New Sensing Systems for Securing Virtual Walls at Outdoor Based on True Differential Digital TMOS

Abstract

This paper presents a non-imaging differential digital passive Infra-Red (PIR) remote sensing system using CMOS-SOI-MEMS transistors as the thermal sensor. A large $660\mu {\mathrm m}\, {\mathrm x}\, 660\mu{\mathrm m}$ pixel area is developed by the 8x8 mosaic matrix of $60\mu {\mathrm m} \,{\mathrm x}\, 60\mu{\mathrm m}$ sub-pixels connected in-parallel. The mosaic sensors, which are manufactured by nano-fabrication methods in CMOS FABs, exhibit enhanced performance and robust manufacturing in wafer level processing and vacuum packaging. Since the sub-pixels are thermally isolated, the thermal time constant of the large pixel is determined by that of the sub-pixel, which is $\sim {\mathrm 80}$ msec when packaged in vacuum of $\sim 1{\mathrm Pa}$. For outdoor operation, two identical large pixels are differentially measured. The pixels view the detected scene with an optics that may be based either on mirror optics or Fresnel plastic lenses. The optics defines a narrow field of view (± 3 degrees) as required for curtain sensors. Furthermore, the optics forms “cockeyed” vision which enables differential measurement that cancels the environmental” noise” and allows outdoor operation. The overall measured performance for detecting human targets at extended ranges and hot spots detection are reported. This sensor outperforms thermopiles and pyroelectric sensors at outdoor operation.