A systematic review of empirical research on learning with 3D printing technology

Although 3D printing (3DP) technology has become an increasingly popular educational tool in recent years, very little is known about the learning benefits of this technology. This systematic literature review synthesized empirical research on learning with 3DP in various educational settings, focusing on publication and study participants' characteristics, curriculum areas, research methodologies, instructional approaches, educational outcomes and benefits. A comprehensive survey of published and unpublished studies identified 78 empirical studies that met the inclusion criteria. In addition to positive effects on learning, 3DP facilitated innovative curriculum development and created opportunities for cross-disciplinary research. The findings revealed five major trends in 3DP learning: (1) prepare a new generation of engineers, (2) democratize additive manufacturing technology and production, (3) support learning using low-cost 3D printed learning aids, (4) produce assistive technologies, and (5) promote creativity and innovation. The review identifies critical gaps in the literature and offers suggestions for future research.     

Low‐cost and easy manufactured dielectric rod antennas based on 3D printing technology

Novel dielectric rod antennas (DRAs) are proposed in this article with the merits of low‐cost and easy fabrication. The printed log‐periodic dipole array is introduced as a feeding source. The cylinder‐shaped rods are perforated with air holes of different shapes and sizes to vary the spatial effective permittivity distribution, which mimics the arrangement of traditional multilayer rod antennas. Comparing with traditional multilayer rods, the proposed DRAs use only a single type of dielectric material while achieving similar bandwidth and gain increment performances. Thanks to 3D printing technology, the proposed antennas can be designed with much increased flexibility. Meanwhile, the fabrication cost and complexity can be drastically reduced, since only a single type of dielectric material is needed. Furthermore, both rod antennas were fabricated and measured. The proposed rod antennas have peak gains of 13.32 to 13.45 dBi, 1‐dB gain bandwidth of 25.2% to 26% and average gains of 12 to 12.5 dBi.     

Enhancing middle school students' scientific learning and motivation through agent‐based learning

Facing students' decreasing motivation to pursue scientific study, schools and educators need to coordinate new technologies with pedagogical agents to effectively sustain or promote students' scientific learning and motivation to learn. Although the provision of pedagogical agents in student learning has been studied previously, it is not clear what benefits the strategy might offer with regard to student motivation. This study proposes an agent‐based mechanism that integrates problem‐solving and inquiry‐based instructions to help students better understand complex scientific concepts and to sustain their motivation to learn science. In this study, a quasi‐experiment was conducted to evaluate the performance and feasibility of our proposed mechanism. The results revealed that the agent‐based mechanism was effective and feasible for enhancing students' learning and motivation to learn. The mechanism was associated with increases in the acquisition of knowledge when compared with the control group. Its effect in promoting and sustaining students' motivation was also statistically significant. Detailed discussions of the findings are provided in this study.     

Exploring 3‐D virtual reality technology for spatial ability and chemistry achievement

We investigated the potential of Second Life^® (SL), a three‐dimensional (3‐D) virtual world, to enhance undergraduate students’ learning of a vital chemistry concept. A quasi‐experimental pre‐posttest control group design was used to conduct the study. A total of 387 participants completed three assignment activities either in SL or using two‐dimensional (2‐D) images. Students were administered an 11‐question chemistry achievement test and two measures of spatial ability (Purdue Visualization of Rotations Test, Card Rotations Test). Although analyses of covariance revealed no statistically significant differences between the two groups as a whole for any of the outcome measures, a subgroup analyses was conducted to decompose the relative impact of 3‐D virtual reality instruction within SL. We found that students classified as having poor spatial ability showed significantly greater improvement in understanding the 3‐D nature of molecules if they did relevant activities in a 3‐D virtual world than those students who only worked with 2‐D images.     

Development of a 42‐in. 2‐D/3‐D switchable display using multi‐view technology for public‐information‐display applications

Abstract— A 42‐in. 2‐D/3‐D switchable display operating in a parallax‐barrier‐type system consisting of liquid‐crystal displays (LCDs) has been developed. The system displays 2‐D images in full resolution, without any degradation to the original 2‐D images, and 3‐D autostereoscopic images with resolutions higher than SVGA with wide viewing zones electrically controlled by the parallax‐barrier system. The system is intended for use in public‐information displays (PIDs), a booming field, and as displays for gaming, medical, and simulation applications.     

