A Tunable Electrostatic MEMS Pressure Switch Pallay, Mark; Miles, Ronald N.; Towfighian, Shahrzad
IEEE transactions on industrial electronics,
11/2020, Letnik:
67, Številka:
11
Journal Article
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In this article, we demonstrate a tunable air pressure switch. The switch detects when the ambient pressure drops below a threshold value and automatically triggers without the need for any ...computational overhead to read the pressure or trigger the switch. The switch exploits the significant fluid interaction of a microelectro-mechanical systems beam undergoing a large oscillation from electrostatic levitation to detect changes in ambient pressure. If the oscillation amplitude near the resonant frequency is above a threshold level, dynamic pull-in is triggered and the switch is closed. The pressure at which the switch closes can be tuned by adjusting the voltage applied to the switch. The use of electrostatic levitation allows the device to be released from their pulled-in position and reused many times without mechanical failure. A theoretical model is derived and validated with experimental data. It is experimentally demonstrated that the pressure switching mechanism is feasible.
Sensing fluctuating airflow with spider silk Zhou, Jian; Miles, Ronald N.
Proceedings of the National Academy of Sciences - PNAS,
11/2017, Letnik:
114, Številka:
46
Journal Article
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The ultimate aim of flow sensing is to represent the perturbations of the medium perfectly. Hundreds of millions of years of evolution resulted in hair-based flow sensors in terrestrial arthropods ...that stand out among the most sensitive biological sensors known, even better than photoreceptors which can detect a single photon (10−18–10−19 J) of visible light. These tiny sensory hairs can move with a velocity close to that of the surrounding air at frequencies near their mechanical resonance, despite the low viscosity and low density of air. No man-made technology to date demonstrates comparable efficiency. Here we show that nanodimensional spider silk captures fluctuating airflow with maximum physical efficiency (Vsilk/Vair ∼ 1) from 1 Hz to 50 kHz, providing an effective means for miniaturized flow sensing. Our mathematical model shows excellent agreement with experimental results for silk with various diameters: 500 nm, 1.6 μm, and 3 μm. When a fiber is sufficiently thin, it can move with the medium flow perfectly due to the domination of forces applied to it by the medium over those associated with its mechanical properties. These results suggest that the aerodynamic property of silk can provide an airborne acoustic signal to a spider directly, in addition to the wellknown substrate-borne information. By modifying a spider silk to be conductive and transducing its motion using electromagnetic induction, we demonstrate a miniature, directional, broadband, passive, low-cost approach to detect airflow with full fidelity over a frequency bandwidth that easily spans the full range of human hearing, as well as that of many other mammals.
•A MEMS filter can function using electrostatic levitation for sensing and actuating.•The filter can withstand very high voltages without becoming unstable.•A high voltage boosts signal-to-noise ...ratio without hindering mechanical response.•The large actuating voltage improves the mechanical performance of the filter.
Traditional MEMS filters use a comb drive structure that suffers from the pull-in instability, which places a significant limitation on the achievable signal-to-noise ratio of the sensor. Because the output signal from a capacitive sensor is linearly related to the applied voltage, it is desirable to use a capacitive sensor that can withstand large voltages upwards of 100 V. However, the pull-in instability causes high voltages to destroy the device and a trade-off between performance and reliability must be made. Electrostatic levitation, which works by pulling electrodes apart instead of together, eliminates the pull-in instability and allows for very high voltages to be applied without damaging or destroying the sensor/actuator. This study theoretically and experimentally demonstrates that a filter based on electrostatic levitation eliminates the voltage limitation of the capacitive sensor, which has historically hampered the performance of the filter. A model of the filter is derived and validated with experimental data. Voltages up to 100 V are applied without damaging the filter.
