基于微波谐振腔的湿度传感器

构建了含水混合物介电特性模型，设计了基于此模型的开路同轴谐振腔传感器，并指出影响其传感特性的两个主要参数是保护盖介电常数和空载谐振频率。鉴于此，针对保护盖材料及空载谐振频率对传感器传感特性的影响进行了全面分析和仿真。加工了具有不同谐振频率的微波谐振腔及不同材料的端口保护盖。实验结果表明，该模型能够很好地指导传感器的设计，同时选取Al2O3作为保护盖材料及具有空载谐振频率为2．5GHz的谐振腔，具有较好的测量效果。     

截止波导介质腔介电常数测量理论与方法研究

本文提出了用截止波导介质谐振腔测量微波材料相对介电常数和微波损耗的方法.利用开波导法给出了腔中TE0ml谐振模的电磁场,导出了利用此模测量介电常数和微波损耗的公式;通过测量频率和谐振曲线,就能算出材料的复介电常数,并对谐振模TE0ml进行了讨论;比较了这种测量方法与原有的短路金属板介质谐振腔法的优劣,结果表明采用截止波导介质谐振腔测量材料的微波损耗时更有优越性.     

基于腔结构的射频微机械谐振元件的设计

对圆柱形复合腔结构微机械谐振元件进行了设计研究,提出了一种基于柱形腔结构的微机械复合谐振元件的设计方法,并对其结构及特性进行了研究.建立了复合腔结构的电磁场数学方程,腔体基于体微机械微细加工技术实现工艺设计,最后对该元件进行了仿真分析.TM010模式下,谐振腔谐振频率为24.313299GHz,Q值为3529.707890,考虑微带耦合时仿真出复合谐振元件的最佳谐振频率为24.75GHz.仿真实验结果和理论值的平均误差不到1%,两者吻合得很好,说明了该设计的可行性.进一步改变结构参数,可获取不同谐振频率的器件,且可在腔体中填充高介电常数介质来减小器件的谐振频率,克服了以往使用腔体结构在低频段时体积过大等问题.     

谐振式光纤陀螺全数字闭环方案的算法研究

谐振式光纤陀螺是一种基于光纤环形谐振腔Sagnac效应的新型惯性传感仪器.与现有的其他类型陀螺相比,具有很多性能上的优势.在此提出了一种基于DSP技术的全数字闭环方案,并为这种方案建立了数学模型.借助用z变换表示各个环节的离散传递函数,设计并优化了跟踪谐振频率的算法,并将此算法在DSP中实现.     

用于金属裂缝检测和测量的微带天线传感器

文中基于微带天线辐射原理设计了用于金属裂缝检测和表征的传感器。传感器实质是由一个金属谐振腔制成,金属谐振腔的谐振频率对传感器的辐射贴片和金属地的电特性极其敏感。把被测金属结构当作传感器的金属地,金属结构的裂缝扩展导致了传感器谐振频率的偏移。因此,通过读取传感器谐振频率的偏移量来检测和表征金属裂缝。从传感器辐射贴片的两个方向对金属裂缝进行了测试,通过实验测试发现:当金属裂缝沿辐射贴片宽度方向存在时,传感器的检测灵敏度是18 MHz/mm,当裂缝沿辐射贴片长度方向存在时,传感器的检查灵敏度是27.5 MHz/mm。传感器由耐高温的氧化铝和金属银浆料制成,因此可以应用到一些高温、高压恶劣环境下。     

加载纤维素敏感膜的小型化微波湿度传感器

提出了一种由互补开口谐振环(CSRR)和叉指电容(IDC)结构组合而成的小型化湿度传感器.利用CSRR-IDC结构的设计,使得传感器在获得高灵敏度的同时,保持着小尺寸.此外,通过加载纤维素敏感膜,进一步增强其湿度灵敏度.根据相对湿度对有效介电常数的影响引起传感器频率偏移的原理,对谐振器的谐振频率偏移量进行测量.在11％...     

