Simon Fleming | The University of Sydney (original) (raw)

Papers by Simon Fleming

Optical fiber sensors drawn from polyurethane are demonstrated. Polyurethane's Young's Modulus is... more Optical fiber sensors drawn from polyurethane are demonstrated. Polyurethane's Young's Modulus is orders of magnitude lower than traditional optical fiber materials, permitting more sensitive optical detection of mechanical perturbations.

2017 3rd International Conference on Electrical Information and Communication Technology (EICT), Dec 1, 2017

The practical realization of low Young's modulus Polyurethane (PU) based optical fibers offers ne... more The practical realization of low Young's modulus Polyurethane (PU) based optical fibers offers new possibilities for sensing on bodies due to its bio-compatibility and high material sensitivity. Here, we experimentally demonstrate a PU fiber pressure sensor using the simplest possible structure (i.e. a capillary) to measure a weak low frequency signal comparable to respiration/heart rate. We characterized the fiber and measured the sensitivity of a PU capillary using a speaker connected to a function generator. The frequency of the modulated signal was recovered using Fourier Transform (FT). This bodes well for applying more sophisticated structures to wearable devices.

APL photonics, May 1, 2018

THz radiation is a more commonplace in research laboratories as well as in everyday life, with ap... more THz radiation is a more commonplace in research laboratories as well as in everyday life, with applications ranging from body scanners at airport security to short range wireless communications. In the optical domain, waveguides and other devices to manipulate radiation are well established. This is not yet the case in the THz regime because of the strong interaction of THz radiation with matter, leading to absorption, and the millimeter size of the wavelength and therefore of the required waveguides. We propose the use of a new material, polyurethane, for waveguides that allows high flexibility, overcoming the problem that large sizes otherwise result in rigid structures. With this material, we realize antiresonant hollow-core waveguides and we use the flexibility of the material to mechanically twist the waveguide in a tunable and reversible manner, with twist periods as short as tens of wavelengths. Twisting the waveguide, we demonstrate the generation of modes carrying orbital angular momentum. We use THz time domain spectroscopy to measure and clearly visualize the vortex nature of the mode, which is difficult in the optical domain. The proposed waveguide is a new platform offering new perspectives for THz guidance and particularly mode manipulation. The demonstrated ability to generate modes with an orbital angular momentum within a waveguide, in a controllable manner, will be beneficial to both fundamental, e.g., matter-radiation interaction, and applied, e.g., THz telecommunications, advances of THz research and technology. Moreover, this platform is not limited to the THz domain and could be scaled for other electromagnetic wavelengths.

Nature Communications, Oct 28, 2013

Using conventional materials, the resolution of focusing and imaging devices is limited by diffra... more Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells.

The fibre drawing technique is utilized for fabricating metamaterials. The ability to engineer bo... more The fibre drawing technique is utilized for fabricating metamaterials. The ability to engineer both the permittivity and permeability is demonstrated. A hyperlens with /176 sub-diffraction focusing is realized. Tunability of 50% is also demonstrated.

Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), 2018

A flexible fiber-drawn material, i.e. polyurethane, allows for novel applications from THz to the... more A flexible fiber-drawn material, i.e. polyurethane, allows for novel applications from THz to the visible. We exploit its elastic properties to generate orbital angular momentum modes, to make pressure sensors and to realize tunable metamaterials.

Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), 2018

We demonstrate thermal poling of fibers with ~50 and ~500 anodes. The second order nonlinearity l... more We demonstrate thermal poling of fibers with ~50 and ~500 anodes. The second order nonlinearity layers are developed surrounding all the rings of wires in the ~50 anode fiber and the outer rings of the ~500 anode fiber.

Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), 2018

Extreme sub-diffraction focusing of THz radiation is obtained by cascading two metamaterial wire ... more Extreme sub-diffraction focusing of THz radiation is obtained by cascading two metamaterial wire array fiber hyperlenses. A record 1/176 of the wavelength is achieved, allowing squeezing 8.8 mm wavelength to a 50 micron spot.

