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Mechanical waves have a wide range of applications in autonomous soft devices such as mechanical logic gates and microrobots. However, the wave velocity is constant in most systems driven by mechanical waves. This significantly limits the application of mechanical waves in some systems (e.g., soft robots capable of sequence control) that possess a spatial distribution of the heterogeneous energy. In this study, a soft spherical shell array composed of soft-shell elements connected by linear springs is proposed to achieve an adjustable wave velocity. Specifically, the effect of the geometric parameters of a single shell on the energy characteristics is quantified by Finite Element simulations. Theoretical and numerical analyses of the wave properties are also provided. Their results show that adjustable wave propagation behaviors can be designed using the geometrical parameters of the elements. This study provides a basis for the design of energy-efficient soft devices such as soft actuators, controllable energy absorbers and shape-morphing systems.

Inverse Synthetic aperture radar (ISAR) imaging deception jamming method of Chirp Modulation Signal is a powerful tool in electronic war. In this paper, an Efficient All-Digital ISAR raw signal deception model for air targets is presented. The proposed procedure is based on an angle-frequency domain analysis: a proper analytical reformulation of the ISAR raw signal expression is presented. It is shown that this reformulation allows us to design a very efficient simulation scheme which applies the joint analysis method of wideband frequency-angle domain. Accordingly, the problem is solved that the target wide frequency band scattering field can’t be effectively simulation in time domain and the computational load of ISAR raw signal deception is dramatically reduced.

The increasing congestion of the RF spectrum is a key challenge for low-power wireless networks using concurrent transmissions. The presence of radio interference can indeed undermine their dependability, as they rely on a tight synchronization and incur a significant overhead to overcome packet loss. In this paper, we present Harmony, a new data collection protocol that exploits the benefits of concurrent transmissions and embeds techniques to ensure a reliable and timely packet delivery despite highly congested channels. Such techniques include, among others, a data freezing mechanism that allows to successfully deliver data in a partitioned network as well as the use of network coding to shorten the length of packets and increase the robustness to unreliable links. Harmony also introduces a distributed interference detection scheme that allows each node to activate various interference mitigation techniques only when strictly necessary, avoiding unnecessary energy expenditures while finding a good balance between reliability and timeliness. An experimental evaluation on real-world testbeds shows that Harmony outperforms state-of-the-art protocols in the presence of harsh Wi-Fi interference, with up to 50% higher delivery rates and significantly shorter end-to-end latencies, even when transmitting large packets.

This paper presents a real-time monocular SLAM algorithm which combines points and line segments. We extend traditional point-based SLAM system with line features which are usually abundant in man-made scenes. The system is more robust and accurate than traditional point-based and direct-based monocular SLAM algorithms. In order to improve the timeliness of multi-feature based SLAM, we propose a novel feature level parallel processing framework and a fast line matching algorithm. For improving the reconstruction accuracy of 3D line segments which is usually affected by unreliable line endpoints, a sample point-based 3D reconstruction algorithm for line segments is proposed. Our system is implemented based on a popular monocular SLAM known as ORB-SLAM and tested on the TUM RGB-D benchmark. The experiment results demonstrate that the proposed system performs better than current state-of-the-art visual SLAM with respect to accuracy.

Concurrent transmission, a novel communication paradigm, has been shown to effectively achieve reliable and energy-efficient flooding in low-power wireless networks. With multiple nodes exploiting a receive-and-forward scheme, this technique works effectively in flooding-based networks, i.e., in one-to-many scenarios. However, application-level scheduling has to be introduced for data collection in wireless sensor networks (WSNs). In this paper, we propose Packet-in-Packet (PiP), an energy-efficient paradigm requiring no application-level scheduling for timely data collection in low-power WSNs. PiP builds on concurrent transmissions, exploiting constructive interference and the capture effect to achieve high reliability and low latency. Moreover, PiP uses a packet concatenation capability to gather single-hop information in a best-effort manner. As a result, PiP significantly reduces collection time. We further compare PiP with a state-of-the-art protocol by extensive experiments in a 30-node FlockLab testbed. Experimental results show that PiP highly reduces collection time (i.e., rounds) and achieves good performance in terms of high reliability of approximately 98.7% and high energy efficiency in all experimental scenarios of the real-world testbed.

In this paper, we present a soft wearable orthotic device for gait assistance. The components of the orthotic device are mainly made of soft materials and the device only has a mass of 680 g worn on the subjects lower extremity, which do not add significant inertia during walking. Fully soft pneumatic artificial muscles (PAMs) with low threshold pressures are utilized as actuators. A bundle of four PAMs are used to provide force for the plantarflexion of ankle joint in certain gait period. The gait cycle is detected by two inertial measurement units (IMUs) mounted on the calf and foot braces, respectively. The orthotic device applies a force of 65 N for ankle plantarflexion, which corresponds to 3.5% of the nominal biological force at the ankle joint during walking.

Concurrent transmission, a novel communication paradigm, has been shown to effectively achieve reliable and energy-efficient flooding in low-power wireless networks. With multiple nodes exploiting a receive-and-forward scheme, this technique works effectively in one-to-many scenarios. However, application-level scheduling has to be introduced for data collection applications. In this paper, we propose Packet-in-Packet (PiP), an energy-efficient paradigm requiring no application-level scheduling for timely data collection in low-power wireless sensor networks. PiP builds on concurrent transmissions, exploiting constructive interference and the capture effect to achieve high reliability, low latency, and high energy efficiency. Moreover, PiP uses a packet concatenation capability to gather single-hop information in a best-effort manner. Experimental results show that PiP achieves high reliability in all experimental scenarios of a real-world testbed.

The physical ground simulation of space defense confrontation is under the contractible time and space coordination of real world. The theoretical foundation of simulation is determined by the uniform constrains that ensured the similarities of geometrical and physical quantities mapping in the two spaces. Under the architectures of space vector linear similarity and time uniform elapse, the sufficient conditions of uniformity of geometrical and physical quantities are proved by the classical physics and mathematical induction. The further derivation inferred the invariance of the guidance methods within the two spaces. The results of mathematic simulation under the ideal conditions demonstrated the validity of the sufficient conditions of uniformity, which are the theoretical foundation of physical simulation of space defense confrontation.

The physical simulation of space interception with two high-speed spacecrafts is often executed on an area-limited marble platform, which could not imitate the high relative speed between two spacecrafts under the accuracy requirement of positions and movements. This paper presents the nonlinear similarity theory which is described under the architecture of the nonlinear geometrical and time-variant transform. The time-variant and nonuniform spatial contraction methods are discussed and the factor function of the geometric transform is deduced preliminarily, which counteract the high relative velocity between of two objects on the platform. Thus the movenment realization of the two high-speed spacecrafts on the platform becomes easier, which reduces the perfomance of floating object. Furthermore the time-variant transform solved the problems of physical simulation in the accuracy of actuators and measurement in the limited platform. The results of mathematic simulation demonstrated the validity of the sufficient conditions of uniformity, which are the novel constraction theory of physical simulation of space interception.