Membrane Transducers Research Articles

A lumped parameter model for strip-shaped dielectric elastomer membrane transducers with arbitrary aspect ratio

Dielectric elastomer (DE) membrane transducers allow to achieve large strain, low energy consumption, low-noise, and highly compact mechatronic devices. To optimize the design of membrane DEs via numerically efficient software tools, as well as to develop accurate control and self-sensing algorithms, a lumped parameter model is required. In the case of rectangular DE strips clamped at both ends and subject to a uniaxial in-plane load, the resulting necking and inhomogeneous deformation turn out to be challenging to be described via standard lumped models, thus making it necessary to rely on numerically involved finite element (FE) tools. In this paper, we present a novel modeling framework that permits to accurately describe clamped DE membranes with generic aspect ratio in a control-oriented fashion. The model is grounded on an anisotropic free-energy function, which maps the inhomogeneities due to clamping within the constitutive membrane behavior. In this way, a lumped description of the DE can be obtained in terms of average stress and stretch quantities. After presenting the model, an extensive validation is performed by means of comparative studies with FE simulations as well as experimental results. It is observed how the proposed model permits to accurately describe the electro-mechanical response of clamped DE membranes for a wide range of aspect ratios, including nearly-uniaxial, nearly-pure shear, as well as intermediate configurations.

Effect of structural boundaries and stress history on at-rest soil pressure of sand

The knowledge of lateral earth pressure is a required input to many issues in geotechnical design and analysis. The determination of lateral earth pressure at rest is often based on a coefficient of earth pressure at rest (K0) for which there is no theoretical basis for its determination. This paper addresses three issues that have direct influence on the measurement of lateral earth pressure at rest: pressure measurement technique, presence of a structural boundary and stress history. The testing was carried out using two different pressure measurement techniques: null gauge technology and deflecting membrane technology. The tests were carried out under two different boundary conditions: free-field conditions and conditions adjacent to a structural boundary. The tests included multiple load–unload cycles. The data generated in this study have indicated that the small deflections required to produce output signals when using deflecting membrane transducers have significant impact on the recorded response. The null soil pressure measurement technique precludes deflection and is therefore inherently more suitable. The effect of a structural boundary must be considered when determining horizontal pressure at rest; the presence of a structural boundary alters the development of vertical soil pressure which is reflected in the magnitude of lateral soil pressure.

Experimental Analysis of Continuous Vibrations in Dielectric Elastomer Membrane Actuators via Three-Dimensional Laser Vibrometry

Dielectric elastomer (DE) membrane transducers are well known for exhibiting large deformations when subject to high voltage. Furthermore, DEs are characterized by an actuation bandwidth of several kilohertz, which allows their use in high-frequency applications, e.g., acoustic ones. The frequency response of DE membranes depends on many parameters such as geometry, pre-stress, and electrode pattern. By properly designing such parameters, it is possible to control vibration modes and resonance frequencies of the membrane, opening up a number of application scenarios. Motivated by this fact, this work presents the first experimental study of continuous vibrations generated in DE membranes via high-voltage excitation. The system under investigation consists of a squared DE membrane with a circular electrode, preloaded out of plane with a linear spring. Vibrations are generated by applying a broadband high-voltage signal to the DE membrane. A 3D laser vibrometer is used to reconstruct the three-dimensional oscillations of scanning points on the membrane surface. Experimental investigations are performed to study the effects of DE geometry and pre-stress on the membrane motion, in terms of resulting frequency spectrum and vibration modes.

Miniaturization of Bragg-multiplexed membrane transducers

This paper reports the miniaturization of Bragg-multiplexed pressure sensing membranes for integrated photonic chips. The analysis compares a novel Fabry–Pérot Bragg grating (FPBG) design that integrally spans a thin (54 µm) silica membrane to a recently reported single Bragg grating (BG) design that resides within the membrane. Unlike the single BG, the FPBG maintains spectral integrity as the dimensions of the membrane become sub-millimetre. In addition it is shown that the FPBG structure can also be used for inherent temperature referencing, having a Bragg thermal sensitivtiy of 13.5 pm °C−1, which can be decoupled from pressure effects. For the reported sub-millimetre membrane, pressure resolution was enhanced by a factor of three and spectral bandwidth reduced by over five-fold.

H-Ras isoform modulates extracellular matrix synthesis, proliferation, and migration in fibroblasts

