No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Multiphysics modeling, implementation and experimentation of a piezoelectrically actuated MEMS digital loudspeaker array
Abstract
The Digital Loudspeaker Array (DLA) is an electroacoustic transducer which receives as input a digital signal and performs the analog conversion directly into the air. It consists of a plurality of radiating elements arranged in a matrix. These elements will be designated by the term “speaklet” when they are reduced in size. The acoustic radiation of a DLA is indeed very sensitive to the size of the matrix due to differences in path length, which makes it especially suitable for MEMS technology. This thesis is on the study of a piezoelectric MEMS DLA. After an introduction that is increasingly focused on the subject, the thesis addresses the multiphysics modeling of the DLA, dimensioning of the speaklets and experimental tests. Analytical formulas, numerical simulations and finite element models are developed and used to predict the mechanical behavior of the presented speaklets, the pressure radiated by the DLA and the electrical power consumption. The speaklet are then dimensioned from the technological stack (set in advance) in order to maximize the pressure level. Experimental tests involving the use of an anechoic chamber, an optical interferometer, a vibrometer and an impedancemeter validate most of the models. Otherwise, these tests are usefull for improving some of them or for showing their limitations. The results have shown the importance of the residual stresses, which cause an initial deformation of the speaklets and modify their resonance frequencies, thus rendering ineffective the use of large radii. In accordance with the models, the static deflection of the speaklets is nonlinear but their dynamic behavior is linear. This enables characterizations using transfer functions. Theory and sound recordings show that a DLA made of such speaklets can produce in the best case the same pressure to that generated by the same matrix driven in an analog way. In our case, more distortions were obtained in digital reconstructions because of non-uniform responses of the speaklets, due to different access resistances. However, the presented DLA has other advantages, the most important being the very low power consumption it is theoretically possible to achieve using the adiabatic charge principle. The piezoelectric MEMS DLA thus appears as a promising technology. The optimization of our first prototype using the developed tools should indeed lead to a DLA able to generate an equivalent presure to that obtained with analog control, but with a far greater electroacoustic efficiency. Future work should then focus on the design of nonlinear speaklets and on the shaping of the pulse of pressure they generate, in order to increase the total pressure level.
ResearchGate has not been able to resolve any citations for this publication.
A method for fabricating flat loudspeakers comprising manufacturing a flat loudspeaker including at least one microspeaker array, having first and second main surfaces; and covering at least one of the main surfaces of the loudspeaker with a cover member including an airtight sound-pressure wave transparent thin polymer film.
Digital loudspeaker arrays (DLAs) are electroacoustic transducers reconstructing acoustic signals out of binary audio streams, usually consisting of a digital signal processing module driving multiple actuators (small loudspeakers). In this work a DLA prototype was implemented using an all-digital audio chain driven by 1-bit sigma-delta signals. The prototype implementation is described and its performance measured and evaluated using frequencydomain and THD analysis. These results also compare the DLA performance when driven by either sigma-delta or PCM input signals.
A theory of smart loudspeaker arrays is described where a modified Fourier technique yields complex filter coefficients to determine the broad-band radiation characteristics of a uniform array of micro drive units. Beamwidth and direction are individually programmable over a 180arc, where multiple agile and steerable beams carrying dissimilar signals can be accommodated. A novel method of stochastic filter design is also presented, which endows the directional array with diffuse radiation properties.
This study presents a novel approach to MEMS microspeakers design aiming to tackle two main drawbacks of conventional microspeakers: their poor sound quality and their weak efficiency. For this purpose, an acoustic emissive surface based on a very light but very stiff structured silicon membrane was designed and microfabricated. This architecture, for which the membrane undesirable vibration modes were reduced to only three within the microspeaker bandwidth, is promising to let the microspeaker produce high sound quality from 300 Hz to 20 kHz. This silicon membrane is suspended by a whole set of silicon springs designed to enable out-of-plane displacements as large as 300 μm. Different geometries of springs were considered and the material maximum stress was analyzed in each case by finite element modeling. The proposed structure promises an efficiency of 10−4, that is to say ten times higher than that of conventional microspeakers.
