Detection Of Small Displacements Research Articles

Differential laser Doppler vibrometry for displacement measurements down to 1 mHz with 1 nm amplitude resolution in harsh environments

Environmental disturbances increasingly limit laser Doppler vibration measurements with decreasing frequency of the moving surface. Particularly limiting for the detection of small displacements of a specimen in a furnace are refractive index fluctuations in the air from heat haze, optical path length fluctuations from thermal expansions in the measurement setup, and mechanical vibrations from the building and other sources. In this paper, we demonstrate how these disturbances can be largely compensated for. In our application, we require a displacement resolution of less than 10 nm to measure the chemical expansion of volume crystals and thin films at an ambient temperature of up to 800 °C. The required sensitivity cannot be achieved with state-of-the-art commercially available laser Doppler vibrometers since they are not designed to operate at frequencies below 0.1 Hz. In order to reduce the dominating low-frequency environmental noise, we employ a differential laser Doppler vibrometer in a setup optimized to minimize low-frequency displacement noise. We prove that the concept of differential measurement can eliminate disturbances by optical turbulence and parasitic mechanical vibrations with a newly constructed laser Doppler vibrometer. The elimination of these noise contributions allows for the first time a displacement sensitivity of about 1 nm for frequencies in the mHz range in a 600 °C environment.

Fiber SPR micro displacement sensor based on heterocore structure of graded index multimode fiber

Based on the self-focusing characteristics of graded index multimode fiber, a fiber SPR micro displacement sensor can be constructed, which has two bottleneck problems of difficult to fabricate and the small displacement detection range. In this paper, we proposed and constructed a new heterocore structure of graded multimode fiber-single-mode fiber-graded multimode fiber to realize the micro displacement sensing, which has stable performance and simple fabrication. By increasing the core diameter of modulation graded multimode fiber and displacement fiber, the displacement detection range of probe was increased. The simulating and testing results indicate that the SPR micro displacement sensor based on the graded multimode heterogeneous core structure can well realize the two-parameter sensing of micro displacement, and its average wavelength and light intensity sensitivity can reach 1.23 nm/μm, and 0.00576 a.u./μm respectively, the measurement resolution is 0.813μm. When using step multimode fiber with core diameter of 40μm in place of single-mode fiber as the displacement fiber, the displacement detection range reaches 50μm which is double that of the reported fiber SPR micro displacement sensor. The proposed fiber SPR micro displacement sensor well solved the two bottleneck problems above, which can be used in the field of micro displacement measurement of structural health monitoring.

Structural process and testing of tunneling attitude sensor based on gravity gradient torque measurements

The function of determining the orientation of a satellite in orbit is known as attitude determination. Depending on the missions, this important function is typically performed by different optical instruments. Due to the limited field of view, multiple optical sensors are placed in all directions to ensure large coverage. A kind of inertial sensor that uses the gravity gradient torque as a reference for attitude determination was proposed recently. At present, the volume of this kind of sensors is large and the accuracy is not high enough. In this paper, we propose an attitude sensor, which is composed of a barbell-shaped sensitive structure with larger moment of inertia and a small displacement detection module based on the tunneling effect. The sensitive structure is fabricated by silicon-on-glass process based on micro-electro-mechanical system technology. As a result, the sensitive structure has a smaller size, and the accuracy of angle measurement can reach 7.3° (3σ) in the range of −20° to +20°.

Modified FMCW system for non-contact sensing of human respiration

Small displacement detection capability becomes an important key for developing non-contact sensor for human respiration based on radar system. Frequency modulated continuous wave (FMCW) radar has been widely studied and applied for many applications. With respect to the conventional perspective, large bandwidth is needed for detecting the small displacement related to the human respiration. Meanwhile, extracting the respiration pattern from Doppler response has a drawback in identifying the small displacement location. In this paper, the modification on FMCW system was proposed for obtaining the capability in detecting the human respiration and its distance from the radar. Detecting the phase value of the low pass filter (LPF), output from conventional FMCW was investigated and applied as a modification concept. The pattern, rate and amplitude of respiration are extracted from phase detector output. Beat frequency detection is still elaborated for synthesising the reference signal for phase detection. The result shows that the modified FMCW system proposed the capability of detecting the rate and amplitude respiration and location of the target.

