Ocean waves are not only a sustainable renewable energy source but also provide valuable information for monitoring marine environments and natural hazards. In this study, we developed a CNT/SEBS-based self-powered marine monitoring sensor utilizing a mechano-electrochemical mechanism, enabling simultaneous ultralow-frequency wave sensing and electrical energy harvesting. The developed sensor generated an open-circuit voltage of up to 60 mV and a short-circuit current of 80 μA/cm2 without an external power source by exploiting variations in electrical double-layer capacitance induced by changes in the electrode–electrolyte interface. The capacitance increased from 0.1 μF to 2.4 μF with increasing immersion area, demonstrating the effectiveness of the proposed sensing mechanism. Furthermore, the CNT/SEBS bilayer exhibited high electrical conductivity together with excellent stretchability and flexibility, maintaining stable electrical responses under repeated water-level fluctuations. The proposed mechano-electrochemical self-powered sensor provides a promising platform for next-generation autonomous marine monitoring systems and sustainable blue-energy harvesting technologies.
This study investigates the effect of mask material and thickness on the silicon etching profile using a high-density plasma (HDP) etching system, aiming to reduce optical loss in silicon-based optical waveguides. As the mask thickness increased, the etching sidewall angle became steeper. An etching profile angle of 87° was obtained when tetraethyl orthosilicate (TEOS) was used as the mask material, while 80° was obtained for photoresist (PR). This is attributed to electron charging on the mask surface in the plasma. The charged mask modifies the distribution and strength of the electric field depending on its thickness, thereby affecting the trajectory of positive ions accelerated toward the substrate by the bias voltage. Furthermore, Plasma diagnostics using optical emission spectroscopy (OES) and surface composition analysis using field emission Auger electron spectroscopy (FE-AES) revealed that changes in the mask material also alter the reaction pathways and formation characteristics of active species and silicon by-products in the plasma. These results suggest that the mask material influences the overall plasma characteristics, including electron density and ion energy, and plays a critical role in the precise control of silicon etching profiles for high-performance optical device fabrication.
Beom Jin Kim, Pil Hong Jeong, Jae Min Lee, Dong Hwan Won, Jeong Ho Lee, Heon Min Lee, Ku Yun Jeong, Keon Park, Kawan Anil, Soon Jae Yu, Yeon Sik Chae, Sung Bae Park
J Korean Inst Electr Electron Mater Eng 2025;38(3):272-277. Published online May 1, 2025
SMD-type 660 nm wavelength semiconductor laser diode device is fabricated using silicon resin molding technology and fabricated a BT resin printed circuit board. BT resin electrode structure printed circuit boards with soldering electrode pads and through holes for heat dissipation were fabricated. The SMD process is an injection molding technique in which the chip is molded from silicon material and then cut by a dicing process to complete the beam emission surface. The fabricated SMD-type semiconductor laser diode exhibits a good near-field beam pattern with no scattering/dispersion caused by the printed circuit board or silicon molding in the emitted laser beam, or reflections around the chip. It was also confirmed that the heat generated at 20 mA operation has good heat dissipation characteristics through the through-hole heat dissipation structure.
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Mitigating Contact‐Constricted Thermal Bottlenecks by Magnetically Programmable hBN Bridge Fillers in Al2O3/Epoxy Composites Yeonwook Jeong, Sabina Ghorsaine, Chan‐Jae Lee, In Kim, Mooho Lee, Hyejeong Lee, Ginam Kim, Jong‐Woong Kim Small.2026;[Epub] CrossRef
Al-Mo thin films were fabricated using combinatorial sputtering system to realize highly sensitive surface acoustic wave (SAW) devices. The Al-Mo sample library was grown with various chemical compositions and electrical resistivities, which provided important information for selecting the most suitable materials for SAW devices. As the SAWs generated from piezoelectric materials are significantly affected by the resistivity and density of the interdigital transducer (IDT) electrodes, three types of Al-Mo thin films with different Al contents were fabricated. The thickness of the Al-Mo thin film used in the SAW-IDT electrode was fixed at 150 nm. As the Al content of the Al-Mo thin film decreased from 81.2 to 30.3 at%, the resistivity decreased slightly from 5.43±0.15 to 4.87±0.1×10-5 Ω-cm, whereas the calculated density increased significantly from 4.1 to 7.9 g/㎤. The SAW device composed of Al-Mo IDT electrodes resonated at 143 MHz without frequency shifts; however, the selectivity of the resonant frequency and insertion loss deteriorated as the Al content decreased. This suggest that the resonant characteristics of the SAW devices fabricated with Al-Mo thin films were more strongly influenced by the material density rather than the electrical properties of the IDT electrodes.
