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