Electroacoustic Devices Research Articles

A method to measure and interpret input impedance of small acoustic components

Many applications would require to characterize the input behaviour of small acoustic components such as small tubes, small rectangular or circular slits, small cavities (or their associations in the form of one-port passive linear acoustic systems). These applications relate to artificial ears, loudspeakers, microphones miniaturized or not (among other electroacoustic devices), and acoustic tools used in precise measurements. Today, these small components are characterized analytically using modelling wherein viscosity, heat conduction, inertia, and compressibility of the fluid are considered, beyond realistic boundary conditions (no slip conditions and no temperature variations near the walls). But the results are usually obtained with a relative uncertainty greater than 50% (due to the geometrical uncertainties of the components). Therefore, it is of importance to characterize experimentally the input properties of these kind of components with a good accuracy, that is to say to measure their input impedance with a relative uncertainty of the order of magnitude of 10 - 2 . These measurements were quite impossible until now because the input impedances of such components are usually much greater than those involved in the measuring set-up. Here a measurement procedure is presented which uses the very precise reciprocity calibration method and the corresponding set-up available on the market. The results obtained on classical elements are discussed by comparison between experimental and theoretical results, showing the precision that would be achieved.

Variety of Electroacoustical Devices by Piezoelectric Materials

Variety of Electroacoustical Devices by Piezoelectric Materials

Integrated Love Wave Device Dedicated to Biomolecular Interactions Measurements in Aqueous Media.

Mass-sensitive electro-acoustic devices such as surface acoustic wave (SAW)micro-balances, capable to operate with aqueous media are particularly favorable for thedevelopment of biosensors. Their dimensions and physical properties offer a large potentialin biological fluid investigations, especially for measuring physical phenomenon (massdeposition, adsorption, pressure...). In this work, we propose a specific gratingconfiguration to lower the influence of viscosity of fluids which reduces the signal dynamicsof the surface wave transducers. A dedicated liquid cell also has been developed to isolatethe electro-active part of the device. The fabrication of the cell is achieved using theSU-8TMphoto-resist, allowing for manufacturing thick structures preventing any contact between thetested liquids and the transducers. Furthermore, the sensing area has been optimized tooptimize the sensor gravimetric sensitivity. The operation of the sensor is illustrated bydetecting bovine serum albumin (BSA) adsorption in the sensing area.

Digital measurement method of dynamic distortion of electroacoustical devices

Digital measurement method of dynamic distortion of electroacoustical devices

Design of high frequency piezoelectric resonators utilizing laterally propagating fast modes in thin aluminum nitride (AlN) films

Highly c-oriented aluminum nitride (AlN) thin piezoelectric films have been grown by pulsed direct-current (DC) magnetron reactive sputter deposition. The films were deposited at room temperature and had a typical full width half maximum (FWHM) value of the (002) rocking curve of around 2°. Resonant devices in thin film plates having surface acoustic wave (SAW) based designs were fabricated by means of low resolution photolithography. The devices were designed to operate with the fast Rayleigh and Lamb modes respectively. Both types of devices exhibited propagation velocities in excess of 10000m/s and sufficient electromechanical couplings. The device measurements illustrate the big potential of these modes for the development of low cost IC compatible electroacoustic devices in the lower GHz range. The basic properties of the modes studied are discussed in a comparative manner. Potential commercial applications are also outlined.

Buried electrode electroacoustic technology for the fabrication of thin film based resonant components

A fabrication process for thin film electroacoustic devices utilizing buried electrodes is presented. A one-step lithography process has been developed to bury electrodes resulting in a planarized surface. The proposed technology is expected to bring about a number of benefits concerning the performance of a variety of thin film electroacoustic devices. With respect to thin film plate acoustic resonators (FPAR), burying the reflector electrodes results in improved reflectivity and potentially lower susceptibility to acousto-migration effects. It is also shown that employing the proposed technology for the fabrication of both thin film bulk acoustic resonators (FBAR) and thin film solidity mounted bulk acoustic resonators (SBAR) eliminates certain macro-structural defects in the piezoelectric film which is a prerequisite for substantially improved device performance and higher power handling capability. The buried electrode electroacoustic (EA) technology is demonstrated for a thin aluminium nitride (AlN) piezoelectric film with electrodes of both molybdenum (Mo) and tungsten (W). The latter have been primarily chosen because of their high electroacoustic material quality. Thin film resonant structures produced by this technology are characterized and their features are discussed.

