Abstract: The present invention provides apparatus for utilizing planar HTS probe coils in substantially coplanar coil sets, each set comprised of a plurality of coils, two such similar sets being positioned on opposite sides of the sample to form a plurality of coil pairs. The coil pairs may be used for excitation of the sample, for receiving the NMR response signal or for both. A feature of the invention is the ability afforded to adjust the coupling between coil pairs to a minimum value to thereby prevent interaction between coil pairs having simultaneously applied high power signals and weak NMR response signals.

Abstract: An infrared imaging microscope uses spatial encoding to divide an sample being examined into a plurality of pixel regions. The spatial encoding is provided by a digitally controlled mask, which is preferably a multiple mirror array, and which masks the imaging radiation directed from a radiation source to the sample. The signal reflected or transmitted from the sample is detected using a single-element detector. As the mask pattern provided by the mask changes, the output signal of the detector is monitored, and the spectroscopic composition of each of the pixel regions is resolved using a spatial decoding method, such as a Hadamard transform. The digital control of the mask allows fast, easily-implemented changes to the masking pattern, and provides a low processing load relative to imaging devices that use multiple-element detectors.

Abstract: A gradient magnetic field generator is provided for generating a spatially varying gradient magnetic field for use with a nuclear magnetic resonance spectroscopy probe having a rotatable sample container. The gradient field generator has a plurality of straight line conductive segments which lie parallel to one another and perpendicular to a plane within which lies a rotation axis about which the sample container rotates. The straight line conductive segments each conduct a current which generates a component of the overall gradient magnetic field. The conductive segments preferably lie in a cylindrical distribution about a stator within which the sample container is rotated. The appropriate currents for the conductive segments may be determined by finding a solution for the Jacobian which defines the magnetic field variations in the three-dimensional space of the stator.

Abstract: An insulated dual-bayonet connector is provided. The connector provides simple alignment and connection for both fluid tubes of a fluid recirculation system. The connector is especially useful for closed-cycle systems, but is also useful for open-cycle gas systems where it is desired to vent a gas in a desired location remote from the item to be cooled or heated by the gas.

Abstract: A method and apparatus precisely controlling the periodic motion of an object is specifically applicable to the control of the rotation of a nuclear magnetic resonance (NMR) spectrometer rotor, and uses a fluid source having a fluid output with a time-varying magnitude. The output of the fluid source is coupled to a stator housing within which the rotor is rotatably disposed such that the time varying fluid pressure from the fluid source impinges upon a plurality of vanes located about a circumference of the rotor. The coupling of the fluid flow to the rotor results in a periodicity of the rotor rotation being proportional to a periodicity of the time varying magnitude of the fluid flow. This, in turn, creates a plurality of stable equilibrium rotation rates at which a frequency locking effect is achieved that tends maintain the rotor periodicity at a predetermined rate, thereby achieving particularly precise and stable rotor rotation.

Abstract: An method for determining the inhomogeneities of the magnetic field of the magnet of an NMR system makes use of unshielded coils while minimizing the effect of eddy currents induced in the magnet components by the gradient fields. A first dataset is acquired by ramping the level of a gradient magnetic field to a maximum value and generating an RF pulse to excite the spins. After a delay time t.sub.1, a single data point is sampled. While the spins are allowed to relax, the gradient field magnitude is changed to the next level. Another RF pulse is generated and, after time t.sub.1, the next data point is sampled. This process continues until a first complete dataset is acquired. The next gradient function is then applied in a similar manner, and the data points sampled after an RF pulse and a delay time of t.sub.2. During sampling of the second dataset, the gradient area for each spatial data point is equal to the gradient area for that spatial point during sampling of the first dataset.

Abstract: A method of reducing radiation damping during free induction decay in NMR measurements of samples having a narrow line width uses the active switching of the quality factor value of the coil circuit of an NMR detection probe. After application of an excitation pulse to the sample, data acquisition is accomplished in periodic samples. The Q of the coil circuit is set to a high value while each sample is being taken, but is reduced significantly in between samples by detuning the coil circuit. Minimization of the high-Q state of the coil circuit and maximization of the difference between the high Q value and the low Q value greatly decrease the detrimental effects of radiation damping on free induction decay. The coil circuit Q is modified automatically by the application of a Q switching signal generated by a controller, such as a computer which controls other aspect of the NMR experiment.

