Recent advancement in optical fiber sensing for aerospace composite structures

Abstract

Optical fiber sensors have attracted considerable attention in health monitoring of aerospace composite structures. This paper briefly reviews our recent advancement mainly in Brillouin-based distributed sensing. Damage detection, life cycle monitoring and shape reconstruction systems applicable to large-scale composite structures are presented, and new technical concepts, “smart crack arrester” and “hierarchical sensing system”, are described as well, highlighting the great potential of optical fiber sensors for the structural health monitoring (SHM) field.

Full text

Photonic Sensors (2013) Vol. 3, No. 4: 345–354
DOI: 10.1007/s13320-013-0133-4 Photonic Sensors
Review
Recent Advancement in Optical Fiber Sensing
for Aerospace Composite Structures 
Shu MINAKUCHI* and Nobuo TAKEDA
Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8561,
Japan
*Corresponding author: Shu MINAKUCHI E-mail: minakuchi@smart.k.u-tokyo.ac.jp
Abstract: Optical fiber sensors have attracted considerable attention in health monitoring of
aerospace composite structures. This paper briefly reviews our recent advancement mainly in
Brillouin-based distributed sensing. Damage detection, life cycle monitoring and shape
reconstruction systems applicable to large-scale composite structures are presented, and new
technical concepts, “smart crack arrester” and “hierarchical sensing system”, are described as well,
highlighting the great potential of optical fiber sensors for the structural health monitoring (SHM)
field.
Keywords: Carbon fiber reinforced plastic (CFRP), Brillouin-based system, fiber Bragg grating (FBG)
Citation: Shu MINAKUCHI and Nobuo TAKEDA, “Recent Advancement in Optical Fiber Sensing for Aerospace Composite
Structures,” Photonic Sensors, DOI: 10.1007/s13320-013-0133-4.
Received: 19 July 2013 / Revised version: 31 August 2013
© The Author(s) 2013. This article is published with open access at Springerlink.com
1. Introduction
Even though the carbon fiber reinforced plastic
(CFRP) is being used in almost all modern
aerospace structures as a primary structural material,
it is still difficult to precisely manufacture large-
scale CFRP structures and ensure their structural
integrity during operation. Hence, there is an urgent
need to develop innovative techniques to monitor
the internal states of composite structures and utilize
the obtained data to improve the structural design,
processing technologies and maintenance methods.
In this context, several structural health monitoring
(SHM) systems have been proposed and evaluated
[1]. Among the developed systems, optical fiber
sensors have attracted considerable attention [2–4],
since they are small, lightweight, immune to
electromagnetic interference, and environmentally
stable, and they have very little signal loss over
extremely long distances. Furthermore, they possess
sufficient flexibility, strength, and heat resistance to
be embedded relatively easily into composite
laminates.
Our previous paper, published in 2007 [5],
presented the development of small-diameter optical
fibers and their fiber Bragg grating (FBG) sensors.
The paper showed several techniques for detecting
composite damage and gave a summary of the
Japanese national project on optical-fiber-based
SHM for feasible applications in aerospace
composite structures. Following the previous paper,
this paper briefly reviews our recent advancement
mainly in Brillouin-based distributed sensing.
Several techniques applicable to large-scale

