Possibilities of Reliable Ultrasonic Detection of Subwavelength Pipework Cracks

An occurrence of cracks in pipework could lead to potentially very dangerous malfunction in some critical engineering systems such as power plants. There is a clear trend of replacing traditional manual testing with non-invasive in-situ methods that should detect crack formation in its early stage. Such as approach would enable replacing of unhealthy pipe components during the regular periodic outages. Ultrasonic testing is known to be a rather mature and reliable technology. However, it suffers from serious problems in detection of the cracks of subwavelength size. This paper attempts to soften aforementioned problems by investigating the influence of a duration of the unipolar excitation signal on the achieved resolution. In addition, the transducer input electricalimpedance of NDT transmitter was measured by using different excitation pulses and their levels and the results are compared with those obtained using traditional frequency sweeping method at low excitation levels. Finally, use of some advanced signal processing algorithms that might lead to the automatic detection of subwavelength voids, in scenarios with low signal-to-noise ratio, is discusse

Laboratorij za određivanja svojstava kompleksnih materijala akustičkim metodama - LOSKSAM

U radu će se opisati rad Istraživačkog laboratorija za određivanja svojstava kompleksnih materijala akustičkim metodama-LOSKSAM osnovanog u sklopu Zavoda za elektroakustiku, Fakulteta elektrotehnike i računarstva, Sveučilišta u Zagrebu. U LOSKSAM-u se provodi karakterizacija elektroakustičkih i ultrazvučnih pretvarača i, kao i pripadajućih elektroničkih i akustičkih komponenata. Razvijaju se sonde za bio-medicinsko djelovanje (terapija, kirurgija) kao i za nedestruktivno ispitivanje materijala. Obavljaju se mjerenja isijane ultrazvučne snage u realnom okruženju, detekcija pojave kavitacije kod ultrazvučnih mjerenja, njeno korištenje u kirurške svrhe te kalibracija svih vrsta elektroakustičkih pretvarača i mjerenja na akustičkim elementima i sustavima

Laboratorij za određivanja svojstava kompleksnih materijala akustičkim metodama - LOSKSAM

U radu će se opisati rad Istraživačkog laboratorija za određivanja svojstava kompleksnih materijala akustičkim metodama-LOSKSAM osnovanog u sklopu Zavoda za elektroakustiku, Fakulteta elektrotehnike i računarstva, Sveučilišta u Zagrebu. U LOSKSAM-u se provodi karakterizacija elektroakustičkih i ultrazvučnih pretvarača i, kao i pripadajućih elektroničkih i akustičkih komponenata. Razvijaju se sonde za bio-medicinsko djelovanje (terapija, kirurgija) kao i za nedestruktivno ispitivanje materijala. Obavljaju se mjerenja isijane ultrazvučne snage u realnom okruženju, detekcija pojave kavitacije kod ultrazvučnih mjerenja, njeno korištenje u kirurške svrhe te kalibracija svih vrsta elektroakustičkih pretvarača i mjerenja na akustičkim elementima i sustavima

The Performance of Inertial Measurement Unit Sensors on Various Hardware Platforms for Binaural Head-Tracking Applications

Binaural synthesis with head tracking is often used in spatial audio systems. The devices used for head tracking must provide data on the orientation of the listener’s head. These data need to be highly accurate, and they need to be provided as fast and as frequently as possible. Therefore, head-tracking devices need to be equipped with high-quality inertial measurement unit (IMU) sensors. Since IMUs readily include triaxial accelerometers, gyroscopes, and magnetometers, it is crucial that all of these sensors perform well, as the head orientation is calculated from all sensor outputs. This paper discusses the challenges encountered in the process of the performance assessment of IMUs through appropriate measurements. Three distinct hardware platforms were investigated: five IMU sensors either connected to Arduino-based embedded systems or being an integral part of one, five smartphones across a broad range of overall quality with integrated IMUs, and a commercial virtual reality unit that utilizes a headset with integrated IMUs. An innovative measurement method is presented and proposed for comparing the performance of sensors on all three platforms. The results of the measurements performed using the proposed method show that all three investigated platforms are adequate for the acquisition of the data required for calculating the orientation of a device as the input to the binaural synthesis process. Some limitations that have been observed during the measurements, regarding data acquisition and transfer, are discussed

