Compliant Membrane Research Articles

Micromachined microphones with integrated optical nanoscale displacement sensors

Micromachined microphones with diffraction-based optical displacement detection are presented. A compliant membrane is made part of a phase-sensitive diffraction grating, and the deflection resulting from external acoustic pressure alters the intensities of the diffracted orders which are monitored with integrated photodiodes. The scheme provides the displacement sensitivity of a Michelson interferometer and can be integrated without beam splitters or critical alignment problems into volumes on the order of 1 mm3. Preliminary characterization with ultrasonic sensors shows a displacement resolution of 1×10−4 Å/Hz1/2 near 100 kHz with 60 μW of laser power incident on the photodetector. Current research is aimed at achieving similar displacement resolution in the audio frequency range while demonstrating the potential for high-fidelity miniature microphone arrays for hearing and measurement applications. The approach is implemented and characterized using microphone membranes with integrated diffraction grating bottom electrodes fabricated on silicon using Sandia National Laboratories’ dedicated processing platform. Preliminary results on nonoptimized implementations show a flat frequency response to 15 kHz with internal noise levels below 40 dBA. [The authors would like to thank NIH and DARPA for supporting this research.]

Freely suspended nanocomposite membranes as highly sensitive sensors.

Highly sensitive sensor arrays are in high demand for prospective applications in remote sensing and imaging. Measuring microscopic deflections of compliant micromembranes and cantilevers is developing into one of the most versatile approaches for thermal, acoustic and chemical sensing. Here, we report on an innovative fabrication of compliant nanocomposite membranes with nanoscale thickness showing extraordinary sensitivity and dynamic range, which makes them candidates for a new generation of membrane-based sensor arrays. These nanomembranes with a thickness of 25-70 nm, which can be freely suspended over large (hundred micrometres) openings are fabricated with molecular precision by time-efficient, spin-assisted layer-by-layer assembly. They are designed as multilayered molecular composites made of a combination of polymeric monolayers and a metal nanoparticle intralayer. We demonstrate that these nanocomposite membranes possess unparalleled sensitivity and a unique autorecovering ability. The membrane nanostructure that is responsible for these outstanding properties combines multilayered polymer/nanoparticle organization, high polymer-chain orientation, and a pre-stretched state.

Collective and Individual Plasmon Resonances in Nanoparticle Films Obtained by Spin-Assisted Layer-by-Layer Assembly

Nanoscale uniform films containing gold nanoparticle and polyelectrolyte multilayer structures were fabricated by the using spin-assembly or spin-assisted layer-by-layer (SA-LbL) deposition technique. These SA-LbL films with a general formula [Au/(PAH-PSS)nPAH]m possessed a well-organized microstructure with uniform surface morphology and high surface quality at a large scale (tens of micrometers across). Plasmon resonance peaks from isolated nanoparticles and interparticle interactions were revealed in the UV-visible extinction spectra of the SA-LbL films. All films showed the strong extinction peak in the region of 510-550 nm, which is due to the plasmon resonance of the individual gold nanoparticles redshifted because of a local dielectric environment. For films with sufficient density of gold nanoparticles within the layers, the second strong peak was consistently observed between 620 and 660 nm, which is the collective plasmon resonance from intralayer interparticle coupling. Finally, we suggested that, for certain film designs, interlayer interparticle resonance might be revealed as an independent contribution at 800 nm in UV-visible spectra. The observation of independent and concurrent individual, intralayer, and interlayer plasmon resonances can be critical for sensing applications, which involve monitoring of optomechanical properties of ultrathin optically active compliant membranes.

Mathematical modelling of comedo ductal carcinoma in situ of the breast.

The growth of a tumour in a cylindrical duct with compliant walls is examined in order to model the early stages of ductal carcinoma in situ (DCIS) of the breast, the earliest known stage of breast cancer. A nutrient-limited growth model is formulated, in which cell movement is described by a Stokes flow constitutive relation. The interactions between the expansive forces created by tumour cell proliferation and the stresses that develop in the compliant basement membrane are studied using asymptotic and numerical methods. In this way we show how the duct wall deforms as the tumour grows and also how the progression of the tumour along the duct depends upon the stiffness of the wall. By varying key parameters we determine how treatment, protease production and the inclusion of the surrounding stroma affect the growth. Finally, we discuss the biological relevance of our results and suggest possible directions for future work.

