Measured Material Parameters Research Articles

Obstacle-based self-calibration techniques for the determination of the permittivity of liquids

Abstract. In this contribution, different obstacle-based self-calibration techniques for the measurement of the dielectric properties of liquids are investigated at microwave frequencies. The liquid under test is contained inside a waveguide, which is connected to the ports of a vector network analyzer. The permittivity of the liquid is characterized on the basis of the measured scattering parameters. In order to extract the material parameters precisely and to eliminate systematic errors of the setup, calibration measurements have to be performed. For this purpose, different self-calibration methods based on the displacement of an obstacle are considered. The presented methods differ in that way, that either transmission and reflection measurements or purely reflection measurements are performed. All these methods have in common that the material parameters are already calculable within a so-called self-calibration procedure. Thus, a full two-port calibration of the whole setup is not necessary. Furthermore, the methods can be realized effectively in a practical setup having the advantage that a rearrangement of the setup is not needed for the material parameter measurements and that the liquid under investigation can pass continuously through the measurement cell. This might be of interest for the application in an industrial process, enabling the continuous flow of the material while the parameter characterization can take place at the same time.

Properties of Building and Plastic Materials in the THz Range

We present measurements of the frequency dependent refractive index and absorption coefficient of a variety of common building and plastic materials between 100 and 1000 GHz. Accurate knowledge of the material parameters is indispensable for the modeling of bound media propagation phenomena including single and multiple reflections, transmission, diffraction and scattering effects. These models are for example required for a reliable channel simulation to investigate signal propagation in future wireless communication systems operating with Gigabit data rates at frequencies above 100 GHz. Also, the measured material parameters can be used for the investigation and development of THz system components.

Low noise laser-based T-ray spectroscopy of liquids using double-modulated differential time-domain spectroscopy

Liquid transmission studies at terahertz frequencies (0.1–10 THz) are valuable for understanding solvation dynamics of salts, exploring long-range structure in mixtures and probing biomolecules in suspension. T-ray (or THz) time-domain spectroscopy, based on terahertz pulse generation from ultrafast lasers, is a sensitive technique for measuring material parameters in this frequency range. This paper proposes and demonstrates a novel technique for increasing the sensitivity and repeatability of liquid studies with T-ray time-domain spectroscopy (TDS), reducing relative parameter measurement errors below 0.0001. The proposed technique combines dual-thickness liquid measurement with rapid modulation (double-modulated differential TDS) to reduce the effect of both thickness-measurement errors and T-ray noise errors below 0.0001. The possible reduction in error is calculated and a liquid differential TDS (DTDS) prototype is demonstrated, incorporating amplitude and mean detection for near-simultaneous measurement of two T-ray waveforms.

Numerical modeling of highly doped Si:P emitters based on Fermi–Dirac statistics and self-consistent material parameters

We have established a simulation model for phosphorus-doped silicon emitters using Fermi–Dirac statistics. Our model is based on a set of independently measured material parameters and on quantum mechanical calculations. In contrast to commonly applied models, which use Boltzmann statistics and apparent band-gap narrowing data, we use Fermi–Dirac statistics and theoretically derived band shifts, and therefore we account for the degeneracy effects on a physically sounder basis. This leads to unprecedented consistency and precision even at very high dopant densities. We also derive the hole surface recombination velocity parameter Spo by applying our model to a broad range of measurements of the emitter saturation current density. Despite small differences in oxide quality among various laboratories, Spo generally increases for all of them in a very similar manner at high surface doping densities Nsurf. Pyramidal texturing generally increases Spo by a factor of five. The frequently used forming gas anneal lowers Spo mainly in low-doped emitters, while an aluminum anneal (Al deposit followed by a heat cycle) lowers Spo at all Nsurf.

Effect of native Al 2O 3 on the elastic response of nanoscale Al films

A continuous, dense aluminum oxide (Al 2O 3) layer of about 5 nm forms on the surface of Al upon exposure to oxygen or dry air. Since the elastic moduli of Al and Al 2O 3 are 69 GPa and 370 GPa, respectively, the elastic modulus of a thin Al film of sub-micron dimension (with the native oxide layer) should be much higher than that of pure Al. However, uniaxial tensile measurements on Al films with thickness down to 50 nm revealed an effective modulus close to 69 GPa. In the present paper, we investigate a plausible mechanism for this discrepancy, namely, the effect of wavy surface oxide layer. Here thin Al films are considered as Al-Al 2O 3 composites. Uniaxial tensile experiments on a free-standing, 200 nm thick Al film are performed using MEMS techniques. The surface morphology of the specimen is characterized by AFM. An analytical model is developed to estimate the effective modulus, Ē, of a wavy oxide layer. The current study shows that the model predictions using measured material parameters agree reasonably well with the experimental results, thus supporting the validity of the proposed mechanism.

