DD275316A1 - RESONATOR ARRANGEMENT FOR MEASURING EPR SIGNALS - Google Patents

Abstract

Resonator arrangement for measuring EPR signals, in particular in EPR tomography in the frequency range from 500 MHz to 10 GHz. By means of the resonator arrangement, a microwave distribution is achieved with which the spins can be excited in a narrow cylindrical disk and whose diameter or the diameter of the disk can be varied over a wide range at a constant frequency and which ensures the most optimal broadband coupling possible. This is achieved by such a resonanzfaehige arrangement, which consists of a wire ring and two parallel outlets of defined length. Fig. 1

Description

For this 2 pages drawings

Field of application of the invention

The wire-ring resonator is used in EPR spectroscopy, in particular in EPR tomography in the frequency range from 500 MHz to 10 GHz. It can be used as a layer-selective resonator and as a surface coil.

The use as a slice-selective resonator causes the excitation of the spins in a cylindrical disc whose diameter corresponds to the inner diameter of the wire ring. The axial field extent determines the spatial resolution in the axial direction. By an axial displacement of the sample, this can be examined by the disk.

A second application is to use as a surface coil for specimens whose dimensions are much larger than the wire ring diameter.

Corresponding to the axial field distribution and the penetration of the microwaves dependent on the sample material, spins can be excited in the surface regions. The use of field gradients in the axial direction makes it possible to measure location dependencies for the surface. The low quality of the wire-ring resonator allows for the dispersion of a person in free-running AFC and the use of impulse techniques in ESE and STE. This is especially true for large wire ring diameters for low frequencies in the L band.

Characteristic dos bekannton Standes dar Technik

In analytical techniques oino Roiho are known by ancestors, with which material properties have been studied by exciting magnetotopic transitions into samples of this material. The most well-known methods of this kind are the magnetic Rosonanz and the electron spin resonance.

For the Erzougon dioser Rosonanzorschoinungon it is orfordorlich to expose the sample to be examined simultaneously a Hochfroquonzfold and a sonkrocht to gerichtoton Konrtantmagnotfeld. The sample is placed in a Roson Gate and positioned there on an orinestone, at which magnetic field lines propagate with high density. A common problem in such investigations is to impart the highest possible sensitivity to the apparatuses used. The orzielbaro sensitivity is proportional to the product of Güto dos used resonator and the fill factor.

The use of surface coils in NMR and EPR is known (Nishikawa, Fujff, Berliner: Journal of Magnetic Resonance, 1985, pp. 62, 79-86). Given was a surface coil with a diameter of 7 mm and a length of the parallel feed lines of 41 mm, which is firmly connected to a coaxial line and is coupled via a coaxial short-circuiting slide.

The disadvantages are that the arrangement is only possible for a defined loop diameter at a fixed predetermined frequency and no critical coupling with coaxial short-circuiting slide.

In order not to have to rotate the sample about two axes in measurements of the spatial distribution of paramagnetic centers, a .schichtselektive excitation would be favorable, which allows a two-dimensional measurement of the layer of a sample. This requires resonators that allow the excitation of a very narrow layer. Such resonators have not previously been used. The resonators previously used and also described in the literature (Ono, Ogata, Chemistry Letters, 1986, pp. 491-494, Ogata, Ono, Fujisawa: Chemistry Letters, 1986, pp. 1681-1684) are unsuitable for layer-selective excitation.

The solution DE 2917794 is also known. Here it is shown that in EPR spectroscopy only cavity resonators with a high quality can be used, due to a high microwave radiation in the GHz range. However, only samples smaller than the dimensions of the resonator and adapted to the highly inhomogeneous field distribution in the resonator can be examined. This results in fill factors η

η =, which are less than 1%.

J Riionator Bl dV

The measured signal intensity is proportional to the product of square of quality and fill factor

s ~ Q 'η,

so that the low quality of the coils is compensated by a filling factor near 1.

Object of the invention

The aim of the invention is to expediently carry out sensitive measurements of EPR signals in bioionic samples in slice-selective regions as well as in the surface region of larger organisms.

Explanation of the essence of the invention

The invention has the object zug'unde to develop a resonator having a Mikrowellenvertailung with which the spins can be excited in a narrow zylino.ischen disc and whose diameter or the diameter of the disc at a constant frequency practice, 'jinen wide Range can be varied and ensures the best possible broadband coupling.