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composite structures are presented, and additionally,
new technical concepts, “smart crack arrester” and
“hierarchical sensing system”, are described.
2. Damage detection using Brillouin
based distributed strain sensing
2.1 Damage monitoring of CFRP bolted joints
using strain distribution
Bolted joints are structural key elements in
current composite aircraft structures [6]. There is an
urgent need to develop a new technique for detecting
bearing failures in their initial stage since these
failures can lead to catastrophic structural damage,
but are invisible from the outside [6–8]. The authors
developed a fiber-optic-based system applicable to
large-scale composite structures having a massive
number of the bolted joints [9]. Optical fibers were
embedded along bolt holes, and the strain change
along the optical fiber induced by bearing failure
was measured by a Brillouin optical correlation
domain analysis (BOCDA), which is a high spatial
resolution distributed strain sensing system
developed by Hotate et al. [10–12].
This study began by investigating damage
modes of the CFRP bolted joints after bearing
failure [13]. Effective embedding positions of
optical fibers were then proposed, and their
feasibility was evaluated by finite element analysis
simulating the damage propagation in the bolted
joint and consequent residual strain change [14].
Finally, verification tests were conducted using
specimens with embedded polyimide-coated optical
fibers at various positions. The results are
summarized in Figs. 1 and 2. It was clearly shown
that the damage could be detected using the residual
strain due to fiber-microbuckling (kinking) damage
or permanent deformation of the neighboring plies.
Furthermore, the damage size and direction could be
estimated from the change in the strain distribution.
The system developed is quite useful for a first
inspection of large-scale composite structures.
(a) After 1st loading (b) After 2nd loading
Fig. 1 Soft X-ray images of damage around the CFRP bolt
hole [9].
50 –50 0
OF-90f
OF-90n
500
1000
50
1500
0
OF-0 OF-45
2nd
1st
1st
2nd
2nd
1st
1st
Bolt-hole
Position (mm)
Position (mm)
Position (mm) Position (mm)
2nd
–50
Stra im (ε)
Stra im (ε)
500
1000
1500
50–50 0500 –50
0
0
Fig. 2 Residual strain distribution along embedded optical
fibers after each loading [9].
2.2 Damage monitoring of sandwich structures
using Brillouin spectral response to non-uniform
strain
In general, the central frequency of a measured
Brillouin gain spectrum (BGS) represents the axial
strain averaged over the spatial resolution of the
measurement system. Thus, the strain change
induced by damage smaller than the spatial
resolution hardly changes the BGS central frequency.
However, the shape of the BGS has information on
the strain distribution within the spatial resolution
[15, 16] and thus can be more sensitive to the
damage. The authors investigated the effects of the
strain profile within the spatial resolution on the

Shu MINAKUCHI et al.: Recent Advancement in Optical Fiber Sensing for Aerospace Composite Structures
347
BGS response [17] and demonstrated that the BGS
becomes broader due to the non-uniform strain
along the optical fiber. When a uniform strain is
applied, the Brillouin frequency is also uniform, and
thus the BGS has only one sharp narrow peak
[Fig. 3 (a)]. When a non-uniform strain is introduced,
however, the Brillouin frequency also becomes
non-uniform, since the Brillouin frequency at each
position on the optical fiber is determined by the
strain at that position. As a result, the BGS
consisting of the total Brillouin scattering within the
spatial resolution becomes broad, as illustrated in
Fig. 3(b). The authors utilized this phenomenon to
detect impact damage in composite sandwich
structures [18]. Pre-pump pulse Brillouin optical
time-domain analysis (PPP-BOTDA) was utilized
for distributed strain measurement [19, 20].
Brillouin scattering
Frequency
F
1
Strain
lntensity
F
2
F
3
F
1
F
1
F
2
F
3
F
1
Frequency
Intensity Strain
Brillouin scatterin
g
Spatial resolution
Spatial resolution
(a) Uniform strain (b) Non-uniform strain
Fig. 3 Brillouin gain spectrum depending on the strain
profile within the spatial resolution [18].
Composite sandwich structures are integral
constructions consisting of two composite facesheets
and a lightweight core, which can maximize the
potentials of composite materials [21]. However,
when the impact or indentation loading is applied,
the core under the loading point crushes, and a
residual dent remains on the facesheet, which
significantly degrades the strength of the sandwich
structure [22]. A schematic of the proposed impact
damage detection system is illustrated in Fig. 4. The
optical fibers are embedded in the adhesive layer
between the facesheet and the core in a reticular
pattern [23], measuring the strain along the bottom
surface of the composite facesheet. The facesheet
dent induces tensile and compressive strain along
the embedded optical fiber at its concave and
convex parts. This non-uniform strain changes the
shape of the BGS, and thus the impact damage can
be detected.
Fig. 4 Schematic of the impact damage detection system
[18].
Firstly, the authors numerically simulated the
response of the optical fiber sensor network to
clarify the effectiveness and limitations of the
proposed damage-detection technique. The proposed
system was then validated by an experiment using a
composite sandwich panel. Figure 5 presents the
9.529.48
–
1.5
–
1
–
0.5
0
9.56 9.6
4m
m
9.64
Before test
Frequency (GHz)
1m
m
6.5m
m
Normalized intensity (dB)
Fig. 5 BGS obtained from the measure point nearest to the
loading point after each indentation loading [18].
spectra obtained from the measurement point nearest
to the loading point. As the damage became larger,
the width of the BGS gradually increased. In
contrast, the peak frequency of the BGS hardly
changed. This means that the distributed strain
measurement using the peak frequency could not
detect the damage. One example of two-dimensional
distributions of the spectrum width is presented in
Fig. 6. In this study, a full width at –1 dB from the
maximum F–1dB was selected as a representative
value for the width of the BGS, and each line
represents the F–1dB distribution along each line of

