Variation Of Refractive Index Research Articles

Linear and Nonlinear Optical Characteristics of Basic Fuchsin-Doped Polyvinyl Alcohol Films for Flexible Optoelectronics

Abstract Polyvinyl alcohol (PVA) containing different levels of basic fuchsine (BF) was prepared using the solution casting method. Characterization via Fourier-transform infrared spectroscopy detailed changes in functional groups within the PVA/BF composites, indicates the hydrogen bonding between OH group of PVA and BF molecules. Optical investigations spanning the 190-2500 nm range demonstrated UV blocking properties in prepared PVA/BF composites (fromn 2.05 to 2.56 eV and from 4.08 to 6.32 eV). Moreover, the studies on optical band gap indicated a decrease with increased BF concentrations, reflecting altered electronic transitions within the prepared composites. The study also employed the single oscillator model provided by Wemple-DiDomenico to elucidate refractive index variations. After incorporating BF dye into the PVA polymer, the values of the dielectric constant as the frequency approaches infinity (ε∞), the dielectric constant of lattice (εL), dispersion energy (Ed), and oscillator energy (Eo) in PVA/BF composite samples showed an increase. Moreover, the nonlinear optical properties, including optical susceptibility and nonlinear refractive index were investigated and discussed. These findings underscore the versatility of PVA doped with BF for various applications including optical filters, and solar cell devices.

Design and simulation of a highly sensitive photonic crystal fiber sensor for malaria detection

This research focuses on developing an innovative optical sensor utilizing photonic crystal fiber with a unique cladding structure. The photonic crystal fiber’s cladding consists of four layers of circular air holes, with two of them filled with hemoglobin. This arrangement renders the photonic crystal fiber sensitive to changes in hemoglobin concentration, primarily investigating its impact on chromatic dispersion – the wavelength-dependent refractive index variation. The study analyzes two specific wavelengths, 1.2 µm and 1.4 µm, finding high sensitivity at 1.2 µm, calculated to be 0.232 ps/(nm·km)/(g/L). The potential application lies in malaria diagnosis through non-invasive blood sample analysis. We selected the refractive index of an infected red blood cell at the ring stage, setting it at n = 1.395. Our proposed sensor demonstrates outstanding performance in diagnosing malaria at an HGB concentration of 38 g/L at 1.2 µm and at an HGB concentration of 40 g/L at 1.4 µm. By monitoring hemoglobin concentration changes, this photonic crystal fiber-based sensor offers a promising method for early and accurate malaria detection, thus potentially improving global healthcare.

Surface Plasmon Resonance Sensor with 2D Materials for Enhanced Refractive Index Detection of Chemical Pollutants in Seawater

This paper introduces a highly sensitive, graphene-based, multilayer surface plasmon resonance (SPR) refractive index sensor is designed for the detection of chemical pollutants in seawater. The sensor structure consists of multiple layers, specifically BK7 glass, Chromium (Cr), Copper (Cu), MXene, and Graphene. SPR sensors have gained significant attention in the field of real-time chemical sensing due to their label-free detection capabilities, high sensitivity, and excellent reproducibility. In this sensor design, the refractive index (RI) of the sensing region is altered by the interaction of chemical pollutants present in the seawater. These variations in RI directly affect the excitation of surface plasmon polaritons (SPPs) at the multilayer sensor interface. This interaction forms the basis for detecting chemical pollutants, as changes in RI modulate the sensor's optical response, which can be accurately measured. The performance of the proposed sensor is thoroughly evaluated using numerical simulations based on the Transfer Matrix Method (TMM). The simulations are carried out over a refractive index range of 1.329 to 1.433, covering the typical RI variations caused by chemical pollutants in seawater. The sensor demonstrated exceptional performance, achieving a maximum sensitivity of 186deg/RIU at an operational wavelength of 633nm. Additionally, the sensor is exhibited a high detection accuracy (DA) of 1.5deg⁻¹ and a figure of merit (FOM) of 205 RIU⁻¹, highlighting its ability to precisely distinguish small changes in refractive index. These results emphasize the potential of this graphene-based SPR sensor configuration for high-performance detection of chemical pollutants, making it an excellent candidate for environmental monitoring applications. Its robust design, combined with its high sensitivity and accuracy, positions it as a promising solution for addressing challenges in seawater pollution detection and monitoring.

