Infrared dielectric function of photochromic thiazolothiazole-embedded polymer

Delamination identification is very important for structural health monitoring of composite laminated structures. In the present study, a two-step delamination identification method using resonant and anti-resonant frequency changes is proposed. The present method can identify the location of delamination and the size nondestructively. As a preparation for delamination identification of a CFRP laminated beam, the beam is divided into two domains. At the first step, the delaminated domain is identified using the anti-resonant frequency changes. At the second step, the delamination location and the size are identified in the delaminated domain using the resonant frequency changes. Delamination identifications of CFRP cantilever beams are conducted using both FEM analysis data and experimental data. As a result, effectiveness of the present method is shown.

Microelectromechanical systems (MEMS) are exposed to a variety of liquid environments in applications such as chemical and biological sensors and microfluidic devices. Environmental interactions between liquids and microscale structures can lead to unpredictable performance of MEMS in liquid environments. In this paper, the mechanical performance of microcantilevers in liquid environments was investigated through a series of experiments: Microcantilever beams were placed in a liquid-filled enclosure and cyclically actuated for ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> cycles. Silicon, silicon with titanium coating, silicon with a polymeric coating (SU-8), and silicon nitride microcantilevers were evaluated in deionized water, saline, and glucose. Microcantilever materials, liquid environments, and load levels (0-5 ± 0.5 MPa) were selected to be representative of sensor applications. The mechanical performance of the microcantilevers was evaluated by periodically monitoring changes in resonant frequency. All specimens performed reliably in air. Significant changes in resonant frequency, often exceeding 1%, were observed for uncoated silicon and titanium-coated microcantilevers immersed in saline and for SU-8-coated microcantilevers immersed in water. The changes in resonant frequency were attributed to mineral deposition for uncoated silicon microcantilevers in saline, corrosion fatigue for titanium-coated silicon microcantilevers in saline, and water absorption for SU-8-coated microcantilevers in water.

Damaged material invariably exhibits a lower resonance frequency than undamaged material due to its reduced stiffness. Under fatigue loading, damage accumulates until failure, so changes in resonance frequency can be utilised as a variable to predict fatigue life. Conventional fatigue life prediction methods have a low success rate, prompting the exploration of alternative approaches. We have presented a novel method for predicting the fatigue life of spruce wood based on changes in resonance frequency during fatigue, using a representative specimen (i.e., one out of five specimens tested, with four used for static strength reference). We conducted a low-cycle fatigue test and monitored the resonance frequency alongside the dynamic and static modulus of elasticity. All three types of data were employed to predict fatigue life using between 40% and 100% of the measurement data. Of the two fatigue life prediction methods investigated, the Weibull cycle density distribution using resonance frequency measurements proved most appropriate. The error decreases monotonically with the amount of resonance frequency measurement data used for fatigue life prediction, reaching its lowest value of 1% when the full resonance frequency dataset is used. The proposed fatigue life prediction method should be further validated with a larger sample size, as fatigue is inherently a statistical phenomenon.

A wireless pH sensor based on the use of salt-independent micro-scale polymer spheres

An ultrasonic force sensor was designed to calculate the socket contact force in a cable connector assembly. The force sensor operates through measuring the relationship between the mechanical force and change in resonance frequency in a piezoelectric tube. The sensor’s aim is to assess the effectiveness of aging electric sockets to ensure their replacement before failure. A network analyzer was used to perform tests on the repeatability and sensitivity of the resonance change in two sets of piezoelectric tubes of different thickness. The hoop mode proved to be the most consistent as well as most sensitive resonance mode. The results show an increase in the change in resonance frequency corresponding to an increase in applied socket contact force. Socket contact forces are measured through a friction-based method. To refine the testing technique, the 3-D modeling software SolidWorks was used to design a prototype socket testing device to hold the tubes for insertion into the socket. The piezoelectric tubes were adapted to perform in the tube holder and the prototype socket testing device was created out of aluminum.

