Development of high Tc SQUID magnetometer system for biological application

在这项研究中，我们开发了用于生物应用的高Tc SQUID磁计系统。首先，我们开发了高性能SQUID，以使用30度偏偏置角度的双螺旋式跳跃。with 30-Degree bicrystal j\， we can routinely obtain the voltage modulation Depth\V>20\V and the flux noise S2\D\T=77 K。双晶体交叉点的传输和噪声特性也是明确的，其次，所谓的直接耦合磁体是制造的。当我们使用一个具有宽线条宽度的传统拾取线圈时，我们可以看到高1/f噪音。这表明，1/f的噪音是从被困在塑料线圈上的通量跳跃中产生的。如果是为了避免通量陷阱，我们将开发一种新型的拾取线圈。一个带有窄线宽度和影响的四个平行环路的拾取线圈的概念是由称为流体水坝的。有了这个拾取线圈，我们可以显著地减少1/f的噪音。flux noise is reduced to S-D2-D11/2-D1=23-D2/Hz-D11/2-D1 at f=1 Hz。This value is only 2. 3 times higher than the white noise of S_D_2__ This means that the magnetic noise of the magnetometer is S·D2B·D11/2·D1=S·D2·D11/2·D2·D2·D1 =460 fT/Hz·D11/2·D1 at f=1 Hz， and S·D2B·D2·D1/2·D1=175 fT/Hz·D11/2·D1 in the white noise region。If we use a large pickup coil with 10 mm by 10 mm size， the effective area will be A-D2-D2= 0. 4 mm-D12-D1。In this case， we can expect S D2B S D11/2 S D1=138 fT/Hz S D11/2 S D1 at f=1 Hz， and S D2B S D2 S D11/2 S D1=52 fT/Hz S D11/2 S D1 in the white noise region。这种敏感性将足以将其应用于磁心电图。

In this research, we developed high Tc SQUID magnetometer system for biological application. First, we developed high performance SQUID utilizing bicrystal junctions with 30-degree misorientation angles. with 30-degree bicrystal junction, we can routinely obtain the voltage modulation depth △V>20μV and the flux noise SィイD2ΦィエD2ィイD11/2ィエD1<12μΦィイD2oィエD2/HzィイD11/2ィエD1 at T=77 K. Transport and noise properties of the bicrystal junctions are also clarified.Next, the so-called direct-coupled magnetometer is fabricated. When we use a conventional pickup coil with wide line-width, we observed high 1/f noise. It is shown that the 1/f noise comes from the hopping of the flux trapped in the pickup coil. In order to avoid the flux trapping, we develop a new type of the pickup coil. The pickup coil consists of 4 parallel loop with narrow line-width and involves the so-called flux dam. With this pickup coil, we can significantly reduce the 1/f noise. The flux noise is reduced to SィイD2ΦィエD2ィイD11/2ィエD1=23 μΦィイD2oィエD2/HzィイD11/2ィエD1 at f=1 Hz. This value is only 2.3 times higher than the white noise of SィイD2ΦィエD2ィイD11/2ィエD1=10μΦィイD1oィエD1/HzィイD11/2ィエD1.In the present magnetometer, the size of the pickup coil is 6 mm by 3 mm, and the effective area of the magnetometer is AィイD2effィエD2=0.12 mmィイD12ィエD1. This means that the magnetic noise of the magnetometer is SィイD2BィエD2ィイD11/2ィエD1=SィイD2ΦィエD2ィイD11/2ィエD1/AィイD2effィエD2=460 fT/HzィイD11/2ィエD1 at f=1 Hz, and SィイD2BィエD2ィイD11/2ィエD1=175 fT/HzィイD11/2ィエD1 in the white noise region. If we use a large pickup coil with 10 mm by 10 mm size, the effective area will be AィイD2effィエD2=0.4 mmィイD12ィエD1. In this case, we can expect SィイD2BィエD2ィイD11/2ィエD1=138 fT/HzィイD11/2ィエD1 at f=1 Hz, and SィイD2BィエD2ィイD11/2ィエD1=52 fT/HzィイD11/2ィエD1 in the white noise region. This sensitivity will be enough for the application to the magnetocardiogram.