Design and analysis of high-sensitivity hormone sensor with KNN behavior prediction for healthcare and biomedical applications

This study presents an advanced sensor system integrating gold metasurfaces with graphene for the detection of reproductive hormones via refractive index variations. The proposed design operates under terahertz (THz) excitation to exploit the unique molecular signatures of hormones and minimize potential interferences. Comprehensive numerical analysis and finite element method (FEM) simulations were conducted to optimize the sensor’s design parameters and evaluate its efficacy. The optimized sensor exhibits exceptional performance metrics, including a peak sensitivity of 375 GHzRIU−1, a figure of merit (FOM) of 7.693 RIU−1, a quality factor (Q) of 2.381, and a limit of detection (LOD) of 0.556 RIU. Furthermore, the sensor demonstrates two-bit encoding capabilities through modulation of graphene’s chemical potential. Integration of a K-Nearest Neighbors (KNN) Regressor model enhances the sensor’s accuracy while reducing required resources and simulation time by approximately 85 %. These findings demonstrate the sensor’s potential for diverse applications, particularly in the biomedical field.

An Mach-Zehnder interferometer refractive index sensor based on self-phase modulation effect in a tapered double-cladding highly nonlinear fiber

An Mach-Zehnder interferometer (MZI) sensor based on self-phase modulation (SPM) effect in a tapered double-cladding highly nonlinear fiber (DCHNLF) was proposed and experimentally verified for refractive index (RI) measurement. The DCHNLF was tapered and the SPM spectrum generated in its untapered region acted as the broadband light source for the sensor. The integration of the SPM effect and the RI detection not only simplified the structure of the sensor, but also enhanced its long-term stability and reliability. Since the effective RI of the outer cladding mode of the tapered DCHNLF was affected by the RI variation, a spectral shift would occur in interference spectrum between the core mode and the outer cladding mode. The tapering treatment enhanced the evanescent wave on the surface of DCHNLF, making the sensor more sensitive to external RI. In the external RI range of 1.3333 ∼ 1.3972, the sensor achieved an excellent sensitivity of 238.51 nm/RIU. In addition, the effect of average pump power and pump wavelength on the sensor performance were experimentally discussed. The results showed that the sensitivity was not affected by the pump condition. This MZI RI sensor has advantages of excellent performance, simple structure and easy fabrication, demonstrating broad application prospects in biomedical research, marine environment monitoring, and human health detection.

Influencing factors of self-aligned imaging in near-field lithography for the Fabry–Perot cavity effect

In near-field lithography, the Fabry–Perot (F-P) cavity enhancement effect can significantly improve image quality and resolution. This paper considers changes in the refractive index and air distance in self-aligned imaging. Simulation results demonstrate that the Fabry–Perot resonator effect achieves effective self-alignment in 3D imaging. The proposed structure builds on traditional near-field imaging structures and F-P resonator research, suggesting a Cu/SiO2 structure as the front layer. Rigorous coupled wave analysis (RCWA), finite element method (FEM), and finite-difference time-domain (FDTD) methods were employed to verify the self-alignment effect on single gratings and rectangular hole arrays. The results indicate that the self-alignment lithography method based on the F-P effect not only enhances lithography contrast and normalized image log-slope (NILS) but also shows robust performance against variations in air distance and complex refractive index. Notably, for the rectangular aperture array structure, with changes in air distance and complex refractive index within a certain range, the NILS remains stable above 2.8, and the contrast stays near 0.70. These simulation results confirm that the F-P resonator-based scheme is viable for plasma imaging lithography with small critical dimensions.

Design and Optimization of Encoded and Tunable Graphene-Silver Metasurface Surface Plasmon Resonance Sensor for Detection of Low Refractive Index Variation in Terahertz Regime

Design and Optimization of Encoded and Tunable Graphene-Silver Metasurface Surface Plasmon Resonance Sensor for Detection of Low Refractive Index Variation in Terahertz Regime

Tapered coreless optical fiber-based refractive index sensor for acetone concentration detection

