隧穿磁电阻效应磁场传感器中低频噪声的测量与研究

基于隧穿磁电阻效应(TMR)的磁场传感器具有很高的磁场灵敏度, 但同时噪声也较大,有效抑制TMR磁场传感器的噪声, 尤其是低频噪声的抑制对于其在高灵敏度要求场合的应用具有重要的意义. 本文采用高精度数据采集卡搭建了噪声测量系统, 测量了全桥结构TMR磁场传感器的噪声频谱图, 发现TMR传感器的噪声在低频段表现为1/f特性, 同时噪声功率谱密度与工作电流平方成正比关系; 低频噪声在自由层翻转区间内噪声急剧增大, 证明了1/f噪声主要来源于磁噪声, 这一结果为TMR磁场传感器的噪声特性优化指明了方向.     

TMR与GMR传感器1/f噪声的研究进展

隧道结磁阻(TMR) 传感器及巨磁阻(GMR) 传感器的1/f噪声在低频段噪声功率密度较大, 是影响其低频下分辨率和灵敏度的主要噪声形式. 本文详细介绍了近年来TMR传感器及GMR传感器1/f噪声的特点、来源、理论模型、检测方法及降噪措施等方面的研究进展, 并就隧道结磁阻传感器1/f噪声的物理模型进行了详细解释. 通过纳米模拟软件Virtual NanoLab对不同MgO厚度的Fe/MgO/Fe型磁性隧道结(MTJ) 进行了隧穿概率和TMR变化率的模拟计算, 得到保守估计与乐观估计的TMR变化率, 分别为98.1%与10324.55%, 同时通过MTJ的噪声模型分析了MgO厚度对TMR传感器噪声的影响. 制备了磁屏蔽系数大于10000的磁屏蔽筒并搭建了磁阻传感器1/f噪声的测试平台, 通过测试验证了磁屏蔽系统对环境磁场具有较好的屏蔽效果, 为噪声检测提供了稳定的磁场空间. 最后分析了TMR与GMR中各种因素对传感器噪声的影响, 提出了影响MTJ传感器1/f噪声的因素及一些降噪措施.     

高灵敏度光纤弱磁传感器

本文报道了一种磁场检测灵敏度为10~(-5)Oe量级的光纤弱磁传感器。文中提供了传感头与检测系统的设计理论和方法。     

光纤法布里-珀罗干涉温度压力传感技术研究进展

光纤法布里-珀罗干涉温度和压力传感器具有灵敏度高、制作简单、成本低、体积小和抗电磁干扰能力强等优点,已被广泛应用于军事和民用领域.在某些环境恶劣,如具有强电磁干扰和腐蚀性,或提供给传感器的安装空间非常有限的特殊工业领域,微型光纤温度和压力传感器发挥着重要的作用,国内外诸多高校、科研院所都在对其进行研究.本文综述了光纤法布里-珀罗干涉仪的基本原理、制备技术、及其压力和温度传感应用的研究进展.详细介绍了湿法化学腐蚀制备法、电弧放电制备法、飞秒激光制备法、聚合物辅助制备法等常见光纤法布里-珀罗腔传感器的制作工艺,分析了不同制作工艺的优缺点;详细介绍了光纤法布里-珀罗干涉仪在温度传感、压力传感和温压一体传感领域的应用;最后对光纤法布里-珀罗干涉温度压力传感器的发展进行了总结和展望.     

热声转换的声表面波电压传感机制

提出了一种基于热声转换的高灵敏声表面波(SAW)电压传感机制并开展实验验证。从传热角度以及微扰理论出发建立了基于热声转换机制的SAW电压传感理论模型,探索了结构参数以及环境因素对SAW电压传感器灵敏度的影响规律。为了验证理论模型,在Y切石英基底上同芯片集成设计MEMS微型加热器与200 MHz声表面波器件以制备SAW电压传感器件,并搭建电压测试平台对传感器件开展性能测试。实验结果表明所制备的SAW传感器件电压与频率响应之间具有二次线性关系且在室温(20℃)下具有与理论相近的电压灵敏度(22.4 kHz/V),此外实验获得的环境温度对电压灵敏度的影响规律与理论相符。基于热声转换机制的SAW电压传感器能够显著的提高电压检测灵敏度。     

光纤布拉格光栅柔性传感器研究进展

光纤光栅传感器具有质量轻、体积小、灵敏度高、抗电磁干扰能力强等优点,尤其具有良好的柔韧性和相容性,可通过特殊制备工艺将光纤光栅与柔性材料制作成高密度分布式感知的柔性传感器.介绍了光纤光栅的基本传感原理;详细介绍了分别采用硅橡胶、纺织品以及其他聚合物作为基底的光纤光栅柔性传感器,并分析了各类柔性传感器的制备工艺技术、结构...     

