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It is necessary to develop effective methods for visually detecting concrete damage because minor damage can affect the performance of concrete materials. However, the non-homogeneous nature of concrete materials limits the application of imaging algorithms that have been widely used in aerospace and mechanical fields; thus, obtaining high-resolution imaging maps is difficult. In this study, feasibility research on concrete damage detection was conducted using the time reversal focusing imaging algorithm. A new method for characterizing various concrete damage conditions with focusing curves was proposed. ABAQUS software was utilized to establish five types of concrete damage, and the imaging quality of the proposed method was evaluated in Python. The effect of the relative position of the damage and the sensors was analyzed. The focusing curve was extracted from the imaging area to further explain the image information. The numerical simulation results show that time reversal focusing had better damage localization than the forward algorithm; time focusing also improved the spatial focusing quality. In addition, focusing curves were used to extract information from the main lobe and to determine the size and location of the damage. [ABSTRACT FROM AUTHOR]

The application of frequency diverse array and multiple-input multiple-output (FDA-MIMO) radar to achieve the joint estimation of target's range and angle is receiving more and more attention. However, its performance is generally affected by the periodicity and time-varying of its beam pattern. Therefore, this paper implements a joint estimation algorithm of target's range and angle based on a new waveform synthesis model of time modulation and range compensation FDA-MIMO (TMRC-FDA-MIMO) radar. At the same time, the multiple signal classification (MUSIC) algorithm is mainly used in FDA-MIMO radar. The huge amount of calculation also brings difficulties to the implementation of the system. Therefore, this paper proposes an improved estimating signal parameters via rotation invariance technique algorithm to solve the problem of large amount of calculation on the basis of ensuring system performance. In addition, the closed form expressions of the Cramér–Rao lower bound and root-mean-squared error of range and angle estimation are derived. Theoretical analysis and simulation verify the effectiveness of the proposed method and demonstrate the excellent performance of the proposed radar system and algorithm. [ABSTRACT FROM AUTHOR]

Focused ultrasound using stretchable ultrasonic arrays is a very attractive method for ultrasound neuromodulation. However, the structure and fabrication of the arrays have brought great challenges for the development of stretchable ultrasonic arrays. In this work, an improved 6 × 6 stretchable two-dimensional ultrasonic array has been proposed based on laser micromachining technology. The structure and shape of the serpentine hinge are optimized to avoid delamination between layers and to reduce the stress concentration during the stretching process. Due to the thorough studies over the effects of laser parameters on the kerf profile, clean and accurate serpentine hinge shapes can be obtained conveniently. Array elements are connected using serpentine hinges to form a stretchable two-dimensional structure. Thus, a reliable electrical connection and stable array structure are formed, which can provide 100% yield and excellent mechanical stretchability. Based on the three-dimensional scanning guidance, simulation results of ultrasonic spatial focusing on a complex surface demonstrate that our device has promising applications for ultrasound neuromodulation.

Frequency diverse array and multiple-input multiple-output (FDA-MIMO) radar is studied more to realise the joint estimation of range and angle. However, the estimation performance of target parameters for linear FDA radar with an identical frequency increment and multiple-input multiple-output (IFI-FDA-MIMO) and logarithmically increased frequency offset linear interval, and multiple-input multiple-output (LIFO-FDA-MIMO) is fundamentally limited by the periodic range-time variation and time-variant dot shape beampattern respectively. In this article, we proposed a joint range and angle estimation algorithm based on a new waveform synthesis model of time modulation and rang compensation FDA-MIMO (TMRC-FDA-MIMO). The emulation results demonstrate that the improved scheme achieves the goal of time-invariant, dot-shaped and low sidelobe beampattern, which is optimised by a new accelerated particle swarm optimisation (NAPSO) algorithm. The performance of target estimation under the Cramer Rao lower bound (CRLB), and the root means square errors (RMSE) of the radar system is analysed. Moreover, the mathematical formula derivation and numerical results verify the performance of the proposed algorithm, which shows that TMRC-FDA-MIMO radar system is superior to others mentioned above. [ABSTRACT FROM AUTHOR]

