Quang Su

Characterization of the performance of capacitive switches activated by mechanical shock

This paper presents experimental and theoretical investigation of a new concept of switches (triggers) that are actuated at or beyond a specific level of mechanical shock or acceleration. The principle of operation of the switches is based on dynamic pull-in instability induced by the combined interaction between electrostatic and mechanical shock forces. These switches can be tuned to be activated at various shock and acceleration thresholds by adjusting the DC voltage bias. Two commercial off-the-shelf capacitive accelerometers operating in air are tested under mechanical shock and electrostatic loading. A single-degree-of-freedom model accounting for squeeze-film damping, electrostatic forces, and mechanical shock is utilized for the theoretical investigation. Good agreement is found between simulation results and experimental data. Our results indicate that designing these new switches to respond quasi-statically to mechanical shock makes them robust against variations in shock shape and duration. More importantly, quasi-static operation makes the switches insensitive to variations in damping conditions. This can be promising to lower the cost of packaging for these switches since they can operate in atmospheric pressure with no hermetic sealing or costly package required.

Response of a biologically inspired MEMS differential microphone diaphragm

The development of a novel, biologically inspired acoustic sensor is presented. The primary goal of this effort is to construct a miniature device that is capable of detecting the orientation of an incident sound source with an accuracy of 2°. The design approach follows from our investigation of the mechanics of directional hearing in the parasitoid fly, Ormia ochracea. This animal has been shown to be able to detect changes in the line of bearing of an incident sound that are as small as 2°. The tympanal structures of the ears of this animal suggest a novel approach to designing very small directionally sensitive microphones. A microphone diaphragm design is presented that has been fabricated using silicon microfabrication technology. Measurements of the static deflection due to intrinsic stress and of the response to sound are shown to be in excellent agreement with predictions. Predicted results indicate that this microphone concept could lead to a practical differential microphone with self-noise as low as 20 dBA.

Development of novel biologically inspired directional microphones

The development of novel directional microphones for hearing aids is described. The mechanisms underlying the design of these unusual microphones were inspired by our earlier study of the ears of the parasitoid fly Ormia ochracea [Miles, et al., J. Acoust. Soc. Am. 98, 3059–3070 (1995)]. The structure of Ormia’s ears inspired new approaches to the design of directional microphones that have the potential to be more sensitive and have lower thermal noise than typical miniature microphones. The mechanisms for directional hearing in this animal are discussed along with the engineering design concepts that they have inspired. Microphones have been fabricated out of silicon that employ either capacitive sensing or optical sensing to convert the diaphragm motion into an electronic signal. Measured results indicate that the directivity of these microphones is very similar to that of an ideal first‐order differential microphone. In addition, novel microphone diaphragms have been fabricated that posses a second‐or...

Beamforming with collocated microphone arrays

A collocated microphone array, including three gradient microphones with different orientations and one omnidirectional microphone, was used to acquire data in a sound‐treated room and in an outdoor environment. This arrangement of gradient microphones represents an acoustic vector sensor used in air. Beamforming techniques traditionally associated with much larger uniformly spaced arrays of omnidirectional sensors are extended to this compact array (1 cm3) with encouraging results. A frequency–domain minimum‐variance beamformer was developed to work with this array. After a calibration of the array, the recovery of sources from any direction is achieved with high fidelity, even in the presence of multiple interferers. SNR gains of 5–12 dB with up to four speech sources were obtained with both indoor and outdoor recordings. This algorithm has been developed for new MEMS‐type microphones that further reduce the size of the sensor array.

Biomimetic direction-sensitive micromachined diaphragm for ultrasonic transducers

This paper presents a novel biomimetic direction-sensitive micromachined diaphragm for ultrasonic transducers. The diaphragm design is based on the mechanical model of the parasitoid fly, Ormia ochraceas ears which achieve directionality through mechanical coupling of the tympanas resonant mode shapes. Micromachining technology has been utilized to fabricate the 3D structured biomimetic diaphragm. It has two 60/spl times/120/spl times/20 /spl mu/m/sup 3/ single crystal silicon (SCS) proof masses and solid stiffeners attached to a 0.8-/spl mu/m-thick silicon nitride diaphragm to create the main resonant mode shapes like the flys ears. Acoustic measurements of the diaphragm using laser vibrometry have demonstrated high directional sensitivity of the device.