Physical review, Sep 19, 2019

We study the effect of resonances on the ability of prisms made of hyperbolic metamaterials in th... more We study the effect of resonances on the ability of prisms made of hyperbolic metamaterials in the canalization regime (such as wire array media) to couple evanescent high spatial frequencies (high-k modes) to low spatial frequencies that propagate in the far-field zone. Using simple analytical models, we calculate the far-field propagation from the hyperprism. The resonant nature of the metal wire segments within the prism yields a transmission function identical to that of a grating, but with periodicity proportional to the wavelength, making the hyperprism function like a nondispersive grating. Numerically compensating the effect of resonances allows the hyperprism to be used as a one-dimensional imaging device able to resolve feature sizes below the diffraction limit if the host medium has a low refractive index. Furthermore, the hyperprism enables coupling of propagating plane waves to a range of high-k modes that can be increased by increasing the angle of the prism. We quantify how this tunable, nondispersive excitation of high-k modes opens up possibilities for new experimental approaches for coupling to plasmonic systems and for increased axial resolution in total internal reflection imaging, in particular in the terahertz spectrum.

IEEE Journal of Selected Topics in Quantum Electronics, 2023

Wearable devices are becoming increasingly important, addressing needs in both the fitness and th... more Wearable devices are becoming increasingly important, addressing needs in both the fitness and the medical markets. In this paper, we describe a novel sensing platform based on a hollow-core polyurethane optical fiber, operating through capillary guidance, that acts as a conformal sensor of pressure or deformation. The novelty is achieved by combining a simple structure (hollow capillary) and a simple detection technique (intensity-based measurement) with unconventional material properties (extreme deformability and high optical absorbance). Used on the wrist and ankle, the sensor allows detailed features of the cardiac pulse wave to be identified with high fidelity, while on the chest it allows the simultaneous measurement of breathing rate and walking cadence. Used together, an array of such sensors (with others) could be incorporated into clothing and provide physiologically rich real-time data for health monitoring.

In this paper the selection of optimal laser parameters for generating surface acoustic waves on ... more In this paper the selection of optimal laser parameters for generating surface acoustic waves on dental enamel is discussed. Spectrophotometric analysis of enamel sections shows two near-IR wavelengths that are strongly absorbed. Simulations of Duhamel's theorem were used to determine the laser damage threshold and the appropriate laser pulse repetition rate.

Journal of Visualized Experiments, Oct 18, 2012

Metamaterials are man-made composite materials, fabricated by assembling components much smaller ... more Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1 . They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2 . This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3 , negative refractive index materials 4 , and lenses that resolve objects below the diffraction limit 5 . However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano-and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7 . Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8 . We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10 , using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 °C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro-and nano-scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Applied Physics Letters, Sep 15, 2008

We report the fabrication of waveguides in lithium tantalate using a 250 kHz high-repetition rate... more We report the fabrication of waveguides in lithium tantalate using a 250 kHz high-repetition rate ultrafast laser at 771 nm and the characterization of the resulting laser induced structure with second harmonic microscopy. Waveguides operating at the 1.5 m telecommunication wavelength were formed above and below the focal volume using pulse energies ranging from 100 to 1.6 J and translation speeds from 100 m / s to 5 mm/ s. The second harmonic microscopy reveals no degradation of the electro-optic coefficient in the guiding region above the focal volume.

We characterize resonances of 3D fiber metamaterials under transmittance at oblique incidence. Th... more We characterize resonances of 3D fiber metamaterials under transmittance at oblique incidence. The resonance frequency of longitudinally invariant resonators increases with the incident angle, while the resonance of disconnected resonators does not.

There is growing demand for biodegradable polymer fibres in tissue engineering and nerve regenera... more There is growing demand for biodegradable polymer fibres in tissue engineering and nerve regeneration. We demonstrate a scalable and inexpensive fabrication technique to produce polycaproactone (PCL) fibres using fibredrawing technique. Here we report on the first successful drawing of hollow-core and solid-core PCL fibres of different cross sections. The demonstrated capacity to tailor the surface morphology of PCL fibres, together with their biodegradability and tissue compatibility, makes them a unique material base for tissue engineering and nerve regeneration applications.

Workshop on Specialty Optical Fibers and Their Applications, 2015

Fibre drawing is a versatile micro-and nano-fabrication process which we have applied to manufact... more Fibre drawing is a versatile micro-and nano-fabrication process which we have applied to manufacture of metamaterials, demonstrating engineered permittivity and permeability, and fabricating a hyperlens. Prospects for extending this approach will be discussed.