Mating behavior in Aedes aegypti mosquitoes occurs mid-air and involves the exchange of auditory signals at close range (millimeters to centimeters) 1–6. It is widely assumed that this intimate ...signaling distance reflects short-range auditory sensitivity of their antennal hearing organs to faint flight tones 7, 8. To the contrary, we show here that male mosquitoes can hear the female’s flight tone at surprisingly long distances—from several meters to up to 10 m—and that unrestrained, resting Ae. aegypti males leap off their perches and take flight when they hear female flight tones. Moreover, auditory sensitivity tests of Ae. aegypti’s hearing organ, made from neurophysiological recordings of the auditory nerve in response to pure-tone stimuli played from a loudspeaker, support the behavioral experiments. This demonstration of long-range hearing in mosquitoes overturns the common assumption that the thread-like antennal hearing organs of tiny insects are strictly close-range ears. The effective range of a hearing organ depends ultimately on its sensitivity 9–13. Here, a mosquito’s antennal ear is shown to be sensitive to sound levels down to 31 dB sound pressure level (SPL), translating to air particle velocity at nanometer dimensions. We note that the peak of energy of the first formant of the vowels of the human speech spectrum range from about 200–1,000 Hz and is typically spoken at 45–70 dB SPL; together, they lie in the sweet spot of mosquito hearing.
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•The mosquito Aedes aegypti hears sound over surprisingly long distances•Behavioral and physiological experiments confirm a range of audibility up to 10 m•Ae. aegypti is sensitive to sound frequencies of 150–500 Hz•The vowel sounds of human speech contain energy at 150–500 Hz
Previous behavioral work shows that mosquitos hear sounds just a few centimeters away. Menda et al.’s behavioral and physiological experiments show that Aedes aegypti mosquitos can hear up to 10 m away. Notably, the vowel sounds of human speech contain frequencies that are spoken at levels which, in principle, are audible to mosquitos.
In this study, we examine the feasibility of designing a MEMS microphone employing a levitation based electrode configuration. This electrode scheme enables capacitive MEMS sensors that could work ...for large bias voltages without pull-in failure. Our experiments and simulations indicate that it is possible to create robust sensors properly working at high DC voltages, which is not feasible for most of the conventional parallel plate electrode-based micro-scale devices. In addition, the use of larger bias voltages will improve signal-to-noise ratios in MEMS sensors because it increases the signal relative to the noise in read-out circuits. This study presents the design, fabrication, and testing of a capacitive microphone, which is made of approximately <inline-formula> <tex-math notation="LaTeX">2~\mu \text{m} </tex-math></inline-formula> thick highly-doped polysilicon as a diaphragm. It has approximately <inline-formula> <tex-math notation="LaTeX">1~\textit {mm}^{2} </tex-math></inline-formula> surface area and incorporates interdigitated sensing electrodes on three of its sides. Right underneath these moving electrodes, there are fixed fingers being held at the same voltage potential as the moving electrodes and separated from them with a <inline-formula> <tex-math notation="LaTeX">2~\mu \text{m} </tex-math></inline-formula> thick air gap. The electronic output is obtained using a charge amplifier. Measured results obtained on three different microphone chips using bias voltages up to 200 volts indicate that pull-in failure is completely avoided. The sensitivity of this initial design was measured to be 16.1 mV/Pa at 200 V bias voltage, and the bandwidth was from 100 Hz to 4.9 kHz.
In this study, the feasibility of obtaining electrical read-out data from a capacitive MEMS accelerometer that employs repulsive electrode configuration is demonstrated. This configuration allows for ...large-stroke vibrations of microstructures without suffering from pull-in failure that exists in conventional accelerometers based on the parallel-plate configuration. With initial fabrication gap of <inline-formula> <tex-math notation="LaTeX">2.75 \mu {m} </tex-math></inline-formula>, the accelerometer can reach a <inline-formula> <tex-math notation="LaTeX">4.2 \mu {m} </tex-math></inline-formula> dynamical displacement amplitude. The accelerometer is tested up to <inline-formula> <tex-math notation="LaTeX">95 ({V}) </tex-math></inline-formula> without exhibiting pull-in failure. For comparison, the pull-in voltage of an accelerometer with same dimensions but with conventional parallel-plate electrode configuration is <inline-formula> <tex-math notation="LaTeX">\textit {0.8} ({V}) </tex-math></inline-formula>. The MEMS device is fabricated using the POLYMUMPs fabrication standard. An electrical circuit is built to measure the capacitance change due to motion of the accelerometer proof-mass. The accelerometer has a mechanical sensitivity of <inline-formula> <tex-math notation="LaTeX">35 \frac {\textit {nm}}{g} </tex-math></inline-formula> and electrical sensitivity of <inline-formula> <tex-math notation="LaTeX">5.3 \frac {\textit {mV}}{g} </tex-math></inline-formula>. The ability to use large bias voltages without the typical adverse effects on the stability of the moving electrode will enable the design of capacitive MEMS accelerometers with enhanced resolution and tunable frequency range.