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the embedded optical fiber. As the damage became
larger, the width of the Brillouin gain spectra
became broader. Consequently, the location and size
of the barely visible damage could be intuitively
estimated. The BGS shape based technique was
further utilized to detect water accumulation in
honeycomb sandwich structures [24].
70
80
90
100
110
F
–1dB
(MHz)
Fig. 6 Two-dimensional distribution of F–1dB near the loading
point after the indentation loading of 3 mm [18].
3. Smart crack arrester with crack
memorizing and detecting capability
In composite sandwich structures, a crack below
the facesheet is difficult to be detected using
conventional non-destructive inspection techniques.
However, an interface crack seriously degrades the
structural integrity [21]. Thus, Hirose et al.
developed a crack arrester (Fig. 7) [25], which is a
semi-cylindrical stiff material inserted into the
interface. When a crack approaches the arrester, the
arrester decreases the energy release rate at the crack
tip by suppressing local deformation around the
crack. In practical applications, the arrester is
arranged in a grid pattern, and the interface crack is
trapped inside the grid (Fig. 7). The arrested crack
should be detected instantaneously, and appropriate
measures must be taken for the damaged area.
Fig. 7 Crack arrester [26].
The authors established the “smart crack
arrester” that arrests, memorizes and detects
interface crack propagation [26]. Figure 8 presents
the schematic of the crack-detection technique. Two
FBG sensors and two metal wires are embedded at
both edges of the arrester. The characteristic strain
state induced by arresting the high-speed crack
propagation is first “memorized” by plastic
deformation of the metal wire, and the consequent
residual strain is then “statically” picked up as a
damage signal by using a birefringence effect of the
FBG sensor [27, 28]. The system does not require a
high-cost dynamic measurement system and can
reliably detect the interface crack in a practical noisy
environment.

p

q
ε
1
ε
2
Wavelength
Intensity
Wavelength
Intensity
Fig. 8 Schematic of the crack-detection technique [it is
important to note that metal wires added can be very thin (e.g.,
diameter less than 1mm), and thus a weight increase is
negligible] [26].
The authors began by numerically simulating the
deformation of the metal wires and the sensors to
evaluate the feasibility of the proposed technique.
The significant advantage of adding the metal wires
was then demonstrated by comparing data from the
proposed technique and the previous approach
without metal wires [29]. Finally, a verification test
was conducted to confirm that an FBG spectral
shape statically obtained after the unloading can
indicate the propagation direction and tip location of
an arrested crack.
4. Life cycle monitoring of the practical
composite panel
When optical fiber sensors are embedded into

