Experimental Study of Cochlear Dynamics With an Intracochlear Acoustic Micro-Actuator

An intracochlear lead-zirconate-titanate (PZT) micro-actuator can complement a cochlear implant electrode array to rehabilitate hearing loss patients with enhanced speech recognition. The presence of the intracochlear micro-actuator has significantly altered the cochlear dynamics, because the actuation now results from the micro-actuator instead of the stapes. To understand sound induction mechanisms by the micro-actuator, we design a test rig that mimics the box model of a human cochlea. The test rig consists of two connected fluid canals, one aluminum membrane sandwiched between the canals, and a PZT thin-film micro-actuator. Frequency response functions of the micro-actuator and the aluminum membrane are measured using a laser Doppler vibrometer and a spectrum analyzer. Measurements are taken when the micro-actuator is in air, in a petri dish surrounded by oil, and in the fluid canals inside the test rig. When the micro-actuator is moved from the petri dish (i.e., an open environment) to the inside of the fluid canals (i.e., a closed environment), the natural frequency and static gain of the micro-actuator both drop significantly indicating substantial increase in stiffness and inertia. A possible reason for the change, which remains to be confirmed, is the squeeze film effect from the fluid between the micro-actuator and the aluminum membrane.

An Analytical Model for Bandwidth Enhancement of Air-Coupled Unsealed Helmholtz Structural CMUTs

Capacitive micromachined ultrasonic transducers (CMUTs) were reported to own high potential in air-coupled ultrasonic applications such as noncontact nondestructive examination and gas flow measurement. The unsealed CMUTs which utilized the squeeze film effect were reported to overcome the narrow output pressure bandwidth of the conventional sealed CMUTs in air operation. This kind of unsealed CMUTs can also be regarded as Helmholtz resonators. In this work, we present the air-coupled unsealed Helmholtz structural CMUTs which utilize both the squeeze film effect and the Helmholtz resonant effect to enhance the output pressure bandwidth. Based on the mechanism of vibration coupling between membrane and air pistons in membrane holes, we propose an analytical model to aid the design process of this kind of CMUTs. We also use finite element method (FEM) to investigate this kind of CMUTs for our analytical model validation. The FEM results show that the significant bandwidth enhancement can be achieved when the Helmholtz resonant frequency is designed close to the fundamental resonant frequency of the CMUT membrane. Compared with the conventional sealed CMUT cell, the 4-hole unsealed Helmholtz structural CMUT cell improves both the 3-dB fractional bandwidth and SPL-bandwidth product around 35 times. Furthermore, it is found that, with more holes under the same hole area ratio or with a smaller ratio of the cavity height to the viscous boundary layer thickness, the Helmholtz resonant effect becomes weaker and thus the output pressure bandwidth decreases.

Jenkins model based ferrofluid lubrication of a curved rough annular squeeze film: Effect of slip velocity

This paper analyzes the combined effect of slip velocity and transverse roughness on the performance of a Jenkins model based ferrofluid lubrication of a squeeze film in curved rough annular plates. The slip model of Beavers and Joseph has been invoked to evaluate the effect of slip velocity. In order to find the effect of surface roughness the stochastic averaging model of Christensen and Tonder has been used. The pressure distribution is obtained by solving the concerned stochastically averaged Reynolds type equation. The load carrying capacity is calculated. The graphical representations of the results indicate that the effect of transverse surface roughness is adverse in general, however, the situation is relatively better in the case of negatively skewed roughness. Further, Jenkins model based ferrofluid lubrication offers some measures in reducing the adverse effect of roughness when slip parameter is kept at reduced level with a suitable ratio of curvature parameters. Lastly, the positive effect of magnetization gets a boost due to the combined effect of variance (-ve) and negatively skewed roughness suitably choosing the aspect ratio.