Membrane Resonance Research Articles

Contribution of cross talk to the uncertainty of microphone calibrations by the electrostatic actuator method

Cross talk in electrostatic actuator calibrations is defined as the response of a test microphone to the actuator excitation voltage when the microphone membrane is frozen, i.e., when the actuator polarization voltage is zero—an unavoidable nuisance effect that contributes to the calibration uncertainty. Two models for the cross talk are considered. In the first, the actuator excitation voltage is coupled to the microphone output through the stray capacitance between the actuator electrode and the microphone backplate; in the second, it is coupled through the ground resistance, which provides a common element between the input and output loops. In the stray capacitance model, at frequencies below the membrane resonance, the cross talk is independent of frequency, but in the ground resistance model it varies inversely with frequency. The frequency dependence of the cross talk thus serves as a discriminator between the two models. Measurements on condenser microphones of various sizes yield results that favor the stray capacitance model. The ratio of cross-talk signal to actuator pressure signal (at 94 dB re: 20 mPa) is found experimentally to be −74 dB for a 1-in. condenser microphone and nearly the same for 1/2-in. and 1/4-in. microphones.

Low-frequency control options in surround-sound critical listening rooms

Acoustically small rooms, which are typically used for critical listening, be it mono or surround, can potentially overwhelm the spatial and spectral textures that contribute to an enjoyable listening experience. The options to control potential modal and speaker boundary interference in rooms include optimal dimensional room ratios, optimal speaker/listener placement, optimal multiple subplacement and dedicated low-frequency absorbers, including quarter-wave traps, anechoic wedges, Helmholtz and membrane resonators, and a relatively new and potentially significant addition, the metal plate resonator, which absorbs efficiently down to 50 Hz with a thickness of only 4 in. The design theory, proof-of-performance evaluation testing methods, and optimal placement guidelines for all of these tools will be reviewed.

Serotonergic modulation of persistent sodium currents and membrane excitability via cyclic AMP‐protein kinase A cascade in mesencephalic V neurons

In rat mesencephalic trigeminal (Mes V) neurons, persistent sodium currents in conjunction with low-threshold potassium currents are critical for generation of subthreshold membrane oscillations and onset of burst behavior. Here we demonstrate that the cAMP/protein kinase A (PKA) signaling pathway modulates persistent sodium currents. In particular, we show that elevation of cAMP suppresses a low-threshold I(NaP) via a PKA intracellular pathway. Bath application of forskolin (20 microM), a stimulant for the production of cAMP, reduced the peak I(NaP). 1,9-Dideoxy-forskolin (20 microM), an inactive form of forskolin, produced minimal effects on I(NaP), and the membrane-permeable cAMP analogue 8-bromo-cAMP (500 microM) mimicked the effect of forskolin. Additionally, preapplication of H89 (2 microM), a specific PKA inhibitor, suppressed the effect of forskolin, suggesting the involvement of the cAMP/PKA intracellular signaling pathway in this modulation. 5-HT receptor stimulation (20 microM) also mimicked the modulation of I(NaP) by forskolin via the cAMP/PKA-dependent signaling pathway. Current clamp analysis demonstrated that voltage-dependent membrane resonance in response to a ZAP input current at depolarized holding potentials (approximately -50 mV) was specifically suppressed by forskolin or 5-HT. Moreover, drug application enhanced frequency adaptation in response to a 1-sec current pulse. These results indicate that modulation of persistent sodium currents by a cAMP/PKA pathway can significantly alter the membrane excitability and discharge characteristics of Mes V neurons.

Magnetic direct generation of acoustic resonances in silicon membranes

High-Q silicon membranes have been fabricated as resonator elements for excitation by magnetic direct generation of acoustic waves. Operating in the thickness shear mode, these inexpensive sensor elements are remotely excited by a planar spiral coil, driven by a radio frequency current and a strong static magnetic field. Modelling and FEM simulation have been done to improve the understanding of the sensor principle. Strong resonances with Q-factors up to 105 could be excited and detected successfully. Mass loading of these resonators shows Sauerbrey-like frequency shifts similar to quartz crystal microbalance sensors.