Luminescent Spectral Rulers for Noninvasive Displacement Measurement through Tissue.

A luminescent spectral ruler was developed to measure micrometer to millimeter displacements through tissue. The spectral ruler has two components: a luminescent encoder patterned with alternating stripes of two spectrally distinct luminescent materials and an analyzer mask with periodic transparent windows the same width as the encoder stripes. The analyzer mask is placed over the encoder and held so that only one type of luminescent stripe is visible through the window; sliding the analyzer over the encoder modulates the luminescence spectrum acquired through the analyzer windows, enabling detection of small displacements without imaging. We prepared two types of spectral rulers, one with a fluorescent encoder and a second with an X-ray excited optical luminescent (XEOL) encoder. The fluorescent ruler used two types of quantum dots to form stripes that were excited with 633 nm light and emitted at 645 and 680 nm, respectively. Each ruler type was covered with chicken breast tissue to simulate implantation. The XEOL ruler generated a strong signal with negligible tissue autofluorescence but used ionizing radiation, while the fluorescence ruler used non-ionizing red light excitation but required spectral fitting to account for tissue autofluorescence. The precision for both types of luminescent spectral rulers (with 1 mm wide analyzer windows, and measured through 6 mm of tissue) was <2 μm, mostly limited by shot noise. The approach enabled high micrometer to millimeter displacement measurements through tissue and has applications in biomechanical and mechanochemical measurements (e.g., tracking postsurgical bone healing and implant-associated infection).

Small displacement detecting method based on multifrequency continuous wave radar system

A small displacement becomes important indicator in identifying a problem that may rises in several systems. Non-Contacting sensor is needed for small displacement detection in several field such as structure health monitoring, landslide monitoring and human vital sign detection. Radar system is potentially implemented as non-contacting sensor for previous mention problems. Detection of small displacement on a target using a radar system requires high accuracy and resolution which gives the consequence of a wide bandwidth requirement. The method of multi-frequency continuous wave radar is then investigated and proposed as a method for detection of small displacement with low bandwidth requirements. Cross correlation and IQ demodulation techniques are applied in post processing. Theoretical analysis and simulation were conducted to study the concept of the proposed method. The results show that the proposed method can determine the location and magnitude of small displacement.

Dual Frequency Continuous Wave Radar for Small Displacement Detection

Dual Frequency Continuous Wave Radar for Small Displacement Detection

Dual Frequency Continuous Wave Radar for Small Displacement Detection

Dual Frequency Continuous Wave Radar for Small Displacement Detection

Exploitation of the Intermittent SBAS (ISBAS) algorithm with COSMO-SkyMed data for landslide inventory mapping in north-western Sicily, Italy

A large scale study of landslide processes was undertaken by coupling conventional geomorphological field surveys with aerial photographs along with an advanced Interferometric Synthetic Aperture Radar (InSAR) analysis of ground instability in north-western Sicily. COSMO-SkyMed satellite images for the period between 2008 and 2011 were processed using the Intermittent Small BAseline Subset (ISBAS) technique, recently developed at the Department of Civil Engineering of the University of Nottingham. The use of ISBAS allowed the derivation of ground surface displacements across non-urbanized areas, thus overcoming one of the main limitations of conventional interferometric techniques. ISBAS provides ground motion information not only for urban but also for rural, woodland, grassland and agricultural terrains, which cover >60% of north-western Sicily, thereby improving by 40 times in some cases, the slope instability investigation capabilities of InSAR methods.ISBAS ground motion data enabled the updating of the landslide inventory for the areas of Piana degli Albanesi and Marineo (over 130km2), which encompass a number of active, dormant and inactive landslides according to the pre-existing landslide inventory maps produced through aerial photo-interpretation and local field checks. An average of ∼7000 ISBASpixelskm−2 allowed the detection of small displacements in regions difficult to access. In particular, 226 landslides – mainly slides, flows and creep and four badlands were identified, comprising a total area of 25.3km2. When compared to the previous landslide inventory maps, 84 phenomena were confirmed, 67 new events were detected and 79 previously mapped events were re-assessed, modifying their typology, boundary and/or state of activity. Because the InSAR method used here is designed to measure slow rates of velocity and therefore may not detect fast-moving, events such as falls and topples, the results for Piana degli Albanesi and Marineo demonstrate the validity of this method to support land management, underlying the time and cost benefits of a combined approach using traditional monitoring procedures and satellite InSAR methods especially if slow-moving slope movements prevail.

