低频

These antennas can cover GSM900/DCS/PCS/UMTS operation. In the chapter 2, the antenna is designed based on the concept of monopole antenna. Furthermore, the antenna structure have two radiant paths and coupled each other at tail end to do impedance matching. In addition, to raise distance between radiation plane and ground will avoid capacitative effect effectually. In the chapter 3, the antenna is designed based on the concept of planar inverted-F antenna. Furthermore, that the antenna structure have two radiant paths and coupled each other at tail end to do impedance matching is similar to chapter 2. But there is a difference in them. We can choose the short position to change input impedance at this structure. In the chapter 4, the antenna is designed based on the concept of planar inverted-F antenna which takes coupled-fed. It will produce the first mode and high-order mode near the frequency, 900MHz. The feature of this type is to reduce the volume effectually. This antenna can not only cover GSM900/DCS/PCS/UMTS operation but maintain good radiation efficiency. Finally, we will compare three antennas, and develop procedure with industrial view, and propose the prospect of the GSM/GPRS antenna in PND, as a conclusion.

在第二章中，我们使用单极天线设计概念，使用双路径架构并於末端耦合来对天线阻抗做匹配，产生涵盖GSM900/DCS/PCS/UMTS四频操作频带，并提高与接地面的辐射高度，以避免电容效应，使天线具有良好的辐射特性；在第三章中，使用倒F形天线设计概念，使用双路径架构於末端耦合，并於辐射臂上采取适当接地点电感效应作输入阻抗匹配，达成涵盖GSM900/DCS/PCS/UMTS系统的四个操作频带；在第四章中，采用倒F形架构并使用耦合馈入方式，使得长辐射金属臂在低频900 MHz附近产生共振，产生低频基频模态及高阶模态，以达成宽频及频宽涵盖GSM900/DCS/PCS/UMTS频带操作，并有效缩减使用体积；最后，分别比较此三种架构的优缺点，再加以业界角度来思考，研发产品天线的流程及思考方向，以及天线应用於可携式导航装置中未来的展望作为本论文的总结。

After take analyzed deeply for the opened magnet circuit with FEMM (Finite Element Method Magnetics) we find out the field distributing that is separated into three sections . One is the main area what we called as positive field section. Beside the main field there are tow areas that are called the inverted field sections. Loudspeaker arise a very serious distortion when the voice coil moving into inverted field areas. The direction of induced current in the coil part of entered inverted field area is same with the current driving into loudspeaker so that total currents increas largely and heat increase rapidly. With more coils moving into inverted area the voice coil will take on negative inductance properties. It is the main reason that voice coil is burned by heating with increasing current due to arise negative inductance. So opened magnetic circuit is not suitable for the woofers in which the voice coil have wider displacement range. When using this kind magnetic circuit design, the voice coil moving range should be less than the range of positive field to avoid loudspeaker arise serious distortion and heating. Even though voice coil moving range is in the positive area, loudspeaker will still arise more distortion because the field distribution is very cliffy at tow sides of the positive area and full range of magnetic field distribution is not parallel that will arise distortion. Base on above reasons, opened magnetic circuit is not an ideal magnetic circuit for low-frequency loudspeakers. But it can be used in mid-range or high-frequency productions.

开式磁路是由2片钕铁硼磁铁和主导磁板和导磁垫片组成，我们在实践过程中发现这种磁路结构不适合于低频扬声器的使用，我们通过使用FEMM（Finite Element Method Magnetics）软件包对该磁路进行了分析，该磁路的磁场范围被分成3个区域，其中在主导磁板附近形成一个正向磁场，在正向磁场的两边存在反向的磁场，音圈在工作时有很大一部分进入了反向磁场中，在反向磁场内线圈的感应电流方向与驱动电流方向相同，使得音圈呈现出负感抗特性，由于音圈的负感抗特性引起电流的增加导致音圈发热甚至烧毁，因此在扬声器中使用开式磁路时，音圈的运动范围应控制在正向磁场范围之内，否则音圈运动到反向磁场区域时将会产生很大的失真和发热，即使在设计时已经将音圈的运动范围控制在正向磁场范围之内，由于正向磁场的2个边缘磁场强度衰减太快，同时开式磁路中磁场的分布不是平行的，而是自由发散的分布，这样肯定会导致扬声器的非线性失真，因此我们得到的结论是：开式磁路并不是一个理想的磁路，它不适合于低频扬声器的使用，但它还可以应用于中高频扬声器。

The opened magnetic circuit is composed as tow NdFeB permanent magnets and a top plate without U-yoke. After take analyzed deeply for the opened magnet circuit with FEMM (Finite Element Method Magnetics) we find out the field distributing that is separated into three sections . One is the main area what we called as positive field section. Beside the main field there are tow areas that are called the inverted field sections. Loudspeaker arise a very serious distortion when the voice coil moving into inverted field areas. The direction of induced current in the coil part of entered inverted field area is same with the current driving into loudspeaker so that total currents increas largely and heat increase rapidly. With more coils moving into inverted area the voice coil will take on negative inductance properties. It is the main reason that voice coil is burned by heating with increasing current due to arise negative inductance. So opened magnetic circuit is not suitable for the woofers in which the voice coil have wider displacement range. When using this kind magnetic circuit design, the voice coil moving range should be less than the range of positive field to avoid loudspeaker arise serious distortion and heating. Even though voice coil moving range is in the positive area, loudspeaker will still arise more distortion because the field distribution is very cliffy at tow sides of the positive area and full range of magnetic field distribution is not parallel that will arise distortion. Base on above reasons, opened magnetic circuit is not an ideal magnetic circuit for low-frequency loudspeakers. But it can be used in mid-range or high-frequency productions.