Journal of Lightwave Technology, Oct 1, 2019

Metamaterials for the mid-infrared spectrum require subwavelength meta-structures with dimensions... more Metamaterials for the mid-infrared spectrum require subwavelength meta-structures with dimensions of a few hundreds of nanometers. Fabrication via fiber drawing is challenging as the Plateau-Rayleigh instability caused by interfacial surface tension between the liquid metal and the dielectric during the drawing leads to fluctuation of the structure, preventing drawing of uniform wire array structures with such dimensions. Here, conventional fiber drawing technique is employed in the fabrication of wire array metamaterial fibers containing tin wires embedded in soda-lime glass. Plateau-Rayleigh instabilities ensuing detrimental deformations on submicron metallic structures are minimized through the selection of materials with favorable rheological properties and the optimization of the drawing parameters. Uniform wire array structures with wire diameter and spacing as small as 143 nm and 286 nm, respectively are demonstrated. The application of this established fabrication process represents a large-volume and low-cost alternative for the production of hyperbolic metamaterials. The new metamaterial fibers achieved open up a range of exciting applications at mid-infrared frequencies, such as lifetime engineering and super-resolution imaging.

Polyurethane (PU) based hollow core fibers are investigated as optical sensors. The flexibility o... more Polyurethane (PU) based hollow core fibers are investigated as optical sensors. The flexibility of PU fibers makes it suitable for sensing mechanical perturbations. We fabricated a PU fiber using the fiber drawing method, characterized the fiber and experimentally demonstrated a simple way to measure deformation, in the form of applied pressure.

Polymers, Feb 14, 2020

Analytical modeling of soft pneumatic actuators constitutes a powerful tool for the systematic de... more Analytical modeling of soft pneumatic actuators constitutes a powerful tool for the systematic design and characterization of these key components of soft robotics. Here, we maximize the quasi-static bending angle of a soft pneumatic actuator by optimizing its cross-section for a fixed positive pressure inside it. We begin by formulating a general theoretical framework for the analytical calculation of the bending angle of pneumatic actuators with arbitrary cross-sections, which is then applied to an actuator made of a circular polymer tube and an asymmetric patch in the shape of a hollow-cylinder sector on its outer surface. It is shown that the maximal bending angle of this actuator can be achieved using a wide range of patches with different optimal dimensions and approximately the same cross-sectional area, which decreases with pressure. We also calculate the optimal dimensions of thin and small patches in thin pneumatic actuators. Our analytical results lead to clear design guidelines, which may prove useful for engineering and optimization of the key components of soft robotics with superior features.

Optical fiber sensors drawn from polyurethane are demonstrated. Polyurethane's Young's Modulus is... more Optical fiber sensors drawn from polyurethane are demonstrated. Polyurethane's Young's Modulus is orders of magnitude lower than traditional optical fiber materials, permitting more sensitive optical detection of mechanical perturbations.

2017 3rd International Conference on Electrical Information and Communication Technology (EICT), Dec 1, 2017

The practical realization of low Young's modulus Polyurethane (PU) based optical fibers offers ne... more The practical realization of low Young's modulus Polyurethane (PU) based optical fibers offers new possibilities for sensing on bodies due to its bio-compatibility and high material sensitivity. Here, we experimentally demonstrate a PU fiber pressure sensor using the simplest possible structure (i.e. a capillary) to measure a weak low frequency signal comparable to respiration/heart rate. We characterized the fiber and measured the sensitivity of a PU capillary using a speaker connected to a function generator. The frequency of the modulated signal was recovered using Fourier Transform (FT). This bodes well for applying more sophisticated structures to wearable devices.

APL photonics, May 1, 2018

THz radiation is a more commonplace in research laboratories as well as in everyday life, with ap... more THz radiation is a more commonplace in research laboratories as well as in everyday life, with applications ranging from body scanners at airport security to short range wireless communications. In the optical domain, waveguides and other devices to manipulate radiation are well established. This is not yet the case in the THz regime because of the strong interaction of THz radiation with matter, leading to absorption, and the millimeter size of the wavelength and therefore of the required waveguides. We propose the use of a new material, polyurethane, for waveguides that allows high flexibility, overcoming the problem that large sizes otherwise result in rigid structures. With this material, we realize antiresonant hollow-core waveguides and we use the flexibility of the material to mechanically twist the waveguide in a tunable and reversible manner, with twist periods as short as tens of wavelengths. Twisting the waveguide, we demonstrate the generation of modes carrying orbital angular momentum. We use THz time domain spectroscopy to measure and clearly visualize the vortex nature of the mode, which is difficult in the optical domain. The proposed waveguide is a new platform offering new perspectives for THz guidance and particularly mode manipulation. The demonstrated ability to generate modes with an orbital angular momentum within a waveguide, in a controllable manner, will be beneficial to both fundamental, e.g., matter-radiation interaction, and applied, e.g., THz telecommunications, advances of THz research and technology. Moreover, this platform is not limited to the THz domain and could be scaled for other electromagnetic wavelengths.