Moderate‐to‐large injection and suction driven channel flows with expanding or contracting walls

AbstractWe consider in this paper the incompressible laminar flow in a porous channel with expanding or contracting walls. While the head‐end is closed by a compliant membrane, the downstream end is left unobstructed. For symmetric injection or suction along the uniformly expanding porous walls, the Navier‐Stokes equations are reduced to a single, nonlinear, ordinary differential equation. The latter is obtained via similarity transformations in both time and space. The resulting equation is then solved both numerically and asymptotically, using perturbations in the crossflow Reynolds number R. Two separate approaches are presented for each of the injection and suction cases, respectively. For the large injection case, the governing equation is first integrated and the resulting third‐order differential equation is solved using the method of variation of parameters. For the large suction case, the governing equation is first simplified near the wall and then solved using successive approximations. Results are then correlated and compared for variations in R and the dimensionless wall expansion rate α. For injection‐induced flow, the asymptotic solution becomes more accurate when R/α is increased. Its deviation from the classic sinusoidal profile arising in nonexpanding channels becomes less significant with successive increases in R. For suction‐induced flows, faster wall contractions increase the effective Reynolds number ‐(α+R), thus leading to more precise approximations. For the same absolute value of R, the suction‐flow approximation tends to be the most accurate of the two and the least sensitive to variations in α. As ‐(α+R) is increased, the suction profile approaches the linear form anticipated in nonexpanding channels. By comparison with the injection‐induced flow, suction is characterized by improved accuracy, sharper flow turning, and larger shear.

Analysis of the sodium recirculation theory of solute-coupled water transport in small intestine.

Our previous mathematical model of solute-coupled water transport through the intestinal epithelium is extended for dealing with electrolytes rather than electroneutral solutes. A 3Na+-2K+ pump in the lateral membranes provides the energy-requiring step for driving transjunctional and translateral flows of water across the epithelium with recirculation of the diffusible ions maintained by a 1Na+-1K+-2Cl- cotransporter in the plasma membrane facing the serosal compartment. With intracellular non-diffusible anions and compliant plasma membranes, the model describes the dependence on membrane permeabilities and pump constants of fluxes of water and electrolytes, volumes and ion concentrations of cell and lateral intercellular space (lis), and membrane potentials and conductances. Simulating physiological bioelectrical features together with cellular and paracellular fluxes of the sodium ion, computations predict that the concentration differences between lis and bathing solutions are small for all three ions. Nevertheless, the diffusion fluxes of the ions out of lis significantly exceed their mass transports. It is concluded that isotonic transport requires recirculation of all three ions. The computed sodium recirculation flux that is required for isotonic transport corresponds to that estimated in experiments on toad small intestine. This result is shown to be robust and independent of whether the apical entrance mechanism for the sodium ion is a channel, a SGLT1 transporter driving inward uphill water flux, or an electroneutral Na+-K+-2Cl- cotransporter.

High quality GaAs grown on Si-on-insulator compliant substrates

Device quality GaAs epilayers were grown by molecular beam epitaxy using Si-on-insulator (SOI) as a compliant substrate. The density of dislocations is significantly reduced in the GaAs epilayers. Based on the dislocation theory and detailed experiments, a model of compliant growth to reduce dislocation density has been developed. As compared to the conventional growth technique, the advantage of reduction of dislocation density in GaAs epilayers grown on a much thinner compliant Si membrane can be predicted with this model. Our experimental results indicate that compliant growth can improve the crystal quality of epilayers on lattice-mismatched substrates significantly. Utilizing this growth technique, the full width at half-maximum of the x-ray rocking curves is measured to be as low as 128 arcsec for 3-μm-thick GaAs epilayers grown on SOI compliant substrates. Furthermore, structures of AlGaAs/GaAs heterojunction bipolar transistor (HBT) have been grown by compliant growth on SOI substrates. The corresponding I–V characteristics demonstrate good performance of the HBTs.