Frequency control of photonic crystal membrane resonators by monolayer deposition

We study the response of GaAs photonic crystal membrane resonators to thin-film deposition. Slow spectral shifts of the cavity mode of several nanometers are observed at low temperatures, caused by cryo-gettering of background molecules. Heating the membrane resets the drift and shielding will prevent drift altogether. In order to explore the drift as a tool to detect surface layers, or to intentionally shift the cavity resonance frequency, we studied the effect of self-assembled monolayers of polypeptide molecules attached to the membranes. The 2-nm-thick monolayers lead to a discrete step in the resonance frequency and partially passivate the surface.

Sodium Channels and Mechanisms of Neuropathic Pain

Na+ channels are large transmembrane proteins with a voltage-gated central pore capable of selectively passing Na+ ions. They are critical determinants of the electrical excitability of sensory neurons and play a key role in pain sensation by controlling afferent impulse discharge. Injury and disease affecting peripheral nerves induces axonopathy and demyelination. These neuropathic changes, in turn, trigger membrane remodeling in injured afferents and perhaps also in uninjured neighbors. A major consequence of the remodeling is increased cellular excitability. This is due in large part to subtype-selective abnormalities in the expression and trafficking of Na+ channels and perhaps also to altered kinetic properties of unitary channels. Hyperexcitable neurons show enhanced membrane resonance, rhythmogenesis, and ectopic spiking. The resulting excess discharge constitutes a primary neuropathic pain signal. In addition, it triggers and maintains central sensitization. This amplifies residual afferent input, yielding tactile allodynia, and it also amplifies ongoing ectopia that exaggerates spontaneous pain. Membrane-stabilizing Na+ channel ligands suppress neuropathic pain by selectively reducing membrane resonance in injured afferents and hence ectopic hyperexcitability. The clinical usefulness of these peripherally acting drugs might be enhanced by reducing their central side effects. Perspective Neuropathic pain is a complex outcome of multiple pathophysiological changes that develop in the peripheral nervous system (PNS) and the central nervous system (CNS) following nerve injury or disease. All or most of the CNS changes are thought to be due to abnormal signaling from the PNS, notably electrical hyperexcitability of peripheral sensory neurons. Because hyperexcitability is associated with abnormal sodium channel regulation, this process is a prime target for therapeutic intervention.

Characterization and modeling of Fano resonances in chalcogenide photonic crystal membranes

We demonstrate resonant guiding in a chalcogenide glass photonic crystal membrane. We observe strong resonances in the optical transmission spectra at normal incidence, associated with Fano coupling between free space and guided modes. We obtain good agreement with modeling results based on three-dimensional finite-difference time-domain simulations, and identify the guided modes near the centre of the first Brillouin zone responsible for the main spectral features.

Theta-frequency membrane resonance and its ionic mechanisms in rat subicular pyramidal neurons

The neuron population of the hippocampal formation exhibits oscillatory activity within the theta (θ) frequency band (4–10 Hz), and the intrinsic resonance properties of individual hippocampal neurons contribute to this network oscillation. The subiculum is the pivotal output region of the hippocampal formation and it is involved in many of the physiological and pathological functions of the limbic system. To study the characteristics and underlying mechanisms of resonance activity in subicular pyramidal neurons, we performed whole-cell patch-clamp recordings from these neurons in rat horizontal brain slices. We applied sinusoidal currents with constant amplitudes and linearly increasing frequencies to measure the resonance frequency of subicular pyramidal neurons. We found that the resonance frequency of subicular pyramidal neurons was about 2 Hz at room temperature and 4–6 Hz at 32–35 °C. The resonance frequency increased at hyperpolarized membrane potentials and decreased at depolarized membrane potentials. We also investigated three sub-threshold currents involved in the resonance: a slow hyperpolarization-activated cation current; an instantaneously activating, inwardly rectifying potassium current; and an inwardly persistent sodium current. The application of ZD7288 abolished the resonance hump, indicating that hyperpolarization-activated cation current generated resonance. The application of Ba 2+ enlarged the resonance hump at hyperpolarized potentials below −80 mV, indicating that inwardly rectifying potassium current attenuated resonance. The application of TTX suppressed the resonance at depolarized potentials, indicating that persistent sodium current amplified resonance when neurons were depolarized. Thus, there is a θ-frequency resonance mediated by hyperpolarization-activated cation current in subicular pyramidal neurons. This θ-frequency resonance of individual subicular pyramidal neurons may participate in the population’s θ oscillation and contribute to the functions of the subiculum.

