title: Glass-windowed ultrasound transducers.
abstract: In research and industrial processes, it is increasingly common practice to combine multiple measurement modalities. Nevertheless, experimental tools that allow the co-linear combination of optical and ultrasonic transmission have rarely been reported. The aim of this study was to develop and characterise a water-matched ultrasound transducer architecture using standard components, with a central optical window larger than 10 mm in diameter allowing for optical transmission. The window can be used to place illumination or imaging apparatus such as light guides, miniature cameras, or microscope objectives, simplifying experimental setups. Four design variations of a basic architecture were fabricated and characterised with the objective to assess whether the variations influence the acoustic output. The basic architecture consisted of a piezoelectric ring and a glass disc, with an aluminium casing. The designs differed in piezoelectric element dimensions: inner diameter, ID=10 mm, outer diameter, OD=25 mm, thickness, TH=4 mm or ID=20 mm, OD=40 mm, TH=5 mm; glass disc dimensions OD=20-50 mm, TH=2-4 mm; and details of assembly. The transducers' frequency responses were characterised using electrical impedance spectroscopy and pulse-echo measurements, the acoustic propagation pattern using acoustic pressure field scans, the acoustic power output using radiation force balance measurements, and the acoustic pressure using a needle hydrophone. Depending on the design and piezoelectric element dimensions, the resonance frequency was in the range 350-630 kHz, the -6 dB bandwidth was in the range 87-97%, acoustic output power exceeded 1 W, and acoustic pressure exceeded 1 MPa peak-to-peak. 3D stress simulations were performed to predict the isostatic pressure required to induce material failure and 4D acoustic simulations. The pressure simulations indicated that specific design variations could sustain isostatic pressures up to 4.8 MPa.The acoustic simulations were able to predict the behaviour of the fabricated devices. A total of 480 simulations, varying material dimensions (piezoelectric ring ID, glass disc diameter, glass thickness) and drive frequency indicated that the emitted acoustic profile varies nonlinearly with these parameters.
authors.affiliation: Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen, Norway; National Centre for Ultrasound in Gastroenterology, Haukeland University Hospital, Jonas Lies vei 65, 5021 Bergen, Norway.
authors.forename: Tostein
authors.initials: T
authors.lastname: Yddal
authors.affiliation: National Centre for Ultrasound in Gastroenterology, Haukeland University Hospital, Jonas Lies vei 65, 5021 Bergen, Norway; Department of Clinical Medicine, University of Bergen, Jonas Lies vei 65, 5021 Bergen, Norway.
authors.forename: Odd Helge
authors.initials: OH
authors.lastname: Gilja
authors.affiliation: School of Engineering, University of Glasgow, 6.03 James Watt South Building, Glasgow G12 8QQ, United Kingdom.
authors.forename: Sandy
authors.initials: S
authors.lastname: Cochran
authors.affiliation: Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen, Norway; School of Electrical and Information Engineering, Chamber of Mines Building, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050, South Africa.
authors.forename: Michiel
authors.initials: M
authors.lastname: Postema
authors.affiliation: National Centre for Ultrasound in Gastroenterology, Haukeland University Hospital, Jonas Lies vei 65, 5021 Bergen, Norway; Department of Clinical Medicine, University of Bergen, Jonas Lies vei 65, 5021 Bergen, Norway; Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen, Norway. Electronic address: Spiros.Kotopoulis@uib.no.
authors.forename: Spiros
authors.initials: S
authors.lastname: Kotopoulis
mesh_terms: D000162:Acoustics; D004867:Equipment Design; D005898:Glass; D014159:Transducers; D014465:Ultrasonics / Q000295:instrumentation*
keywords: Acoustic field simulation; De-fouling; Optical window; Ultrasound transducer