Deflection Signal Research Articles

Optical sensing of materials movements occurring at a plant surface with a probe beam

Optical sensing of materials movements across a plant surface with a probe beam is reported. It is based on monitoring of deflection of a probe beam passing through a vicinity of the plant surface. The deflection of the probe beam was caused by concentration gradients of chemical species involved in the materials moments in physiological activities of the plant. Typha angustifolia L. was used as a model plant. The beam deflection at different locations of both leaves and roots in respiration process were monitored and compared. It is found that deflection signals changed with time and locations. Experimental results showed that the beam deflection method could be used for noninvasive sensing and monitoring of materials movements across the plant surface.

Contact type dependency of texture classification in a whiskered mobile robot

Actuated artificial whiskers modeled on rat macrovibrissae can provide effective tactile sensor systems for autonomous robots. This article focuses on texture classification using artificial whiskers and addresses a limitation of previous studies, namely, their use of whisker deflection signals obtained under relatively constrained experimental conditions. Here we consider the classification of signals obtained from a whiskered robot required to explore different surface textures from a range of orientations and distances. This procedure resulted in a variety of deflection signals for any given texture. Using a standard Gaussian classifier we show, using both hand-picked features and ones derived from studies of rat vibrissal processing, that a robust rough-smooth discrimination is achievable without any knowledge of how the whisker interacts with the investigated object. On the other hand, finer discriminations appear to require knowledge of the target’s relative position and/or of the manner in which the whisker contact its surface.

Thermally actuated tapping mode atomic force microscopy with polymer microcantilevers.

This paper demonstrates a thermally actuated tapping mode atomic force microscopy (AFM) with a polymer cantilever. The cantilever (350x250x3 microm(3)) is made from polyimide and includes an embedded resistive heater for thermal actuation. The oscillation of the cantilever is due to the stress gradient caused by alternating heating and cooling from the periodic ac excitation of the heater. The tip oscillation amplitude is 5-10 nm in air. The oscillation occurs at 2omega and is a linear function of the applied voltage. The maximum oscillation amplitude is seen at 0.8 Hz with a 3dB frequency of 26 Hz. The damping of the oscillation due to tip-sample interaction is used to image the sample without any optomechanical feedback. Scans with a 200 nm tall grating indicate a resolution comparable to deflection signal from the AFM in contact mode.

Micromechanical rotation rate sensor having error suppression

A micromechanical rotation rate sensor has a seismic mass and driving devices which cause a driving vibration of the seismic mass in a first direction x. The rotation rate sensor has measuring devices which measure a deflection of the seismic mass in a second direction y, and generate a deflection signal. The deflection includes a measurement deflection caused by a Coriolis force and an interference deflection, the interference deflection being phase-shifted with respect to the measurement deflection by 90°. Compensation devices are provided at the seismic mass to reduce the interference deflection. Regulation devices are provided, to which the deflection signal is supplied as an input variable, which demodulate an interference deflection signal from the deflection signal, and which generate a compensation signal from the interference deflection signal, which is supplied to the compensation devices.

Frequency-dependent viscoelasticity measurement by atomic force microscopy

We demonstrate a new technique for investigating viscoelastic properties of soft materials using the atomic force microscope. A small oscillatory voltage is added to the deflection signal of the atomic force microscope causing a vertical oscillatory sample motion. Monitoring the amplitude and phase of this motion allows determination of the viscous and elastic moduli of the sample as a function of frequency during contact imaging. This technique is applied to suspended poly(vinyl alcohol) nanofibers and poly(vinyl alcohol) hydrogels, giving results similar to those measured using traditional static methods. However, the moduli of both the fibers and the hydrogels show a significant frequency dependence. The Young's modulus of the fibers increases with frequency, while for the viscoelastic hydrogels, the storage modulus dominates the mechanical response at low frequency whereas the loss modulus dominates at high frequency.

Development of Infrared Photothermal Deflection Spectroscopy (Mirage Effect) for Analysis of Condensed-Phase Aerosols Collected in a Micro-Orifice Uniform Deposit Impactor

The potential of mid-infrared photothermal deflection spectrometry for aerosol analysis is demonstrated. Ammonium nitrate aerosols are deposited on a flat substrate using a micro-orifice uniform deposit impactor (MOUDI). Photothermal spectroscopy with optical beam deflection (mirage effect) is used to detect deposited aerosols. Photothermal deflection from aerosols is measured by using pulsed infrared laser light to heat up aerosols collected on the substrate. The deflection signal is obtained by measuring the position of a spot from a beam of light as it passes near the heated surface. The results indicate non-rotating impaction as the preferred MOUDI impaction method. Energy-dependent photothermal measurement shows a linear relationship between signal and laser intensity, and no loss of signal with time is observed. The detection limit from the signal-mass curve is 7.31 ng. For 30 minutes collection time and 30 L/min flow rate of the impactor, the limit of detection in terms of aerosol mass concentration is 0.65 microg m(-3).