开式磁路是由2片钕铁硼磁铁和主导磁板和导磁垫片组成，我们在实践过程中发现这种磁路结构不适合于低频扬声器的使用，我们通过使用FEMM（Finite Element Method Magnetics）软件包对该磁路进行了分析，该磁路的磁场范围被分成3个区域，其中在主导磁板附近形成一个正向磁场，在正向磁场的两边存在反向的磁场，音圈在工作时有很大一部分进入了反向磁场中，在反向磁场内线圈的感应电流方向与驱动电流方向相同，使得音圈呈现出负感抗特性，由于音圈的负感抗特性引起电流的增加导致音圈发热甚至烧毁，因此在扬声器中使用开式磁路时，音圈的运动范围应控制在正向磁场范围之内，否则音圈运动到反向磁场区域时将会产生很大的失真和发热，即使在设计时已经将音圈的运动范围控制在正向磁场范围之内，由于正向磁场的2个边缘磁场强度衰减太快，同时开式磁路中磁场的分布不是平行的，而是自由发散的分布，这样肯定会导致扬声器的非线性失真，因此我们得到的结论是：开式磁路并不是一个理想的磁路，它不适合于低频扬声器的使用，但它还可以应用于中高频扬声器。

The time of peak value of low frequency u wind isprior to the peak of rainfall in flood years;(3) There are low frequency OLRmoves northward at low-latitude and southward at mid-latitude at the same time inflood years , the join point is between 20-30 N.

3涝年低频OLR在经向上同时存在由低纬度向北和由中高纬向南的传播，二者交汇在20～30°N之间。旱年则没有显著的汇合区。(4)影响我国东部的低频气旋和反气旋源地在北半球中纬度太平洋和低纬的菲律宾附近。

Methods Seventy six aged patients with ostalgia caused by primary osteoporosis, whose T numerus less than certified value 2.5 were randomized into two groups: 1. Applying only CT (36 cases); 2. CT combined with Low frequency transduction pulsed electromagnetic fields (36 cases); Two groups simultaneously were given Calcium 600 mg and injected CT 50IU, ten days later injected 50IU every two days in two months, Low frequency transduction pulsed electromagnetic fields treatment was made by Tianjin Jinxitong company, frequency 20-40Hz, and treated 20 minutes by this machine, totally 30 days. Six months later we examined their Bone density again.

将存在骨质疏松性骨痛同时经DEXA骨密度仪检测T值低于标准值2.0以下的老龄原发性骨质疏松症患者76人随机分为两组：①单纯应用鲑鱼降钙素组（36人）；②联合应用药物及低频电磁场组（36人），两组同时每日给予钙而奇D600片1粒，CT按每日肌肉注射50IU，10d后改为隔日肌注50IU连续应用2个月，低频电磁场治疗采用天津金希统公司生产的XT2000B型OP治疗仪，频率为20~40Hz，每天治疗20min，共治疗30d， 6个月后复查骨密度。

When the magnitudes and directions of the electric and magnetic dipoles were matched, the radiation in backward and sideward direction was obviously restrained.

当TEM喇叭天线与低频补偿回路形成电偶极子和磁偶极子满足匹配条件时，天线低频辐射的单向性将得到提高。

According to the characteristics of multi-generator model and results of system digital simulation research, a new design and set scheme of underfrequency load shedding equipment on the basis of multi-generator system is developed in this paper.

同时根据多机模型特点及仿真结果提出了一种基于多机系统的低频减载设计和整定新方案，与传统方案相比，该方案提高了低频减载性能及系统运行方式的适应性。

low frequency electrotherapy on acupoints combined with magnetic force vibration heat may obviously improve the vertebroarterial cervical spondylopathy patients dizziness symptom,and is an effective way to treat vertebroarterial cervical spondylopathy.

低频穴位电刺激结合磁热可显著改善椎动脉型颈椎病患者眩晕症状和体征，是治疗椎动脉型颈椎病的一种有效方法。颈椎病；低频电疗法；磁热

Considering influence of external vibration on ultra-low frequency standard vibration systems, the vibration insulating foundation for vibration tables and a laser vibrometer is studied.

针对超低频标准振动系统易受外界振动干扰的问题，研究了超低频标准振动台与激光测振仪的隔振基础设计技术。

In this paper, the effects of the rigid body motions and low frequency surface errors on the image quality were analyzed. Quadratic equations were used to build the mathematical model of the Wolter type I and II X-ray telescopes and reduce the computational complexity of ray tracing. With the help of a self-developed optical surface analysis code, the effects of the perturbations of the mirrors on the image quality was analyzed and the growth of the image spot formed by deformed telescopes was calculated, this is important for giving the reasonable fabrication tolerance.

在本篇文章中，详细分析了刚体运动误差和低频表面误差对成像质量的影响；使用空间解析几何学的二次曲面方程建立Wolter I、II型X射线掠入射望远镜镜片的数学模型，降低光线追踪的计算复杂度；借助自主开发的光学仿真软件分析了国内研制的X射线成像望远镜的刚体运动误差和低频表面误差对成像质量的影响，计算出像点艾里斑半径均方根值随误差变化的增长率，对工程上提出合理的制造公差的误差容限有重要的指导意义。

As she looked at Warrington's manly face, and dark, melancholy eyes, she had settled in her mind that he must have been the victim of an unhappy attachment.

每逢看到沃林顿那刚毅的脸，那乌黑、忧郁的眼睛，她便会相信，他一定作过不幸的爱情的受害者。

Maybe they'll disappear into a pothole.

也许他们将在壶穴里消失