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Laser Doppler Vibrometry (LDV) is the workhorse for hard disk drive dynamic testing and has contributed significantly to the development of modern hard disk drives. With increasing areal densities, and component as well as drive miniaturization the performance requirements for laser Doppler vibrometers (LDVs) have continuously grown to confront the...
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... original phase information is immediately differentiated to achieve velocity data. Using an additional DSP circuit, phase unwrapping can be performed in real-time resulting in a synchronous output of displacement in addition to the velocity data ( figure 11, lower part). The resolution of the displacement data is limited by the D/A conversion to 15pm per bit. ...
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Citations
... The dc terms I r and I m are filtered out, while the I het is sent to the demodulator. Demodulation can be performed either in the analog domain, using a frequency-to-voltage converter or in the digital domain, by sampling the signal I het (t) and using digital signal processing (DSP) techniques [44,45]. Although good performance can be achieved with analog demodulation, digital approaches provide better performance in terms of stability and linearity, with the arctangent phase IQ demodulation being the most popular method for decoding the LDV signal [46]. ...
We demonstrate a compact heterodyne Laser Doppler Vibrometer (LDV) based on the realization of optical frequency shift in the silicon nitride photonic integration platform (TriPleX). We theoretically study, and experimentally evaluate two different photonic integrated optical frequency shifters (OFSs), utilizing serrodyne and single-sideband (SSB) modulation. Both OFSs employ stress-optic modulators (SOMs) based on the non-resonant piezoelectrical actuation of lead zirconate titanate (PZT) thin-films, deposited on top of the silicon nitride waveguides with a wafer-scale process. To improve the modulation bandwidth of the SOMs we investigate a novel configuration of the electrodes used for the actuation, where both electrodes are placed on top of the PZT layer. Using this top-top electrode configuration we report frequency shift of 100 kHz and 2.5 MHz, and suppression ratio of the unwanted sidebands of 22.1 dB and 39 dB, using the serrodyne and the SSB OFS, respectively. The best performing SOM structure induces 0.25π peak-to-peak sinusoidal phase-shift with 156 mW power dissipation at 2.5 MHz. We use the SSB-OFS in our compact LDV system to demonstrate vibration measurements in the kHz regime. The system comprises a dual-polarization coherent detector built in the PolyBoard platform, utilizing hybrid integration of InP photodiodes (PDs). High quality LDV performance with measurement of vibration frequencies up to several hundreds of kHz and displacement resolution of 10 pm are supported with our system.
... where µ is the responsivity of the PD, θ dc = θ D (t) − θ D (t) is the constant phase difference between the two arms due to their path length difference, dc = µ |a| 2 + |ηb| 2 /2 is the dc part of the photocurrent signal, and P m = η|ab| is the amplitude of the ac part. Many methods can be used to retrieve θ D (t); here, a commonly used method is explained [18]. ...
... Figure 8c shows the linear baseline fitting of one section, with Figure 8d displaying the obtained deviations for all complete sections. The deviations are averaged and fitted to Equation (18), as shown in Figure 8e. With the parameters of the fitted function (x f d = −0.223 ...
Optical coherent detection is widely used for highly sensitive sensing applications, but nonlinearity issues pose challenges in accurately interpreting the system outputs. Most existing compensation methods require access to raw measurement data, making them not useful when only demodulated data are available. In this study, we propose a compensation method designed for direct application to demodulated data, effectively addressing the 1st and 2nd-order nonlinearities in both homodyne and heterodyne systems. The approach involves segmenting the distorted signal, fitting and removing baselines in each section, and averaging the resulting distortions to obtain precise distortion shapes. These shapes are then used to retrieve compensation parameters. Simulation shows that the proposed method can effectively reduce the deviation caused by the nonlinearities without using the raw data. Experimental results from a silicon-photonics-based homodyne laser Doppler vibrometry prove that this method has a similar performance as the conventional Heydemann correction method.