Abstract: A nuclear magnetic resonance cross polarization probe uses a dual-coil arrangement in which a single-turn inner coil is surrounded by a solenoid coil. The inner coil is tuned to the frequency of a relatively high Larmor frequency nuclei type, such as proton. The solenoid coil is tuned to a lower Larmor frequency nuclei type. An inner sample region surrounded by the inner coil has a first magnetic field component induced by an electrical signal at the relatively high frequency in the inner coil. An electrical signal at the lower frequency is input to the solenoid coil and results in the generation of a magnetic field alternating at the lower frequency. This field induces a current in the inner coil at the lower frequency that, in turn, induces a magnetic field component in the inner region at the lower frequency.

Abstract: A method of shimming an NMR magnet uses a plurality of 1D projections through a sample volume to determine the inhomogeneities of the field of the NMR magnet. The frequency distributions obtained are assembled from the phase signals of the various projections. In order to avoid frequency errors due to phase wrapping, the phase of each signal is monitored over time for discontinuities indicative of aliasing. For each phase wrap, the signal is "unwrapped" by adjusting the value of the phase signal by 2.pi.. The same method is used to establish a shim field map for each of the shim coils being used. With one shim coil at a time being driven with a predetermined current, the detection method is repeated to acquire a shim-base frequency map for each shim coil. The base frequency map is then subtracted from the shim-base frequency maps to obtain shim field maps. The proper shim currents are then acquired through matrix operations on the shim field maps and the base frequency map.

Abstract: A sample changer for a spectrometer of the type having a generally vertical sample loading air shaft in which an upflowing air stream is present. The sample changer includes a support for positioning at the spectrometer and a carriage movably supported by the support which carriage has an array of generally vertical passages extending entirely through the carriage, those passages being adapted to contain sample holders. The sample changer also includes an actuator for moving the carriage relative to the support to position each passage over the air shaft so that that passage becomes an extension of the air shaft whereby the sample holder in that shaft may be buoyed up and supported in its passage by the air stream from the airshaft.

Abstract: B.sub.1 (RF) gradient echo pulse sequences are combined with frequency-selective pulse sequences to selectively suppress a solvent resonance signal by preventing the formation of an echo for the solvent resonance, while allowing the formation of an echo for the sample resonances under study. The RF gradient pulses may be planar or radial pulses. A pulse sequence for suppressing a solvent resonance signal in NMR experiments comprises a pair of (RF) gradient pulses which sandwich a selective inversion pulse sequence. In accordance with one embodiment of the invention, the RF gradient pulses are anti-symmetric (have opposite phase) and the selective inversion pulse sequence comprises a homogeneous frequency-selective inversion pulse, such as a .pi. pulse, applied in time between the two RF gradient pulses.

Abstract: A composite RF pulse is created from a sequence of conventional homogeneous RF pulses and conventional gradient RF pulses and the composite pulse generates a gradient magnetic field with a spatially varying amplitude, but a spatially independent phase. In one embodiment of the invention, the pulse sequence consists of four conventional gradient RF pulses interspersed with two conventional homogeneous RF pulses. In another embodiment of the invention, a conventional gradient RF pulse is combined with a conventional homogeneous RF pulse and the pulse pair is repeated in order to generate an effective magnetic field with a spatially varying amplitude, but a spatially independent phase.

Abstract: A small sample imaging apparatus replaces the dewar which normally passes along the axis of an NMR imaging probe. The small sample imaging apparatus incorporates an integral RF coil and capacitor resonant circuit. The coil and capacitor are positioned adjacent to each other and remotely at the end of a projecting stalk. Stray inductance effects are thereby avoided and the stalk physically positions the resonant circuit at substantially the properly centered location. The stalk which positions the coil and capacitor may be formed from a length of rigid coaxial cable which carried RF energy to the resonant circuit. When large samples are imaged, the conventional probe coil insert can be utilized in the normal manner. However, when smaller samples are images, the adapter can be attached to the probe and the adaptor resonant circuit can be utilized.