Ras GTPases are ubiquitous plasma membrane transducers of extracellular stimuli. In addition to their role as oncogenes, Ras GTPases are key regulators of cell function. Each of the Ras isoforms exhibits specific modulatory activity on different cellular pathways. This has prompted researchers to determine the pathophysiological roles of each isoform. There is a proven relationship between the signaling pathways of transforming growth factor-β1 (TGF-β1) and Ras GTPases. To assess the individual role of H-Ras oncogene in basal and TGF-β1-mediated extracellular matrix (ECM) synthesis, proliferation, and migration in fibroblasts, we analyzed these processes in embryonic fibroblasts obtained from H-Ras knockout mice (H-ras(-/-)). We found that H-ras(-/-) fibroblasts exhibited a higher basal phosphatidylinositol-3-kinase (PI3K)/Akt activation than wild-type (WT) fibroblasts, whereas MEK/ERK 1/2 activation was similar in both types of cells. Fibronectin and collagen synthesis were higher in H-ras(-/-) fibroblasts and proliferation was lower in H-ras(-/-) than in WT fibroblasts. Moreover, H-Ras appeared indispensable to maintain normal fibroblast motility, which was highly restricted in H-ras(-/-) cells. These results suggest that H-Ras (through downregulation of PI3K/Akt activation) could modulate fibroblast activity by reducing ECM synthesis and upregulating both proliferation and migration. TGF-β1 strongly increased ERK and Akt activation in WT but not in H-ras(-/-) fibroblasts, suggesting that H-Ras is necessary to increase ERK 1/2 activation and to maintain PI3K downregulation in TGF-β1-stimulated fibroblasts. TGF-β1 stimulated ECM synthesis and proliferation, although ECM synthesis was higher and proliferation lower in H-ras(-/-) than in WT fibroblasts. Hence, H-Ras activation seems to play a key role in the regulation of these effects.

A novel urea conductometric biosensor based on zeolite immobilized urease

A new approach was developed for urea determination where a thin film of silicalite and zeolite Beta deposited onto gold electrodes of a conductometric biosensor was used to immobilize the enzyme. Biosensor responses, operational and storage stabilities were compared with results obtained from the standard membrane methods for the same measurements. For this purpose, different surface modification techniques, which are simply named as Zeolite Membrane Transducers (ZMTs) and Zeolite Coated Transducers (ZCTs) were compared with Standard Membrane Transducers (SMTs). Silicalite and zeolite Beta with Si/Al ratios 40, 50 and 60 were used to modify the conductometric electrodes and to study the biosensor responses as a function of changing zeolitic parameters. During the measurements using ZCT electrodes, there was no need for any cross-linker to immobilize urease, which allowed the direct evaluation of the effect of changing Si/Al ratio for the same type of zeolite on the biosensor responses for the first time. It was seen that silicalite and zeolite Beta added electrodes in all cases lead to increased responses with respect to SMTs. The responses obtained from ZCTs were always higher than ZMTs as well. The responses obtained from zeolite Beta modified ZMTs and ZCTs increased as a function of increasing Si/Al ratio, which might be due to the increased hydrophobicity and/or the acid strength of the medium.

Performance of membrane pressure transducers in granular materials of various particle sizes

There have been numerous attempts to measure the pressure that granular materials exert on storage and processing equipment, but no completely satisfactory method has yet been developed. The present work examines two membrane transducers immersed in a bedding of granular food materials. Pressure generated by the particles deformed a 27-mm diameter duralumin membrane equipped with a strain gauge. Ten types of granular materials, with equivalent particle diameters ranging from 0.1 (coarse flour) to 7 mm (peas), were tested. The procedures and equipment were set up to calibrate the transducer under air pressure and through a layer of granular materials with several levels of moisture content. Our results showed that to assure a standard error of calibration constants of < 1%, the diameter of the transducer membrane should be ≥ 12 times the particle dimension. Transducer readouts depended on the position of the membrane relative to the flat surface in which the transducer was installed. When the membrane was located 0.45mm above the surface, the measured signal was 8–11% higher, while for a position 0.3 mm below the surface, the signal was 3–8% lower, than when the membrane was fitted directly onto the surface. Experiments performed with seeds demonstrated that their higher moisture content increased the measured signal. The transducer should therefore be calibrated in a bedding of material with a moisture content similar to that in which it will be used.

Characterization and modeling of a piezoelectric micromachined ultrasonic transducer with a very large length/width aspect ratio

The objective of the current study was to characterize and model the performance of piezoelectric micromachined ultrasonic transducers (pMUTs) with large length/width aspect ratios. Single-element pMUTs with 20 different dimensions corresponding to aspect ratios ranging from 5:1 to 23:1 were designed. Multiple samples were fabricated for each design so that statistically meaningful data could be obtained. The pMUTs were characterized by the impedance measurement combined with an equivalent circuit analysis. A one-dimensional composite beam model was also used to correlate the equivalent circuit components with the structural parameters, and gain insight into the performance characteristics of pMUTs. The resonant frequencies were observed to decrease with the width of the membrane, but have no appreciable length dependence. With the correction of parasitic capacitance, the effective coupling coefficients were observed to increase with the width up to around 150 µm and then decrease. However, they did not show clear and consistent length dependence. The variation of the coupling coefficient as a function of width of the membrane was shown to be mainly due to the relative ratios between the electrode and membrane widths rather than membrane width itself. Although the model presented in this study was a simple one-dimensional electro-mechanical model, it did seem to offer both good qualitative and quantitative insights into the performance of pMUTs and provide a convenient tool for designing thin membrane transducers with a large aspect ratio. The model can also take into consideration the residual stress effect and offer an even more realistic prediction.