基于低温共烧陶瓷的无线无源双参数传感器特性分析

设计并制备了一种可应用于恶劣环境的基于LTCC(低温共烧)陶瓷的集成温度和压力的双参数传感器。温度变化使LTCC基底介电常数变化,引起LC谐振电路的谐振频率变化;压力使LC谐振电路的电容极板间距离减小,从而使谐振频率发生变化,然后通过无线磁耦合的方式读取传感器信号。在高温压力复合平台对传感器温度和压力特性进行了测试和分析。实验结果表明:测量的传感器谐振频率随压力成线性减小;在相同压力下,传感器谐振频率随着温度的升高而减小;温度升高会使压力传感器响应灵敏度提升。     

便携高精度大气折射率测试仪的设计

准确测量蒸发波导的关键是对大气折射率的精确测量.根据空腔谐振器的谐振频率随充入气体介质不同而变化的原理,设计了一种由谐振腔传感器、高精度标准频率振荡器、混频器、数据处理等单元组成的便携高精度大气折射率测试仪.在开放性大气环境下,通过检测谐振传感器的谐振频率变化,得到流过谐振器气体的折射率.实验证明:该仪器的误差小于常规气象仪器测量误差,并且具有测量速度快、精度高、便于携带等优点.该设备已成功应用于大气折射率精细结构的实际测量,从而为利用蒸发波导实现舰船雷达、通信系统的超视距传播奠定了基础.     

微波谐振腔微扰测量法在线监测烟支湿度及密度

时微波谐振腔微扰法检测基本理论和工作原理进行了论述,给出了含有微量水分介质的等效介电常数的计算式,建立了烟支密度和湿度与谐振腔谐振点的频偏及半功率点带宽的数学表达式,设计了适用于烟支湿度密度连续测量的谐振器及检测系统,可实现烟支湿度密度的在线连续测量.该系统采用TM010谐振模,以扫频法检测谐振腔空腔和有烟支状态下的幅频特性,获得谐振频率、峰值功率及半功率带宽.根据相关数学式得到了烟支的湿度和密度.该检测方法具有快速、连续、分辨力高、无污染和操作安全简便等优点.     

一种谐振式加速度传感器及其设计

为解决当前模拟输出式加速度传感器测试精度相对较低的问题,利用谐振式传感器重复性好、分辨率高、稳定性优良的特点,设计了一种谐振式加速度传感器.通过理论计算,得出了线加速度与敏感元件谐振频率之间的关系,并通过有限元软件对其进行了仿真计算.计算结果显示,传感器在空载状况下谐振频率的理论计算结果与有限元分析结果分别为722.2Hz与720.87Hz.在1g加速度下两种计算方法得到的谐振频率计算结果分别为727.3Hz与726.28Hz,两种情况的相对误差仅为0.18%与0.14%.对加工完毕的加速度传感器进行了测试,测试结果表明:在谐振状态下,传感器的敏感元件的谐振频率大约为718.2Hz,与理论计算及仿真结果基本接近,证明了设计的正确性.     

圆筒形电容式粮食水分传感器的数学模型与影响因素分析

分析了粮食的介质特性,说明了圆筒形电容式粮食水分传感器的测量原理,得出了传感器电容参数与被测粮食含水量关系的数学模型.运用粮食的导电浴盆效应得出了传感器的等效电路,讨论了影响传感器电容量的因素,为圆筒形电容式粮食水分传感器的设计提供了理论依据.     

Low Cost Microwave Sensor for Moisture Content Measurement in Paper Milling Industry

The interest about RF and microwave sensors for the measurement of dielectric properties of materials during industrial processes has been growing recently. Microwave sensors are particularly attractive for their ability of performing non-invasive measurements. An interesting field of application is the real-time moisture measurement during industrial processes. A smart active sensor for measuring the moisture content of felts used in the paper milling industry and more generally of sheet-like materials, is here proposed. The sensor consists of a cavity backed slot resonator interacting with the material under test through near fields. The design aspects of the sensor and the related measuring front-end are discussed with respect to the dielectric properties of the material, and to the resonator response. The parametric sensitivity of the measuring method with the distance between the sample and the sensor surface and the sample thickness is also analyzed. An inversion procedure based on an Artificial Neural Network (ANN) approach is proposed in order to determine the moisture content of the felts. Measurements on several reference felts, with different density, thickness, and moisture content levels, ranging from dry to waterlogged state, proved the effectiveness of the proposed sensor architecture and the ANN-based inversion procedure.     

绝缘纸板干燥过程微水分检测机理与试验

绝缘纸板中的微水分对电力变压器的使用寿命有严重影响,因此,实时精确监测绝缘纸板微水分含量对于电力变压器的生产具有重要意义.由于绝缘纸板微水分含量的变化必然引起材料介电性能的变化,对介电性能进行检测即可有效检测微水分含量的变化.文中采用边缘场电容传感器技术研究绝缘纸板介电性能的变化过程.分析了频率对电容传感器检测信号的影响因素.通过对绝缘纸板的介电极化和介电损耗的研究,提出了频率对电信号影响的理论模型.根据试验数据和介电谱曲线,建立了无油绝缘纸板内的水分质量分数与复介电常数关系的数学模型.     