Experiments on concrete under shock loading

On detonations or hypervelocity impacts concrete structures are loaded with shockwaves. These shockwaves cause a steep increase in pressure within the wavefiont which propagates at high velocity. For a numerical simulation of such process a constitutive material law F = f (E, E, T) is needed which adequately describes concrete under these conditions. As basis for such a constitutive law tests on concrete under explosive loads were performed and different material parameters were investigated. We report our approach to measure material parameters during tests with different explosive charges on concrete and our model tests for demolition work. We got first experience in using a new temperature sensor, called the atomic layer thermopile, to measure the temperature raise caused by the adiabatic compression. This sensor was developed for performance measurement of high energetic laser pukes, The mode of operation of this sensor is based on the temperature g-adient between the sensor surface and the base of the device. Very fast response time is possible, because there is no need of getting a complete heat transfer from the ambient concrete temperature to the whole sensor. Responsible for the output voltage proportional to the temperature rise is the thermal Seebeck-effect which can be splitted in a longitudinal and a transversal component due to the orientation of the layers. For stress measurement manganin gauges and for strain measurement ordinary strain gauges were used. For the application of these methods at high velocity loads in concrete special encapsulations are needed in order to save the functionality and to provide fast rise times of the output signals. Results of the measurements will be shown and remaining problems will be discussed.

Characterization of damage modes in dental ceramic bilayer structures Information on product names and suppliers in this article does not imply endorsement by NIST.

Results of contact tests using spherical indenters on flat ceramic coating layers bonded to compliant substrates are reported for selected dental ceramics. Critical loads to produce various damage modes, cone cracking, and quasiplasticity at the top surfaces and radial cracking at the lower (inner) surfaces are measured as a function of ceramic-layer thickness. It is proposed that these damage modes, especially radial cracking, are directly relevant to the failure of all-ceramic dental crowns. The critical load data are analyzed with the use of explicit fracture-mechanics relations, expressible in terms of routinely measurable material parameters (elastic modulus, strength, toughness, hardness) and essential geometrical variables (layer thickness, contact radius). The utility of such analyses in the design of ceramic/substrate bilayer systems for optimal resistance to lifetime-threatening damage is discussed. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 137–145, 2002; DOI 10.1002/jbm.10091

New optomechanical technique for measuring layer thickness in MEMS processes

Dimensional metrology improvements are needed to achieve the fabrication of repeatable devices. This research presents a new optomechanical technique for measuring the thickness of a suspended material in two distinct microelectromechanical system (MEMS) fabrication processes. This technique includes design of test structure, choice of measurement tools, method of measurement, and computation of thickness. Two tools, the stylus profilometer and optical interferometer, are used to take measurements. Non-contact measurements are possible on structures as narrow as 5 /spl mu/m. Local thickness measurements are achievable with combined standard uncertainty values of less than 10 mm. Benefits of using the new technique include greater likelihood of fabricating repeatable devices and more accurate measurements of material parameters. The proposed technique is also applicable for measuring layers that are thinner and made of materials other than the conventional suspended material used in this research.

Comparative study of nonlinear-optical polymers for guided-wave second-harmonic generation at telecommunication wavelengths

We report on the linear and nonlinear-optical properties of 4-dimethylamino-4′-nitrostilbene (DANS), 4-diethylamino-1-nitrobenzyl (DANB), and 4-[N-ethyl-N-(2-hydroxyethyl)]amino-4′-nitroazobenzene) (Disperse Red 1;DR1) side chain polymers whose second-harmonic generation at the telecommunication wavelength of 1.55 μm was investigated. Measured ultraviolet–visible–near-infrared spectra were analyzed with an inhomogeneously broadened line-shape model, in particular, in the long-wavelength tail of the electronic transitions, which determines the absorption loss at the second-harmonic wavelength. The nonlinear-optical coefficients were measured at different poling temperatures and poling fields by the Maker fringe technique. On the basis of the measured material parameters we calculated the normalized conversion efficiencies for guided-wave second-harmonic generation at 1.55 μm. The DR1 polymer exhibited the best nonlinearity–absorption trade-off, with a calculated normalized conversion efficiency of several hundred percent per watt, whereas the figures of merit for DANS and DANB are lower and comparable with each other.