Small Displacement Detection of Biological Signals Using the Cyclic Frequency Method

A new signal processing method called the Cyclic Frequency method is proposed for small displacement detection of vital signals such as heart rate and respiration using the CW radar method. We have presented experimental results of small displacement detection to confirm the validity of the method. The displacement amplitude 2.5 mm can be detected with a propagation frequency of 24.15 GHz. We may increase the propagation frequency for smaller displacement amplitude or target velocity.

FMCW Radar for Small Displacement Detection of Vital Signal Using Projection Matrix Method

Small displacement detection has been studied for extracting heart rate signal from the respiratory variation component of the human body with the FMCW radar method. And a new signal processing method of vital signal has been proposed for suppression of unrequired variation components called projection matrix method. We have presented experimental results of small displacement detection to confirm the validity of the method.

Optical detection of ultrasound on rough surfaces using speckle correlated spatial filtering

There are numerous techniques for the optical detection of ultrasound but many of these are of very limited application on optically rough surfaces. Techniques that work on rough surfaces are often complicated, inefficient and expensive. In this paper a new technique for the optical detection of ultrasound on rough surfaces is presented. It is a variation on the knife-edge (KE) technique but adapted for rough surfaces by replacing the knife-edge with a speckle correlated spatial filter (SCSF) which is implemented using a spatial light modulator (SLM). This technique is conceptually and practically simple and may be implemented using relatively low cost components. It is also relatively general and may also be applied to the detection of small displacements in many circumstances.

Determination of nanometer vibration amplitudes by using a homodyne photorefractive crystal interferometer

We report a low cost and high accuracy interferometric technique for detecting nanometer vibrations by using a photorefractive crystal interferometer based on two-wave mixing within a Bi12SiO20 (BSO) crystal. The results of small displacement detection on the sample (1–2 nm) and comparison between the sensitivity of Michelson and photorefractive adaptive interferometers are presented. Furthermore, the effect of an external electric field applied to the photorefractive crystal on the Signal to Noise Ratio (SNR) and on the vibrometer sensitivity is investigated.

A “gentle” nodal suspension for measurements of the acoustic attenuation in materials

Loss angle measurements in ultralow mechanical loss materials is normally affected by a large systematic error due to the excess losses introduced by the suspension system used to hold the samples. Crystals such as sapphire and silicon or amorphous materials such as fused silica can have loss angles in the range of 10(-10)-10(-7); such materials are of extreme interest in the detection of small displacements as it is required in quantum measurements, frequency stabilization, Micro Electro-Mechanical Systems (MEMS), and gravitational wave research. In the system proposed here the sample is suspended in equilibrium on top of a sphere, touching on one of the nodal points of vibration. The advantage of this system, as compared to others used so far, is twofold: (i) one surface only of the sample is touched and the contact surface is minimized because of the absence of applied forces; (ii) some relevant parameters of the suspension can be measured and eventually varied, giving the experimentalist the possibility to identify whether the measured loss is limited by the suspension system in use or it is an intrinsic property of the sample under investigation. The measurements of a 75 mm diameter and 3 mm thickness disk of Suprasil 311 gave a loss angle phi of 5x10(-8).