This paper reports on mass sensing with 33 nm thick single-crystalline cantilevers by a double-beam laser Doppler vibrometer. The resonant frequency of an oscillating thin cantilever beam is very sensitive to a loaded mass. However, the drift of the resonance, due to gas adsorption and mechanical instability, limits the minimum detectable mass in general. Two cantilevers for sensing and its reference will compensate their influences. Two cantilevers were made to self-oscillate by electrostatic actuation at different resonant frequencies. A 10 pg sample (a particle of organosilicon monomer) was mounted at the end of one cantilever, and thermogravimetry of the sample using the two cantilevers was demonstrated. The cantilevers were heated up by a heater in vacuum, and the change in mass was detected from the change in resonant frequency. The exact temperature change can be estimated from the change in resonant frequency of one cantilever as a reference. The derivative of the frequency change, corresponding to desorbed mass, clearly shows a peak of mass desorption at about 270 °C.

We report fluorescence excitation spectra of individual impurity molecules in a new system: terrylene in a Shpol'skii matrix of hexadecan, Studies of optical incoherent saturation, fluorescence microscope images, and resonance frequency changes are reported for the 0-0 electronic transition at 1.7 K. For four stable molecules, the low-power optical line width at 1.7 K is 40 +/- 2 MHz full width at half-maximum, the saturation intensity is near 1 W/cm(2), and the peak detected count rate can reach 11000 counts per second. Most single molecules either are stable or require many minutes of irradiation before the resonance frequency changes suddenly, but some show spectral changes on a time scale of seconds. Since higher laser power increases the average rate of frequency shifts, this effect represents a light-driven change in the local environment analogous to nonphotochemical hole-burning in large ensembles. Several two-state molecules have been observed, and a preliminary characterization of this light-driven ''molecular switch'' has been completed. Multistate behavior also occurs. This work demonstrates that Shpol'skii matrices should provide fertile ground for the generation of a large number of new materials in which single-molecule spectra can be obtained.

This research investigated the monitoring of very early‐age hydration process (VEAHP) of concrete containing refuse‐derived fuel (RDF) ash, a waste product from waste incineration plants. The experiment was conducted on concrete cube specimens made with 30% RDF ash and 70% cement. The lead zirconate titanate (PZT) patch in embedded form known as embedded piezo sensor (EPS) is placed inside the concrete specimen to monitor the changes during the hydration process for up to 8 h using the electromechanical impedance (EMI) technique. The changes in resonance frequency and amplitude during the VEAHP were determined to qualitatively analyze the EMI signatures. Further, the root‐mean square deviation (RMSD) is determined to quantify the changes. Results revealed that the variation in resonance peak and amplitude of the conductance signature during VEAHP is effectively captured by the EPS. The trend of the growing RMSD index values of RDF–based concrete followed a similar trend to the conventional concrete. Hence, the proposed method for monitoring and assessing the VEAHP of concrete made with RDF ash offers several advantages of reliability, quantitative precision, robustness, and real‐time capability. This work provides an approach to balance enhanced concrete performance with environmental safety when using RDF ash.

This paper reports on fabrication and characterization of resonant-type mechanical MEMS magnetic sensors using magnetostrictive FePd sputtered film. The sensor has a thin Si resonator bridge with a PZT piezoelectric thin film element for excitation. The resonator is pulled by other bridges with the FePd film when magnetic flux is applied. The sensor was fabricated from an SOI wafer by sol-gel PZT deposition, FePd sputtering, and Si etching processes. The completed sensor showed a resonant peak with a Q factor of 229 at 26.39 kHz. When magnetic flux was applied along the micro-bridges, resonant frequency drastically decreased due to relaxation of initial deflection of the resonant bridge. Magnetic flux can be detected by resonant frequency change with a sensing resolution of 0.2 Gauss per 0.1 Hz. When excitation frequency was fixed at slightly below the resonant frequency, amplitude of the bridge vibration slightly decreased with increasing magnetic flux in low magnetic flux region. High sensitive sensing of magnetic flux was difficult by the amplitude change. It was found that the magnetic sensor showed large thermal drift.

