array are both printed on an FR4 substrate. The presented antenna with the AMC structure is manufactured and measured in order to confirm the simulated results in terms of S-parameters, radiation patterns, gain, and diversity parameters. According to the measurements, the suggested antenna exhibits peak gains of 3.34 dBi and 7.48 dBi at 2.45 GHz and 5.8 GHz, respectively. The SAR value of body tissue can be reduced by around 99% while the front-to-back ratio (FBR) is noticeably enhanced. The proposed AMC-supported MIMO antenna is applicable for WBAN and WLAN applications based on the above good performances.
Within the framework of the first-order small perturbation method, we derive the statistics of the layered rough surface index and the normalized difference polarization index for three-dimensional layered structure with slightly rough interfaces illuminated by a monochromatic plane wave and for multilook returns. We establish closed-form expressions for the probability density function and the cumulative distribution function. The first- and second-order moments are given by relation recurrences. We validate from Monte Carlo simulations the obtained theoretical formulas.
This paper presents a proposal for a high birefringμeμnce photonic crystal fiber (C-PCF) with a doped liquid into two first ring holes, which is analyzed by the finite element method. It is demonstrated that the proposed fiber has a birefringence value of about 2.643 × 10-2 at wavelength λ = 1.55 µm and temperature T = 25˚C. Also, a high chromatic dispersion of -272 ps/nm/km, an effective area of 1.693 µm2, and a confinement loss of 0.058 dB/m for the x-polarization method were obtained at the same wavelength and temperature. The temperature influence on the modal properties has also been studied. We will demonstrate through the result that the fiber we propose can be used in both sensing and chromatic dispersion applications such as flattened dispersion fibers.
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