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| CHEMO-OPTICAL SENSORS |
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MOEMS FOR AIR POLLUTION MONITORING |
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Microsystem |
| The system is designed for gas concentration measurements. It can work independently from the computer and has its own power supply. The measured data are managed to the computer if the system is serially connected to the computer, dedicated software for acquisition and interpretation data being performed. In this way, the "classical" stationary laboratory equipment for air pollution measurements is replaced by a real-time, small size measurement system. |
| Configuration of the hybrid microsystem using chemo-optical silicon sensor (1-radiation source, 2-optical fiber, 3-chemo-optical silicon sensor, 4-transimpedance preamplifiers, 5-microcontroller) |
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| Hardware configuration |
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The system is realized in the SMD mounting technique, chips and discrete devices being mounted on the same card. It is composed of four different modules: |
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1. The radiation source module
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| It includes the radiation source (high intensity IR diode) and its driver. The radiation source functions in large pulses (400 mA front current), in order to compensate the small amount of radiation that reaches the photodiode through the sensor's waveguide. The measurements are synchronous with the pulses generated by the radiation source, for noise elimination. |
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| IR |
λ = 904 nm
P = 5 mW
Ipeak = 1 A |
| Driver |
f = 17 - 200 Hz
fill factor = 1/30 - 1/20 |
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| 2. The sensor module |
| This module includesthe chemo-optical sensor and the preamplifiers??The sensitive layer is a silicon dioxide obtained by sol-gel technology. Their chemo-optical properties are enhanced for ?=904 nm. The optical wave-guide core is made by silicon oxinitride in the CVD technique. The buffer and cover of the wave-guide are made by silicon dioxide in the CVD technique. The P+N photodiodes are realized in the planar technology.
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| Refractive index |
1.67 |
| Thickness |
0.5 μm |
| Width |
15 μm |
| Responsivity (λ = 904 nm) |
0.45 A/W |
| Length |
100 μm |
| Transimpedance |
Az=12 MΩ |
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| 3. Data acquisition and storage module |
| Microcontroller INTEL 8051 |
64 kb RAM
64 kb EEPROM
8 bit word |
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| 4. Power supply module |
| Alkaline cell |
4 x 1.5 V |
| Microcontroller power supply |
+ 4.5 ... 5.5 V |
| Double power supply for preamp |
± 4.5 ... 5.5 V |
| Medium supply current |
300 mA |
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| Dedicated software |
| The system includes an internal software, programming the frequency of the generated signal and data acquisition and management, resident in the microcontroller. For calibration or concentration measurements a software for data interpretation and managing is also designed, which is resident in the computer and is used while the system is connected to the computer. |
| Main features |
| Size |
| Card (steclotextolit) |
100 x 100 x 10 mm |
| Case (plastic) |
110 x 110 x 40 mm |
| Weight |
350 g |
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| Chemo-optical characteristics |
| Waveguide |
904 nm |
| Spectral bandwidth |
80 nm |
| Power output |
20 mW |
| Coupling coefficient |
0.02 % |
| Reference photocurrent |
40 nA |
| Photodiodes current ratio
(measuring / reference) |
0.1 ... 0.9 |
| Concentration domain (ammonia) |
50 ... 1000 ppm (EPA limit 400 ppm) |
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