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349
composite materials during manufacturing, the
sensor can be used to continuously monitor the
manufacturing process itself, in-service usage and
damage. By combining all the information obtained
by the distributed sensing network, we can
accurately evaluate the structural health (Fig. 9). The
authors demonstrated life cycle monitoring of a
representative CFRP stiffened panel manufactured
by vacuum assisted resin transfer molding (VARTM)
[30].
Fig. 9 Life cycle monitoring. [30].
Figure 10 depicts the schematic of the specimen.
A single optical fiber was embedded between the
stiffeners and the skin during the laminate lay-up
process. In order to confirm the repeatability of
measurement, the optical fiber went two circuits in
the panel, monitoring the same place with two lines
of the single optical fiber. PPP-BOTDA was used for
the distributed sensing. Figure 11 shows the obtained
residual strain distributions after manufacturing
from the two lines of the embedded optical fiber. For
better comparison, the horizontal axis is expressed
in the distance from one end of the panel. The two
lines measured quite similar strain distributions,
confirming the high repeatability and reliability of
the fiber-optic-based process monitoring. Almost the
uniform compressive strain of 250  was induced in
the whole structural area, indicating that the
specimen was perfectly injected and cured. The
results also agreed well with the measurement by
FBG sensors, validating the measurement accuracy
of the distributed sensing. Subsequently, the
manufactured panel was assembled, and low-
velocity impact loadings were applied. The fiber-
optic network successfully monitored the strain
change during the assembly and also detected two
damages located near each other. After the impact
tests, the embedded optical fiber still worked
correctly, and the mechanical strain distribution
around the damaged area could be obtained. The test
result confirmed the effectiveness of life cycle
monitoring by fiber-optic-based distributed sensing
for developing highly-reliable composite structures.
Fig. 10 Schematic of the representative CFRP stiffened
panel specimen [30].
–
800
0
–
400
–
600
–
200
200
–
1 0 1 2 3 4 5
Position
(
m
)
Strain (ε)
Fig. 11 Distribution of the thermal residual strain obtained from two lines embedded in the same position [30].

Photonic Sensors
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This life cycle monitoring concept was further
demonstrated in complex-shaped parts [31, 32], and
the advanced quality control method based on sensor
responses was proposed. A hybrid Brillouin-
Rayleigh system that can separately measure the
strain and temperature distribution was also utilized
for composite process monitoring [33].
5. Full-field shape reconstruction using
distributed strain data
Shape reconstruction systems, which derive
displacement from strain data, are especially suitable
for understanding the global conditions of structures.
Once an optical fiber network is embedded in the
whole body of a structure, the shape reconstruction
system can be applied not only to real-time
deformation monitoring in the operation time, but
also to distortion monitoring in the manufacturing
process of composites. However, most previous
work about shape reconstruction focused on only
simple test structures since with conventional
measurement systems (e.g., strain gauges and FBG
sensors) the number or location of sensing points
was limited [34, 35].
Our research group constructed a shape
reconstruction algorithm using a finite element (FE)
model of the target structure, taking advantage of
characteristics of the distributed strain data obtained
by PPP-BOTDA [36, 37]. The remarkable point is
that, using not only raw strain data but also
information of the non-uniformity of strain
distribution profiles, the algorithm appropriately
considers the data reliability for accurate shape
reconstruction. The constructed algorithm was
applied to the reconstruction of the deflection of a
composite laminate specimen, in which an optical
fiber network was embedded (Fig. 12). The results
indicated that reconstruction accuracy was greatly
improved by using weight values determined from
the non-uniformity index of the strain distribution
profile for each data point (Fig. 13). Moreover, the
authors demonstrated that the prior information of
identification parameters, which were the
node-displacements of the FE model, could be
provided for accurate shape reconstruction of
complex deformation using the non-uniformity
index.
Clamp
Load
Fig. 12 Setup of cantilever plate bending test [37].
–
80
–
40
0
–
120
450 300 150 0 600 400
800
0
200
xy
Deflection
(
mm
)
Fig. 13 Reconstructed deflection of the composite laminate
specimen: the real points in the figure are the measured
deflections using the laser displacement meter, and the
reconstructed deflection shows good agreement with the
measured deflection [37].
6. Hierarchical sensing system with high
monitorable area, robustness, and
repairability
When conventional fiber-optic-based systems
[Fig. 14 (a)] are applied to large-scale structures for
monitoring the randomly induced damage such as
the impact damage [22], they are unsatisfactory in
the following three properties: robustness,
repairability, and monitorable area. Specifically, a
failure at only one point on a sensing optical fiber
leads to a breakdown of the entire sensing network.
Moreover, once the optical fiber is disconnected, the
damaged part needs to be repaired. However, it is
quite difficult to access and reconnect the damaged

