For the first time, expandable graphite (EG) and aluminum hydroxide (ATH) was combined to improve the flame retardancy of polyisocyanurate-polyurethane (PIR-PUR) foam. The limited oxygen index increased from 26.5 for the PIR-PUR matrix to an incredible value of 92.8 when 24 phr (parts per 100 of matrix) EG and 60 phr ATH were incorporated into the matrix. Based on morphology observation and thermogravimetric analysis, it was speculated that two factors contributed to the improvement of flame retardancy primarily. First, ATH could effectively induce "villi" like particles, which was useful to form a dense char. The compact char layer could effectively impede the transport of bubbles and heat. Second, ATH and EG accelerated the initial degradation and fluffy char was quickly generated on the surface of the composites. Thus, the degradation of the composite was slowed down and the diffusion of volatile combustible fragments to flame zone was delayed.

This paper proposes a low-power delta-sigma capacitance-to-digital converter (CDC) for a capacitive sensor. The input of the capacitive sensor employs a zoomed-in technique with the offset capacitor to extend the input capacitance range. The proposed CDC uses a third-order switched capacitor deltasigma modulator to provide a digital output, based on a cascade of integrators with a feed forward (CIFF) structure. The current-starved operational transconductance amplifiers (OTAs) are applied in the delta-sigma modulator's first integrator to improve the current efficiency and reduce the power consumption. An autozeroing technique is used in the OTAs to reduce their offset and noise. The circuit was implemented in a 0.18-µm CMOS technology and occupies an area of 0.496 mm 2. The measurable capacitance range of the CDC can be varied from 0 to 8 pF. In a measurement time of 0.8 ms, the delta-sigma CDC achieved a 12.7 effective number of bits while consuming 18.6-µA current from a 2-V supply voltage. INDEX TERMS Capacitive sensors, delta-sigma modulation, low power.

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