Abstract: A plurality of measurements are made with a probe containing a material sample with a known frequency spectrum. The probe is positioned in one spot in the magnet bore in the presence of a field gradient along a predetermined axis. Prior to each measurement, the gradient strength is increased by a predetermined constant amount. The resulting measurement values are mathematically manipulated to yield a set of values which can be used to set the shim coil currents based on known equations for the field generated by each shim coil. The method can be used with a material sample with a simple NMR spectrum or a complex NMR spectrum. If a sample with a complex NMR spectrum is employed in the measurement, the spectral complexity can be removed by deconvolution during the manipulation of the measurement values.

Abstract: A multiple-pulse RF pulse sequence applied to abundant nuclei after excitation and in the presence of a spatial magnetic field gradient significantly reduces the resonant line width thereby increasing image resolution relative to other known pulse sequences. The RF pulse sequence is constructed from selected sets of known six-pulse cycles called dipolar decoupled inversion pulses. The dipolar decoupled inversion pulses are, in turn, constructed from standard solid echo pulse pairs. The magnetic field gradient is periodically varied during application of the RF pulses to preserve imaging information.

Abstract: Coherence transformation selectivity is improved by using combinations of homogeneous RF pulses and "radial" RF pulses that have a uniform RF field strength throughout the sample, but whose phase (relative to the detection coil phase) has a spatial dependence such that all possible phase differences are equally represented throughout the sample. The use of radial pulses allows the spin coherences in the sample to evolve in spatial waves and the observation, or suppression, of a given coherence can be selected by using a receiver coil which has a predetermined symmetry relative to the symmetry of the spatial wave.

Abstract: An NMR probe is designed to generate both a homogeneous RF field over the sample volume and, alternatively, a "radial" field comprising two orthogonal gradient fields generated simultaneously in the transverse plane or a linear gradient field. The homogeneous field is generated by means of a known homogeneous coil construction, such as a Helmholtz coil or modified Helmholtz coil. The radial field can be generated by means of an inverted Helmholtz coil, either modified or unmodified, and the linear field can be generated by a Golay type coil, which coils are positioned coaxially with the homogeneous coil. The two coils are connected in parallel to the RF signal generator and switching can be accomplished either by means of an active switch or by detuning one of the coil resonant circuits when the other coil is in use.

Abstract: A composite RF pulse for NMR experiments is created by applying to a sample a radial pulse followed by a .pi. homogeneous pulse. The radial pulse has a uniform RF field strength throughout the sample and a phase relative to the detection coil phase with a spatial dependence such that all possible phase differences are equally represented throughout the sample. The composite pulse converts the radial RF pulse into a spatially-varying z rotation. The creation of a spatially-varying composite z pulse based on a radial pulse allows for a simple and direct application of a radial pulse in a manner analogous to many known B.sub.0 gradient NMR experiments (such as multiple-quantum filters, quadrature detection, and solvent suppression).

Abstract: The quadrature channels of an RF generator in an NMR spectrometer are aligned relative to one another by applying pulse sets to pairs of channels that are 180.degree. out of phase. The effect of the pulses in one channel is the opposite of the pulses in the other channel. As a result, the magnetization of the sample returns to the direction in which it started when the amplitudes of the pulses applied to each channel are equal. The magnetization returns to the initial direction even in the presence of RF inhomogeneities. The characteristic magnetization pattern can be easily observed and used to adjust the relative pulse amplitudes equal and the absolute pulse amplitudes to .pi./2.

Abstract: In an NMR solid-state imaging experiment, second averaging is carried out during the experiment to reduce the effects of unwanted interactions that obscure the results of an interaction of interest. The second averaging is arranged so that the second averaging interaction and the interaction of interest are along the same axis, but are separated in time. The second averaging interaction is further designed to introduce a multiple of .pi./2 phase offset between applications of the interaction of interest. In this way, even when the sum of the actual resonance frequency and the second averaging frequency are zero, the spin dynamics are still modulated and a second averaging takes place.An additional advantage is provided in that the resonance frequency can be sampled in such a fashion that the second averaging frequency does not appear in the observed resonance frequency.