利用强度调制DFB光纤激光传感器进行声发射检测

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"这篇论文探讨了使用强度调制的分布式反馈光纤激光(DFB-FL)传感器进行声发射检测的方法和技术。研究了DFB-FL传感器对外部声发射的强度响应，通过与参考压电接收器的校准，确定了该传感器的动态灵敏度。在所使用的DFB-FL中，最小可检测信号为5kHz时的2×10^-6 m/s。通过采用小波包技术对收集到的信号进行分析，证实了这种基于强度调制的DFB-FL传感器可以有效用于声发射信号的检测。" 本文主要涉及以下知识点： 1. **声发射检测(Acoustic Emission, AE)**：声发射技术是一种无损检测方法，它利用材料内部产生的瞬态声波来探测结构的缺陷或异常。AE技术广泛应用于工业领域，如材料裂纹检测、机械故障诊断等。 2. **分布式反馈光纤激光器(DFB Fiber Laser)**：DFB光纤激光器是一种特殊的光纤激光器，其内部结构包含一个周期性的布拉格光栅，用于选择性反射特定波长的光，实现单模激光输出。DFB-FL因其高稳定性、窄线宽和可调谐性而在传感应用中受到青睐。 3. **强度调制**：在本文中，DFB-FL的光强会随外部声发射事件而变化，这种变化被用来探测声波。强度调制使得DFB-FL能够将声波信号转换为光信号，便于后续的电子处理和分析。 4. **动态灵敏度**：动态灵敏度是传感器对变化信号的响应能力，文中提到的2×10^-6 m/s是在5kHz时的最小可检测信号，这表示传感器能捕捉到非常微弱的声发射信号。 5. **参考压电接收器**：用于校准DFB-FL的动态灵敏度，压电接收器是一种常见的声波检测器，可以直接将声波信号转化为电信号，提供一个基准对比。 6. **小波包技术**：这是一种信号处理技术，通过分解和分析信号的不同频率成分，可以提供更详细的信号特征信息。在本文中，小波包用于分析由DFB-FL收集的声发射信号，确认了传感器的有效性。 7. **光学通信和信息科学(OCIS)代码**：文章提到的OCIS代码060.2370, 140.3490, 140.3510分别对应光纤器件、光纤通信和光电子传感系统等领域，表明本文的研究内容属于这些专业范畴。这篇研究展示了如何利用强度调制的DFB-FL传感器进行声发射检测，并通过实验验证了其在非破坏性检测中的潜力和有效性。这种技术有望在结构健康监测、材料性能评估和故障预测等方面发挥重要作用。

Acoustic emission detection using intensity-modulated

DFB fiber laser sensor

Tan Yang (杨郯)

, Ying Song (宋颖)

, Wentao Zhang (张文涛)

*, and Fang Li (李芳)

School of Traffic and Transportation, Shijiazhuang Tiedao University, Shijiazhuang 050043, China

Optoelectronic System Lab, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China

*Corresponding author: zhangwt@semi.ac.cn

Received August 27, 2016; accepted October 14, 2016; posted online November 14, 2016

The bonded distributed feedback (DFB) fiber laser (FL) acoustic emission sensor and the intensity response of

the DFB-FL to external acoustic emissions are investigated. The dynamic sensitivity of the DFB-FL is calibrated

by a referenced piezoelectric receiver. In the DFB-FL we used here, the minimum detectable signal is

2×10

−6

m∕s at 5 kHz. Using wavelet packet technology, the collected signals are analyzed, which confirms

that an intensity-modulated DFB-FL sensor can be used to detect acoustic emission signals.

OCIS codes: 060.2370, 140.3490, 140.3510.

doi: 10.3788/COL201614.120602.

The acoustic emission (AE) technique as a kind of new

nondestructive testing technology has a broad potential

application in the field of nondestructive testing.

Traditional AE sensors are usually made of piezoelectric

(PZT) ceramic materials, which are not only susceptible

to electromagnetic interference, but also unsuitable for

being embedded into structures. Fiber optic sensors have

considerable advantages over traditional PZT sensors,

such as a small diameter, light weight, flexibility, immun-

ity to electromagnetic interference, durability, ease of

installation and multiplexing, and a simultaneous mea-

surement of temperature and strain

[1–5]

. These character-

istics are very suitable for real-time health monitoring

of structures in their service life cycle

[3,6]

. Recently, distrib-

uted feedback (DFB) fiber laser (FL) -based sensors, in-

cluding strain sensing

[6,7]

, and acoustic sensors

[8–10]

have

attracted a lot of interest due to their higher resolution.

Compared with the fiber Bragg grating (FBG), DFB-

FL sensors have an ultra-narrow line-width and higher

output power, which result in an ultrahigh strain resolu-

tion

[11,12]

. Many papers use the interference method of

demodulation, however, the method of demodulation sys-

tem is complex, and the cost is high. Using the intensity

characteristics of the DFB-FL to detect a signal, the

demodulation system is simple, and the detection of the

signal frequency band is wide

[13]

In this Letter, we present the bonded intensity response

of the DFB-FL to the external AE signal, and the acoustic

measurement based on the AE is done on an aluminum

plate to prove the feasibility of the sensing scheme. We

reveal the sensitivity response curve of the intensity-type

DFB-FL sensor to external AE signals and explain the

minimum of the stress wave that can be detected by

the method.

First, we explain the focus of this Letter, which is to use

the intensity characteristics of the DFB-FL as the receiver

of the AE signal. When there is external AE signal applied

on the phase-shift grating, the fiber is physically stressed

due to the elasticity of the fiber, and the refractive index

of the fiber is modifie d because of the photo-elasticity

[14]

The relationship between the length of the fiber grating

(l), the refractive index (n), and the elastic wave can

be expressed as

ΔlðtÞ¼l

−

ð1 − 2μÞP

ðtÞ

;

Δn

ðtÞ

¼ n

ðtÞ

ð1 − 2μÞð2P

þ P

;

(1)

where P

ðtÞ

is the amplitude of the elastic waves, E is the

Young’s modulus of the fiber, P

and P

are elasto-

optical coefficients, and μ is Poisson’s ratio of the fiber.

Therefore, the grating coupling coefficient and the

refractive index of the FL influences its output power.

As a result, the effect of the externa l AE signal modula-

tion, which may contribute significan tly to the DFB-FL’s

intensity, should be analyzed and discussed.

As shown in Fig.

1, a 980 nm pump laser is used before

the wavelength division multiplexer. The output laser of

the DFB-FL goes through the isolator, wavelength divi-

sion de-multiplexer, and into the detector. The analog/

digital (A/D) card is used to sample the output voltage

signal of the detector and transmit the signal to the per-

sonal computer (PC). The collective digitized signal is

then processed using the Fourier transform to evaluate

Fig. 1. Intensity FL AE sensing scheme. ISO, isolator.

COL 14(12), 120602(2016) CHINESE OPTICS LETTERS December 10, 2016

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