Innovative technologies are needed to support and augment the development of various types of deformable mirrors (DM), such as Micro Electro Mechanical Systems (MEMS), segmented, bimorph and membrane types that are currently used in adaptive-optic (AO) systems. The paper discusses the results of initial studies that, could, potentially, be employed for full characterization of the dynamic behavior of adaptive optics mirrors. The experimental data were obtained from a typical bimorph mirror using both, a Shack-Hartman wavefront sensor (SHWFS) and an Imaging Laser Doppler Vibrometer (ILDV) developed exclusively by AS&T Inc. These two sensors were employed for quantitative measurement of both the spatial and temporal dynamics of the DM under broadband excitation via the piezo electric drive elements. The need to characterize the spatial and temporal dynamic response of current and future DM mirror designs is essential for optimizing their performance to a level adequate for high bandwidth AO systems, such as those employed for real-time compensation of wavefront perturbations.
In this paper we discuss the background and principles of an optical non-contact sensor fusion concept, the Interferometric Correlator for Acoustic Radiation and Underlying Structural Vibration (ICARUSV) and give practical example of its capabilities, focusing on its ability to simultaneously capture, visualize and quantitatively characterize full-field non-stationary structural dynamics and unsteady radiated sound fields or transient flow fields around the structure of interest. The ICARUSV’s multi-sensor design is based on a parallel architecture and therefore the data capture is fast and inherently support a wide variety of spatio-temporal or spatio-spectral analysis methods which characterize the structural or acoustic/flow field dynamics as it occurs in real time, including short-lived transient events. No other technology available today offers this level of multi-parameter multi-dimensional data1.
Innovative technologies are needed to support and augment the development of various types of deformable mirrors (DM), such as Micro Electro Mechanical Systems (MEMS), segmented, bimorph and membrane types that are currently used in adaptive-optic (AO) systems. The paper discusses the results of initial studies that, could, potentially, be employed for full characterization of the dynamic behavior of adaptive optics mirrors. The experimental data were obtained from a typical bimorph mirror using both, a Shack-Hartman wavefront sensor (SHWFS) and an Imaging Laser Doppler Vibrometer (ILDV) developed exclusively by AS and T Inc. These two sensors were employed for quantitative measurement of both the spatial and temporal dynamics of the DM under broadband excitation via the piezo electric drive elements. The need to characterize the spatial and temporal dynamic response of current and future DM mirror designs is essential for optimizing their performance to a level adequate for high bandwidth AO systems, such as those employed for real-time compensation of wavefront perturbations.
Insight into transient structural interactions, including coupled vibrations and modal non-degeneracy (mode splitting) is
important to the development of current and next generation vibratory gyroscopes and MEMS resonators. Device
optimization based on characterization of these effects is currently time consuming and limited by the requirement to
perform spatially distributed measurements with existing single point sensors. In addition, the effects of interest and the
diagnosis of their underlying causes and dependences are not readily revealed by traditional modal and finite element
analyses. This paper, accordingly, discusses the design of a novel multi-channel fiber-optic heterodyne vibrometer which
addresses this requirement directly. We describe a fiber-optic interferometer design which incorporates many standard
fiber-optic telecommunications components, configured to support dynamic imaging of the real-time structural behavior
of macro and micro vibratory resonators, including planar and 3D micro electromechanical systems (MEMS). The
capabilities of the new sensor are illustrated by representative data obtained from a variety of 3D vibratory MEMS
structures currently under development.
We describe a unique high-speed Doppler imaging vibrometer configured for rapid full-field measurement of arbitrary
solid body vibrations without temporal or spatial measurement multiplexing. The instrument design employs a staring
16×16 measurement beam matrix and passive fiber-optic focal plane array, remotely coupled to distributed parallel
receivers and digital processors. High-speed data captured by the instrument indicate the rich dynamic complexity to be
found even in comparatively simple coupled mechanical systems with transient features that are otherwise difficult to
observe. The system provides a new tool for instantaneous non-contact full-field vibration measurement of structural
dynamics, including, but not limited to, transient or non-repeatable phenomenon.
