Patent No. 4585999 Radiofrequency amplifier based on a dc superconducting quantum interference device
Patent No. 4585999
Radiofrequency amplifier based on a dc superconducting quantum interference device (Hilbert, et al., Apr 29, 1986)
Abstract
A low noise radiofrequency amplifier (10), using a dc SQUID (superconducting quantum interference device) as the input amplifying element. The dc SQUID (11) and an input coil (12) are maintained at superconductivity temperatures in a superconducting shield (13), with the input coil (12) inductively coupled to the superconducting ring (17) of the dc SQUID (11). A radiofrequency signal from outside the shield (13) is applied to the input coil (12), and an amplified radiofrequency signal is developed across the dc SQUID ring (17) and transmitted to exteriorly of the shield (13). A power gain of 19.5.+-.0.5 dB has been achieved with a noise temperature of 1.0.+-.0.4 K. at a frequency of 100 MHz.
Notes:
A radiofrequency amplifier as described
herein would have particular use in nuclear magnetic resonance (NMR) imaging
systems, wherein very low level radiofrequency signals are generated by resonating
hydrogen nuclei in a tissue specimen. For hydrogen nuclei in a field of one
tesla, the resonance frequency is 42.57 MHz. Since the intensity of the emitted
signal is proportional to the number of resonant nuclei in the specimen, it
is desirable that the detecting amplifier has as low a noise level as possible
so that the signals from very small volumes of the specimen may be handled.
The foregoing description of a preferred embodiment has been presented for purposes
of illustration and description. It is not intended to be exhaustive or to limit
the invention to the precise form described, and obviously many modifications
and variations are possible in light of the above teaching. The embodiment was
chosen in order to explain most clearly the principles of the invention and
its practical application thereby to enable others in the art to utilize most
effectively the invention in various embodiments and with various modifications
as are suited to the particular use contemplated. Although the amplifier has
use in NMR imaging systems, it can be used in other applications wherein very
low level radiofrequency signals must be detected. It is intended that the scope
of the invention be defined by the claims appended hereto.
Comments