Frequency Discrimination Characteristics of Cochlear Basilar Membrane Using a Fluid/Structure Model

ABSTRACTThis paper addresses the vibratory mechanics associated with frequency discrimination of basilar membrane within the cochlear of the inner ear. Periodic excitation is provided to the oval window, which results in generation of waves within the fluid-filled cochlear traveling towards the apex. These waves interact with the compliant basilar membrane structure causing its vibratory motion. Solution procedure of the fluid/structure model consists of a two-step process. First, a finite element calculation (ANSYS) solves for the membrane vibration with an initial harmonic pressure distribution. Second, a control volume analysis links the resultant vibratory motion with the fluid pressure acting on the basilar membrane, thus a pressure feedback loop is accomplished. Results show that dominant factors affecting vibratory characteristics of the basilar membrane are its structural geometry and attenuation of pressure wave as it travels away from the oval window. Calculations clearly capture the designed function of the basilar membrane, principally its frequency discrimination behavior.

Study on deformation of a microphone membrane using multiple-wavelength interferometry

Determination of deformation of a microphone membrane under electrical loads (varying voltage) is of fundamental importance for the design and fabrication of a microphone. This paper reports a technique for measuring the deformation of a thin membrane (2 μm) in a silicon-based condenser microphone. A typical condenser microphone consists of two parts: a compliant membrane and a perforated rigid backplate. Interference patterns under various interference filters with wavelengths of 700, 589 and 532 nm are recorded through a microscope by a CCD sensor. A simple algorithm for recording both integral and fractional fringes using different wavelengths is presented. From the fringe pattern deformation of the membrane in the sub-micron range is obtained. The proposed method enhances the lateral resolution and improves measurement accuracy.

Micro-Scale Electrohydrodynamic Pumped High Performance Actuation

A new type of actuation device has been conceptualized that meets the needs of both large displacement force and bandwidth within a package more compact than the currently available magnetostrictive and stack-type piezoelectric actuators of similar rating. This concept relies on micro-scale electrohydrodynamic (EHD) pumping of a dielectric liquid within small channels. Configured as an actuator, the EHD pump(s) would be used to move fluid between two reservoirs—each having a compliant membrane that interfaces to the world to provide the means to achieve vibration cancellation or micro actuation. Ordinarily limited to generating flow in macroscale applications, the EHD pump, when operating in a thermal induction mode, is shown to exhibit an exciting scaling law as its size is reduced. As the pump volume to surface area decreases, the energy going toward increasing pressure in the pump has an increasingly larger effect. Since the volume/surface area is proportional to 1/ a, where a is the characteristic width or diameter of the channels comprising the pump, the pressure head generated scales similarly. Analytical and numerical studies have shown the EHD-pumped actuator to be capable of delivering equal force and bandwidth to magnetostrictive and stack-type piezo actuators, but with considerably greater displacement and a smaller size. Further, this type of actuator offers the possibility for deployment in active vibration control or micro actuation applications at significantly greater temperatures than for piezoelectric and magnetostrictive devices.

Long-wavelength InGaAs quantum wells grown without strain-induced warping on InGaAs compliant membranes above a GaAs substrate

Long-wavelength photoluminescence at 1.35 μm has been measured from an InGaAs quantum-well heterostructure deposited on disk-shaped InGaAs (xIn=0.05) compliant-film membranes. Strain-induced warping is avoided by utilizing a single pedestal to suspend each compliant-film disk over a GaAs substrate. Cathodoluminescence (CL) spectra verify the long-wavelength emission, and panchromatic CL images reveal that strong emission occurs only on compliant film structures supported by 1-μm-diam pedestals.

Acute traumatic rupture of the thoracic aorta: Delayed treatment with endoluminal covered stent. A report of two cases

Acute traumatic rupture of the thoracic aorta: Delayed treatment with endoluminal covered stent. A report of two cases

Hemodynamic forces induce the expression of heme oxygenase in cultured vascular smooth muscle cells.

