Two-axis Measurement Research Articles

Single-shot quantitative phase contrast imaging based on deep learning.

Quantitative differential phase-contrast (DPC) imaging is one of the commonly used methods for phase retrieval. However, quantitative DPC imaging requires several pairwise intensity measurements, which makes it difficult to monitor living cells in real-time. In this study, we present a single-shot quantitative DPC imaging method based on the combination of deep learning (DL) and color-encoded illumination. Our goal is to train a model that can generate an isotropic quantitative phase image (i.e., target) directly from a single-shot intensity measurement (i.e., input). The target phase image was reconstructed using a linear-gradient pupil with two-axis measurements, and the model input was the measured color intensities obtained from a radially asymmetric color-encoded illumination pattern. The DL-based model was trained, validated, and tested using thirteen different cell lines. The total number of training, validation, and testing images was 264 (10 cells), 10 (1 cell), and 40 (2 cells), respectively. Our results show that the DL-based phase images are visually similar to the ground-truth phase images and have a high structural similarity index (>0.98). Moreover, the phase difference between the ground-truth and DL-based phase images was smaller than 13%. Our study shows the feasibility of using DL to generate quantitative phase imaging from a single-shot intensity measurement.

A Novel Low-Cost DIC-Based Residual Stress Measurement Device

Residual stress often has a significant impact on part performance and lifetime. Existing measurement techniques using strain gauges or non-destructive methods are often expensive and time-consuming. This paper presents a low-cost, novel measurement device that uses digital image correlation with the hole-drilling method to quantify the magnitude and preferred orientation of these locked-in forces. A two-axis measurement device that rapidly drills and images the surface around the hole was developed to measure residual stresses as a function of depth with sub-millimetre resolution. Validation of the device and DIC methodology was performed using a four-point bending specimen and comparison with conventional strain gauge methods. The results showed strong correlations between the two measurement techniques, as well as the theoretical estimates. The total cost of production was estimated to be approximately £380, which is significantly cheaper than competitors. The device also substantially reduced the cost per measurement point (less than £1 vs. £50+) and shortened the experiment duration from 2 h per point to 45 min per measurement. A functional, rapid, economical device has been designed and produced, which is currently being used for residual stress analysis of industrial samples. The presented design is completely open-source, and the relevant links are provided.

Time-lapse imaging using dual-color coded quantitative differential phase contrast microscopy.

.Significance: Quantitative differential phase contrast (qDPC) microscopy enhances phase contrast by asymmetric illumination using partially coherent light and multiple intensity measurements. However, for live cell imaging, motion artifacts and image acquisition time are important issues. For live cell imaging, a large number of intensity measurements can limit the imaging quality and speed. The minimum number of intensity measurements in qDPC can greatly enhance performance for live imaging.Aim: To obtain high-contrast, isotropic qDPC images with two intensity measurements and perform time-lapse imaging of biological samples.Approach: Based on the color-coded design, a dual-color linear-gradient pupil is proposed to achieve isotropic phase contrast response with two intensity measurements. In our method, the purpose of designing a dual-color coded pupil is twofold: first, to obtain a linear amplitude gradient for asymmetric illumination, which is required to get a circular symmetry of transfer function, and second, to reduce the required number of frames for phase retrieval.Results: To demonstrate the imaging performance of our system, standard microlens arrays were used as samples. We performed time-lapse quantitative phase imaging of rat astrocytes under a low-oxygen environment. Detailed morphology and dynamic changes such as the apoptosis process and migration of cells were observed.Conclusions: It is shown that dual-color linear-gradient pupils in qDPC can outperform half-circle and vortex pupils, and isotropic phase transfer function can be achieved with only two-axis measurements. The reduced number of frames helps in achieving faster imaging speed as compared to the typical qDPC system. The imaging performance of our system is evaluated by time-lapse imaging of rat astrocytes. Different morphological changes in cells during their life cycle were observed in terms of quantitative phase change values.