This paper reports on a 3mm×3mm×0.003mm piezoelectric membrane acoustic device, which works as a microphone and a microspeaker. It has a 0.5μm thick zinc oxide (ZnO) piezoelectric thin film on a 1.5μm thick low-stress silicon nitride membrane, made of LPCVD. The maximum deflection in the center of membrane, using laser Doppler vibrometer (LDV), is 1μm at 7.3kHz with input drive 15V0-P (zero-peak). The output sound pressure level (SPL) of microspeaker is 76.3dB SPL at 7.3kHz, and 83.1dB SPL at 13.3kHz with input drive 15V0-P. The distance between the reference microphone and piezoelectric microspeaker is 1cm. The sensitivity of the microphone is 0.51mV/Pa at 7.3kHz with noise level of 18dB SPL.
Recent developments in Digital Loudspeakers have resulted in the introduction of Digital Transducer Arrays (DTA). In most implementations, DTA loudspeakers are driven by PCM encoded audio signals, usually resampled and requantised to an appropriate number of bits, in accordance to the number of the transducers constituting the DTA topology. However, given that DTAs generally increase harmonic distortion, especially for off-axis listening positions, optimization in signal encoding and bit-to-transducer assignment, is necessary. Here, a number of novel, alternative strategies are examined, concerning the input signal encoding via PCM-to-PWM conversion, as well as techniques for bit-assignment on the transducers of a DTA. These tests are supported by simulation results and comparisons between these alternative methods, for different operating parameters.
Digital loudspeaker arrays currently are based on small moving-coil speakers to reconstruct acoustic signals out of binary audio streams. An overview of significant performance issues for such systems is given here to explain frequency response and speaker discrete transition rates due to the digital data. Detailed simulations provided comparisons for a 32-speaker DLA with similar arrangements of speakers driven by analogue signals. These tests produce novel results for electrical power requirements and array sensitivity, concluding that these two systems achieve comparable performance.
Loudspeaker Arrays driven by digital bitstreams are direct digital-signal to acoustic transducers, usually comprising of a digital signal processing module driving actuators. Current research efforts are focusing on topologies directly driven by multi-bit digital bitstreams. In this work, the above investigations are extended to the case of using 1-bit signals such as Sigma-Delta for driving such topologies, using time and frequency domain analysis. Simulation results will be presented for idealized actuators. Finally, an optimized architecture for such a loudspeaker will be proposed, based on this analysis.
A microelectromechanical-systems (MEMS)-based electromagnetically actuated loudspeaker to reduce form factor, cost, and power consumption, and increase energy efficiency in hearing-aid applications is presented. The MEMS loudspeaker has multilayer copper coils, an NiFe soft magnet on a thin polyimide diaphragm, and an NdFeB permanent magnet on the perimeter. The coil impedance is measured at 1.5 Omega, and the resonant frequency of the diaphragm is located far from the audio frequency range. The device is driven by a power-scalable, 0.25-mum complementary metal-oxide semiconductor class-D SigmaDelta amplifier stage. The class-D amplifier is formed by a differential H-bridge driven by a single bit, pulse-density-modulated SigmaDelta bitstream at a 1.2-MHz clock rate. The fabricated MEMS loudspeaker generates more than 0.8-mum displacement, equivalent to 106-dB sound pressure level (SPL), with 0.13-mW power consumption. Driven by the SigmaDelta class-D amplifier, the MEMS loudspeaker achieves measured 65-dB total harmonic distortion (THD) with a measurement uncertainty of less than 10%. Energy-efficient and cost-effective advanced hearing aids would benefit from further miniaturization via MEMS technology. The results from this study appear very promising for developing a compact, mass-producible, low-power loudspeaker with sufficient sound generation for hearing-aid applications.