Shu MINAKUCHI et al.: Recent Advancement in Optical Fiber Sensing for Aerospace Composite Structures
351
fiber, especially when embedded. Furthermore, the
fiber-optic sensing obtains basically a one-
dimensional strain (temperature) distribution along
the thin fiber. Hence, the damage far from the
sensing fiber cannot be detected, since it induces no
significant strain (temperature) change in the fiber.
To overcome these drawbacks, the authors proposed
a hierarchical fiber-optic-based sensing system
analogous to the nervous system in vertebrates [38].
In the hierarchical system [Fig. 14 (b)], several kinds
of specialized devices are hierarchically combined
to form a sensing network. Specifically, numerous
three-dimensionally structured sensor devices are
distributed throughout the whole structural area and
connected with an optical fiber network (which is
not embedded into the structure) through
transducing mechanisms. The distributed “sensory
nerve cell” devices detect the damage, and the fiber-
optic “spinal cord” network gathers the damage
signals and transmits the information to a measuring
instrument. Since the optical fiber is attached to the
back surface of the structure, the fiber rarely breaks
when the structure is damaged. If by any chance the
optical fiber is broken, the disconnected parts can be
readily reconnected using a fusion splicer, since the
optical fiber is relatively easily accessible. Finally,
in the hierarchical system, several sensor devices
connected to different optical fibers are placed in the
same area; in Fig. 14 (b), two independent comb-like
sensor devices share the same monitoring area.
Hence, a failure at just one point in the devices or
the fiber optic network does not affect the
monitoring performance, and therefore, the
hierarchical system has high redundancy and
robustness.
In order to validate the hierarchical concept, a
hierarchal impact damage detection system was
developed with surface-crack sensing devices based
on comparative vacuum monitoring (CVM), which
was originally developed by Structural Monitoring
Systems Ltd. in Australia [39–41]. The surface-
mounted sensing devices are initially vacuumed, and
an optical fiber network monitors the internal
pressure in all of the deployed devices. Since the
impact damage increases the internal pressure of the
vacuumed device in the damaged area, one can
identify the sensor device where the pressure change
occurs and thus locate the damaged area. The
proposed impact damage detection system was
applied to a CFRP skin-stringer fuselage
demonstrator (Fig. 15). The barely visible impact
damage (BVID) was successfully detected from a
strain increase in the optical fiber in the damaged
area, and it was confirmed that the hierarchical
system has the better repairability, higher robustness,
and a wider monitorable area compared to existing
fiber-optic-based systems.
Composite structure
(a) Existing sensing system utilizing optical fiber network
(b) Hierarchical sensing system combining distributed
sensor devices and optical fibers
Fig. 14 Schematic of the sensing system [38].
Fig. 15 Hierarchical surface-crack detection system deployed
in the CFRP fuselage structure [38].
Recently, the sensitivity and durability of the
hierarchical system were significantly improved by

