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-band electron paramagnetic resonance spectrometer for use in vivo and in studies of aqueous biological samples
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Image of FIG. 1.
FIG. 1.

Block diagram of the -band spectrometer with Automatic Frequency Control for biological studies in vivo and in vitro.

Image of FIG. 2.
FIG. 2.

(Left) Dielectric Resonator-Oscillator based on an bipolar transistor, , (Motorola 3046-type) in a Clapp configuration with a serial resonant circuit in its base. is a single-turn coil that also provides coupling with the dielectric resonator disk, , (Trans-Tech Products 4500 Series Temperature Stable Dielectric Resonator, 30.8 mm diameter, 13.8 mm height) for stabilizing the frequency of oscillation. is a movable dielectric tuning disk, 30.8 mm diameter, 5.0 mm height, driven by an ultrafine-pitch (0.5 mm/turn) screw. is a one-half turn loop providing power output. , , , , , , , . Components marked by asterisks were optimized at assembly time to provide the best performance. (Right) Varactor diode-based system that provides modulation of the output frequency; , .

Image of FIG. 3.
FIG. 3.

Diagram of the external-loop type resonator with a circuit allowing maintaining a constant -factor during measurements. This is achieved by intentionally lowering the maximum attainable -factor by coupling in a variable resistance implemented by means of a photoresistor illuminated by an externally controlled light-emitting diode (LED). (Inset) Dependence of the factor for the empty resonator on LED current.

Image of FIG. 4.
FIG. 4.

Schematic diagram of a whole-body -band resonator. The whole-body type of resonator has an internal diameter of 30 mm and can accommodate a small mouse. Its construction is based on the bridge-gap concept.

Image of FIG. 5.
FIG. 5.

Schematic view of the cross section of the 415 Gauss permanent magnet. 1, Base steel plate; 2, Support column; 3, Ferrite mosaic; 4, Magnet pole; 5, Scan coil.

Image of FIG. 6.
FIG. 6.

Schematic diagram of the magnetic modulation unit. Frequency from a 1 MHz clock is divided 40-fold to yield 25 kHz. A four-quadrant selector allows coarse phase adjustment in 90° intervals. The resultant square wave is integrated giving a symmetric sawtooth, which is further converted to a sine wave using an AD639 trigonometric function converter. Following fine phase adjustment the modulation amplitude is set and the modulation current is delivered to the coils via a power amplifier.

Image of FIG. 7.
FIG. 7.

4.5 micromole/liter solution of Tempone in 0.9% saline (top, 9 scan average; bottom, single scan). Microwave power 30 mW, receiver gain 10 000, modulation amplitude 0.2 Gauss, scan range 40 Gauss, scan time 20 s, time constant 100 ms.


Generic image for table
Table I.

Parameters of the -band frequency generator.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: L-band electron paramagnetic resonance spectrometer for use in vivo and in studies of aqueous biological samples