古建筑木构件含水率变化的单边核磁共振现场无损检测技术

In China, the ancient architecture with wood members accounts for more than fifty percent of the total ancient architecture. More and more ancient architecture became a tourist attraction, so that the work of maintenance and protection of the wood members in ancient architecture were increased significantly. Wood will be inevitably damaged in different degrees with time. The moisture content directly.reflects the condition of the wood material as well as the safety performance of the wood components. The existing methods on moisture content detection are not suit for moisture content detection of the wood members in ancient architecture because of destructive effect, the small range of measurements or the devices limited for on site measurement. The project proposals to employ unilateral magnetic resonance method for non-destructively detecting the moisture content of the wood members in ancient architecture. The research content includes: (1) Since the moisture in wood is relatively less, an unilateral magnetic resonance sensor with high sensitivity which could measure different layers will be developed; (2) Study the nuclear magnetic resonance (NMR) characteristics which representing the moisture content of wood, and establish the relationship between moisture content and NMR characteristics; (3) Measure the moisture content of the wood members in ancient architecture on the scene. Hope to provide accurate and quantitative evaluation parameters for the maintenance and protection of the wood members in ancient architecture by the project.

我国现存的木质古建筑约占所有古建筑的50%以上，越来越多的古建筑开放成为旅游景点，维修和保护古建筑木构件的任务量明显增加。木材在长期使用的过程中，不可避免地会受到不同程度的损害。含水率是直接反映木材材质状况以及木构件安全性能的一项重要指标。现有的木材含水率检测方法或对木材造成损坏,或测量深度不够不适用于古建筑木构件，或因设备本身局限不适用于现场测量。本申请提出一种单边核磁共振方法拟实现古建筑木构件含水率的现场无损检测。研究内容包括：（1）根据木材水分含量较少的特点，研究灵敏度高且能够实现深度方向分层测量的单边核磁共振传感器；（2）研究表征木材含水率的核磁共振特征量，建立特征量与含水率之间的关系；（3）对古建筑木构件含水率进行现场实验测量。希望通过本项目的研究为古建筑木构件的维修和保护提供准确的定量评估参数。

我国现存的木质古建筑约占所有古建筑的50%以上，越来越多的古建筑开放成为旅游景点，维修和保护古建筑木构件的任务量明显增加。木材在长期使用的过程中，不可避免地会受到不同程度的损害。含水率是直接反映木材材质状况以及木构件安全性能的一项重要指标。现有的木材含水率检测方法或对木材造成损坏,或测量深度不够不适用于古建筑木构件，或因设备本身局限不适用于现场测量。本项目的研究按计划书内容执行，要点如下：1）单边核磁共振传感器的电磁设计：由于古建筑木质结构的表面分成平面和弧面两种，因此设计了两种单边核磁共振传感器，一种单边核磁共振传感器的射频线圈为平面线圈，灵敏区域也为平面，另一种单边核磁共振传感器的射频线圈表面为弧面，其灵敏区域也为弧面。2）木构件的单边核磁共振信号的处理方法：由于单边核磁共振信号信噪比相对较差，提出了用小波降噪技术，以信号信噪比和均方误差作为评价指标，比较了不同小波基和阈值下的降噪效果。Matlab仿真表明，小波在磁共振的自旋回波信号降噪处理中表现出较好效果。3）含水率测量实验研究：分别使用两种传感器对不同形状的木材水分含量进行了测试，观察到了不同深度水分分布与横向弛豫时间T2有关，并发现木材含水率与T2谱曲线积分面积成正比。同时用传统的称重法进行了对比测量，实验结果得到了验证。