Finite Element Analysis Modeling of Pulse-Laser Excited Photothermal Deflection (Mirage Effect) from Aerosols

A finite element analysis method for numerical modeling of the photothermal deflection spectroscopy of aerosols is presented. The models simulate pulse-laser excited photothermal deflection from aerosols collected on a plane surface substrate in air medium. The influence of the aerosol and substrate properties on the transient photothermal deflection signal is examined. We have previously obtained experimental results for photothermal deflection spectrometry of aerosols deposited onto a plate from an impactor system (O. O. Dada and S. E. Bialkowski, Appl. Spectrosc. 62, 1336 (2008)). This paper supports the validity of the experimental results presented in that paper and helps in answering some of the questions raised. The modeling results presented here demonstrate that the (peak) normalized transient temperature change profile and (peak) normalized transient photothermal deflection profile are a good approximation and invariant with number of particles, inter-particle distance, and particulate shape, which suggests that the photothermal deflection signal amplitude may be calibrated linearly with total mass of aerosols and the method could be applied to analysis of complex aerosols.

Temperature-dependent imaging of living cells by AFM

Characterization of lateral organization of plasma membranes is a prerequisite to the understanding of membrane structure–function relationships in living cells. Lipid–lipid and lipid–protein interactions are responsible for the existence of various membrane microdomains involved in cell signalization and in numerous pathologies. Developing approaches for characterizing microdomains associate identification tools like recognition imaging with high-resolution topographical imaging. Membrane properties are markedly dependent on temperature. However, mesoscopic scale topographical information of cell surface in a temperature range covering most of cell biology experimentation is still lacking. In this work we have examined the possibility of imaging the temperature-dependent behavior of eukaryotic cells by atomic force microscopy (AFM). Our results establish that the surface of living CV1 kidney cells can be imaged by AFM, between 5 and 37 °C, both in contact and tapping modes. These first temperature-dependent data show that large cell structures appeared essentially stable at a microscopic scale. On the other hand, as shown by contact mode AFM, the surface was highly dynamic at a mesoscopic scale, with marked changes in apparent topography, friction, and deflection signals. When keeping the scanning conditions constant, a progressive loss in the image contrast was however observed, using tapping mode, on decreasing the temperature.

A THEORETICAL STUDY FOR PHOTOTHERMAL DEFLECTION FOR THE THERMAL CONDUCTIVITY MEASUREMENT OF ANISOTROPIC MATERIALS

We have analyzed the three-dimensional thermal conduction in anisotropic materials using nonsymmetric-Fourier transforms. The distribution of temperature fields which corresponds to the variation of the anisotropic ratio of thermal conductivities was obtained. The differences of the temperature fields for each material give rise to distinctions in the deflection of a probe beam. By using the relation between the temperature fields and the deflection of the probe beam, a complete theoretical treatment of the photothermal deflection has been performed for thermal conductivity measurement in an anisotropic medium. Principal and effective thermal conductivity were determined from the deflection angle and phase angle with the relative position between the heating and probe beams. The influence of the parameters, such as modulation frequency of the heating beam, the thermal conductivity, the angle between crystalline direction and probe beam direction, was investigated. Consequently, the overall effects between both thermal properties of anisotropic materials and experimental parameters and deflection signals were proposed in this study.

Dynamic cutting force on-line estimation using a 4-electrode cylindrical capacitive displacement sensor mounted on a high speed milling spindle

In this paper, a 4-electrode cylindrical capacitance displacement sensor (CCDS) is presented as an indirect force sensor for a high speed milling spindle. A rotor-bar system for the magnetic exciter is designed to investigate the tool deflection with respect to the applied cutting force. To extract the deflection signal from the CCDS, the dynamic orbital motion at each rotating speed of spindle is predetermined and then subtracted from the CCDS signal. The CCDS signal is also used as a reference sync signal. The rotor-bar system is designed so that the rotor affects the tool-spindle dynamics only as an added mass but does not contribute to the bending property. The additional effect of the rotor mass in the exciter setup is compensated for by an experimental modeling. The cutting force can be estimated by using modified CCDS signals and FRF. Cutting experiments are conducted to show reliable performances of the proposed approach by high speed machining applications.

Detector effects in photothermal deflection experiments

We report on the theoretical analysis of a detector type influence on the normal deflection signal in photothermal experiments. Two cases are examined. In the first, the quadrant photodiode was considered as the detector; in the second the signal from the position detector, which measures the central moment displacement of the probe beam, was analyzed. Both analyses were carried out within the framework of the complex ray theory. The normal photodeflection signal was found to depend on the type of detector used in the photothermal deflection experiments for some parameters of its setup.

