Yuejin Zhao

Beijing Institute Of Technology, Peping, Beijing, China

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Publications (83)63.34 Total impact

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    ABSTRACT: Terahertz (THz) emission from laser-induced air-plasma is presented. The frequency spectra of THz wave are investigated using an air-biased-coherent-detection method. The frequency spectra are measured under different pump-pulse and probe-pulse energies. The frequency spectra become narrow with the increasing pump power and we speculate it caused by collision behavior. Meanwhile, the bandwidth of the frequency spectra is broadened by the increasing probe power, which can be explained by pulse compression. Based on this finding, the optimal frequency spectrum of THz can be achieved by regulating the probe and pump beam.
    Chinese Optics Letters 08/2014; 12(8). · 1.07 Impact Factor
  • Optik - International Journal for Light and Electron Optics 01/2014; 125(1):84-88. · 0.77 Impact Factor
  • Optik - International Journal for Light and Electron Optics 12/2013; 124(23):6058-6062. · 0.77 Impact Factor
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    ABSTRACT: A new method of pulse signal de-noising based on wavelet transform and coherent averaging method is proposed. Pulse signal is complex and weak, generally submerged by the interference of baseline drift, motion artifact and high frequency noise. Consequently, it's difficult to measure the heart rate by processing only one single-channel pulse signal, especially when the noise frequency and the pulse signal frequency are in the same frequency range. In this paper, multichannel pulse signal processing based on wavelet transform and coherent averaging is proposed to solve the above problem. First, the detail coefficients and approximation coefficients of each channel signal are obtained by N layer wavelet decomposition, then reconstructing the signal with high layers coefficients as the high frequency noises always exist in low layers coefficients. In this way we can filter out the high frequency interference. Second, the centerline of the upper and lower envelope curve obtained by cubic spline estimation is subtracted from each reconstructed signal so as to eliminate the baseline drift completely. Finally, the heart rate is acquired with the coherent averaging method which results in the noise being offset each other and the pulse signal being enhanced in the frequency range of pulse wave. The pulse signal and three kinds of noise signals simulated with the superposition of different frequency sin signal were analyzed, besides the experiment of six channel pulse signals measured simultaneously based on PhotoPlethysmoGraphy (PPG) were conducted. The simulation and experiment results showed that this method was superior to the traditional single channel.
    11/2013;
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    ABSTRACT: In the development process of satellite control systems and solar sensors, conventional solar simulators can‟t show variations in the solar shape and intensity in the state of solar occultation, so we set up a solar simulation and test platform. A method is put forward to simulate the wavefront error based on deformable mirror (DM). In this paper, the main relevant parameters which describe the atmospheric turbulence are introduced. The statistic characteristics of optical wavefront phase influenced by atmospheric turbulence are presented, and analyzed by the method of Zernike modes. A piezoelectric DM with 109 electrodes manufactured by OKO is used as the wavefront phase modulator. The important technology parameter about the deformable mirror is tested. Owing to the linear superposition, we have a research in the optical influence function and voltage deflection. The method of Karhunen-Loeve function is used in the simulation of optical wavefront, because it is statistically independent and can be expanded into the form of Zernike polynomials. We can get the coefficient matrix of random turbulence wavefront, and then link up with surface of the mirror. According to the relationship between deformation of the mirror and the voltage, we can deduce the voltage control matrix, and change the surface of the mirror as we conceive. The numerical results indicate that wavefront error can be introduced to the distribution maps of solar shape and intensity in different orbital position and any tangent point by DM in the light path.
    11/2013;
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    ABSTRACT: This paper presents a new optical structure which achieves super-resolution by means of changing the complex amplitude of light wave. It also establishes the numerical simulation of the structure. Placed in front of the aperture of optical system, this new structure can modulate the light wave by changing the amplitude transmittance, and also make the central maximum of the Airy Pattern narrower to achieve super-resolution. We analyze modulation effects of many kinds of transmittance function. The numerical simulated result shows that the central maximum of the Point Spread Function (PSF), modulated by transmittance function whose edge value is greater than central value, becomes narrower than that of the idea optical system. It is also concluded that this optical structure is insensitive to different wavelength compared with the phase shifting apodizer, which brings about less chromatic dispersion. This conclusion is extremely useful to realize the super-resolution.