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developing embeddable CVM sensor devices [42]. A
further advance to be combined with a self-healing
concept was also demonstrated.
7. Conclusions
This paper briefly reviewed our recent
advancement mainly in Brillouin-based distributed
sensing. Several systems applicable to large-scale
composite structures were presented, and new
technical concepts, “smart crack arrester” and
“hierarchical sensing system”, were described as
well, highlighting the great potential for optical fiber
sensors in the SHM field.
Open Access This article is distributed under the terms
of the Creative Commons Attribution License which
permits any use, distribution, and reproduction in any
medium, provided the original author(s) and source are
credited.
References
[1] C. Boller, F. K. Chang, and Y. Fujino, Encyclopedia of
structural health monitoring. Chichester, UK: Wiley,
2009.
[2] K. S. C. Kuang and W. J. Cantwell, “Use of
conventional optical fibers and fiber Bragg gratings
for damage detection in advanced composite
structures: a review,” Applied Mechanics Reviews, vol.
56, no. 5, pp. 493–513, 2003.
[3] G. F. Fernando, “Fibre optic sensor systems for
monitoring composite structures,” Reinforced Plastics,
vol. 49, no. 11, pp. 41–49, 2005.
[4] G. Luyckx, E. Voet, N. Lammens, and J. Degrieck,
“Strain measurements of composite laminates with
embedded fiber Bragg gratings: criticism and
opportunities for research,” Sensors, vol. 11, no. 1, pp.
384–408, 2011.
[5] N. Takeda, Y. Okabe, and T. Mizutani, “Damage
detection in composites using optical fibre sensors,”
Proceedings of the Institution of Mechanical
Engineers Part G: Journal of Aerospace Engineering,
vol. 221, no. 4, pp. 497–508, 2007.
[6] S. D. Thoppul, J. Finegan, and R. F. Gibson,
“Mechanics of mechanically fastened joints in
polymer–matrix composite structures – a review,”
Composites Science and Technology, vol. 69, no. 3–4,
pp. 301–329, 2009.
[7] Y. Xiao and T. Ishikawa, “Bearing strength and failure
behavior of bolted composite joints (part i:
experimental investigation),” Composites Science
and Technology, vol. 65, no. 7–8, pp. 1022–1031,
2005.
[8] Y. Sato, T. Utsunomiya, T. Takatoya, and I. Susuki,
“Application of smart bolt to early stage damage
monitoring of composite shear fastener joint,”
Transactions of the Japan Society of
Mechanical Engineers A, vol. 74, no. 737, pp. 90–96,
2008.
[9] S. Minakuchi, T. Nakamura, T. Nadabe, M. Nishikawa,
N. Takeda, M. Kishi, et al., “Damage detection of
CFRP bolted joints using embedded optical fibers
with BOCDA system,” Journal of the Japan Society
for Aeronautical and Space Science, vol. 59, no. 690,
pp. 176–182, 2011.
[10] K. Hotate and T. Hasegawa, “Measurement of
Brillouin gain spectrum distribution along an optical
fiber using a correlation-based technique –
proposal, experiment and simulation,” IEICE
Transactions on Electronics, vol. E83-C, no.3, pp.
405–412, 2000.
[11] K. Y. Song, Z. He, and K. Hotate, “Distributed strain
measurement with millimeter-order spatial resolution
based on Brillouin optical correlation domain
analysis,” Optics Letters, vol. 31, no. 17, pp.
2526–2529, 2006.
[12] K. Y. Song and K. Hotate, “Distributed fiber strain
sensor with 1-kHz sampling rate based on Brillouin
optical correlation domain analysis,” IEEE
Photonics Technology Letters, vol. 19, no. 23, pp.
1928–1930, 2007.
[13] T. Nadabe, M. Nishikawa, S. Minakuchi, T.
Nakamura, and N. Takeda, “Modeling of fiber
kinking damage for bearing failure in bolted joints of
CFRP laminates,” Journal of the Japan Society for
Composite Materials, vol. 37, no. 5, pp. 172–181,
2011.
[14] T. Nadabe, M. Nishikawa, S. Minakuchi, T.
Nakamura, J. T. Siivola, and N. Takeda, “Numerical
analysis for damage detection in CFRP bolted joints
using strain measurement,” Journal of the Japan
Society for Composite Materials, vol. 38, no. 1, pp.
22–29, 2012.
[15] T. Horiguchi, T. Kurashima, M. Tateda, K. Ishihara,
and Y. Wakui, “Brillouin characterization of fiber
strain in bent slot-type optical-fiber cables,” Journal
of Lightwave Technology, vol. 10, no. 9, pp.
1196–1201, 1992.