Magnetoelastic beam with extended polymer for low frequency vibration energy harvesting

Ambient energy in the form of mechanical kinetic energy is mostly considered waste energy. The process of scavenging and storing such energy is known as energy harvesting. Energy harvesting from mechanical vibration is performed using resonant energy harvesters (EH) with two major goals: enhancing the power scavenged at low frequency sources of vibrations, and increasing the efficiency of scavenging energy by increasing the bandwidth near the resonant frequency. Toward such goals, we propose a piezoelectric EH of a composite cantilever beam with a tip magnet facing another magnet at a distance. The composite cantilever consists of a piezoelectric bimorph with an extended polymer material. With the effect of the nonlinearity of the magnetic force, higher amplitude can be achieved because of the generated bi-stability oscillations of the cantilever beam under harmonic excitation. The contribution of the this paper is to demonstrate lowering the achieved resonant frequency down to 17 Hz compared to 100 Hz for the piezoelectric bimorph beam without the extended polymer. Depending on the magnetic distance, the beam responses are divided to mono and bi-stable regions, for which we investigate static and dynamic behaviors. The dynamics of the system and the frequency and voltage responses of the beam are obtained using the shooting method.

Experimental and Theoretical Investigation of New Capacitive Switches Activated by Mechanical Shock and Acceleration

This paper presents experimental and theoretical investigation into the characteristics and performance of a new class of switches (triggers) actuated at or beyond a specific level of mechanical shock or acceleration. The principle of operation of the switches is based on dynamic pull-in instability induced by the combined interaction between electrostatic and mechanical shock forces. Two commercial off-the-shelf capacitive accelerometers operating in air are tested under mechanical shock and electrostatic loading. A single-degree-of-freedom model accounting for squeeze-film damping, electrostatic forces, and mechanical shock is utilized for the theoretical investigation. Good agreement is found between the simulation results and experimental data. Our results indicate that designing these new switches to respond quasi-statically to mechanical shock makes them robust against variations in shock shape and duration. More importantly, this makes the switches insensitive to variations in damping conditions. This can be promising to lower the cost of packaging for these switches since they can operate in atmospheric pressure with no hermetic sealing or costly package required.Copyright

Sound source localization with a gradient array using a coherence test

The localization of sound sources is difficult when the number of sources is greater than the number of sensors. An algorithm is described that can localize in such acoustic scenes by utilizing a statistical coherence test to identify desirable time–frequency bins where the MUSIC and minimum‐variance spectral estimators are applied. Localization results are then obtained by integrating across the selected time–frequency bins. The algorithm was used to localize signals in azimuth and elevation from a co‐located microphone array consisting of one omnidirectional microphone and three gradient microphones. With 2.5 seconds of five speech sources, the azimuth and elevation estimates produced by the algorithm, over a hundred realizations of additive white Gaussian noise, had biases under four degrees and standard deviations less than two degrees. The algorithm was also used to compare the localization performance, in azimuth, of an array of two co‐located gradient microphones with an array of two 15‐cm‐spaced o...

A silicon nitride microphone diaphragm inspired by the ears of the parasitoid fly Ormia ochracea

A differential microphone is described that has been designed to employ similar operating principles to that of the ears of the parasitoid fly, Ormia ochracea. The ears of this fly have been shown to be highly directional even though they are only about 1 mm across [R. N. Miles, D. Robert, and R. R. Hoy, J. Acoust. Soc. Am. 98, 3059–3070 (1995)]. Analyses of the mechanics of this biological system suggest novel approaches to the design of miniature directional microphones. Finite element analysis results for the acoustic resonse of a 1 mm by 2 mm silicon nitride microphone diaphragm are presented. The diaphragm responds to pressure gradients in a manner that is inspired by Ormia’s ears. Predicted results for the natural frequencies, mode shapes, frequency response and directivity of our design are shown to compare closely with measured data obtained for a prototype silicon nitride diaphragm. [Work supported by NIH and DARPA.]

A biologically inspired silicon differential microphone with active Q control and optical sensing

A MEMS differential microphone is described in which the diaphragm design is inspired by the mechanics of directional hearing in the fly Ormia ochracea. The 1 mm by 3 mm diaphragm is designed to rotate about a central pivot in response to sound pressure gradients. The diaphragm is designed to have its dominant resonance mode within the audible frequency range and to have as little viscous damping as possible (to minimize the effects of thermal noise). The motion of the diaphragm is detected using an optical sensing scheme that includes a semiconductor laser (VCSEL), photodetectors, a mirror, and a diffraction grating. To minimize the adverse effects of the light damping on the response, an active feedback system is implemented to achieve active Q control. This uses the output of the optical detection scheme to drive the diaphragm through a capacitive actuator. The microphone and optoelectronics are packaged into an assembly that can be incorporated into a mock behind-the-ear hearing aid. The microphone is...