dB Cm-1 Research Articles

Flexible and Robust Core-Shell PANI/PVDF@PANI Nanofiber Membrane for High-Performance Electromagnetic Interference Shielding.

Developing high-performance electromagnetic interference (EMI) shielding materials that are lightweight and flexible and have excellent mechanical properties is an ideal choice for modern integrated electronic devices and microwave protection. Herein, we report the preparation of core-shell polyaniline (PANI)-based nanofiber membranes for EMI shielding through seed polymerization. Electrospinning a PANI solution leads to homogeneously dispersed PANI on the nanofiber surface, with abundant attachment sites for aniline through electrostatic adsorption and hydrogen bonding interaction, allowing PANI to grow on the nanofiber surfaces. This stable core-shell heterostructure provides more interfaces for reflecting and absorbing microwaves. The PANI/PVDF@PANI membranes achieved a shielding efficiency (SE) of 44.7 dB at a thickness of only 1.2 mm, exhibiting an exceptionally high specific EMI shielding effectiveness (SE/t) of 372.5 dB cm-1. Furthermore, the composite membrane exhibits outstanding mechanical stability, durability, air permeability, and moisture permeability, also making it suitable for applications such as EM shielding clothing.

Fatigue-resistant hydrogel optical fibers enable peripheral nerve optogenetics during locomotion.

We develop soft and stretchable fatigue-resistant hydrogel optical fibers that enable optogenetic modulation of peripheral nerves in naturally behaving animals during persistent locomotion. The formation of polymeric nanocrystalline domains within the hydrogels yields fibers with low optical losses of 1.07 dB cm-1, Young's modulus of 1.6 MPa, stretchability of 200% and fatigue strength of 1.4 MPa against 30,000 stretch cycles. The hydrogel fibers permitted light delivery to the sciatic nerve, optogenetically activating hindlimb muscles in Thy1::ChR2 mice during 6-week voluntary wheel running assays while experiencing repeated deformation. The fibers additionally enabled optical inhibition of pain hypersensitivity in an inflammatory model in TRPV1::NpHR mice over an 8-week period. Our hydrogel fibers offer a motion-adaptable and robust solution to peripheral nerve optogenetics, facilitating the investigation of somatosensation.

Non-covalent Supramolecular 1D Alternating Copolymer in Crystal toward 2D Anisotropic Photon Transport.

To realize organic integrated optoelectronic circuits, there is a need for anisotropic optical waveguides at the micro/nanoscale. Anisotropic alignment of one-dimensional (1D)-ordered supramolecular structures composed of light-emissive π-conjugated molecules in a crystal may meet the requirements of such waveguides. Here, we designed a bipyridyl-appended acrylonitrile-based π-conjugated molecule 1, which produced a 1D supramolecular polymer constructed through non-covalent bonding between a lone pair in 1 and a σ-hole in 1,4-diiodo-2,3,5,6-tetrafluorobenzene 2. The 1D copolymer of 1 and 2 is aligned horizontally with the two-dimensional (2D) crystal surface because of the angle-controlled supramolecular synthons. As a result of control over the non-covalent bonding direction, anisotropic photoluminescence and photon transport (optical waveguiding) characteristics are realized by orienting the transition dipole moment horizontally with respect to the 2D surface. Compared with the loss coefficient αL =52dBcm-1 for the long-axis direction of the 2D platelet cocrystal, a very large difference of αS =2111dBcm-1 is present in the crystal short-axis direction. The anisotropic waveguiding ability, αL/αS, is estimated to be 41, which is more than an order of magnitude greater than previously reported 2D platelet crystal waveguides. This supramolecular synthon provides an approach to designing anisotropic photon transporters and highly regulated optical logic circuits.

Optical gain at 1.55 µm of Er(TMHD)3 complex doped polymer waveguides based on the intramolecular energy transfer effect.