Both nitric oxide (NO) and carbon monoxide (CO) are vessel wall-derived messenger molecules that cause platelet inhibition and vasodilation by activating guanylyl cyclase in target cells. Since vascular smooth muscle cells (SMCs) are exposed to shear and tensile stresses, this study examined the effects of these hemodynamic forces on the enzymes that generate NO and CO in SMCs. Monolayers of cultured rat aortic SMCs were subjected to shear stress using a modified cone and plate viscometer, or cyclic elongational stretch using a compliant silastic culture membrane. Shear stress stimulated time-dependent increases in mRNA and protein for inducible heme oxygenase-1 (HO-1), the enzyme which forms CO as a byproduct of heme degradation. The threshold level of shear necessary to induce HO-1 expression was between 5 and 10 dynes/cm2. In contrast, shear stress did not stimulate inducible NO synthase (iNOS) expression. Cyclic stretch also induced the expression of HO-1 but not of iNOS mRNA. Exposure of vascular SMCs to shear stress stimulated the production and release of CO as demonstrated by the CO-dependent increase in intracellular cGMP levels in coincubated platelets. In addition, ADP-stimulated aggregation was inhibited in platelets exposed to sheared SMCs but not in platelets exposed to untreated control SMCs. Treatment of sheared SMCs with the HO-1 inhibitor, tin protoporphyrin-IX, blocked the antiaggregatory effect of the cells, whereas the iNOS inhibitor, methyl--arginine, had no effect. These results indicate that hemodynamic forces induce HO-1 gene expression and CO production in vascular SMCs, and that SMC-derived CO inhibits platelet aggregation. Thus, CO is a novel endogenous vessel wall-derived messenger molecule that may be selectively induced by hemodynamic forces to inhibit platelet reactivity and preserve blood fluidity at sites of vascular injury.

Imaging Pneumatic Proximity‐to‐tactile Sensing

The mainstream of current research work in array tactile sensors concentrates on using a soft compliant membrane as a means of transmitting the effect of variable external stimuli to the discrete sensing elements. The soft compliant devices are usually made of a thin flexible substrate such as pressure sensitive pads, conductive materials, conductive coatings, piezoelectric polymers or elastomers. A large number of tactile sensor designs using these types of materials have been investigated by researchers. These include the use of anisotropically conductive silicone rubber (ACS), sponges containing carbon particles or felted carbon fibres, piezoelectric polymers such as polyvinylidene fluoride (PVF2) and conductive elastomers such as Dynacom materials consisting of silicone rubber mixed with metallic compounds.

Induced vibration dynamic touch sensor system and method

An induced vibration dynamic touch sensor comprises a compliant membrane adapted for sliding contact with an object so as to induce vibrations in the membrane, and a transducer assembly for converting the vibrations into electrical signals. The electrical signals are processed to produce a normalized spectral signature characteristic of the size and shape of the object, and the sizes and shapes and nature of its surface features. A pattern vector is extracted from the spectral signature and subjected to discriminant analysis to classify and recognize the object. The invention is capable of discriminating between objects differing in diameter by as little as 1/32 inches and differing in spacing by as little as 0.01 inches.

Theory and design of disposable clinical blood viscometer.

A disposable clinical whole blood viscometer which can produce viscosity measures over a wide range of shear rates in a single rapid determination has been developed and is currently under test. The design is based upon the time varying flow of blood through a capillary. The flow is driven by the pressure in a fixed volume air chamber and transmitted to the sample through a compliant membrane. The time varying pressure in the air chamber is measured by a suitable transducer. The instantaneous shear stress of the blood in the capillary is proportional to the air pressure, while the instantaneous shear rate is proportional to the pressure-time derivative. Proper design ensures that the system operates as a first order dynamic system with flow resistance entirely determined by the nonlinear sample viscosity. By constructing the air chamber in two parts coupled by a quick disconnect fitting the design can allow for the blood-containing part of the instrument to be discarded, eliminating handling and cleaning of blood contacted components. The entire determination is completed in less than a minute, so that anticoagulants are not necessary. Tests on a prototype show that the instrument gives results in excellent agreement with those obtained on a cone-plate rheogoniometer.

