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A novel and simple six-band metamaterial absorber is proposed in the terahertz region, which is composed of an I-shaped absorber and circular ring with four gaps and a continuous metal ground plane separated by only 0.125 mm polyimide dielectric substrate. Initially, I-shaped resonator gives three bands at 0.4, 0.468 and 0.4928 THz with the absorptivity of 99.3%, 97.9% and 99.1%, respectively. The purpose of this paper is to improve the number of bands, for which the authors added the circular ring with four gaps, so the simulated metamaterial absorber exhibited six absorption peaks at 0.3392, 0.3528, 0.3968, 0.4676, 0.4768 and 0.492 THz, with the absorption rate of 91.4%, 94.2%, 94.9%, 90.3%, 77.5% and 97.4%, respectively. The surface current distribution and angle independence are explained for all the six frequencies which are used to analyze the absorption mechanism clearly. Structure maximum uses the squares and circles, so it will make the fabrication easy. The multiband absorbers obtained here have potential applications in many engineering technology, thermal radiation, material detection and imaging and optoelectronic areas.

This paper presents the design of the six-band metamaterial absorber which is from the I-shaped resonator and circular ring with four gaps and the metallic ground plane separated by the 0.125 polyimide dielectric substrate. The absorber exhibited six absorption peaks at 0.3392, 0.3528, 0.3968, 0.4676, 0.4768 and 0.492 THz, with the absorption rate of 91.4%, 94.2%, 94.9%, 90.3%, 77.5% and 97.4%, respectively. From the fabrication point of view, the proposed six-band metamaterial absorber has a very simple geometrical structure, and it is very easy to be fabricated.

The authors present a new and simple design of six-band absorber based on an I-shaped absorber and circular ring with four gaps and a metallic ground plane separated by a polyimide layer having the thickness of 0.125 mm. Six different resonance absorption peaks are found at 0.3392, 0.3528, 0.3968, 0.4676 , 0.4768 and 0.492 THz. Surface current distribution and angle independence plot have been studied to understand the absorption behavior of the designed terahertz metamaterial absorber.

The multiband absorbers obtained here have potential applications in many engineering technology, thermal radiation, material detection, security, sensors, imaging and optoelectronic areas.

The purpose of this paper is to present the design of a piezoelectric vibration energy generator with a power conditioning circuit to power a wireless sensor node. Frequency and voltage characterization of the piezoelectric energy harvester is performed. A single-stage AC–DC power converter that integrates the rectification and boosting circuit is designed, simulated and implemented in hardware.

The designed power conditioning circuit incorporates bridgeless boost rectification, a lithium ion battery as an energy storage unit and voltage regulation to extract maximum power from PZT-5H and to attain higher efficiency. The sensor node is modelled in active and sleep states on the basis of the power consumption. Dynamic modelling of the lithium ion battery with its state of charging and discharging is analysed.

The test result shows that the energy harvester produces a maximum power of 65.9 mW at the resonant frequency of 21.4 Hz. The designed circuit will operate even at a minimum input voltage of 0.5 V. The output from the harvester is rectified, boosted to a 7-V DC output and regulated to 3.3 V to the power C_Mote wireless sensor node. The conversion efficiency of the circuit is improved to 70.03 per cent with a reduced loss of 19.76 mW.

The performance of the energy harvester and the single-stage power conditioning circuit is analysed. Further, the design and implementation of the proposed circuit lead to an improved conversion efficiency of 70.03 per cent with a reduced loss of 19.76 mW. The vibration energy harvester is integrated with a power conditioning circuit to power a wireless sensor node C_Mote. The piezoelectric vibration energy harvester is implemented in real time to power C_Mote.

A novel low profile frequency selective surface (FSS) with a band-stop response at 10 GHz is demonstrated. The purpose of this designed FSS structure is to reject the X-band (8-12 GHz) for the application of shielding. The proposed FSS structure having the unit cell dimension of 8 × 8 mm², the miniaturization of the FSS unit cell in terms of λ₀ is 0.266 λ₀ × 0.266 λ₀, where λ₀ is free space wavelength. The designed FSS provides 4 GHz bandwidth with insertion loss of 15 dB. The transverse electric (TE) and transverse magnetic (TM) modes of the proposed design are same because of polarization independent characteristics and hold the angularly stable frequency response for both TE and TM mode polarization. Both the simulation and measurement results are in good agreement to each other.

