Stanford University
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The story of how low frequency radio waves connect space, underground, and everything in between

When:
Thursday, May 23, 2019 12:00 PM
Where:
Mitchell 350/372
Audience:
Faculty/Staff, Students, Alumni/Friends, Members
Sponsor:
Geophysics Department

Geophysics Department Seminar

Speaker: Morris Cohen; Associate Professor, Electrical and Computer Engineering, Georgia Tech

The Story of How Very Low Frequency Radio Waves Connect Space, Underground, and Everything in Between

The simple act of recording very low frequency (VLF) radio waves (3-30 kHz) is incredibly simple, yet unlocks a bevy of connections across science and engineering.  Lightning releases VLF energy which travel thousands of miles, allowing lightning to be characterized, geolocated, and integrated into weather forecasting. VLF waves reflect from the ionospheric D-region (60-90 km altitude), sensing a region too low for satellites yet too high for balloons, which in turn affects a number of critical communication systems (submarine, nuclear fleet, HF, aviation industry). Perhaps the most surprising impact of VLF waves is in the `space weather’ environment, where solar flares and coronal mass ejections unleash a dynamic chain of events that can lead to massive power outages and widespread communication blackouts.

On the engineering side, VLF waves can be used to peer underground and inside metal boxes, where higher radio frequencies cannot reach.  VLF waves can even be used for cybersecurity and diagnostics of the power grid. Existing instruments can receive exceptionally weak VLF magnetic fields, but transmitting VLF waves requires novel antenna designs, since the long wavelengths (10-100 km) makes conventional antennas difficult to implement.

In this talk, we will review the generation, propagation, and reception of VLF radio waves, and discuss its various applications in both scientific and engineering areas.

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