The research on frequency measurement for the designed resonator used to detect infrared radiation by means of tracking the change in resonance frequency of the resonator with temperature attributed to the infrared radiation from targets is presented in this paper. The research provides the basis for the integrated design of the uncooled infrared MEMS resonance structure and its measuring circuits.
A kind of frequency tracking circuit based on phase-locked loop (PLL) is studied for the resonant infrared sensor in the paper. The operating principle of the PLL is analyzed. 74HC4046 as the core component of the circuit is selected; starting the lock circuit is researched; a closed-loop frequency tracking circuit based on 74HC4046 is built. Software simulation proves that the frequency tracking of the circuit can achieve the order of MHz and has good frequency stability and tracking performance, which lays a foundation for the construction of the follow-up resonant sensor excitation/detection circuit.
For a designed sensor with bi-material resonator which is used to detect infrared (IR) radiation by means of tracking the change in resonance frequency of the resonator with temperature attributed to the IR radiation from targets, in accordance with electromagnetic theory, the relationship between the electrical driving force exerted on the resonator and the exciting voltage applied across two electrodes of the capacitor in the sensor is presented. According to vibration theory, the dependence of the driving force on the exciting voltage is analyzed. The result of analysis is used to guide the vibration mode and frequency-amplitude response simulations of the resonator. The simulation value is approximately equal to the measured value, which demonstrates that the analysis result is effective and practicable.
A resonant infrared thermal sensor with high sensitivity, whose sensing element is a bimaterial structure with thermal expansion mismatch effect, is presented. The sensor detects infrared radiation by means of tracking the change in resonance frequency of the bimaterial structure with temperature attributed to the infrared radiation from targets. The bimaterial structure is able to amplify the change in resonance frequency compared with a single material structure for a certain mode of vibration. In accordance with the vibration theory and the design principle of an infrared thermal detector, the resonant sensor, which can be arranged in an array, is designed. The simulation results, by using finite element analysis, demonstrate that the dependence of resonance frequency on temperature of the designed structure achieves 1 Hz/10 mK. An array of 6×6 resonant thermal sensors is fabricated by using microelectronics processes that are compatible with integrated circuit fabrication technology. The frequency variation corresponding to the temperature shift is obtained by electrical measurement.
A resonant infrared thermal sensor with high sensitivity, whose sensing element is a bi-material structure with thermal
expansion mismatch effect, is presented in this paper. The sensor detects infrared radiation by means of tracking the
change in resonance frequency of the bi-material structure with temperature change attributed to the infrared radiation
from targets. The bi-material structure can amplify the change in resonance frequency compared to a single material
sensing structure. In accordance with the theory of vibration mechanics and design principle of infrared thermal detector,
the bi-material resonant sensor by means of which an array can be achieved is designed. The simulation results, by
ANSYS software analysis based on multi-layer shell finite element, demonstrate that the dependence of resonance
frequency on temperature of the designed sensing structure achieves 1Hz/0.01°C. A microarray with 6×6 resonant
infrared sensors is fabricated based on microelectronics processes being compatible with integrated circuit fabrication
technology. The frequency variation corresponding to the temperature shift can be obtained by electrical measurement.
AlSiNx bi-material thermal strain structure is used in uncooled optic readout infrared focal plane array (UOR IR FPA)
pixel based on Micro-Electro-Mechanical Systems (MEMS) technology. In this paper, the problems that the AlSiNxstructure prevents FPA pixel scaling down and fill factor improving, and the Au reflection layer of the pixel leads to
larger readout light energy loss are analyzed. The feasibility of AlSiNx instead of AlSiNx in the UOR IR FPA
fabrication is researched in detail. The theoretical analyzing and simulation results demonstrate that, with optimized
thicknesses and their matching designing of SiNx and Al, the thermal-mechanical response of AlSiNx bi-material
structure is improved to 1.8 times and the intensity of optic readout signal is improved to about 2 times compared with
AuSiNAlSiNx one.
Bi-material cantilever is an important basic structure in MEMS device. Most of the materials with thermal property fit
for bi-material are not adhering together steadily. An adhesive layer in between is needed. In this paper, based on the
thermal stress and combined deformation in Mechanics of Materials, a model related to the physics properties, structure
dimension, and the tilt angle caused by thermal stress is set up. A research of how to select the materials and how to
determinate the thickness and other size of a bi-material cantilever is carry out by this model, further more, an optic read
out IR image chip pixel is designed that shows this model is simple and practical.
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