Based on the intramolecular energy transfer mechanism between organic ligand TMHD (2, 2, 6, 6-tetramethyl-3, 5-heptanedione) and central Er3+ ions, optical gains at 1.55 µm were demonstrated in three structures of polymer waveguides using complex Er(TMHD)3-doped polymethylmethacrylate (PMMA) as the active material. With the excitation of two low-power UV light-emitting diodes (LEDs) instead of 980 or 1480 nm lasers, relative gains of 3.5 and 4.1 dB cm-1 were achieved in a 1-cm-long rectangular waveguide with an active core of Er(TMHD)3-doped PMMA polymer. Meanwhile, relative gain of 3.0 dB cm-1 was obtained in an evanescent-field waveguide with cross-section of 4 × 4 µm2 using passive SU-8 polymer as core and a ∼1-µm-thick Er(TMHD)3-doped PMMA as upper cladding. By growing a 100 nm thick aluminum mirror and active lower cladding, the optical gain was doubled to 6.7 dB cm-1 in evanescent-field waveguides because of the stimulated excitation of Er3+ ions in the upper and lower cladding and the improved absorption efficiency.

Optical Amplification at 637 and 1067 nm Based on Organic Molecule AQ(PhDPA)2 and NdIII Complex Codoped Polymer Waveguides.

Based on the molecular energy transfer mechanism, relative gains at 1067 and 637nm wavelengths are achieved in thermally activated delayed fluorescence molecule AQ(PhDPA)2 and Nd complex with chelating phosphine oxide as ligands codoped polymer waveguides, with the excitation of low-power UV light-emitting diodes (LEDs) instead of traditional semiconductor lasers as pump sources. For AQ(PhDPA)2 -Nd(DBTTA)3 (DBFDPO) (DBTTA = dibenzotetrathienoacene, DBFDPO = 4,6-bis (diphenylphosphoryl) dibenzofuran) -codoped polymethylmethacrylate (PMMA), and AQ(PhDPA)2 -Nd(DBTTA)3 (FDPO) (FDPO = 9,9-bis (diphenylphosphorylphenyl) fluorene)-codoped PMMA polymers with a mass ratio of 1:4 respectively, when they are spin-coated as upper claddings, the relative gains of 2.2 and 1.8dB cm-1 at 1067nm are obtained in evanescent-field waveguides with cross-section of 4 × 8µm2 under excitation of 300mW 405nm LED, and the gains of 3.9 and 4.9dB cm-1 at 637nm are achieved with pumping of 530mW 450nm LED respectively. By growing a 100nm-thick aluminum reflector with the waveguides, the optical gain at 1067 and 637nm can be enhanced to 3.5 and 6.1dB cm-1 , corresponding to AQ(PhDPA)2 -Nd(DBTTA)3 (DBFDPO) and AQ(PhDPA)2 -Nd(DBTTA)3 (FDPO)-codoped PMMA polymers, respectively.

A nanoscale inorganic coating strategy for stabilizing hydrogel neural probes in vivo.

Hydrogels with adaptable optical and mechanical characteristics show considerable promise for light delivery in vivo with neuroengineering applications. However, the unlinked amorphous polymer chains within hydrogels can cause volumetric swelling after water absorption under physiological conditions over time. Chemically cross-linked poly(vinyl alcohol) (PVA) hydrogels showcase fatigue-resistant attributes and promising biocompatibility for the manufacture of soft neural probes. However, possible swelling of the PVA hydrogel matrix could impact the structural stability of hydrogel-based bioelectronics and their long-term in vivo functionality. In this study, we utilized an atomic layer deposition (ALD) technique to generate an inorganic, silicon dioxide (SiO2) coating layer on chemically cross-linked PVA hydrogel fibers. To evaluate the stability of SiO2-coated PVA hydrogel fibers mimicking the in vivo environment, we conducted accelerated stability tests. SiO2-coated PVA hydrogel fibers showed improved stability over a one-week incubation period under a harsh environment, preventing swelling and preserving their mechanical and optical properties compared to uncoated fibers. These SiO2-coated PVA hydrogel fibers demonstrated nanoscale polymeric crystalline domains (6.5 ± 0.1 nm), an elastic modulus of 73.7 ± 31.7 MPa, a maximum elongation of 113.6 ± 24.2%, and minimal light transmission loss (1.9 ± 0.2 dB cm-1). Lastly, we applied these SiO2-coated PVA hydrogel fibers in vivo to optically activate the motor cortex of transgenic Thy1::ChR2 mice during locomotor behavioral tests. This mouse cohort was genetically modified to express the light-sensitive ion channel, channelrhodopsin-2 (ChR2), and implanted with hydrogel fibers to deliver light to the motor cortex area (M2). Light stimulation via hydrogel fibers resulted in optogenetically modulated mouse locomotor behaviors, including increased contralateral rotation, mobility speeds, and travel distances.