磁性流体薄片高电压电流光学测量的研究

研究一种用磁性流体薄片对高压电流进行光学测量的电流传感器。设计原理基于磁性流体的光透射率随垂直磁场强度的变化而变化的关系。磁性流体受到垂直外磁场作用,原先无序的磁性颗粒将凝聚在一起形成条条磁链,从而引起磁性流体的光透射率的变化。采用磁性流体作为传感媒介设计的传感结构避免了基于法拉第效应的光磁式电流互感器对环境干扰敏感造成信噪比不高和传统的电磁式电流互感器的高压绝缘的缺陷。通过改变磁性流体的浓度和基液,或者改变传感头的结构,来达到实际需要的传感灵敏度和响应时间。     

结构改进的厘米尺寸谐振腔的磁场传感特性

基于光力谐振腔的磁力仪在应用时主要受限于灵敏度和检测带宽两个指标.本文设计了一种厘米尺寸的回音壁模式谐振腔结构,可探测6 Hz至1 MHz频率范围内的交变磁场,在无磁屏蔽、室温环境下、无直流偏置磁场时,其最佳灵敏度在123.8 kHz可达530 pT·Hz~(–1/2),探测带宽和最佳灵敏度分别为同尺寸谐振腔的11倍和1.67倍.该磁场传感器仅需100μW的光功率,功耗很低.后续通过优化系统噪声、提升器件磁场响应能力等手段可进一步提升其传感性能,有望在电力系统故障监测和医学诊断等领域发挥其应用潜力.     

基于PVA/Fe_(3)O_(4)水凝胶的锥形光纤磁传感EI北大核心CSCD

为了研究磁性水凝胶的磁致折射率变化及其在磁致光传感领域的应用,通过共混法制备了聚乙烯醇/四氧化三铁(PVA/Fe_(3)O_(4))磁性水凝胶,并基于光纤端面反射法测试了该磁性水凝胶在不同外加磁场下的折射率变化,测得其磁致光折射率变化规律。在此基础上设计了磁性水凝胶锥形光纤传感结构。实验表明,在环境温度22℃,磁粒子浓度2.1%时,6.4~22.6 mT范围内基于磁性水凝胶的光纤磁场传感元件波长偏移灵敏度为86.42 pm/mT;磁粒子浓度2.9%时,5.5~30 mT范围内该传感元件波长偏移灵敏度为51.42 pm/mT。该类磁性水凝胶在光纤磁传感测量方面具有良好的应用价值。     

基于Mach-Zehnder干涉仪的单模光纤声波传感器的研究

光纤传感器是20世纪70年代中期发展起来的一种新型传感器.它与普通的传感器相比,具有灵敏度高、抗电磁干扰、耐腐蚀、防燃等优点,因此在温度、应力、磁场等传感领域都有着广泛的应用.本文研究的光纤声波传感器,其基础为Mach-Zehnder(M-Z)全光纤干涉仪,我们主要的工作集中在传感臂探头的制作.所研制的基于M-Z干涉仪...     

Thermal magnetic noise control in the ultra-high-density read head

In order to reduce the resistance of tunnel magnetoresistive (TMR) read heads, a large stripe height sensor structure was proposed. The thermal magnetic noise, called as mag-noise, in this type of TMR heads was simulated by micromagnetic modeling using the Landau–Lifshitz–Gilbert (LLG) gyro-magnetic equation. It is found that for the same hard bias strength, both the sensitivity and the mag-noise of TMR heads increase as the sensor height increases. The signal-to-noise ratio (SNR) is reduced at large stripe height. The large increase in the demagnetization field resulting from the stripe height increase causes the weakening of the effective bias field, thus increasing the mag-noise significantly. Low mag-noise and high SNR can be obtained by increasing the hard bias strength and reducing the spacer between the hard bias and the free layer. An extended hard bias structure has been proposed to further increase SNR of TMR heads.     

Proposed spin amplification for magnetic sensors employing crystal defects

Recently there have been several theoretical and experimental studies of the prospects for magnetic field sensors based on crystal defects, especially nitrogen vacancy (NV) centers in diamond. Such systems could potentially be incorporated into an atomic force microscopy-like apparatus in order to map the magnetic properties of a surface at the single spin level. In this Letter we propose an augmented sensor consisting of an NV center for readout and an "amplifier" spin system that directly senses the local magnetic field. Our calculations show that this hybrid structure has the potential to detect magnetic moments with a sensitivity and spatial resolution far beyond that of a simple NV center, and indeed this may be the physical limit for sensors of this class.     

比率型碳点荧光传感器检测机理与应用研究进展

比率型荧光传感器由于具有抗干扰能力强和灵敏度高等优点,在食品安全、金属离子检测、环境污染分析等许多领域显示出巨大的应用潜力。而碳点作为一种新型荧光材料,不仅具有优良的荧光性能,而且毒性低、易于表面功能化,非常适合构建比率型荧光传感器。本文就近年来比率型碳点荧光传感器在检测领域的研究进展进行综述,重点阐述了碳点的荧光检测机理,并根据碳点使用情况的不同,对不同类型的比率型碳点荧光传感器进行了分类总结。最后提出了该领域亟待解决的困难和问题,并对其在分析物检测方面的发展方向进行了展望。     

基于石墨烯/石墨烯卷轴复合薄膜高灵敏度柔性压力传感器

一维导电材料例如纳米线,大量应用于柔性压力传感器中. 但是一维材料和基底之间接触时相互作用力较弱,使得传感器灵敏度、响应时间、和循环寿命等性能指标有待进一步提高. 针对这些问题,设计了石墨烯/石墨烯卷轴多分子层复合薄膜作为传感器导电层. 石墨烯卷轴具有一维结构,而石墨烯的二维结构可以牢固地固定卷轴,以确保高导电性复合薄膜与基底之间的粘附性,同时整体结构的导电通道得到了增加. 由于一维和二维结构的协同效应,实现了应变灵敏度系数3.5 kPa^-1、 响应时间小于50 ms、能够稳定工作1000次以上的压阻传感器.     

