High-resolution swath bathymetry using MIMO sonar system

For increasing the cross-track resolution, the multiple input multiple output （MIMO） technique is introduced into the swath bathymetry system and a new swath bathymetry approach using MIMO sonar is proposed. The MIMO sonar is composed of two parallel transmitting uniform linear arrays （ULAs） and a receiving ULA which is perpendicular to the former. The spacing between the two transmitting ULAs is equal to the product of the receiving sensor number and the receiving inter-sensor spacing. Furthermore, two narrowband linear frequency modulation （LFM） pulses, sharing the same frequency band but with opposite modulation slopes, are used as transmitting waveforms of the two transmitting ULAs. With such an array layout and transmitting signals, the MIMO sonar can sound a swath with the cross-track resolution doubling that of the traditional multibeam sonar using a Mills cross array. Numerical examples are provided to verify the effectiveness of the proposed approach.

Low complexity MIMO sonar imaging using a virtual sparse linear array

A multiple-input multiple-output（MIMO） sonar can synthesize a large-aperture virtual uniform linear array（ULA） from a small number of physical elements. However, the large aperture is obtained at the cost of a great number of matched filters with much heavy computation load. To reduce the computation load, a MIMO sonar imaging method using a virtual sparse linear array（SLA） is proposed, which contains the offline and online processing. In the offline processing, the virtual ULA of the MIMO sonar is thinned to a virtual SLA by the simulated annealing algorithm, and matched filters corresponding to inactive virtual elements are removed. In the online processing, outputs of matched filters corresponding to active elements are collected for further multibeam processing and hence, the number of matched filters in the echo processing procedure is effectively reduced. Numerical simulations show that the proposed method can reduce the computation load effectively while obtaining a similar imaging performance as the traditional method.

Compensating for intensity loss in a large-aperture MIMO sonar imaging system

To reduce the computation burden of a large-aperture multiple-input multiple-output（MIMO） sonar imaging system,the phase-shift beamformer（PSBF） is used at the cost of bringing the intensity loss（IL）.The cause of the IL is analyzed in detail and a variable termed as IL factor is defined to quantify the loss amount.To compensate for the IL,two methods termed as intensity compensation for the PSBF（IC-PSBF） and the hybrid beamforming（HBF）,respectively,are proposed.The IC-PSBF uses previously estimated IL factors to compensate for output intensities of all PSBFs;and the HBF applies the IC-PSBF to the center beam region and the shifted-sideband beamformer（SSBF） to the side beam region,respectively.Numerical simulations demonstrate the effectiveness of the two proposed methods.

Design and validation of a navigation system of multimodal medical images for neurosurgery based on mixed reality

Purpose: This paper aims to develop a navigation system based on mixed reality, which can displaymultimodal medical images in an immersive environment and help surgeons locate the target areaand surrounding important tissues precisely.Methods: To be displayed properly in mixed reality, medical images are processed in this system.High-quality cerebral vessels and nerve fibers with proper colors are reconstructed and exported tomixed reality environment. Multimodal images and models are registered and fused, extracting theirkey information. The multiple processed images are fused with the real patient in the same coordinatesystem to guide the surgery.Results: The multimodal image system is designed and validated properly. In phantom experiments,the average error of preoperative registration is 1.003 mm and the standard deviation is 0.096 mm.The average proportion of well-registered areas is 94.9%. In patient experiments, the surgeons whoparticipated in the experiments generally indicated that the system had excellent performance andgreat application prospect for neurosurgery.Conclusion: This article proposes a navigation system of multimodal images for neurosurgery basedon mixed reality. Compared with other navigation methods, this system can help surgeons locate thetarget area and surrounding important tissues more precisely and rapidly.

Interfacial Reinitiation of Free Radicals Enables the Regeneration of Broken Polymeric Hydrogel Actuators

Living organisms,from plants to animals,have inspired and guided the design and fabrication of polymeric hydrogels with biomimetic morphology,shape deformation,and actuation behavior.However,the existing polymeric hydrogels are fragile and vulnerable,which seriously hinders further application.Therefore,endowing hydrogels with a biomimetic self-growth property and regenerating the macroscopic shape of hydrogels after they suffer significant damage are highly desirable for the next generation of adaptive biomimetic hydrogels.Inspired by the tail regeneration of geckos,we herein report an efficient and universal strategy of interfacial diffusion polymerization(IDP),which can regenerate the polymeric layer at a solid–liquid interface,thereby growing new hydrogels on the existing hydrogel layers.Through changing the solvent viscosity and/or monomer type of the hydrogel precursor,diverse new hydrogels have been regenerated to endow the initial hydrogels with additional fluorescent functions and/or actuating properties.Due to the high efficiency and universality of IDP,an injured hydrogel actuator can be repaired,regenerated,and recovered to its initial condition,even after suffering severe damage such as cutting or piercing.We believe that the regeneration strategy of polymeric hydrogels will inspire the design of biomimetic materials and motivate the fabrication of the next generation of soft robots with adaptive and multifunctional properties.