NM20216A-F
7
CHAPTER 1
Technical data
1.1.
The probe unit
1.1.1.
General
• Number of MEG channels: 306 channels
• Sensor coverage: whole cortex, 1220 cm
2
• Measurement positions: supine, upright
• Minimum room height required: 2.3 m
• Dimensions and weights: see chapter 2
1.1.2.
Sensors
• Type of sensors: 102 identical plug-in triple-sensor-units with two
orthogonal planar gradiometer flux transformers, one magnetometer
flux transformer, and three dc-SQUIDs (Superconducting Quantum
Interference Devices).
• Field components:
B
z
, ∂
B
z
/
∂
x
and
∂
B
z
/
∂
y
• Sensor distance from the outside helmet surface of the dewar: average
18 mm
• Material and construction of dc SQUIDs: all-refractory thin-film
structures on silicon
• Average triple-sensor-unit spacing: 34 mm
• Size of gradiometers and magnetometers: 28 mm
×
28 mm
• Type of SQUIDs: dc SQUIDs
• Material and construction of gradiometers and magnetometers: all-
refractory thin-film structures on silicon
• Base length of gradiometers: 17.0 mm
• Effective total surface area of each oppositely wound gradiometer
coil: 2.7 cm
2
and for the magnetometer coils 7.6 cm
2
.
• RF interference suppression: integrated
RC
-shunts.
• Low frequency interference suppression: with hardware and compu-
tational compensation.
• Integrated heater elements for de-trapping.
• Balance: better than 10
-3
for gradiometers.
1
