Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a "positive feedback loop" effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the "print-it-all" paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration. The fundamental attributes and challenges/barriers of Additive Manufacturing (AM).The evolution of research on AM with a focus on engineering capabilities.The affordances enabled by AM such as geometry, material and tools design.The developments in industry, intellectual property, and education-related aspects.The important future trends of AM technologies.

The status, challenges, and future of additive manufacturing in engineering

Wireless power technology offers the promise of cutting the last cord, allowing users to seamlessly recharge mobile devices as easily as data are transmitted through the air. Initial work on the use of magnetically coupled resonators for this purpose has shown promising results. We present new analysis that yields critical insight into the design of practical systems, including the introduction of key figures of merit that can be used to compare systems with vastly different geometries and operating conditions. A circuit model is presented along with a derivation of key system concepts, such as frequency splitting, the maximum operating distance (critical coupling), and the behavior of the system as it becomes undercoupled. This theoretical model is validated against measured data and shows an excellent average coefficient of determination of 0.9875. An adaptive frequency tuning technique is demonstrated, which compensates for efficiency variations encountered when the transmitter-to-receiver distance and/or orientation are varied. The method demonstrated in this paper allows a fixed-load receiver to be moved to nearly any position and/or orientation within the range of the transmitter and still achieve a near-constant efficiency of over 70% for a range of 0-70 cm.

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Analysis, Experimental Results, and Range Adaptation of Magnetically Coupled Resonators for Wireless Power Transfer

A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.

Inductive power transfer

Inductive power transfer (IPT) was an engineering curiosity less than 30 years ago, but, at that time, it has grown to be an important technology in a variety of applications. The paper looks at the background to IPT and how its development was based on sound engineering principles leading on to factory automation and growing to a $1 billion industry in the process. Since then applications for the technology have diversified and at the same time become more technically challenging, especially for the static and dynamic charging of electric vehicles (EVs), where IPT offers possibilities that no other technology can match. Here, systems that are ten times more powerful, more tolerant of misalignment, safer, and more efficient may be achievable, and if they are, IPT can transform our society. The challenges are significant but the technology is promising.

Inductive Power Transfer

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1240&context=me_pubs

Machine Learning for High-Throughput Stress Phenotyping in Plants

Wireless power transfer is demonstrated mathematically and experimentally for M primary coils coupled to N secondary coils. Using multiple primary coils in parallel has advantages over a single primary coil. First, the reduced inductance of the transmitting coils makes the amplifier less sensitive to component variations. Second, with multiple receiving coils, the power delivery to an individual receiver is less sensitive to changes in the loads attached to other coils. By using a 16 cm by 18 cm primary and a 6 cm by 8 cm secondary coil, going from a 1:2 coupling to a 2:2 coupling, we show an increase in received power from 1.8 to 9.5 W, with only a small change in coupling efficiency. The advantages of the multiple primary coil topology increase the feasibility of charging multiple wireless portable devices simultaneously.

A Loosely Coupled Planar Wireless Power System for Multiple Receivers

Soil water sensing for water balance, ET and WUE

A 20 cm by 20 cm transmitting coil is designed for an inductively-coupled power transfer system. The coil design is a spiral, whose geometry is optimized to ensure an even magnetic field distribution. This guarantees uniform power delivery regardless of recieving coil position. The transmitting coil is tested using Litz wire, a switchmode power amplifier, and a 6 cm by 8 cm recieving coil connected to a rectifier and a variable load. The system achieves a maximum efficiency of 80.9% and a maximum power delivery of 11.8 W. At a fixed load, the power delivery has a coefficient of variation of 2.2% as the recieving coil's position is varied on the transmitter. In general, the system efficiency is high and insensitive to receiver placement as well as loading conditions.

Transmitting coil achieving uniform magnetic field distribution for planar wireless power transfer system

In wireless power systems for charging battery-operated devices, the selection of component values guaranteeing certain desired performance characteristics can be a tedious trial-and-error process, either sweeping component values in circuit simulations or changing components by hand. This difficulty is compounded by the variable nature of the load resistance presented by a device under charge. This brief considers component selection for a specific wireless power system architecture, which is an open-loop class-e inverter using a series-parallel arrangement for load impedance transformation. Formulas for the optimal receiver, transmitter, and class-e components are derived given a set of constraints on the resistance, phase, quality factor, and drain voltage waveform. Using a 16 cm times 18 cm primary and a 4 cm times 5 cm secondary coil, the derived formulas are used to build a wireless power system. We show that the system has desirable performance characteristics, including a power delivery of over 3.7 W, peak efficiency of over 66%, and decreasing power delivery with increasing load resistance.

Design and Optimization of a Class-E Amplifier for a Loosely Coupled Planar Wireless Power System

A method to determine various operating modes of a high-efficiency inductive wireless power transfer system which is capable of supporting more than one receiver is proposed. The three operating modes are no-load, safe, and fault modes. The detection scheme probes the transmitter circuitry periodically to determine the operating mode. For power saving, the transmitter is powered down when there is no valid receiver placed on the transmitting coil. If any conductive or magnetic object that can affect the total effective inductance of the transmitting coil is located nearby, the system will enter the fault mode and shut down the transmitter so that it will not be damaged. The safe mode is the nominal operation mode when the power transmission efficiency is high with minimum power loss and zero-voltage switching operation of the class-E transmitter is achieved. The determination of the operating mode is achieved by analyzing the transmitting coil voltage and supply current space, requiring no communication link between the transmitter and receiver. The linear relationship between the power delivery and the supply current can be used to calculate the power delivered to the load(s).

Joaquin Casanova

Papers

A Loosely Coupled Planar Wireless Power System for Multiple Receivers

Soil water sensing for water balance, ET and WUE

Transmitting coil achieving uniform magnetic field distribution for planar wireless power transfer system

Design and Optimization of a Class-E Amplifier for a Loosely Coupled Planar Wireless Power System

Method of Load/Fault Detection for Loosely Coupled Planar Wireless Power Transfer System With Power Delivery Tracking