The low-temperature deposition of BaNi(2-x)CoxFe16O27 thin films with a Ba hexaferrite structure for electromagnetic shielding was studied. The BaNi(2-x)CoxFe16O27 thin films produced through the spin spray process were suitable for thin film deposition on a flexible substrate because it crystallized well at low temperature below 90℃. The change in shielding characteristics depending on the Co content of the BaNi(2-x)CoxFe16O27 thin film was investigated, and excellent shielding characteristics with S21 of -1 dB were obtained in a wide frequency range of 26~40 GHz when the Co content was 0.4 or more. The purpose of this study is to analyze changes in shielding properties caused by change in Co content in relation to phase changes in BaNi(2-x)CoxFe16O27 and obtain basic data for developing excellent flexible electromagnetic wave shielding materials.
An algorithm was developed to detect and block serial arc currents using HPF. The AC series arc problem is that the load current is greater than the fault current and no leakage current occurs. As a solution, an arc detection method utilizing differences in high- frequency amplitudes was developed. HPT was applied to the load current and FFT was applied to eliminate low frequencies. An algorithm has been developed to detect arc waveforms when they exceed a certain value compared to the average of normal waveforms. Using one cycle of data, arc detection is faster and arc accidents are prevented.
Phase evolution, sintering behavior, microstructure, and microwave dielectric properties of (1-x) mol Ba3V4O13 - (x) mol BaV2O6 system were investigated. The sintered specimens of all compositions consisted of Ba3V4O13 and BaV2O6, and no secondary phase was observed. As x increased, the linear shrinkage decreased to the composition of x=0.5, and then increased again, implying that Ba3V4O13 and BaV2O6 phases interfered mutually with each other during sintering. All compositions showed a dense microstructure with a large grain growth. Cracks were observed in some compositions because of the relatively high sintering temperature of 620~640℃. As x increased, the dielectric constant increased, while the quality factor was maintained from about 50,000 GHz to about 70,000 GHz up to the composition of x=0.9, and then decreased to 20,987~27,180 GHz at the composition of x=1.0. As x increased, the temperature coefficient of the resonance frequency showed a (+) value from a (-) value. The dielectric constant, the quality factor, and the temperature coefficient of resonant frequency of x=0.7 composition sintered at 640℃ for 4 hours were 10.61, 71,126 GHz, and -4.9 ppm/℃, respectively. This composition showed a good chemical compatibility with Al powder, indicating that the Ba3V4O13-BaV2O6 ceramics are a candidate material for ULTCC (Ultra-Low Temperature Co-fired Ceramics) applications.
Phase evolution, thermal and microwave dielectric properties of cordierite-Al2O3 composite were investigated. As the content of Al2O3 increased, mullite, sapphirine, and spinel were formed as secondary phases, implying that cordierite may be decomposed by the reaction with Al2O3. All sintered specimens exhibited dense microstructures. The densification occurred through liquid phase sintering. As the content of Al2O3 increased, the thermal expansion coefficient and the dielectric constant increased, whereas the quality factor decreased. The thermal expansion coefficient, the dielectric constant, and the quality factor of the 90 wt% cordierite 10 wt% Al2O3 composite sintered at 1,425℃ were 2.9×10-6 K-1, 5.1, and 34,844 GHz, respectively.
Recently, infrared (IR) and near-infrared (NIR) light-emitting diodes (LEDs) were widely used for home medical applications owing to its low output power and wide exposed area for curing. For deep penetration of the light under the skin, multiple LEDs with wavelengths of 700~10,000 nm were located on a flexible printed circuit board. When multiple wavelengths of LEDs were soldered on a circuit board, the lifetime of LED module highly depends on LEDs with a short lifetime. The mean time to failure (MTTF) was able to calculate with the experimental results under high temperature and the Arrhenius model. The results of this study could help companies to approve the warranty of LED modules and its product.