A new 1.4-GHz soil moisture sensor

Moisture content determination in agriculture and civil engineering is a common process which needs special sensors with high accuracy, durability and compatibility with the measurement environment. A new 1.4-GHz soil moisture sensor using microstrip transmission line is presented. The proposed sensor consists of two separate parts: (1) A sensor head, which is a microstrip transmission line to be placed in the soil, and (2) an electronic transceiver which sends a sinusoidal wave into the sensor head at one end of the transmission line, and receives the traveled wave from the other end. Transmitter is basically a Colpitts oscillator, and the receiver is a phase detector that measures the phase shift due to velocity variation caused by the moisture content of soil. At a certain frequency, the velocity of a microwave traveling through a media depends on the permittivity of that media. The proposed sensor is implemented and tested on one sample of typical soil. The main advantages of the proposed sensor are its high accuracy, quickness of measurement, its low cost and ease of implementation. Since the sensor has low power consumption, it can be recommended for low-power applications such as wireless sensor network.     

Application of resonant monopole antenna for determination of complex permittivity of liquids,powdered and granular materials

The article describes a sensor based on the resonant monopole antenna and its application for dielectric properties measurement. Generally, the sensor can be used in microwave characterization of various material but the article is focused on sensing liquids, powdered and granular materials for which the sensor can be plunged into medium under test without special mechanical treatment (or adjusting) a sample. The measured magnitude of the reflection coefficient at the resonance frequency is used for reconstructing complex permittivity by proper de-embedding procedure based on 3D EM simulator CST Microwave Studio.     

Development of velocity sensor with high frequency band and its application to a vibration isolate table

The vibration sensors are widely used in the field of vibration control and measurement. In applying the modern control theory to anti-vibration controlled objects, the state variables both the velocity and displacement become useful signals. Then, the velocity sensor in comparison with the acceleration sensor, which is in generally used, is very useful. However, its frequency band is limited by high frequency resonance due to the electrical stiffness. If the velocity sensor having flat frequency band is developed, this sensor becomes easy to handle not only in the control field but also in the measurement filed. Then, this paper shows that the inverse notch filter, which is inserted in the closed loop, flattens out the frequency response originally having high frequency resonance. Firstly, the block diagram of the velocity sensor as a closed system is shown. Its sensitivity, the low break point frequency, and the high frequency resonance are formulated. Secondly, the gain and phase margins are calculated and we try to improve the frequency response based on these indices. Finally, the application of improved velocity sensor to an anti-vibration apparatus is shown.     

The Analysis of Multi-Layer Conductor-Backed Coplanar Waveguide for Moisture Sensor Application

The analysis of conductor-backed coplanar waveguide moisture sensor by using numerical method is described. The effective dielectric constant, characteristic impedance and dielectric loss of this multi-layer structure are calculated at various moisture contents with respect to protective layer thickness. The analysis shows that calculated values are drastically affected by a small thickness of the protective layer. The experimental results of the attenuation of sensor at various moisture contents agree reasonably with the theoretical data based on the above analysis. The information available from this study is important for estimating of the dynamic range and optimal design of the sensor.     

Temperature effect on the reference frequency of FDR soil moisture sensor

The FDR automatic soil moisture sensor must determine reference frequency in the air and water. Experimental studies show that the water reference frequency is influenced by water temperature. The variation of the reference frequency of the sensor is measured with the change of the water temperature,then analysis the influence of the volume water content measurement of the sensor,analysis found that the error is not more than 3% for the measurement of the volumetric water content of the temperature.     

Microwave Sensing of Moisture Content in Concrete Using Open-Ended Rectangular Waveguide

The existence of moisture in concrete is a major cause of damage to the concrete structure, so there is an increasing need for nondestructive detection and monitoring of moisture content in concrete. Microwave nondestructive testing (MNDT) techniques have advantages over other NDT methods (such as radiography, ultrasonic, and eddy current) regarding low cost, good penetration in nonmetallic materials, good resolution and requirement of only one face of material for testing. In this paper, microwave open-ended rectangular waveguide was used to measure the electromagnetic properties of Portland cement concrete (PCC) over a frequency range of 7.0 to 13.0 GHz. PCC specimens of six different water cement ratio (w/c) were prepared. PCC dielectric properties were evaluated at different moisture content ranges from saturated to oven dry. The results show reflection coefficients, dielectric constants and loss factors increase with increasing moisture content of PCC. At the same values of moisture content, the reflection coefficients, dielectric constants and loss factors of PCC increase with decreasing w/c ratio. The measured values of reflection coefficients, dielectric constants and loss factors can be used to determine the moisture content of PCC.