Here, a multi-band metamaterial absorber (MMA) is proposed. The MMA (multi-band metamaterial absorber) consists of a symmetrical snowflake resonator layer and an underlying metal plate, separated by a dielectric layer. Furthermore, the snowflake resonator is composed of several branches which leads to multiple resonant modes. The coupling of each resonant mode leads to an absorption enhancement effect. The structure is optimized to achieve perfect absorption at three resonant frequencies. Simulation results show that the MMA achieves three narrow absorption peaks with absorptivity of 94.6%, 98.95%, and 98.82% in the range of 15~36 GHz. The absorption mechanism is analyzed in detail at all three resonant frequencies, and the structure size and resonant frequency are calculated and matched quantitatively. By means of analog circuit, the absorption spectrum of the absorber is verified. In addition, the application of the proposed MMA as liquid sensor is realized by analyzing the frequency shift of the absorption peaks. The sensitivity of the refractive index sensor based on the proposed MMA is 11.64 GHz/RIU, the quality factor is 1236, and the figure of merit (FoM) is 151.33 RIU-1 at one of the resonant frequencies, when the analyte thickness is 5.5mm and the refractive index range is 1 to 1.48.
Composite materials have been widely applied in flexible devices for years. Many researchers focused on the resistance properties of these materials but usually induced or ignored the impact of contact resistances or even Schottky barriers. In this paper, we propose a modified four-contact method to accurately measure the resistivities or sheet resistances of flexible composite materials. By measuring the resistance between each pair of electrodes with different voltage polarities, either ohmic or Schottky resistances can be eliminated through calculation. At the same time, this method is easily integrated into flexible devices, so the actual values of material resistances under pressure can be tested.
The gridless planar flexible sensors based on BP neural network have attracted wide interests in the design of smart sensing devices due to their high accuracy and low cost. In order to obtain the effective measurement data from the multichannel electrodes in a gridless planar sensor simultaneously, and to avoid the mutual crosstalk between the electrodes, a time-division multiplex piezoresistive measurement system based on serial port communication function is proposed in this work. A proportional amplification circuit is designed in this system to convert resistance signals into potential signals, and a STM32 is used as the main control chip to control two multiplexers to realize time-division multiplex transmission. The measured potential signals are converted by ADC and sent to computer with the help of USART. A PCB is designed and fabricated accordingly, and the fast and accurate multi-channel data synchronization acquisition is achieved.
In this work, an ultra-long single-span 10Gbps SDH optical communication system was built up and tested. The 10G signal transmitted from the bit error tester with an additional 10G XFP transponder module, and looped back to the bit error tester. All the conditions and results presented were verified as error-free for over 12h. The 10G XFP module was used to perform an optical-electric-optical (OEO) conversion, so that the modulation parameters can be adjusted for nonlinearity optimization, which will be discussed elsewhere. The total distance of the fiber is over 220km, and the maximum power of the signal injected into fiber is over 17dBm, indicating that the SBS threshold is suppressed over 17dBm with the help of the 10G XFP optimization. What is interesting is, a clear wide shoulder was observed in the output signal spectrum at the transmission fiber output, provided that the fiber input power exceeds 17dBm. After careful analysis and simulation, we attributed this shoulder generation to the intra-band FWM effect, which is caused due to the FWM interaction between the carrier wave and the modulation wave within the band. The error tester will identify the shoulder as the noise level, and the maximum input power is restrained by equivalent optical signal noise ratio (OSNR) due to the intra-band FWM effect. So that the maximum transmission distance will be restricted even if the stimulated Brillouine scattering (SBS) threshold can be further enhanced. Other nonlinear effects including self-phase modulation (SPM), and group velocity dispersion (GVD) are also analyzed.
A broadband THz metamaterial absorber was designed based on the transmission line theory, and the inductive mesh structure was selected as the meta-surface. The absorber samples were fabricated by electrohydrodynamics(EHD)-based printing technology, which is a cost-effective and high-precision technology for flexible electronic device fabrication. The absorption in (98-353) GHz exceeded 90%, and the experimental data matched well with the theoretical and simulation results. It was also proven that the absorption spectra were insensitive to the linewidth and surface resistance of the inductive mesh structure, so that the design has high tolerance to possible fabrication error.