A fast-response optical fiber sensor is designed and fabricated to detect different concentrations of volatile acetone. The proposed sensor structure was fabricated by splicing a segment of tapered coreless fiber (CLF) amid two single-mode fibers (SMF). Herein, tuned tapered diameters and lengths of CLF’s cladding were immersed in various concentrations of the acetone solutions to sense the effective refractive index (RI) variations. Accordingly, the sensor’s performance with tuned diameters at different lengths of the CLF was optimized to realize the suitable size of amplified evanescent fields. The sensor responded remarkably towards acetone concentrations, with a superior sensitivity of 336.102 nm/RIU, 0.163 nm/%, and 27.531 × 10−5 nm/ppm at 5 cm length and 60 µm taper diameter of CLF. The examined sensor possesses a fast response time with a minimum detection limit of 0.244 RIU, 5.025%vol, and 2.9 ppm. Though the rapid evaporation (volatility) of the acetone compound exempted it from air pollutants, many industrial and human body processes produce acetone which needs to be detected. The examined sensor may have the potential to detect in a non-invasive approach with high accuracy and rapid diabetes in humans, lung cancer, etc.

Ultra Enhancement of the Resolution of the Divergence Beam-Based SPR Sensor Using a Wavelet Filter

Surface Plasmon Resonance (SPR) sensors are highly sensitive to refractive index variations, making them ideal for biosensing and chemical detection applications. However, their performance can be constrained by noise, resolution limits, and signal distortions, particularly in divergence beam-based configurations. This research presents an ultra-enhancement of the performance of divergence beam-based SPR sensors by employing advanced wavelet filtering techniques. Wavelets, with their multi-resolution analysis capability, are applied to denoise and refine the sensor signal, significantly improving key performance metrics, including resolution, mean square error (MSE), root mean square error (RMSE), signal-to-noise ratio (SNR), sensitivity matrix (SM), and combined sensitivity factor (CSF).The wavelet filter effectively decomposes the SPR signal into distinct frequency bands, separating noise while retaining high-frequency components required for accurate sensing. This results in a significant reduction in MSE and RMSE of 30 and 92.26%, respectively, while simultaneously improving SNR by 54.08%, maintaining signal quality. The wavelet filter significantly improved the resolution of the SPR sensor by 99.95% (1.3772×10-7 RIU), allowing for more precise detection of refractive index changes and boosting diverge beam-based SPR sensor performance. In addition, a sensitivity matrix (SM) and combined sensitivity factor (CSF) were improved by 42 and 41.94%, respectively, allowing for a more thorough evaluation of the sensor's performance across multiple operational parameters. Simulation and experimentation show that wavelet filtering surpasses standard filtering approaches in terms of noise suppression and signal clarity. This technology has considerable potential for improving the accuracy and reliability of SPR sensors in high-sensitivity applications

The substituent effect on pulsed laser beam self-action manifestation in azo-azomethine PMMA composites thin films in visible and near IR ranges

Efficiency of nonlinear optical response was studied for a set of azo-azomethines dyes with substituted electron-withdrawing/donating groups, being embedded in poly(methyl methacrylate) (PMMA) matrix, via self-action effects manifestation of mode-locked Nd:YAG laser single pulses in visible at 532 nm, and in near IR at 1064 nm ranges. Photoinduced variations of refractive index and optical absorption/bleaching are crucially dependent on electron-donating/accepting substituents' properties with |Re(χ(3))| ∼ 10−7 esu and |Im(χ(3))| ∼ 10−9 esu efficiencies correspondingly at moderate laser excitation up to 10 MW/cm2. Incorporation of the azomethine group has provided tendency for fractional self-focusing effect manifestation in visible range against reference Azo dye, while at 1064 nm – self-defocusing one. For some dyes magnitudes of |Re(χ(3))| in near IR range are comparable and even higher than for the corresponding ones at 532 nm due to resonant cascaded three photon excitation into the peak vicinity of π→π∗ transitions of the dyes. It was established linear relationship between second-order hyperpolarizabilities under pulsed and CW laser excitation in visible range, being preliminary irradiated within full spectra of UV lamp for CW laser diagnostics mode. It proofs a suggestion that picosecond range single pulses transfer dyes into the same excited state as full spectrum of a mercury lamp irradiation – conventional tool for the smart molecules’ isomerization. Analysis of the experimental data has shown a high potential for the azo-azomethines dyes doped polymer composites in nonlinear optical applications.