Nature Communications, Oct 28, 2013

Using conventional materials, the resolution of focusing and imaging devices is limited by diffra... more Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells.

The fibre drawing technique is utilized for fabricating metamaterials. The ability to engineer bo... more The fibre drawing technique is utilized for fabricating metamaterials. The ability to engineer both the permittivity and permeability is demonstrated. A hyperlens with /176 sub-diffraction focusing is realized. Tunability of 50% is also demonstrated.

Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), 2018

A flexible fiber-drawn material, i.e. polyurethane, allows for novel applications from THz to the... more A flexible fiber-drawn material, i.e. polyurethane, allows for novel applications from THz to the visible. We exploit its elastic properties to generate orbital angular momentum modes, to make pressure sensors and to realize tunable metamaterials.

Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), 2018

We demonstrate thermal poling of fibers with ~50 and ~500 anodes. The second order nonlinearity l... more We demonstrate thermal poling of fibers with ~50 and ~500 anodes. The second order nonlinearity layers are developed surrounding all the rings of wires in the ~50 anode fiber and the outer rings of the ~500 anode fiber.

Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), 2018

Extreme sub-diffraction focusing of THz radiation is obtained by cascading two metamaterial wire ... more Extreme sub-diffraction focusing of THz radiation is obtained by cascading two metamaterial wire array fiber hyperlenses. A record 1/176 of the wavelength is achieved, allowing squeezing 8.8 mm wavelength to a 50 micron spot.

Physical review, Sep 19, 2019

We study the effect of resonances on the ability of prisms made of hyperbolic metamaterials in th... more We study the effect of resonances on the ability of prisms made of hyperbolic metamaterials in the canalization regime (such as wire array media) to couple evanescent high spatial frequencies (high-k modes) to low spatial frequencies that propagate in the far-field zone. Using simple analytical models, we calculate the far-field propagation from the hyperprism. The resonant nature of the metal wire segments within the prism yields a transmission function identical to that of a grating, but with periodicity proportional to the wavelength, making the hyperprism function like a nondispersive grating. Numerically compensating the effect of resonances allows the hyperprism to be used as a one-dimensional imaging device able to resolve feature sizes below the diffraction limit if the host medium has a low refractive index. Furthermore, the hyperprism enables coupling of propagating plane waves to a range of high-k modes that can be increased by increasing the angle of the prism. We quantify how this tunable, nondispersive excitation of high-k modes opens up possibilities for new experimental approaches for coupling to plasmonic systems and for increased axial resolution in total internal reflection imaging, in particular in the terahertz spectrum.

IEEE Journal of Selected Topics in Quantum Electronics, 2023

Wearable devices are becoming increasingly important, addressing needs in both the fitness and th... more Wearable devices are becoming increasingly important, addressing needs in both the fitness and the medical markets. In this paper, we describe a novel sensing platform based on a hollow-core polyurethane optical fiber, operating through capillary guidance, that acts as a conformal sensor of pressure or deformation. The novelty is achieved by combining a simple structure (hollow capillary) and a simple detection technique (intensity-based measurement) with unconventional material properties (extreme deformability and high optical absorbance). Used on the wrist and ankle, the sensor allows detailed features of the cardiac pulse wave to be identified with high fidelity, while on the chest it allows the simultaneous measurement of breathing rate and walking cadence. Used together, an array of such sensors (with others) could be incorporated into clothing and provide physiologically rich real-time data for health monitoring.

In this paper the selection of optimal laser parameters for generating surface acoustic waves on ... more In this paper the selection of optimal laser parameters for generating surface acoustic waves on dental enamel is discussed. Spectrophotometric analysis of enamel sections shows two near-IR wavelengths that are strongly absorbed. Simulations of Duhamel's theorem were used to determine the laser damage threshold and the appropriate laser pulse repetition rate.