Development of a sensor for non-invasive intracranial pressure measurement in the newborn

A new system has been developed for the non-invasive monitoring of intracranial pressure (ICP) across the anterior fontanelle in the newborn. The system comprises a very small pneumatic sensor linked via two vinyl tubes to an instrument where the ICP value is dislayed. The sensor is simply bonded to the anterior fontanelle, using industrial collodion normally used for attaching EEG electrodes. The sensor body is injection moulded in semi-flexible polyurethane with a very thin, compliant membrane bonded to its front surface. Using these manufacturing techniques the sensors are made to be disposable thus minimizing the risk of cross infection. ICP characteristics can now be recorded continously in a wide range of neonates and the evaluation of currently used therapeutic treatments for lowering elevated ICP can be carried out safely and accurately.

Global mechanical consequences of reduced cement/bone coupling rigidity in proximal femoral arthroplasty: A three-dimensional finite element analysis

Component loosening in total hip arthroplasty is often accompanied by substantial bony remodelling, associated initially with reduced stiffness of the cancellous bone bordering the cement, and eventually with the formation and proliferation of a compliant fibrous membrane at the bone/cement interface. An anatomically based three-dimensional finite element model has been developed to explore the salient stress changes occurring with progressive degradation of the stiffness of the cancellous bone in a thin zone bordering the cement. This border zone, modelled as a distinct linearly elastic and isotropic material layer, assumed a geometry and a range of mechanical properties inferred from eventual membrane thickness apparent in recent animal studies of component loosening. The major variables considered were: stiffness (elastic modulus) and compressibility (Poisson ratio) of the border zone, stiffness changes in the outlying cancellous bone, resultant hip contact force, and trochanteric muscle loadings. The results for the limiting case of a non-degraded border zone compared reasonably with previous studies of femoral reconstructions having rigid bone-to-cement attachment. Progressive decay of border zone stiffness produced complex changes in load transmission. Foremost among these were a generalized increase in stress levels (especially of transverse-plane tension) in the proximo-lateral cancellous bone, and a corresponding generalized decrease in stress levels in the proximomedial cancellous bone. There were also large bending moment increases in the prosthesis and its cement mantle, especially at mid-stem. At almost all sites, the critical stress levels were those developed for peak stance-phase loading, rather than for the lower loads (and different resultant contact force directions) occurring elsewhere in the gait cycle. The elevated proximo-lateral cancellous bone stresses occurring with eventual membrane development, consistent with localized bony hypertrophy seen in recent animal studies, may be a response to hoop stresses occurring during pistoning of the tapered cement mantle.

Stabilization of laminar boundary layers by compliant membranes

Direct numerical simulations have been performed to study boundary layer flow over a compliant membrane. While coupling directly to the fluid dynamics code through the wall boundary condition, this membrane model displays many of the important features of other compliant coatings. While membrane parameters are identified that increase the critical Reynolds number by a factor of 2 compared with the rigid wall, this is mitigated by a significant increase in the growth rates in the unstable region. A detailed analysis of the temporal evolution and spatial structure of the terms in the kinetic energy balance equation shows significant differences in the behavior of two different classes of modes of the system: class A waves, which are destabilized by increased dissipation in the membrane, and class B waves, which are stabilized by membrane dissipation. For class A waves, the dominant dissipative mechanism is viscous damping in the fluid augmented by negative energy production, the principal stabilization mechanism seen in the ‘‘smart wall’’ algorithm simulations. For class B waves, direct transfer of energy to, and dissipation by, the membrane dominates stabilization of the flow. For class A waves, the membrane stabilizes the flow not by dissipating energy, but by modifying the flow to decrease energy production and enhance viscous dissipation in the fluid.

Vibration isolating surface protector with high traction properties

This invention is related to a vibration isolating surface protector having high traction properties. A soft compliant substantially platelike foam cushion is bonded to a substantially rigid backing plate and the periphery of the cushion has an integrally coated compliant membrane. When an axial or oblique force is applied to the backing plate surface remote from the cushion, the cushion and membrane compress, yielding extraordinary traction properties.