Micromachined in-plane acoustic pressure gradient sensors

textThis work presents the fabrication, modeling, and characterization of two first-generation acoustic in-plane pressure gradient sensors. The first is a micromachined piezoelectric microphone. The microphone structure consists of a semi-rigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The rotation of the beam structure is transduced by piezoelectric cantilevers, which deflect when the beam structure rotates. Sensors with both 10 and 20-μm-thick beam structures are presented. An analytical model and multi-mode, multi-port network model utilizing finite-element analysis for parameter extraction are presented and compared to acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multi-mode model. A noise model for the sensor and readout electronics is presented and compared to measurements. The second sensor is a capacitive sensor which is comprised of two vacuum-sealed, pistons coupled to each other by a pivoting beam. The use of a pivoting beam can, in principle, enable high rotational compliance to in-plane small-signal acoustic pressure gradients, while resisting piston collapse against large background atmospheric pressure. A design path towards vacuum-sealed, surface micromachined broadband microphones is a motivation to explore the sensor concept. Fabrication of surface micromachined prototypes is presented, followed by finite element modeling and experimental confirmation of successful vacuum-sealing. Dynamic frequency response measurements are obtained using broadband electrostatic actuation and confirm a first fundamental rocking mode near 250 kHz. Successful reception of airborne ultrasound in air at 130 kHz is also demonstrated, and followed by a discussion of design paths toward improve signal-to-noise ratio beyond that of the initial prototypes presented. A method of localizing sound sources is demonstrated using the piezoelectric sensor. The localization method utilizes the multiple-port nature of the sensor to simultaneously extract the pressure gradient and pressure magnitude components of the incoming acoustic signal. An algorithm for calculating the sound source location from the pressure gradient and pressure magnitude measurement is developed. The method is verified by acoustic measurements performed at 2 kHz.Electrical and Computer Engineerin

CHARACTERIZATION OF BIO-INSPIRED MEMS UNDERWATER ACOUSTIC SENSOR USING A STANDING WAVE TUBE

NPS has developed MEMS-based underwater sensors based on the auditory structure of the fly Ormia ochracea. The sensor produces an output signal based on sound interacting with two mechanically coupled wings attached to a substrate using two torsional legs. The MEMS sensor operates at a resonance frequency determined by the geometrical structure. This thesis discusses the characterization of a water-filled standing wave tube, which is a device that is commonly used to characteristic directional acoustic sensors. The standing wave tube generates a plane wave along its axis and provides a convenient way to characterize the directional response of MEMS sensors for underwater applications. Two MEMS sensors were tested with simulated resonance frequencies of 450 Hz and 640 Hz, respectively. The MEMS sensors operate similarly to pressure-gradient microphone and are expected to exhibit an output signal dependent on the cosine of the incidence angle of sound. Both sensitivity and directionality measurements were taken in the standing wave tube using an underwater omnidirectional loudspeaker as a sound source. This research shows the standing wave tube is a viable testing device for MEMS sensor characterization, and the NPS-designed MEMS sensors for underwater applications clearly demonstrated characteristics of a directional acoustic sensor.Lieutenant, United States NavyApproved for public release; distribution is unlimited

Interface Circuits for Microsensor Integrated Systems

ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Recent advances in sensing technologies, especially those for Microsensor Integrated Systems, have led to several new commercial applications. Among these, low voltage and low power circuit architectures have gained growing attention, being suitable for portable long battery life devices. The aim is to improve the performances of actual interface circuits and systems, both in terms of voltage mode and current mode, in order to overcome the potential problems due to technology scaling and different technology integrations. Related problems, especially those concerning parasitics, lead to a severe interface design attention, especially concerning the analog front-end and novel and smart architecture must be explored and tested, both at simulation and prototype level. Moreover, the growing demand for autonomous systems gets even harder the interface design due to the need of energy-aware cost-effective circuit interfaces integrating, where possible, energy harvesting solutions. The objective of this Special Issue is to explore the potential solutions to overcome actual limitations in sensor interface circuits and systems, especially those for low voltage and low power Microsensor Integrated Systems. The present Special Issue aims to present and highlight the advances and the latest novel and emergent results on this topic, showing best practices, implementations and applications. The Guest Editors invite to submit original research contributions dealing with sensor interfacing related to this specific topic. Additionally, application oriented and review papers are encouraged.

Nonlinear mechanics and nonlinear material properties in micromechanical resonators