Journal of Visualized Experiments, Oct 18, 2012

Metamaterials are man-made composite materials, fabricated by assembling components much smaller ... more Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1 . They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2 . This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3 , negative refractive index materials 4 , and lenses that resolve objects below the diffraction limit 5 . However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano-and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7 . Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8 . We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10 , using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 °C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro-and nano-scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Applied Physics Letters, Sep 15, 2008

We report the fabrication of waveguides in lithium tantalate using a 250 kHz high-repetition rate... more We report the fabrication of waveguides in lithium tantalate using a 250 kHz high-repetition rate ultrafast laser at 771 nm and the characterization of the resulting laser induced structure with second harmonic microscopy. Waveguides operating at the 1.5 m telecommunication wavelength were formed above and below the focal volume using pulse energies ranging from 100 to 1.6 J and translation speeds from 100 m / s to 5 mm/ s. The second harmonic microscopy reveals no degradation of the electro-optic coefficient in the guiding region above the focal volume.

We characterize resonances of 3D fiber metamaterials under transmittance at oblique incidence. Th... more We characterize resonances of 3D fiber metamaterials under transmittance at oblique incidence. The resonance frequency of longitudinally invariant resonators increases with the incident angle, while the resonance of disconnected resonators does not.

There is growing demand for biodegradable polymer fibres in tissue engineering and nerve regenera... more There is growing demand for biodegradable polymer fibres in tissue engineering and nerve regeneration. We demonstrate a scalable and inexpensive fabrication technique to produce polycaproactone (PCL) fibres using fibredrawing technique. Here we report on the first successful drawing of hollow-core and solid-core PCL fibres of different cross sections. The demonstrated capacity to tailor the surface morphology of PCL fibres, together with their biodegradability and tissue compatibility, makes them a unique material base for tissue engineering and nerve regeneration applications.

Workshop on Specialty Optical Fibers and Their Applications, 2015

Fibre drawing is a versatile micro-and nano-fabrication process which we have applied to manufact... more Fibre drawing is a versatile micro-and nano-fabrication process which we have applied to manufacture of metamaterials, demonstrating engineered permittivity and permeability, and fabricating a hyperlens. Prospects for extending this approach will be discussed.

Journal of Lightwave Technology, Oct 1, 2019

Metamaterials for the mid-infrared spectrum require subwavelength meta-structures with dimensions... more Metamaterials for the mid-infrared spectrum require subwavelength meta-structures with dimensions of a few hundreds of nanometers. Fabrication via fiber drawing is challenging as the Plateau-Rayleigh instability caused by interfacial surface tension between the liquid metal and the dielectric during the drawing leads to fluctuation of the structure, preventing drawing of uniform wire array structures with such dimensions. Here, conventional fiber drawing technique is employed in the fabrication of wire array metamaterial fibers containing tin wires embedded in soda-lime glass. Plateau-Rayleigh instabilities ensuing detrimental deformations on submicron metallic structures are minimized through the selection of materials with favorable rheological properties and the optimization of the drawing parameters. Uniform wire array structures with wire diameter and spacing as small as 143 nm and 286 nm, respectively are demonstrated. The application of this established fabrication process represents a large-volume and low-cost alternative for the production of hyperbolic metamaterials. The new metamaterial fibers achieved open up a range of exciting applications at mid-infrared frequencies, such as lifetime engineering and super-resolution imaging.

Polyurethane (PU) based hollow core fibers are investigated as optical sensors. The flexibility o... more Polyurethane (PU) based hollow core fibers are investigated as optical sensors. The flexibility of PU fibers makes it suitable for sensing mechanical perturbations. We fabricated a PU fiber using the fiber drawing method, characterized the fiber and experimentally demonstrated a simple way to measure deformation, in the form of applied pressure.

Polymers, Feb 14, 2020

Analytical modeling of soft pneumatic actuators constitutes a powerful tool for the systematic de... more Analytical modeling of soft pneumatic actuators constitutes a powerful tool for the systematic design and characterization of these key components of soft robotics. Here, we maximize the quasi-static bending angle of a soft pneumatic actuator by optimizing its cross-section for a fixed positive pressure inside it. We begin by formulating a general theoretical framework for the analytical calculation of the bending angle of pneumatic actuators with arbitrary cross-sections, which is then applied to an actuator made of a circular polymer tube and an asymmetric patch in the shape of a hollow-cylinder sector on its outer surface. It is shown that the maximal bending angle of this actuator can be achieved using a wide range of patches with different optimal dimensions and approximately the same cross-sectional area, which decreases with pressure. We also calculate the optimal dimensions of thin and small patches in thin pneumatic actuators. Our analytical results lead to clear design guidelines, which may prove useful for engineering and optimization of the key components of soft robotics with superior features.