A ladder network impedance model for lossy wave phenomena

The ratio of Bessel functions J1(z)/J0(z) often occurs in the calculation of impedance of lossy components in electroacoustic devices. In particular, the electric impedance of hearing aid receivers or loudspeakers has a term proportional to a Bessel function ratio of this form when losses due to eddy currents are taken into account. This so-called semi-inductance has been notoriously difficult to model in simple lumped-parameter circuit calculation tools such as SPICE. This paper presents a simple ladder network derived from the Bessel function ratio expressed as a continuous fraction. The same transformation has been used to model the acoustic impedance of small cavities with losses at the thermal boundary layer.

Equalizable electro-acoustic device used in commercial panels and method for converting said panels

Electro-acoustic device which when installed in continuous ceiling, partition or wall panels available in the market made of mineral fibre, plasterboard, multi-laminated wood, etc. converts them into flat, invisible radiators of high-fidelity sound by its special characteristic of being equalizable for each type of panel at the time of manufacture and assembly.

Chronobiological Background to Cathemerality: Circadian Rhythms in Eulemur fulvus albifrons (Prosimii) and Aotus azarai boliviensis (Anthropoidea)

Cathemeral activity, in which the animals’ motor activity is almost evenly distributed throughout the dark and the light portion of the day, has been described in various lemur genera (Eulemur, Hapalemur) and in the owl monkey Aotus azarai of the Argentinean Chaco. Proximate and ultimate factors responsible for this behaviour are still being debated. However, the chronobiological background of the behaviour has largely been ignored. We studied E. fulvus albifrons and A. a. boliviensis under controlled laboratory conditions to assess whether their activity rhythm is endogenously regulated by a circadian timing system that obeys general rules found in other mammals, or whether there are characteristic differences. To this end, we carried out long-term activity recordings on individuals of both subspecies kept under constant light and various light-dark cycles (LDs) using a PC-controlled electro-acoustic device in combination with telemetric body temperature measurements. Both subspecies developed free-running circadian activity and body temperature rhythms with periods deviating from 24 h in constant light, and LDs turned out to be the most efficient Zeitgeber synchronizing this endogenous rhythmicity to the external 24-hour day. The luminosity prevailing during the dark time of the LD had a decisive effect on levels of activity in the lemurs and induced strong masking effects on their circadian activity pattern. The results indicate that, from a chronobiological viewpoint, both species should be considered as dark active primates. Their diel activity rhythm is regulated by a normally responding circadian timing system and strong activity inhibiting or enhancing direct effects of light intensity. Thus, hypotheses on proximate and/or ultimate factors of cathemerality in primates must also consider its circadian background.

Prediction of the thermal sensitivity of surface acoustic waves excited under a periodic grating of electrodes

The prediction of the temperature sensitivity of surface acoustic wave (SAW) devices still requires improvement because the nature of the implemented surface modes and the devices' complexity strongly change from the early basic Rayleigh-wave-based devices. To address this problem, a theoretical analysis and a numerical tool have been developed to predict the thermal dispersion of general electro-acoustic devices. The proposed model accounts for the electrode contribution to the frequency-temperature law. The computed thermal sensitivities are compared to experimental results for different kinds of substrates and waves.

Gigahertz-range electro-acoustic devices based on pseudo-surface-acoustic waves in AlN∕diamond∕Si structures

Diamond and AlN are, respectively, the nonpiezoelectric and the piezoelectric materials showing the highest acoustic velocities. Consequently, pseudo-surface-acoustic waves (PSAWs) in AlN∕diamond structures exhibit the highest surface wave velocities among all known layered structures. Phase velocity dispersion curves and attenuation for PSAW propagating along this structure have been calculated for different electrical boundary conditions. An experimental delay line, designed to operate at low PSAW attenuation conditions, as predicted by theoretical results, has been implemented and tested. A good accordance between experimental results and theoretical predictions was found. It is expected that devices based on PSAW propagation in AlN∕diamond structures are suitable to operate at frequencies several times higher than those of available devices, at a given linewidth resolution limit in the transducers technology.

Thin, lightweight acoustic actuator tile

A thin, lightweight electroacoustic actuator device covering a large surface area providing a high piston-like output over the frequency range of from at least 30 to in excess of 500 Hz comprising a stiff, lightweight face plate; a backing structure disposed below the face plate; at least one driver structure disposed between the face plate and the backing structure; and flexible structure flexibly connecting the at least one driver to the face plate.

Pulsed electro-acoustic technique applied to in-situ measurement of charge distribution in electron-irradiated polymers

Dielectric materials are frequently used in satellite structures for substantial savings in weight. Their dielectric nature and the effect of different forms of radiation encountered in space combine to accumulate electrical charges resulting in the occurrence of electrostatic discharges which cause harmful interference with the electronic parts of the satellite, leading to its malfunction or to a total loss of equipment control. Therefore, the behavior of dielectrics under irradiation must be investigated before being used in space. A pulsed electroacoustic (PEA) device was mounted in an irradiation chamber to monitor the spatial distribution of electrons implanted into polymer films during electronic irradiation. Internal charge accumulation was clearly identified. Penetration depth versus energy was double checked by comparing PEA with surface potential data.