Flat panel speaker

A loudspeaker is disclosed having a back plate, a driver attached to the back plate, the driver being responsive to an electrical signal, an enhancer having a neck and a mouth, the neck attached to the driver and movable in accordance with the movement of the driver, a thin film membrane defining a hole, the membrane attached to the enhancer such that the hole corresponds in size and location with the mouth of the enhancer, a frame for supporting the membrane and maintaining it in a taut state, a rubber type adhesive for dampening the membrane resonances and for adhering the membrane to the frame, and a clamp ring for clamping the membrane to the frame. Clarity of sound can be further improved by including a plurality of sound breathers in the back plate of the speaker. For improved sound radiation capability, especially in the middle and high frequency sound ranges, the size and the shape of the enhancer can be modified in various ways, including a frustoconical, parabolic, or bell-shaped enhancer.

BioMEMS Sensor Systems for Bacterial Infection Detection

The spread of drug-resistant bacteria represents a growing worldwide health problem. The most efficient way to fight drug-resistant bacteria is to detect their colonies, identify their type, monitor their growth, and destroy them before they reach the human body. A gravimetric biomedical micro-electro-mechanical sensor (BioMEMS) system operating in the pico-gram range (10(-)(12) g/cm(2)) has been proposed for detecting growth of drug-resistant bacterial colonies. The sensor is based on a MEMS metal-coated thin piezoelectric membrane resonator. A combination of shear horizontal surface acoustic (SHSAW), Bleustein-Gulyaev, skimming and 'leaky' waves, generated in the resonator, are highly sensitive to mass, density, viscoelastic, and electrochemical changes at the resonator/bacteria interface. Measuring resonant frequency shifts of the composite resonator provides information about the mass and type of the bacterium colony growing on the resonator.

Persistent Sodium Currents in Mesencephalic V Neurons Participate in Burst Generation and Control of Membrane Excitability

The functional and biophysical properties of a persistent sodium current (I(NaP)) previously proposed to participate in the generation of subthreshold oscillations and burst discharge in mesencephalic trigeminal sensory neurons (Mes V) were investigated in brain stem slices (rats, p7-p12) using whole cell patch-clamp methods. I(NaP) activated around -76 mV and peaked at -48 mV, with V1/2 of -58.7 mV. Ramp voltage-clamp protocols showed that I(NaP) undergoes time- as well as voltage-dependent inactivation and recovery from inactivation in the range of several seconds (tau(onset) = 2.04 s, tau(recov) = 2.21 s). Riluzole (< or =5 microM) substantially reduced I(NaP), membrane resonance, postinhibitory rebound (PIR), and subthreshold oscillations, and completely blocked bursting, but produced modest effects on the fast transient Na+ current (I(NaT)). Before complete cessation, burst cycle duration was increased substantially, while modest and inconsistent changes in burst duration were observed. The properties of the I(NaT) were obtained and revealed that the amplitude and voltage dependence of the resulting "window current" were not consistent with those of the observed I(NaP) recorded in the same neurons. This suggests an additional mechanism for the origin of I(NaP). A neuronal model was constructed using Hodgkin-Huxley parameters obtained experimentally for Na+ and K+ currents that simulated the experimentally observed membrane resonance, subthreshold oscillations, bursting, and PIR. Alterations in the model g(NaP) parameters indicate that I(NaP) is critical for control of subthreshold and suprathreshold Mes V neuron membrane excitability and burst generation.