Design and prototype manufacturing of a feed system for Ku‐band satellite communication by using 3D FDM/PLA printing and conductive paint technology

In this study, the realization of a Ku‐band feed system for reflector antenna in satellite communication systems is presented using 3D printing and conductive paint methods. The system includes a corrugated conical horn antenna designed to operate at 10.5 to 18.5 GHz and an H‐plane waveguide diplexer to operate at 10.7 to 12.75 GHz and 17.3 to 18.4 GHz in receive (RX) and transmit (TX) bands, respectively. In the manufacturing of the structures, fused deposition modeling (FDM) technology and polylactic acid material are processed for 3D printing, where nickel and silver conductive‐based paints are used for coating purpose. The measurement results of the feed system are found to be in good agreement with simulations that the combined (nickel‐coated antenna and silver‐coated diplexer) structure has return loss of more than 10 dB and high gain performance of 12 to 17 dBi within the RX and TX bands of 10.7 to 12.75 GHz and 17.4 to 18.8 GHz, respectively; while rejection (isolation) level between TX and RX ports is higher than 60 dB. The complex structure containing several detailed shapes inside shows that this low‐cost production technique as compared to high‐cost CNC‐based metallic production technology can be used for the prototype structures or proof‐of‐concept type studies of Ku‐band systems.     

Using cross‐talk simulation to predict the performance of anaglyph 3‐D glasses

Abstract— The anaglyph 3‐D method is a widely used technique for presenting stereoscopic 3‐D images. Its primary advantage is that it will work on any full‐color display (LCDs, plasmas, and even prints) and only requires that the user view the anaglyph image using a pair of anaglyph 3‐D glasses with usually one lens tinted red and the other lens tinted cyan (blue plus green). A common image‐quality problem of anaglyph 3‐D images is high levels of cross‐talk — the incomplete isolation of the left and right image channels such that each eye sees a “ghost” of the opposite perspective view. An anaglyph cross‐talk simulation model has been developed which allows the amount of anaglyph cross‐talk to be estimated based on the spectral characteristics of the anaglyph glasses and the display. The model is validated using a visual cross‐talk ranking test which indicates good agreement. The model is then used to consider two scenarios for the reduction of cross‐talk in anaglyph systems and finds that a considerable reduction is likely to be achieved by using spectrally pure displays. The study also finds that the 3‐D performance of commercial anaglyph glasses can be significantly better than handmade anaglyph glasses.     

Time‐ and State‐Dependent Input Delay‐Compensated Bang‐Bang Control of a Screw Extruder for 3D Printing

In this paper, a delay‐compensated bang‐bang control design methodology for the control of the nozzle output flow rate of screw extruder‐based three‐dimensional printing processes is developed. A geometrical decomposition of the screw extruder in a partially and a fully filled regions allows to describe the material convection in the extruder chamber by a one‐dimensional hyperbolic partial differential equation (PDE) coupled with an ordinary differential equation. After solving the hyperbolic PDE by the method of characteristics, the coupled PDE–ordinary differential equation's system is transformed into a nonlinear state‐dependent input delay system. The aforementioned delay system is extended to the non‐isothermal case with the consideration of periodic fluctuations acting on the material's convection speed, which represent the process variabilities due to temperature changes in the extruder chamber, resulting to a nonlinear system with an input delay that simultaneously depends on the state and the time variable. Global exponential stability of the nonlinear delay‐free plant is established under a piecewise exponential feedback controller that is designed. By combining the nominal, piecewise exponential feedback controller with nonlinear predictor feedback, the compensation of the time‐dependent and state‐dependent input delay of the extruder model is achieved. Global asymptotic stability of the closed‐loop system under the bang‐bang predictor feedback control law is established when certain conditions related to the extruder design and the material properties, as well as to the magnitude and frequency of the materials transport speed variations, are satisfied. Simulations results are presented to illustrate the effectiveness of the proposed control design. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of 3D depth on the resolution and the observed image for auto‐stereoscopic multi‐view 3D display

In auto‐stereoscopic multi‐views, blurring occurs due to the incomplete separation of views for non‐zero depths. How this blur affects a 3D image was investigated using the commercial multi‐view 3D. The 3D input signal consisted of the square pattern and the gratings of various width and gray level values of G1 and G2. The various combinations of G1 and G2 were used to investigate the dependence of blur on gray G1 and G2 values. The 3D depth caused blurring, which caused a decrease in contrast modulation. Hence, the 3D resolution determined from contrast modulation was affected by the depth and became worse with increasing depth. Therefore, 3D resolution may be used to define the depth range within which the image degradation due to blurring is acceptable. Blur edge width values at the boundaries of gray G1 and G2 were measured and found to be similar irrespective of G1 and G2 values at the same depth. This was because blur was caused by the incomplete separation of views that are independent of G1 and G2. Hence, the blurriness of the observed 3D image is determined only by the depth. The 3D resolution and blur edge width might be useful to characterize the performance of auto‐stereoscopic multi‐view 3D.     