A small-signal equivalent circuit model and FEM often guide CMUT design. The small-signal model is usually derived using a combination of numerical and FEM analysis. A strictly analytical approach to CMUT design is desired because it provides design intuition and efficient numerical analysis. In this paper, we show that the mass-spring-damper model used for many MEMS structures accurately captures the behavior of a CMUT with a circular plate. We provide equations for the CMUT's equivalent mass-spring-damper parameters, pull-in point, and equivalent circuit parameters. Comparison with FEM shows that the model accurately captures the CMUT's behavior for a wide range of designs. Using this model, we can derive simple design equations, calculate the small-signal model for frequency response simulations,. and simulate the CMUT's large-signal transient behavior.
To verify the principal functionality of a digital loudspeaker the experimental construction of a digital loudspeaker was designed. This system consists of signal processing unit and transducer array. Both parts offer 8-bit precision and wide a spectrum of sampling frequencies. The signal processing unit is based on a programmable logic device which provides a flexible system for preparing a driving signal. The transducer array is formed by conventional dynamic transducers arranged in a circle. The initial measurements and listening tests provide acceptable results that are valuable for further digital loudspeaker developments.
This book contains four parts. The first one is dedicated to concepts. It starts with the definitions and examples of what is piezo-pyro and ferroelectricity by considering the symmetry of the material. Thereafter, these properties are described within the framework of Thermodynamics. The second part described the way to integrate these materials in Microsystems. The third part is dedicated to characterization: composition, structure and a special focused on electrical behaviors. The last part gives a survey of state of the art applications using integrated piezo or/and ferroelectric films.
A theoretical discussion is given of optical telephone receivers employing the optoacoustic effect, which are here called photophones, for use in an optical‐fiber telephone subscriber loop. The basic receiver consists of an absorption cell, a response‐equalizing device such as a gas column or diaphragm, a tapered acoustic tube acting as a transformer, and an earpiece similar to a conventional telephone earpiece including a response‐equalizing device. These photophones are designed to give a flat (3‐dB) response to intensity modulated light over the telephone voice band 300–3300 Hz. The optoacoustic effect is treated on the basis of a pseudogas model for solid absorbers in the form of a fine mesh disbusrsed in a gas. We find that the sensitivity (the optical power modulation required to produce a sound pressure level SPL = 81 dB in a closed volume of 6 cm3, representing the earpiece pressed against the ear) is 2.8 and 0.9 mW for the air‐filled and xenon‐filled photophones, respectively.Subject Classificati...
A 7-bit digital multiple-voice-coil loudspeaker and a constant-current driver have been constructed and evaluated. Two's complement coding offers the best compromise between complexity, excessive power consumption, and distortion due to baseline drift. The effect of motion impedance and mutual coupling in a multiple-coil system is found to magnify the effective impedance of an individual coil by its weighting in the binary representation. This effect places an unreasonable demand on the output impedance of the driver unless damping is controlled, which can be achieved most effectively by a short-circuited voice coil. Optimum damping occurs when the damping resistance is equal to the negative resistance of an individual coil.
The technique of oversampling and noise shaping has the potential to improve the resolution of digital loudspeaker systems at the expense of increasing the signal bandwidth. Previous work has shown that the acoustic radiator in a digital loudspeaker system can act as a reconstruction filter if the oversampled signal bandwidth exceeds the transducer bandwidth. If the oversampled signal is within the transducer bandwidth, the use of reconstruction filters has to be considered in the system. This paper presents an investigation of reconstruction with both pre-acoustic and post-acoustic filtering. Mathematical modeling suggests that the reconstruction in a direct digital-to-analogue loudspeaker should take place before the summation of the digital bitstreams to avoid intermodulation distortion. This is counter-intuitive because the electronic driving signals are no longer digital in the digital loudspeaker system.