A Novel Approach to Extending the Linearity Range of Displacement Inductive Sensor

This paper presents a meander-type displacement inductive sensor, usable for the detection of small displacements (less than 0.5 mm) in the plane. It also describes design, realization, and the input inductance measurement of sensor. A displacement in two directions can be detected by using two sensor elements, each having a pair of meander coils. In each pair, one of the coils is fixed and between its terminals the input inductance was measured, while the other coil is short-circuited. If one coil is moved above the other, in directions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> - and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -axes, coupling between the coils will change, as well as the input inductance, which serves as a measure of displacement. In order to achieve better linearity of the sensor, longitudinal gaps are inserted in the middle of each conductive segment of one fixed coil. Four sets of inductive sensors were realized: without gap and with three different gaps. Planar, low-cost PCB technology was chosen for our prototype. In addition, an improved model of the inductive sensor is proposed. The input inductance of displacement sensor was calculated and compared with measured values. A good agreement was found.

3P7a-6 Precise Tissue Elasticity Reconstruction Based on Detection of Small Displacements(Poster Session)

3P7a-6 Precise Tissue Elasticity Reconstruction Based on Detection of Small Displacements(Poster Session)

Heisenberg limit for displacements with semiclassical states

We analyze the quantum limit to the sensitivity of the detection of small displacements. We focus on the case of free particles and harmonic oscillators as the systems experiencing the displacement. We show that the minimum displacement detectable is proportional to the inverse of the square root of the mean value of the energy in the state experiencing the displacement (Heisenberg limit). We present a measuring scheme that reaches this limit using semiclassical states. We examine the performance of this strategy under realistic practical conditions by computing the effect of imperfections such as losses and nonunit detection efficiencies. This analysis confirms the robustness of this measuring strategy by showing that the experimental imperfections can be suitably compensated by increasing the mean energy of the input state.

Can spatial and temporal motion integration compensate for deficits in local motion mechanisms?

We studied the motion perception of a patient, AMG, who had a lesion in the left occipital lobe centered on visual areas V3 and V3A, with involvement of underlying white matter. As shown by a variety of psychophysical tests involving her perception of motion, the patient was impaired at motion discriminations that involved the detection of small displacements of random-dot displays, including local speed discrimination. However, she was unimpaired on tests that required spatial and temporal integration of moving displays, such as motion coherence. The results indicate that she had a specific impairment of the computation of local but not global motion and that she could not integrate motion information across different spatial scales. Such a specific impairment has not been reported before.

Single molecule tracking scheme using a near-field scanning optical microscope

The use of a near-field scanning optical microscope (NSOM) to measure the diffusion of fluorescently tagged molecules on a quasi-two-dimensional system is described. The heart of the apparatus lies in the circular motion of the NSOM probe, allowing the detection of small displacements on single molecules. Using a 100 nm tip, and a simulated diffusion coefficient of D∼1×10−12 m2/s, we found that molecules can be tracked within ∼40 nm over several seconds. We foresee that D as large as ∼5×10−12 m2/s can be measured with minor modifications to the experimental setup. These values of D encompass those found in many liquid crystalline systems, particularly lipids in bilayer membranes.

Neurophysiological Contributions to Luminance and Chromatic Mechanisms in a Hyperacuity Task

We recently reported (paper presented at ARVO 1997) psychophysical evidence as to contributions of luminance and chromatic mechanism in a hyperacuity task, namely detection of small displacements. Achromatic or chromatic (430, 550, 690 nm) edges were presented on white or chromatic (550 nm) backgrounds, and displacement thresholds measured as a function of luminance contrast. Above 3% (achromatic detection threshold), all conditions yielded nearly identical contrast/threshold curves; we believe a luminance mechanism to be responsible. In chromatic conditions, below 3% contrast, large (&gt;100 s arc) displacements were detectable; presumably chromatic mechanisms are responsible. We have now carried out equivalent physiological experiments. Data were consistent with cells of the magnocellular (MC) pathway underlying the luminance mechanism. Opponent S-cone or parvocellular (PC) cells became responsive to displacements in the chromatic conditions. S-cone cells were very responsive to the 430 nm edge, and responded at low contrasts matching the psychophysical thresholds. L, M-cone opponent cells were responsive to the 690 nm edge, but less so than was expected from the psychophysical data. Our data suggest MC-cells underlie a luminance hyperacuity mechanism. Additional factors (eg cell numerosity) may have to be considered for chromatic spatial mechanisms.