    11/2013;
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    ABSTRACT: In the optical imaging system, deep depth of focus brings larger imaging space, thereby obtaining more information from object space, but also correcting defocus error caused by variety reasons. Thus deep depth of focus has profound significance in the practical application. The information optical imaging system based on the wave-front coding is a general interest among the current research of focal depth extension area. A special designed phase mask been added in the optical system, which could encode object information obtained from the designed focal depth range. By this mean, the OTF and MTF become insensitive to defocussing. Thus equal blurred middle images could be obtained, being processed by phase mask decided by the optical system which was known both by designing and testing and digital image process technology, the final clear image with extended depth of focus could be acquired. In this paper, the detail of a novel image restoration algorithm for the wave-front coding system was discussed. We aim at a specific designed wave-front coding imaging lens, using the edge condition and wavelet transform for an improved Wiener filtering processing. The result of simulation and experimental shown this algorithm could quickly decode the obtained blurred middle image. In the premise of retain more details, this method could product a good image restoration within with whole range of the designed depth of focus. The peak of signal-to-noise (SNR) ratio and the information entropy have been promoted. So does the control of the blurred edge and the ringing effect.
    11/2013;
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    ABSTRACT: A new cardiac rate measurement method is proposed. Through the beam splitter prism, the common-path optical system of transmitting and receiving signals is achieved. By the focusing effect of the lens, the small amplitude motion artifact is inhibited and the signal-to-noise is improved. The cardiac rate is obtained based on the PhotoPlethysmoGraphy (PPG). We use LED as the light source and use photoelectric diode as the receiving tube. The LED and the photoelectric diode are on the different sides of the beam splitter prism and they form the optical system. The signal processing and display unit is composed by the signal processing circuit, data acquisition device and computer. The light emitted by the modulated LED is collimated by the lens and irradiates the measurement target through the beam splitter prism. The light reflected by the target is focused on the receiving tube through the beam splitter prism and another lens. The signal received by the photoelectric diode is processed by the analog circuit and obtained by the data acquisition device. Through the filtering and Fast Fourier Transform, the cardiac rate is achieved. We get the real time cardiac rate by the moving average method. We experiment with 30 volunteers, containing different genders and different ages. We compare the signals captured by this method to a conventional PPG signal captured concurrently from a finger. The results of the experiments are all relatively agreeable and the biggest deviation value is about 2bmp.
    Proc SPIE 09/2013;
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    ABSTRACT: A method that remotely measures blood oxygen saturation through two cameras under regular lighting is proposed and experimentally demonstrated. Two narrow-band filters with their visible wavelength of 660nm and 520nm are mounted to two cameras respectively, which are then used to capture two photoplethysmographic (PPG) from the subject simultaneously. The data gathered from this system, including both blood oxygen saturation and heart rate, is compared to the output of a traditional figure blood volume pulse (BVP) senor that was employed on the subject at the same time. Result of the comparison showed that the data from the new, non-contact system is consistent and comparable with the BVP senor. Compared to other camera-based measuring method, which requires additional close-up lighting, this new method is achievable under regular lighting condition, therefore more stable and easier to implement. This is the first demonstration of an accurate video-based method for non-contact oxygen saturation measurements by using ambient light with their respective visible wavelength of 660nm and 520nm which is free from interference of the light in other bands.
    Optics Express 07/2013; 21(15):17464-71. · 3.55 Impact Factor
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    ABSTRACT: The modified generalized cubic phase mask (GCPM) has recently been applied in wavefront coding systems including infrared imaging and microscopy. In this paper, the stationary phase method is employed to analyze the GCPM characteristics. The SPA of the modulation transfer function (MTF) under misfocus aberration is derived for a wavefront coding system with a GCPM. The approximation corresponds with the Fast Fourier Transform (FFT) approach. On the basis of this approximation, we compare the characteristics of GCPM and cubic phase masks (CPM). A GCPM design approach based on stationary phase approximation is presented which helps to determine the initial parameter of phase mask, significantly decreasing the computational time required for numerical simulation.
