Asymmetries in wing inertial and aerodynamic torques contribute to steering in flying insects.

Maneuvering in both natural and artificial miniature flying systems is assumed to be dominated by aerodynamic phenomena. To explore this, we develop a flapping wing model integrating aero and inertial dynamics. The model is applied to an elliptical wing similar to the forewing of the Hawkmoth Manduca sexta and realistic kinematics are prescribed. We scrutinize the stroke deviation phase, as it relates to firing latency in airborne insect steering muscles which has been correlated to various aerial maneuvers. We show that the average resultant force production acting on the body largely arises from wing pitch and roll and is insensitive to the phase and amplitude of stroke deviation. Inclusion of stroke deviation can generate significant averaged aerodynamic torques at steady-state and adjustment of its phase can facilitate body attitude control. Moreover, averaged wing angular momentum varies with stroke deviation phase, implying a non-zero impulse during a time-dependent phase shift. Simulations show wing inertial and aerodynamic impulses are of similar magnitude during short transients whereas aerodynamic impulses dominate during longer transients. Additionally, inertial effects become less significant for smaller flying insects. Body yaw rates arising from these impulses are consistent with biologically measured values. Thus, we conclude (1) modest changes in stroke deviation can significantly affect steering and (2) both aerodynamic and inertial torques are critical to maneuverability, the latter of which has not widely been considered. Therefore, the addition of a control actuator modulating stroke deviation may decouple lift/thrust production from steering mechanisms in flapping wing micro aerial vehicles and increase vehicle dexterity through inertial trajectory shaping.

Direct Intracochlear Acoustic Stimulation Using a PZT Microactuator.

Combined electric and acoustic stimulation has proven to be an effective strategy to improve hearing in some cochlear implant users. We describe an acoustic microactuator to directly deliver stimuli to the perilymph in the scala tympani. The 800 µm by 800 µm actuator has a silicon diaphragm driven by a piezoelectric thin film (e.g., lead-zirconium-titanium oxide or PZT). This device could also be used as a component of a bimodal acoustic-electric electrode array. In the current study, we established a guinea pig model to test the actuator for its ability to deliver auditory signals to the cochlea in vivo. The actuator was placed through the round window of the cochlea. Auditory brainstem response (ABR) thresholds, peak latencies, and amplitude growth were calculated for an ear canal speaker versus the intracochlear actuator for tone burst stimuli at 4, 8, 16, and 24 kHz. An ABR was obtained after removal of the probe to assess loss of hearing related to the procedure. In some animals, the temporal bone was harvested for histologic analysis of cochlear damage. We show that the device is capable of stimulating ABRs in vivo with latencies and growth functions comparable to stimulation in the ear canal. Further experiments will be necessary to evaluate the efficiency and safety of this modality in long-term auditory stimulation and its ability to be integrated with conventional cochlear implant arrays.