L Spassov

A rotated Y-cut quartz resonator with a linear temperature–frequency characteristic

Abstract A miniature thermosensitive quartz resonator with a single rotated Y-cut has been designed, the temperature–frequency characteristic of which has a linear character. Precise temperature–frequency analyses of four groups of resonators with different orientations have been carried out. It is shown that it is possible to construct a miniature quartz temperature sensor with high sensitivity and small non-linearity.

Thermosensitive quartz resonators at cryogenic temperatures

Abstract The temperature-frequency characteristics (TFCs) of thermosensitive yxbl/10°54′/11°06′-cut quartz resonators are investigated in the temperature range 300-4.2 K. The linear character of the TFC is kept within the range 300–170 K but after that a non-linearity is observed, which can be expressed approximately by a polynomial of third order. The resonators have high temperature sensitivity, 80 mK at 4.2 K and 1 mK at temperatures over 30 K, and are insensitive towards magnetic fields. The investigations show that the temperature-sensitive sensor could be used as a temperature sensor for cryogenic temperatures.

Quartz resonator with SnO2 thin film as acoustic gas sensor for NH3

Abstract A quartz resonator with a thin SnO2 deposited film was investigated as a sensor for detecting the presence of ammonia in the ambient. The SnO2 film was used as a gas sensing element. Considerable variations of the resonance frequency Δf = 15 ÷ 119 Hz were observed depending on the NH3 concentrations in the range of 10 ÷ 5000 ppm. These variations were reversible at the conditions of the experiment carried out and no hysterisis was observed at these conditions. The mass Δm of the adsorbed substance was calculated as a function of the ammonia concentration c. The character of this dependence was well described with Δm = 2.4 c,0.3 that is an equation based on the Freundlich isotherm adsorption model.

Piezoelectric quartz resonators as highly sensitive temperature sensors

Abstract The physical principles of piezoresonance quartz sensors are discussed. More attention is paid to the physical principles and limits of thermosensitive quartz resonators as temperature-measuring sensors. Experimental data from the construction of a new type of ultraminiature thermosensitive resonator with high sensitivity (1022 Hz/°C) and good linearity are quoted. Finally we mention several other possible applications of thermosensitive quartz resonators in measuring other physical values such as vacuum, fluid velocity, electrical current and power, heat conductivity and power of laser emissions.

EFFECT OF PLASMA POLYMERIZATION CONDITIONS ON THE HUMIDITY SORPTIVE PROPERTIES OF THIN FILMS OBTAINED FROM HEXAMETHYLDISILOXANE IN GLOW DISCHARGE

Abstract The humidity sorptive powers of polymer coatings deposited on quartz resonators has been studied. The polymer was obtained from hexamethyldisiloxane by plasma polymerization under different operating conditions of glow discharge current density, gas phase pressure, polymer film thickness and modification of the polymer surface in an ammonia plasma. The sensitivity of the films to humidity was enhanced by operating at the highest current density and pressure and by raising the film thickness and exposure to the ammonia plasma.

An application of a thermosensitive quartz resonator for liquid flow rate measurement

The temperature‐frequency dependence of a thermosensitive quartz resonator is used for the measurement of liquid flow rate. Because of a special quartz cut the resonator has very high temperature sensitivity which allows very small temperature changes to be detected. Using a heater the resonator is heated to a temperature higher than the ambient temperature. The resonator and the heater are designed together as a measuring probe which is placed in the path of a flowing liquid. The liquid flow cools the resonator and causes a frequency change. Using another resonator the temperature difference between the temperatures of the heated resonator and the ambient liquid is measured. In a number of experiments the relationship between the resonator temperature and water flow rate is investigated. A theoretical analysis for this relationship is delivered too. It is found that when the water flow rate is varied from 0.1 to 1.4 m/s the resonator temperature changes within 15 °C.

A thermosensitive quartz resonator with a built‐in microheater as a multipurpose sensor

A design of a thermosensitive quartz resonator with a built‐in microheater is suggested. The resonator uses a piezoelement of a special crystal cut and has a very high‐temperature sensitivity. Because of the linear temperature‐frequency characteristic of the resonator, it can be used as a temperature sensor in a wide temperature range—from −20 to 100 °C. The change of the heater’s input power at a constant ambient temperature leads to a corresponding resonator’s frequency change. Because of the linearity of the resonator’s temperature‐frequency characteristic the power‐frequency dependence is also linear. In such a way the resonator can be utilized as an electrical power meter in the range of 0–400 mW with a sensitivity of about 136 Hz/mW. Using the heater, the resonator can be heated to temperatures higher than the ambient temperature. If the resonator is placed in a path of a flowing liquid, the liquid flow cools the resonator and causes a frequency change, related to the flow rate. The dependence of the resonator’s temperature change on the water flow rate at different input powers has been studied in the range of 0.1–1.2 m/s.

An attempt for NH/sub 3/ detection based on quartz resonator with thin SnO/sub 2/ film

The sensitivity of quartz resonators with a thin layer of tin oxide (SnO/sub 2/) deposited on them is investigated for the registration of ammonia in air. The measurements are carried out at NH/sub 3/ concentrations from 10 ppm to 5000 ppm. A correlation is found between the relative change of the resonators frequency (/spl Delta/f/f) and concentration in the investigated interval. The dependence can be described by equation such as f(x)=ax/sup /spl alpha//+b. To obtain the relationship between the thickness of the thin tin oxide and sensitivity of quartz resonator, the thickness of SnO/sub 2/ is changed from 40 nm to 120 nm. With increase of thin SnO/sub 2/ thickness the resonators sensitivity considerably increases. The highest values in the alteration of the frequency of the quartz resonators are registered by a layer thickness of 120 nm. The changes in the sensitivity of sorption as a function of ammonia concentration at different SnO/sub 2/ thicknesses are calculated. It is shown that at small concentrations, the sensitivity of the thinner layers is higher than of the thicker. At a concentration of 70 ppm, this dependence becomes inverse and shows a tendency to constant values at concentrations over 5000 ppm. The results obtained show that the quartz resonator-thin SnO/sub 2/ film system could be used for detection of NH/sub 3/ concentrations down to 10 ppm. Such a system could be used for development of an acoustic sensor for monitoring NH/sub 3/ contamination in the environment.

INFLUENCE OF VACUUM RAPID THERMAL ANNEALING ON SOME PROPERTIES OF QUARTZ RESONATORS

Abstract The influence of rapid thermal annealing (RTA) on the parameters of quartz resonators and their amplitude–frequency characteristics has been investigated. The resonators were an AT-cut quartz substrate with Al-electrodes 120 nm thick deposited by electron beam evaporation at 1.10 −5 mbar. The samples were subjected to RTA at the temperature of the heater 700°C, 800°C and 900°C for a time from 15 s to 180 s in vacuum at 5.10 −5 mbar. A correlation between the electrical parameters of the resonators and their amplitude–frequency characteristics from one side and RTA conditions from another side have been established. The conditions under which the quartz resonators parameters were improved have been found.

A Thermosensitive Quartz Resonator With A Build-in Microheater As A Multipurpose Sensor

The resonator uses a piezoelement of a special crystal cut with a very high temperature sensitivityabout 1000 WOC, which allows temperature changes of 0,001 OC to be detected. Because of the linear temperature-frequency characteristic the resonator can be used as a temperature sensor in wide temperature range-from 40 to 150OC. Thie temperature-frequency characteristic has been investigated in the given range.