Computational Modeling of Light Scattering in Polymer Nanoparticles for Optical Characterization

The scattering of light by polymeric nanoparticles is a crucial phenomenon in various applications, ranging from nanomedicine to nanophononics. This study introduces a theoretical framework for differentiating between absorption and scattering spectra in light interactions with these nanoparticles. Characteristic spectral data of nanoparticles synthesized via the reprecipitationmethod and suspended in an aqueous medium analyzed under electromagnetic radiation. These nanoparticles exhibit two primary optical phenomena: absorption and scattering. To fully understand their optical response, it is essential to separate these phenomena. This study established a relationship between wavelength variation, nanoparticle size, and radiation loss due to scatteringin an aqueous medium. Additionally, we calculated extinction efficiency and extinction factors as functions of wavelength, taking into account variations in nanoparticle radii and refractive indices.

Spiral shaped highly sensitive rectangular PCF-based cancer cells detector in terahertz regime

Abstract The increasing fatality rate of cancer in the modern world has become a global concern. To address this issue, early detection of cancer cells in human blood is essential. In this article, a rectangular spiral shaped photonic crystal fiber has been proposed for sensing cancer cells in terahertz regime. The proposed PCF based sensor features a square shaped core surrounded by rectangular air holes of different sizes in a spiral manner. Finite element method based COMSOL Multiphysics software has been used for the design and analysis of the model. The model is sensitive to refractive index variation for the identification of cancer cells. The values of effective refractive index, effective mode area, relative sensitivity, non-linearity, and confinement loss are obtained for MCF-7, MDA-MB-231, Jurkat, HeLa, Basal and PC-12. The PCF based sensor resulted in excellent results of relative sensitivity and Confinement loss as good as 99.377% and 8.59 × 10−12 dBm−1 respectively. Furthermore, the present PCF based sensor model is fabrication feasible, and we hope that it can be utilized at industrial level for biosensing applications in terahertz waveguide regime.

Accommodating version of a schematic eye for emmetropia and myopia.

To develop an accommodating, wide-angle, schematic eye for emmetropia and myopia in which spectacle refraction and accommodation level are input parameters. The schematic eye is based on an earlier unaccommodated refraction-dependent eye for myopia developed by Atchison in 2006. This has a parabolic gradient index lens and parameters derived from biometric and optical measurements on young adults. Several parameters are linearly dependent upon spectacle refraction (anterior radius of curvature of the cornea, axial length and vertex radii of curvature and conic asphericities of a biconic retina). The new accommodated schematic eye incorporates accommodation-dependent changes in several lens-related parameters. These changes are based on literature values for anterior chamber depth, lens thickness, vitreous chamber depth, lens surface radii of curvature and lens front surface asphericity. A parabolic variation of refractive index with relative distance from the lens centre is retained, with the same edge and centre refractive indices as the earlier model, but the distribution has been manipulated to maintain focus near the retina for the emmetropic case at 0 and 4 D accommodation. The asphericity of the lens back surface is changed so that spherical aberration and peripheral refraction approximately match typical literature trends. The model is used to compare spherical aberration and peripheral refraction in eyes with up to 4 D of myopia and 4 D of accommodation. The levels of spherical aberration in the unaccommodated schematic eyes are similar to literature values for young adults, but the changes in spherical aberration with accommodation are approximately two-thirds of that found in an experimental study. As intended, peripheral refractions in the accommodated schematic eyes are similar to those of their unaccommodated counterparts. The wide-angle model extends the range of schematic eyes to include both refraction and accommodation as variable input parameters. It may be useful in predicting aspects of retinal image quality.

Design of an all-optical tunable 2D photonic crystal in As2S3 film

Amorphous arsenic trisulphide (As2S3) chalcogenide glass is widely used in photonics and optoelectronics due to its wide transparency in the infrared spectral range, its high linear refractive index (nAs2S3 = 2.42), which can be significantly modified by light with a suitable wavelength, and its important optical nonlinearity. In this work, we report the design of an all-optical tunable two-dimensional photonic crystal in a geometry which consists in a hexagonal lattice of holes patterned in As2S3 film with the aim to exhibit photonic band gap in the near infrared domain. We numerically investigated the possibility to all-optically tune the photonic band gap of an already patterned photonic crystal in As2S3 modifying only its refractive index by illumination with light of wavelength λ at the band gap energy (λ = 514.5 nm) or shorter, without affecting the lattice geometry. The influence of the variation of As2S3 refractive index (Δn) on the spectral position of the band gap and on its width has been determined for the light-induced modification of Δn up to the value of 0.09. For this value of Δn, a shift of almost 50 nm of the central wavelength of the photonic band gap has been obtained. These results are of great interest in the field of photonics offering a versatile solution to fabricate all-optical tunable photonic crystals in any optical material whose refractive index can be modified by light.