Nonlinear Generation of Airborne Sound by Waves of Ultrasonic Frequencies

The results of research into the design and optimization of laboratory sources of intense airborne ultrasound are reported. Two types of sources are studied: multielement arrays of small-size piezoelectric radiators and single membrane transducers of a capacitor type. The measured characteristics of the ultrasound fields and the audible sound fields generated in air due to the nonlinear interaction of high-frequency waves are presented. Applications of nonlinear acoustic problems in air are discussed.

Hybrid Actuation in Coupled Ionic / Conducting Polymer Devices

ABSTRACTIonic polymer membrane actuators represent a relatively new and exciting entry into the field of smart materials. Several key limitations of these transducers have prevented them from experiencing widespread use, however. For example, the bandwidth of these devices is limited at very low frequencies by characteristic relaxation and at high frequencies by the low elastic modulus of the polymer. In this paper, an overview of the initial results of work with hybrid ionic / conducting polymer actuators is presented. These hybrid actuators are devices that combine the electromechanical coupling of ionic polymer actuators and conducting polymer actuators into one coupled device. Initial results show that these hybrid devices have the potential to offer marked advantages over traditional ionic polymer membrane transducers, including increased stress and strain generation and higher actuation bandwidth. Details of the preparation of these devices and performance metrics are presented and comparisons to baseline materials are made.

The radiation field characteristics of piezoelectric polymer membrane transducers when operating into air

This paper describes the evaluation of the radiation field characteristics of PVDF membrane transducers, whereby the active area is defined by an appropriate electrode pattern when operating into air. Measurement, including conventional scanning of the fields and laser vibrometry, is supplemented by finite element modeling over the frequency range 500 kHz to 1.1 MHz. Contrary to expectation, the surface displacements are nonuniform, giving rise to premature axial focusing of the field. This is shown to be caused by generation of the zero order symmetrical Lamb wave, arising from the electric field discontinuity at the electrode boundary of the transducer.

Properties and principles of mycelial flow: A tube rheometer system for fermentation fluids

A tube rheometer system has been constructed for aseptic study of the rheology and fundamental flow properties of mycelial fermentation fluids. The rheometer consists of a U-formed tube circuit starting and ending inside the fermentor. The mash is pumped through the tubes with a lobe rotor pump. The flow is measured by an electromagnetic flow meter. Pressure drops have been measured with a system of differential membrane transducers for different flow rates. The rheometer system was tested with Newtonian and non-Newtonian fluids.

Differential effects of tumor promoters on cAMP production: Inhibition of receptor-mediated and potentiation of cholera toxin-mediated stimulation

Tetradecanoylphorbol-acetate and other tumor promoters inhibit prostaglandin E 2 and isoproterenol-induced cAMP accumulation in mouse thymocytes but markedly potentiate cAMP production induced by cholera toxin. Cholera toxin is known to stimulate cAMP production by inducing ADP-ribosylation of the α-subunit of a guanine nucleotide-binding regulatory (G) protein, resulting in activation of the catalytic unit of adenylate cyclase. G proteins have been implicated as plasma membrane transducers for a variety of additional signals. It is possible that the growth promoting and co-mitogenic properties of tumor promoters are related to their effects on G proteins.

On the chemical and structural basis of membrane transducer and receptor systems

Evolution was based initially on polynucleotide systems. From these there developed the polynucleotide-based protein biosynthetic system. Membrane transducers are required by the most primitive cells and must have appeared at a very early stage. They would therefore also be expected to involve polynucleotides. There is substantial biochemical evidence for polynucleotide involvement in membrane transducers. There does not appear to be any reasonable alternative. Many biologically active substances show good matching to a polynucleotide receptor site that gives a good account of receptor function. There appears then to be no doubt that polynucleotides provide the basis of membrane transducers.

Dynamic Film Pressure Measurements in Journal Bearings for Use in Rotor Balancing

The paper presents the results of an experimental investigation where membrane transducers in the journal bearing wall are used to measure the dynamic oil-film pressures caused by rotor unbalance whirl. The results are applied successfully to balancing the rotor, and the experimental measurements of amplitude and pressure response are found to agree well with theoretical predictions, based on a linear analysis. The measurement accuracy of the pressure transducers compare favorably with the accuracy obtained with shaft displacement probes.

A balance panel, amplifier, and trigger device for nictitating membrane transducers

Description and circuit are provided for a balance panel, amplifier, and trigger device for nictitating membrane devices.

Design of membrane transducers with cantilever strain gauge

Design of membrane transducers with cantilever strain gauge

Nictitating membrane and corneo-retinal transducers for conditioning in rabbits.

Nictitating membrane and corneo-retinal transducers for conditioning in rabbits.

Theory of mechano-electric membrane transducers

An explanation is sought and obtained for the periodic oscillations of the fluids in membrane oscillator experiments. The procedure involves analysis of the equations of motions of a lattice containing fixed charges. The method is similar to those employed in the dynamical theory of lattice motions. It is demonstrated that the reciprocal relations of Born & Huang are not valid for charged membrane motions, when symmetry of electrical charge distributions are absent. Expressions for the phenomenological coefficients and the dielectric constants of the membrane system are also presented.