Shu MINAKUCHI et al.: Recent Advancement in Optical Fiber Sensing for Aerospace Composite Structures
353
[16] H. Naruse, M. Tateda, H. Ohno, and A. Shimada,
“Dependence of the Brillouin gain spectrum on
linear strain distribution for optical time-domain
reflectometer-type strain sensors,” Applied Optics,
vol. 41, no. 34, pp. 7212–7217, 2002.
[17] S. Minakuchi, T. Mizutani, H. Tsukamoto, M. Nishio,
Y. Okabe, and N. Takeda, “Brillouin spectral
response depending on strain non-uniformity within
centimeter spatial resolution and its application to
internal damage detection in large-scale
composite structures,” Structural Durability &
Health Monitoring, vol. 4, no. 4, pp. 199–219,
2008.
[18] S. Minakuchi, Y. Okabe, T. Mizutani, and N. Takeda,
“Barely visible impact damage detection for
composite sandwich structures by optical-fiber-based
distributed strain measurement,” Smart
Materials and Structures, vol. 18, no. 8, pp. 085018,
2009.
[19] K. Kishida, C. H. Li, and K. Nishiguchi, “Pulse
pre-pump method for cm-order spatial resolution of
BOTDA,” in Proc. SPIE, vol. 5855, pp. 559–562,
2005.
[20] Neubrex Co., Ltd., 2013 (available from
http://www.neubrex.com/).
[21] D. Zenkert, The handbook of sandwich construction.
Warrington: Engineering Materials Advisory
Services Limited, 1997.
[22] S. Abrate, Impact on composite structure.
Cambridge, UK: Cambridge University Press,
1998.
[23] S. Minakuchi, Y. Okabe, and N. Takeda, “Real-time
detection of debonding between honeycomb core
and facesheet using a small-diameter FBG sensor
embedded in adhesive layer,” Journal of Sandwich
Structures and Materials, vol. 9, no. 1, pp. 9–33,
2007.
[24] S. Minakuchi, H. Tsukamoto, and N. Takeda,
“Detecting water accumulation in honeycomb
sandwich structures by optical-fiber-based
distributed temperature measurement,” Journal of
Intelligent Material Systems and Structures, vol. 20,
no. 18, pp. 2249–2255, 2009.
[25] Y. Hirose, M. Hojo, A. Fujiyoshi, and G. Matsubara,
“Suppression of interfacial crack for foam core
sandwich panel with crack arrester,” Advanced
Composite Materials, vol. 16, no. 1, pp. 11–30,
2007.
[26] S. Minakuchi, I. Yamauchi, N. Takeda, and Y. Hirose,
“Memorizing and detecting an arrested crack in a
foam-core sandwich structure using embedded
plastic materials and fiber-optic sensors,” Smart
Materials and Structures, vol. 21, no. 5, pp. 055025,
2012.
[27] R. Gafsi and M. A. El-Sherif, “Analysis of
induced-birefringence effects on fiber Bragg
gratings,” Optical Fiber Technology, vol. 6, no. 3, pp.
299–323, 2000.
[28] A. P. Zhang, B. O. Guan, X. M. Tao, and H. Y. Tam,
“Experimental and theoretical analysis of fiber
Bragg gratings under lateral compression,”
Optics Communications, vol. 206, no. 1–3, pp.
81–87, 2002.
[29] S. Minakuchi, I. Yamauchi, N. Takeda, and Y. Hirose,
“Detecting an arrested crack in a foam-core
sandwich structure using an optical fiber sensor
embedded in a crack arrester,” Advanced
Composite Materials, vol. 20, no. 5, pp. 419–433,
2011.
[30] S. Minakuchi, N. Takeda, S. Takeda, Y. Nagao, A.
Franceschettic, and X. Liu, “Life cycle monitoring
of large-scale CFRP VARTM structure by
fiber-optic-based distributed sensing,” Composites
Part A: Applied Science and Manufacturing, vol. 42,
no. 6, pp. 669–676, 2011.
[31] S. Minakuchi, T. Umehara, K. Takagaki, Y. Ito and N.
Takeda, “Life cycle monitoring and advanced quality
assurance of L-shaped composite corner part using
embedded fiber-optic sensor,” Composites Part A:
Applied Science and Manufacturing, vol. 48, pp.
153–161, 2013.
[32] K. Takagaki, S. Minakuchi, and N. Takeda,
“Fiber-optic-based life cycle monitoring of
through-thickness strain in thick CFRP pipes,”
Journal of the Japan Society for Composite
Materials, vol. 39, no. 4, pp. 143–151, 2013.
[33] Y. Ito, S. Minakuchi, T. Mizutani, and N. Takeda,
“Cure monitoring of carbon-epoxy composites by
optical-fiber-based distributed strain-temperature
sensing system,” Advanced Composite Materials,
vol. 21, no. 3, pp. 259–271, 2012.
[34] R. T. Jones, D. G. Bellemore, T. A. Berkpff, J. S.
Sirkis, M. A. Davis, M. A. Putnum, et al.,
“Determination of cantilever plate shapes using
wavelength division multiplexed fiber Bragg grating
sensors and a least-squares strain-fitting algorithm,”
Smart Materials and Structures, vol. 7, no. 2, pp.
178–188, 1998.
[35] C. C. Quach, S. L. Vazquez, A. Tessler, J. P. Moore,
E. G. Cooper, and J. L. Spangler, “Structural
anomaly detection using fiber optic sensor and
inverse finite element method,” in AIAA Guidance,
Navigation, and Control Conference and Exhibit,
San Francisco, CA, Aug. 15–18, pp. 2005–6357,