Effect and experiment of curvature radius of 3‐D printed conformal load‐bearing antenna array on EM performance

Prototypes of a special conformal load‐bearing antenna array (CLAA) which has nondevelopable surface, are designed, fabricated, and tested, and the effect of the substrate curvature radius on its EM performance is also researched in this work. A novel three‐dimensional (3‐D) printing technology and fabrication equipment based on micro‐droplet spraying and metal laser sintering are proposed to create patch array and divider network on a non‐developable curved rigid substrate. In order to compare with conventional technology (such as chemical etching), a planar CLAA prototype with two patches, operating frequency at 5GHz, is designed and fabricated by two different technologies, the surface roughness, fabrication tolerance, and EM performance are tested and compared. Finally, a spherical CLAA prototype with eight patches, operating frequency at 13GHz, is designed and fabricated by the novel 3D printing, measured EM performance demonstrate the applicability of additive manufacturing for this special CLAA.     

“3D 机械制图”教学中提高学生读图能力的实践与思考

随着以三维实体结构的表达方式为主干,三维设计表达方法和二维工程图 表达方法并重的知识结构体系的教学改革的不断深入,越来越多的人开始了解它,相关文献 也逐渐增多。因为随着计算机科学技术的发展,计算机技术已逐渐渗透到其他科学当中,同 时使得社会的产业结构也在悄悄的发生着变化,工程制图作为一门古老的学科也迎接着新科 技时代到来所带来的变革。因此,为了顺应时代的发展,图学教育完成由二维投影表达三维 立体过渡到直接三维设计将是历史发展的必然趋势。 论文结合十多年来讲授“3D 机械制图”的实践,总结多年的教改实际,针对如何改善 学生空间想象能力,更好地完成三维到二维的过度这一问题,介绍了作者近年来的教学实践 与思考。     

Optical simulation for cross‐talk evaluation and improvement of autostereoscopic 3‐D displays with a projector array

Abstract— Multi‐view spatial‐multiplexed autostereoscopic 3‐D displays normally use a 2‐D image source and divide the pixels to generate perspective images. Due to the reduction in the resolution of each perspective image for a large view number, a super‐high‐resolution 2‐D image source is required to achieve 3‐D image quality close to the standard of natural vision. This paper proposes an approach by tiling multiple projection images with a low magnification ratio from a microdisplay to resolve the resolution issue. Placing a lenticular array in front of the tiled projection image can lead to an autostereoscopic display. Image distortion and cross‐talk issues resulting from the projection lens and pixel structure of the microdisplay have been addressed with proper selection of the active pixel and adequate pixel grouping and masking. Optical simulation has shown that a 37‐in. 12‐view autostereoscopic display with a full‐HD (1920 × 1080) resolution can be achieved with the proposed 3‐D architecture.     

Effect of number of views to the viewing experience with autostereoscopic 3‐D displays

Abstract— The observers' 3‐D viewing experience when the way the content is created and shown on an autostereoscopic 3‐D display alternate is evaluated. The observer's depth impression, and the perceived contour accuracy and image naturalness or peskiness of the content shown on a 3‐D display, has been investigated. In addition, the consequences of the way the content is created to the results from the optical characterization for the same display have been studied. The alternation of the content was realized in two different ways. Firstly, the number of views for creating the image was varied. Two, five, and 14 views were used; the main focus being on testing the same display and treating it as an ordinary two‐view and a 14‐view display with inter‐sub‐view crosstalk. Also, the intermediate condition where five views with non‐uniform view‐specific crosstalk were used has been investigated. Secondly, the way the content is created was varied by using images with computer‐generated content and photos. The effect of these parameters on viewing experience as such and especially the effect of 3‐D crosstalk on the viewing experience were studied.     