Acoustically Actuated Flextensional Si&amp;lt;tex&amp;gt;$_x$&amp;lt;/tex&amp;gt;N&amp;lt;tex&amp;gt;$_y$&amp;lt;/tex&amp;gt;and Single-Crystal Silicon 2-D Micromachined Ejector Arrays

We propose using two-dimensional (2-D) micromachined droplet ejector arrays for environmentally benign deposition of photoresist and other spin-on materials, such as low-k and high-k dielectrics used in IC manufacturing. Direct deposition of these chemicals will reduce waste as well as production cost. The proposed device does not harm heat or pressure sensitive fluids and they are chemically compatible with the materials used in IC manufacturing. Each element of the 2-D ejector array consists of a flexurally vibrating circular membrane on one face of a cylindrical fluid reservoir. The membrane has an orifice at the center. A piezoelectric transducer generating ultrasonic waves, located at the open face of the reservoir, actuates the membranes. As a result of this actuation, droplets are fired through the membrane orifice. Ejector arrays were built with either Si/sub x/N/sub y/ or single-crystal silicon membranes using two different fabrication processes. We show that single-crystal silicon membranes are more uniform in their thickness and material quality than those of Si/sub x/N/sub y/ membranes. The single-crystal silicon membrane-based devices showed thickness and material uniformity across all the membranes of an array. This improvement eliminated nonuniform membrane resonance frequencies across an array as observed with Si/sub x/N/sub y/ membrane-based devices. Therefore, it should be possible to repeatably build devices and to predict their dynamic characteristics. Using the fabricated devices, we demonstrated water ejection at 470 kHz, 1.24 MHz, and 2.26 MHz. The corresponding droplet diameters were 6.5, 5, and 3.5 /spl mu/m, respectively.

Dopaminergic modulation of photopic temporal transfer properties in goldfish retina investigated with the ERG

The influence of dopamine (DA) through either D1- or D2-dopamine receptors (D1-/D2-R) onto temporal transfer properties of the retina has been investigated using the ERG. Single flash responses and flicker responses were measured in the vitreous under photopic illumination conditions after application of either D1-/D2-R agonists or antagonists. All DA-R drugs did change the single flash responses, but only blockade of D2-R or activation of D1-R also changed the temporal transfer properties. In the Bode plot the gain characteristic was changed and thereby the upper limit frequency reduced. The action of DA is discussed on the base of a membrane resonance model in the outer retina versus a feed-forward inhibition model in the inner retina.

Dopaminergic modulation of photopic temporal transfer properties in goldfish retina investigated with the ERG

The influence of dopamine (DA) through either D1- or D2-dopamine receptors (D1-/D2-R) onto temporal transfer properties of the retina has been investigated using the ERG. Single flash responses and flicker responses were measured in the vitreous under photopic illumination conditions after application of either D1-/D2-R agonists or antagonists. All DA-R drugs did change the single flash responses, but only blockade of D2-R or activation of D1-R also changed the temporal transfer properties. In the Bode plot the gain characteristic was changed and thereby the upper limit frequency reduced. The action of DA is discussed on the base of a membrane resonance model in the outer retina versus a feed-forward inhibition model in the inner retina.

Characterizing the spatial uniformity of thin-film stress, modulus, and strength via novel experimental techniques

Controlling thin-film stress magnitudes and nonuniformities is a persistent and pervasive challenge for applications ranging from the semiconductor industry to nanotechnology. Consequently, the ability to measure the intensity and spatial distribution of film stress accurately is essential for fabrication process optimization. In addition to intrinsic stress, thin-film properties such as the fracture strength and biaxial modulus are also important. However, these properties are typically different from bulk values and are more difficult to measure. But such data can be obtained from experimental measurements using the pressure bulge tool and the membrane resonance tool. This paper describes novel extensions of both methods to characterize global thin-film properties. Arrays of freestanding membrane windows are fabricated across a silicon substrate (or mask). Individual membranes are tested to provide a discrete assessment of the thin-film properties, which allows for the determination of gradients in the film across the substrate.

Thickness and temperature dependence of stress relaxation in nanoscale aluminum films

We have found that stress relaxation of nanoscale Al thin films is strongly dependent on both film thickness and temperature. Films 33, 107, and 205 nm thick prepared by evaporation onto a silicon nitride membrane substrate were studied using membrane resonance. A single thermal cycle to 300 °C was used to establish a stress, after which the time dependence of the stress was measured for the three film thicknesses at 50, 75, and 100 °C. The relaxation rate is highest for the highest temperature and the thinnest film. A dislocation locking mechanism is suggested as a possible explanation for the observed thickness dependence.

