JPH0497602A - Frequency variable resonator - Google Patents

Abstract

PURPOSE:To realize a resonance frequency with a high Q and to vary the frequency even at a frequency of 10kHz or below by forming an equivalent inductance of Josephson junction in a ring and varying the equivalent inductance with an external magnetic field so as to change the resonance frequency. CONSTITUTION:The resonator consists of a substrate 1, a superconducting ground plane 2, a dielectric film 3, a string line 4, a ring 5, a Josephson junction 6 and a magnetic field generating means (coil) 7. Since an equivalent inductance of a Josephson junction whose inductance varies with an external magnetic field is formed in a ring resonator, the frequency variable resonator is realized by varying the inductance of the ring with the magnetic field. Thus, the resonance frequency with a high Q is obtained and the resonance frequency is changed in a small range as a frequency of 10kHz or below.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a microstrip type resonator used in high frequency measuring instruments and the like, and more particularly to a resonator whose resonant frequency can be changed.

<Prior art> Figures 3(a), (b), and (c) show the configuration of a conventionally used microstrip line type.
Figure (a) shows a linear resonator, (b) shows a U-shaped resonator, and (C) shows a disk resonator. These resonators have various shapes of resonators 11a, llb, ll in the vicinity of the lip line 10.
The resonant frequency is obtained by arranging the resonator c, but one resonant wavelength is determined by the shape of the fixed resonator.

In FIG. 4, a variable capacitor 11 is connected to one end of a strip line 10, and by changing the capacitance, the resonant frequency is made variable. Furthermore, a device is known in which the frequency of about 800 MHz to IGHz is made variable by using a varactor diode.

<Problems to be Solved by the Invention> However, in the above-mentioned prior art, the resonance frequency shown in FIG. 3 is fixed.

The device shown in FIG. 4 has a problem in that it is difficult to obtain a resonant frequency with a high Q value. In addition.

There are also reports of using superconducting materials to obtain resonators with high Q values.1 For example, in the case of metallic superconducting films, 10
However, it is difficult to change the resonant frequency under the following conditions.

The present invention has been made to solve the problems of the prior art described above, and an object of the present invention is to provide a resonator that can obtain a high Q resonance frequency and change the frequency even below IOK.

Means for Solving the Problems> The configuration of the present invention for solving the problems of the prior art described above includes a superconducting ground plane formed on a substrate and a dielectric film formed on the superconducting ground plane. A ring made of a superconducting thin film having a Josephson junction formed on the dielectric film, a strip line provided near this ring, and a magnetic field generating means placed a predetermined distance above the ring. It is characterized by having the following.

Effect> Since the equivalent inductance of the Josephson junction is configured within the ring, if this equivalent inductance is changed by an external magnetic field, the resonant frequency will change. And the magnetic field from the coil is independent of temperature.

<Example> The present invention will be described below with reference to one drawing. FIG. 1 shows an embodiment of the present invention, and (a) is a plan view.

(b) is a sectional view taken along the line AA in the figure (a). In these figures, 1 is a substrate with a low dielectric constant such as MgO or LaAl2O3, 2 is a ground plane ((G-P) made of a superconducting material, and 3 is a Si formed on G-P.
It is a dielectric film made of O2, Al2O3, etc. 4 is a strip line for input/output made of a superconducting material, 5 is a ring made of a superconducting material, and a Josephson junction 6 is formed in the middle of this ring. 7 is a magnetic field generating means (coil) arranged above the ring at a predetermined distance.

In the above configuration, if the radius of the ring 5 is a, the inductance without the Josephson junction 6 is LO, the capacitance of the ring is C, and the phase velocity of the electromagnetic wave in the strip line 4 is Vp, then the resonant frequency in this case is The relationship between f0 and vp can be expressed by the following equation.

f o = V D / λ = (Vl) / (2za
) I ・ n...-■λ; Wavelength of resonance frequency (n=1.2.3...) Vp=1/F "te...■.

Next, a Josephson junction is provided in the ring, the critical current of the Josephson junction is IC, and the current and voltage flowing through the junction are I and V, respectively.From the Josephson effect.

I=Icsinθ...■V=
(qi/2e)iθ/8t) ... ■θ; On the phase difference of the order parameter of Josephson junction; h/2π (h is a blank constant) e: It can be expressed as electronic charge.

■If we differentiate the equation with time, we get 8I/8t=Iccosθ(Bθ/8t)−・・■So from the equations, V= ('R/2e) (I/c cos o>
−@(eI/at) =LJ (θ I/at)
...■LJ z ('h/2e) (1/Ic c
os θ), and therefore the Josephson junction equimetrically carries an inductance of LJ.

Next, superconducting rings containing Josephson junctions are generally rf
Although it is called -3QUID, if the magnetic flux inside the ring is Φ1 based on the quantization conditions for the magnetic flux inside this ring.

θ=2π(Φi/Φo+1)...■
1=0.1.2... Φo=h/2e; Can be expressed in terms of magnetic flux quantum.

The relationship between Φi and external magnetic flux Φχ is Φχ=+LIC5in(2rΦ1/Φ, >...■L;
Given by the inductance of the ring, Φχ with α=2πLIC/Φ0 as a parameter
The relationship between and Φ1 is shown in Figure 2.

In the figure, when α is 1, Φi has a valence of 1 with respect to Φχ.

When α>1, it becomes multivalent. Therefore, if the inductance of the ring is set so that α is 1, and the critical current IC is selected, θ is uniquely determined for Φχ, and as a result, from equation 0, L is determined by Φχ.
J can be uniquely changed.

Now, if the inductance of the resonator is Lt, this inductance can be expressed as L↑(Φχ)=LO−LJ(Φχ).

Therefore, it is possible to change fo by changing VE) by ΦX in the equations (1) and (2).

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, the equivalent inductance of the Josephson junction that changes depending on the external magnetic field is configured in the ring resonator, so that the inductance of the ring can be changed depending on the magnetic field. By doing so, a variable frequency resonator can be realized, and since the ring is made of a superconducting material, the loss is extremely small, so it inherently has a high Q value6.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the present invention (a> and (a
) A-A cross-sectional view (b) in Figure 2 shows the magnetic flux quantum Φ. , FIG. 3, FIG. 3, and FIG. 4 are diagrams showing the relationship between the magnetic flux Φ1 inside the ring and the external magnetic flux Φχ, which are configuration diagrams of the conventional device. 1...Substrate, 2...Superconducting ground brain, 3.
... Dielectric film, 4... Strip line, 5... Ring 6... Josephson junction, 7... Magnetic field generating means (coil). Agent: Nobuaki Ozawa, patent attorney. N N 勺 ℃ N

Claims (1)

[Claims] A ring consisting of a superconducting ground plane formed on a substrate, a dielectric film formed on this superconducting ground plane, a superconducting thin film having a Josephson junction formed on this dielectric film, and this ring. 1. A variable frequency resonator comprising: a strip line provided near the ring; and magnetic field generating means provided above the ring at a predetermined distance.