Laser Vibrometry System Research Articles

Single-Point and Surface Quality Assessment Algorithm in Continuous Production with the Use of 3D Laser Doppler Scanning Vibrometry System.

In the current economic situation of many companies, the need to reduce production time is a critical element. However, this cannot usually be carried out with a decrease in the quality of the final product. This article presents a possible solution for reducing the time needed for quality management. With the use of modern solutions such as optical measurement systems, quality control can be performed without additional stoppage time. In the case of single-point measurement with the Laser Doppler Vibrometer, the measurement can be performed quickly in a matter of milliseconds for each product. This article presents an example of such quality assurance measurements, with the use of fully non-contact methods, together with a proposed evaluation criterion for quality assessment. The proposed quality assurance algorithm allows the comparison of each of the products' modal responses with the ideal template and stores this information in the cloud, e.g., in the company's supervisory system. This makes the presented 3D Laser Vibrometry System an advanced instrumentation and data acquisition system which is the perfect application in the case of a factory quality management system based on the Industry 4.0 concept.

Electromechanical response of poly(vinylidenefluoride) thin films under acoustic stimuli

Understanding and controlling the vibration of piezoelectric components induced by oscillating external stimuli is essential to develop smart sensing and energy harvesting devices that convert mechanical energy into electricity. Piezoelectric polymers based on poly(vinylidenefluoride) (PVDF) thin films are amongst the most widely studied materials for flexible sensors and harvesters. Despite the large amount of research on these materials, their electromechanical response under acoustic sound stimuli has not yet been studied in detail. In this work, a thorough investigation on the mechanical vibrations and electrical response of PVDF circular plates of different diameters in response to multiple sound wave frequencies (100 Hz–10 kHz) has been carried out to gain further understanding of the resonance behavior and acousto-electric conversion mechanisms of vibrating PVDF thin films. The work is based on experimental data generated using an integrated piezo-acoustic laser vibrometry system and on a theoretical framework based on the continuum theory of thin plates. The developed model enables the prediction of the resonance frequencies in dependence of the plates’ diameter, and suggests that the electrical voltage generated during vibrations is not solely originating from the piezoelectric properties of the films, but might be affected by additional factors, including the triboelectric effect. The results of this study are expected to have a strong impact on the investigation of piezoelectric vibrating plates and on the development of different types of transducers and energy harvesting devices.

Imaging of barely visible impact damage on a composite panel using nonlinear wave modulation thermography

Thermosonics is a well-established non-destructive evaluation (NDE) technique that uses an infrared camera to visualise material damage by capturing the frictional heating at crack surfaces when the sample under inspection is vibrated. A high power ultrasonic horn is typically used to generate vibrations, which is pressed against the surface of the test component. However, the direct contact between the horn and the surface generates acoustic chaos and high-amplitude vibrations, which can lead to non-reproducible and unreliable measurements and, ultimately, they can harm the structural integrity of components. This paper proposes an alternative to thermosonics, here named as nonlinear wave modulation thermography, for the detection and imaging of material flaws on a damaged carbon fibre composite panel. This material inspection technology combines the concept of nonlinear wave modulation spectroscopy using dual excitation with contact piezoelectric transducers and thermographic equipment. Whilst nonlinear ultrasonic modulation was used to enhance the sensitivity to micro-cracks, an infrared camera was used for defect visualisation. A nonlinear narrow sweep excitation method was employed to experimentally identify the dual excitation frequencies that resulted in high-amplitude damage resonance effects causing frictional heat at crack surfaces. A laser vibrometry system was also used to create a spatial mapping of the amplitude of sidebands. Nonlinear wave modulation thermography has proved to successfully detect barely visible impact damage in composites in a quick and reliable manner, thus overcoming the limitations of traditional optical thermography and thermosonics.

Vector surface velocity measurement using contour scanning laser vibrometers for the detection of landmines

Much work has been done studying the detection of buried landmines using acoustic excitation and measuring the vibration response of the ground using Laser Doppler Vibrometry (LDV). We examine the benefits of measuring the full three-dimensional velocity response of the ground surface when a landmine is present. Three-dimensional velocity measurements provide a richer data set for identification of buried targets and avoid potential errors associated with projecting the surface velocity vector onto a single laser line of sight direction. We present results of a study conducted using landmines buried in sand in a laboratory environment. The data were obtained using a novel five-axis laser vibrometry system, which uses a single point LDV system to measure the surface of the sand from multiple angles at each measurement location. Data will be presented showing the consequences of a buried landmine on the three-dimensional velocity response of a contoured ground surface.

Effects of spatial modes on ladar vibration signature estimation

Ladar-based vibrometry has been shown to be a powerful technique in enabling the plant identification of machines. Rather than sensing the geometric shape of a target laser vibrometers sense motions of the target induced by moving parts within the system. Since the target need not be spatially resolved, vibration can be sensed reliably and provide positive identification at ranges beyond the imaging limits of the aperture. However, as the range of observation increases, the diffraction-limited beam size on the target increases as well, and may encompass multiple vibrational modes on the target's surface. As a result, vibration estimates formed from large laser footprints illuminating multiple modes on a vibrating target will experience a degradation. This degradation is manifest as a spatial low-pass filtering effect: high-order mode shapes, associated with high-frequency vibrations, will be averaged out while low-frequency vibrations will be affected less. A model to predict this phenomenology is proposed for both pulse-pair and cw vibrometry systems. The cw model is compared to results obtained using an off-the-shelf laser vibrometry system.

A vibration model for frequency analysis of arterial tubes with tissue

Vibro‐acoustography is a new noncontact imaging method based on the radiation force of ultrasound. We extend this technique for tissue characterization of arterial tubes by vibration techniques. The arterial tube can be excited remotely by ultrasound at its resonant frequencies where the vibration and acoustic emission of the tube can be measurable. From these resonant frequencies, the material properties of the arterial tube can be found. A theory for a tube with tissue is formulated using first‐order shear deformation theory to include the effects of transverse shear deformation and rotary inertia. A wave propagation approach is applied for easy handling of the boundary conditions. Experimental studies were carried out on a silicone tube embedded in a cylindrical gel phantom. A confocal transducer is used to produce the radiation force of ultrasound for exciting the tube–phantom structure. The vibration of the tube and the phantom are measured with a laser vibrometry system. The fundamental mode of a tu...