Stereoscopic 3‐D display with optical correction for the reduction of the discrepancy between accommodation and convergence

Abstract— This paper describes a method for reducing the discrepancy between accommodation and convergence when viewing stereoscopic 3‐D images. The method uses a newly developed stereoscopic 3‐D display system with a telecentric optical system and a mobile LCD. The examination of a mono‐focal lens showed that a correction lens having the appropriate refractive power and conditions for presenting stereoscopic 3‐D images clearly reduces the discrepancy between accommodation and convergence. The authors also developed a stereoscopic 3‐D display that uses dynamic optical correction to reduce the discrepancy between accommodation and convergence. The display equalizes the theoretical points of accommodation and convergence. The purpose of the development was to expand the regeneration range of a stereoscopic 3‐D image having the appropriate accommodation. An evaluation of the developed display showed that it resolves the discrepancy between convergence and accommodation.     

An alternative to language learner dependence on L2 caption‐reading input for comprehension of sitcoms in a multimedia learning environment

Most second/foreign language (L2) learners have difficulty understanding listening input because of its implicit and ephemeral nature, and they typically have better reading comprehension than listening comprehension skills. This study examines the effects of using an interactive advance‐organizer activity on the DVD video comprehension of L2 learners to provide an alternative to the scenario of L2 learners experiencing sensory overload in a multimedia learning environment that presents pictures, printed words and speech words. A total of 95 intermediate university‐level L2 learners with an average TOEIC (Test of English for International Communication) score of 565 were placed in four conditions for an English‐language DVD viewing task, including an advance‐organizer group, a captions group, a captions plus advance‐organizer group, and a control group. The study concludes that using advance organizers as an instructional strategy facilitated participant listening comprehension and reduced participant dependence on L2 caption‐reading input by 50% for initial comprehension. Participants also held a positive attitude towards an interactive advance‐organizer activity. The details concerning the role of L2 captions in multimedia listening are also discussed. The findings provide insight into teaching listening to L2 learners who learn most of their L2 in a more reading‐dependent classroom setting and typically have enhanced L2 literacy skills.     

Experimental insight into the temperature effects on DC and microwave characteristics for a GaAs pHEMT in multilayer 3‐D MMIC technology

This paper is focused on studying the behavior of a GaAs pseudomorphic high electron mobility transistors (pHEMT) with respect to the temperature. The tested pHEMT is realized using the multilayer three‐dimensional (3‐D) monolithic microwave integrated circuit (MMIC) technology. The analysis is based on temperature‐dependent on‐wafer measurements carried out from 298 K to 373 K. The experiments consist of DC characteristics and scattering parameters in the broad frequency range from 45 MHz to 40 GHz. The effect of the temperature on the measured transistor performance is analyzed in detail and then, to gain a better insight and understanding of the device behavior, the achieved measurements are used for extraction and validation of a small‐signal equivalent‐circuit model for different temperature conditions. This study shows that, by heating the studied device, the observed performance variations depend remarkably on the selected bias condition. In particular, the output current and transconductance are degraded at higher gate‐source voltage and improved as the transistor is driven towards the pinch‐off. This is due to the counterbalancing of temperature‐dependent effects contributing in opposite ways to the resultant behavior of the transistor. Therefore, depending on the given application, an appropriate selection of the bias and temperature conditions is essential to guarantee adequate transistor performance.     

Robust design of iterative learning control for a batch process described by 2D Roesser system with packet dropouts and time‐varying delays

Batch process, working as a best choice for low‐volume and high‐value products in manufacturing, has been widely used in chemical industries. The actuator faults and time delays often occur in practical production. This paper develops an iterative learning control (ILC) design for a batch process described by two‐dimensional (2D) Roesser system with packet dropouts and time‐varying delays. The phenomenon of actuator faults is regarded as an arbitrary stochastic sequence satisfying the Bernoulli random binary distribution. Firstly, the ILC design for a batch process is transformed into stability analysis for a 2D stochastic system with time‐varying delays. Secondly, for analyzing the stability of 2D stochastic systems, we derive the stability condition in terms of linear matrix inequality. Then, we give a procedure to get the control gain for the ILC design. An injection modeling process as an example with simulations in different cases of data dropout is given to demonstrate the validity of the proposed method. Furthermore, the proposed method has a better result by comparing the existing methods.