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We developed a compact sensor module for hydroponics that measures the nutrient concentration and water level using simple oscillator circuits. Oscillation frequencies are measured and are found to change in response to the resistance and capacitance between metal wires on a printed circuit board submerged in liquid fertilizer. A microprocessor is mounted on the sensor board for measurement and communication...
This paper presents a frequency-mode capacitive sensor readout front-end operating in a wide temperature range. First, a biased varactor temperature compensation (BVTC) is proposed to compensate the aggregate temperature gradients from the sensor and the oscillator circuit, achieving a nullified temperature coefficient for the oscillation frequency. Second, a temperature coherent quantization (TCQ)...
A high accuracy sensor module for hydroponic culture system was developed. The module measures water level, temperature, and nutrient concentration values by using a single device equipped with a low-cost ribbon cable and electrodes. The module has two oscillators and the water level and the concentration value are converted into frequencies of the oscillator signals. After the conversion mechanism...
Timekeeping based on a 32kHz XTAL still remains the most popular, cost effective, low power, accurate solution for low-power portable applications. Simple solutions with overall accuracies of a few 100ppm are based on the combination of a through-hole or SMD XTAL together with an oscillator implemented as part of the application SoC (micro-controller, cell phone). As a single-ppm error represents...
In this paper, a frequency output temperature sensor based on a 4% Niobium doped 20/80 Zr/Ti Lead Zirconate Titanate (PNZT) capacitor is proposed. The sensor capacitance vs temperature and capacitance vs voltage characteristics are experimentally measured below the Curie temperature of the ferroelectric capacitor. The capacitance of the 20/80 (Zr/Ti) composition PNZT capacitor changes by 29% for a...
In this paper, a capacitive temperature sensor based on polyvinylidene fluoride (PVDF) capacitor is explored. The PVDF capacitor is characterized below its Curie temperature. The capacitance of the PVDF capacitor changes vs temperature with a sensitivity of 16pF/°C. The linearity measurement of the capacitance-temperature relation shows less than 0.7°C error from a best fit straight line. An LC oscillator...
Ethyl alcohol (ethanol) is one of the most common organic compounds used in medical and industrial applications. Because of its human amiability, ethanol has become a perfect solvent for organic matter with varying concentration levels for different purposes. Nevertheless, ethanol has a unique character that makes it evaporates at a level of temperature, which is called flash point. Storing ethanol...
In this paper, a wireless capacitive pressure sensor developed for the health monitoring of aircraft engines has been demonstrated. The sensing system is composed of a Clapp-type oscillator that operates at 131 MHz. The Clapp oscillator is fabricated on an alumina substrate and consists of a Cree SiC MESFET, thin film inductor, Compex chip capacitors and Sporian Microsystem capacitive pressure sensor...
We present the design of an ultra-low power, wireless capacitance/temperature sensing device for continuous intraocular pressure monitoring. The device is wirelessly powered and demonstrates a power consumption of 2.3μW at 1.5V during continuous reading. The chip converts both capacitance and temperature to frequency using a time-interleaved relaxation oscillator, which modulates RF backscatter...
This paper reports on the first demonstration of series tuning for lateral micromechanical oscillators and its application in a temperature-compensated 427MHz AlN-on-Si reference oscillator. The sustaining amplifier is a 13mW tunable TIA implemented in 0.18μm CMOS that uses shunt-parasitic cancellation to increase the tuning by 12× to 810ppm. The tunable oscillator along with a 2mW on-chip temperature...
This paper presents a voltage-controlled oscillator (VCO) operating up to 250degC and usable as a simple frequency modulation (FM) transmitter in wireless sensor networks (WSN). The device is a simple LC oscillator which uses the channel depletion capacitance as a variable capacitor controlled by the gate voltage VG to enable the sustained oscillating behaviour of a tank circuit. The context of operation,...
Temperature (T) dependent transport measurements of cylindrical shaped gate-all-around silicon nanowire MOSFETs (SNWFETs) were performed. Single electron tunneling behaviors were observed at 4.2 K and one of the devices exhibited anomalously strong current peak which survived even at room temperature. The observed peak was interpreted as an evidence of transport through single impurities in the channel.
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