This work presents the fabrication of a high fill factor Fresnel microlens array (MLA) by employing a low-cost home-built maskless exposure lithographic system. A phase relief structure was generated on a photoresist-coated silicon wafer, replicated in Polydimethylsiloxane (PDMS) and electrostatically bonded to a glass substrate. Optical characterization was based on the evaluation of the maximum intensity of each spot generated at the MLA focal plane as well as its full width at half maximum (FWHM) intensity values. The resulting FWHM and maximum intensity spot mean values were 50 ± 8% µm and 0.71 ± 7% a.u , respectively. Such a MLA can be applied as Shack-Hartmann wavefront sensors, in optical interconnects and to enhance the efficiency of detector arrays.
LTCC technology continues to be an attractive option for fabrication of sensors, sensor packages and complex micro-systems. The objective of this work is to present LTCC sensors developed by CSEM Brasil with a focus on capacitive type wireless soil moisture sensor (SMS) for precision farming that is capable to measure soil moisture in real time and transmit the data to 80 m distance (line of sight). The sensor is constructed from 4 functional blocks: PCB (printed circuit board) base including the capacitive electrodes, LTCC block carrying the electronics and soldered on PCB, voltage regulator and wireless unit. Tests conducted with 28 prototypes reveal that the sensor response is over 1.00 V at full humidity and reproducible whilst the battery consumption is around 200 mW, permitting a battery life of 5 years at a measurement frequency of 1 sampling per minute.
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