Photonic Sensors
354
2005.
[36] M. Nishio, T. Mizutani, and N. Takeda, “Shape
reconstruction of composite structures using
high-resolution distributed strain data from Brillouin
scattering based optical fiber sensing system,”
Journal of the Japan Society for Aeronautical
and Space Science, vol. 56, no. 658, pp. 522–529,
2008.
[37] M. Nishio, T. Muzutani, and N. Takeda, “Structural
shape reconstruction with consideration of the
reliability of distributed strain data from a
Brillouin-scattering-based optical fiber sensor,”
Smart Materials and Structures, vol. 19, no. 3, pp.
035011, 2010.
[38] S. Minakuchi, H. Tsukamoto, H. Banshoya, and N.
Takeda, “Hierarchical fiber-optic-based sensing
system: Impact damage monitoring of large-scale
CFRP structures,” Smart Materials and Structures,
vol. 20, no. 8, pp. 085029, 2011.
[39] Structural Monitoring Systems Ltd., 2013 (available
from: http://www.smsystems.com.au/).
[40] D. P. Barton, “Comparative vacuum monitoring
(CVM™),” in Encyclopedia of Structural Health
Monitoring. Chichester, UK: Wiley, 2009, pp.
1849–1865.
[41] D. Roach, “Real time crack detection using
mountable comparative vacuum monitoring
sensors,” Smart Structures and Systems, vol. 5, no. 4,
pp. 317–328, 2009.
[42] S. Minakuchi, H. Banshoya, S. Ii, and N. Takeda,
“Hierarchical fiber-optic delamination detection
system for carbon fiber reinforced plastic
structures,” Smart Materials and Structures, vol. 21,
no. 10, pp. 105008, 2012.