Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-03-02
2001-07-31
Hannaher, Constantine (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
Reexamination Certificate
active
06268604
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to the field of tunneling displacement sensors and more specifically to an integrated sensor module including an electron tunneling infrared sensor, such as a Golay cell.
A tunneling displacement sensor made using standard silicon wafer processing techniques and based upon a thermal detection principle, one example of a Golay cell, is described in A miniature high-sensitivity broad-band accelerometer based on electron tunneling transducers, Rockstad, Howard K., et al. Sensors and Actuators, vol. 43, pp. 107-114, 1994 and incorporated here by reference. Referring to
FIG. 3
, the sensor comprises a gas chamber
19
, a membrane
14
at the base of the gas chamber which carries a membrane conductor
15
, and a tip
23
below the membrane conductor
15
in a second chamber
17
. With a proper spacing set up between the tip
23
and the membrane conductor
15
, for example 10 Angstroms, tunneling action occurs. Infrared radiation impacting the sensor heats the gas in the first chamber
19
increasing the pressure on and causing displacement of the membrane
14
and conductor
15
. The membrane displacement is registered as a change in the tunneling current from the tip terminal
12
.
A variable high voltage bias is applied to a deflection electrode
16
creating an electrostatic force to adjust the spacing between the tip
23
and the membrane
15
for tunneling. Traditionally, the high voltage source has been manually adjusted to establish the tunneling condition which is essential for detecting any force acting on the sensor membrane.
SUMMARY OF THE INVENTION
In one aspect of the invention, a sensor module includes an electron tunneling sensor having a bias input and an output. The sensor produces an output signal in response to a proper bias condition in the sensor. A control circuit has an input connected to the sensor output and an output connected to the bias input. The control circuit includes a feedback circuit which dynamically adjusts the bias signal in response to changes in the output signal to re-balance the sensor to the proper bias condition.
Embodiments may include one or more of the following features. An output circuit for conditioning the sensor output for use by external circuitry may be provided. The output circuit may provide an amplified representation of the sensor output signal. The control circuit may include a filter having a predetermined frequency response. The control circuit may include a first amplifier having an input connected to the sensor and an output. The control circuit may further include an integrating amplifier having an input connected to the output of the first amplifier and an output connected to the bias input. An output buffer having an input connected to the output of the first amplifier may be provided with a clamp for limiting to within a preselected range the magnitude of the output. The sensor may include a Golay cell.
In another aspect of the invention, a measurement system includes an infrared radiation generator having a radiation output for providing a radiation signal and a signal generator having a signal output. A chopper modulator has an input connected to the radiation output, a modulation input connected to the signal output, and a chopper output. The chopper modulator provides a modulated radiation signal on the chopper output. An electron tunneling sensor has a bias input and an output and the sensor produces an output signal in response to a proper bias condition in the sensor. A control circuit has an input connected to receive the sensor output signal and an output connected to provide a bias signal to the bias input. The control circuit includes a feedback circuit which dynamically adjusts the bias signal in response to changes in the sensor output signal to re-balance the sensor to the proper bias condition. An output circuit connected to the control circuit provides a sensor output to an output device.
In another aspect of the invention, a control circuit is provided for operating an electron tunneling sensor of the kind having a sensor output and a deflection input. The control circuit includes a first input for connection to the sensor output for sensing the level of tunneling activity in said sensor. A bias output for connection to the deflection input of the sensor is provided to adjust the bias level to the sensor. A variable bias circuit has a bias control input connected to the first input and an output connected to the bias output. The bias circuit is responsive to signals from the bias control input and dynamically adjusts the bias signal in response to changes in the tunneling activity to re-balance the sensor to the proper bias condition.
In another aspect of the invention, a method of operating an electron tunneling sensor of the kind having a sensor output and a deflection input includes receiving an output signal from the sensor output for sensing the level of tunneling activity in the sensor. A deflection bias level is dynamically adjusted. The deflection bias level is output to the deflection input of the sensor. Changes in the output signal indicative of changes in the tunneling activity are sensed and the deflection bias level is dynamically adjusted in response to the changes to re-balance the sensor to the proper bias condition.
Other aspects, features, and embodiments will become apparent from what follows.
REFERENCES:
patent: 3891843 (1975-06-01), Parkin
patent: 5436452 (1995-07-01), Kenny et al.
California Institute of Technology
Fish & Richardson PC
Hannaher Constantine
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