Prashanth Vooka

Bio: Prashanth Vooka is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Capacitive sensing & Capacitance. The author has an hindex of 4, co-authored 8 publications receiving 69 citations. Previous affiliations of Prashanth Vooka include Indian Institutes of Technology.

A Direct Digital Readout Circuit for Impedance Sensors

Abstract: A new, simple and high-accuracy impedance-to-digital converter (IDC) is proposed in this paper. Conventionally, the parameters of sensors that can be modeled using a parallel combination of a capacitor ( ${C}$ ) and a resistor ( ${R}$ ) are measured using ac bridges, excited from a sinusoidal source. Recently, with the widespread use of digital systems in instrumentation, capacitance-to-digital converters and resistance-to-digital converters gained a lot of importance. An IDC that accepts sensors having ${C}$ and ${R}$ in parallel and provides digital outputs directly proportional to the ${C}$ and ${R}$ values is presented in this paper. This can be used not only for sensors whose ${C}$ and ${R}$ values vary with the measurand but also when ${C}$ or ${R}$ of a sensor needs to be measured keeping the output not affected by parasitic ${R}$ or ${C}$ present in parallel with the sensing element. Another application of the IDC is in the measurement of the dissipation factor of dielectric materials. The proposed IDC is based on a dual-slope technique, and hence provides high accuracy and immunity to noise and interference. A prototype of the proposed IDC has been developed and tested in the laboratory. Accuracy of the prototype IDC developed was 0.15% for the measurement of ${C}$ and 0.04% for the measurement of ${R}$ . The total conversion time of the prototype converter developed is 3 s, and its total power dissipation is 175.8 mW. The IDC was also interfaced with a polymer-based impedance humidity sensor, measured its ${C}$ and ${R}$ values for a range of humidity, computed the humidity, and compared its performance with another instrument, showing the practicality of the proposed IDC.

An Improved Capacitance-to-Digital Converter for Leaky Capacitive Sensors

Abstract: This paper presents a capacitance-to-digital converter (CDC) that employs a novel approach to perform an accurate measurement of capacitance of a leaky capacitive sensor. This CDC employs a sinusoidal source for excitation, which is advantageous for various sensing applications, including ice detection, liquid level measurement, humidity measurement, proximity sensing, and so on. Recently, an impedance-to-digital converter (IDC) based on the dual-slope conversion technique has been reported. It can measure the value of capacitance even when a parallel resistance is present, but requires a large number of sinusoidal excitation cycles to complete a conversion, leading to poor update rate. The CDC proposed in this paper gives much higher (about 125 times) update rate compared with the IDC as it requires only a few excitation cycles for the conversion, but still gives an accurate output due to the use of a specially designed clock, which helps to count the number of charge packets received by the integrator capacitor during the deintegration. Other than the operation of the CDC, this paper also describes an outcome of a thorough analysis conducted to quantify the effect of various circuit parameters on the output of the new CDC. A prototype of the improved CDC has been developed, and its performance parameters, such as accuracy (±0.27%), conversion time (24 ms), effect of parallel resistance, and so on, have been tested, and the results are reported in this paper.

A novel capacitance-to-digital converter for capacitive sensors with AC excitation

Abstract: Several planar coil designs have been investigated for application in accurate AC conductivity measurements in the wide frequency range. The measurement method is based on the eddy-current probe-coils solutions proposed by Dodd and Deeds [1]. Coils parameters related to the theoretical model and measurement equipment used have been considered. The coil parameters affecting the performance of the model and the measurement instrument in the specified frequency range have been investigated. Different designs were investigated including coils on a printed circuit board (PCB), coils on flexible substrate and on site manufactured coils winded from a copper wire with different diameters. The goal was to reach the inductance of the different coils to match the best-accuracy of the measuring instrument. Amongst the others, the important factor was to achieve the diameter of the coils small enough for practical applications. Measured resistance (a) and inductance (b) deviations from 30 kHz value. Calculated conductivity deviations (c) from 30 kHz value. 15ST017

Capacitance-to-digital converter for leaky capacitive sensors

Abstract: A novel capacitance-to-digital converter (CDC) that performs an accurate measurement of the capacitance of a leaky capacitive sensor is presented. The conversion technique of this CDC is novel, which helps to achieve the highest interference rejection compared with the exiting CDC topologies. The digital output from the CDC is directly proportional to the sensor capacitance, Cx . It provides an accurate output even in the presence of a parasitic leakage resistance, R p, parallel to the sensor. A prototype CDC has been developed and tested. Worst-case error was found to be 0.1%. The CDC employs a sinusoidal excitation for the sensor, and is suitable for a variety of applications such as proximity or touch detection, detection of ice, level sensing, humidity measurement, etc. This CDC is well suited for applications where the conventional schemes fail to work due to the extreme interference from other sources, e.g. power line.

