Dual in-plane electronic speckle pattern interferometry system with electro-optical switching and phase shifting

Measurement of In-Plane Displacement in Two Orthogonal Directions by Digital Speckle Pattern Interferometry

The measurement of in-plane displacement in two orthogonal directions is of considerable significance for modern industries. This paper reports on a spatial carrier phase-shift digital speckle pattern interferometry (DSPI) for the simultaneous measurement of in-plane displacement in two orthogonal directions. The object is illuminated from a single direction and observed from four symmetrical directions simultaneously. One pair of the four observation directions is sensitive to in-plane displacement in one direction, and the other pair is sensitive to in-plane displacement in the perpendicular direction, resulting in the displacement in two directions being measured independently. The polarization property of light is used to avoid cross-interference between the two pairs of beams. Spatial carrier frequencies are generated by aperture misalignment, and the displacement in two directions is modulated onto the same interferogram. With a spatial carrier phase-shift technique, the displacement can be separated in the frequency domain and the phase can be evaluated from a single interferogram in real time. The capability of DSPI is described by theoretical discussions and experiments.

Deformation reconstruction by means of surface optimization. Part II: time-resolved electronic speckle pattern interferometry

An analysis of time-resolved electronic speckle pattern interferograms using an optimization algorithm is shown to provide full-field measurements of transient surface deformation. The arrangement uses a continuous-wave laser and high-speed camera to capture speckle images, with the recovery of the time-resolved deformation achieved by spatiotemporal processing using an optimization algorithm. It is shown that the process allows imaging of high-speed non-monotonic out-of-plane displacements with sub-micrometer amplitude. Time-resolved amplitude and phase recovery is demonstrated by analyzing the out-of-plane deformation of harmonic and transient events in a friction membranophone.

Deformation reconstruction by means of surface optimization. Part I: Time-averaged electronic speckle pattern interferometry

Electronic speckle pattern interferometry is a well-known experimental technique for full-field deformation measurements. Although speckle interferometry techniques were developed years ago and are widely used for the visualization of the operating deflection shapes of vibrating surfaces, methods for accurate reconstruction of the observed deflection shape are still an active topic of research. Determination of the relative phase of the motion of vibrating objects is especially difficult and normally phase maps are calculated by direct transformation of the experimentally obtained interferometric images. An alternative method of phase reconstruction is described that involves solving the inverse problem via surface optimization. Compared to previously developed optimization methods, this method offers a higher spatial resolution and is more suitable for analysis of complex vibration patterns.

Strain field measurement by transverse digital holography

The technique generally referred to as speckle correlation interferometry may be described as transverse digital holography when phase stepping is applied, because phase stepping allows complete maps to be obtained of the transverse displacement of an object surface. This paper describes the analysis of these maps to obtain surface strain by fitting data to flat surfaces for least square error within sections of the map. Examples are shown for measuring rotation, thermal contraction, and strains around the tip of a notch. Only uniaxial strain is measured; however, the possibility for biaxial measurement is considered.

Measurement of Strain Distributions in Mouse Femora with 3D-Digital Speckle Pattern Interferometry

Bone is a mechanosensitive tissue that adapts its mass, architecture and mechanical properties to external loading. Appropriate mechanical loads offer an effective means to stimulate bone remodeling and prevent bone loss. A role of in situ strain in bone is considered essential in enhancement of bone formation, and establishing a quantitative relationship between 3D strain distributions and a rate of local bone formation is important. Digital speckle pattern interferometry (DSPI) can achieve whole-field, non-contacting measurements of microscopic deformation for high-resolution determination of 3D strain distributions. However, the current system does not allow us to derive accurate strain distributions because of complex surface contours inherent to biological samples. Through development of a custom-made piezoelectric loading device as well as a new DSPI-based force calibration system, we built an advanced DSPI system and integrated local contour information to deformation data. Using a mouse femur in response to a knee loading modality as a model system, we determined 3D strain distributions and discussed effectiveness and limitations of the described system.

Evaluation of two-dimensional displacement components of symmetrical deformation by phase-shifting electronic speckle pattern interferometry

A method for the isolation of two-dimensional (2D) displacement components by using one phase map obtained by phase-shifting electronic speckle pattern interferometry (ESPI) is presented. When the typical ESPI is used for displacement measurement, a mixed phase distribution of deformation is measured. If the deformation of the object is symmetrical, two components of deformation can be separated from each other by using the mixed phase distribution. We turn over the mixed phase map first to obtain the second phase map, and then overlap them. Two displacement components can be separated from each other by boundary alignment and algebraic calculation between the two phase maps. This method has been proved feasible by a typical three-point bending experiment. Some experimental results are offered and compared with the results obtained by a dual-beam symmetrical illuminations experiment. This technique presented provides an alternative approach to 2D deformation measurement.