Optimization of excitation for piezoceramic ultrasonic transducers in nonlinear and thermal variable operating conditions

U ovom radu prikazani su rezultati istraživanja metoda elektromehaničke i akustičke karakterizacije piezokeramičkih uzoraka i ultrazvučnih pretvarača. Istražene su uobičajene normirane metode karakterizacije, uočeni su problemi i nedostatci postojećih rješenja s naglaskom na promatranje parametara piezoelemenata pri visokim razinama pobude. Fokus je stavljen na promjene parametara piezokeramičkih elemenata ovisno o pobudnoj razini i temperaturi te na problem impedancijskog neprilagođenja piezokeramika s pobudnim sustavom pri različitim vrstama pobude. Napravljeno je modeliranje temperaturnog i impedancijskog utjecaja na parametre piezoelemenata, te su predložene nove metode elektromehaničke i akustičke karakterizacije čime su stvorene pretpostavke za unaprjeđenje procesa karakterizacije piezoelemenata predviđenih za rad u promjenjivim uvjetima. Sva mjerenja provedena su s posebnim naglaskom na rad pri rezonantnom i usko oko rezonantnog područja s pojavom nelinearnih efekata. Piezokeramički elementi razmatrani su kao crna kutija – elektromehanički šesteropol. Prikazani su ekvivalentni električni krugovi ultrazvučnih pretvarača navedeni u standardu, pri čemu su definirani bitni parametri izvedeni iz osnovnih jednadžbi. U mehaničkoj domeni prikaz piezokeramičkih elemenata ostvaren je kao titrajni sustav masa spojenih oprugom. Napravljena su mjerenja piezokeramika kao i već sastavljenih pretvarača, te su prikazani fizički parametri koji određuju rezonantne karakteristike. Mjereni parametri napona, struje, pomaka i akustičkog tlaka povezani su s parametrima električne, mehaničke i akustičke domene. Eksperimenti su realizirani u laboratorijskom okruženju s kontroliranim uvjetima. Promjene parametara piezokeramičkih elemenata promatrane su za tri definirane temperature i pri različitim opterećenjima.Electromechanical and acoustic characterization research results of piezoceramic samples and ultrasonic transducers are presented in this paper. The standardized methods of characterization were investigated, and problems of existing solutions were noticed, with an emphasis on piezoelectric parameters at high excitation levels. The focus is on changes in the parameters of piezoceramic elements depending on the excitation level and temperature and on the problem of impedance mismatch at different types of excitations, which makes the efficiency of power transmission between the excitation electronic circuit and the ultrasonic transducer inconsistent. The influence of excitation on the transducer parameters depending on the pulse signal shape is considered. Modelling of temperature and impedance influence on piezoelectric parameters was made, and new methods of electromechanical and acoustic characterization were proposed, which created preconditions for improving the process of characterization of piezoelectric elements intended for operation in variable conditions

Optimization of excitation for piezoceramic ultrasonic transducers in nonlinear and thermal variable operating conditions