Transducers with the direct D/A conversion, sometimes called digital transducers, either loudspeakers or earphones, are searching their ways into being. There have been several attempts to design such devices, but none of them left research laboratories and made its way to commercial use yet. Most of them use "classical" electroacoustic transduction principles, i.e. electrodynamic or electrostatic. In this article the possibility to use opto-acoustic transduction principle is explored. First, the principles of physical phenomena used in this transducer are revised. Then, some construction details in light of their usage in the digital earphone are described.
A bit-grouped digital transducer array loudspeaker with different numbers of nominally identical transducers for each bit has been developed. The direct digital-to-acoustic conversion process produces a sound field whose quality is shown to be spatially dependent and highly influenced by real effects including non-uniform transducer frequency responses, transducer mismatching and baffle size. Spatial sound pressure and total harmonic distortion maps show that reducing the array size leads to improved reconstruction due to reduced phase distortion. For a given sampling rate and signal frequency, total harmonic distortion decreases as the listening distance is increased. A new criterion for the sweet-spot location in digital arrays is proposed based on the difference between the distortion introduced by path-length differences and the inherent quantisation distortion.
PZT is a piezoelectric material which exhibits very good performances for microsystems actuation. In this work, the problem of sol-gel deposited PZT integration is discussed. First, state of the art of piezoelectric MEMS and PZT is presented. Then, the fabrication of homogeneous (100) and (111) oriented PZT thin films is presented. Layers thicknesses are comprised between 100 nm and 2 µm. Thirdly, ferroelectric and piezoelectric properties of the two oriented thin films are compared. For (100) oriented films, the d31 piezoelectric coefficient was greater than -150 pm/V and the e31,f reaches -16 C/m2. For (111) oriented films, the d31 and e31,f reach -100 pm/V and -14 C/m2 respectively. To explain observed differences, domain walls pinning was studied. Next, fabrication and characterization of a low voltage, fully packaged and thermally stabilized RF MEMS piezoelectric switch is presented. At the off-state, the switch isolation is -44 dB at 2 GHz. At the on-state, insertion losses are -0.74 dB at 2 GHz. The integration of a metallic gauge in a piezoelectric cantilever is also presented. Finally, developed processes are integrated in membranes fabrication without any degradation. A preliminary reliability study is presented. The fail mechanism of our components is an aging mechanism. This shows that our sol-gel deposition process is well-controlled on 8 inches wafers.
We report initial experiments on voice-band acoustic transducers (receivers) designed to accept digital (pcm) signals and directly convert the received bits into analog acoustic output. We describe experimental designs for 4, 5, and 6-bit digital receivers and for an acoustic system that functions as the desampling filter for the decoded signals. We report measurements on the frequency response, amplitude linearity, and signal-to-quantizing noise for the digital receivers and show that these quantities fall into expected design ranges. Though relatively primitive in their initial forms, the transducers accomplish direct digital conversion with acceptable fidelity and suggest a further means for minimizing per-line equipment complexity in digital voice systems.
A photophone consisting of a light guiding fiber, an absorption cell containing charred cotton suspended in air, an exponentially tapered tube, and a standard earpiece volume has been made and tested. The pressure in the earpiece versus the frequency in the 300-3300-Hz telephone band for a given optical power input agrees well with the theory of the preceding paper. We conclude that the charred cotton suspended in air can be treated simply as light-absorbing air. Measurements were also made on a photophone which included an air column equalizer to resonate with the absorption cell in order to flatten the frequency response. The high-frequency (1500–3300 Hz) response was enhanced as expected thought not quite as much as predicted.