Detection of kerosene adulteration in automobile fuel by a low-loss surface plasmon resonance (SPR) chemical sensor.

A surface plasmon resonance (SPR) chemical sensor with gold as the sensitive material has been designed to detect the adulteration of petrol by kerosene. Samples of petrol adulterated with kerosene were prepared in different ratios by volume (v/v). Kerosene concentrations ranging from 0% to 80% can be detected by monitoring the optical spectra, and the properties of the sensor were analyzed using the COMSOL Multiphysics software. The sensor shows a high spectral sensitivity of 7117 nm per RIU and a sensing resolution of 1.4 × 10-4 RIU. The excellent sensing properties and a low confinement loss of 5.4 dB cm-1 render the sensor competitive in SPR sensing applications.

Nonlinear properties of laser-processed polycrystalline silicon waveguides for integrated photonics.

We report nonlinear optical characterization of cm-long polycrystalline silicon (poly-Si) waveguides at telecom wavelengths. Laser post-processing of lithographically-patterned amorphous silicon deposited on silica-on-silicon substrates provides low-loss poly-Si waveguides with surface-tension-shaped boundaries. Achieving optical losses as low as 4 dB cm-1 enabled us to demonstrate effects of self-phase modulation (SPM) and two-photon absorption (TPA). Analysis of the spectral broadening and nonlinear losses with numerical modeling reveals the best fit values of the Kerr coefficient n2=4.5×10-18 m W-1 and TPA coefficient βTPA=9.0×10-12 m2 W-1, which are within the range reported for crystalline silicon. On-chip low-loss poly-Si paves the way for flexible integration of nonlinear components in multi-layered photonic systems.

Durability study of a gellan gum-based tissue-mimicking phantom for ultrasonic thermal therapy.

Stability and duration of ultrasonic phantoms are still subjects of research. This work presents a tissue-mimicking material (TMM) to evaluate high-intensity therapeutic ultrasound (HITU) devices, composed of gellan gum (matrix), microparticles (scatterers), and chemicals. The ultrasonic velocity and attenuation coefficient were characterized as a function of temperature (range 20 °C-85 °C). The nonlinear parameter B/A was determined by the finite amplitude insertion substitution (FAIS) method, and the shear modulus was determined by a transient elastography technique. The thermal conductivity and specific heat were determined by the line source method. The attenuation was stable for 60 days, and in an almost linear frequency dependence (0.51f0.96 dB cm-1), at 20 °C (1-10 MHz). All other evaluated physical parameters are also close to typical soft tissue values. Longitudinal ultrasonic velocities were between 1.49 and 1.75 mm μs-1, the B/A parameter was 7.8 at 30 °C, and Young's modulus was 23.4 kPa. The thermal conductivity and specific heat values were 0.7 W(m K)-1 and 4.7 kJ(kg K)-1, respectively. Consistent temperature increases and thermal doses occurred under identical HITU exposures. Low cost, longevity, thermal stability, and thermal repeatability make TMM an excellent material for ultrasonic thermal applications. The TMM developed has the potential to assess the efficacy of hyperthermia devices and could be used to adjust the ultrasonic emission of HITU devices.