The proposed FSS design contains square-shaped PEC material, which is placed on the substrate and the shape of the circle and rectangle is etched over the PEC material. The PEC material of the patch dimension is 0.0175 mm. The substrate used for the proposed design is FR4 lossy with the thickness of 0.8 mm and permittivity εr = 4.3 having a loss tangent of 0.02.

To find a new design and miniaturized FSS structure is discussed.

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The purpose of this paper is to fabricate an ethanol sensor which has bio-friendly and eco-friendly properties compared to the commercially available ethanol sensors.

This paper describes the construction of a highly sensitive ethanol sensor with low ppm level detection at room temperature by integrating three techniques. The first deals with the formation of organic/inorganic p-n heterojunction. Second, tuning of structural parameters such as length, diameter and density of Zinc Oxide (ZnO) nanostructure was achieved through introduction of the Fe dopant into a pure ZnO seed layer. Furthermore, ultra-violet (UV) light photoactivation approach was used for enhancing the sensing performance of the fabricated sensors. Four different sensors were fabricated by combing the above approaches. The structural, morphological, optical and material compositions were characterized using different characterization techniques. Sensing behavior of the fabricated sensors toward ethanol was experimented at room temperature with and without UV illumination combined with stability studies. It was observed that all the fabricated sensors showed enhanced sensing performance for 10 ppm of ethanol. In specific, FNZ (Fe-doped ZnO seeded Ni-doped Zn nanorods) sensor exhibited a higher response at 2.2 and 13.5 s for 5 ppm and 100 ppm of ethanol with UV light illumination at room temperature, respectively. The photoactivated FNZ sensor showed quick response and speedy recovery at 18 and 30 s, respectively, for 100 ppm ethanol.

In this study, the authors have experimentally analyzed the effect of Fe (in ZnO seed layer and ZnO NRs) and Ni (in ZnO NRs) dopants in the room temperature sensing performance (with and without UV light) of the fabricated ethanol sensors. Important sensing parameters like sensitivity, recovery and response time of all the fabricated sensors are reported.

The Fe doped ZnO seeded Ni doped Zn nanorods (FNZ sample) showed a higher response at 2.2 s and 13.5 s for very low 5 ppm and 10 ppm of ethanol at room temperature under UV light illumination when compared to the other fabricated sensors in this paper. Similarly, this sensor also had quick response (18 s) and speedy recovery (30 s) for 100 ppm ethanol.

This paper aims to propose a laser micro-machined 4 × 4 elements microstrip array antenna suitable for 5 G millimeter wave (mm-wave) applications. Each patch element of the array is excited with same amplitude and phase that is achieved with proper novel impedance matching stub. The proposed antenna achieves a simulated gain of 13.15 dBi and a measured return loss of −24.80 dB at 28.73 GHz with a total bandwidth of 7.48 GHz. The designed antenna is directional with a directivity of 15.1 dBi at 28.73 GHz, whereas fabricated on a low cost FR4 substrate with a substrate thickness of 0.074 λ mm. The antenna is realized with an aperture size of 2.24λ × 3.26λ.

The antenna structure starts from the design of single element called unit cell. The single element is designed using the transmission line model equations of a rectangular patch. To design a 28 GHz microstrip patch antenna, a dielectric material with lower permittivity and having thickness (h) less than 1 mm is required. This specification gives better gain and efficiency by reducing surface waves and mutual coupling between elements. The inset width is optimized to achieve the minimum reflection coefficient (S11). The single element has been arranged with a minimum spacing of λ/2 (5.3571 mm) in an H plane and E plane. It is connected using the microstrip lines with proper impedance matching. The four 2 × 2-sub array cell subsystems are connected with a corporate feed together formed the 4 × 4-array cell. Rectangular planar array method is used to arrange the elements in the 4 × 4 array cell.