Metal-free ultrathin terahertz absorber with independently tunable dual narrow bands

Abstract A technique is introduced to precisely control the resonance behaviour of a metal-free graphene-based terahertz absorber by independently tuning dual resonant peaks. The proposed ultrathin absorber features a multilayer configuration, with two isolated resonator layers of patterned graphene on dielectric (SiO2) substrates, and a thin graphite sheet at the bottom serving as a reflector. The stacked arrangement enables independent tunability of the high-absorptivity resonant peaks at 7.33THz and 9.34THz. The structure, with a thickness of just λ/15 of the free-space wavelength, offers a compact design suitable for space-constrained applications. Its symmetrical geometry ensures polarization insensitivity and stable performance for incident angles up to 60°. Simulated results, analysed via CST Studio and validated with an Equivalent Circuit Model (ECM), demonstrate excellent thermal stability. Furthermore, the narrowband response of the proposed absorber improves its sensitivity for refractive index variations induced by biomolecular interactions validating its suitability in biosensing applications. The absorber demonstrates peak absorption across both the resonant frequencies with an analyte optimised at 1.5μm thickness. Sensitivity levels of 1.1THz/RIU and 1.05THz/RIU along with figure-of-merit (FOM) values of 2.11 and 2.23. are recorded for the lower and upper bands, respectively. The absorber offers enhanced selectivity owing to low values of full-width at half maximum (FWHM). High Q-factors of 12.85 and 19.3, confirm its strong potential for refractive index sensing. 

Determination of adipogenesis stages of human umbilical cord-derived mesenchymal stem cells using three-dimensional label-free holotomography

Adipogenesis involves complex changes in gene expression, morphology, and cytoskeletal organization. However, the quantitative analysis of live cell images to identify their stages through morphological markers is limited. Distinct adipogenesis markers on human umbilical cord-derived mesenchymal stem cells (UC-MSCs) were identified through holotomography, a label-free live cell imaging technique. In the MSC-to-preadipocyte transition, the nucleus-to-cytoplasm ratio (0.080 vs. 0.052) and lipid droplet (LD) refractive index variation decreased (0.149 % vs. 0.061 %), whereas the LD number (20 vs. 65) increased. This event was also accompanied by the downregulation and upregulation of THY1 and Preadipocyte Factor-1 (PREF-1), respectively. In the preadipocyte to immature adipocyte shift, cell sphericity (0.20 vs. 0.43) and LD number (65 vs. 200) surged, large LDs (>10 μm3) appeared, and the major axis of the cell was reduced (143.7 μm vs. 83.12 μm). These findings indicate features of preadipocyte and immature adipocyte stages, alongside the downregulation of PREF-1 and upregulation of Peroxisome Proliferator-Activated Receptor gamma (PPARγ). In adipocyte maturation, along with PPARγ and Fatty Acid-Binding Protein 4 upregulation, cell compactness (0.15 vs. 0.29) and sphericity (0.43 vs. 0.59) increased, and larger LDs (>30 μm3) formed, marking immature and mature adipocyte stages. The study highlights the distinct adipogenic morphological biomarkers of adipogenesis stages in UC-MSCs, providing potential applications in biomedical and clinical settings, such as fostering innovative medical strategies for treating metabolic disease.

Effect of titanium oxide (TiO2) nanoparticles on the opto-mechanical properties of polyethylene terephthalate (PET) fibers

Polyethylene terephthalate (PET) is widely used in various applications due to its excellent mechanical properties and chemical resistance. However, PET fibers still lack specific features and functionalities that can be improved via nano-additives, particularly metal oxides. In this study, we investigate the effect of adding TiO2 nanoparticles to PET to form PET/TiO2 fibers and examine their opto-mechanical properties. This study utilizes optical interferometric techniques to assess how mechanical stretching influences the optical and mechanical properties of PET fibers treated with TiO2 nanoparticles. A Mach–Zehnder interferometric setup, integrated with a versatile device capable of mechanically stretching samples, is used to achieve this task. Variations in refractive index and birefringence along the longitudinal axis of undrawn and drawn PET/TiO2 fibers are examined. The research meticulously explores the fluctuations and spatial variations in the refractive index and birefringence properties, exhibiting anisotropy in optical behavior, along the longitudinal axis of unstretched and stretched PET/TiO2 fibers. The findings and outcomes derived from this comprehensive study provide substantive information that can facilitate the enhancement and optimization of the coupled optical and mechanical properties of materials explicitly engineered for advanced applications.