A plasmaloudspeaker is a transducer that produces sound by means of an ionized gas channel rather than the voice coil of a conventional loudspeaker.Plasmaloudspeakers characteristically have a flat frequency response at the higher acoustic frequencies because of their ‘‘massless’’ membrane; however, their low‐frequency response is limited. In this article, a comprehensive model for the electrical and thermodynamic operation of the electrical discharge is presented that explains the frequency‐dependent behavior of the discharge’s electrical impedance and acoustic response. The characteristic acoustic frequency response is shown to result from a spatial variation of the temperature relaxation time throughout the plasma channel due to the temperature dependence of that time constant. To support the model, electrical and sound‐pressure level measurements in helium, argon, and air are presented.
A model is presented of a type of loudspeaker which operates by release of compressed air through an aperture, the area of which is made to vary with time; the air passes into a throat and then into a duct, which radiates sound from its open end. Theoretical analysis leads to simple equations describing the acoustic characteristics of the device, and a numerical example is given of their use when applied to a particular loudspeaker built at the Institute of Sound and Vibration Research in the University of Southampton. Details of the experimental work and results are presented in a companion paper.
This paper describes the theory, construction, and operation of a transducer that is capable of transmitting an analog acoustic signal when driven by a digital input signal. The digital signal drives a capacitive dielectric transducer whose active surface area is proportional to the magnitude of the digital signal. The output of the transducer contains the original digitized analog signal in addition to higher frequency Fourier components that result from the sampling process. The unwanted additional signal is attenuated by coupling the transducer output into an acoustic low-pass filter whose response is determined by using electrical circuit analysis techniques. The results indicate that the experimental transducer system is useful for generating acoustic signals that have an upper frequency limit of 8 kHz. With suitable modifications, wider frequency performance is attainable.
An electrodynamic transducer (1) for use in a loudspeaker system for converting an n-bit digitized electric signal (11) into an acoustic signal comprises n voice-coil devices (4.1, 4.2, . . . 4.n) which cooperate with a magnet system (3). The voice-coil devices each comprise a conductor whose length is the same for all the voice-coil devices. The areas of the perpendicular cross-sections of the conductors increase each time by a factor of two starting from the voice-coil device (4.n) corresponding to the least significant bit and going to voice-coil devices corresponding to consecutive more significant bits. The invention enables the transducer to be constructed in a simple manner if the transducer is a moving-coil loudspeaker or if it is a ribbon-type loudspeaker.
This work describes the development, construction, theoretical analysis and experimental evaluation of a novel type of electropneumatic sound source. The source has been specifically developed with a view to its application in active noise control systems applied in hostile environments, such as those found in the exhaust systems of gas turbines and internal combustion engines. This need arises in view of the relative fragility and large physical size of conventional loudspeakers and the high degree of non-linearity of existing electropneumatic transducers. In the new design a gas bearing is used to support the friction free motion of a sliding plate which is used to modulate the supply of compressed air. The sliding plate is driven by an electrodynamic vibrator. Experimental results demonstrate that this arrangement reduces harmonic distortion to at least 20 dB below the fundamental driving frequency for most operating conditions. In a companion paper a theoretical analysis of the transducer is presented by Chapman and Glendinning which enables predictions to be made of the acoustic volume velocity (source strength) produced by the transducer as a function of the upstream pressure and displacement of the sliding valve. The predictions of this theoretical model are found to be in good agreement with experimental results.
This paper demonstrates a low-power electromagnetic microspeaker with a PDMS membrane for hearing aids application. For a 1.76mW power input, the speaker with a 3.5mm in diameter and 3.3µm thick membrane can generate a sound with the sound pressure level (SPL) of 106dB @1kHz in a 2c.c. coupler. INTRODUCTION Low-power consumption and small form factor are two critical criteria in the development of the next generation hearing aids for long-term operation. Because the speaker component would consume at least a half of the total power in hearing aids (1), recent researches have focused on the improvement of the power-efficiency in terms of new microspeaker designs, such as the utilization of electrostatic/piezo- actuated membrane, balanced membrane design for least magnetic reluctance, Cu-Ni nanocomposite coil or Ni-coated magnetic diaphragm for electromagnetic force enhancement…etc. (1-9). In these designs, electrostatic-actuated microspeaker consumes only dynamic power (2). Though no DC power loss indicates high power efficiency, an inevitable high DC-biased voltage required for membrane actuation makes the design not suitable for the development of CMOS-based hearing aids. Piezoelectric-driven microspeaker can have a lower actuation voltage in comparison with the electrostatic one (3). ~6V operating voltage is still too high to be used for small-battery-driving based hearing aid systems. In addition, process complexity and CMOS incompatibility still make the technology difficult for the application of low-cost manufacture.