An Assembly Quality Inspection System for Bone Conduction Implant Transducers

We designed and implemented a two-axis measurement system to inspect the assembly quality condition of a bone conduction implant (BCI) transducer. The system consists of a laser Doppler vibrometer (LDV), XY manual stage, and two digital scale calipers capable of displaying a position coordinate system. To measure the vibration of the cantilever constituting the transducer vibrational membrane, an XY coordinate system was obtained using FEA software. Based on the derived XY coordinate system, the cantilever vibration displacement of the vibrational membrane was measured for each coordinate using the LDV at 0.5, 0.9, and 2 kHz. To visualize the measured area, we developed a Matlab-based application and then visualized the motion of the cantilever. The alignment and misalignment models of the vibrational membrane and permanent magnet were designed using finite element analysis (FEA) software, and the measured cantilever motions of the vibrational membrane were then compared. Finally, to numerically compare the vibration magnitude of the cantilever, the standard deviation was calculated based on the displacement of each edge of the cantilever. The fabricated BCI transducer had a higher standard deviation (3.5 times at 0.5 kHz, 2.3 times at 0.9 kHz) than the ideally aligned FEA model, but the standard deviation was about eight times lower (at 0.5 and 0.9 kHz) than that of the misaligned case. The results of the numerical comparison indicated that the manufactured BCI transducer was very well assembled.

High-speed optical three-axis vector magnetometry based on nonlinear Hanle effect in rubidium vapor

The magnetic-field-compensation optical vector magnetometer based on the nonlinear Hanle effect in alkali metal vapor allowing two-axis measurement operation has been further elaborated for three-axis performance, along with significant reduction of measurement time. The upgrade was achieved by implementing a two-beam resonant excitation configuration and a fast maximum searching algorithm. Results of the proof-of-concept experiments, demonstrating 1 μTB-field resolution, are presented. The applied interest and capability of the proposed technique is analyzed.

Two-Axis Temperature-Insensitive Accelerometer Based on Multicore Fiber Bragg Gratings

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We report a compact two-dimensional accelerometer based upon a simple fiber cantilever constructed from a short length of multicore optical fiber. Two-axis measurement is demonstrated up to 3 kHz. Differential measurement between fiber Bragg gratings written in the multicore fiber provides temperature-insensitive measurements. </para>

Parametric Processing for Two-Dimensional Digital Sun Sensors: Algorithms, Modelling, and Testing

This paper presents the modeling, algorithm development, and laboratory testing of a two-axis digital sun sensor. The basis for our modeling is the Sinclair Interplanetary SS-330, a sensor that employs a single linear array to provide two-axis measurements of the sun vector. The detector illumination simulation includes consideration of Fresnel diffraction, finite pixel size, the extended nature of the sun, and a detector-noise model to synthesize artificial images. Simulated images agree with actual sensor images to within about 3.2% (root mean square). Algorithm studies contrast the performance of existing peak-detection routines (e.g., peak detections and centroiding) with more sophisticated parametric algorithms. Laboratory studies confirm that thesemodified algorithms can provide a threefold performance improvement over the baseline sensor processing. These results also evaluate the simulation’s ability to provide accurate estimates of sensor performance. Although the simulations qualitatively replicate many behaviors, they are not yet accurate enough to be used in place of hardware validation.

Novel sensor design for torque magnetometry

Torque magnetometry is a powerful method to determine a sample's magnetic properties. In a torque magnetometer, the sample under interest is mounted on a suitable sensor, the core part of the instrument. Piezoresistive atomic force microscope tips are proven to be very useful torque sensors and have already been optimized for the specific needs of torque magnetometry. However, this type of sensor did not offer the possibility of measuring torque along two perpendicular directions simultaneously without sacrificing sensitivity. In this article we demonstrate a fundamentally new sensor design based on the piezoresistive readout technique, which offers a large variability of measurement modes. With a symmetric arrangement of the sensor legs, concurrent two-axis measurements are easily possible with two separate readout circuits. Furthermore, the variability can be exploited by fabricating a thermometer on the sample platform to directly measure the sample temperature. Test measurements are in good agreement with elasticity calculations.

