Sumet Umchid

Development of calibration techniques for ultrasonic hydrophone probes in the frequency range from 1 to 100 MHz

The primary objective of this work was to develop and optimize the calibration techniques for ultrasonic hydrophone probes used in acoustic field measurements up to 100 MHz. A dependable, 100 MHz calibration method was necessary to examine the behavior of a sub-millimeter spatial resolution fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also, it was of interest to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (high intensity focused ultrasound) applications. In addition to the development and validation of a novel, 100 MHz calibration technique the innovative elements of this research include implementation and testing of a prototype FO sensor with an active diameter of about 10 microm that exhibits uniform sensitivity over the considered frequency range and does not require any spatial averaging corrections up to about 75 MHz. The results of the calibration measurements are presented and it is shown that the optimized calibration technique allows the sensitivity of the hydrophone probes to be determined as a virtually continuous function of frequency and is also well suited to verify the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined to be about +/-12% (+/-1 dB) up to 40 MHz, +/-20% (+/-1.5 dB) from 40 to 60 MHz and +/-25% (+/-2dB) from 60 to 100 MHz. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will constitute a universal reference tool in the wide, 100 MHz bandwidth.

Development of ultrasonic power measurement standards in Thailand

Measurement of power output levels of diagnostic and therapeutic ultrasound equipment has become increasingly important to determine exact patient exposure levels in case a potential risk exists to the patient and to ascertain whether the ultrasound devices are performing satisfactorily. The objective of this work was to establish standards for ultrasonic power in Thailand by developing a primary level ultrasonic power measurement system. This system is being set up at the National Institute of Metrology, Thailand (NIMT) and it will be able to determine the ultrasonic output power in the frequency range from 1 MHz to 20 MHz, and in the power range from 1 mW to 20 W. The implementation of the system utilizes a radiation force balance technique based on the method recommended in the International Electrotechnical Commission (IEC 61161). Three ultrasonic transducers with three different resonance frequencies, 1 MHz, 5 MHz and 10 MHz were used as an ultrasonic source to test the performance of the developed system. The results of the measurements from the developed primary system at the National Institute of Metrology, Thailand (NIMT) are presented in comparison with those measured from the commercial ultrasound power meter (UPM). It is shown that the measurements yielded results that were consistent within a measuring uncertainty of ±5%. In addition, the results also show that the developed system is currently capable of determining the ultrasonic output power in the frequency range from 1 MHz to 10 MHz, and in the power range from 1 mW to 500 mW.

Design and Development of the Ultrasound Power Meter with a Three Axis Alignment System for Therapeutic Applications

The total output power from medical ultrasound devices must be determined and strictly regulated to ensure patient safety and to evaluate the performance of the ultrasound devices. The objectives of this research were to design and develop an ultrasound power meter with a three axis alignment system to measure the total output power from medical ultrasound devices especially for therapeutic applications. The implementation of this work utilizes a radiation force balance technique based on the method recommended in the International Electrotechnical Commission (IEC 61161). An ultrasound therapy machine was used as an ultrasonic source. To verify the performance of the developed system, the total output powers measured from our developed ultrasound power meter were compared with those measured from the commercial ultrasound power meter (UPM) and compared with those measured from the standard ultrasonic power measurement system at the National Institute of Metrology, Thailand (NIMT) at five nominal intensity values (0.5, 1, 1.5, 2, 3 W/cm2) with three frequencies, 0.86, 2 and 3 MHz, and four output pulse modes; continuous wave (100 % duty cycle), 1:2 (50 % duty cycle), 1:5 (20 % duty cycle) and 1:10 (10 % duty cycle). The correlation coefficients and measuring uncertainty were then calculated. The results show that the developed system is currently able to determine the ultrasonic output power in the power range from 100 mW to approximately 12 W.