The data from a monitored structure/object should be easy acquired, processed and sent to the user, who can assess the
health of a structure in short time and schedule necessary maintenance in order to prevent accidences. Systems which
provide such information are fundamental for Structural Health Monitoring (SHM).
In the paper novel optical sensor designed for in-plane displacement and strain monitoring in crucial points of a big
engineering and civil structures is presented. It combines two techniques: Grating Interferometry (GI) and Digital
Speckle Pattern Interferometry (DSPI).
GI requires specimen grating attached to the surface of an object under test. It is the unique technique which may provide
the information about fatigue process and increased residual stresses.
DSPI works with a rough object surface but due to differential measurements cannot be simply used for long time
monitoring but to explore the actual behavior of a structure.
The sensor which combines these techniques provides user with wide possibilities concerning functionality, measuring
range, object surface and environmental conditions.
The crucial issue in implementation of this sensor is the choice of its location(s) at the investigated structure. Therefore
it is proposed to be as one of the elements of hierarchical sensors net, which gives complete information about structure
state. As the method for supporting the choice of GI/DSPI sensor location we proposed the system based on 3D digital
The paper presents mechanical and optical sensor design along with laboratory tests of main component such as sensor
heads in form of monolithic (plastic) and cavity waveguides. Finally the possible application of proposed sensor in
combination with 3D DIC system is presented.
Among many coherent optical methods one should distinguished Grating Interferometry (GI) which allows accurate
in-plane displacement measurements and Digital Speckle Pattern Interferometry (DSPI) used for in-plane and
out-of-plane measurements. Development of sensors based on both methods mentioned above as complementary ones
will provide user universal group of sensors from which depending on measurement requirements such as measuring
range, object surface profile and measurement conditions the most appropriate can be chosen.
In-plane displacement measurements are of interested of different branches of industry - from micro (i.e.:
characterization of MEMS or MOEMS) to civil engineering (i.e.: Structural Health Monitoring systems). In the paper the
new optical coherent sensor for in-plane displacement and strain measurements is presented. The sensor combines GI
and DSPI methods in one device which can be used for testing of objects with different types of surfaces. GI requires the
specimen grating attached at the surface but provides very good measurement accuracy however DSPI can be applied for
testing of objects with rough surfaces but due to higher noise gives lower accuracy. The sensor can work in three modes:
as GI only, DSPI only and both GI and DSPI simultaneously. The third mode can by useful when the specimen grating
is attached on the part of object under test only.
In the paper the theoretical background of the sensor is presented. For confirmation of GI/DSPI sensor possibilities
the specially designed demonstrator is described and the exemplary results obtained during its laboratory tests are shown.
Successful application of proposed sensor is possible due to its miniaturization, simplicity of operation by user
(compact structure and automation of measurement procedure) and low cost. The last mentioned condition will
be possible due to low cost replication techniques with usage of silicon technology.
Deep Proton Writing (DPW) is a rapid prototyping technology allowing for the fabrication of micro-optical and micro-mechanical
components in PMMA, which are compatible with low-cost replication technologies. Using DPW, a high-precision
2D fiber connector featuring conically-shaped micro-holes for easy fiber insertion, was realized. When
populating these fiber connectors by fiber insertion and fixation, a critical issue is the accurate control of the fiber
protrusion. The use of laser interferometry to measure the fiber's facet position with respect to the connector surface to
within a few micrometers, is inconvenient in view of the measurement range as compared to the fiber dimensions. In this
paper, we propose an interferometric method for in-situ monitoring of the fiber insertion depth, based on the
phenomenon of low temporal coherence light interference in a Twyman - Green setup. In addition, achieving a few
micrometers measurement range with low coherence light requires vertical scanning of the sample under test. The design
of the experimental setup and the achieved measurement results are shown and discussed.
In the paper the multiwavelength interferometer with automatic data analysis based on phase fraction method is
described. It is used to extend measurement range without losing sensitivity, especially to calibrate long gauge blocks.
Numerical simulations and experimental work results have been shown to confirm proper functioning of this method.
However, stabilization of environmental conditions and light sources has significant influence on correctness of
measurement results. To match those requirements measurement system, which will be built for Polish Central Office of
Measures, has been designed. This design is based on Twyman-Green interferometer and assumes usage of two highly
stabilized laser sources. Optical and mechanical design of this system has been shown. Moreover, system for monitoring
and stabilization of environmental conditions is required.