Abstract: A low-inductance package for multiple paralleled devices includes an electrically insulating substrate having three power terminals direct-bonded to the upper surface thereof and a conductive pad direct-bonded to the lower surface thereof for connection to a heat sink. Two groups of multiple parallel-coupled devices are each soldered to one of the three power terminals and are further connected in a half-bridge configuration such that one of the three power terminals is common to both groups of devices. The package further includes a pair of first Kelvin terminals, i.e., a first Kelvin control terminal and a first Kelvin source terminal, and a pair of second Kelvin terminals, i.e., a second Kelvin control terminal and a second Kelvin source terminal. The Kelvin terminals are soldered to the appropriate power terminals, depending upon the particular circuit configuration.

Abstract: A cryogenic solid-state semiconductor power device, has the actual device chip mounted on a substrate of a material of very high thermal conductivity, which is positioned in a a bath of cryogenic fluid. The substrate may be formed of beryllia, beryllium, alumina, aluminum nitride, diamond and the like materials.

Abstract: A gradient current speed-up circuit, for use in a higher-speed NMR imaging system having an associated gradient coil, has a gradient power amplifier receiving an input analog signal controlling the current in an amplifier output circuit connected in series between first and second portions of a single gradient coil. Semiconductor switching elements selectively connect the coil portion-amplifier-coil portion between first and second potential sources, and are turned on and off in selected patterns to cause a current to be suddenly applied to, and removed from, flow through the associated gradient coil and the amplifier output circuit.

Abstract: A gradient current speed-up circuit, for use in a higher-speed NMR imaging system having an associated gradient coil, has a gradient power amplifier receiving an input analog signal controlling amplifier output current, and a transformer having a primary winding and a pair of secondary windings connected in series with the amplifier output and the coil. Semiconductor switching elements selectively connect the primary winding between first and second potential sources, and are turned on and off in selected patterns to cause a current to be suddenly applied to, and removed from, flow through the associated gradient coil; the amplifier output current is changed with the gradient coil current lags behind an amplitude commanded by a master input signal.

Abstract: A method of reducing slice profile degradation due to gradient signal amplitude ripple, has steps of: sensing the gradient signal ripple amplitude; normalizing the sensed ripple signal amplitude responsive to the gradient amplitude commanded; and modulating the RF signal amplitude with the adjusted-amplitude ripple signal, to cause the RF and gradient magnetic fields to have an effective vector pointing substantially in the same direction, during the slice-selection interval, as would the effective field vector formed with a gradient field devoid of ripple. Apparatus for reducing the slice profile degradation modulates the RF signal with the ripple envelope obtained from the output of the gradient signal amplifier, by a signal controlled by the gradient amplifier input.

Abstract: A gradient current speed-up circuit, for use in a higher-speed NMR imaging system with a gradient power amplifier and an associated gradient, coil, has a high-voltage power supply which is selectively connected to the associated gradient coil, typical via a plurality of semiconductor switching elements, to supply a pulse of a very high voltage when fast coil rise and fall times are needed. The gradient coil is connected between selected ones of semiconductors devices which are turned on and off in selected patterns, to cause the direction of coil current flow to be determined.

Abstract: A cryogenically-cooled RF power amplifier utilizes a plurality of metal-oxide-semiconductor field-effect transistors configured on a heat sink having at least one surface in contact with a cryogenic fluid, and having input means for coupling RF driving power into the plurality of cryogenically-cooled MOSFETs and output means for coupling an amplified level of RF power from the cooled MOSFETs to an antenna.

Abstract: A gradient current speed-up circuit, for use in a higher-speed NMR imaging system with a gradient power amplifier and an associated gradient coil, has an energy-storage element, with an inductance typically between 5 and 20 times the inductance of the associated gradient coil. A plurality of semiconductor switching elements receive the current output of the energy-storage element; and the associated gradient coil is connected between selected ones of these semiconductors devices. The semiconductor devices are turned on and off in selected patterns, to cause the energy-storage element current to be suddenly applied to and removed from flow through the associated gradient coil.

Abstract: A method for NMR spectroscopy metabolite imaging utilizes the steps of: applying to a desired portion of a sample a pulsed phase-encoding linear magnetic gradient signal in at least one of the three orthogonal dimensions of a Cartesian coordinate set, prior to acquisition of free-induction-decay NMR response signals from the sample portion; substantially eliminating from at least the sample portion eddy current fields induced responsive to the phase-encoding gradient pulses; maximizing the signal-to-noise ratio of the NMR response signals; and displaying the data resulting from Fourier transformation of the received response data. A high-field NMR imaging system is provided with self-shielded gradient coils, to subsantially remove eddy-current effects, and at least one of maximized-SNR antenna, of quadrature-driven volume RF coil and/or surface RF coil types are utilized for both transmission of the excitation RF pulses and reception of the RF response signals.

Abstract: An unconditionally-stable, ultra-low-noise RF preamplifier, for an operating frequency within the range from about 15 MHz. to about 500 MHz., has a first stage in which a MESFET device is operated in the common-source configuration, with an active load providing an effective impedance to the first stage to cause the stability factor K for the entire preamplifier to exceed a value of 1.00 over the entire frequency range. A second stage, acting as at least a portion of the active load on the first state, containing a plurality of active devices coupled in parallel to provide a substantially constant input impedance over the frequency range.

Abstract: In one embodiment, referred to as the "high-pass" version, the radio frequency (RF) coil is made up of two conductive loop elements, each including serially-connected capacitors. The loop elements are electrically interconnected by axial conductive segments having inherent inductances associated therewith. Electrically, the coil can be viewed as a slow wave delay line structure wrapped around a cylinder and connected to itself. The coil can be energized by connecting a source of RF power across one of the capacitors in the loop elements. In another embodiment, termed the "band-pass" version, the axial conductive segments, as well as the conductive loop elements, are provided with capacitors.

Abstract: A four-way power splitter/combiner apparatus comprises five unbalanced ports, configured as a common port and four other ports, with power introduced into the common port, over a relative wide frequency band, being substantially equally divided between the four other ports, and vice versa. Each of the first and second ports of each pair of the four other ports has a substantially in-phase signal thereat, with the first in-phase pair of ports having a substantially 180.degree. signal phase difference from the substantially in-phase signals at the other pair of ports. Each of the balun and 2-to-1 transformers of the push-pull 4-port apparatus can be fabricated of a magnetically-decoupled coaxial cable assembly, wherein the cables are all of the same characteristic impedance as the load impedance magnitude at each of the five ports.

Abstract: A low-noise radio-frequency preamplifier, especially suited for use in the reception channel of a nuclear magnetic resonance spectrometer and the like, utilizes a low-noise input stage having a plurality of bipolar junction transistors effectively connected in radio-frequency parallel, but with each of the plurality of parallel bipolar transistors isolated from one another for direct current flow through at least one electrode thereof.