    Optics Communications 07/2013; s 298–299:67–74. · 1.44 Impact Factor
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    ABSTRACT: We aim to study the short-wave infrared (SWIR), medium-wave infrared (MWIR), and long-wave infrared (LWIR) imaging ability based on optical readout bimaterial microcantilever focal plane array (FPA) uncooled infrared imaging system. First, the principle of the bimaterial microcantilever sensing and the fabrication of the microcantilever array are introduced. Second, the optical-thermal-mechanical sensing theories based on the FPA are given. Finally, an optical readout microcantilever FPA infrared imaging system is developed for SWIR, MWIR, and LWIR imaging experiments. The experimental results show that the system can acquire the clear images of the SWIR, MWIR, and LWIR targets.
    Optical Engineering 02/2013; · 0.88 Impact Factor
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    ABSTRACT: It has been shown that bimaterial microcantilevers can deform as their temperature changes owing to the absorption of infrared radiation. Considering the principle of the cantilever, there must be a temperature detection limit and the microcantilever will be invalid beyond a tolerable temperature. In the paper, we aim to prove the limit and provide an approach to obtain the tolerable target temperature for infrared imaging. A microcantilever array damage experiment using an infrared laser as target was conducted and a method based on optical reflection and CCD measurement principle was proposed to measure the cantilever's critical deflection angle. Furthermore, the tolerable target temperature based on the imaging system was calculated.
    Optics & Laser Technology 02/2013; · 1.37 Impact Factor
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    ABSTRACT: Students from China are always intelligent but lack of creativity. These are somewhat stereotypes. This is partially because of the reserved or implicit culture. In an objective point of view, it is also because of the limited education resources. In the single assessment criterion education circumstance, students chase for the high marks even without knowing their interests or aptitudes. In a 12-week open experimental course, Optoelectronic Instrument Experiments (OIE), we try to encourage the students to dig their aptitudes and bring them into full play to earn more credits for the course. Self-assessment and mutual-evaluation for technical proficiency, communication skills, collaboration and leadership are carried out for the final evaluation. We also communicate with the students the speciality and skill a qualified engineer needs. We hope to help them prepare themselves for engineering-related jobs in the further.
    Frontiers in Education Conference, 2013 IEEE; 01/2013
  • Feng Wen, Yuejin Zhao, Xiaomei Yu
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    ABSTRACT: To measure glucose accurately, a high sensitivity piezoresistive four-set Wheatstone bridge structure microcantilevers glucose biosensor was developed. The microcantilevers with a piezoresistor were fabricated using a series of bulk silicon processes based on a silicon-on-insulator wafer. An improved Wheatstone bridge readout circuit with voltage closed-loop auto-zero and high-gain magnified functions is proposed. The sensing microcantilever gold-coated surface was functionalised by immobilising a self-assembled monolayer of 4-mercaptophenylboronic acid, the reference cantilever was not functionalised. The relationship between a piezoresistive bridgeout caused by the microcantilevers bending and glucose solution concentration was obtained at 5 and 15 mM. Experimental results demonstrated that the output voltage induced by microcantilevers bending is proportional to the glucose concentrations and the sensitivity is up to 0.1 V/mM.
    Micro & Nano Letters 01/2013; 8(6):298-301. · 0.85 Impact Factor
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    ABSTRACT: A novel passive single-channel THz imaging system employing a Cassegrain antenna of 390 mm in diameter and Schottky diodes as detecting part, and the cooperation of a high-speed line scanning mirror driven by a crank-rocker mechanism and a frame scanning mirror as two-dimensional optical-mechanical scanning part is described in this paper. The single frame imaging time of the system is only 20s, the field of view (FOV) is 30° × 36°, and the angle resolution is up to 0.6°. The experimental results show that the low cost, simple structure and efficient system can clearly image the human body, and effectively detect dangerous items concealed under the clothes.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2013 38th International Conference on; 01/2013