A study is presented of a dynamic capacitive sensor configuration that is intended to impose minimal force and resistance to motion on the moving electrode. The aim is to enable the use of moving ...electrodes having arbitrary levels of compliance without suffering the adverse effects of large bias voltages such as pull-in instability. This configuration would facilitate the incorporation of highly compliant and thin electrode materials that present the least possible resistance to motion. This type of material is particularly useful for sensing sound. Measured results show that for the highly compliant acoustic sensor design examined here, a large bias voltage of 400 volts can be applied without influencing its motion. The electrical sensitivity to sound is found to be approximately 0.5 V/pascal, two orders of magnitude greater than typical acoustic sensors.
The design of repulsive electrostatic actuators having enlarged travel range is achieved by combining the boundary element approach and a genetic algorithm. The boundary element method enables ...calculating the electrostatic forces without time consuming finite element simulations. Once a static equation that uses a model of effective lumped mass solves the travel ranges, the GA maximizes travel ranges by optimizing the dimensional parameters. The effectiveness of the scheme is demonstrated with extensive experimental results showing the travel ranges of a micro out-of-plane actuator are increased by up to 190%. The developed platform can improve the signal-to-noise ratios and the performance of general multi-electrode systems.
Jumping spiders (Salticidae) are famous for their visually driven behaviors 1. Here, however, we present behavioral and neurophysiological evidence that these animals also perceive and respond to ...airborne acoustic stimuli, even when the distance between the animal and the sound source is relatively large (∼3 m) and with stimulus amplitudes at the position of the spider of ∼65 dB sound pressure level (SPL). Behavioral experiments with the jumping spider Phidippus audax reveal that these animals respond to low-frequency sounds (80 Hz; 65 dB SPL) by freezing—a common anti-predatory behavior characteristic of an acoustic startle response. Neurophysiological recordings from auditory-sensitive neural units in the brains of these jumping spiders showed responses to low-frequency tones (80 Hz at ∼65 dB SPL)—recordings that also represent the first record of acoustically responsive neural units in the jumping spider brain. Responses persisted even when the distances between spider and stimulus source exceeded 3 m and under anechoic conditions. Thus, these spiders appear able to detect airborne sound at distances in the acoustic far-field region, beyond the near-field range often thought to bound acoustic perception in arthropods that lack tympanic ears (e.g., spiders) 2. Furthermore, direct mechanical stimulation of hairs on the patella of the foreleg was sufficient to generate responses in neural units that also responded to airborne acoustic stimuli—evidence that these hairs likely play a role in the detection of acoustic cues. We suggest that these auditory responses enable the detection of predators and facilitate an acoustic startle response.
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•We present evidence that jumping spiders, famously visual, perceive airborne sounds•Spiders responded to low 80 Hz tones by freezing—an acoustic startle response•Neural recordings revealed units in the brain that respond to airborne acoustic cues•Neural responses to 80–380 Hz (∼65 dB SPL) persisted at far-field distances (>3 m)
Jumping spiders are renowned visual specialists. Here, Shamble et al. provide evidence that they also respond to airborne acoustic cues. Behaviorally, stimuli caused spiders to freeze, while neural responses to stimuli of ∼65 dB SPL persisted even at ranges of 3 m, well beyond what has been previously reported in similar systems.
SignificanceThe sense of hearing in all known animals relies on possessing auditory organs that are made up of cellular tissues and constrained by body sizes. We show that hearing in the orb-weaving ...spider is functionally outsourced to its extended phenotype, the proteinaceous self-manufactured web, and hence processes behavioral controllability. This finding opens new perspectives on animal extended cognition and hearing-the outsourcing and supersizing of auditory function in spiders. This study calls for reinvestigation of the remarkable evolutionary ecology and sensory ecology in spiders-one of the oldest land animals. The sensory modality of outsourced hearing provides a unique model for studying extended and regenerative sensing and presents new design features for inspiring novel acoustic flow detectors.
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