... Reflector 1, the glass, and the cylindrical lens were fixed on translation stage 1 (BOIC, MTS314) to change the distance between the excitation and detection. Ultrasonic detection was performed using a laser Doppler Vibrometer (Polytec, OFV-5000, OFV-505) [32], with the parameters listed in Table 2. The signal was amplified by an amplifier (MWPA, MWLA-00020G30, 5 KHz ∼ 2 GHz, 30 dB), collected and displayed using an oscilloscope (Rigol DS4024, bandwidth 200 MHz), and finally sent to a PC for signal processing and F-SAFT calculation. ...
An accurate frequency-domain synthetic aperture focusing technology (F-SAFT) based on 2-D equivalent velocity mapping is proposed for laser ultrasonic testing (LUT) to detect and image internal defects in specimens. The equivalent velocity mapping varies with depth and spatial frequency to match the characteristics of the separated excitation and detection commonly used in LUT. Bulk acoustic waves are non-destructively excited by a line-shaped laser source and are detected by a laser Doppler Vibrometer. By compensating for the distance shift arising from the separation of the laser spots, the imaging defect location is corrected. Several optimisations of the algorithm are carried out: the calculation time of the equivalent velocity is reduced by simplifying its expression, and the imaging quality, especially for defects with a shallow depth, is improved by the 2-D equivalent velocity mapping. The results show that compared with traditional F-SAFT, the optimised F-SAFT algorithm can not only improve the imaging quality but also locate the defect more accurately with separated excitation and detection.
... However, because of the rapid drop in pressure as speech propagates through the air, the working distance for traditional acoustic sensors is very Manuscript limited [1]. Laser Doppler Vibrometers (LDVs) work differently by detecting Doppler signals in the coherent signals scattered from a target that is set in motion by speech [2]. By measuring these Doppler signals, a time-resolved measurement of the target's displacement can be made. ...
Laser Doppler Vibrometers (LDVs) enable the acquisition of remote speech signals by measuring small-scale vibrations around a target. They are now widely used in the fields of information acquisition and national security. However, in remote speech detection, the coherent measurement signal is subject to environmental noise, making detecting and reconstructing speech signals challenging. To improve the detection distance and speech quality, this paper proposes a highly accurate real-time speech measurement method that can reconstruct speech from noisy coherent signals. First, the I/Q demodulation and arctangent phase discrimination are used to extract the phase transformation caused by the acoustic vibration from coherent signals. Then, an innovative smoothness criterion and a novel phase difference-based dynamic bilateral compensation phase unwrapping algorithm are used to remove any ambiguity caused by the arctangent phase discrimination in the previous step. This important innovation results in the highly accurate detection of phase jumps. After this, a further innovation is used to enhance the reconstructed speech by applying an improved waveform-based linear prediction coding method, together with adaptive spectral subtraction. This removes any impulsive or background noise. The accuracy and performance of the proposed method were validated by conducting extensive simulations and comparisons with existing techniques. The results show that the proposed algorithm can significantly improve the measurement of speech and the quality of reconstructed speech signals. The viability of the method was further assessed by undertaking a physical experiment, where LDV equipment was used to measure speech at a distance of 310m in an outdoor environment. The intelligibility rate for the reconstructed speech exceeded 95%, confirming the effectiveness and superiority of the method for long-distance laser speech measurement.
... The angle bisector of two beams is usually set to be perpendicular to the moving direction of the target. By detecting the beating frequency of the combined optical field using a photodiode (PD), one can retrieve the velocity of the target [6]. On the contrary, laser Doppler vibrometry only sends one light beam to the target, and the corresponding reflected light is then captured by the sensor and mixed with a reference light signal inside of the sensor (internal interference). ...
... A typical demodulation method of the heterodyne signal is an arctangent phase demodulation method in the digital domain [6]. In this method, the photocurrent signal is first converted to a voltage signal V het (t) via a transimpedance amplifier (TIA). ...
