Enver Sadikoglu

High pressure focused ultrasound field characterization

High intensity focused ultrasound (HIFU) transducers are novel and very attractive tools for cancer therapy. They produce very high pressure acoustic fields up to tens of MPa at the focus; thus, acoustic characterization of HIFU fields must be investigated in order to ensure the safe and effective use in clinical applications. A needle hydrophone has been used for HIFU transducer characterization in the newly designed home made system at TUBITAK UME (The Scientific and Technological Research Council of Turkey, the National Metrology Institute) Ultrasound laboratory. TUBITAK UME HIFU measurement system was controlled by a Labview based data translation program. The driving signal was generated by signal generation card and output from the hydrophone was fed directly into a DSO oscilloscope card. The controlling program executed a “capture-analyze-move” cycle, allowing a large number of measurements to be made. Field scanning measurements are made between 1 MPa, 2 MPa, and 3 MPa pressures. Theoretical model...

Laser pistonphone as an alternative tool for microphone absolute calibration at low frequencies

Laser pistonphone for absolute microphone calibration in low frequency range has been realized at UME. According to the operation principle of pistonphone, the motion of a piston, which is driven electro-mechanically in a closed acoustical coupler, produces a sound pressure. Accurate measurements of the piston displacement by laser interferometry enable accurate determination of the sound pressure and, as a result, the pressure sensitivity of the microphone exposed to the sound pressure inside the coupler. Homodyne Michelson interferometer with He-Ne laser was used for displacement measurements. Since the pistonphone is operating at low frequencies, the fringe-counting method was used for the signal processing. Calibrations of LS1P microphones with the uncertainty less that 0. 15 dB have been performed using laser pistonphone. Other possible metrological applications of laser pistonphone are also described in the paper.

The calibration of a prototype occluded ear simulator designed for neonatal hearing assessment applications

An innovative family of ear simulators has been conceived for the calibration and traceability of audiometric equipment. Each device within the family has been designed for a particular key age group, covering neonates through to adults. The age-specific ear simulators are intended to improve the quality of hearing assessment measurements for all test subject age groups, and will be proposed as the next generation of standardised ear simulators for audiometric applications. The family of ear simulators shares a common design and modeling approach, and the first prototype devices for neonatal applications have been manufactured. The objectives of this study were to develop calibration methods, verify conformance to the design goals, demonstrate that the device is capable of being calibrated reliably, and show that its performance is ultimately suitable for international standardisation and eventual adoption into clinical practices. Four national measurement institutes took part in a round-robin calibration comparison and an analysis of the results showed that these objectives were achieved.

Comparison of the input electrical power measurement methods for HIFU transducers

HIFU (High Intensity Focused Ultrasound) transducers are attractive tools for cancer therapy. They must be used carefully for operator and patient safety as they produce very high powers up to a few hundred watts, and characterized in many ways. The ultrasonic power of a transducer is directly proportional to the applied input electrical voltage, current and consequently electrical power. Internationally accepted methods for measurements of ultrasonic output power up to 10 W are well established in the IEC 61161 standards [1]. The same method was used for higher powers up to 150 W with an uncertainty of 4.7% for 1.1 MHz and 5.0% for 3.3 MHz in an intercomparison between national metrology institutes [8]. In this paper, input electrical power of the HIFU transducer, which is mainly converted into ultrasonic energy, was determined. 3 methods for the measurement of electrical power delivered to a reactive ultrasonic (HIFU) transducer were compared. Electrical power measurements were realized with an expanded uncertainty of 3.3 % for up to 50 W and 4.3 % for up to 100 W in the frequency range between 0.93 MHz and 3.1 MHz. Measurement devices were calibrated and verified by establishing traceability to electrical and ultrasonic standards at TÜBİTAK UME (The Scientific and Technological Research Council of Turkey, National Metrology Institute) primary laboratories. Electrical power measurement results obtained by this method were also compared with two different conventional power meters. Electrical power measurement results detailed in this paper showed an agreement with each other and conventional power meters.

Low frequency calibration of hydrophones by self-mixing interferometry at UME

Realization and dissemination of the unit of sound pressure in water are carried out through calibration of hydrophones and underwater acoustic transducers. Different calibration methods applicable for different frequency ranges are available for this purpose. For calibration of reference hydrophones at low frequencies air-water pistonphone has been constructed at Turkish National Metrology Institute (UME). One of the main parts of the calibration system is optical interferometer. Two different interferometer types were used for the precise displacement measurements. The hydrophone calibrations performed by using air-water pistonphone both with homodyne Michelson interferometer and diode laser based self-mixing interferometer, ECDL.