Polysquaraines: Novel humidity sensor materials with ultra-high sensitivity and good reversibility

Abstract: Various materials have been successfully applied in commercial humidity sensors, but their response/recovery time and sensitivity need to be improved. In this paper, a novel humidity sensor was fabricated based on a polysquaraine (PMPS), which is of resonance-stabilized zwitterionic structure. Relative humidity (RH) in the range of 33–95% was able to determine by testing the impedance response at room temperature (25 °C). The variation of impedance is greater than four orders of magnitude, the highest among all conjugated polymer materials. The response/recovery time is as short as 3/16 s, comparable to that of most commercial humidity sensors. Electrical doping and hydronium transportation are attributed to the impedance change. The results indicate that polysquaraines may be promising materials in humidity sensing.

A time domain bridge-based impedance measurement technique for wide-range lossy capacitive sensors

Abstract: In this paper, a new, simple and accurate impedance measurement technique (IMT) for wide range lossy capacitive sensor is proposed. The proposed technique accepts sensors having capacitance ‘Cx’ with lossy resistance ‘Rx’ in parallel. The proposed IMT is based on the separation of in-phase and quadrature components, which is achieved by using phase to time converter. For comparative study, two circuit configurations are proposed. In first proposed solution, the sensor parameters are measured by separating the real and imaginary part of the output electrical signal. In the second proposed configuration, the measurement range is enhanced using an auto-balancing approach, which is achieved by monitoring phase difference between input and output voltages. Experimental evaluation of the proposed configurations reveals that the first configuration is able to estimate the sensor capacitance in the range 200–1200 pF and lossy resistance in the range of 100 kΩ–1.2 MΩ with a maximum error of 6%. The second configuration exhibits an enhanced range of 100–2000 pF for sensor capacitance and 33 kΩ–3 MΩ for lossy resistance with a maximum error of 5%. The IMT was interfaced with a fabricated γ-Al2O3 based impedance humidity sensor, measured its Cx (70 pF–800 pF) and Rx (35 kΩ–4 MΩ) at different concentration of humidity, calculated the humidity, and compared its performance with existing techniques, showing the practicality of the proposed IMT.

A Direct Digital Readout Circuit for Impedance Sensors

Abstract: A new, simple and high-accuracy impedance-to-digital converter (IDC) is proposed in this paper. Conventionally, the parameters of sensors that can be modeled using a parallel combination of a capacitor ( ${C}$ ) and a resistor ( ${R}$ ) are measured using ac bridges, excited from a sinusoidal source. Recently, with the widespread use of digital systems in instrumentation, capacitance-to-digital converters and resistance-to-digital converters gained a lot of importance. An IDC that accepts sensors having ${C}$ and ${R}$ in parallel and provides digital outputs directly proportional to the ${C}$ and ${R}$ values is presented in this paper. This can be used not only for sensors whose ${C}$ and ${R}$ values vary with the measurand but also when ${C}$ or ${R}$ of a sensor needs to be measured keeping the output not affected by parasitic ${R}$ or ${C}$ present in parallel with the sensing element. Another application of the IDC is in the measurement of the dissipation factor of dielectric materials. The proposed IDC is based on a dual-slope technique, and hence provides high accuracy and immunity to noise and interference. A prototype of the proposed IDC has been developed and tested in the laboratory. Accuracy of the prototype IDC developed was 0.15% for the measurement of ${C}$ and 0.04% for the measurement of ${R}$ . The total conversion time of the prototype converter developed is 3 s, and its total power dissipation is 175.8 mW. The IDC was also interfaced with a polymer-based impedance humidity sensor, measured its ${C}$ and ${R}$ values for a range of humidity, computed the humidity, and compared its performance with another instrument, showing the practicality of the proposed IDC.