Microelectromechanical Systems are ubiquitous in modern technology, with applications ranging from accelerometers in smartphones to ultra-high precision motion stages used for atomically-precise positioning. With the appropriate selection of materials and device design, MEMS resonators with ultra-high quality factors can be fabricated at minimal cost. As the sizes of such resonators decrease, however, their mechanical, electrical, and material properties can no longer be treated as linear, as can be done for larger-scale devices. Unfortunately, adding nonlinear effects to a system changes its dynamics from exactly-solvable to only solvable in specific cases, if at all. Despite (and because of) these added complications, nonlinear effects open up an entirely new world of behaviors that can be measured or taken advantage of to create even more advanced technologies. In our resonators, oscillations are induced and measured using aluminum nitride transducers. I used this mechanism for several separate highly-sensitive experiments. In the first, I demonstrate the incredible sensitivity of these resonators by actuating a mechanical resonant mode using only the force generated by the radiation pressure of a laser at room temperature. In the following three experiments, which use similar mechanisms, I demonstrate information transfer and force measurements by taking advantage of the nonlinear behavior of the resonators. When nonlinear resonators are strongly driven, they exhibit sum and difference frequency generation, in which a large carrier signal can be mixed with a much smaller modulation to produce signals at sum and difference frequencies of the two signals. These sum and difference signals are used to detect information encoded in the modulation signal using optical radiation pressure and acoustic pressure waves. Finally, in my experiments, I probe the nonlinear nature of the piezoelectric material rather than take advantage of the nonlinear resonator behavior. The relative sizes of the linear and nonlinear portions of the piezoelectric constant can be determined because the force applied to the resonator by a transducer is independent of the dielectric constant. This method allowed me to quantify the nonlinear constants

ULTRASONIC IMAGING AND TACTILE SENSING FOR ROBOTIC SYSTEMS

This research develops several novel algorithms that enhance the operation of ultrasonic and tactile sensors for robotic applications. The emphasis is on reducing the overall cost, system complexity, and enabling operation on resource-constrained embedded devices with the main focus on ultrasonics. The research improves key performance characteristics of pulse-echo sensor systems -- the minimum range, range resolution, and multi-object localization. The former two aspects are improved through the application of model-based and model-free techniques. Time optimal principles precisely control the oscillations of transmitting and receiving ultrasonic transducers, influencing the shape of the pressure waves. The model-free approach develops simple learning procedures to manipulate transducer oscillations, resulting in algorithms that are insensitive to parameter variations. Multi-object localization is achieved through phased array techniques that determine the positions of reflectors in 3-D space using a receiver array consisting of a small number of elements. The array design and the processing algorithm allow simultaneous determination of the reflector positions, achieving high sensor throughputs. Tactile sensing is a minor focus of this research that leverages machine learning in combination with an exploratory procedure to estimate the unknown stiffness of a grasped object. Gripper mechanisms with full-actuation and under-actuation are studied, and the object stiffness is estimated using regression. Sensor measurements use actuator position and current as the inputs. Regressor design, dataset generation, and the estimation performance under nonlinear effects, such as dry friction, parameter variations, and under-actuated transmission mechanisms are addressed.Ph.D

Ultra-high-speed imaging of bubbles interacting with cells and tissue

Ultrasound contrast microbubbles are exploited in molecular imaging, where bubbles are directed to target cells and where their high-scattering cross section to ultrasound allows for the detection of pathologies at a molecular level. In therapeutic applications vibrating bubbles close to cells may alter the permeability of cell membranes, and these systems are therefore highly interesting for drug and gene delivery applications using ultrasound. In a more extreme regime bubbles are driven through shock waves to sonoporate or kill cells through intense stresses or jets following inertial bubble collapse. Here, we elucidate some of the underlying mechanisms using the 25-Mfps camera Brandaris128, resolving the bubble dynamics and its interactions with cells. We quantify acoustic microstreaming around oscillating bubbles close to rigid walls and evaluate the shear stresses on nonadherent cells. In a study on the fluid dynamical interaction of cavitation bubbles with adherent cells, we find that the nonspherical collapse of bubbles is responsible for cell detachment. We also visualized the dynamics of vibrating microbubbles in contact with endothelial cells followed by fluorescent imaging of the transport of propidium iodide, used as a membrane integrity probe, into these cells showing a direct correlation between cell deformation and cell membrane permeability

Capacitive ultrasonic transducers fabricated using microstereolithography

Air-coupled thin-membrane capacitive ultrasonic transducers have been developed that use microstereolithography fabrication with architectures comprised entirely of partially metalised photopolymer. These devices derive considerable advantages from rapid prototyping technology, in that they are cheap to produce, and benefit from the design-to-product lead times inherent in the production of components using stereolithography. To date membranes have been produced with thicknesses ranging from 30 to 90 μm with aspect ratios in the range of 100 - 1000. These devices have been shown to operate both as transmitters and as receivers of ultrasound, and have a bandwidth approaching 100% with a centre frequency of 100 kHz. The method of fabricating these devices allows for easy modification for various applications including structural health monitoring and immersion, as well as affording the possibility of integrated focussing or wave-guiding architecture and packaging that can be incorporated into a single build. Fundamental or subtle changes to a given transducer design may be achieved incurring little additional cost or time. This novel approach to transducer fabrication enables the bespoke manufacture of specific transducer architectures from a computer aided design package using polymers that exhibit different material properties to materials used in silicon micromachining, but at the same time allow for fabrication on a scale that is approaching that of microfabrication. The versatility of 3-D rapid prototyping allows the realisation of more complicated structures than was possible previously. This work examines these transducers in terms of their characterisation and their operation in conjunction with other transduction architecture, such as focussing parabolic mirrors that were also produced using the same manufacturing technology. In addition, their operation in contacting acoustics and the reception of surface acoustic waves has been demonstrated. Immersion studies using these devices have found that that they hold promise for operation in a variety of different media. These transducers are seen as an important prototype development tool in the field of capacitive ultrasonic transduction and microphone-speaker design