The design concept is simple which includes the combination of corporate feed and insect feed. It is compact in size and easy to fabricate. The bandwidth of fabricated prototype antenna array is achieved as 7.48 GHz from 24.98 GHz to 32.46 GHz. The mutual coupling is very less though the antenna array is placed with minimum spacing between adjacent elements. This is because of the microstrip feeding structure with minimum phase shift. The gain can be further enhanced with increasing number of array element and proper designing of feed line. Owing to the advantages of low profile, wide bandwidth and high gain, the designed array will be potentially useful in 5 G wireless communications.

The measured antenna offers bandwidth 7.48 GHz (24.98 GHz-32.46 GHz) with centered frequency 28.73 GHz. The agreement between simulated and measured results is good. The VSWR is observed 0.32 < 2, offers good impedance matching and low mutual coupling. It gives better E-Field and H-field radiation patterns of the 4 × 4 array antenna structure at 28 GHz. The total gain of 13.14 dBi is achieved at the center frequency. The total efficiency of 63.42 per cent is achieved with FR4 substrate.

This paper aims to present the design of a cantilever beam with various kinds of geometries for application in energy harvesting devices with a view to enhance the harvested power. The cantilever beams in rectangular, triangular and trapezoidal geometries are simulated, designed and evaluated experimentally. A power conditioning circuit is designed and fabricated for rectification and regulation.

The analytical model based on Euler–Bernoulli beam theory is analyzed for various cantilever geometries. The aluminum beam with Lead Zirconate Titanate (PZT) 5H strip is used for performing frequency, displacement, strain distribution, stress and potential analysis. A comparative analysis is done based on the estimated performance of the cantilevers with different topologies of 4,500 mm³ volume.

The analysis shows the trapezoidal cantilever yielding a maximum voltage of 66.13 V at 30 Hz. It exhibits maximum power density of 171.29 W/mm³ at optimal resistive load of 330 kΩ. The generated power of 770.8 µW is used to power up a C-mote wireless sensor network.

This study provides a complete structural analysis and implementation of the cantilever for energy harvesting application, integration of power conditioning circuit with the energy harvester and evaluation of the designed cantilevers under various performance metrics.

The purpose of this paper is to propose a miniaturized tri-band bandstop filter that finds application in a modern dense communication system where size and multi-band plays a vital role.

In this paper, the authors propose a miniaturized tri-band microstrip bandstop filter which combines the conventional bandstop filter and spur microstrip line structures such that this design achieves tri-band operation at 1.8 GHz and 3 GHz. The overall length of the microstrip filter is found to reduce from 126 to 45 mm because of introduction of spur lines and via-hole grounding. The addition of spur lines replaces two resonators, introduces two additional resonant frequencies and enhances the −6 dB bandwidth of the center frequency by 14 %.The addition of via-holes in each resonator reduces its length into half of its original length, thereby reducing filter size.

Resonance occurs at three different frequencies 1.8, 2.4 and 3 GHz. The filter size reduces from 126 to 45 mm, and the −6 dB rejection bandwidth of center frequency improves by 14 %.

The overall filter size is reduced by 65% and it resonates at three different frequencies 1.8, 2.4 and 3 GHz with an improved bandwidth of 10 % around the center frequency.

Various approaches have been made to alter the vibration sensing properties of zinc oxide (ZnO) films to achieve high sensitivity. This paper aims to report the experimental study of the fabrication of precursor molar ratio concentration varied ZnO nanostructures grown on rigid substrates using the refresh hydrothermal method. The effect of these fabricated ZnO nanostructures-based vibration sensors was experimentally investigated using a vibration sensing setup.

ZnO nanostructures have been grown using low temperature assisted refresh hydrothermal method with different precursor molar concentrations 0.025 M (R1), 0.075 M (R2) and 0.125 M (R3). Poly 3,4-ethylenedioxythiophene polystyrene sulfonate, a p-type material is spun coated on the grown ZnO nanostructures. Structural analysis reveals the increased intensity of the (002) plane and better c-axis orientation of the R2 and R3 sample comparatively. Morphological examination shows the changes in the grown nanostructures upon increasing the precursor molar concentration. The optical band gap value decreases from 3.11 eV to 3.08 eV as the precursor molar concentration is increased. Photoconductivity study confirms the formation of a p-n junction with less turn-on voltage for all the fabricated devices. A less internal resistance of 0.37 kΩ was obtained from Nyquist analysis for R2 compared with the other two fabricated samples. Vibration testing experimentation showed an improved output voltage of the R2 sample (2.61 V at 9 Hz resonant frequency and 2.90 V for 1 g acceleration) comparatively. This also gave an increased sensitivity of 4.68 V/g confirming its better performance when compared to the other fabricated two samples.

