Wide-Band, Low-Noise, Low-Power Seismometer for SQM
search and Lunar Science
Talso Chui,Joseph Young (Jet Propulsion Laboratory, California Institute of
Technology)Ho Jung Paik (University of Maryland)
Third International Conference on Particle and Fundamental Physics in Space
April 21, 2006, Beijing, China.
Konstantin Penanen
Why a Different Seismometer?
Earth Seismometry: Background
The USGS Low-Noise Model[Peterson, J., 1993. Observations and modeling of background seismic noise. Open-file report 93-322, U. S. Geological Survey,
Albuquerque, New Mexico.]
10-14
10-13
10-12
10-11
10-10
10-9
10-8
10-7
10-6
Dis
pla
cem
en
t no
ise
de
nsi
ty (
m/H
z1/2
)
0.001 0.01 0.1 1 10Frequency [Hz]
Thermal + Electronics Noise Goal
USGS Low Noise Model
Cy2
Al
Cy1
Cx2x1C
x2Cx1C
25 cm
5 cm
5 cm
Seismometer Concept(Contributed by Prof. Ho Jung Paik, UM)
• Pendulum natural frequency = fo = 0.4 Hz on the Moon
• Two pairs of capacitors for displacement measurement.
• Two pairs of capacitors for applying DC voltage to reduce fo and to balance tilt.
• Why reduce fo ?
• Thermal noise of seismometer:
• Target: Q = 104, fo= 0.01 Hz,
m = 0.27 kg.
Cross Section View
CN1
CN2
CN4
CN3
Test Mass
Capacitor Plates
Cylindrical
mQ
TkS oBy
41)(
2
y
x
Seismometer Fabrication (Contributed by Prof. Ho Jung Paik, UM)
Seismometer Housing
Seismometer Capacitor Plates
Q = 4000. Frequency reduced from 1 Hz to 0.35 Hz.
Seismometer Electronics Concepts
• Used by LISA.• LISA measurement scales to
10-14 m-Hz-1/2 in x for x = 10-4 m.[W. J. Weber et al., Class. and Quantum Grav. 19, 1751, 2002.]
Based on 0.001 ppm tunnel-diode oscillator
[C. T. Van Degrift, Rev. Sci. Instrum. 46, 599 (1975).]
Concept: A Concept: B
A circuit board with two tunnel-diode oscillator circuits. It was populated with only one tunnel-diode for testing.
Tunnel Diode
X
Seismometer Based on Tunnel-Diode Oscillators
TDOSC
1 TestMass
TDOSC
2C1 C2
LPF
Mixer
Counter
out
out
Computer
BufferAmp
BufferAmp
z
y
x = z - y
Seismometer based on tunnel-diode oscillator.
• Operates at wide temp. range: 400 K to 1K.
• Use very low power: <10 mW.• Suitable for operation thru
lunar night.• A 5 kg Lithium Ion can supply
1 W through lunar night.• Radioisotope Heater Unit
(RHU) to keep electronics warm.
y
2
4
6
0.001
2
4
6
0.01
2
A (
ppm
)
0.001 0.01 0.1 1
Sampling time, (s)
Aeroflex/Metelics MBD 1057-H20 tunnel diode(modern part)
Thermal Noise
Thermal Noise + Shot Noise
Tunnel-Diode Oscillator Evaluation(Contributed by Joseph Young)
dei2
Current Bias Diode di
Square-root of the Allan variance A
P
Tk
Qf
f B
eA 2
1
Thermal Noise Limit:
67eQ
W 4.2 P
Shot Noise density
A138
Tunnel-Diode Oscillator Evaluation (Contributed by Joseph Young)
200
150
100
50
0
Fo
rwa
rd c
urr
en
t (µ
A)
0.40.30.20.10.0Forward voltage (V)
290K
77K
4K
Aeroflex/MetelicsMBD1057-E28X #4
Temp. Change
290 K 0%77 K +1.6%4.2 K +3.7%
Relative freq. change of a 10 MHz Oscillator versus Temp.
Operates from 300 K to 4 K without adjustment
Thermal Cycles:20 times to 77K 6 times to 4K
Continuously operated over 1 month.
Expected Seismometer Displacement Noise Density Sy( f )1/2
10-14
10-13
10-12
10-11
10-10
10-9
Sy(
f)1
/2
( m
/ H
z1/2
)
0.01 0.1 1 10 100 1000
f ( Hz )
Apollo Seismometers
Thermal Noise of Test Mass
Tunnel-Diode Oscillator Noise
Bridge Circuit, 15 V drive