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This paper presents experimental and theoretical piezoelectric photoacoustic spectra of ZnSe samples after different surface treatments: grinding, polishing, and etching. The modification of the Jackson and Amer theory, presented in the paper, enabled numerical interpretation of the spectra in the model of a mechanically damaged surface layer. The nature of the characteristic peak observed at E = 2.65 eV below the energy gap is explained as caused by the Urbach absorption tail and the damaged surface layer of a sample. The correlation between the microhardness of the Zn1-x Be x Se and ZnSe crystals and the thickness of the mechanically damaged surface layer was observed.

This paper presents experimental results of quantitative DC measurements carried out by the use of a scanning thermal microscope equipped with nanofabricated thermal probes, and their numerical simulations done by finite element analysis. In the proposed method, the probe resistance variations are measured for the sample-to-air transition. It is shown that taking the signal measured in air as a reference makes the measurement less sensitive to instabilities of ambient conditions. This paper also presents a simple theoretical model describing the phenomena associated with heat transfer in the probe–sample system. Both experimental and numerical results confirm the theoretical findings. The registered signal can be related to the thermal conductivity of different materials, which makes the method useful for determining the local thermal conductivity.

This paper is a description of theoretical models applied for the numerical interpretation of the experimental amplitude and phase frequency thermoacoustic characteristics observed for the transistor’s packaging TO-39 with model holes of known radii in the packaging. They are essential from the point of view of determination of the sensitivity of the thermoacoustic method applied for the measurements of the air-tightness of packagings of electronic elements. In this paper, two models of the thermoacoustic signal are described, which are based on a transformation of the thermoacoustic effect to an electrical circuit: CRC and CRLC. Additionally, a method of extraction of the signal, coming from the hole in the packaging, from the total thermoacoustic signal, of the TO-39 packaging, is presented and discussed. The limitation of this method of detection of the air-tightness, caused by the thermoacoustic signal of the air-tight packaging, is also discussed.

This paper is a review of analog front-end circuitry used in photoacoustic equipment with microphone or piezoelectric detection. A block structure of the front end as well as detailed circuit diagrams of preamplifiers dedicated for piezoelectric sensors and measurement condenser and electret microphones are described. The presented circuits are optimized toward low-noise operation. Practical remarks regarding the design of the remaining analog blocks are also given. The analysis shows that it is possible to design an analog front end for which specifications will be comparable with the best commercial solutions.

Solutions which reduce the impact of the external acoustic noise on the photoacoustic signal rely often on the appropriate modification of the photoacoustic cell structure. The goal is to obtain a frequency response of the cell which suppresses the external noise as much as possible. Another approach is differential detection, in which two microphones are used, and assuming that the external noise signal components from both microphones are identical, their subtraction should result in canceling the external noise. The main difficulty of that solution is that both microphone signal paths should be calibrated to have virtually identical characteristics. The paper presents a differential photoacoustic cell with digital differential detection.

The paper describes how mechanical dimensions of a differential open photoacoustic Helmholtz cell affect its operation. The influence of the diameter and length of the internal and external ducts and the volume of the acoustic buffers on the frequency response of the cell, as well as on the attenuation of the external acoustic noise, was studied. The analysis was performed by means of computer simulations based on a model in which loss-corrected transmission line duct definitions were used. The results showed that under proper selection of the cell dimensions, its frequency response at the frequencies around the main resonance is nearly identical as in the case of the conventional, closed Helmholtz resonator. The length of the ducts is only slightly related to the frequency of resonance, and does not noticeably affect the Q- factor of the cell. A decrease of the duct diameters and an increase of the buffer volumes improve attenuation of the external acoustic noise. It should be possible to obtain external acoustic noise rejection as high as 80 dB, which is a substantial improvement in comparison to the previous designs, which reported this value at the level of 40 dB to 50 dB.

This paper presents an apparatus for the calibration of long-stem platinum resistance thermometers at the argon triple point $$(T_{90} = 83.8058\,\hbox {K})$$ , designed at the Institute of Low Temperature and Structural Research, Poland (INTiBS). A hermetically sealed cell filled at the Istituto Nazionale di Ricerca Metrologica, Italy with high purity gas (6N) is the main element of this apparatus. The cell is placed in a cryostat fully immersed in liquid nitrogen. A temperature-controlled shield ensures the quasi-adiabatic condition needed for proper realization of the phase transition. A system for correcting the temperature distribution along the thermometer well is also implemented. The cell cooling and argon solidification is carried out by filling the thermometer well with liquid nitrogen. A LabVIEW computer program written at INTiBS automatically controls the triple-point realization process. The duration of a melting plateau in the apparatus lasts for about 24 h. The melting width for $$F$$ between 20 % and 80 % was $${

In this paper, experimental photoluminescence (PL) and piezoelectric photothermal (PPT) spectra of selected II–VI binary crystals are presented and analyzed. The quantitative analysis of the photothermal spectra was performed using a modified and extended Jackson–Amer model. The values of the bandgap energies of investigated semiconductors were computed from the PT amplitude and phase spectra. From the temperature dependence of the exciton emission so-called “excitonic energy gaps” have been determined. It follows from the theory that the exciton binding energy is the difference of these two values of energy gaps derived from PPT and PL spectroscopy.

