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Bulletin of the Seismological Society of America; October 2005; v. 95; no. 5; p. 1940-1946; DOI: 10.1785/0120040187
© 2005 Seismological Society of America
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A Simple Technique to Extend the Bandwidth of Electromagnetic Sensors

Antonio Pazos1, Gerardo Alguacil2 and José Martín Davila1

1 Real Instituto y Observatorio de la Armada
Cecilio Pujazón s/n
1100 San Fernando, Cádiz, Spain
pazos{at}roa.es
mdavila{at}roa.es
 (A.P., J.M.D.)

2 Instituto Andaluz de Geofísica
Observatorio de la Cartuja
Universidad de Granada
18.071 Granada, Spain
alguacil{at}iag.ugr.es
 (G.A.)

Electromagnetic sensors are typically loaded with an external resistance value that provides an effective damping factor of 0.7. The velocity response of the sensor is given by a third-order equation but can be approximated by an equation of second order if the coil inductance is neglected. We propose to use a capacitor in series with the resistance (series RC load) instead of a resistance only. The transfer function is then given by a fourth-order equation that can be reduced to a third-order one, as a zeros-poles analysis shows. This is the simplest and cheapest way to extend the response of an electromagnetic sensor. If appropriated values of R and C are selected, then the flat band of the frequency response is increased by moving the corner frequency down by a factor of 1/4 without any effective gain reduction.




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E. Th. Koutsoukos and N. S. Melis
Broadening the Response of Short-Period Sensors: An Application to the Sprengnether S-7000 Seismometer
Bulletin of the Seismological Society of America, August 1, 2007; 97(4): 1212 - 1220.
[Abstract] [Full Text] [PDF]


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