It is necessary to develop effective methods for visually detecting concrete damage because minor damage can affect the performance of concrete materials. However, the non-homogeneous nature of concrete materials limits the application of imaging algorithms that have been widely used in aerospace and mechanical fields; thus, obtaining high-resolution imaging maps is difficult. In this study, feasibility research on concrete damage detection was conducted using the time reversal focusing imaging algorithm. A new method for characterizing various concrete damage conditions with focusing curves was proposed. ABAQUS software was utilized to establish five types of concrete damage, and the imaging quality of the proposed method was evaluated in Python. The effect of the relative position of the damage and the sensors was analyzed. The focusing curve was extracted from the imaging area to further explain the image information. The numerical simulation results show that time reversal focusing had better damage localization than the forward algorithm; time focusing also improved the spatial focusing quality. In addition, focusing curves were used to extract information from the main lobe and to determine the size and location of the damage.

In this article, a novel technique is applied to achieve time-invariant spatial focusing performance for static and moving target by applying an irregular frequency modulation method to a frequency diverse array (FDA) waveform transmission system. The FDA radar can improve the anti-noise ability of the system by the means of concentrating the waveform energy on the required range or angle sector. However, the synthesized waveform has high sidelobes and is time-varying during the transmission waveform. In view of the above problems, a new waveform synthesis model of rang compensation frequency diverse array (TMRC-FDA) is established and the effect of parameter ς on the waveform synthesis is analyzed. A new accelerated particle swarm optimization algorithm is used to optimize the distribution of parameter ς . The numerical simulation results show that the proposed TMRC-FDA waveform synthesis method achieves the goal of time invariance and reduces the waveform sidelobes. At the same time, it has better performance in terms of waveform focus compared to log-frequency offset FDA based on time-modulated and fixed parameters ς . [ABSTRACT FROM AUTHOR]

Next-generation wireless networks are expected to support an exponentially increasing number of users and demands of data, which all rely on the essential media: spectrum. Spectrum sharing among heterogeneous networks is a fundamental issue that determines network performance. Previous works have focused on a “dynamic spectrum access” mode associated with the cognitive radio technology. These works all focused on the discovery of available spectrum resource either in the time domain or in the frequency domain, i.e., by separating different users’ transmission. To initiate a new paradigm of spectrum sharing, the unique characteristics of the technologies should be utilized in the next-generation networks. The 5G networks are featured either by wide bandwidth like mm-wave systems, or by large-scale antennas like massive MIMO. Those two trends can lead to a common phenomenon: the spatial focusing effect. Based on this focusing effect, we propose a general spatial spectrum sharing framework that enables concurrent multi-users spectrum sharing without the requirement of orthogonal resource allocation. Moreover, we design two general network association protocols either in a centralized manner or in a distributed manner. Simulation results show that both the time reversal wideband and the massive MIMO system can achieve high throughput performance with the spatial spectrum sharing scheme. [ABSTRACT FROM PUBLISHER]

Driven by the demand for supporting the rapidly increasing wireless traffic, the next-generation communication system, i.e., the 5G system, needs to accommodate a massive number of users and judiciously manage the interference. One promising candidate, the time reversal (TR) system, uses a large bandwidth and designs transmitting waveforms, such that the environment acts as a matched filter and the transmitted signal adds up coherently at the intended users. Therefore, the energy is focused only at the intended users with reduced interference to others. The other candidate, massive MIMO system, utilizes a large number of antennas to focus on the energy to the users and reduce the mutual interference. However, the massive number of users poses a limit on system performance due to increasing interuser interference, and the system has to make a judicial selection of transmitting users. In this paper, we propose a scheduler that maximizes the system weighted sum rate while satisfying the minimum rate requirements of the transmitting users. The optimization problem is transformed into a mixed integer quadratically constrained quadratic programming with linear time complexity. We also investigate the impact of imperfect channel information on the proposed scheduler algorithm and reveal similar channel estimation error distribution between the TR and massive MIMO system. We evaluate the performance of the proposed scheduler in different scenarios and the results show that the proposed scheduler has several desirable characteristics, including low time complexity, suitable on versatile system structure, and robustness against imperfect channel information. [ABSTRACT FROM PUBLISHER]

