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This paper proposed a compact, high-sensitive S-band microwave sensor for low permittivity characterization. The proposed microwave sensor is inspired by a metamaterials-based maze-shaped split-ring resonator (MS-SRR) configuration, and its overall dimensions are 25 mm × 20 mm × 0.79 mm. The unloaded state of the proposed sensor achieved two robust band-stop notches in its transmission response at 2.77 GHz and 3.08 GHz, respectively. These distinctive features enable the real-time measurement of permittivity in low-permittivity materials. The MS-SRR configuration accomplished strong electric-field intensity, which increased the interaction between the field and testing material, resulting in a highly sensitive measurement. A sensitivity of 11.91% is observed for the first resonance peak and 12.01% for the second peak within the permittivity range from 1 to 2.0. Moreover, the proposed sensor is also competent in measuring the permittivity range between 3 and 10 with a sensitivity of 9.47%–4.93% for the first peak and 9.57%–4.83% for the second peak. The resonance frequency shifting by the influence of material under test (MUT) is presented as a function of permittivity using a regression model. The simulated, measured and formulated results agree well. Finally, the proposed compact and high-sensitive microwave sensor holds promise for low permittivity characterization applications.

Akses terhadap air bersih dan aman sangat penting untuk menjaga kehidupan, mendukung ekosistem, dan meningkatkan kesejahteraan manusia. Namun, sumber-sumber air di seluruh dunia semakin terancam oleh polusi, aktivitas industri, dan perubahan lingkungan. Pemantauan kualitas air secara real-time menjadi sangat penting untuk memastikan ketersediaan air minum yang aman dan melindungi lingkungan perairan. Penelitian ini bertujuan untuk merancang alat yang mampu secara real-time memantau kondisi air di proyek WESLIC dengan menggunakan teknologi Internet of Things (IoT). Alat ini menggunakan sensor pH-4502C untuk mengukur tingkat keasaman dan kebasaan air, dan data kemudian dikirim ke platform Internet of Things (IoT) melalui perangkat ESP8266. Data ini dapat diakses melalui web atau smartphone. Hasil dari penelitian ini adalah sebuah alat yang mampu memantau nilai pH air menggunakan sensor pH-4502C dan menampilkan data melalui aplikasi Blynk. Hasil perbandingan antara nilai sensor pH meter analog dan pH meter digital menunjukkan perbedaan yang tidak signifikan. Analisis hasil pengujian menghasilkan rata-rata presentasi kesalahan sebesar 1,79%, dengan tingkat akurasi sensor pH sebesar 98,21%. Hal ini menunjukkan bahwa sensor pH berfungsi dengan baik dan dapat melakukan pemantauan melalui aplikasi Blynk, dengan mengirimkan pemberitahuan jika pH air berada di bawah 6 atau di atas 8. Hasil pemantauan dapat divisualisasikan melalui aplikasi Blynk pada smartphone

AbstractThis article presents a wideband metamaterial absorber (WMMA) for the visible and near-infrared (NIR) region application. The proposed metamaterial absorber comprises three layers of sandwiched (metal-dielectric-metal) model based on Nickel-Polyamide-Nickel. The multiple resonators on top layers achieve an average absorption of 98.16% over a range from 380 to 2300 nm with a compact unit cell size of 100 × 100 × 42 nm3. The designed WMMA shows 99% perfect absorption for a large bandwidth of 685 nm. Considering its wideband absorption, the physical absorption phenomenon was also explained in terms of the proposed WMMA's surface electric field, magnetic field, and current distribution. Also, the effects of materials and structural parameters on absorption performance with a FOM have been studied. The absorption performance is analysed with various polarization angles to demonstrate polarization insensitivity. The designed WMMA shows the absorption of >70% at large incident angles of 70°. The perceptible contribution of this WMMA is large unity absorption bandwidth at visible to NIR region with high incident angle stability, polarisation insensitivity, thermal robustness of the constituting metal and simple nanostructure geometry. Therefore, the proposed WMMA has good potential in sensors, thermal emitters, photodetectors, and absorber applications.

