Receive coils

A ring specimen is cut from the tube. Two coils are wrapped around this ring, one exciter coil and one receiver coil. The exciter coil N1 should cover the entire ring so that there are no field losses when ring is saturated. The sinusoidal exciter current which can be measured at... 

Electromagnetic (EM) Conductivity Measures the electrical conductivity of materials in microohms over a range of depths determined by the spacing and orientation of the transmitter and receiver coils, and the nature of the earth materials. Delineates areas of soil and groundwater contamination and the depth to bedrock or buried objects. Surveys to depths of SO to 100 ft are possible. Power lines, underground cables, transformers and other electrical sources severely distort the measurements. Low resistivities of surficial materials makes interpretation difficult. The top layers act as a shunt to the introduction of energy info lower layers. Capabilities for defining the variation of resistivity with depth are limited. In cases where the desired result is to map a contaminated plume in a sand layer beneath a surficial clayey soil in an area of cultural interference, or where chemicals have been spilled on the surface, or where clay soils are present it is probably not worth the effort to conduct the survey. 

Toroidal System Resistivity (after Gearhart-Halliburton). The system uses one toroidal transmitter operating at 1 kHz and a pair of toroidal receiver coils mounted on the drill collars. Figure 4-277 shows a sketch of a toroid. 

Single-quantum coherence is the type of magnedzadon that induces a voltage in a receiver coil (i.e., Rf signal) when oriented in the xy-plane. This signal is observable, since it can be amplified and Fourier-transformed into a frequency-domain signal. Zero- or multiple-quantum coherences do not obey the normal selection rules and do not... 

DEPT (distortionless enhancement by polarization transfer) A onedimensional C-NMR experiment commonly used for spectral editing that allows us to distinguish between CH, CH2, CH, and quaternary carbons. Detectable magnetization The magnetization processing in the x y -plane induces a signal in the receiver coil that is detected. Only single-quantum coherence is directly detectable. 

The quantity of interest is the precession of the components perpendicular to B0 that are measured in the experiment by induced voltage in the coil, which is subsequently amplified and demodulated. We can write them either as individual components Mx, M, or by a vector M+, which combines both of them. In the static field, the precession about B0 occurs with the Larmor frequency w0 = /B0. If we neglect those processes which dampen the amplitude of the rotating transverse magnetization as precession proceeds, this already describes the frequency that we pick up with our receiver coil, and it is the third and perhaps the most important of our three fundamental equations of NMR ... 

The development of microcoil techniques has been reviewed by Minard and Wind [24, 25] and by Webb [26]. In a more recent publication Seeber et al. reported the design and testing of solenoidal microcoils with dimensions of tens to hundreds of microns [27]. For the smallest receiver coils these workers achieved a sensitivity that was sufficient to observe proton NMR with an SNR of unity in a single scan of 10 pm3 (10 fL) of water, containing 7 x 1011 proton spins. Reducing the diameter of the coil from millimeters to hundreds of microns thus increases its sensitivity greatly, allowing analysis of pL to pL sample volumes. 

D. A. Seeber, R. L. Cooper, L. Ciobanu, C. H. Pennington 2001, (Design and testing of high sensitivity micro-receiver coil apparatus for nuclear magnetic resonance and imaging), Rev. Sci. Instrum. 72, 2171. 

A long capillary with a computer-controlled switching valve (the instruments must be separated by 2-3 metres because of the strong magnetic field) connects the exit from the HPLC with the probehead. The latter is completely different in its construction from conventional probeheads instead of the NMR tube there is a small flow cell, the volume of which is 40-100 pi. The transmitter and receiver coils are attached directly to the cell in order to maximize the sensitivity. 

These systems work by placing a sample between the pole pieces of a magnet (electromagnet or permanent), surrounded by a coil of wire. Radio frequency (r.f.) is fed into the wire at a swept set of frequencies. Alternatively, the magnet may have extra coils built onto the pole pieces which can be used to sweep the field with a fixed r.f. When the combination of field and frequency match the resonant frequency of each nucleus r.f. is emitted and captured by a receiver coil perpendicular to the transmitter... 

Of course, there is no point in overfilling your NMR tubes. This can make shimming more difficult (but certainly not impossible as in the case of too low a sample depth) but more importantly, it merely wastes materials and gives rise to unduly dilute samples giving reduced signal/noise. Any sample outside the receiver coils does not give rise to signal. 

Inverse geometry Term used to describe the construction of a probe that has the 1H receiver coils as close to the sample as possible and the X nucleus coils outside these 1H coils. Such probes tend to give excellent sensitivity for 1H spectra at the expense of X nucleus sensitivity in 1-D techniques. They offer a lot of compensation in terms of sensitivity of indirectly detected experiments. 

Probe Region of the spectrometer where the sample is held during the acquisition of a spectrum. It contains the transmitter and receiver coils and gradient coils (if fitted). 

Fig. 7 A zirconium rotor (A), and several types of caps (B) Kel-F, (C) boron nitride, and the stator (D) in which the doubly tuned transmitter/receiver coil (E) is inserted. Here, the rotor is 22 mm in length and 7 mm in outer diameter.

Receiver coil, superconducting, 23 860-861 Receivers, in refrigeration systems,... 

Superconducting parameters, 23 819 Superconducting receiver coil, 23 860-861 Superconducting switch, 23 858-859 Superconducting transition temperature, 23 818... 

---