Photoconductivity study confirms the formation of a p-n junction with less turn-on voltage for all the fabricated devices. A less internal resistance of 0.37 kΩ was calculated from the Nyquist plot. Vibration testing experimentation proves an increased sensitivity of 4.68 V/g confirming its better performance when compared to the other fabricated two samples.

Vibration testing experimentation proves an increased sensitivity of 4.68 V/g for R2 confirming its better performance when compared to the other fabricated two samples.

The proposed metamaterial absorber (MMA) has the following advantages: first, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is indium tin oxide (ITO)-Polyimide-ITO, ITO-Teflon-ITO and ITO-polyethylene terephthalate (PET)-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.

This absorption device consists of the top circular resonator, the middle insulating SiO₂ medium layer and the bottom metallic copper ground plane placed on a substrate. The conductivity of the copper metal is s = 5.8 × 10⁷ s/m. As the transmission of the MMA structure is zero, the substrate materials can be selected randomly. Totally four combinations of terahertz MMA are designed and simulated here which are ITO- SiO₂ –ITO, ITO-Polyimide-ITO, ITO-Teflon-ITO and ITO- PET-ITO for the same planar structure.

Compared with previous MMAs, the proposed MMA has the following advantages: First, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is ITO-polyimide-ITO, ITO-Teflon-ITO and ITO- PET-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.

First, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is ITO-polyimide-ITO, ITO-Teflon-ITO and ITO-PET-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.

The proposed structure consists of copper as a ground plane and 50 µm polyimide dielectric layer is placed in between the ground panel and top radiating patch. Octagon and pentagon shapes are combined to form a unit cell. This structure exhibits seven absorption peaks within the short frequency range 0.3–0.5 terahertz (THz) without any interference. Under normal incidence, this structure achieves the absorption of 96.9%, 95.3%, 98.7%, 91.7%, 96.5%, 95% and 97.8% at 0.3136 THz, 0.377 THz, 0.4060 THz, 0.4085 THz, 0.4240 THz, 0.4436 THz and 0.4648 THz, respectively. This study aims to provide a range of applications in THz dielectric sensing, thickness sensing, communications, wavelength selective radiation and detecting.

Multi-band THz metamaterial absorbers (MMA) from previous research are having a large unit size because of the presence of stacked layers and multiple resonators within a single unit cell. This leads to difficulty while implementing in practical applications. In this study, a new MMA has been presented at seven distinct frequencies without using stacked layers and multiple resonators.

This structure exhibits seven absorption peaks within the short frequency range 0.3–0.5 THz without any interference. Under normal incidence this structure achieves the absorption of 96.9%, 95.3%, 98.7%, 91.7%, 96.5%, 95% and 97.8% at 0.3136 THz, 0.377 THz, 0.4060 THz, 0.4085 THz, 0.4240 THz, 0.4436 THz and 0.4648 THz, respectively. The polarization and angle insensitivity of the design have been validated by numerical simulation up to 90° of oblique incidence. The effects of variation in geometrical parameters on absorption response are demonstrated. The physical mechanism of the structure is analysed by electric and magnetic field distributions. The resonant frequency ranges and the number of bands in this work are compared with previously reported papers. In THz range, this is the first time a single planar structure provides seven-band high-level absorption performance.

The highlights of the proposed seven-band THz MMA structure, in comparison with previous THz metamaterials, are as follows: this has a simple unit-cell structure and high resonant mechanism within the short frequency range 0.3–0.5 THz; this MMA can provide seven-band high-level absorption performance in a single planar structure for the first time in THz range; and this structure is polarization and incident angle independent in nature.