X-ray diffraction analysis of the layer structure in a ferroelectric liquid crystal with a chiral nematic–chiral smectic C phase transition

A half-V-shaped switching ferroelectric liquid crystal (FLC) is a promising candidate for fast response displays. In the half-V FLC display, a liquid crystal with a chiral nematic–chiral smectic C phase transition is used, and the smectic layer is formed by cooling from N* to SmC* with an applied d.c. field. We studied the layer structure by means of X-ray measurements for two axes (ω and χ). By using a point-focused X-ray tube and optimizing the slit width, we succeeded in the two-axis measurement with a commercial X-ray system. The ω–χ profile of the half-V FLC showed two broad peaks in an arc-shaped high-intensity area. Our interpretation of this result is that the major part of the layer consists of a tilted-bookshelf structure and that the minor part consists of a near-bookshelf structure. Since optical microscopy observations on the half-V FLC cells showed a stripe-shaped texture, we consider that the coexistence of the tilted-bookshelf and the near-bookshelf structures forms the stripe-shaped patterns. The radius of the arc-shaped high-intensity area was nearly equal to the molecular tilt angle. This result can explain why the half-V FLC showed a desirable black appearance in spite of the stripe-shaped texture.

Controlling three-axis attitude rates on a pointing system using nonlinear observer and two-axis measurements

A new observer design method that allows for estimating the angular rates along a vehicle's three principal axes is described. The observer uses measurements from a single two-axis angular rate sensor (gyro) and determines the rates for the third axis using a nonlinear ob- server. Unlike conventional approaches where the equations governing vehicle motion (Euler's equations) are linearized and then an observer is constructed based on the linear model, this method does not require linearization of the system. Instead, a pseudo-linear representation is used. The pseudo-linear model is obtained by systematically decompos- ing a nonlinear system into linear and nonlinear terms. The nonlinear components are then redefined as an auxiliary set of state variables and/or inputs. This leads to an augmented linear system representation that is mathematically equivalent to the original nonlinear system. This method enables standard linear observer design techniques to be ap- plied and develops observers that are capable of estimating the third- axis angular rates using measurements corresponding to the other two axes. The effectiveness of this approach is illustrated with an example. The case studied is the complete attitude rate determination and control of a spinning spacecraft. Computer simulation results show that the new approach provides excellent three-axis attitude control, yet requires an- gular rate sensors for only two axes. © 1997 Society of Photo-Optical Instrumen- tation Engineers. (S0091-3286(97)03004-3)

Determinations of nerve and glial cell volumes in histological sections

Summary A method is described for determination of nerve and glial cell volumes in usual histological sections. The brain or spinal cord are split into two halves along the midline. Following simultaneous histological treatment both halves are embedded in the same paraffin block in such a way as to obtain transverse sections from one half and sagittal sections from the other. In transverse sections major (a) and minor (b) axes of cell body or nucleus are measured, while sagittal sections are used for measuring the third axis (c). From the mean lengths of the axes their ratio is estimated to deduce an expression for calculating the c axis from a and b values. The volume can then be calculated from two-axis measurements using the three-axis ellipsoidal formula. In such a way, rat spinal motoneurones, Deiters' neurones and layer V motor cortex pyramids were investigated. As judged from optical reconstruction, the neuronal volume can be determined from two axes by the following equations: V = 1/6π ab [(a + b)/3] (for motoneurone soma); V = 1/6π ab √ab (for Deiters' neuronal soma); V = 1/6π ab √a2−b2 (for cortical pyramidal soma); V = 1/6π ab2 (for motoneurones and Deiters' neuronal nucleus). The nuclear volumes of perineuronal glia can be calculated according to the formula V = 1/6 π a2b for satellites of spinal motoneurones or Deiters' neurones, and V = 1/6 π ab2 for satellites surrounding cortical pyramids.