Xiang Zhong

A seesaw-type approach for enhancing nonlinear energy harvesting

Harvesting sustainable mechanical energy is the ultimate objective of nonlinear energy harvesters. However, overcoming potential barriers, especially without the use of extra excitations, poses a great challenge for the development of nonlinear generators. In contrast to the existing methods, which typically modify the barrier height or utilize additional excitations, this letter proposes a seesaw-type approach to facilitate escape from potential wells by transfer of internal energy, even under low-intensity excitation. This approach is adopted in the design of a seesaw-type nonlinear piezoelectric energy harvester and the energy transfer process is analyzed by deriving expressions for the energy to reveal the working mechanism. Comparison experiments demonstrate that this approach improves energy harvesting in terms of an increase in the working frequency bandwidth by a factor of 60.14 and an increase in the maximum output voltage by a factor of 5.1. Moreover, the output power is increased by a factor of 51.3, which indicates that this approach significantly improves energy collection efficiency. This seesaw-type approach provides a welcome boost to the development of renewable energy collection methods by improving the efficiency of harvesting of low-intensity ambient mechanical energy.Harvesting sustainable mechanical energy is the ultimate objective of nonlinear energy harvesters. However, overcoming potential barriers, especially without the use of extra excitations, poses a great challenge for the development of nonlinear generators. In contrast to the existing methods, which typically modify the barrier height or utilize additional excitations, this letter proposes a seesaw-type approach to facilitate escape from potential wells by transfer of internal energy, even under low-intensity excitation. This approach is adopted in the design of a seesaw-type nonlinear piezoelectric energy harvester and the energy transfer process is analyzed by deriving expressions for the energy to reveal the working mechanism. Comparison experiments demonstrate that this approach improves energy harvesting in terms of an increase in the working frequency bandwidth by a factor of 60.14 and an increase in the maximum output voltage by a factor of 5.1. Moreover, the output power is increased by a factor of...

Analysis of calibration accuracy of cameras with different target sizes for large field of view

Visual measurement plays an increasingly important role in the field o f aerospace, ship and machinery manufacturing. Camera calibration of large field-of-view is a critical part of visual measurement . For the issue a large scale target is difficult to be produced, and the precision can not to be guaranteed. While a small target has the advantage of produced of high precision, but only local optimal solutions can be obtained . Therefore, studying the most suitable ratio of the target size to the camera field of view to ensure the calibration precision requirement of the wide field-of-view is required. In this paper, the cameras are calibrated by a series of different dimensions of checkerboard calibration target s and round calibration targets, respectively. The ratios of the target size to the camera field-of-view are 9%, 18%, 27%, 36%, 45%, 54%, 63%, 72%, 81% and 90%. The target is placed in different positions in the camera field to obtain the camera parameters of different positions . Then, the distribution curves of the reprojection mean error of the feature points’ restructure in different ratios are analyzed. The experimental data demonstrate that with the ratio of the target size to the camera field-of-view increas ing, the precision of calibration is accordingly improved, and the reprojection mean error changes slightly when the ratio is above 45%.

Measurement of Unmanned Aerial Vehicle Attitude Angles Based on a Single Captured Image

The limited load capacity and power resources of small-scale fixed-wing drones mean that it is difficult to employ internal high-precision inertial navigation devices to assist with the landing procedure. As an alternative, this paper proposes an attitude measurement system based on a monocular camera. The attitude angles are obtained from a single captured image containing five coded landmark points using the radial constraint method and three-dimensional coordinate transformations. The landing procedure is simulated for pitch angles from −15∘ to −40∘, roll angles from −15∘ to +15∘ and yaw angles from −15∘ to +15∘. For roll and pitch angles of approximately 0∘ and −25∘, respectively, the accuracy of the method reaches 0.01∘ and 0.04∘. This UAV attitude measurement system obtains an attitude angle by a single captured image, which has great potential for assisting with the landing of small-scale fixed-wing UAVs.

Pulse-Width Multiplexing ϕ-OTDR for Nuisance-Alarm Rate Reduction

A pulse-width multiplexing method for reducing the nuisance-alarm rate of a phase-sensitive optical time-domain reflectometer (ϕ-OTDR) is described. In this method, light pulses of different pulse-widths are injected into the sensing fiber; the data acquired at different pulse-widths are regarded as the outputs of different sensors; and these data are then processed by a multisensor data fusion algorithm. In laboratory tests with a sensing fiber on a vibrating table, the effects of pulse-width on the signal-to-noise ratio (SNR) of the ϕ-OTDR data are observed. Furthermore, by utilizing the SNR as the feature in a feature-layer algorithm based on Dempster–Shafer evidential theory, a four-pulse-width multiplexing ϕ-OTDR system is constructed, and the nuisance-alarm rate is reduced by about 70%. These experimental results show that the proposed method has great potential for perimeter protection, since the nuisance-alarm rate is significantly reduced by using a simple configuration.

A morphology phase unwrapping method with one code grating

This paper presents a fast and robust phase unwrapping method with only one code grating, named the morphology phase unwrapping (MPU) method. Using mathematical morphology operations, more than 36 fringe orders can be obtained accurately from only one code grating rather than at least three code gratings. Comparison experiments demonstrate that MPU has the highest robustness with a high quality factor (Q > 99.9%) under different conditions. Fast-changing facial expressions are reconstructed, indicating potential applications in the fields of augmented reality and virtual reality.

A multimodal and multidirectional vibrational energy harvester using a double-branched beam

Vibrational energy harvesters, which are generally based on a single cantilever beam, are mainly effective for excitations perpendicular to the beam. However, typical ambient vibrations are of multifrequency and are multidirectional. To achieve full harvesting of multifrequency vibrational energy in multiple directions, this letter proposes a multidirectional vibrational energy harvester utilizing multimodal vibrations of a double-branched beam that has four natural frequencies below 22u2009Hz. Comparison experiments in different directions demonstrate an improvement of energy harvesting when this double-branched beam is used. Under horizontal excitation, the maximum open-circuit voltage is increased to 1845%. Under vertical excitation, the average power density is increased over 3800 times. The experimental results indicate that this structural design significantly improves the energy collection efficiency in both horizontal and vertical directions, even with a lighter structural weight.Vibrational energy harvesters, which are generally based on a single cantilever beam, are mainly effective for excitations perpendicular to the beam. However, typical ambient vibrations are of multifrequency and are multidirectional. To achieve full harvesting of multifrequency vibrational energy in multiple directions, this letter proposes a multidirectional vibrational energy harvester utilizing multimodal vibrations of a double-branched beam that has four natural frequencies below 22u2009Hz. Comparison experiments in different directions demonstrate an improvement of energy harvesting when this double-branched beam is used. Under horizontal excitation, the maximum open-circuit voltage is increased to 1845%. Under vertical excitation, the average power density is increased over 3800 times. The experimental results indicate that this structural design significantly improves the energy collection efficiency in both horizontal and vertical directions, even with a lighter structural weight.