... Moreover, it is also easier to implement a miniaturized homodyne LDV than a heterodyne LDV, mainly because a miniaturized optical frequency shifter is not simple to implement. A typical demodulation method of the heterodyne signal is an arctangent phase demodulation method in the digital domain [6]. In this method, the photocurrent signal is first converted to a voltage signal ( ) via a transimpedance amplifier (TIA). ...
Laser Doppler vibrometry (LDV) is a non-contact vibration measurement technique based on the Doppler effect of the reflected laser beam. Thanks to its feature of high resolution and flexibility, LDV has been used in many different fields today. The miniaturization of the LDV systems is one important development direction for the current LDV systems that can enable many new applications. In this paper, we will review the state-of-the-art method on LDV miniaturization. Systems based on three miniaturization techniques will be discussed: photonic integrated circuit (PIC), self-mixing, and micro-electrochemical systems (MEMS). We will explain the basics of these techniques and summarize the reported miniaturized LDV systems. The advantages and disadvantages of these techniques will also be compared and discussed.
... Non-destructive techniques (NDT) are considered an effective analysis method for frescoes conservation status detection. The laser Doppler vibrometry (LDV) technique has demonstrated its large potential in terms of spatial resolution [1][2][3][4], moreover, as a non-destructive method, is suitable for ancient and delicate artworks [5,6]. Several authors addressed the diagnostic of artworks through laser-based methods successfully [7][8][9]. ...
Delamination is one of the most common issue that can affect frescoes and wall painting in general. Non-destructive techniques (NDT) are considered an effective analysis method for frescoes conservation status detection. The objective of this work was to determine the structural integrity of plaster in the United States Capitol Building through structural vibration analysis. The plaster was excited with sound, causing it to vibrate at a miniscule level. The resulting vibrations were measured using a laser vibrometer and then utilized to reveal the location and size of unseen irregularities in the structure. More than 50 individual scans were performed and analyzed using scanning laser Doppler vibrometer (LDV). The analysis identified many anomalies and assessed the status of some areas that were intact. This procedure was performed on each of the frescoes adorning the walls and ceiling of the rooms to discover areas where the painted plaster has lost adherence to the underlying architecture. The frescos were classified into three categories: intact, anomalous, in need of further analysis. A comparison with data recorded in 2004 of the same frescoes has been also performed.
... The Nyquist frequency (one half of the camera framerate) determines the absolute maximum possible vibration frequency that can be recorded. However, this upper bound can prove quite noisy, and it is more typical to limit analysis to a quarter of the sampling frequency: a 1000 frames-per second recording would typically only be used for frequency analysis up to around 250 Hz, whereas laser vibrometry has a very high sample rate and is typically rated to measure signals up to 2 MHz [24]. ...
... Another consideration that must be thought through before employing this technique is that of vibrational signal noise, which will depend on experimental design and the vibrational axis chosen to examine. Although the resolution of phase-based video vibrometry has been shown to be accurate down to a few thousandths of a pixel [6], it is still of much lower resolution than a laser vibrometer, which is rated on the order of nanometers [24]. Performing stereo vision also increases the measurement noise over that of two-dimensional video vibrometry because of camera calibration error and binocular vision effects. ...
Simple Summary
Spiders often use their webs as sensory mechanisms, obtaining from them such information as the location of prey, the presence of rival spiders, and the characteristics of potential mates. Examining how this information is transmitted through the web and received by spiders is a promising biological area of research that could provide insight into a spider’s world and lead to new technologies that leverage these discoveries. In this paper, we develop a novel noncontact technique using two video cameras that is capable of analyzing vibrational signals transmitted through spiderwebs and validate this technique against the current standard of laser Doppler vibrometry. By combining the principles of stereo vision and video vibrometry, we can automatically extract three-dimensional vibrational information at any point in the spiderweb across time, and study how these signals propagate through the web. We show that this technique produces results comparable to those of standard laser vibrometry.