This paper presents a MEMS structure of electrodynamic loudspeakers dedicated to mobile phone applications. The major goals are to obtain a high electroacoustic conversion efficiency and a high fidelity acoustic quality. The originalities lie in a rigid silicon membrane and in its suspension by a set of silicon beams. The moving coil is a planar copper microcoil electroplated on the silicon membrane whose microstructure was optimized for providing both rigidity and lightness of the mobile part. This paper presents different magnetic structures of the motor for this MEMS loudspeaker. These structures are ironless, only made out of permanent magnets which are bonded on the substrate. They are studied and optimized thanks to analytical formulations of the magnetic field created by the permanent magnets. Results are presented for a deep RIE etched 7,5 mm radius silicon membrane structured with 40 stiffening ribs and on a 30μ m thick microcoil with 35 turns.
This paper reports on a new microspeaker actuated by a thin film PZT actuator for low voltage operation and low power consumption. The proposed microspeaker is implemented using microelectromechanical systems (MEMS) technology to reduce form factor and it is composed of flexible polyimide membrane for higher output pressure. We successfully fabricated the microspeaker and demonstrated its feasibility by measuring sound pressure level from 200 Hz to 10 kHz. The SPL (Sound Pressure Level) measured was 79 dB at 1 kHz, 87 dB at 5 kHz and 90 dB at 10 kHz respectively, with an actuation voltage of 13 V.
Biaxial flexure tests have been used extensively for the strength measurements of monolithic brittle materials. However, despite the increasing applications of multilayered structures, characterization of their strengths using biaxial flexure tests is unavailable. This is because the analytical description of the relation between the strength and the fracture load for multilayers subjected to biaxial flexure tests is nonexistent. To characterize the biaxial strength of multilayers, an analytical model is developed in the present study to derive the general closed-form solutions for the elastic stress distributions in thin multilayered disks subjected to biaxial flexure tests. To verify the analytical solutions, finite element analyses are performed on trilayered disks subjected to ring-on-ring tests. Good agreement is obtained between analytical and numerical results. The present closed-form solutions hence provide a basis for evaluating the biaxial strength of multilayered systems. Depending upon the strength of the individual layers and the stress distribution through the thickness of the multilayer during testing, cracking can initiate from any layer under tension.
The physical design of the response-equalizing components of the acoustic transformer-coupled photophone is presented. Two possible equalizers for the absorption cell—a gas column and a loaded diaphragm— are discussed; one equalizer for the earpiece, consisting of a diaphragm and screen, is also discussed. The optimization, equalization, and physical realization of a direct-coupled photophone (one not containing an exponentially tapered tube acting as an acoustic transformer) is also presented. It is found that its response is poorer than the transformer-coupled photophone by 25 dB.
Subject Classification: [43]85.86, [43]85.40, [43]85.60.
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
The radiation pattern and the position-dependent distortion in a digital transducer array loudspeaker have been investigated and simulated by computer. Harmonic distortion in the sound field is significant and varies with different transducer arrangements. The directivity increases with increasing frequency and varies with the transducer selection procedure. Randomizing the selection of transducers at each sample interval improves the directivity but introduces high-frequency noise into the radiated sound field.
