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JUNE 2019 I DESIGN007 MAGAZINE 75 ductors that were narrower than the glass weave geometry, and then inspected many circuits to evaluate which had the low and high Dk configuration from the local trace environment. In this study, we used a worst-case sce- nario laminate, which was a pure resin sys- tem without any filler particles. Additional- ly, the laminate had one layer of glass rein- forcement. From that study, and consider- ing the low and high Dk from the local trace environment, we found a difference in Dk of 0.090 at 77 GHz when using 106 glass. When using 1080 glass, we saw a Dk differ- ence of 0.14 at 77 GHz, and when using a spread glass (i.e., no openings in the glass- weave pattern), we saw a difference in Dk of 0.020 at 77 GHz. Also, as part of our glass weave study, we evaluated a ceramic-filled laminate us- ing 1080 glass and compared the results to the unfilled laminate (as previously de- scribed) using the same glass style. Again, comparing the low and high Dk conduc- tors as shown in Figure 1 for the local trace environment, we saw a Dk difference of 0.010 for circuits using 1080 glass with a ceramic-filled resin system. The same test- ing with the unfilled system mentioned ear- lier showed a Dk difference of 0.090. This shows that the ceramic particles used as filler in some laminates help to mitigate the glass weave effect. Many available laminates do not contain woven glass, so the glass weave effect is not an issue. Some laminates intended to be used at mmWave frequencies do feature glass reinforcement; however, these lami- nates use a spread glass with ceramic filler. They are optimum for minimizing concerns of glass weave effect for mmWave and high- speed digital applications. DESIGN007 John Coonrod is technical marketing manager at Rogers Corporation. To read past columns or contact Coonrod, click here. New Approach Captures Detailed Mid-infrared Images for Medical Diagnostics Researchers have developed a unique high-resolution imaging method that can capture mid-infrared spectral images of fast events or dynamic processes that take place on the order of milliseconds. This spectral range is used for many applications because it can reveal the de- tailed chemical composition of a sample. "This novel approach could one day be used to pre- screen medical biopsies to identify the ones that need closer examination," said Peter Tidemand-Lichtenberg, a member of the research team from DTU Fotonik in Denmark. The researchers drew on a process known as nonlin- ear frequency conversion in which energy is added to a photon to change its wavelength, and hence its color. Al- though frequency conversion, or upconversion, is often used to change the wavelength of a laser's output, the researchers from DTU Fotonik developed a detection sys- tem that could shift an entire mid-IR image into the near- infrared wavelength range while preserving all the spa- tial information. The system incorporates a new mid-infrared light source developed by collaborators from The Institute of Photonic Sciences (ICFO). This single-wavelength light source can be tuned to different wavelengths and it also uses frequency conversion to generate the mid-infrared light. In fact, the researchers used the same pulsed near- infrared laser for two things: to generate the tunable mid- IR light and to achieve the image upconversion. "This approach yields high peak power pulses in per- fect synchronism, eliminating the need for sophisticat- ed temporal control of the pulses, leading to images with a good signal-to-noise ratio," explained Tidemand-Lich- tenberg. (Source: OSA)

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