An improved spectrophotometric method tests the Einstein-Smoluchowski equation: a revisit and update.

Theoretical prediction and experimental measurements of light attenuation in chemically pure and optically transparent solvents have attracted continuous attention, due in part to their curious nature, and in part to the increasing requirements of solvent-related applications. Yet hitherto, a majority of accurate spectrophotometric measurements of transparent solvents upon visible light radiation often end up using long-path-length cells, usually over dozens of cm, rendering the measure costly and complex; meanwhile, the guidance for choosing the Einstein-Smoluchowski equation or its variants as the best formula to predict the light scattering in solvents has remained elusive. Here we demonstrate a simple, versatile and cost-effective spectrophotometric method, enabling a sensitivity of 10-4 dB cm-1 over a 0.5 cm differential path length based on using standard double-beam spectrophotometer. We prove that this method reduces the path length by a factor of 100 while still making its closest approach to the record-low measurement of solvent extinction. We also validate that all the present equations used for predicting the light scattering in the solvent possess similar capacities, suggesting that the criterion for the choice of the appropriate formula simply depends on the equation's practicability. Following the elucidation of the wavelength range where the light scattering dominates the extinction, we further identify differences between scattering coefficients via the theoretical predictions and experimental measures, exposing the need for an improved theory to account for the solvent scattering phenomenon.

Direct UV written integrated planar waveguides using a 213 nm laser.

We present the first demonstration of integrated waveguides in planar silica devices fabricated using direct UV writing with 213 nm laser light. Waveguides were produced with different writing fluences and the NA and MFD of each were measured. Single mode waveguides were achieved at fluence values one-tenth that typically required when operating with a 244 nm laser, allowing for more rapid fabrication. A maximum in-plane index change of 2.4 ×10-3 for a writing fluence of 5 kJ cm-2 was estimated from NA measurements. Finally cutback measurements were performed and a propagation loss of 0.42 ± 0.07 dB cm-1 was directly measured, though losses as low as 0.2 ± 0.03 dB/cm are indicated through calculations.

Stress-induced optical waveguides written by an ultrafast laser in Nd3+, Y3+ co-doped SrF2 crystals.

In this paper, we report on the ultrafast laser-induced birefringence, refractive index changes, and enhanced photoluminescence properties in the volume of neodymium (Nd), yttrium (Y) co-doped strontium fluoride (SrF2) and Nd, Y co-doped calcium fluoride (CaF2) crystals. The optical waveguides written with 500kHz repetition rate provided lowest propagation loss of 1.63±0.21 dB cm-1 for transverse magnetic (TM) polarization at 632.8nm in Nd,Y:SrF2 crystal. The measured retardance can be interpreted by stress-induced birefringence related to the permanent volume expansion, photo induced by a non-spherical irradiated zone. The absorption, steady-state, and time-resolved photoluminescence properties are also carried out in and out of the laser irradiated zone, enabling the local changes of the Nd and Y network in Nd,Y:SrF2, as well as well-preserved Nd fluorescence in the written optical waveguides.

Acoustic Characterisation of Konjac Glucomannan Gel as a Medical Phantom

Acoustic properties are the main criteria to evaluate the compatibility of tested materials as a medical phantom. We determined the acoustic properties of konjac glucomannan (KGM) gel to verify its compatibility as a medical phantom. The acoustic properties measurement employed ultrasonic insertion technique and utilized two identical transducers of 5 MHz center frequencies. One KGM gel block with 5.62 mm thickness was used as sample to determine its longitudinal speed, acoustic impedance and attenuation coefficient at three different water temperatures; (21.5 ± 0.1), (22.5 ± 0.1) and (23.5 ± 0.1) °C. Findings indicated that its longitudinal speed and acoustic impedance increased from (1495 ± 1) to (1499 ± 1) m s-1 and (1.555 ± 0.001) to (1.559 ± 0.001) × 106 kg m-2 s-1 as the water temperature increased from (21.5 ± 0.1) to (23.5 ± 0.1) °C. It also indicated that its attenuation coefficient varied around (0.1303 ± 0.0107) to (0.1373 ± 0.0103) dB cm-1 with increasing water temperature. KGM gel is compatible to be a medical phantom since its acoustic properties are comparable to the acoustic properties of human soft tissue.

