Chapter 5: Multi-Squid Devices and Their Applications

Ilmoniemi, Risto J.; Knuutila, Jukka; Ryhänen, Tapani; Seppä, Heikki

doi:10.1016/s0079-6417(08)60044-x

Cited by 19 publications

(4 citation statements)

References 127 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…New uses of multi-SQUID devices are to be expected now that more reliable and higher-sensitivity sensors have become available, and at a lower cost than before . For exam-pie, geomagnetic instruments (for reviews, see Clarke, 1983 andIlmoniemi et al , 1989) and magnetic monopole detectors (Cabrera, 1982;Tesche et al , 1983) have been used for some time already.…”

mentioning

confidence: 99%

Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain

et al. 1993

Self Cite

View full text Add to dashboard Cite

Magnetoencephalography(MEG) is a noninvasive technique for investigating neuronal activity in the living human brairi. The time resolution of the method is better than 1 ms and the spatial discrimination is, under favorable circumstances, 2 -3 mm for sources in the cerebral cortex. In MEG studies, the weak 10 fT -1 pT magnetic fields produced by electric currents fiowing in neurons are measured with multichannel SQUID {superconducting quantum interference device) gradiometers. The sites in the cerebral cortex that are activated by a stimulus can be found from the detected magnetic-field distribution, provided that appropriate assumptions about the source render the solution of the inverse problem unique. Many interesting properties of the working human brain can be studied, including spontaneous activity and signal processing following external stimuli. For clinical purposes, determination of the locations of epileptic foci is of interest. The authors begiri with a general introduction and a short discussion of the neural basis of MEG. The mathematical theory of the method is then explained in detail, followed by a thorough description of MEG instrumentation, data analysis, and practical construction of multi-SQUID devices. Finally, several MEG experiments performed in the authors laboratory are described, covering studies of evoked responses and of spontaneous activity in both healthy and diseased brains. Many MEG studies by other groups are discussed briefiy as well.

show abstract

mentioning

confidence: 99%

Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain

et al. 1993

Self Cite

View full text Add to dashboard Cite

show abstract

“…To be practical, this application requires a measurement system capable of extensively mapping the biomagnetic field distribution in a short period of time. For this reason, the incorporation of a large number of magnetic field sensors to form multichannel systems has been the preferred approach [4]. Since the magnitude of the biomagnetic fields of interest can be as low as a few tens of fT, it is generally regarded [2] that the sensors must have a minimum magnetic field noise & B of 10 m Hz-112 or better down to 1 Hz.…”

Section: An Important Applicationmentioning

confidence: 99%

“…Although the preamplifier used in their electronics contributed a voltage noise of only 1. 4 nV Hz"12, the performance of their DC SQUID at that time was such that the voltage-flux transfer function aV/a@ N 2 pV (Do at the optimal operating point. Direct coupling of the SQUID to the preamplifier would therefore have resulted in a contribution from the electronics to the flux noise = * " ( l aV/a(D l)-' of 7 x HZ"'~, a totally unacceptable value for applications.…”

Section: An Important Applicationmentioning

confidence: 99%

Integrated DC SQUID magnetometer with simplified read-out

Cantor¹,

Drung²,

Peters³

et al. 1990

Supercond. Sci. Technol.

View full text Add to dashboard Cite

A process is described for fabricating all refractory, integrated DC SQUID magnetometers for biomagnetic measurement applications. The process consists of only four lithographic steps and three sputter depositions. Several magnetometers have been fabricated and successfully operated in a flux-locked-loop mode using a simplified read-out technique that does not require the use of an impedance matching circuit between the SQUID and the preamplifier in the room-temperature electronics. Noise measurements have been carried out with a superconducting shield installed, from which a typical value for the magnetic flux noise square root SPhi =2*10-5 Phi 0 Hz-1/2 in the white noise region was determined. The onset of 1/f noise was observed to occur at about 1 Hz. Although the magnetic flux noise square root SPhi is relatively high, the field noise square root SB= square root SsGF(B/ Phi ) has been minimised by choosing a large SQUID inductance LS=550 pH in order to achieve a high magnetic field sensitivity B/ Phi =0.27 nT/ Phi 0. In this way, a typical value for the magnetic field noise square root SB of 5 fT Hz-1/2 has been attained. This low value of square root SB makes these magnetometers well suited for biomagnetic measurement applications.

show abstract

“…For details, the reader is referred to several past and recent reviews and references therein [1][2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%