Radiation noise due to EMI noise generated by the driving circuits of LED lighting devices in a medical imaging room was reduced by decreasing the noise source in the driving circuits and changing the number of corrections in EMI filters. Noise attenuation and filter changes enabled driving circuits that reduced the electromagnetic waves. Such circuits were efficiently designed by using capacitors and inverters in a given space. Therefore, the malfunction of radiation devices can be minimized by using EMI-reduction filter circuits, and reliable operation of medical devices can be expected by blocking electromagnetic waves.
This study investigated the microstructure and piezoelectric properties of lead-free 0.74(Bi1/2Na1/2)TiO3-0.26SrTiO3 (BNST26) piezoelectric ceramics sintered using a microwave furnace. For comparison, specimens were also prepared using a conventional furnace sintering (CFS). Average grain sizes of 2.4 μm and 3.2 μm were obtained in the sample sintered at 1,100℃ for 5 min using microwave sintering (MWS) and at 1,175℃ for 2 h using CFS, respectively. To quantify the changes in the microstructures and electrical properties according to the sintering conditions, the polarization hysteresis, bipolar and unipolar strain curves, and temperature dependence of permittivity were evaluated. As a result, it was determined that the Pmax (maximum polarization), Pr (remanent polarization) and Smax (maximum strain) values tend to increase with the average grain size. Based on these results, it is concluded that the MWS method can produce lead-free ceramics with superior performance in a relatively short time compared to the conventional CFS method.
The aim of this study is to improve the fault decision ability of FRTU (Feeder remote terminal unit) in DAS (Distribution automation system). FRTU uses the FI (Fault indicator) algorithm based on fault current pickup and operation of the protection device. Even if the inrush current flows or the protection device is sensitive to the transient current, FRTU may indicate incorrect fault information. To address these problems, we propose an improved fault recognition algorithm that can be applied to FRTU. We will detect a specific wave that is indicative of a fault, and use this information to identify a fault wave. The specific wave-detection algorithm is based on the duration and periodicity of the voltage, current, and harmonic variations. In addition, we propose fault recognition algorithms using voltage factor variation analysis and DWT (Discrete wavelet transform). All the wave data used in this study were actual data stored in FRTU.
The aim of this investigation is to detect specific waveforms in a distribution line prior to the occurrence of a fault. Conditions were introduced such that a feeder remote terminal unit (FRTU) of the distribution automation system selects and stores fault waveforms from the different waveforms detected in the distribution line. In addition, an algorithm was developed to detect specific waveforms from the fault waveforms stored using the FRTU. This algorithm exploits the duration and periodicity of harmonic changes in voltage and current. The efficacy of the algorithm was confirmed based on the measurements of fault waveforms in an actual distribution line. The results indicated that faults in a distribution line can be predicted via experimental measurements.
To study the frequency response characteristics of alternating-current-driven organic light-emitting diodes (OLEDs), we fabricated blue-fluorescent OLEDs and analyzed their electroluminescent characteristics according to the alternating current voltage and frequency. The luminance-frequency characteristics of alternating-current-driven OLED was similar to that of a low-pass filter，and the luminance of high-voltage OLED decreased at higher frequency than low-voltage OLED. The luminance characteristics of the OLED according to the frequency is due to the capacitive reactance in the OLED, generated during the alternating current driving. The frequency response characteristics of the OLED according to the voltage is due to the decrease in internal resistance of the organic layer. In addition, the negative voltage component of the alternating current did not affect the frequency response of the OLED. Therefore, the electroluminescent characteristics of OLED with an alternating current power of 60 Hz are not influenced by the frequency.
The amount of electric power for photovoltaic power generation depends on the location of the power plant and the direction of solar cell. The solar cell controls the generation of solar power plants. Therefore, the structure of solar cell, manufacturing method, and optic technology were factors contributing to increased solar cell efficiency; however, the technical limit has been reached. Herein, we propose a new method to increase the solar cell efficiency using a wavelength conversion technology that converts ultraviolet and infrared rays, which are not effectively used in solar cells, into effective wavelength of solar cell. We used fluoride Na(Ca)YF4 phosphor for wavelength conversion. Then, a wavelength-conversion fluorescent paste, prepared using an organic-silicon binder, was used to prepare a film that was applied to Si solar cells. It was confirmed that conversion efficiency improved by 5% or more.