Correlation between Modeling and Measurement of Material Parameters for Thermoplastic Materials Under High-Speed Impact Events

Determining material properties for input into high speed impact event simulations is a very difficult task. Generation of these material properties first requires a knowledge of how they are used in the respective analytical tool. Three statistically designed studies were completed to investigate the sensitivity of a dynamic finite element code to material parameter inputs. The critical material parameters were found to be a function of the type of response studied as well as the functionality of the specific component. It was determined that the method of material property generation used for the present work provides good correlation with experimentally measured results.

MWIR DLPH HgCdTe photodiode performance dependence on substrate material

Mid wavelength infrared p-on-n double layer planar heterostructure (DLPH) photodiodes have been fabricated in HgCdTe double layers grown in situ by liquid phase epitaxy (LPE), on CdZnTe and for the first time on CdTe/sapphire (PACE-1). Characterization of these devices shed light on the nature of the material limits on device performance for devices performing near theoretical limits. LPE double layers on CdZnTe and on PACE-1 substrates were grown in a horizontal slider furnace. All the photodiodes are p-on-n heterostructures with indium as the n-type dopant and arsenic the p-type dopant. Incorporation of arsenic is via implantation followed by an annealing step that was the same for all the devices fabricated. The devices are passivated with MBE CdTe. Photodiodes have been characterized as a function of temperature. R0Aimp values obtained between 300 and 78K are comparable for the two substrates and are approximately a factor of five below theoretical values calculated from measured material parameters. The data, for the PACE-1 substrate, indicates diffusion limited performance down to 110K. Area dependence gives further indications as to the origin of diffusion currents. Comparable R0Aimp for various diode sizes indicates a p-side origin. R0A and optical characteristics for the photodiodes grown on lattice-matched CdZnTe substrates and lattice mismatched PACE-1 are comparable. Howover, differences were observed in the noise characteristics of the photodiodes. Noise was measured on 50 × 50 µm devices held under a 100 mV reverse bias. At 110K, noise spectrum for devices from the two substrates is in the low 10−15 A/Hz1/2 range. This value reflects the Johnson noise of the room temperature 1010 Ω feedback resistor in the current amplifier that limits the minimum measurable noise. Noise at 1 Hz, −100 mV and 120K for the 4.95 µm PACE-1 devices is in the 1–2 × 10−14 A/Hz1/2, a factor of 5–10 lower than previously grown typical PACE-1 n+-on-p layers. Noise at 120K for the 4.60 µm PACE-1 and LPE on CdZnTe was again below the measurement technique limit. Greatest distinction in the noise characteristics for the different substrates was observed at 163K. No excess low frequency noise was observed for devices fabricated on layers grown by LPE on lattice-matched CdZnTe substrates. Photodiode noise measured at 1Hz, −100 mV and 163K in the 4.60 µm PACE-1 layer is in the 1–2×10−13 A/Hz1/2, again a factor of 5–10 lower than previously grown PACE-1 n+-on-p layers. More variation in noise (4×10−13−2×10−12 A/Hz1/2) was observed for devices in the 4.95 µm PACE-1 layer. DLPH devices fabricated in HgCdTe layers grown by LPE on lattice-matched CdZnTe and on lattice-mismatched PACE-1 have comparable R0A and quantum efficiency values. The distinguishing feature is that the noise is greater for devices fabricated in the layer grown on lattice mismatched substrates, suggesting dislocations inherent in lattice mismatched material affects excess low frequency noise but not zero bias impedance.

Weakest-link statistics of cleavage fracture

A weakest-link model of cleavage fracture is developed as follows based on the random distribution of microcracks with respect to orientation: P = 1 − exp 1 2 ∫ V EYZ ln S c0 σ 1 − δV V 0 This model contains only two well-defined and easily measured material parameters S c0 and V 0, it avoids the difficulty in evaluating the strength distribution density function of microcracks g( S) as involved in all the previous statistical models of cleavage fracture. The model yields a conservative evaluation of the cumulative probability of failure. With this model, the statistical distribution of fracture toughness for cleavage initiation can be quantitatively predicted by means of numerical analysis.

