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Using Millimeter Wave Technology to Prevent Future Viral Outbreaks
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cally a fusion peptide — to infect host cells. This fusion process does not evolve and change as quickly as other parts of the pro- tein, so if it can be nullified, potentially broadly-acting antiviral strategies can be developed. The researchers needed a way to observe
the microscopic process of the spike protein’s shape shifting during fusion. “We have unique facilities for doing such confirmation dynamics of proteins,” says Dunnam. “We send out very short, well-defined pulses, but at millimeter wavelengths. The induced electron spin resonance signals exhibit an intrinsically high SNR and band- width, resulting in several orders of mag- nitude improvement in speed and resolu- tion over NMR methods.” Virginia Diodes, Inc. (VDI) built the
world’s highest-power solid-state coher- ent 240 GHz source that puts out 500 mW for Cornell’s ACERT center. “Increased power enables a very short pulse that provides increased spectral coverage of the sample,” adds Dunnam. “However, at half a watt we can’t afford to give up anything through insertion loss, hence we require an extremely effi- cient isolator.”
Expanding MMW R&D VDI referred Dunnam to MMW technolo-
gy specialist Micro Harmonics for the produc- tion of an isolator that operates at such high frequencies with low insertion loss. Ultimately,
CAD drawing of Cornell’s spectrometer.
neering challenges faced at such high fre- quencies. The relatively increased power enables a very short pulse that provides increased spectral coverage of the protein
the company delivered a component with only 1.2 dB of insertion loss at 240 GHz. Under a two-phased NASA contract,
Micro Harmonics developed a line of advanced isolators for applications that span frequencies from 50 to 330 GHz. The incredi- bly low insertion loss is achieved by reducing the length of an internal ferrite rod as much as possible. The design saturates the ferrite with an unusually strong magnetic bias field, which enables the incident signal to rotate the required 45° in the shortened rod. Dunnam goes on to point out other engi-
sample. But after the last transmitted pulse in this application, full receiver sensitivity to the reflected decaying electron spin signal is required within 10 nanoseconds. “Any kind of ringing in the system that is
due to reflections can increase ‘dead time’ and obscure results, so all the impedance mis- matches and spurious signals in the system must be less than 0.1%.” states Dunnam. “Additionally, the solid-state source multiplier conversion efficiency and stability can be adversely impacted by out-of-phase signals being reflected back. Low port reflection in the isolator helps keep all that in check.” The source could be destroyed by too
much reflected energy, and since it was expensive to fabricate, it needed to be protected. Lastly, the issue of heat absorption
must be addressed even at sub-watt transmitter power levels. Power in the reverse signal is absorbed within the iso- lator, creating heat. Historically, high heat was not an issue as there was very little power available from solid-state sources at MMW frequencies, but as Dunnam points out, 500 mW at 240 GHz is, relatively speaking, a lot. In his research center’s application
of studying viral proteins, wavelengths are short and components are necessari-
ly small and fragile. To overcome the problem of high heat
loads, the Micro Harmonics isolators selected by Dunnam incorporate diamond heatsinks into their design. Diamond is the ultimate
Continued on next page
June, 2021
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