We investigated the phase evolution, microstructure, and microwave dielectric properties of Na- and Zr-doped Ba(Mg0.5W0.5)O3 [i.e., (Ba1-2xNa2x)(Mg0.5-xZrxW0.5)O3] ceramics. BaWO4 as a secondary phase was observed in all compositions, and it increased as the dopant concentration increased. All specimens revealed a dense microstructure. For the composition of x=0.01, polyhedral grains were observed. As the dopant concentration increased, the densification and the grain growth were promoted by a liquid phase. The quality factor(Q×f0) decreased remarkably, whereas the dielectric constant (εr) tended to decrease as the dopant concentration increased. The dielectric constant, quality factor, and temperature coefficient of the resonant frequency of the composition of x=0.01 sintered at 1,700℃ for 1 h were 18.6, 216,275 GHz, and -22.0 ppm/℃, respectively.
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Structural, microstructural, opto-electronic and dielectric studies of Ba(Mg1-xZnx)1/2W1/2O3 (0.00 ≤ x ≤ 0.40) ceramics for dielectric resonators application Farhan Ullah, Asad Ali, Tanveer Ahmad, Salhah Hamed Alrefaee, Hala Siddiq, Farkhod Rakhmonov, Naseem Akhter, Vineet Tirth, Ali Algahtani, Abid Zaman Ceramics International.2026; 52(16): 31004. CrossRef
With trend of the miniaturization and the high-functionalizing of mobile communication system, low-loss microwave dielectric materials are widely used for high frequency communication components. These dielectric materials should be co-sintered with highly electric-conducting metal such as silver or copper for high-frequency and thick film process application. Sintering temperature of Ca[(Li1/3Nb2/3)1-xTix]O3-δ, which has excellent dielectric properties such as εr above 40, quality factor (Q·f0) above 16,000 GHz, and TCF (temperature coefficient of resonant frequency) of -20~-10 ppm/℃, is reported as high as 1,175℃, so it could not be co-sintered with silver or copper. Therefore in this study, low-temperature melting glasses of Zn-B-O and Zn-B-Si-O systems were added to Ca[(Li1/3Nb2/3)1-xTix]O3-δ to lower its sintering temperature under 900℃ without losing excellency of dielectric properties. With 15 weight % of Zn-B-Si-O glass and sintered at 875℃, specimen showed density of 4.11 g/cm3,ε r of 40.1, Q·f0 of 4,869 GHz, and TCF of -5.9 ppm/℃. With 15 weight % of Zn-B-O glass and sintered at 87 5℃, specimen showed density of 4.14 g/cm3, εr of 40.4, Q·f0 of 7,059 GHz, and TCF of -0.92 ppm/℃.
Electrical and optical properties of the AC voltage driven organic light-emitting diodes were investigated by measuring the electroluminescence of the device. Device structure of ITO(170 nm)/TPD(40 nm)/Alq3(60 nm)/LiF(0.5 nm)/Al(100 nm) was manufactured using a thermal evaporation. Sinusoidal and square-type AC voltage was applied to the device using a function generator. Amplitude of the applied voltage was 9.0 V, and a frequency was varied from 50 Hz to 50 kHz. Electroluminescence out of the device was measured in a Si photodetector simultaneously with the applied voltage together. An intensity and a delayed residual luminescence from the device were depended on the frequency of the sinusoidal voltage. It is thought to be due to a contribution of the capacitive nature in the equivalent circuit of the device. An electron mobility was estimated using a time constant obtained from the luminescence of the device driven by the square-type AC voltage.
In this research, we focused on the improvement of cy3 dye’s characteristics for LCD color filter. Solubility and thermal stability are main characteristics of dyes for LCD color filter. We performed experiment to change counter cation of cy3 dyes with alkoxy substituent for these purposes. These cy3 dyes (1b∼5b) were prepared through the synthetic procedure of three steps. The synthesized new cy3 dyes were charaterized by using NMR, FT-IR, UV/Vis spectroscopy, and TGA. These cy3 dyes showed purple color and maximum absorption wavelength (λmax) in the range of 578∼590 nm in UV/Vis spectrum. We confirmed that solubility and thermal stability of cy3 dyes were dependent on the structure of counter cation. Cy3 dyes with alkoxy substituent have good solubility in organic solvents such as dichloromethane, methanol, and acetone. Especially, Cy3 dye with 4-nitrobenzyl counter cation (5b) gave excellent solubility characteristics.