保偏微纳光纤倏逝场传感器

近年来,保偏微纳光纤以其高双折射特性和强倏逝场效应引起了研究者的关注.本文从保偏微纳光纤的结构类型、制备方法和模式双折射特性等出发,介绍了目前不同类型保偏微纳光纤倏逝场传感器的构造特征与实现方法,利用保偏微纳光纤在两个垂直偏振方向的倏逝场对外界的不同响应,可制成偏振相关的干涉型或光栅型等传感器件.本文探究了包括超高折射率灵敏度特性和温度不敏感特性等的内在产生机理,并考察了保偏微纳光纤倏逝场传感器在折射率、湿度、磁场和特异性DNA分子探测等方面的应用,其结果对微纳光纤及其传感器的研究和应用具有重要的意义.     

Tunable and highly sensitive temperature sensor based on graphene photonic crystal fiber

Optical fiber temperature sensors have been widely employed in enormous areas ranging from electric power industry, medical treatment, ocean dynamics to aerospace. Recently, graphene optical fiber temperature sensors attract tremendous attention for their merits of simple structure and direct power detecting ability. However, these sensors based on transfer techniques still have limitations in the relatively low sensitivity or distortion of the transmission characteristics, due to the unsuitable Fermi level of graphene and the destruction of fiber structure, respectively. Here, we propose a tunable and highly sensitive temperature sensor based on graphene photonic crystal fiber (Gr-PCF) with the non-destructive integration of graphene into the holes of PCF. This hybrid structure promises the intact fiber structure and transmission mode, which efficiently enhances the temperature detection ability of graphene. From our simulation, we find that the temperature sensitivity can be electrically tuned over four orders of magnitude and achieve up to ～ 3.34×10^-3 dB/(cm·℃) when the graphene Fermi level is ～ 35 meV higher than half the incident photon energy. Additionally, this sensitivity can be further improved by ～ 10 times through optimizing the PCF structure (such as the fiber hole diameter) to enhance the light-matter interaction. Our results provide a new way for the design of the highly sensitive temperature sensors and broaden applications in all-fiber optoelectronic devices.     

A review of mixed-potential type zirconia-based gas sensors

A robust and reliable gas sensing device is considered as a convenient and practical solution for gas concentration monitoring that has become a mandatory requirement in different field of applications. For in situ hazardous gases detection, a mixed-potential type gas sensor has been regarded as a promising solid-state gas sensor. For the past three decades, there has been a significant progress in achieving high performance in mixed-potential type sensors. Therefore, this review is focused on reporting the development of mixed-potential type gas sensors with combined yttria-stabilized zirconia (YSZ) as the base solid electrolyte material and various classes of electrode materials for their potential utilization as a high-performance sensing electrode. The underlying sensing mechanism of a mixed-potential type YSZ-based sensor is elaborated here in detail. Transformation in design and configuration of this type of sensor is also covered in this report. In addition, recent progresses on mixed-potential type gas sensors development for detection of several target gases, such as carbon monoxide, hydrocarbons, nitrogen oxides, hydrogen, and ammonia, are reviewed. Strategies to improve the sensing characteristic, particularly gas sensitivity and selectivity, are also reported. Based on the understanding of the fundamental sensing mechanism and the requirements for high-performance gas sensors, challenges and future trends for this type of gas sensor development are discussed.     

Magnetic Relaxometry with an Atomic Magnetometer and SQUID Sensors on Targeted Cancer Cells

Magnetic relaxometry methods have been shown to be very sensitive in detecting cancer cells and other targeted diseases. Superconducting Quantum Interference Device (SQUID) sensors are one of the primary sensor systems used in this methodology because of their high sensitivity with demonstrated capabilities of detecting fewer than 100,000 magnetically-labeled cancer cells. The emerging technology of atomic magnetometers (AM) represents a new detection method for magnetic relaxometry with high sensitivity and without the requirement for cryogens. We report here on a study of magnetic relaxometry using both AM and SQUID sensors to detect cancer cells that are coated with superparamagnetic nanoparticles through antibody targeting. The AM studies conform closely to SQUID sensor results in the measurement of the magnetic decay characteristics following a magnetization pulse. The AM and SQUID sensor data are well described theoretically for superparamagnetic particles bound to cells and the results can be used to determine the number of cells in a cell culture or tumor. The observed fields and magnetic moments of cancer cells are linear with the number of cells over a very large range. The AM sensor demonstrates very high sensitivity for detecting magnetically labeled cells does not require cryogenic cooling and is relatively inexpensive.