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Terahertz radiation generator – Linked micro-magnetrons

Microelectromechanical system-based reverse magnetron

Medical & Biotechnology Sensors

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Terahertz (THz) radiation has applicability in fields where intense sources of radiation are needed, such as in improvised explosive device detection, airport security, semiconductor applications, medical imaging, and spectroscopy for large chem-bio molecules. Most current sources of THz radiation are either very dim, very inefficient, or both. While quantum cascade lasers can be as bright as 50 mW, they require cryogenic cooling. Unfortunately, other devices capable of generating intense sources of THz radiation are uniformly bulky and difficult to transport (such as free electron lasers and synchrotron radiation sources).

The microelectromechanical system is based on a reverse magnetron. The cathode is shown in green and the anode in blue.

Magnetrons have featured prominently in the production of intense microwave radiation. While the external configurations of different conventional magnetrons vary, the basic internal structures are generally the same—a central filament or cathode, an outside anode cylinder around the cathode, an antenna, and magnets. The motion of electrons is due to the combined influence of cross electric (radial) and magnetic (axial) fields.

In this case, the radiation frequency is near to the cyclotron frequency and amplification is achieved as the whirling cloud of electrons, influenced by the high voltage and the strong magnetic field, forms a rotating pattern that resembles the spokes in a spinning wheel. The electrons interact with an alternating current flow in the resonant cavities configured at the inner surface of the anode. But, in order to achieve radiation frequencies in the THz region, unrealistically large magnetic fields, of several Tesla, are required.

Naval scientists have envisioned and patented a THz reverse micro magnetron which includes a cathode ring and anode post located within the center of the cathode ring. An applied voltage between the cathode ring and the anode post causes field-emitted electrons to be accelerated radially inwards producing radiation. In a MEMs configuration, each THz reverse magnetron apparatus is less than 200 μm, so 100’s of these devices can be configured on a chip and connected by a conducting substrate. A substantial power enhancement can be achieved by positioning the chip in a large confocal cavity with all THz reverse micro magnetrons coupled electromagnetically through cavity mirrors. With the confocal cavity configurations, the range of Q values (at 1 THz) is from 106 to 107. Because there can be several hundred THz reverse micro magnetrons on a chip, each coupled through a feedback mechanism, there is a substantial power enhancement. Even assuming a 1% efficiency, the THz power can be from about 150 mW to about 1 W. This is in contrast to conventional quantum cascade lasers in the THz which yield a maximum of about 20 mW and which need to be cooled at liquid helium temperatures, with efficiencies of the order of 0.01%.

This US patent 8,624,497 is directly related to US patent 8,446,096. The ‘497 patent adds scalloping to the interior wall of the cathode ring and also embodies claims related to configurations involving many micro magnetrons on a chip connected by a substrate assembly.

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Yes
Yes
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4%
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50%
50%

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