In this research, we focused on the development of cy3 dye with high thermal stability and good solubility for LCD color filter. Cy3 dyes were prepared through the synthetic procedure of two steps. The synthesized cy3 dyes were characterized by using NMR, FT-IR, UV/Vis spectroscopy, and TGA. These cy3 dyes showed maximum absorption wave length (λmax) in the range of 549∼555 nm in UV/Vis spectrum. And we confirmed that solubility characteristics and thermal stability of cy3 dyes were dependent on the structure of counter cation. Cy3 dyes with methyl counter cation and ethyl counter cation have good solubility in organic solvents such as chloroform, ethanol, and PGME. Moreover, Cy3 dye with ethyl counter cation gave excellent thermal stability in TGA thermograms. And Cy3 dye with ethyl counter cation showed good result in photoresist film test.
The artificial light sources for growth of plant are usually high-pressure sodium lamp, metal haloids lamp, and fluorescent light; however, these light sources have relatively weaker Red and Blue lights that are necessary for growth of plants. Especially the effect of Photosynthetic Photon Flux Density (PPFD) is pointed out as the weakness. Meanwhile, LED light source can be selected by specific wavelength to greatly improve the effect of PPFD. In this regard, this paper aims to investigate the promotion of plant growth by measuring photosynthetic photon flux density (hereafter referred to as PPFD) according to changes in light quality of the LED light sources. Towards this end, LED light sources for plant growth were produced with 4 kinds of mono-chromatic lights and 6 kinds of combined lights by mixing red, blue, green and white lights. A comparative analysis was conducted to investigate the effects of optical properties and PPFD on plants (green leaf lettuce) using the produced light sources. The results monochromatic light has fastest growth rate, but plant growth conditions have poor. This being so, mixed light is suitable for the green leaf lettuce.
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Biodiversity in CEA: lighting strategies for enhanced contents of phytochemicals and nutraceuticals in plants G. Samuolienė, K. Laužikė, G. Kudirka, R. Sutulienė, I. Gudžinskaitė, A. Viršilė Acta Horticulturae.2024; (1391): 239. CrossRef
A comparative study has been attempted for microwave and conventional sintering of lead-freeBi0.5Na0.5TiO3(BNT)-based multilayer ceramic actuators(MLAs). It was found that microwave sintering(MWS) could be successfully applied to the co-firing of piezoceramic/AgPd MLAs with a 10 timesshorter firing cycle as well as 100℃ lower firing temperature (850℃) for sufficient densification thanconventional furnace sintering (950℃). Furthermore, MWS-derived specimens showed better electricfield-induced strain than that of CFS-derived specimens by effectively suppressing interdiffusions betweenceramic and electrode layers.
In this paper, we studied the magnetic composite sheets for electromagnetic wave noise absorber of quasi-microwave band by using soft magnetic FeSiCr and Fe50Ni flakes with the thickness of about 1 μm and polymer. The magnetic hysteresis curve including saturation magnetization and residual magnetization and the complex permeability characteristics of the composite sheets were investigated to clarify the mixing effect on electromagnetic wave absorption properties. The saturation magnetization was decreased about 10% while the residual magnetization was increased about 15% and the real parts of complex permeability at below 500 MHz were increased 0.6～4 while those values at above 500 MHz were decreased 0.4～2.5 according to the change of contents of FeSiCr and Fe50Nipowders. As a result, the reflection loss can be moved to the lower frequency from 2∼3 GHz to 1∼1.5GHz as the contents of Fe50Ni flaky powder into FeSiCr flaky powder was increased up to 50%.
In this paper, a measurement method to obtain the optical properties of a liquid base on a side-polished single mode fiber was proposed and demonstrated. The device showed periodic resonance coupling against wavelengths. The refractive index and dispersion characteristics of a liquid were calculated by use of the spacings of periodic resonance wavelengths of the device. The thermo-optic coefficient of the liquid was obtained by monitering the shift of resonance wavelengths of the devices with change of environmental temperature.
