Ryszard Jachowicz

A thin-film capacitance humidity sensor

Abstract A thin-film capacitance humidity sensor, fabricated using typical planar MOS technology, is described. The device responds to reversible changes in the surface conductance of a thin dielectric film deposited over planar interdigitated electrodes. Interelectrode capacitance measurements in the frequency range 1 – 100 kHz showed an accuracy of 7% of relative humidity over the range 17% – 65% relative humidity, and better accuracy at higher humidities, the accuracy being limited primarily by hysteresis. A theoretical model of device operation based on distributed RC transmission lines, in which the moisture-dependent surface conductance serves as the only conductive path, is presented. It is found from experiment, and confirmed with the model, that the interelectrode region is less useful for moisture meaurement than the region of the dielectric surface directly over the electrodes. This observation is then used as the basis of modified sensor designs, both for improved incremental sensitivity and for increased range of useful operation.

The ink-jet printing humidity sorption sensor—modelling, design, technology and characterization

This paper presents a humidity sorption sensor made with an ink-jet printing technique. Nafion was applied as a humidity sorption material. After the presentation of sensor construction and sensor fabrication technology, a lot of effort has been made for detailed sensor tests and characterization. The sensor model based on a RC transmission line with distributed parameters (Jachowicz and Senturia 1981/1982 Sensors Actuators 2 171–86) has been carefully described and validated by a comparison with the sensor empirical parameters, measured in a broad range of measurement frequencies. On the basis of achieved results, some general conclusions for humidity sorption sensors on both the sensor fabrication technology and the sensor modelling have been made and presented in this paper.

Sub-cooled water detection in silicon dew point hygrometer

Abstract A new type of silicon dew point detector is presented in this paper. The fabricated detector structures contain a thermometer, two heaters, a capacitive interdigitated sensor for the detection of water, sub-cooled water, as well as ice. The test results of sub-cooled water recognition are carefully described. The theoretical model of the capacitive interdigitated sensor describing the principle of detection is also discussed.

The empirical verification of the FEM model of semiconductor pressure sensor

The paper deals with empirical examination and computer modelling of a piezoresistive semiconductor pressure sensor for a range of 100 kPa. Based on the FEM model of the sensor, the membrane deflection and the state of stress were calculated. The output voltage signal of a piezoresistive bridge was computed on the basis of stress distribution. The verification of the model was carried out by comparison of computed results with direct measurements of membrane deflection as well as with sensor output signal. The optical interferometry was applied to measure the distribution of the deflection of sensor membrane. A description of the measurement set-up and measurement accuracy discussion is presented as well.

A non-contact passive electromagnetic transmitter to any capacitive sensor : design, theory, and model tests

Abstract This paper presents a non-contact passive electromagnetic interface especially dedicated to capacitive sensors. In contrast to radio transmitters cooperating with remote sensors, our interface is extremely simple and requires integration only for the single plane coil with the capacitive semiconductor sensor structure. The interface structure and theoretical calculations done with the use of the Grover method are discussed in the paper. Presented data from interface tests proved that the interface can successfully operate with the frequency of some 11 MHz obtaining sensitivity of some 15 Ω/pF in the range of 0–22 pF.

Dew point hygrometer with heat injection—principle of construction and operation

Abstract A new idea for the construction of a dew point hygrometer and its operation based on a new approach to the hygrometer mirror temperature stabilization by additional heat injection into the mirror is presented. The problem of negative aspects of dew overcondensation on the hygrometer performance is carefully discussed. Results from the test for different measurement system parameters as well as for both stable and dynamically changed air humidity are presented. Discussion of the measurement results and some advice for optimal criteria for hygrometer control are also included.

Optimal measurement procedures for a dew point hygrometer system

Optimal measurement and control procedures with adaptive algorithms based on dynamically evaluated output signals for operating a dew point hygrometer are discussed. The influence of dew condensation and evaporation time constants and the amplitude of mirror overheating and overcooling, as well as limits of the flow rate of the measured gas and the thickness of the dew layer upon dew point detection and the accuracy of the dynamically measured mirror temperature, are described. Flow diagrams for computer procedures and schematic diagrams of electronic measurement systems are included. >

A MEMS-based super fast dew point hygrometer—construction and medical applications

The paper shows how MEMS (micro-electro-mechanical system) technology and a modified principle of fast temperature control (by heat injection instead of careful control of cooling) can considerably improve the dynamic parameters of dew point hygrometers. Some aspects of MEMS-type integrated sensor construction and technology, whole measurement system design, the control algorithm to run the system as well as empirical dynamic parameters from the tests are discussed too. The hygrometer can easily obtain five to six measurements per second with an uncertainty of less than 0.3 K. The meter range is between ?10 ?C and 40 ?C dew point. In the second part of the paper (section 2), two different successful applications in medicine based on fast humidity measurements have been discussed. Some specific constructions of these super fast dew point hygrometers based on a MEMS sensor as well as limited empirical results from clinical tests have been reported too.

Semiconductor pressure sensor based on FET structure

As a next step in capacitive pressure sensor development, a new sensor structure based on field effect transistor has been proposed. The sensor build up on active FET structure, has a big advantage in reference to the semiconductor capacitive sensors. Its voltage output signal (or current signal) can be simply measured in contrary to relatively difficult measurements of capacitance. An other sensor advantage is because of one side wafer processing during sensors fabrication. The sensor construction as well as details of sensor fabrication technology are described. The results of computer simulation of the sensor are discussed. High sensor pressure sensitivity and relatively low sensor dependence on temperature are very important measurement features of the PS-FET sensors.<<ETX>>

Smart sensors interface for wireless data and power transmission

The paper presents the interface designed for wireless data and power transmission. The interface operation idea was tested using build up hardware and software. The sample construction of the temperature sensor embedded with this type interface was designed. Measurements show that the sensor can be wirelessly supplied with energy and is capable to sent data (temperature readings) in 5 cm distance. The interface is universal and can be used after some modifications with any type of sensors.