Abstract
From courtship rituals, to prey identification, to displays of rivalry, a spider’s web vibrates with a symphony of information. Examining the modality of information being transmitted and how spiders interact with this information could lead to new understanding how spiders perceive the world around them through their webs, and new biological and engineering techniques that leverage this understanding. Spiders interact with their webs through a variety of body motions, including abdominal tremors, bounces, and limb jerks along threads of the web. These signals often create a large enough visual signature that the web vibrations can be analyzed using video vibrometry on high-speed video of the communication exchange. Using video vibrometry to examine these signals has numerous benefits over the conventional method of laser vibrometry, such as the ability to analyze three-dimensional vibrations and the ability to take measurements from anywhere in the web, including directly from the body of the spider itself. In this study, we developed a method of three-dimensional vibration analysis that combines video vibrometry with stereo vision, and verified this method against laser vibrometry on a black widow spiderweb that was experiencing rivalry signals from two female spiders.
... Once a combined raw signal CH combined has been calculated according to Eq.2, we can obtain the phase information from it. To do this, we use phase demodulation according to the arctangent method 13 . ...
A limiting factor for Laser-Doppler vibrometer (LDV) measurements is the laser speckle effect, which occurs when measuring on rough surfaces. This effect limits the minimally detectable vibration amplitudes and increases the noise level. In order to reduce the impact of the effect, signal diversity is used in the state of the art. In a previous publication, we demonstrated a newly developed algorithm that combines raw signals, improving the signal quality of an algorithm from the literature. In this article, we examine its real-time capability and evaluate the application range of our algorithm. In addition, we briefly address an extension of the setup to allow the measurement of the 3D velocity vector.
... However, given the size of black-widow spider legs and strain amplitudes that we expect, it is difficult to manufacture strain sensors small enough not to disrupt natural body mechanics. Laser Doppler vibrometry (LDV), however, allows contact-free measurement of movement at near picometer sensitivity (Johansmann et al., 2005) and we can infer joint bending from the relative motion of different leg segments under the reasonable assumption that these behave as rigid bodies at the low frequencies under consideration. We exploit the sensitivity of LDV, in combination with multi-body dynamic modelling (MBD), to study the effects of the body, its size, and posture on the tuning of leg joints in the female black-widow spider. ...
Several studies have described vibration producing behaviours across many web-building spiders, and vibratory communication is thought to play an integral role during male-female interactions. Despite the presumed ubiquity of vibratory communication in this group of spiders, very little is known about the characteristics and functions of the signals involved, how signals are produced and transmitted through webs, or how vibrations are perceived. In this thesis, I used the western black widow spider, Latrodectus hesperus, as my focal organism, to investigate the details of vibratory communication from sender to the receiver. My results show that male L. hesperus courtship vibration signals comprise three distinct components (abdominal tremulation, bounce and web plucks), each produced using different signal production mechanism. Larger males produced bounce and web pluck signals with high power, which suggests that these signals may carry information about male traits. I found that during the early phase of courtship, males produced these different signal components haphazardly, with little temporal organization among the individual components (unstructured signaling). However, during the later phase of courtship, as males approach females, males intermittently organized signal components into a stereotyped temporal sequence (structured signaling). I tested the importance of these composite multicomponent signals, and found that males that displayed these structured signals more often were more likely to successfully copulate and copulate sooner. Vibrations arriving at the females are transmitted through the legs. My results show that the more distal joints of the legs (i.e. tarsus-metatarsus joint) move more to higher frequencies, and more proximal joints are tuned to lower frequencies. This suggests that female leg-joints play an important role in segregating vibration frequencies, and this may have important implications for prey/mate discrimination, as well as vibration source localization. These results show that L. hesperus males employ multiple signal components during courtship, and provide novel insights into emergent signal complexities in a web-building spider, previously thought to be ‘simple’ signalers. Additionally, the spider body mechanics can play a key role in influence vibration perception.
... Unfortunately there is no straight rule about using tracking or not [34,35]. Usually, the user is invited to use the filter and try some measurements. ...
Laser Doppler vibrometry relies on the Doppler effect of a laser beam to measure the vibration velocity of a target.