Relaxation in shape-memory alloys—Part II. Thermo-mechanical model and proposed experiments

A variety of relaxation phenomena such as stabilization of martensite, rubber-like behavior, evolving hysteresis loops and stabilization of interfaces have been observed in various shape-memory alloys. These effects adversely impact technological applications. In Part I of this paper we proposed a phenomenological, but predictive, model of the mechanical behavior of these materials. We showed that this model reproduces the experimental observations. In this part, we extend this model to include the effects of temperature and the austenite-martensite transformation. Once again, the predictions from this extended model agree with experimental observations. We can therefore conclude that the basic phenomenological ideas combined with a few easily measured material parameters is sufficient to predict the behavior of these materials. Finally, we propose new experiments in order to probe longstanding issues concerning the mechanism responsible for the relaxation.

The effects of pressure and stage of ensilage on the mechanical properties and effluent production potential of grass silage

Direct‐cut grass silage was ensiled without compression in laboratory silos for 0–75 d. On occasions during this period, the silage was subjected to creep compression tests at three pressure levels for a period of 5 h and effluent production was measured. Precision‐chopped Italian ryegrass (Lolium multiflorum) was ensiled in the first experiment, whereas flail‐harvested perennial ryegrass (Lolium perenne) was ensiled in the second. Pressure levels were 11·3, 16·9 and 22·5 kPa for Experiment 1 and 5·7, 11·3 and 16·9 kPa for Experiment 2. Moisture contents of the ensiled herbage were 815 and 856 g kg−1 for Experiments 1 and 2 respectively. The consolidation of the grass silage was described by a Burgers body model. Effluent production was more closely related to strain than to compressibility. Linear regression equations for the relationship between strain and effluent production are presented. There was a significant positive linear relationship between pressure and effluent production at each silo opening time in both experiments. The time course of effluent production was fitted to a negative exponential curve. The time that elapsed before effluent release in each experiment was a function of both pressure and time after ensilage. The results of the experiments were compared with the predictions of two models of effluent production. Reasonable agreement between predicted and actual effluent production could be obtained provided the measured material parameters were used and immediate saturation of the forage was assumed. Using the models highlighted the need for a better understanding of saturation development in the silage.

Material figures of merit for spatial soliton interactions in the presence of absorption

The effects of linear and two-photon absorption on bright spatial soliton propagation are studied. A spatial soliton switch that achieves gain through the novel mechanism of colliding, dragging, or trapping of two fundamental solitons of different widths is proposed. Figures of merit for use in evaluating the suitability of absorbing nonlinear media for soliton switching applications are presented. The main effect of linear absorption is to limit the propagation distance, which places an upper bound on the width of the soliton in order to fit sufficient characteristic soliton propagation lengths within the device. The optical limiting nature of two-photon absorption places an upper bound on the gain that an interaction can achieve. The combined effects of linear and two-photon absorption are to reduce the gain upper bound imposed by two-photon absorption alone with the addition of the soliton width constraint. A maximized gain upper bound is determined solely by material parameters and is compared among three promising nonlinear materials. It is shown numerically that the spatial soliton dragging interaction requires shorter propagation distances and achieves greater gain than the collision interaction and that both are tolerant to the presence of absorption and can provide, with high contrast, gains of three or greater using measured material parameters. These results warrant pursuing the implementation of spatial soliton-based logic gates.

One-Dimensional Analytical Constant Parameter Linear Electromagnetic-Magnetomechanical Models of a Cylindrical Magnetostrictive (Terfenol-D) Transducer

A method is presented for including motional and eddy current effects when analytically modeling electrical impedance functions of cylindrical magnetostrictive transducers. To approximate eddy current effects, onedimensional analytical constant parameter linear electromagnetic models of a cylindrical magnetostrictive transducer are developed. Maxwell's equations are solved for the magnetic field strength as a function of radial position. Closed form expressions for magnetic flux as a function of radial position are then derived, from which transducer electrical impedance functions are formulated. Two different physical models of the transducer are considered. The first model results in the classic eddy current solution for a rod in a wound wire solenoid. The second physical model includes the effects of a conducting external cylindrical housing. Motional effects are incorporated into the electromagnetic models via the magnetomechanical model, which is a frequency and load dependent, complex valued expression for the "dynamic magnetic permeability" of the magnetostrictive material within the transducer. The functional form for this dynamic magnetic permeability is derived by comparing the transduction equations for the magnetostrictive material with those for the transducer containing the material. Electrical impedance functions for both physical models are compared with an experimental measurement for a particular magnetostrictive transducer (using Terfenol-D) in its low signal linear range of operation. The second physical model was found to offer the better simulation of the experimental measurement of the transducer's electrical impedance, with errors in magnitude or phase of less than + 5% for excitation frequencies between 100 and 10,000 Hz (the asrun mechanical resonant frequency was 8800 Hz). Experience has shown that measured material parameters typically yield simulations of electrical impedance functions within i 10%. Predictions of electrical impedance functions for Terfenol-D transducers, calculated based on estimated or published Terfenol-D parameters, can be in error by well over 40%. Thus, the accuracy of model results seem to be controlled primarily by the accuracy with which magnetostrictive material parameters are known.

