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Real-time visual localization of needles is necessary for various surgical applications, including surgical automation and visual feedback. In this study we investigate localization and autonomous robotic control of needles in the context of our magneto-suturing system. Our system holds the potential for surgical manipulation with the benefit of minimal invasiveness and reduced patient side effects. However, the nonlinear magnetic fields produce unintuitive forces and demand delicate position-based control that exceeds the capabilities of direct human manipulation. This makes automatic needle localization a necessity. Our localization method combines neural network-based segmentation and classical techniques, and we are able to consistently locate our needle with 0.73 mm RMS error in clean environments and 2.72 mm RMS error in challenging environments with blood and occlusion. The average localization RMS error is 2.16 mm for all environments we used in the experiments. We combine this localization method with our closed-loop feedback control system to demonstrate the further applicability of localization to autonomous control. Our needle is able to follow a running suture path in (1) no blood, no tissue; (2) heavy blood, no tissue; (3) no blood, with tissue; and (4) heavy blood, with tissue environments. The tip position tracking error ranges from 2.6 mm to 3.7 mm RMS, opening the door towards autonomous suturing tasks.

Characterization of a newly developed class of passive nonreciprocal acoustic metamaterials is presented in an attempt to quantify their ability of controlling the flow and distribution of acoustic energy in acoustic cavities and systems. The proposed nonreciprocal acoustic metamaterial (NAMM) cell consists of a one-dimensional acoustic cavity provided with piezoelectric flexible boundaries connected to an array of anti-parallel diodes to introduce the nonlinear damping effect that tends to break the reciprocity of the energy flow through the NAMM cell. A comprehensive experimental characterization of prototypes of the NAMM cells is presented here in order to investigate the effect of various anti-parallel diode arrangements on the nonreciprocal behavior of the cell. Furthermore, the experimental characterization aims also at demonstrating the effectiveness of the proposed NAMM in tuning the directivity, flow, and distribution of acoustic energy propagating through the metamaterial.

Experimental realization of a new class of active Nonreciprocal Gyroscopic Meta-Material (NGMM) is presented. The proposed active NGMM system consists of a one-dimensional acoustic cavity provided with piezoelectric boundaries that act as sensors and actuators. These active boundaries are integrated with linear dynamic control capabilities that virtually synthesize a gyroscopic control action in order to generate desirable non-reciprocal characteristics of tunable magnitude and phase shift. The dynamics of a prototype of the NGMM cell are identified experimentally and the theoretical characteristics of the virtual gyroscopic controller are predicted for various control gains for both forward and backward propagations. The theoretical predictions are validated experimentally using a dummy NGMM cell to act as a physical dynamic controller. Such a preferred arrangement is coupled with analog controllers in order to enable fast execution of the controller and, in turn, enhance the bandwidth of its operating frequency. The time and frequency response characteristics of the NGMM cell are measured for different control gain and the behavior is evaluated for both forward and backward propagations. The obtained experimental results are found to be in close agreement with the theoretical predictions. The presented concept, controller design, and implementation of the NGMM can be extended to various critical structures to achieve realistic acoustic diode configurations in a simple and programmable manner.