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44 DESIGN007 MAGAZINE I MAY 2018 4. Understanding Common-Mode Noise, by Pulse Electronics. 5. High-Speed Signal Propagation, by How- ard Johnson. Barry Olney is managing director of In-Circuit Design Pty Ltd (iCD), Aus- tralia, a PCB design service bureau that specializes in board-level simulation. The company developed the iCD Design Integrity software incorporating the iCD Stackup, PDN and CPW Planner. The software can be downloaded from To contact Olney, or read past columns, click here. ground voltage that drives the antennae at the source. PDN noise is the main driver of radiated emissions. • The goal of a low impedance PDN is real- ized by minimizing the spacing between the power and ground planes and by using low impedance decoupling capacitors with low inductance mounting. DESIGN007 References 1. Barry Olney's Beyond Design columns: Return Path Discontinuities, Uncommon Sense- Differential Pairs, Stackup Planning Parts 1-4. 2. Electromagnetic Compatibility Engineer- ing, by Henry Ott. 3. What is Differential and Common-Mode Current? by Ron Brewer. U of T Engineering researchers have developed a hand- held 3D skin printer that deposits even layers of skin tissues to cover and heal deep wounds. The team believes it to be the first device that forms tissue in situ, depositing and set - ting in place in two minutes or less. Their research, led by Navid Hakimi (MIE PhD candidate) under the supervision of Professor Axel Guenther (MIE, IBBME), and in collaboration with Dr. Marc Jeschke, director of the Ross-Tilley Burn Centre at Sunnybrook Hospital, was recently published in the Journal Lab on a Chip. For patients with deep skin wounds, all three skin lay- ers—the epidermis, dermis and hypodermis—may be heav- ily damaged. The current preferred treatment is called split-thickness skin gr afting, where healthy donor skin is grafted into the surface epidermis and part of the underly - ing dermis. Split-thickness grafting on large wounds requires enough healthy donor skin to traverse all three layers, and sufficient graft skin is rarely available. This leaves a portion of the wounded area ungrafted or uncovered, leading to poor heal - ing outcomes. Although a large number of tissue-engineered skin substitutes exist, they are not yet widely used in clinical settings. The handheld skin printer resembles a white-out tape dispenser — except the tape roll is replaced by a microdevice that forms tissue sheets. Vertical stripes of "bio ink," made up of protein-based biomaterials including colla - gen, the most abundant protein in the dermis, and fibrin, a pr otein involved in wound healing, run along the inside of each tissue sheet. The handheld device is the size of a small shoe box and weighs less than a kilogram. The researchers hope that one day they can begin running clinical trials on humans, and eventually revolutionize burn care. "Several steps are needed, but we are con - fident we will get there," says Guenther. Researchers Develop Handheld 3D Skin Printer

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