Structural, optical, and acoustic characterization of high-quality AlN thick films sputtered on Al2O3(0001) at low temperature for GHz-band electroacoustic devices applications

Aluminum nitride thin and thick films were grown on Al2O3(0001) substrates by reactive radio frequency-sputtering technique at 180°C. The AlN films, 0.022–6.2μm thick, were stress-free, uniform, transparent, and extremely adhesive to the substrate. Their structural properties were investigated by x-ray diffraction measurements: the resulting films were highly c-axis oriented, with a full width at half maximum of the (0002) rocking curve in the range from 1.6° to 1.0° for AlN film thickness ranging between 0.022 and 6.2μm. The crystalline quality of AlN films was extremely good even at high thicknesses, as shown by the presence of the AlN(0004) reflection and by the narrow (0.12°–0.20°) diffraction peaks. Optical measurements of the transmission in the visual and infrared region demonstrated that the AlN films have low absorption and scattering. The extinction and the absorption coefficients, α and Ke, were estimated at λ⩾600nm(α=850±50cm−1,Ke=0.0040±0.0005). The piezoelectric strain constant d33 was measured for all the sputtered films: the mean d33 value was (4.2±0.7)×10−12 C∕N, which is very close to the value of the AlN single crystal. Surface acoustic wave (SAW) delay lines were photolithographically defined on the free surface of the AlN films grown on bare or metallized Al2O3(0001) substrates. Harmonic modes operating at frequencies up to about 2.4GHz were obtained just by using a conventional photolithographic technique with 7.5μm linewidth. The phase and group velocities of SAWs propagating in AlN∕Al∕Al2O3 and in AlN∕Al2O3 structures, along and normal to the Al2O3 a axis, were estimated for different AlN thicknesses. The experimental measurements were compared with the theoretical data and found to be in good agreement.

Gigahertz-band electroacoustic devices based on AlN thick films sputtered on Al2O3 at low temperature

Piezoelectric aluminum nitride films, 1.4–6.2 μm thick, have been grown on z-cut Al2O3 substrates by reactive rf sputtering at 180 °C. The films were clear, uniform, stress free, and highly adhesive to the substrate. Surface acoustic wave (SAW) delay lines with harmonic modes operating at frequencies up to about 2.4 GHz were obtained using only conventional optical lithography at 7.5 μm line width resolution. The phase velocity and the electromechanical coupling factor of SAWs propagating along zx-Al2O3/AlN and zy-Al2O3/AlN structures were investigated and found to be in good agreement with the theoretical predictions. The Al2O3/AlN first-order temperature coefficient of frequency was estimated for different film thickness to wavelength ratio values, and the temperature-compensated SAW delay line was obtained.

Finite element simulation of non-linear acoustic generation in a horn loudspeaker

The loudspeaker is an electro-acoustic device for sound reproduction which requires the distortion as small as possible. The distortion may arise from the magnetic non-linearity of the york, the uneven magnetic field distribution, the mechanical non-linearity at the diaphragm suspension and the acoustic non-linearity due to the high sound pressure and velocity in the duct-radiation system. A horn is sometimes provided in front of the vibrating diaphragm radiator, which plays an important role to increase the efficiency by matching the acoustic impedance between the radiator and the ambient medium. The horn is in many cases folded twice or three times to shorten the length, which further degrades the reproduction quality. The sound intensity and velocity are apt to attain very high in the small cross-sectional area in the throat and in the folded regions, which may cause the distortion due to the non-linear effect of the medium. The present paper is to investigate the frequency characteristics of the loudspeaker numerically evaluating the generation of the harmonics and sub-harmonics. An axisymmetric folded horn is considered for which the wave equation with the non-linear term retained is solved by the finite element method. The solution is made in time domain in which the sound pressure calculated at the opening end of the horn is Fourier-transformed to the frequency domain to evaluate the distortion, while the wave marching in the horn is visualized.

Behavior of soybean oil-in-water emulsion stabilized by nonionic surfactant

A soybean oil-in-water emulsion was prepared using nonionic Tween series surfactants. The effects of temperature, hydrophilic–lipophilic balance (HLB) value of the surfactant, and surfactant-to-oil ratio on the size of emulsion drops were investigated with an acoustic and electroacoustic devices. In the case of Tween 85, the influence of pH and electrolyte on the ζ potential of emulsion drops was examined. ζ potential appears to be strongly dependent on pH, varying in the case of high concentrations of NaCl from +60 to −90 mV. High concentrations of Na + and K + are capable of separating the oil phase from the emulsion. Divalent cations such as Ca 2+ and Mg 2+ lead to two points of zero charge at high concentrations, which is not observed for the case of hydrolyzable trivalent species like Al 3+ and Fe 3+.