Dynamical Theory of the Pearling Instability in Cylindrical Vesicles.

We give a simple theory for recent experiments of Bar-Ziv and Moses% Phys. Rev. Lett. {\bf73} (1994) 1392, in which tubular vesicles are excited using laser tweezers to a ``peristaltic'' state. Considering the hydrodynamics of a bilayer membrane under tension, we reproduce some of the qualitative behavior seen and find a value for the wavelength of the instability in terms of independently measured material parameters, in rough agreement with the experimental values.

Resonant techniques for studying the complex electrodynamic response of conducting solids in the millimeter and submillimeter wave spectral range

In order to study the electrodynamic properties of highly conducting materials in the millimeter and submillimeter wave range, we have developed two resonant techniques which allow us to measure the complex conductivity of metals with unprecedented accuracy. In the frequency range from 8 to 37 cm−1, we employ a Fabry–Perot resonator consisting of a dielectric plate in optical contact with the sample; in the millimeter wave range (1–3 cm−1) the resonant structure is a copper cavity which is perturbed by replacing the endplate by the sample. The purpose of a resonant structure for measuring material parameters is to increase the interaction of the electromagnetic radiation with the material. In so doing, these two resonant structures not only improve the sensitivity of the measurement but also allow for the direct determination of both components of the complex optical parameters of the material.

Simulation and validation of temperature effects on the nematorheology of aligning and nonaligning liquid crystals

We present a comprehensive nonlinear numerical analysis of the temperature dependent nematorheological shear behavior, using experimentally measured material parameters of typical nematic, low molar mass, rodlike liquid crystals. We consider a typical aligning nematic (5CBP:4‐n‐pentyl‐4’‐cyanobiphenyl) and a typical nematic (8CBP:4‐n‐octyl‐4’‐cyanobiphenyl) exhibiting both aligning and nonaligning behavior during shearing. The accuracy of the numerical results is established by a thorough validation procedure based on recently available experimental rheological data corresponding to the same model materials. Very good semiquantitative agreement between experiments and simulations is found for both the aligning and nonaligning materials. Despite the simplified model geometry, the simulations are able to capture both details and salient transient and steady rheological features that characterize the multiple regime transitions of nonaligning nematics, as they are cooled towards the smectic A phase.

The use of supercomputer modelling of high-temperature failure in pipe weldments to optimize weld and heat affected zone materials property selection

The creep deformation and damage evolution in a pipe weldment has been mod­elled by using the finite-element continuum damage mechanics (CDM) method. The finite-element CDM computer program Damage xx has been adapted to run with increased speed on a Cray XMP/416 supercomputer. Run times are suffi­ciently short (20 min) to permit many parametric studies to be carried out on vessel lifetimes for different weld and heat affected zone (HAZ) materials. Finite-element mesh sensitivity was studied first in order to select a mesh capable of correctly predicting experimentally observed results using the least possible com­puter time. A study was then made of the effect on the lifetime of a butt welded vessel of each of the commonly measured material parameters for the weld and HAZ materials. Forty different ferritic steel welded vessels were analysed for a constant internal pressure of 45.5 MPa at a temperature of 565 °C; each ves­sel having the same parent pipe material but different weld and HAZ materials. From these studies it has been concluded that good creep rupture ductility and strength of the weld material are necessary to achieve long vessel lifetimes. Vessel lifetimes are not strongly influenced by the HAZ material properties provided that the rupture strength is maintained above that of the parent pipe material, and that the ductility is greater than one half of that for the parent pipe material. Also it is found that the optimum design can be achieved with both the weld and the HAZ materials having properties of high primary creep strain, mean sec­ondary creep strain, mean rupture strain, and long rupture lifetime, relative to the base or parent pipe material. A lifetime improvement has been demonstrated of 30% over that obtained for the initial materials property data. A methodology for weldment design has been established which uses supercomputer-based CDM analysis techniques; it is quick to use, provides accurate results, and is a viable design tool.