U ovom radu prikazani su rezultati istraživanja metoda elektromehaničke i akustičke karakterizacije piezokeramičkih uzoraka i ultrazvučnih pretvarača. Istražene su uobičajene normirane metode karakterizacije, uočeni su problemi i nedostatci postojećih rješenja s naglaskom na promatranje parametara piezoelemenata pri visokim razinama pobude. Fokus je stavljen na promjene parametara piezokeramičkih elemenata ovisno o pobudnoj razini i temperaturi te na problem impedancijskog neprilagođenja piezokeramika s pobudnim sustavom pri različitim vrstama pobude. Napravljeno je modeliranje temperaturnog i impedancijskog utjecaja na parametre piezoelemenata, te su predložene nove metode elektromehaničke i akustičke karakterizacije čime su stvorene pretpostavke za unaprjeđenje procesa karakterizacije piezoelemenata predviđenih za rad u promjenjivim uvjetima. Sva mjerenja provedena su s posebnim naglaskom na rad pri rezonantnom i usko oko rezonantnog područja s pojavom nelinearnih efekata. Piezokeramički elementi razmatrani su kao crna kutija – elektromehanički šesteropol. Prikazani su ekvivalentni električni krugovi ultrazvučnih pretvarača navedeni u standardu, pri čemu su definirani bitni parametri izvedeni iz osnovnih jednadžbi. U mehaničkoj domeni prikaz piezokeramičkih elemenata ostvaren je kao titrajni sustav masa spojenih oprugom. Napravljena su mjerenja piezokeramika kao i već sastavljenih pretvarača, te su prikazani fizički parametri koji određuju rezonantne karakteristike. Mjereni parametri napona, struje, pomaka i akustičkog tlaka povezani su s parametrima električne, mehaničke i akustičke domene. Eksperimenti su realizirani u laboratorijskom okruženju s kontroliranim uvjetima. Promjene parametara piezokeramičkih elemenata promatrane su za tri definirane temperature i pri različitim opterećenjima.Electromechanical and acoustic characterization research results of piezoceramic samples and ultrasonic transducers are presented in this paper. The standardized methods of characterization were investigated, and problems of existing solutions were noticed, with an emphasis on piezoelectric parameters at high excitation levels. The focus is on changes in the parameters of piezoceramic elements depending on the excitation level and temperature and on the problem of impedance mismatch at different types of excitations, which makes the efficiency of power transmission between the excitation electronic circuit and the ultrasonic transducer inconsistent. The influence of excitation on the transducer parameters depending on the pulse signal shape is considered. Modelling of temperature and impedance influence on piezoelectric parameters was made, and new methods of electromechanical and acoustic characterization were proposed, which created preconditions for improving the process of characterization of piezoelectric elements intended for operation in variable conditions

Optimization of excitation for piezoceramic ultrasonic transducers in nonlinear and thermal variable operating conditions

U ovom radu prikazani su rezultati istraživanja metoda elektromehaničke i akustičke karakterizacije piezokeramičkih uzoraka i ultrazvučnih pretvarača. Istražene su uobičajene normirane metode karakterizacije, uočeni su problemi i nedostatci postojećih rješenja s naglaskom na promatranje parametara piezoelemenata pri visokim razinama pobude. Fokus je stavljen na promjene parametara piezokeramičkih elemenata ovisno o pobudnoj razini i temperaturi te na problem impedancijskog neprilagođenja piezokeramika s pobudnim sustavom pri različitim vrstama pobude. Napravljeno je modeliranje temperaturnog i impedancijskog utjecaja na parametre piezoelemenata, te su predložene nove metode elektromehaničke i akustičke karakterizacije čime su stvorene pretpostavke za unaprjeđenje procesa karakterizacije piezoelemenata predviđenih za rad u promjenjivim uvjetima. Sva mjerenja provedena su s posebnim naglaskom na rad pri rezonantnom i usko oko rezonantnog područja s pojavom nelinearnih efekata. Piezokeramički elementi razmatrani su kao crna kutija – elektromehanički šesteropol. Prikazani su ekvivalentni električni krugovi ultrazvučnih pretvarača navedeni u standardu, pri čemu su definirani bitni parametri izvedeni iz osnovnih jednadžbi. U mehaničkoj domeni prikaz piezokeramičkih elemenata ostvaren je kao titrajni sustav masa spojenih oprugom. Napravljena su mjerenja piezokeramika kao i već sastavljenih pretvarača, te su prikazani fizički parametri koji određuju rezonantne karakteristike. Mjereni parametri napona, struje, pomaka i akustičkog tlaka povezani su s parametrima električne, mehaničke i akustičke domene. Eksperimenti su realizirani u laboratorijskom okruženju s kontroliranim uvjetima. Promjene parametara piezokeramičkih elemenata promatrane su za tri definirane temperature i pri različitim opterećenjima.Electromechanical and acoustic characterization research results of piezoceramic samples and ultrasonic transducers are presented in this paper. The standardized methods of characterization were investigated, and problems of existing solutions were noticed, with an emphasis on piezoelectric parameters at high excitation levels. The focus is on changes in the parameters of piezoceramic elements depending on the excitation level and temperature and on the problem of impedance mismatch at different types of excitations, which makes the efficiency of power transmission between the excitation electronic circuit and the ultrasonic transducer inconsistent. The influence of excitation on the transducer parameters depending on the pulse signal shape is considered. Modelling of temperature and impedance influence on piezoelectric parameters was made, and new methods of electromechanical and acoustic characterization were proposed, which created preconditions for improving the process of characterization of piezoelectric elements intended for operation in variable conditions