Confinement and transverse standing acoustic resonances in free-standing membranes

Brillouin light scattering (BLS) reveal standing wave acoustic resonances in unsupported 100 and 200 nm thick, SiN membranes. In contrast to supported thin films where discrete high frequency (GHz) longitudinal standing wave excitations were recently reported, transverse standing resonances are observed by light scattering in an unsupported laminar structure. Due to the boundary conditions imposed by the free upper and lower surfaces, the standing wave resonances are quantized in frequency. The resonances provide for a direct, nondestructive, measure of all principal elastic constants ${(C}_{11}{,C}_{44})$ that completely characterize the mechanical properties of the membrane. In addition, the two lowest order Lamb waves (dilational and flexural modes) of the membrane are observed. The results are compared to BLS performed on nitride films atop a Si underlayer when it is found that all standing resonances transform to leaky modes leading to featureless light scattering spectra.

Characterizing Thin-Film Stress Fields by Resonance of Membrane Arrays

ABSTRACTControlling thin-film stress magnitudes and nonuniformities is a persistent and pervasive challenge for applications ranging from the semiconductor industry to nanotechnology. Consequently, the ability to accurately measure the intensity and spatial distribution of film stress is essential for fabrication process optimization. This paper describes novel extensions of the membrane resonance method to characterize in-plane film stress gradients. Arrays of freestanding membrane windows are fabricated by first depositing thin films over a silicon substrate. Back-etching then creates an array of membrane windows which are sequentially resonated with a compatible drive electrode. The technique was used to determine stress uniformity across electron projection lithography masks, which incorporate membrane window arrays. In addition, a procedure is presented for identifying the two principal stresses in individual membranes.

Development of inward rectification and control of membrane excitability in mesencephalic v neurons.

The present study was performed to assess the postnatal development and functional roles of inward rectifying currents in rat mesencephalic trigeminal (Mes V) neurons, which are involved in the genesis and control of oral-motor activities. Whole cell voltage-clamp recordings obtained from Mes V neurons in brain stem slices identified fast (I(KIR)) and slow (I(h)) inward rectifying currents, which were specifically blocked by BaCl(2) (300-500 microM) or 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride (ZD 7288, 10 microM), respectively. The whole cell current density for these channels increased between postnatal days 2 to 12 (P2-P12), and the time courses for I(h) activation and deactivation were each well described by two time constants. Application of ZD 7288 produced membrane hyperpolarization in the majority of cells and prolonged afterhyperpolarization repolarization. Additionally, in the presence of ZD 7288, spike frequency was decreased and adaptation was more pronounced. Interestingly, these neurons exhibited a voltage-dependent membrane resonance (<10 Hz) that was prominent around resting potential and more negative to rest and was blocked by ZD 7288. These results suggest that I(h) contributes to stabilizing resting membrane potential and controlling cell excitability. The presence of I(h) imparts the neuron with the unique property of low-frequency membrane resonance; the ability to discriminate between synaptic inputs based on frequency content.

Resonance and selective communication via bursts in neurons having subthreshold oscillations

Revealing the role of bursts of action potentials is an important step toward understanding how the neurons communicate. The dominant point of view is that bursts are needed to increase the reliability of communication between neurons [Trends Neurosci. 20 (1997) 38]. In this paper we present an alternative but complementary hypothesis. We consider the effect of a short burst on a model postsynaptic cell having damped oscillation of its membrane potential. The oscillation frequency (eigenfrequency) plays a crucial role. Due to the subthreshold membrane resonance and frequency preference, the responses (i.e. voltage oscillations) of such a cell are amplified when the intra-burst frequency equals the cell's eigenfrequency. Responses are negligible, however, if the intra-burst frequency is twice the eigenfrequency. Thus, the same burst could be effective for one cell and ineffective for another depending on their eigenfrequencies. This theoretical observation suggests that, in addition to coping with unreliable synapses, bursts of action potentials may provide effective mechanisms for selective communication between neurons.