This article proposed a labyrinth shape circular split ring resonator (LC-SRR) based microwave sensor for material permittivity characterization at L to S-band applications. The proposed sensor achieved miniaturized dimensions of only 25 × 20 mm2 by utilizing fractal technology. This new design strategy adopts a unique and compact structure and high electromagnetic (EM) field intensity, contributing to a more precise sensing mechanism in the microwave frequency range. The design geometry achieved resonant frequency at 2.57 GHz with a notch depth of −29.5 dB. The design evolution, metamaterial characteristics, equivalent circuit model, and electric (E) and magnetic (H) fields are presented to understand the stopband characteristics at the resonant frequency. A high sensitivity of 10.50 % is achieved for the proposed sensor for the permittivity range from 1 to 2. The reflection and transmission characteristics of the proposed LC-SRR based sensor are validated by fabricating and measuring the prototype. Moreover, the sensor performance is validated using different dielectric materials (Roger RT5880, Roger RO4350B, and FR-4) The measurement results show consistency with simulation results. Finally, the miniaturized low-profile sensor structure and high sensitivity to characterize the permittivity of the material makes the proposed sensor suitable for low-permittivity sensing applications.

The purpose of this study is to investigate the impact of military expenditure on unemployment in Bangladesh, examining the cointegration among unemployment, military expenditure, and foreign direct investment. It also sheds light on the short and longrun dynamics of the variables under consideration. The study employs the ARDL bounds testing approach to investigate the cointegration among the variables using time series annual data from the period of 1990-2018. The dependant variable is unemployment and military expenditure and FDI are the independent variables. Thisresearch found a long run relationship among the variables. An increase in military expenditure significantly reduces unemployment in the short run, however, no significant long-run relationship is found. The higher FDI, the higher unemployment in the long run. This study contributes to fill the research gap regarding theimpact of military expenditure and FDI on unemployment. To the best of our knowledge, this is the first study to examine the relationship among unemployment, military expenditure and FDI in Bangladesh using ARDL bounds testing approach with time series annual data.

The secrecy performance of realistic wireless multicast scenarios can be significantly deteriorated by the simultaneous occurrence of multipath and shadowing. To resolve this security threat, in this work an opportunistic relaying-based dual-hop wireless multicast framework is proposed in which the source dispatches confidential information to a bunch of receivers via intermediate relays under the wiretapping attempts of multiple eavesdroppers. Two scenarios, i.e. non-line of sight (NLOS) and line of sight (LOS) communications along with the multiplicative and LOS shadowing are considered where the first scenario assumes $\eta -\mu $ and $\eta -\mu $ /inverse Gamma (IG) composite fading channels and the latter one follows $\kappa -\mu $ and $\kappa -\mu $ /IG composite fading channels as the source to relay and relay to receiver’s as well as eavesdropper’s links, respectively. Secrecy analysis is accomplished by deriving closed-form expressions of three familiar secrecy measures i.e. secure outage probability for multicasting, probability of non-zero secrecy multicast capacity, and ergodic secrecy multicast capacity. We further capitalize on those expressions to observe the effects of all system parameters which are again corroborated via Monte-Carlo simulations. Our observations indicate that a secrecy tradeoff between the number of relays and number of receivers, eavesdroppers, and shadowing parameters can be established to maintain the admissible security level by decreasing the detrimental influences of fading, shadowing, the number of multicast receivers and eavesdroppers.

This article presents numerical analysis of an ultrathin concentric hexagonal ring resonator (CHRR) metamaterial absorber (MMA) for ultrawideband visible and infrared optical window applications. The proposed MMA exhibits an absorption of above 90% from 380 to 2500 nm and an average absorbance of 96.64% at entire operational bandwidth with a compact unit cell size of 66 × 66 nm2. The designed MMA shows maximum absorption of 99% at 618 nm. The absorption bandwidth of the MMA covers the entire visible and infrared optical windows. The nickel material has been used to design the top and bottom layer of MMA, where aluminium nitride (AlN) has been used as the substrate. The designed hexagonal MMA shows polarization-independent properties due to the symmetry of the design and a stable absorption label is also achieved for oblique incident angles up to 70 °C. The absorption property of hexagonal ring resonator MMA has been analyzed by design evaluation, parametric and various material investigations. The metamaterial property, surface current allocation, magnetic field and electric field have also been analyzed to explore the absorption properties. The proposed MMA has promising prospects in numerous applications like infrared detection, solar cells, gas detection sensors, imaging, etc.