According to the invention this is achieved by a rest nanzfähige arrangement consisting of a wire ring and two parallel outlets of defined length, the length I and the distance a in the, parallel wire lines of diameter d of the wire ring are determined, and that the energy supply via a parallel wire line the same distance, which is severed after n · V2 and overlaps with a coming of the supply line parallel wire line with a distance a over a length ü without touching the lines, and that of the overlap length ü and the distance h between the parallel wire lines the degree of coupling depends. Depending on the embodiment, the parallel wire lines can be directly overlapped or trombone similar pushed into each other. The wire ring resonator according to the invention has by its novel microwave coupling relative to the surface. Spool the following advantages and opportunities: The coupling to the microwave line is achieved «by the overlap of the parallel wire line ends of the wire ring resonator and the Mikrowellenenergiezuführenden coaxial cable. The optimization of the coupling is achieved by:

- displacement of the supply lines,

- mechanically, by means of screw-on transformer,

- electronically, by means of varactor diode.

The quality Q is <l-5 times higher (450-500) due to the critical coupling and thus the maximum resonator diameter could previously be 0 20 mm (for L-band) orhöhl.

Ausführungsboisplol

The invention is to be approximated on the basis of oinos execution bussis. Show:

FIG. 1a: wire ring rooter with Mikroollcnkopplung in raumlichor representation;

Fig. I u: wire ring microsorber with Mikroollollonkopplung in plan view;

Fig .: Crahtringresonatorin trombone-like arrangement;

FIG. 3: wire ring microsorber with screw transformer; FIG.

Fig.4: Wire ring resonator with varactordiodo.

The wire ring resonator shown in Figure 1 consists of the parallel wire piece 4 with the length I and the distance a and the wire ring 5 with the diameter d. For reasons of coupling, the length I is increased by η · ^x Mn = 0,1,2 ...) 3. The size of the diameter d determines the inductive component of the resonator, while the length I and the distance a form the capacitive component. At constant d and constant a, an increase of I leads to a reduction of the resonance frequency f ₀ .

The dimensions of the wire ring resonator must satisfy the following condition: d; I; a; <λ The equation for calculating the wire ring resonator is:

f = ¹ f ^2a 1 ⁵

⁰ and LneM _o (5a + 2l) J

For example, for a resonance frequency f ₀ = 1.9 GHz and a loop diameter d = 10 mm, a loop length I = 2 mm results. FürV2 = 79mm is required for coupling the total length l + η · ^x h = 81 mm.

For coupling to the microwave line and for mechanical stabilization, the wire ring resonator is fitted in a special holder made of a material with a low microwave attenuation. The also fitted in this holder, parallel wire ends 2 of the power supply coaxial cable 1 are arranged so that the extended by η Kh Paralleldrah'.ctücke the wire ring resonator and the coaxial cable overlap and have on the overlap length ü each dan distance h. For isolation and to ensure a defined distance h for an optimal coupling condition, a dielectric film with a defined thickness is placed between the parallel wire ends.

By varying the overlap length ü and the distance h, the wire ring resonator can be adapted to the feed line.

FIGS. 2, 3 and 4 show further coupling or tuning possibilities of the resonator.

Claims (6)

A resonator arrangement for measuring EPR signals in a sample, characterized in that said resonant structure consists of a wire ring (5) open on one side, the diameter of which is smaller than the wavelength of the exciting microwave, and a parallel wire line (3), (4) whose length is also smaller than the wavelength used is made, wherein the dimensions of the wire ring (5) and the parallel conductor piece (4) determines the Resonanzfre _M uence, and that for the purpose of coupling this parallel conductor piece (4) galvanically with a second, open at one side parallel lead piece (3), whose line length is η times the half wavelength (n · V2; η = 0,1,2 ...) is connected, said second parallel piece of line (3) at the open side with a third, open on one side, parallel lead piece (2), which is directly connected to the supplying coaxial line (1) is electrically coupled via the microwave fold and d The spatial assignment of the two open pan-axis ends was a measure of the coupling between the resonator and the supply cable (1). 2. Resonator arrangement according to claim 1, characterized in that overlap both open parallel conductor ends (2), (3) to a constant length ü and that by a change in the distance h, between the two parallel lines, the coupling is varied. 3. resonator arrangement according to claim 1, characterized in that for a variable coupling with a constant distance between the lines, the overlap length ü is varied. 4. resonator arrangement according to claim 3, characterized in that for the purpose of coupling the open line ends are pushed into one another. 5. resonator arrangement according to claim 1, characterized in that the parallel wire lines are overlapped ur i the coupling change by means of a screw transformer which is removed at a distance of V2 from the wire ring and the incoming parallel wire line is approximated, is reached. 6. resonator assembly according to claim 1, characterized in that the parallel wire lines are overlapped, and that is located between the two ends of the feeding parallel wire line, a varactor diode, which is at a distance of V2 from the wire ring, with which the coupling varies electronically can be.