Pressure sensors have many applications in medical fields. Conducting rubber film with good piezoresistive characteristics was synthesized and used for a special micro pressure sensor design. The film features adjustable measurement range, good mechanical robustness, and room-temperature fabrication. The resistance-pressure curve was measured, and the repeatability was checked. The specially designed micro sensor can be used for the measurement of human body liquid pressure.
ZnS thin film has wide applications in optoelectronics area, including photocatalysis and solar cells. The water bath is a popular ZnS thin film fabrication method, with merits of high efficiency, easy-operation, low cost, and uniform deposition. In this report, ZnSO47H2O and thiourea were mixed in the water bath for reaction at a constant temperature with mechanical stirring. Thus-deposited ZnS thin film was then annealed in Ar. The impacts of different pH, different concentration, different water bath temperature, and different annealing temperature and time were studied to find the optimal condition. The optimal results were as follows: the mixture of 0.056mol/L thiourea and 0.0532mol/L ZnSO47H2O in water was titrated to pH=10.7 by ammonia, followed by water bath reaction at 85°C, then annealed in Ar at 300°C for 1.5h. Thus fabricated ZnS thin film has the best surface flatness and film uniformity, with high optical transmittance.
The osteofascial compartment syndrome is a common syndrome in orthopedics clinical practice. The body fluid pressure is the key indicator of the need for surgery. The traditional needling pressure measurement method is traumatic, single-point, and wired, which is very inconvenient in practice. As a promising alternative measurement method, anon-invasive, multi-point, and wireless flexible wearable pressure measurement sensor was proposed in this work. The sensor has 7 flexible pressure measurement units to realize multi-point measurement. The units were fabricated by unique printing electronics technology, with high precision and flexibility. ZigBee protocol was used for real-time wireless data transmission. A35.9mm*56.6mm flexible printed circuit board(FPCB)was designed and optimized for the pressure readout and wireless communication. The FPCB was powered by a small 3V button battery. Typical specifications of the sensor are as follows: sensing unit size 10*4 mm; measurement range [0, 100] N; measurement precision 2.5 N; maximum wireless transmission distance50 m; maximum bending radius 2 mm. Further optimization and experiments, including animal experiments, are in progress.
The silver nanoparticle (AgNP) based conducting wire is a fundamental element of flexible electronic devices, especially in the printing electronics area. Its resistance change mechanisms under pressure is of both scientific interest and practical importance. AgNP-based conducting wires were fabricated on flexible substrates by electrospraying printing technology, and three possible resistance change mechanisms were studied: vertical deformation (VD) of the AgNP wire due to vertical pressure, horizontal wire elongation (HWE) along with the flexible substrate due to vertical pressure, and local micro deformation (LMD) at the touching edge. Analysis of the experiment data revealed that the resistance change due to VD was negligible, the resistance change due to PWE was one order of magnitude smaller than the measured value, and the resistance change due to PWE was the dominating mechanism.
In this article, we made a preliminary study on the main influencing factors of sparkle spots, put forward the concept of "sparklingness" to characterize the strength of sparkle spots, and proposed a standard measurement method for the sparklingness. We proposed to use 532 nm green laser pointer as the testing light source, let the light pass through the film and form a sparkle spots image at the receiving CCD or a piece of white paper. A standard image processing method was used to obtain an index number standing for the scattering status of the laser, which is defined as “sparklingness”. In the experiment, we also analyzed the power dependence of sparklingness. With proper calibration, the measurement error of the sparklingness can be minimized, and it can be used as a physical quantity to describe the film quality as of the sparkle issue. This work can be a useful reference for further study of the sparkle issue in optical films.
Acrylic (PMMA) possesses excellent optical transparency, good chemical stability as well as many other merits such as the feasibilities in dyeing and manufacturing. But its poor hardness and wear resistance restrict its industrialized applications. In order to improve the hardness and wear resistance, SiO2 films were coated on PMMA substrates by both dip coating method and aerosol spraying method in this work. Heating curing method was carried out after the coating of SiO2 film, and consequently, the mechanical properties, optical properties and surface morphology were characterized and compared. The experimental results showed that the SiO2 films prepared by aerosol spraying method has a better performance in both hardness and wear resistance, compared with the films prepared by dip coating method. In the optimized conditions, the hardness of the PMMA was improved from 3H to ~8H, and the non-abrasion rubbing times increased from less than 100 times to 5000 times with a loading of 500g weight after the coating of SiO2 film, indicating the improvement of the wear resistance.