Noninvasive carotid artery elastography using multielement synthetic aperture imaging: Phantom and in vivo evaluation.

Vascular elastography can visualize the strain distribution in the carotid artery, which could be useful in assessing the propensity of advanced plaques to rupture. In our previous studies, we demonstrated that sparse synthetic aperture (SA) imaging can produce high quality vascular strain elastograms. However, the low output power of SA imaging may hamper its clinical utility. In this study, we hypothesize that multi-element defocused emissions can overcome this limitation and improve the quality of the vascular strain elastograms. To assess the impact of attenuation on the elastographic performance of SA and (multi-element synthetic aperture) MSA imaging, we conducted experiments using heterogeneous vessel phantoms with ideal (0.1 dB cm-1 MHz-1 ) and realistic (0.75 dB cm-1 MHz-1 ) attenuation. Further, we validated the results of the phantom study in vivo, on a healthy male volunteer. All echo imaging was performed at a transmit frequency of 5 MHz, using a commercially available ultrasound scanner (Sonix RP, Ultrasonix Medical Corp., Richmond, BC, Canada). The results from the phantom results demonstrated that plaques were visible in all strain elastograms, but those produced using MSA imaging had less artifacts. MSA imaging improved the elastographic contrast to noise ratio (CNRe) of the vascular elastograms by 14.58 dB relative to SA imaging, and 9.1 dB relative to compounded plane wave (CPW) imaging. Further, the results demonstrated that the elastographic performance of MSA imaging improved with increase in (a) the number of transmit-receive events and (b) the size of the transmit sub-aperture, up to 13 elements. Using larger sub-apertures degraded the elastographic performance. The results from the in vivo study were in good agreement with the phantom results. Specifically, using a defocused multi-element transmit sub-aperture for SA imaging improved the performance of vascular elastography. The results suggested that MSA imaging can produce reliable vascular stain elastograms. Future studies will involve using coded excitations to improve the CNRe and frame-rate of the proposed technique for vascular elastography.

Study of the pedestal process for reducing sidewall scattering in photonic waveguides.

In this work we investigate the principles of an alternative method for defining sidewall in optical waveguides fabricated using planar technology. The efficiency of this method is demonstrated through simulations and experimental results regarding propagation losses of a solid core ARROW waveguide fabricated on silicon substrate. It is well known that waveguides fabricated using sidewalls etched via Reactive Ion Etching (RIE) can present high sidewall roughness, especially if metallic hard-masks are used. This is largely responsible for the undesirable losses observed in these waveguides. The basic strategy of the proposed method is to do the etching step, in the fabrication of the waveguides, before the deposition of the core, so as to have the lower cladding layer and part of the silicon substrate etched away. Only after this, is the core of the waveguide deposited. This results in a waveguide sustained by a silicon pedestal. With this process, losses as low as 0.45 dB cm-1 for multimode and 0.84 dB cm-1 for single mode waveguides are obtained. The numerical simulations demonstrate that roughness in sidewalls implicates in propagation losses which are at least five times larger that those in the bulk of the material, thus corroborating the idea behind the proposed method.