UWB radio has the potential to offer good performance in terms of localization precision. Time Reversal channel pre-filtering facilitates signal detection and also helps to increase the received energy in a targeted area. This paper assesses the quantitative and qualitative contributions of the Time Reversal (TR) technique associated with an Ultra Wideband (UWB) localization system applied to a railway odometry problem. The analytical and simulation results for Power Delay Profile, equivalent channel model and focusing gain of the TR-UWB are given. The contribution of the TR technique associated with UWB radio to enhance the localization resolution is analysed. To perform these studies, and to be representative of the proposed railway application, a deterministic channel model is used. The analytical simulation and experimental results show that time reversal has very promising characteristics regarding its association with the UWB in terms of localization error. These results also indicate that the TR-UWB technique delivers improved performance over UWB only localization approach, that could benefit the development of the proposed railway application. [ABSTRACT FROM AUTHOR]

Direct-sequence (DS) code-division-multiple-access (CDMA) signaling allows multiple users to communicate simultaneously over the same bandwidth at the expense of a reduced rate. Due to severe cochannel interference (CoI) in multipath rich underwater channels, no more than 4 users have been demonstrated. Multiple-input-multiple-output (MIMO) communication also allows multiple users. Using parallel/sequential interference cancellation schemes, experimental results show similar limitations on the number of users. To extend the number of users beyond four (as required for certain applications), it is proposed to combine CDMA with MIMO, utilizing the spatial-temporal processing gain of passive-phase conjugation, and the approximate-orthogonality of the spreading codes to remove the (increased) CoI. The receiver algorithm uses simple matched filters without explicit channel-equalization and CoI cancellation. The algorithm performance is studied as a function of input-SNR, using simulated data based on experimentally measured channel impulse responses. M-sequences with 127, 255 and 511 chips are used. One finds that 255/511 chips are generally required to support 8 users, and 127/255 chips are needed to support 6 users for the channel studied. Multiuser communications are demonstrated with at-sea data for 8 users, with spreading codes of 511 chips, yielding zero bit errors. The data rate is \sim 8 bits/s/user, given 4 kHz bandwidth. [ABSTRACT FROM PUBLISHER]

In an indoor environment, there commonly exist a large number of multipaths due to rich scatterers. These multipaths make the indoor positioning problem very challenging. The main reason is that most of the transmitted signals are significantly distorted by the multipaths before arriving at the receiver, which causes inaccuracies in the estimation of the positioning features such as the time of arrival (TOA) and the angle of arrival (AOA). On the other hand, the multipath effect can be very constructive when employed in the time-reversal (TR) radio transmission. By utilizing the uniqueness of the multipath profile at each location, TR can create a resonating effect of focusing the energy of the transmitted signal only onto the intended location, which is known as the spatial focusing effect. In this paper, we propose exploiting such a high-resolution focusing effect in the indoor positioning problem. Specifically, we propose a TR indoor positioning system (TRIPS) by utilizing the location-specific characteristic of multipaths. By doing so, we decompose the ill-posed single-access-point (AP) indoor positioning problem into two well-defined subproblems. The first subproblem is to create a database by mapping the physical geographical location with the logical location in the channel impulse response (CIR) space, whereas the second subproblem is to determine the real physical location by matching the estimated CIR with those in the database. To evaluate the performance of our proposed TRIPS, we build a prototype to conduct real experiments. The experimental results show that, with a single AP working in the 5.4-GHz band under the non-line-of-sight (NLOS) condition, our proposed TRIPS can achieve perfect 10-cm localization accuracy with zero-error rate within a 0.9 m by 1 m area of interest. [ABSTRACT FROM PUBLISHER]

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This paper presents the results of indoor wideband measurements investigating the space--time properties of wireless signal transmission with online time-reversal (TR) precoding. The measurements were conducted using a new TR wideband multiple-input--multiple-output (MIMO) channel sounder operating at 2.45 GHz with a bandwidth of 240 MHz. Both line-of-sight (LOS) and non-line-of-sight (NLOS) propagation conditions were investigated. Spatial focusing and temporal compression can clearly be seen with TR precoding, which may be useful for future wireless system applications. Channel hardening due to TR is also observed under both LOS and NLOS conditions. [ABSTRACT FROM AUTHOR]