We have investigated the optical properties of plamonic waveguide with tapered structure based on InP material for photonic integrated circuit(PIC). The proposed plasmonic waveguide is covered with the Ag thin film to generate the plasmonic wave on metallic interface. The optical characteristics of plasmonic waveguide were calculated using the three-dimensional finite-difference time-domain method. The plasmonic waveguide was fabricated with the lengths of 2 to 10 μm and the widths of 400 to 700 nm, respectively. The plasmonic mode and optical loss were measured. The optimum plasmonic length is 10 μm and widths are 600 and 700 nm in the fabricated waveguide. This plasmonic waveguide can be directly integrated with other conventional optical devices and can be essential building blocks of PIC.
This paper carried out the comparative analysis on ground impedance of a carbon block and a copper rod. Two types of grounding electrode were compared; a carbon block (L: 1 m, ф : 245 mm)buried at depth of 0.8m and a three-linked copper rod (L : 1 m, : ф : 10 mm) of equilateral triangles with 1 m spacing. Ground impedance depending on applied current was evaluated by the application of a sine wave current with 60 Hz~3.5 MHz, fast-rise pulse with rising time of 200 ns, a standard lightning impulse of 8/20 ㎲ and a 600 Hz square wave. Ground impedance for both electrodes were almost the value below 100 KHz, and increased rapidly afterwards. The maximum ground impedance appeared 400 Ω at around 1.5 MHz. Ground impedance of the block was lower at the square wave and was higher at fast-rise pulse that of the copper rod. Also, impedance as ages showed no difference for the 8 months. From the results, it is likely that ground performance for both electrodes shows no difference against commercial frequency and lighting impulse current, while the copper rod shows better performance against fast-rise pulse with rise-time of a few hundred ns.
PTFE composites for use of microwave substrate were fabricated by impregnation and heat treatment fabrication with glass fabric. This study shows dielectric properties such as dielectric constant and loss can be controlled by thickness of PTFE composite with of pressure condition in heating press process. The dielectric constant of the PTFE composites has decreasing tendency as given higher pressure condition. The dielectric loss has similar result too. Especially, the case of the dielectric loss was affected by the condition of pressure at heating press and had the best performance under 3 MPa. In order to see the reason why thickness conditions make different, their microstructures were also observed.
This paper dealt with the radiated electromagnetic wave detection of partial discharge (PD) in oil for insulation diagnostics of oil-immersed transformers. Three types of electrode system were fabricated to simulate the insulation defects that could occur in oil-immersed transformers. Frequency components of radiated electromagnetic wave in oil was measured by broadband bi-conical antennas of 300 MHz∼2 GHz and a spectrum analyzer of 9 kHz∼3 GHz. Frequency component of electromagnetic waves from PD in oil were highly distributed at 500 MHz. From the result, a narrow-band monopole antenna with the center frequency of 500 MHz was fabricated. We could detect PD signal in insulation oil without an influence of external noise by a measurement system which consists of the prototype monopole antenna, a LNA (Low Noise Amplifier), an oscilloscope and a spectrum analyzer.
The effect of address discharge characteristics by selective reset method is investigated to prevent the weakness of address discharge in the middle of a TV-field without increase of the black luminance. To reduce black luminance in AC PDP usually, the first subfield during one TV frame adopted the conventional rising ramp-reset waveform, whereas the other subfields adopted the subsidiary reset waveform without rising ramp type. As the wall charge for the address discharge was accumulated by only the rising ramp waveform during the first reset period, the wall charge on three electrodes was disappeared as time passed and the address discharge would be weakened in the rear subfields. To prevent a reduction of the address discharge characteristics without decrease the black luminance, the modified rising ramp reset waveform was adopted only in the sixth subfield. As a result, a modified driving method could improve the address discharge characteristics compared with selective reset driving scheme with almost the same black luminance.
The effect of co-sputtering condition on the structural properties of MgxZn1-xO thin films grown by RF magnetron co-sputtering system was investigated for manufacturing ZnO/MgZnO structure LED. MgxZn1-xO thin films were grown with ZnO and MgO target varying RF power. Structural properties were investigated by X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The ZnO thin films have sufficient crystallinity on the high RF power. As RF power of ZnO target increased, the contents of MgO in the MgxZn1-xO film decreased. LED was manufactured using ZnO/MgZnO multi-layer on p-GaN/Al2O3 substrate. Threshold voltage of multi-layer LED was appeared at 8 V, and it was luminesced at wave length of 550 nm.
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