By Marcus Wild

Marcus Wild

Within the maritime industry, ships use SONAR (Sound Navigation and Ranging) systems in order to make maps of the seabed. The problem with SONARs, is that they can have a tendency to overheat. Indeed, SONARs are composed of materials which exhibit energy loss, i.e., a percentage of the energy input into these materials is converted to heat. High temperatures can cause the SONARs to perform inefficiently and over time will damage the materials. Our aim is to predict the temperature rise in the materials used in SONARs. This will help us to design more efficient SONARs which in turn will allow us to push the performance of these systems.

High temperatures can cause the SONARs to perform inefficiently and over time will damage the materials.

SONARs emit sound waves, which then bounce off the seabed and return to the ship, in the same way that a bat or a dolphin uses sound to find its prey. SONARs are made of many components, but one of the most important components is the piezoelectric (piezo means squeeze) material. When pressure is applied to this type of material, an electric current is produced and reversely, when an electric current is applied to this material, it generates a sound wave (like a microphone and an amplifier). This behaviour is very useful and this material is the driving mechanism behind the sound wave generated by SONAR. However, some of this energy is also converted into heat, and too much heat will damage the SONAR.

In order to predict the heating in the piezoelectric material, the material properties such as the stiffness, electric characteristics (specifically, electric permittivity) and the electromechanical coupling factor (how easily the material converts mechanical energy like sound to electrical energy and vice versa) need to be characterised accurately.
Once these material characteristics have been determined, the power dissipation as a function of space and frequency can be calculated. The calculated power dissipation density, which can be thought as the amount of input energy converted to heat, for one particular frequency is shown in Fig. 1.

Figure 1: Power dissipation density as a function of position along the length of the rod.

Therefore, based on the calculated material parameters and the theory surrounding piezoelectric materials, the power dissipation at the centre of the rod should be more significant than at the edges of the rod. Using the curve in Fig. 1, we can now attempt to predict the temperature rise in a piezoelectric rod. An experimental setup was designed, shown in Fig. 2, in order to achieve this. The piezoelectric rod is placed in an insulating box in order to have a more stable convection rate (cooling due to air flow). A voltage is applied to the piezoelectric rod at a particular frequency through the copper wire in order to cause self-heating. Three thermocouples are attached at different positions along the side of the rod to measure the distribution of the temperature as the piezoelectric heats up.  This setup is duplicated in a Finite-Element-Method software called COMSOL in order to model the temperature rise at the thermocouple positions.

Fig. 3 shows the comparison between the modelled and measured temperature rise at the thermocouple positions. Although there are discrepancies between the measured and modelled temperature curves, the overall trend between the thermocouples does seem to have been captured well. This would suggest that the power dissipation density curve does indeed resemble the predicted curve shown in Fig. 1. Although this work does require a more accurate experimental setup and thermal material parameters in order to add confidence to this conclusion, we are confident that this a good first step to predicting the temperature in piezoelectric materials.

Tormod Njølstad

Tormod Njølstad (59) was hired as Innovation Manager in the Ultrasound group at ISB in September 2018.

Tormod left his safe and permanent position as Associate Professor at Department of Electronic Systems at NTNU and established New Index in January 2003 in Trondheim, founded on his patented idea from year 2000 of making an interactive pen for projectors, which could modernize education at universities and in schools. The brand new technology he and his colleagues developed, transformed data projectors to be interactive data projectors that could completely replace the popular, but expensive interactive whiteboards.

New Index’ scalable and instant e-whiteboard was selected by the European Commission as one of the winners of the European Information Society Technologies (IST) Prize 2004, Europe’s most distinguished award for groundbreaking IST products.

• Further reading: Pris til pekeverktøy (norwegian/TU.no)

During several years, Tormod and his colleagues demonstrated New Index’ progress in business-to-business trade shows in US and Europe, invited potential partners to Trondheim, and were invited to demonstrate the New Index’ technology in their head quarters in US, UK, and of course: in Japan! Tormod is no more sure about on how many trips to Japan he made over the years.