Ultra-wideband (UWB) technology is envisioned for future wireless high-data-rate transmission. A UWB system with multiple antennas takes advantage of the rich scattering environment to increase the data rate. On the other hand, given rich multipath, time reversal (TR) uses scatterers to create space and time focalization at a target point by coherent addition of all scattered contributions at that point. This paper analyzes the performance of an impulse TR-multiple-input-multiple-output (MIMO)-UWB system with a simple one-correlator receiver. The performance analyses are based on UWB spatial channels measured in an office environment. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a novel configuration concept of crystal chips for time-of-flight (TOF) crystal-analyzer neutron inelastic scattering spectrometers, which simultaneously achieve time-focusing, spatial-focusing and momentum-correcting abilities. This concept will be adopted for the planned TOF near-backscattering spectrometer, DIANA which has been proposed for construction at the Japan Proton Accelerator Research Complex (J-PARC). We will first discuss the new analyzer layout method satisfying both time- and spatial-focusing and momentum-correction concepts and then the focusing performances as evaluated by Monte-Carlo simulations and compared to the generally used energy-focusing analyzer configuration. [Copyright &y& Elsevier]

We propose and evaluate the performance of the time reversal technique in impulse radio ultrawideband (UWB) communications. The evaluation was based on measured channel impulse responses of a 4times1 multiple input single output (MISO) system in the UWB frequency bandwidth of 3 to 5 GHz with both vertical and horizontal polarization at the receiver. The results show that there is a great potential in combining time reversal and UWB technique with respect to both reducing the receiver complexity and improving the system performance. Simultaneous communication is illustrated with 5 users, each with a bit error rate (BER) of less than 10-3 at an average signal to noise ratio (SNR) of 15 dB [ABSTRACT FROM PUBLISHER]

Applying the analogies between beam propagation and pulse propagation, so-called space and time variance matrices are presented, respectively. Straightforwardly, characteristics of paraxial light beam propagation and pulse propagation are described in space and time variance matrices, respectively. [Copyright &y& Elsevier]

The authors discuss immersive audio systems and the signal processing issues that pertain to the acquisition and subsequent rendering of 3D sound fields over loudspeakers. On the acquisition side, recent advances in statistical methods for achieving acoustical arrays in audio applications are reviewed. Classical array signal processing addresses two major aspects of spatial filtering, namely localization of a signal of interest, and adaptation of the spatial response of an array of sensors to achieve steering in a given direction. The achieved spatial focusing in the direction of interest makes array signal processing a necessary component in immersive sound acquisition systems. On the rendering side, 3D audio signal processing methods are described that allow rendering of virtual sources around the listener using only two loudspeakers. Finally, the authors discuss the commercial implications of audio DSP [ABSTRACT FROM PUBLISHER]

The multi-path effect makes high speed broadband communications a very challenging task due to the severe inter-symbol interference (ISI). By concentrating energy in both the spatial and temporal domains, time-reversal (TR) transmission technique provides a great potential of low-complexity energy-efficient communications. In this paper, a novel concept of time-reversal division multiple access (TRDMA) is proposed as a wireless channel access method based on its high-resolution spatial focusing effect. It is proposed to use TR structure in multi-user downlink systems over multi-path channels, where signals of different users are separated solely by TRDMA. Both the single-transmit-antenna scheme and its enhanced version with multiple transmit antennas are developed and evaluated in this paper. The system performance is investigated in terms of its effective signal-to-interference-plus-noise ratio (SINR), the achievable sum rate and the achievable rates with outage. And some further discussions regarding its advantage over conventional rake receivers and the impact of spatial correlations between users are given at the end of this paper. It is shown in both analytical and simulation results that desirable properties and satisfying performances can be achieved in the proposed TRDMA multi-user downlink system, which makes TRDMA a promising candidate for future energy-efficient low-complexity broadband wireless communications. [ABSTRACT FROM AUTHOR]