Effect of beam sizes on the amplitude and phase of photothermal deflection signals for both uniform and nonuniform heating

A detailed theoretical treatment of a one- (1D) and three-dimensional (3D) photothermal deflection (PTD) technique is presented. Important effects of the probe beam size occur in PTD experiments when the radius of this beam is of the order of magnitude of the thermal diffusion length. The calculation of this effect is checked by experiments in paraffin oil at low modulation frequency as well as for 1D and for 3D. In this last case, we have considered two kinds of deflection: normal and transverse, and we have studied their variation for different values of the pump beam radius. The coincidence between theoretical and experimental curves confirms the validity of our theoretical model.

The boundary effects of the shock wave dispersion in discharges

Interaction of shock waves with a weakly ionized gas generated by discharges has been studied. An additional thermal mechanism of the shock wave dispersion on the boundary between a neutral gas and discharge has been proposed [A. Markhotok, S. Popovic, and L. Vuskovic, Proceedings of the 15th International Conference on Atomic Processes in Plasmas, March 19–22, 2007 (NIST, Gaitersburg, MD, 2007)]. This mechanism can explain a whole set of thermal features of the shock wave-plasma interaction, including acceleration of the shock wave, broadening or splitting of the deflection signals and its consecutive restoration. Application has been made in the case of a shock wave interacting with a laser induced plasma. The experimental observations support well the results of calculation based on this model.

Enthalpy Changes during Photosynthetic Water Oxidation Tracked by Time-Resolved Calorimetry Using a Photothermal Beam Deflection Technique

The energetics of the individual reaction steps in the catalytic cycle of photosynthetic water oxidation at the Mn 4Ca complex of photosystem II (PSII) are of prime interest. We studied the electron transfer reactions in oxygen-evolving PSII membrane particles from spinach by a photothermal beam deflection technique, allowing for time-resolved calorimetry in the micro- to millisecond domain. For an ideal quantum yield of 100%, the enthalpy change, Δ H, coupled to the formation of the radical pair Y Z ⋅ + Q A − (where Y Z is Tyr-161 of the D1 subunit of PSII) is estimated as −820 ± 250 meV. For a lower quantum yield of 70%, the enthalpy change is estimated to be −400 ± 250 meV. The observed nonthermal signal possibly is due to a contraction of the PSII protein volume (apparent Δ V of about −13 Å 3). For the first time, the enthalpy change of the O 2-evolving transition of the S-state cycle was monitored directly. Surprisingly, the reaction is only slightly exergonic. A value of Δ H(S 3 ⇒ S 0) of −210 meV is estimated, but also an enthalpy change of zero is within the error range. A prominent nonthermal photothermal beam deflection signal (apparent Δ V of about +42 Å 3) may reflect O 2 and proton release from the manganese complex, but also reorganization of the protein matrix.

Cantilever Micro-rheometer for the Characterization of Sugar Solutions.

The volume required for the rheological characterization of fluids can beminimized by using micromechanical cantilevers as viscosity sensors. Here, a simplemeasurement tool for the characterization of sugar solutions is proposed. The sensorconsists of a micromechanical cantilever as used in an atomic force microscopy which isintegrated into a closed fluid handling system. Fluid properties are derived from an analysisof the power spectral density of the fluctuations of the cantilever deflection signal. The dataacquisition system is operated with standard consumer computer components, which limitsthe costs for the hardware. Measurements with different sugar solutions indicate that thesensor system provides reliable viscosity values for sugar concentrations as they occur inbiological systems. The viscosities of the sugar solutions could be evaluated with an errorsmaller than 5 %.

Multiobjective Static Output Feedback Control Design for Vehicle Suspensions

This paper presents an approach to design multiobjective static output feedback 2 H / ∞ H / 2 GH controller for vehicle suspensions by using linear matrix inequalities (LMIs) and genetic algorithms (GAs). A quarter-car model with active suspension system is studied in this paper and three main performance requirements for an advanced vehicle suspension are considered. Among these requirements, the ride comfort performance is optimized by minimizing the 2 H norm from the road disturbance to the sprung mass acceleration, the road holding performance is improved by constraining the ∞ H norm from the road disturbance to the tyre deflection to be less than a given value, and the suspension deflection is guaranteed to be less than its hard limit by constraining the generalized 2 H norm from the road disturbance to the suspension deflection. In addition, the controller gain can be constrained naturally in GAs, which can avoid the actuator saturation problem. A static output feedback controller, which only uses the available sprung velocity and suspension deflection signals as feedback signals, is obtained. This multiobjective controller is realized by using GAs to search for the possible control gain matrix and then to resolve the LMIs together with the minimization optimization problem. The approach is validated by numerical simulation which shows that the designed static output feedback controller can achieve good active suspension performances in spite of its simplicity.