Design and optimization of a polarization-insensitive terahertz metamaterial absorber for sensing applications

This study presents dual-band Terahertz (THz) metamaterial absorbers (MA) designed with square resonators for sensing applications. The absorber is made up of a plasmonic ring resonator, a middle polyimide layer, and a lower metal plate, which enhances its absorption capabilities. The position of annular strips and patch units is strategically adjusted to tune and optimize the absorber’s performance precisely. The proposed metamaterial (MA) consistently absorbs over 99 % within the frequency range from 1.4 to 2.8 THz at 1.6 THz for peak-1 and 2.3 THz for peak-2. The peaks labeled as ‘f1’ and ‘f2’ have a spectral width of 0.02 THz and high-quality factors (Q-factors) of 23 for peak-1 and 29 for peak-2, respectively. This makes them remarkably sensitive to variations in the environmental refractive index (RI). It is important to observe that the refractive index of most samples falls within the range of 1.0–2.0, highlighting the potential applications of this sensor.

Fluorine fluid experimental determination of the refractive index, spectral and thermal variation, and transparency quantification of the MezzoCielo telescope

The MezzoCielo (or "half of the sky") is a telescope that aims to revolutionize the way astronomical observations are carried out: once operational, it will be able to continuously patrol the whole sky due to its extremely large field of view estimated to be around 104 square degrees, showing, at the same time, the spatial resolution required for scientific purposes. It is a monocentric optical device designed on the concept of an optical sphere; the latter requires the filling of its inner volume with special fluid in order to be actually convergent with a reasonable focal ratio (for spherical aberration reduction). This fluid must exhibit two main properties, namely, a low refractive index and an extremely high transparency in the visible range. In addition, many other characteristics are also required: thermal and chemical stability over time, no toxicity or flammability, and compatibility with glass and metals are some examples. On the basis of these considerations, two fluorine liquids have been selected: the fluids commercially known as FC-72, perfluorohexane with n d = 1.251 at T = 25°C, and Novec7200, ethoxy-nonafluorobutane with n d = 1.282 at T = 25°C. In this work, the experimental evaluation of their optical properties (refractive index and transparency) in the visible range and in the thermal interval [-10,+25]°C has been carried out in order to verify the data supplied by the manufacturer and to fully characterize their optical behaviour both spectrally and thermally. All the employed techniques have been firstly applied to commercial pure water, for which extensive literature could be used as reference for the procedures validation.

Terahertz photonic crystal fiber-based edible oil sensor: Performance evaluation and identification

This model introduced an innovative hollow-core optical waveguide with an octagonal core, specifically designed for rapid detection of various food oil contaminations is founded on the principles of Photonic Crystal Fiber (PCF). By analyzing the refractive index (RI) variations between pure and contaminated oil, we evaluate other essential optical parameters. The characteristics inherent to the suggested food oil sensor are examined using COMSOL Multiphysics v6.1, employing the Finite Element Method (FEM). Highly precise mesh components are included to provide optimal simulation accuracy. The outcomes from the suggested sensor model demonstrate exceptionally strong relative sensitivity of 98.52 % for castor oil, 98.46 % for sunflower oil, 98.41 % for mustard oil, 98.32 % for olive oil, and 98.03 % for coconut oil, all measured at 2 THz. Additionally, the simulation shows a very low confinement loss of 2.37 × 10−12 cm-1, a numerical aperture of 0.242, effective area of 1.1459 × 10–7 m², and effective material loss of 0.0038 cm-1 for castor oil under optimal structural circumstances. The straightforward design of the PCF in the sensor indicates that it can be implemented with ease, given these standard performance indicators. Therefore, it is anticipated that this sensor will open improved avenues for detection and identification of several distinct food oil contaminations. It can be produced using standard fabrication processes.