A digital loudspeaker is one that does not contain any form of embedded digital-to-analog converter. From a consideration of the mathematical operations describing the digital-to-analog conversion process in a digital loudspeaker, it is concluded that the use of N identical analog filters (where N is the number of bits) filtering each bit driver separately offers a practical alternative to digital signal processing. The implementation of a multiple-driver multiple-voice-coil digital loudspeaker is described. The effect of component tolerances in the crossover and compatibility with the requirements of the current drive are evaluated. The interactions between motion emf, driving current, and mutual coupling emfs are considered. It is concluded that this method of crossover implementation is both viable and achievable.
A novel piston-type micromirror with a stroke of up to 20 µm at 20 V formed out of a silicon-on-insulator wafer with integrated piezoelectric actuators was designed, fabricated and characterized. The peak-to-valley planarity of a 2 mm diameter mirror was better than 15 nm, and tip-to-tip tilt upon actuation less than 30 nm. A resonance frequency of 9.8 kHz was measured. Analytical and finite element models were developed and compared to measurements. The design is based on a silicon-on-insulator wafer where the circular mirror is formed out of the handle silicon, thus forming a thick, highly rigid and ultra-planar mirror surface. The mirror plate is connected to a supporting frame through a membrane formed out of the device silicon layer. A piezoelectric actuator made of lead–zirconate–titanate (PZT) thin film is structured on top of the membrane, providing mirror deflection by deformation of the membrane. Two actuator designs were tested: one with a single ring and the other with a double ring providing bidirectional movement of the mirror. The fabricated mirrors were characterized by white light interferometry to determine the static and temporal response as well as mirror planarity.
The performance of a microspeaker was evaluated according to its sound pressure level (SPL). Generally, it is desirable for a microspeaker to have a constant and high SPL that covers the whole audio frequency range. A microspeaker has a relatively high and even SPL for frequencies higher than the first resonance frequency, but its performance is subpar for frequencies below that first resonance frequency. Many sound sources, including people's voices, have low frequency ranges; therefore, it is critical to improve the low-range performances of the microspeaker. This paper presents a method to improve the low-range SPL by improving the magnetic circuit structure and changing the diaphragm shape. To improve the electromagnetic force, the existing two-magnet circuit structure was changed to a one-magnet circuit structure, and the magnet volume was maximized in the process. Accordingly, the wire diameter was expanded and more coils can now be used at the same resistance. Therefore, despite the increase in the air gap, the electromagnetic force improved. In addition, the shape and material of the diaphragm were changed, and the vibration system mass was increased. Due to these changes, the first resonance frequency decreased and the low-range characteristics improved. This study analyzed this new microspeaker design through electromagnetic, mechanical and acoustic coupling relations, in addition to conducting verification through pilot product manufacture and experiments.
Conditioned spectral analysis (CSA) and virtual source analysis (VSA) are two techniques currently used nowadays to post-treat measurements on multiple input multiple output (MIMO) systems. Those techniques are based on the estimation of cross-spectral quantities between outputs and the so-called “references”. In some measurement situations, all outputs cannot be acquired simultaneously, several measurement passes are necessary (using a scanning system, a robot or a laser vibrometer). An approach is proposed in this paper to adapt CSA and VSA to MIMO systems requiring a multi-pass acquisition. The approach is based on the average over all passes of a set of reference channels, and on the correction of cross-spectral quantities by using transfer functions and averaged reference spectra. An academic experiment is finally realized to illustrate the proposed approach.
This paper is focused on a hermetically sealed cavity which can be electrostatically excited and driven as a loudspeaker. The actuation principle is based on a diaphragm that is rolling against the cavity bottom to reach both large displacements and strong electrostatic forces. The loudspeaker is primarly intended for airborne ultrasound. Test speakers have been manufactured by micromachining in silicon using anisotropic and isotropic etching, and wafer bonding. Experiment shows an acoustic output of 112 dB in sound pressure level at the resonance frequency of 127 kHz, measured at a distance of 10 mm with 50 V peak-to-peak in applied driving voltage. An empirical Q-value of 7 is found. Measurements indicate that the resonance frequency of the loudspeaker can be tuned with an applied biasing voltage.