Feedback based simultaneous correction of imaging artifacts due to geometrical and mechanical cross-talk and tip-sample stick in atomic force microscopy

This paper presents a feedback scheme that simultaneously corrects, in real time, for the imaging artifacts caused by cantilever and photosensor misalignments as well as misinterpretations in relative lateral position of the tip with respect to the sample due to the tip-sample stick in atomic force microscopy (AFM). The optical beam bounce method, typically used in AFM for imaging, is sensitive to inaccuracies of cantilever geometry and the relative misalignment of the laser source, cantilever, and the laser sensitive diode from the intended design. These inaccuracies, which contribute to the geometrical cross-talk between the normal and the lateral signals, become prominent at the atomic and subnanometer scales, and thereby impede high resolution imaging studies. The feedback scheme accounts for these artifacts and makes imaging insensitive to, in fact, practically independent of these inaccuracies. This scheme counteracts the lateral twisting dynamics of the cantilever, and as a result, it avoids the misinterpretation problem of the relative lateral position of the cantilever tip from the sample and thereby avoids the corresponding imaging artifacts that are typically prominent in contact mode friction force microscopy (FFM). The feedback scheme consists of simultaneously regulating the normal as well as the lateral cantilever deflection signal at their respective set points. This not only removes the imaging artifacts due to geometrical misalignments, mechanical cross-talk, and irregular sliding but also the corresponding compensatory control signal gives a more accurate real time measure of the lateral interaction force between the sample and the cantilever as compared to the lateral deflection signal used in FFM. Experimental results show significant improvement, and in some cases, practical elimination of the artifacts. The design and implementation of a split piezoassembly needed for the lateral actuation for the feedback scheme are also presented.

Harnessing bifurcations in tapping-mode atomic force microscopy to calibrate time-varying tip-sample force measurements

Torsional harmonic cantilevers allow measurement of time-varying tip-sample forces in tapping-mode atomic force microscopy. Accuracy of these force measurements is important for quantitative nanomechanical measurements. Here we demonstrate a method to convert the torsional deflection signals into a calibrated force wave form with the use of nonlinear dynamical response of the tapping cantilever. Specifically the transitions between steady oscillation regimes are used to calibrate the torsional deflection signals.

Shockwave Acceleration and Attenuation in Glow Discharge Argon Plasma

Experimental investigations of the shockwave propagation in the direction parallel to the electric field in low-pressure longitudinal glow discharge argon plasmas are performed by the simultaneous multipoint laser deflection technique. In the newly developed shock tube at Troy University, Mach 1.5-2.2 shockwaves are produced by a fast capacitor discharge (quarter period tau1/4 = 1.4 mus ). In this paper, the shock propagation measurements are extended to the low pressure limit down to 3.6 torr while confirming the earlier measurements performed at gas pressures 15 torr and above. The shockwaves are launched through a plasma medium inside the shock tube, where the deflections of the laser beams are recorded on a fast oscilloscope. An average shockwave velocity in the plasma is determined from the time history of the laser deflection signals. The shockwave speed and the broadening of the laser deflection signals in the plasma are found to be dependent on the plasma discharge current. Shockwave speeds increase by 18% for the plasma at 3.6 torr over a range of plasma discharge current I = 0-150 mA and by 46% for the plasma at 15 torr over I = 7-150 mA. In addition, shockwave amplitudes are attenuated in the plasma and show linear dependence on the shockwave speed or Mach number.

Lateral force-distance curve technique

Nano-mechanical properties of single biomolecules and polymers as well as interaction forces between specific molecular pairs have been intensively studied during the last two decades by using atomic force microscopy with force measurement technique. In these experiments, molecules were pulled up from the substrate in vertical direction. However, it is also interesting to develop a similar lateral force-distance technique in which sample molecules stay lain on the solid surfaces during mechanical stretching. Thus, wider possibilities can be opened up to study the stretched macromolecules by other microscopy/spectroscopy methods. Since typical atomic force microscopes have the lateral scanner ranges up to ∼100 μm, very long macromolecules can be studied and manipulated in this way. As an example, up to 8 μm stretching of self-polymerized poly(ethylene glycol)-bis-thiol on gold surface was observed. It was also confirmed that even in the lateral force-distance curves (50-300 nm above surface), the vertical cantilever bending, not torsion, was mainly responsible for the observed deflection signal. This made lateral force data analysis simpler since the normal force constants are easier to estimate than torsion ones. The force curves in our method were also free of any interference fringes. They had horizontal and easy identifiable baselines.