Thermal fatigue resistance of vertebrate bone: A comparative study of endothermic and ectothermic species using resonant ultrasound spectroscopy.

Spectroscopic ellipsometry (SE) [1, 2] is a powerful non-destructive technique to determine the structure of silicon-based materials such as amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si :H). In analyzing the SE spectra, the Bruggeman effective medium approximation (EMA) [3, 4] is usually used to model a thin film as a mixture of amorphous silicon and voids. In these models, however, precise knowledge of the dielectric functions of the various components is required in order to obtain reliable estimation of the structural parameters. This requirement is particular critical to the amorphous component because the structure of amorphous silicon is known to depend considerably on the preparation procedures [5]. So far, the dielectric functions used for modeling a-Si1 x :Hx have been based on certain dielectric functions without consideration of the preparation method. It may not be clear, particularly for thin films of amorphous silicon prepared by novel method, whether it is relaxed or unrelaxed dielectric functions which are appropriate for the modeling. In the present work the scope of the problem is assessed by constructing dielectric functions for relaxed and unrelaxed a-Si1 x :Hx thin films using measured a-Si dielectric functions, and fitting, respectively, using simulated dielectric functions for bulk unrelaxed and relaxed a-Si1 x :Hx on the surface roughness and void concentration parameters. The tetrahedron model [3, 4] is applied to construct the complex dielectric functions for relaxed (e 1⁄4 e1r þ ie2r) and unrelaxed (e 1⁄4 e1ur þ ie2ur) a-Si1 x :Hx, by using the dielectric functions for relaxed and unrelaxed a-Si [5], respectively. For details we refer to the work of Mui and Smith [3], [4]. The complex dielectric functions constructed for relaxed and unrelaxed a-Si1 x :Hx components with various hydrogen concentrations are shown in Fig. 1. It is seen that the relaxed and unrelaxed spectra exhibit different peak position and amplitude. Moreover, as the hydrogen content increases, the complex dielectric functions shift to higher photon energy with lower peak values. The complex dielectric functions for the relaxed (unrelaxed) a-Si1–x :Hx film are constructed using a three-layer structure: the first layer is a surface roughness layer, modeled using the EMA, consisting of 50% voids, 50% layer 2. Layer 2 is modeled using the EMA, consisting of a mixture of relaxed (unrelaxed) a-Si1 x :Hx and voids. The substrate is smooth silicon dioxide (SiO2). Fractional void concentrations in layer 2 are varied from 0.01 to 0.26 in the simulations. The thickness of layer 1 is set to be 0.001 mm, while the film thickness (layer 2) is fixed at 1 mm. The incidence angle is set to be 75 . The constructed complex dielectric functions for relaxed a-Si1 x :Hx films are then fitted using unrelaxed a-Si :H spectra, applying a nonlinear regression based on the Levenberg-Marquardt method [6], and vice-versa. In order to avoid interference caused by the interface, the fits are done above 1.75 eV. We denote the void concentration and the thickness of the surface roughness by Cvoid and TR respectively. The fitting error of the void concentration and the thickness of surface roughness are denoted by DCvoid and DTR, respectively, i.e. Cvoid 1⁄4 Cconstructed void Cfit void , similarly for DTR. In order to reveal the quality of the modeling, we define