THz imaging has become a hot research topic in recent years, thanks to its merits of non-contact, strong penetration,
immunity to hostile environments, and nondestructive detection. However, its spatial resolution is limited by the
relatively long wavelength, so the location and measurement precision can only reach the level of the imaging
wavelength, which has become a severe limitation of THz imaging. A simple way using surface plasmonic polartons
(SPPs) to improve the location and measurement precision of THz by one order of magnitude was proposed in this
manuscript, which can realize subwavelength THz imaging.
Because of the electromagnetic field enhancement effect in subwavelength scale, the surface plasmon wave (SPW) has been widely used in beam forming, bio-prospecting, and subwavelength structure design. But most research work is in the visible light or terahertz frequency band, and the surface plasmonic material (SPM) is usually limited to metals. In the microwave band, complex structures have to be used to achieve the desired subwavelength effects, making use of both metal and dielectric materials. In this paper, we propose the excitation of SPW in the microwave range using a simple structure and the material of indium tin oxide (ITO). By measuring the electric field profile during the propagation process, the excitation of SPW in ITO was verified. At the same time, frequency dependence was seen during the propagation process. Therefore, ITO can be a good SPM in the microwave band, just like metals in the visible light band. Considering the transparent characteristics of ITO, it can have many interesting applications.
This article studied the interference enhancement and modulation introduced by surface plasmon polaritons (SPPs) in a double-concentric-ring structure. Young’s double-slit interference experiment is a classic experiment in the history of physics, and has many modifications with deep impacts in many areas including physics, optics, and electromagnetics. In this work, to use the classic bull’s eye structure to produce the surface plasmon polariton effect, a double-concentricring- hole structure was used instead of the double-slit structure to generate optical interference, and the bull’s eye structure was applied in the surroundings to generate surface plasmonic wave for modulation of the interference. For structure details, a concentric double-ring-hole was etched in a silver film, with a series of periodic concentric-ringshaped shallow grooves etched in both the upper and bottom surfaces of the silver films. Simulation results showed that the interference of the double-ring-hole could be modulated by SPPs, generating new transmission spectra with desired peak positions and intensities. The transmission peak intensity could be enhanced by 2 to 6 times. The proposed structure can be used as a powerful and convenient tool to adjust the transmission spectra, which can have promising applications in the design and implementation of optical devices for filtering and sensing, especially in the sub-wavelength structure size range.
KEYWORDS: Titanium dioxide, Thin films, Aluminum, Glasses, Thin film deposition, Thin film solar cells, Crystals, Scanning electron microscopy, Thin film coatings, Coating
Titanium dioxide thin film plays an important role in thin film solar cells, and has promising future in everyday applications including air cleaning and self-cleaning glass. With the concepts of flexible solar cells and wearable devices being more and more popular, there is increasing interest to coat titanium dioxide thin films on flexible substrates, such as aluminum foils. Many methods have been used to fabricate titanium dioxide thin films, such as dip-coating, spin coating, aerosol spray, plasma-assisted coating, electrospraying, and so on. Among them, electrospraying is especially suitable for thin film deposition on flexible substrates. This work reports fabrication of dense and uniform titanium dioxide thin films on glass as well as flexible aluminum foil using multi-jet electrospraying technique.
Silica microballs have a wide range of applications in the field of optics, electronics, biotechnology,chemical industry, and so on. In this work, a new approach, electrospraying, was used to coat the silica microballs onto the glass substrate, and the coating results were compared to spin-coating and dip-coating. Good microball size control could be achieved using the electrospraying method. X-Ray Diffraction (XRD) results showed that amorphous silica microballs were obtained. From Scanning Electron Microscopy (SEM) images, we can see that uniform microball size was achieved. In general, the results are better than what can be achieved by spin-coating, and comparable to that of dip-coating. However, electrospraying has great potential in mass production, especially for large-area fabrication.
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