As one of the basic devices of spintronics, spin valve contains abundant physical effects in addition to its high magnetoresistance ratio (MR) value. Owing to the spin filter effect in two dimensional (2D) materials especially transition metal dichalcogenides (TMDs), the spin polarized current from ferromagnetic electrodes (FEs) passing through the 2D materials makes high- and low-resistance states in FE/2D/FE vertical junctions according to magnetization alignment of FEs. In this work, we fabricate vertical spin valve junctions utilizing exfoliated thin layer of molybdenum diselenide (MoSe2) with the help of ultra-clean transfer technique. The current–voltage (I–V) performances exhibit an ohmic contact between the MoSe2 and FEs. The MoSe2 which act as the interlayer shows metallic behavior. We found a magnetoresistance ratio varies from 1.1% at 4K to 0.3% at 300K and independent of bias current. Combined with the reported resistive-switching (RS) performance of similar structure in the MoSe2 based memory device, our result is prospective to be conducive for future spintronic applications.
Due to the larger orbital arc and longer synthetic aperture time in medium Earth orbit (MEO) synthetic aperture radar (SAR), it is difficult for conventional SAR imaging algorithms to achieve a good imaging result. An improved higher order nonlinear chirp scaling (NLCS) algorithm is presented for MEO SAR imaging. First, the point target spectrum of the modified equivalent squint range model-based signal is derived, where a concise expression is obtained by the method of series reversion. Second, the well-known NLCS algorithm is modified according to the new spectrum and an improved algorithm is developed. The range dependence of the two-dimensional point target reference spectrum is removed by improved CS processing, and accurate focusing is realized through range-matched filter and range-dependent azimuth-matched filter. Simulations are performed to validate the presented algorithm.
Adaptive sliding receive-window (ASRW) technique was usually introduced in airborne squint synthetic aperture radar (SAR) systems. Airborne squint spotlight SAR varies its receive-window starting time pulse-by-pulse as a function of range-walk, namely, the linear term of range cell migration (RCM). As a result, a huge data volume of the highly squint spotlight SAR echo signal can be significantly reduced. Because the ASRW technique changes the echo-receive starting time and Doppler history, the conventional image algorithm cannot be employed to directly focus airborne squint spotlight ASRW-SAR data. Therefore, a fast image-formation algorithm, based on the principle of the wave number domain algorithm (WDA) and azimuth deramping processing, was proposed for accurately and efficiently focusing the squint spotlight ASRW-SAR data. Azimuth deramping preprocessing was implemented for eliminating azimuth spectrum aliasing. Moreover, bulk compression and modified Stolt mapping were utilized for high-precision focusing. Additionally, geometric correction was employed for compensating the image distortion resulting from the ASRW technique. The proposed algorithm was verified by evaluating the image performance of point targets in different squint angles. In addition, a detailed analysis of computation loads in the appendix indicates that the processing efficiency can be greatly improved, e.g., the processing efficiency could be improved by 17 times in the 70-deg squint angle by applying the proposed image algorithm to the squint spotlight ASRW-SAR data.
A novel scheme for tunable optical pulse generation based on fiber sagnac loop was proposed and studied. The key
parameters of the optical pulse were analyzed and testified by simulations and experiments. The repetition rate of optical
pulse is twice the frequency of external square wave modulation signal and can be tuned directly by varying modulation
frequency. The maximal peak value can be achieved when the peak-peak value of the square wave modulation signal
was equal to the half-wave voltage of the phase modulator. Experimental results agree well with theoretical predictions
and simulations.
A wavelength division multiplied (WDM) polarization-maintain fiber sensor system for simultaneous temperature
and pressure measurement is proposed. The system comprises a PANDA fiber polarimetric temperature sensor and a
highly birefringent photonic crystal fiber (PCF) polarimetric pressure sensor, which are multiplexed by use of a
WDM beam splitter/combiner and interrogated in wavelength domain by using a combination of a broadband source
and an optical spectrum analyzer. Preliminary experiments demonstrate a temperature sensitivity of about 1.16nm/oC
and a pressure sensitivity of 2.42nm/MPa with respectively 162.7mm of PANDA fiber and 262.8mm of PCF.
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