Experimental Rig to Improve the Geophysical and Geomechanical Understanding of CO2 Reservoirs

We intend to perform experiments that simulate real Carbon Capture and Storage (CCS) conditions in the laboratory, and hence provide the necessary knowledge to interpret field seismic surveys. Primarily, our research is focused on determining seismic rock properties (i.e., wave velocities and attenuation) of real and artificial 50mm diameter brine-CO2-bearing sandstone and sand samples that are representative host rocks of real CCS scenarios. Accordingly, we have integrated into a new triaxial cell system both an ultrasonic pulse-echo method for accurate velocity (± 0.3%) and attenuation (± 0.1dB cm-1) measurements, and an electrical resistivity tomography (ERT) method to monitor homogeneity of pore fluid distribution within the samples. The use of ERT provides calibration data for field scale techniques (such as marine controlled source electromagnetic surveying) but also allows measurements of bulk resistivity, fluid diffusion monitoring, flow pathway characterization, and determination of the relative permeability for different brine/brine-CO2 ratios. By simultaneously measuring ultrasonic P- and S-wave velocities and electrical resistivity, we also provide data for joint inversion of seismic and electric field data. Furthermore, the stress-strain behaviour of the sample is continuously monitored with the aid of electrical gauges, so that we deal consistently and simultaneously with the geophysical and geomechanical response of the reservoir when submitted to CO2 injections.

650-nm All-Polymer Thermo-Optic Waveguide Switch Arrays Based on Novel Organic–Inorganic Grafting PMMA Materials

All-polymer thermo-optic (TO) waveguide switch arrays at 650-nm wavelength based on novel organic-inorganic grafting poly(methyl methacrylate) (PMMA) materials are successfully designed and fabricated. The thermal stability and optical properties of the sol-gel materials are studied. The TO coefficient of organic-inorganic grafting PMMA core material is obtained as -1.65×104 °C-1. The characteristic parameters of the embedded waveguide and arrayed electrode heaters are carefully designed and simulated. The propagation loss of a 4-μm wide straight waveguide is 0.85 dB cm-1. The M-Z interferometer TO switch on-off time is 600 μs. The extinction ratio is ~ 8.2 dB and the applied electric power as the switching power is ~ 22.6 mW. The device could have great potential in biomedical applications. The technique could be well suited for polymer optical fiber integrated network systems.

Optical properties of wide single-mode strip and grating loaded channel waveguides

New wide single-mode strip and grating loaded (SGL) channel waveguides made of silicon nitride on the oxide buffer layer of a planar silicon-on-insulator waveguide are studied. The central 10-lm-wide strip produces a multi-mode channel waveguide and diffraction gratings with a period 0.6 lm built on the structure edges produce mode-dependent additional losses due to radiation to the surrounding medium. The optical properties of these waveguides are discussed using the results of a three-dimensional numerical simulation by the FDTD and BPM methods. It is shown that a wide SGL waveguide is quasi-single-mode one because ithas a small propagation loss (∼ 0.3 dB cm-1) for the fundamental mode and a high (up to -20 dB cm-1) loss forthe higher order modes. The new SGL waveguides are CMOS compatible and can become basic for fabricating new photonic elements, including tunable optical filters and multi-plexers based on the multireflector technology.

Optical amplification in a first-generation dendritic organic semiconductor.

We report a study of a new class of organic semiconductor as an optical gain medium. We demonstrate amplification of violet light by use of stimulated emission in a solution of a first-generation bis-fluorene-cored semiconducting dendrimer. Amplification is also observed in the solid state by means of amplified spontaneous emission in an optically pumped dendrimer planar waveguide. Gains of 36 dB cm(-1) at 420 nm and 26 dB cm(-1) at 390 nm in solution and 350 dB cm(-1) in the solid state are obtained. These results show that semiconducting dendrimers have potential as visible laser and amplifier materials.

Optical planar and channel waveguides in the new nonlinear crystal Ca_4YO(BO_3)_3 (YCOB) fabricated by He+ implantation

We report the first study of optical planar and channel waveguides fabricated in the new nonlinear crystal Ca4YO(BO3) by use of MeV He+-implantations. The nx, ny, and nz refractive index modifications are studied. Losses in nonannealed YCOB waveguides measured with a CCD camera are found to be less than 2 dB cm(-1). This work is the first step toward the investigation of frequency conversion within the obtained guiding structures.