A dream comes true

In 2011 his dream came true: The largest data projector manufacturer in the world, EPSON in Japan, decided to include and integrate the New Index’ technology into their product roadmap, realizing Tormod’s patented idea from 2000 of an interactive projector. EPSON acquired New Index and the operation continued in Trondheim for seven years under the new company name EPSON Norway Research and Development AS. Already 6 month after the acquisition, the first interactive projector model was launched in the market by the joint work of the engineers in the Trondheim-based subsidiary of EPSON and the EPSON’s engineers in Japan.  Today (2018) there are nine different interactive EPSON projector models in sale with interactive technologies developed by Tormod and his colleagues in Trondheim, with a world marked share of about 70%.

Next goal: Innovation of new ultrasound methods, technologies and products for a better world

Tormod has gained a lot of experience from this long journey from an idea to world-wide distributed products. Now he is ready to learn more about ultrasound. In his new role as Innovation Manager in Ultrasound at NTNU, Tormod defines his mission to find out how ultrasound research can be transferred into new ultrasound methods and new ultrasound products for a better world as NTNU’s slogan.

Twenty-nine experts and researchers associated with CIUS participated at IUS, the IEEE International Ultrasound Symposium in Kobe, Japan, in October 2018. Not only the number of attendees, but also the number of presentations from CIUS was impressively high.

Kaja, Sebastien, Hans, Stefano, Ole Marius, Tung; Solveig, Thong, Annette, Christiana, Morten, Jørgen, Ali; Tore, Andreas, Yucel, Alfonso, Lasse, Per Kristian ; Kenneth, Marcus, Andreas, Erlend, Tormod and Lars. Not present: Erik, Stine, Petter and Thomas.

The overall scientific contribution from the CIUS group included 13 posters and 13 oral presentations from the CIUS’ partners NTNU, UiO, HSN, Sintef, GE Vingmed, Halfwave, InPhase and Relab.

From a CIUS perspective, there were also special achievements to be reported.

PhD candidate Stefano Fiorentini receives the second-best award in the 2018 IEEE IUS SA-VFI Challenge.

Stefano Fiorentini, NTNU, was awarded second-best in the 2018 IEEE IUS SA-VFI Challenge, within estimation of blood flow velocities, a practical contest which was announced ten months before the conference. Thomas Grønli, NTNU, was nominated as one of three finalists of the Best Student Paper competition. It was also an honor that Professor Lasse Løvstakken, NTNU, was appointed Invited speaker on the subject “Next-generation echocardiography – opportunities and challenges”.

In the final Highlight Session, well-recognized experts summed up the most important scientific achievements presented at IUS.

The first panelist, Professor Ton van der Steen, focused a.o. on NTNU’s achievements within 4D mechanical wave mapping of the heart and on NTNU’s Deep learning activities within echocardiography. His message was that “NTNU exemplifies how the close scientific work between clinicians and ultrasound technology researchers at NTNU steers the direction and guarantees the relevance and quality of the academic research in an exemplary way”*.

He also disclosed that he deliberately choose to focus on one university to emphasize the translation and that he could also have put together a similar set of slides for e.g. Leuven, Duke, New York, Rotterdam.

It was a good introduction for me as Innovation Manager to be at IUS with CIUS. My impression is that Norwegian academic researchers and industry R&D groups associated with CIUS have an excellent international standing. Within several fields, NTNU/CIUS is leading in the world defining new, relevant and innovative ultrasound methods and solutions.

* Quoted with permission from Professor Ton van der Steen at Erasmus MC and TU Delft.

About the author

Tormod Njølstad

After just having started as Innovation Manager in Ultrasound at ISB at NTNU, Tormod Njølstad (59) was invited to travel with his new Ultrasound colleagues to the largest and most important international ultrasound conference, the IEEE IUS conference, in Kobe, Japan, this year. Being there, Tormod got a rough overview over the current main ultrasound research directions. He observed how the ultrasound research groups in Norway are beyond state of the art, and he got to know his new colleagues also at a more personal level.

You can read more about Tormod here.