Diode Bolometer Dual-Band Imaging Sensor
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Solution Overview
Problem
Bolometers used in imaging arrays suffer from self-heating during resistance measurement, making accurate temperature readings difficult, and are limited to detecting a single band of radiation, with thermistors being expensive and difficult to process, and diode-based systems requiring individual calibration for each device.
Innovation Solution
A diode-based bolometer is configured to operate as both a thermometer and a photocell, using its junction to detect infrared radiation and additional radiation bands like ultraviolet or visible light, with a dual-band imaging sensor formed by an array of such diodes, employing pairs of measurements with different biasing currents to avoid calibration and utilize additional layers for enhanced radiation absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large currents are used to bias each thermistor to obtain sensitive temperature measurement, then temperature measurement sensitivity is improved, but self-heating occurs making accurate temperature readings difficult
Solution Approach 1:
The patent changes the measurement parameter from resistance (which requires large bias currents and causes self-heating) to voltage measurement under constant current bias. By operating the diode in the forward bias region and measuring voltage rather than resistance, the system achieves temperature sensitivity without the harmful self-heating effects that plagues thermistor-based bolometers.
2Ease of manufacture
If a diode is used in lieu of a thermistor in a bolometer, then processing difficulty is reduced, but individual calibration is required for each diode which is time consuming and expensive
Solution Approach 1:
The patent makes the diode serve multiple functions: it acts as both the temperature-sensing element (thermometer function) and the radiation-detecting element (photocell function). This multi-functionality eliminates the need for separate calibration procedures for each diode, as the same device that detects radiation also provides the temperature reference, and the system can operate in dual-band mode without additional calibration steps.
Solution Approach 2:
The diode bolometer is self-calibrating through its dual operating modes. By alternating between bolometer mode (measuring temperature changes from infrared radiation) and photocell mode (measuring direct radiation effects), the system uses its own characteristics to establish the relationship between voltage changes and radiation intensity, eliminating the need for external calibration equipment and procedures for each individual device.
3Device complexity
If a bolometer is configured to detect a single band of radiation, then detection simplicity is maintained, but the ability to detect multiple spectral bands is lost
Solution Approach 1:
The diode bolometer inherently supports dual-band detection because the diode junction responds to both infrared radiation (through temperature-dependent voltage changes) and visible/near-infrared radiation (through direct photovoltaic effects). By switching between bolometer operation mode and photocell operation mode, the same physical device can detect both spectral bands without requiring separate detector elements or complex optical path modifications.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for accurate dual-band imaging without the need for individual calibration, reducing costs and improving temperature resolution by leveraging the diode's temperature-dependent I-V curve and photovoltaic response, enabling detection of multiple spectral bands with improved manufacturing ease.
Implementation Method 1
the temperature dependence of its current-voltage (I-V) curve, is used as the basis for measuring temperature
Implementation Method 2
the same diode may be operated as a photocell to detect radiation that is capable of interacting with the electrons in the junction of the diode
Implementation Method 3
Infrared radiation that is incident upon the thermistor changes the temperature, and hence the resistivity of the thermistor
Data Source
AI summary
A sensor that is responsive to at least two distinct spectral bands, e.g., infrared radiation and ultraviolet or infrared and visible light makes use of the junction of a diode-based bolometer as a photocell in addition to its temperature dependence for detecting infrared radiation. More specifically the diode bolometer is arranged to work in the conventional manner, in that an electrical characteristic of the diode, e.g., the temperature dependence of its current-voltage (I-V) curve, is used as the basis for measuring temperature, and hence, infrared radiation. Additionally, the same diode may be operated as a photocell to detect radiation that is capable of interacting with the electrons in the junction of the diode. This may be achieved by detecting a change in the operating point of the diode based given its present biasing in response to noninfrared radiation incident upon the diode.