Flexible electronics covers a wide spectrum of applications including flexible display, flexible solar cell, printed RFID, flexible lighting and others. Currently, it has been estimated that there are about 1500 worldwide research units working on various aspects of flexible electronics. Market analysis estimates the revenue of flexible electronics can reach 30 billion USD in 2017 and over 300 billion USD in 2028. Region-wise, the research activities in Europe cover a wide range of topics - from materials, process, to system and applications. In the US, research is primarily driven by military applications. Asian companies invest heavily in flexible display. Based on the potential product categories, flexible display is expected to have 40% of the market share in 2019 and e-paper is a major product therein. Flexible photovoltaic will have about 30% market share. Both the above product categories are based on existing industrial infrastructure, e.g. the FPD and PV industry. The market share of printed RFID will shrink to only 10%~15%, much lower than four-year ago's optimistic estimation. Flexible lighting's share will be about 10%, whereas the major part will be OLED lighting in which research centers and companies in Europe and Japan have heavily invested. The remaining part, about 10%~15%, will be on sensors and batteries which are quite important for enabling new business. Examples in this category include large area flexible speaker, printed battery, etc. Based on the core technologies of flexible modules, ITR?s R&D strategy focuses on the integration of system and application capabilities to quickly demonstrate feasible products and scenarios. One of the examples, a paper-thin speaker has won 2009 Technology Innovation Award of Wall Street Journal in the consumer electronics category and also won the best of best Red dot design. The thickness of the speaker can be made under 1mm with a wide sound spectrum and high sound quality. Owing to its ultra thin f- - eature, we integrated this new sound module into ceiling audio, automobile and 3C products, which creates a highly differentiated market segment from the traditional speaker market. Due to the immaturity of flexible electronics industry, venture capital has been approached to support commercialization in the early product stages. ITRI has designed a "virtual venture" mechanism which helps technical teams create new business. Although it is not yet mature, it has been expanding rapidly and dynamically. The keys to success include grasping the tempo, building up a complete value chain, and attracting the necessary entities to join the efforts and cooperate.
We found that very thin carbon nanotube films, once fed by sound frequency electric currents, could emit loud sounds. This phenomenon could be attributed to a thermoacoustic effect. The ultra small heat capacity per unit area of carbon nanotube thin films leads to a wide frequency response range and a high sound pressure level. On the basis of this finding, we made practical carbon nanotube thin film loudspeakers, which possess the merits of nanometer thickness and are transparent, flexible, stretchable, and magnet-free. Such a single-element thin film loudspeaker can be tailored into any shape and size, freestanding or on any insulating surfaces, which could open up new applications of and approaches to manufacturing loudspeakers and other acoustic devices.
In this paper, an electrodynamic planar loudspeaker driven by a digital signal is experimentally discussed. The digital loudspeaker consists of 22 voice coils, 11 permanent magnets, a diaphragm with streamlined sections molded in plastic, and a suspension made of handmade Japanese paper between the diaphragm and the frame. First, the acoustic responses are affected by the arrangement of the voice coils, so an asymmetric arrangement is studied. This asymmetric arrangement is designed to obtain as flat a frequency response to an analog signal as possible. This arrangement is compared with a symmetric one and results show that the flatness of the frequency response around 1 kHz and 4 kHz is improved and that the sound reproduction band is from 40 Hz to 10 kHz. Second, to evaluate the acoustic responses to a digital signal, the digital loudspeaker is driven with a pulse code modulation signal. Results show that the digital loudspeaker can reproduce pure sound with a total harmonic distortion of less than 5% from 40 Hz to 10 kHz, exceeding this value only in a narrow frequency band near 4 kHz. This digital loudspeaker was demonstrated to have good linearity over its dynamic range of 84 dB.