Piezoelectric Lead ZirconateTitanate (PZT) ceramics based acoustic transducers are widely used in a multitude of applications as sensors and actuators. Different modeling techniques are used by transducer designers to test the original designs without building costly prototypes. The equivalent circuit of piezoelectric vibrator represented by Van Dykemodel is used to plot the resonant curve. Based on the application, piezoelectric materials in the acoustic transducers are subjected to a variety of environmental conditions. This results in the shift in the resonant frequency. This paper reports the effect of change in temperature and pressure on the thickness mode response of equivalent circuit of piezoelectric Lead ZirconateTitanate (PZT) ceramic. The ranges considered are suitable for under water applications. With varying conditions of temperature and pressure, the changes in resonant and anti-resonant frequencies of the piezoelectric material are noted. Using these practically obtained values, parameters of the model are computed and the shift in the resonance curve is observed for the conditions considered. The values of resonant and anti-resonant frequencies obtained from the model response match with those obtained experimentally for the given conditions. Other material constants required for building realistic Finite Element Analysis models can be computed using these practically obtained values of resonant and anti-resonant frequencies.

Silicon microcantilevers were coated by pulsed laser deposition with vanadium dioxide (VO2) (monoclinic M1 phase) and V1−xCrxO2 with x near 0.024 (monoclinic M2 phase), and their mechanical characteristics were studied as a function of temperature through the films’ insulator-to-metal transition (IMT). The undoped VO2 films grew with (011)M1 planes parallel to the substrate, while Cr-doped VO2 films grew oriented with (201)M2 and (2¯01)M2 planes parallel to the substrate. In both cases, the films transformed reversibly through the IMT to the tetragonal (rutile, R) phase, with film (110)R planes oriented parallel to the substrate. The fundamental resonant frequencies of the cantilevers were measured as the temperature was cycled from ambient temperature, through the IMT, and up to 100 °C. Very high resonant frequency changes were observed through the transition for both types of samples, with increases during heating of over 11% and over 15% for the cantilevers coated with pure and Cr-doped VO2, respectively. From the resonant frequencies measured at room temperature for the bare and coated cantilevers in each case, the effective Young’s moduli of the films were determined. The values obtained, assuming bulk densities for the films, are 156 ± 7.5 GPa for VO2 (M1 phase) and 102 ± 3 GPa for Cr-doped VO2 (M2 phase). Strong curvature changes during the transition to the R phase were also observed for cantilevers coated with both types of films, but these were significantly higher in the case for the Cr-doped film. Curvature changes for temperature ranges outside the IMT region were small and attributed to differential thermal expansion between film and silicon substrate. From measured cantilever tip displacements in this post-transition range—for the undoped VO2-coated microcantilevers—a rough estimate of 110 GPa was obtained for the effective Young’s modulus for R-phase VO2. The substantially higher changes in resonant frequency and curvature for V1−xCrxO2-coated cantilevers suggest that this material may be even more useful than M1-phase VO2 for prospective microelectromechanical or optomechanical device applications in which ample frequency tunability—in oscillators or filters—or large displacements—in actuators—within a small temperature range is desirable. Since M2-phase V1−xCrxO2 with Cr composition of a few atomic percent retains other desirable properties of VO2, such as very high resistivity changes through the IMT and a transition temperature fairly close to ambient temperature, multifunctionality is not impaired and in fact may be enhanced for some applications.

Thalamo-cortical mechanisms underlying changes in amplitude and frequency of human alpha oscillations

With the rapid development of industrial production and aerospace, how to measure the plasma density has also developed rapidly. So a radio-frequency plasma transducer based on a three-layer dielectric substrate antenna with a high dielectric constant is introduced. The top and bottom layers are dielectric plates, which protect the internal antenna structure and improve the equivalent permittivity of the antenna. The middle layer is the structure layer of the designed antenna. And the antenna size is 3.8 × 2 × 1.8 mm3. When the plasma frequency changes from 0.3 GHz to 7 GHz, the corresponding dielectric substrate antenna resonant frequency (RF) changes from 4.076 to 5.213 GHz. The minimum unit is 0.1 GHz, and all the measurement accuracy is more than 90%. The method based on the effective dielectric constant of plasma will change under different plasma frequencies, so the RF of the antenna is different. In this paper, the radio-frequency plasma transducer is studied theoretically and analyzed numerically.