The Potential of Speech as the Calibration Sound for Level Calibration of Non-Laboratory Listening Test Setups

The pandemic of COVID-19 and the resulting countermeasures have made it difficult or impossible to perform listening tests in controlled laboratory environments. This paper examines the possibility of using speech for level calibration of sound reproduction systems used in listening tests performed in non-laboratory conditions, i.e., when such tests are distributed through the means of electronic communication and performed in a home environment. Moreover, a larger pool of potential test subjects can be reached in this manner. The perception of what the “normal” level of reproduced speech should be was examined through a listening experiment by letting the listeners set the level of reproduced speech samples as they saw fit, depending on the used sound reproduction system, the (non)existence of visual stimulus, and the voice of the speaker. The results show that the perception of normal speech level is highly individual when it comes to setting that level by listening to reproduced speech. The interindividual differences between the subjects are considerably larger than the impact of the three main effects. The understanding of what the “normal” level of read speech should be was examined experimentally as well by asking the subjects to read a paragraph of text, depending on the visual stimulus. The results show that the “normal” level of read speech is reasonably consistent and averages at 55 dBA at a normal conversational distance of 1 m, in a room with room acoustics conditions typical for home environment and low background noise, and with the visual stimulus that mimics the interlocutor put within the personal space of the reader. A preliminary proposal is given of a level calibration method for non-laboratory listening experiments based on these results, and some of its aspects that require further research are discussed

The Potential of Speech as the Calibration Sound for Level Calibration of Non-Laboratory Listening Test Setups

The pandemic of COVID-19 and the resulting countermeasures have made it difficult or impossible to perform listening tests in controlled laboratory environments. This paper examines the possibility of using speech for level calibration of sound reproduction systems used in listening tests performed in non-laboratory conditions, i.e., when such tests are distributed through the means of electronic communication and performed in a home environment. Moreover, a larger pool of potential test subjects can be reached in this manner. The perception of what the “normal” level of reproduced speech should be was examined through a listening experiment by letting the listeners set the level of reproduced speech samples as they saw fit, depending on the used sound reproduction system, the (non)existence of visual stimulus, and the voice of the speaker. The results show that the perception of normal speech level is highly individual when it comes to setting that level by listening to reproduced speech. The interindividual differences between the subjects are considerably larger than the impact of the three main effects. The understanding of what the “normal” level of read speech should be was examined experimentally as well by asking the subjects to read a paragraph of text, depending on the visual stimulus. The results show that the “normal” level of read speech is reasonably consistent and averages at 55 dBA at a normal conversational distance of 1 m, in a room with room acoustics conditions typical for home environment and low background noise, and with the visual stimulus that mimics the interlocutor put within the personal space of the reader. A preliminary proposal is given of a level calibration method for non-laboratory listening experiments based on these results, and some of its aspects that require further research are discussed

The Performance of Inertial Measurement Unit Sensors on Various Hardware Platforms for Binaural Head-Tracking Applications

Binaural synthesis with head tracking is often used in spatial audio systems. The devices used for head tracking must provide data on the orientation of the listener’s head. These data need to be highly accurate, and they need to be provided as fast and as frequently as possible. Therefore, head-tracking devices need to be equipped with high-quality inertial measurement unit (IMU) sensors. Since IMUs readily include triaxial accelerometers, gyroscopes, and magnetometers, it is crucial that all of these sensors perform well, as the head orientation is calculated from all sensor outputs. This paper discusses the challenges encountered in the process of the performance assessment of IMUs through appropriate measurements. Three distinct hardware platforms were investigated: five IMU sensors either connected to Arduino-based embedded systems or being an integral part of one, five smartphones across a broad range of overall quality with integrated IMUs, and a commercial virtual reality unit that utilizes a headset with integrated IMUs. An innovative measurement method is presented and proposed for comparing the performance of sensors on all three platforms. The results of the measurements performed using the proposed method show that all three investigated platforms are adequate for the acquisition of the data required for calculating the orientation of a device as the input to the binaural synthesis process. Some limitations that have been observed during the measurements, regarding data acquisition and transfer, are discussed