We describe a hybrid system for real-time, full-field vibrometry, incorporating features of high-speed electronic speckle
pattern interferometry (ESPI) and laser Doppler vibrometry (LDV). Based on a 2D interferometric sensor array,
comprising 16 × 16 parallel illumination and detection channels, the matrix laser vibrometer (MLV), captures full-field
data instantaneously, without beam scanning. The instrument design draws on the advantages of scale offered by modern
telecommunications fiber optic and digital electronics. The resulting architecture, comprising a compact measurement
probe linked by fiber optic umbilical to a remote electronics unit, facilitates practical application of the system in fullfield
measurement of transient vibrations and rapid non destructive testing of composite materials.
This article describes the development and application of a 16x16 array (matrix) laser vibrometer based on a parallel
architecture which supports fast 2D measurement of arbitrary (steady state, non-steady state, transient) solid body
vibrations without beam scanning. The small size and low weight of the measurement probe, which is linked to a remote
detector/processor unit via a flexible armoured fibre-optic umbilical, enables deployment in areas with restricted access.
Incorporating aspects of high-speed electronic speckle pattern interferometry (ESPI) and laser Doppler vibrometry
(LDV), the design is based on a hybrid fiber-optic/bulk optic interferometer which operates at a wavelength of 1550 nm.
Test data illustrate high-speed capture of transient vibrations, showing the full 2D temporal evolution of surface
deformation, including multiple resonant modes, of a center-pinned metal plate excited by a 1-50 kHz frequency chirp
of 109 ms duration. We discuss preliminary data showing detection of sub-surface defects in composite materials, based
on non-contact (frequency chirped) acoustic resonance of the locally damaged structure. For large area NDT the probe
can be mounted on a lightweight XY gantry for automated multi-frame measurements.
Several experiments have demonstrated the potential of Laser Doppler Vibrometry, in conjunction with acoustic-toseismic coupling or mechanical shakers, for the detection of buried landmines. For example, experiments conducted by The University Of Mississippi and MetroLaser, Inc. have shown the ability to scan a one square meter area in less than 20 seconds with a 16-beam multi-beam LDV (MB-LDV), and find the landmines under a variety of soil conditions. Some critical requirements for this technology are to reduce the measurement time, increase the spatial resolution, and reduce the size of the systems. In this paper, MetroLaser presents data from three optical systems that help achieve these requirements: 1) A Compact MB-LDV, 2) A two dimensional, or Matrix Laser Doppler Vibrometer (MX-LDV), and 3) A Whole-field Digital Vibrometer (WDV). The compact MB-LDV produces a 1-D array of beams, which may be scanned over the target surface with a scanning mirror. The size of the new, compact MB-LDV system has been reduced to approximately 17" x 11" x 9", thus enhancing its capability for field applications. The MX-LDV, to be developed in 2006, produces a 16x16 array of beams over a one meter area, allowing the ground velocity of the entire area to be measured in a single measurement. The WDV uses a camera-based interferometry system to take a snapshot of the ground vibration over a one meter square area with very high spatial resolution. Field tests for this system are scheduled for mid-2006.
Development of pressure sensor for the instrumentation of experimental aerodynamic facilities has traditionally concentrated on electrical techniques. Such transducers have temporal and spatial resolutions that are currently insufficient to provide the accurate measurement of turbulent flows behind turbine rotor stages, for example. We present result obtained in a turbine test rig form a simple fiber optic pressure sensor based upon the interferometric response of an extrinsic cavity formed between the interrogation fiber and a reflective diaphragm. We discuss the design trade-offs, optical interrogation and temperature sensitivity of such a configuration, and demonstrate the success of the design in small-scale shock tube experiments. We then describe the application of the sensor in a full scale turbine test facility.
The use of computational fluid dynamics (CFD) to model the temperature and pressure distributions which drive complex thermodynamic processes in gas turbine systems contributes to more cost efficient turbine design and development.
There is considerable demand in the field of turbomachinery research to make in-situ measurements of temperature, heat flux, and pressure in large-scale flow rigs. This is driven by the desire to increase engine efficiency and reliability by improving our understanding of the flow regimes within compressors and turbines.