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    ABSTRACT: Project-based course is based on teamwork and most of work is done and presented as a team. Team grouping rule is one of the most important issues. In project-based experimental course Optoelectronic Instrument Experiments (OIE), several different rules were attempted, each of which produced complaints by some students. After several trials of different grouping rule, we realized that there is no perfect rule which can satisfy everyone. Instead of changing the rule, trying to find a way to persuade the students to accept and support their group willingly might be a better solution. In this semester, the project teams are entirely determined by lot and several teamwork inspirational approaches are introduced to inspire team spirit in the course. Our purpose is to find a way to make student learn the interpersonal skill of working in team. Let's do it, not just deal with it inactively.
    Frontiers in Education Conference, 2013 IEEE; 01/2013
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    ABSTRACT: Step frequency signal is one of the more commonly used radar signal for high range resolution, it commonly used in radar target recognition. The wavelength of Terahertz signal is shorter than that of the microwave, so it is easy to realize the high range resolution. The paper first introduces the step frequency signal to obtain the one-dimensional distance image, and analyze the principle of high resolution range profiles of step frequency radar. Then, the 0.2THz step frequency radar systems are introduced. Finally, the high resolution range profiles are achieved by the simulation of Matlab. The simulation results show that the step frequency THz radar can reach centimeter level high resolution on stationary targets. For moving targets exist distance divergence and coupling shift. With greater speed, the greater the distortion.
    Proc SPIE 12/2012;
  • Ze Li, Xiaohua Liu, Yuejin Zhao, Cunlin Zhang
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    ABSTRACT: In reconstruction algorithms of CS, the ROMP algorithm is better than others, but, to obtain the better result, it's very important to estimate the sparsity of the image accurately. To solve this problem, an improved algorithm was proposed, in order to determine the best iterative number automatically, this algorithm determines whether the iterative number is the best or not by the previous result. Experimental result shows that the result of this improved algorithm is better than the result of the previous ROMP algorithm with deterministic iterative number.
    Proc SPIE 12/2012;
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    ABSTRACT: Compared with traditional microwave and millimeter wave radars, Terahertz radar has wide signal bandwidth and a very narrow antenna beam, which is beneficial to the realization of high resolution imaging. And as an instantaneous narrowband and synthetic wideband waveform, stepped frequency radar signal has been widely exploited in many applications, since it allows high range resolution with modest requirements of the system bandwidth. As an instantaneous narrowband and synthetic wideband waveform, stepped frequency radar signal has been widely exploited in many applications, since it allows high range resolution with modest requirements of the system bandwidth. This paper presents the design of a 0.2THz stepped frequency imaging radar system with operating bandwidth of 12 GHz, thus, a theoretical range resolution below 1.25 cm. The simulation of the system is implemented by using system design parameters. An experimental trial has been performed, and one-dimensional range profile of the stationary target is obtained by Imaging Experiment using THz radar. Results show that the THz radar imaging system could achieve the target detection and centimeter-level range resolution.
    Proc SPIE 12/2012;
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    ABSTRACT: Compared with the traditional infrared imaging technology, the new type of optical-readout uncooled infrared imaging technology based on MEMS has many advantages, such as low cost, small size, producing simple. In addition, the theory proves that the technology's high thermal detection sensitivity. So it has a very broad application prospects in the field of high performance infrared detection. The paper mainly focuses on an image capturing and processing system in the new type of optical-readout uncooled infrared imaging technology based on MEMS. The image capturing and processing system consists of software and hardware. We build our image processing core hardware platform based on TI's high performance DSP chip which is the TMS320DM642, and then design our image capturing board based on the MT9P031. MT9P031 is Micron's company high frame rate, low power consumption CMOS chip. Last we use Intel's company network transceiver devices-LXT971A to design the network output board. The software system is built on the real-time operating system DSP/BIOS. We design our video capture driver program based on TI's class-mini driver and network output program based on the NDK kit for image capturing and processing and transmitting. The experiment shows that the system has the advantages of high capturing resolution and fast processing speed. The speed of the network transmission is up to 100Mbps.
    Proc SPIE 12/2012;

Publication Stats

90 Citations
63.34 Total Impact Points

Institutions

  • 2007–2013
    • Beijing Institute Of Technology
      • School of Optoelectronics
      Peping, Beijing, China
  • 2007–2012
    • Capital Normal University
      • Department of Physics
      Beijing, Beijing Shi, China
  • 2009
    • Rensselaer Polytechnic Institute
      Troy, New York, United States