基于螺旋缠绕光纤的分布式声波传感分量信号采集机理研究

常规分布式光纤声波传感(DAS)技术利用光纤对轴向应变敏感的特点开展单分量信号采集,在开展三分量振动信号采集时,通常需要对光纤进行螺旋缠绕布置。在采用不同的角度进行缠绕时,光纤的轴向位置必然不同,导致光纤对X,Y,Z3个方向的振动信号具有不同的敏感性。针对上述问题,通过建立单根螺旋缠绕光纤的数学模型,确定了光纤轴向应变的影响因素,推导了螺旋光纤轴向应变与光纤所在位置处3个方向真实应变之间的数学映射关系,定量分析了不同缠绕角度、不同旋转角度条件下三分量振动信号对光纤轴向应变的影响,并采用波动方程模拟的三分量数字信号对螺旋光纤轴向应变所接收到的等效信号进行了验证。分析结果表明,螺旋光纤在轴向方向上采集到的信号强度取决于X,Y,Z三分量信号自身的强度、光纤缠绕角度以及缠绕过程中光纤各点的相对空间位置,随着缠绕角度的增大,螺旋光纤对沿缠绕轴方向的地震波信号敏感性增强,对垂直于缠绕轴方向的信号敏感性减弱,垂直于缠绕轴方向的两个分量地震波信号在数值上呈现出周期性和互补性变化规律,为利用螺旋缠绕光纤开展分布式声波传感三分量振动信号的采集提供了理论基础。

Conventional distributed acoustic sensing (DAS) technology takes advantage of the sensitivity of optical fibers to axial strain to carry out single-component signal acquisition.When carrying out three-component vibration signal acquisition,a helical winding arrangement of the optical fiber is usually required.However,when different angles are used for winding,the axial position of the optical fiber is bound to be different,which leads to different sensitivities of the optical fiber to vibration signals in the three directions (X,Y,Z).In view of this issue,a mathematical model of a helically winding optical fiber was established to determine the factors affecting the axial strain of the fiber,and the mathematical mapping relationship between the axial strain of the helical optical fiber and the true strain in the three directions at the location of the optical fiber was derived.Then,the influence of the three-component vibration signal on the axial strain of the optical fiber was quantitatively analyzed under the conditions of different winding angles and rotation angles,and the equivalent signal received by the axial strain of the spiral optical fiber was verified by the three-component digital signal simulated by the wave equation.The results of the analysis showed that the strength of the three-component signal collected in the axial direction of the helical optical fiber depends on the actual strength of the X,Y,and Z three-component signals,the winding angle,and the relative spatial position of the fiber during the winding process.As the winding angle increases,the sensitivity of the helical optical fiber to the seismic wave signal along the winding axis increases,and the sensitivity to the signal perpendicular to the winding axis decreases.The two-component seismic wave signals perpendicular to the winding axis appear numerically cyclical and complementary,providing a theoretical basis for the acquisition of the three-component vibration signal of a distributed acoustic sensor by using a helically winding optical fiber.

国家自然科学基金项目(42074162,41774137)资助。