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Author Topic: The research frontier: 1,000,000 MHz = 1 THz  (Read 3426 times)
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AB2EZ
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"Season's Greetings" looks okay to me...


« on: June 24, 2008, 11:39:41 AM »

The Defense Advanced Projects Research Agency (DARPA) has recently posted the following request for proposals:

Terahertz Electronics

Solicitation Number: BAA08-51

Posted Date: June 13, 2008 4:00 pm EST

Current Response Date: August 29, 2008

Classification Code: A -- Research & Development

DARPA is soliciting innovative research proposals in Terahertz (THz) Electronics. Proposed research should investigate innovative approaches that enable revolutionary advances in electronic devices and integrated circuits achieving THz frequencies (at least 1.0 x 10**12 cycles per second). Specifically excluded is research that primarily results in evolutionary improvements to the existing state of practice.

http://www.darpa.mil/mto/solicitations/baa08-51/index.html

Some quotes from the solicitation document:

"THz Power Amplifiers. The proposer will demonstrate a power amplifier
device capable of amplifying radiation at THz frequencies. Approaches may
include, but are not limited to, vacuum electronic devices (such as travelling
wave tubes and extended interaction klystrons) or photonic amplifiers, but
must be compact and amenable to integration with solid-state exciters. Device
performance characteristics will be consistent with the program metrics (see
section D below) taking into account predicted losses when the devices are
integrated into an assembly. Note that high-power sources (as opposed to
amplifiers) are not responsive to this BAA."

[AB2EZ comment: at 1 THz, the wavelength is 0.3 millimeters... so we are talking about some pretty small tubes :-)]

"Recently, compact, micromachined vacuum electronic devices have made it possible to produce compact and relatively high power sub-MMW sources. This technology offers one possible path to achieving efficient THz transmitters, but significant hurdles remain. The most obvious such hurdle is the complex and difficult frequency scaling required for this technology to achieve 1.0THz operation."

So... maybe someday we will see the 5th edition of the Radiotron Designers Handbook, updated with a section on THz tubes and circuits.

Best regards
Stu

P.S. I plan to submit a proposal in response to this solicitation... jointly with a colleague at NJIT... on the subject of low noise, high bandwidth (at baseband or i.f.) receivers for THz systems. Note that the sensitivity of any THz receiver will be fundamentally limited by a combination of thermal effects (as in classical radio frequency communication systems) and quantum effects (as in optical communication systems). At 1 THz frequency, if the absorbing medium (e.g., the atmosphere), through which the THz radiation is propagating, is at room temperature (293K), then the Boltzmann energy, kT, is roughly comparable to the photon energy, hf. I.e., kT ~ 4 x 10**-21 Joules, and hf ~ 6.6 x 10**-22 Joules . I hope to have a chance to combine what I have learned over the years about the design of low-noise radio frequency receivers with what I learned during my earlier research career about the design of optical frequency receivers.
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Sam KS2AM
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« Reply #1 on: June 24, 2008, 04:19:44 PM »


DARPA is soliciting innovative research proposals in Terahertz (THz) Electronics. Proposed research should investigate innovative approaches that enable revolutionary advances in electronic devices and integrated circuits achieving THz frequencies (at least 1.0 x 1012 cycles per second).

So... maybe someday we will see the 5th edition of the Radiotron Designers Handbook, updated with a section on THz tubes and circuits.

Best regards
Stu

P.S. I plan to submit a proposal in response to this solicitation...

I also plan on submitting a related proposal to the FCC to designate 3.870 - 3.890 THz,  i.e.  3.870 X 1012 to 3.890 X 1012 Hz, exclusively as the AM (phone) Window.


Sam / KS2AM
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WBear2GCR
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« Reply #2 on: June 26, 2008, 11:12:28 AM »

ok,

thinking out loud...

at what point does the effective velocity of the oscillating frequency - hauling that electron back and forth, vibrating as it were - become equivalent to the speed of light?

if the frequency becomes high enough is there a quantum effect wherein there appears to be only one singular electron?

or is there actually a frequency limit due to the mass of the electron beyond which it either can or will not go, or beyond which it will disintegrate in to some other subatomic particles?

                   _-_-bear
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AB2EZ
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"Season's Greetings" looks okay to me...


« Reply #3 on: June 26, 2008, 01:33:37 PM »

Bear

at what point does the effective velocity of the oscillating frequency - hauling that electron back and forth, vibrating as it were - become equivalent to the speed of light?

The detection (receiving) device generally consists of:

a. An antenna, which has to be comparable in size to the wavelength c/f ~ 0.3 mm, or larger. Typically it is much larger.
 
and

b. An electronic or an electro-optic device, that responds to the 1THz voltage produced across the "feed point" of the antenna.

If the electronic device depends upon the physical movement of electrons and/or holes across a region containing an electric field (analogous to the region between the cathode and the anode of a vacuum tube), then that region must be thin enough for the electrons and/or holes to travel through the region in a fraction of 10**-12 seconds. If you assume that the average carrier velocity (i.e., the average speed at which electrons or holes move through the region in the presence of the electric field) is 3 x 10**6 meters per second (1% of the speed of light, as an illustrative example), then the thickness of the region through which they have to travel must be less than 3 micrometers. Thus, one of the challenges of working at 10**12 Hz is that some of the dimensions of the devices have to be quite small.

On the other hand, making things with features that are less than 3 micrometers thick is well within the art of photo lithography (<0.1 micrometers) and well within the art of epitaxial layer growth (<0.001 micrometers)

if the frequency becomes high enough is there a quantum effect wherein there appears to be only one singular electron?

Generally speaking, there will be a "shot noise" effect associated with the flow of a fairly small number of electrons and/or holes across the electronic or electro-optic device during each cycle of the THz signal. You could view this as a quantum effect... particularly in the case where the electrons and/or holes are produced by illuminating the device with a pulse of light... in order to generate "photocarriers" within the device for the THz field to act upon.

or is there actually a frequency limit due to the mass of the electron beyond which it either can or will not go, or beyond which it will disintegrate in to some other subatomic particles?

If I recall correctly (and I may not be up to date on the latest physical theory), an electron is considered to be a fundamental particle... which cannot be broken down into "smaller" constituents. [I don't think anyone really knows what an electron is].
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