When open photoacoustic cells are considered, attenuation of external noise is a serious issue. This paper describes how mechanical dimensions of a differential open photoacoustic Helmholtz cell influence its signal-to-noise (S/N) ratio. The analysis was performed by means of computer simulations based on the loss-improved transmission line model. This research showed that the mechanical parameters noticeably affect the signal-to-noise ratio. According to the presented results, optimal selection of the dimensions is a factor which can substantially improve the signal-to-noise ratio of the examined photoacoustic cell. Due to the very good acoustic properties of the cell, it should be possible to obtain an S/N ratio of over 100 dB.

This paper concerns the studies of temperature and frequency behavior of the complex impedance, electric modulus, and electric conductivity due to an ionic current in liquid γ-butyrolactone (GBL) and γ-valerolactone (GVL). The frequency of the applied electric stimulus (500 Hz to 5 MHz) corresponds to the static dielectric regime of the lactones. The studies were performed in the temperature range of 263 K to 313 K. It was shown that in the static dielectric case, the dc ionic conductivity (σDC) and the static dielectric permittivity \({(\varepsilon_{\rm s})}\) determine the relaxational behavior of the impedance (Z*) and the electric modulus (M*) of the molecular liquids and both spectra are of the Debye-type characterized by the same conductivity relaxation time (τσ). Both σDC and τσ of GBL and GVL fairly well fulfill an Arrhenius temperature dependence with very similar values of the thermal activation energy \({{\rm E}_{\sigma_{\rm DC}} \approx {\rm E}_{\tau_\sigma} \approx 25 \,{\rm kJ} \, . \, {\rm mol}^{-1}}\) . The temperature dependence of the static dielectric permittivity and its temperature derivative is analyzed and interpreted in terms of the dipolar aggregation in the studied lactones.

In a typical photoacoustic measurement system, signal detection is usually implementedwithasinglemicrophoneoranotherpressuresensor.Asolutionpresented in this paper consists of an array of 14 MEMS microphones equipped with dedicated andindividuallycontrollablesignalpaths,basedonprogrammablegainamplifiersand analog-to-digitalconverters.Further,digitalsignalprocessingandrecordingareimple- mented in an FPGA-based hardware system. Use of multiple microphones increases the signal amplitude and the signal-to-noise ratio and allows for measurements of pressure-field distribution inside the photoacoustic cell.

Open photoacoustic cells are often used in continuous-flow photoacoustic measurements. Such cells are sensitive to external noise penetration. The improved open photoacoustic Helmholtz cell has much better external noise attenuation than the previously known designs. This paper describes how mechanical dimensions of such a cell influence its signal-to-noise ratio. The analysis was performed by means of computer simulations based on the loss-improved transmission line model. This research showed that the mechanical parameters affect signal-to-noise noticeably and, if they are properly chosen and applied in the design of the improved open cell, the resulting signal-to-noise ratio may be improved by almost 60 dB in comparison to previous designs of open photoacoustic Helmholtz cells.

The use of thermoelements is a commonly applied method in industry and engineering. It provides a wide measurement range of temperature, a direct voltage signal from the transducer, low cost of the thermoelement, and its resistance to many unfavorable factors which occur in an industrial environment. Unfortunately, thermoelements may not be resistant to interferences of a strong electromagnetic field because of the nature and design of a transducer. Induction heating is the most commonly used type of heating, at present, for metals. In order to guarantee the correctness of the carried out heating process, it is essential to control the temperature of the heated element. The impact of a strong electromagnetic field upon the thermocouple temperature measurement of the inductively heated elements has been analyzed in this paper. The experiment includes dozens of measurements where the following parameters have been varied: frequency of the current which feeds the heating inductor, power supplied to the heating system, geometry of heat inductor, and the charge material and its geometrical dimensions. Interferences of the power-line frequency have been eliminated in part of the carried out measurements.

Quantitative thermal measurements with spatial resolution allowing the examination of objects of submicron dimensions are still a challenging task. The quantity of methods providing spatial resolution better than 100 nm is very limited. One of them is scanning thermal microscopy (SThM). This method is a variant of atomic force microscopy which uses a probe equipped with a temperature sensor near the apex. Depending on the sensor current, either the temperature or the thermal conductivity distribution at the sample surface can be measured. However, like all microscopy methods, the SThM gives only qualitative information. Quantitative measuring methods using SThM equipment are still under development. In this paper, a method based on simultaneous registration of the static and the dynamic electrical resistances of the probe driven by the sum of dc and ac currents, and examples of its applications are described. Special attention is paid to the investigation of thin films deposited on thick substrates. The influence of substrate thermal properties on the measured signal and its dependence on thin film thermal conductivity and film thickness are analyzed. It is shown that in the case where layer thicknesses are comparable or smaller than the probe–sample contact diameter, a correction procedure is required to obtain actual thermal conductivity of the layer. Experimental results obtained for thin SiO $$_{\mathrm {2}}$$ and BaTiO $$_{\mathrm {3 }}$$ layers with thicknesses in the range from 11 nm to 100 nm are correctly confirmed with this approach.

One of the major issues in the use of the resonant photoacoustic cell is the resonance frequency of the cell. The frequency is not stable, and its changes depend mostly on temperature and gas mixture. This paper presents a new method for tracking resonance frequency, where both the amplitude and phase are calculated from the input samples. The stimulating frequency can be adjusted to the resonance frequency of the cell based on the phase. This method was implemented using a digital measurement system with an analog to digital converter, field programmable gate array (FPGA) and a microcontroller. The resonance frequency was changed by the injection of carbon dioxide into the cell. A theoretical description and experimental results are also presented.