Dynamic Electrophoretic Mobility of a Concentrated Dispersion of Particles with a Charge-Regulated Surface at Arbitrary Potential

The dynamic electrophoretic mobility of a concentrated dispersion of biocolloids such as cells and microorganisms is modeled theoretically. Here, a biological particle is simulated by a particle, the surface of which contains dissociable functional groups. The results derived provide basic theory for the quantification of the surface properties of a biocolloid through an electroacoustic device, which has the merit of making direct measurement on a concentrated dispersion without dilution. Two key parameters are defined to characterize the phenomenon under consideration: the first, A, is associated with the pH of the dispersion, and the second, B, is associated with the equilibrium constant of the dissociation reaction of the functional group. We show that if A is large and/or B is small, the surface potential is high, and the effect of double-layer polarization becomes significant. In this case the dynamic electrophoretic mobility may have a local maximum and a phase lead as the frequency of the applied electric field varies. Due to the hydrodynamic interaction between neighboring particles, the dynamic electrophoretic mobility decreases with the concentration of dispersion.

A High Performance Pocket-Size System for Evaluations in Acoustic Signal Processing

Custom-made hardware is attractive for sophisticated signal processing in wearable electroacoustic devices, but has a high initial cost overhead. Thus, signal processing algorithms should be tested thoroughly in real application environments by potential end users prior to the hardware implementation. In addition, the algorithms should be easily alterable during this test phase. A wearable system which meets these requirements has been developed and built. The system is based on the high performance signal processor Motorola DSP56309. This device also includes high quality stereo analog-to-digital-(ADC)- and digital-to-analog-(DAC)-converters with 20 bit word length each. The available dynamic range exceeds 88 dB. The input and output gains can be adjusted by digitally controlled potentiometers. The housing of the unit is small enough to carry it in a pocket (dimensions 150 × 80 × 25 mm). Software tools have been developed to ease the development of new algorithms. A set of configurable Assembler code modules implements all hardware dependent software routines and gives easy access to the peripherals and interfaces. A comfortable fitting interface allows easy control of the signal processing unit from a PC, even by assistant personnel. The device has proven to be a helpful means for development and field evaluations of advanced new hearing aid algorithms, within interdisciplinary research projects. Now it is offered to the scientific community.

Structural and electroacoustic studies of AlN thin films during low temperature radio frequency sputter deposition

AlN is a material used in a wide variety of applications such as electroacoustic devices, blue diodes, IR windows, thermal conductors, metal–insulator–semiconductor structures, integrated circuit packaging, etc. In this work thin piezoelectric AlN polycrystalline films have been grown on Si and SiO2 using rf magnetron sputter deposition in an Ar/N2 gas mixture. The structural properties of the films have been optimized by varying the deposition parameters, such as process pressure, gas mixture, substrate temperature, discharge power, etc. [K. Tominaga et al., Jpn. J. Appl. Phys., Part 1 35, 4972 (1996); H. Okana et al., ibid. 31, 3446 (1992); K. Kazuya, T. Hanabusa, and K. Tominaga, Thin Solid Films 281-282, 340 (1996)]. It was found that the best film texture was obtained for a particular set of parameters, namely process pressure of 4 mTorr, substrate temperature 350 °C, discharge power 350 W, and a gas mixture of 25% Ar and 75% N2. The films as examined by x-ray diffraction exhibited a columnar structure with a strong (001) texture, and a full width at half maximum (FWHM) rocking curve of 1.6°. Atomic force microscopy measurements indicated a surface roughness with a rms value of 8 Å. Classical nonapodized transversal surface acoustic wave filters operating at a frequency of 534 MHz were fabricated to characterize the electroacoustic properties of the films. The measurements indicated a coupling coefficient of 0.37% and a phase velocity of 4900 m/s. Further, thin epitaxial films were grown on (001)α-Al2O3 (sapphire) under the same deposition conditions except the substrate temperature. The films exhibited a (001)AlN//(001)α-Al2O3 plane orientation with a (002) rocking curve FWHM value of about 0.4°, showing a relatively good alignment of the c axis. The in-plane orientation was [110]AlN//[120]α-Al2O3 corresponding to a rotation of the AlN film of 30° with respect to the (001)α-Al2O3 surface. Cross-sectional transmission electron microscopy studies indicated a population of both thread and edge dislocations with decreasing concentrations with film thickness.