SHOU Wen-de, JIA Long-yang, JI Xiang, HU Bing

A new radiation force balance for acoustic power measurement of ultrasonic phased array

SHOU Wen-de1,3, JIA Long-yang1,2, JI Xiang3, HU Bing1,2

(1.Shanghai Institute of Ultrasound in Medicine, Shanghai 200233, China; 2.Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai 200233, China; 3.Shanghai Jiao Tong University, Shanghai 200030, China)

The ultrasonic phased array has been used for research and application of focused ultrasonic treatment for at least 20 years. However, due to the complexity of its working modes, there is still lack of simple convenient and effective method to measure the acoustic power transmitted by the phased array. In this paper,a new radiation force balance (RFB) method based on a absorbing target of convex spherical segment is proposed for measuring the output acoustic power of the array. The measurement principle, system and procedures of this method are described, and the ratio=/for various combinations of array elements is derived, where c is speed of sound in water,is the output acoustic power and F is the axial radiation force acting on the target,which provides a basis of designing and applying the measurement system.

radiation force balance (RFB); phased array; spherical segment; absorbing target

0 Introduction

It is known that the radiation force balance (RFB) method is the preferred method for acoustic power measurement[1-2]. However, due to changeable operating setting and acoustic beam orientation, the existing RFB is not suitable for multi-mode acoustic power measurements of the ultrasonic phased array. In this paper, a new RFB method based on a convex absorbing target is proposed to achieve this measurement.

1 Principle

Ultrasonic phased array incorporates dozens or even hundreds of small planar piston transducer elements, which are generally installed on the inner surface of a large spherical segment.During the operation, the phases, sometimes with the amplitudes together, of the driving voltages applied to array elements are controlled to obtain various required acoustic focusing characteristics (including multi-beam) of the array, for which, the performances of all array elements are required to be independent of each other theoretically. Therefore, in the design of the ultrasonic phased array, some technical measures in the acoustic structure and manufacturing process need to be taken to minimize the interaction between elements.

Thus, the transmitting acoustic power of theth transducer is

Fig.1 Schematic diagram of ultrasonic phased array and convex spherical absorbing target

Moreover, when theelements simultaneously transmit acoustic power, the total axial radiation forceacting on the absorbing target is equal to

Thus, the total acoustic power transmitted by the phased array with the combination ofelements can be determined from the measured total axial radiation force as follows:

Fig.2 is a schematic diagram of the measurement system. The geometric relationship between a phased array and a convex absorbing target remains as shown in Fig.1. The absorbing target is suspended by three nylon wires, and the upper ends of the nylon wires are evenly distributed on a ring-shaped frame above the tank. In order to increase the inertial mass of the main balance system, restrain the transient response of the balance and improve the stability and repeatability of the force reading, the counterweight 1 is added in the degassed water under the absorbing target. On the outer circumference of the ring-shaped frame, a long handle located at the same plane of the frame is installed, and the extension line of the central axis of the handle passes through the center of the ring-shaped frame. The long handle and a supporting wedge (as a fulcrum) form a lever system.On the right-hand end of the lever there is a counterweight 2 to balance the sinking force of the target plus the counterweight 1. A counterweight 3 is suspended at a proper position on the right of the fulcrum, and itsweight is adjusted to make its downward force close to the middle value of the measurement range of the electronic balance.

3 Conclusion and discussion

[1] IEC 60150 Ed.1: 1963 Testing and calibration of ultrasonic therapeutic equipment.

[2] IEC 61161: 2013 Ultrasonics-power measurement-radiation force balances and performance requirements.

輻射力天平法測(cè)量相控陣超聲換能器的聲功率

壽文德1,3，賈龍洋1,2，吉祥3，胡兵1,2

(1. 上海超聲醫(yī)學(xué)研究所，上海 200233；2. 上海交通大學(xué)附屬第六人民醫(yī)院，上海 200233；3. 上海交通大學(xué)生物醫(yī)學(xué)工程學(xué)院，上海 200030)

輻射力天平；相控陣；球缺；吸收靶

TN911

A

1000-3630(2019)-06-0629-03

10.16300/j.cnki.1000-3630.2019.06.005

2019-11-06;

2019-11-25

Fund: National Natural Science Foundation of China(81271597)

Author: SHOU Wende (1941－), male, was born in Zhuji, Zhejiang province, China. He research fields is is ultrasonic field measurement and transducer calibration.

SHOU Wende, E-mail: wdshou@163.com