RU2814447C1 - Ultrasonic radiation power meter - Google Patents

Abstract

FIELD: measurement; acoustics.

SUBSTANCE: invention relates to technical acoustics. Ultrasonic radiation power meter is made in the form of a single measurement system consisting of a measuring tank installed on a mass meter, which is pressed into a metal housing. Measuring tank is made of transparent organic glass; there are holes in the housing of the mass meter: one threaded hole – for installation of the transducer holder stand, two others – for installation of the ultrasonic radiation force transmission device, made in the form of two posts of the target rocker, on which there is a target rocker with an absorbing target made of ultrasound-absorbing foamed polyurethane and having a surface consisting of pyramidal projections on one side.

EFFECT: higher accuracy of measurements.

6 cl, 2 dwg

Description

The invention relates to technical acoustics and can be used to measure the power of ultrasonic radiation incident on an absorbing target in the form of a collimated, focused or slightly divergent beam of ultrasonic energy in water, generated by emitters (sensors) of medical ultrasonic equipment.

There are known instruments for measuring the power of ultrasound (US) in water (ultrasonic wattmeters, ultrasonic radiometers, ultrasonic power meters in water, etc.), the basis of which is the method of gravitational balancing of the radiation effect of an ultrasonic wave falling vertically from above or below onto one in the water target (reflective or absorbing type). The radiation effect (force F) of an ultrasonic wave is related to its power P by a simple relationship:

for an ideal absorbing target

or for an ideal reflective target

where c is the speed of sound in the propagation medium (in water);

- the angle between the direction of propagation of the ultrasonic wave and the normal to the reflecting surface.

To record radiation exposure (force F), most modern meters use electronic scales.

The International Electrotechnical Commission (IEC) standard IEC 61161:2013 [1] and the national standard GOST R IEC 61161-2019 [2] harmonized with it in Appendix F provide 9 options for constructing ultrasonic radiation power meters. The invention in question can be attributed to arrangement B with the absorbing target of FIG. 1.

The layout given in GOST R IEC 61161-2019 has the following disadvantages:

1) An opaque water tank makes it much more difficult to control the measurement area. During installation of the transducer and during its operation, air bubbles may appear on its active surface, which have a significant impact on the result of ultrasonic power measurements.

The opaque water tank significantly complicates the alignment of the emitter over the target.

The target is attached to the beam, which transmits force to the scales, using flexible fasteners - fishing line or thin wire. This method of fastening leads to problems during operation. During measurements, a target suspended by 2 support points may tip over as a result of exposure to an uneven acoustic field. In addition, the absorbing target may have positive buoyancy, which will cause it to float to the surface in the measuring tank.

A transducer holder that is not attached to the meter requires more space at the meter's operating site and must have its own stable support, which leads to increased manufacturing complexity.

The technical result obtained from the implementation of the invention is the possibility of constructing a power meter with better measurement accuracy, better ergonomics during operation and lower cost. The appearance of the meter is shown in figure 2, where 1 is a measuring tank, 2 is an absorbing target, 3 is a target rocker arm, 4 is a mass meter (electronic scales), 5 is a metal case, 6 is a target rocker arm strut.

Thus, in the meter under consideration, the measuring tank 1 is made of transparent organic glass, which allows visual inspection of the surface of the emitter and the target in the underwater space for the presence of air bubbles, which allows them to be removed in a timely manner, increasing the reliability of measurements. In [1] [2] and [3] it is said that released air bubbles on the surface of the emitter or target lead to a significant change in the results of measuring ultrasonic power, and their timely removal reduces the measurement error. The use of transparent plexiglass as a material for the measuring tank makes it possible to reduce power measurement errors that arise when the side lobes of the transducer are reflected from the walls of the tank. Plexiglas has a significantly higher absorption coefficient of ultrasound than, for example, silicate glass, due to its low density and lower hardness. Also, the transparent tank greatly simplifies the alignment of the ultrasonic transducer strictly above the target and makes it possible to ensure their alignment, which increases the reliability of measurements.

If the transducer is round (which is typical for most ultrasonic transducers), then the ideal installation is above a round target, when the axes of the transducer and the target coincide. The transverse displacement of the transducer relative to the absorbing target (i.e., the axes remain parallel), the radius of which is greater than the radius of the transducer so much that no significant part of the ultrasonic beam extends beyond the boundaries of the target, does not affect the results of radiation force measurements. The tilt of the transducer relative to the target reduces the projection of the radiation force in proportion to the cosine of the angle α between the axes, which for actually achievable α≤5° with visual inspection reduces the radiation force by only 0.4%.

The absorbing target 2 is mounted on a stainless steel rocker arm 3, which prevents the target from tipping over when an uneven acoustic flow falls on it and makes the target's buoyancy indicator unimportant. The rigid target beam ensures a more accurate transfer of the additional radiation force of ultrasound to the sensitive element of the mass meter due to the absence of deformation during measurements. If the connection of the target with the scales is carried out using a suspension on a flexible fishing line or wire, then it is necessary to ensure negative buoyancy of the target, otherwise the power measurements will be incorrect. Even a target with negative buoyancy can float up during the measurement process, since ultrasonic exposure leads to its heating and thermal expansion. The rocker arm in the meter under consideration is made in the form of a rigid rod, which ensures the transfer of the additional radiation force of the ultrasonic beam to the scale pan. In this case, the absorbing target is glued to the rocker arm, which eliminates the possibility of the target overturning or floating up. The absorbing target of the meter, made of chemically resistant polyurethane foam, is made, on one side, in the form of a surface consisting of pyramidal protrusions 4-5 mm high with an angle of inclination between the side surfaces of the pyramids of 60° ± 2°. This shape of the target surface significantly reduces the level of ultrasonic power reflected from it, improving its absorption properties.

The mass meter 4 is pressed into the metal body 5 of the meter, which allows for reliable fastening of the mass meter and the body without the use of fasteners such as bolts or screws. Such fastening allows not to violate the warranty conditions of the manufacturer of the mass meter during the manufacture of the power meter and leads to a reduction in the cost of its maintenance in general. A mass meter with such attachment to the body can be replaced with a mass meter with a larger or smaller LEL, if necessary, without compromising the integrity of the scales themselves.

The structural elements of the meter that transmit the additional radiation force of ultrasonic radiation to the sensitive element of the mass meter are made in the form of two pillars of the target rocker arm 6. The pillars are located opposite each other, which ensures uniform distribution of the force transmitted to the sensitive element of the mass meter. This design of the mechanism transmitting the radiation force of ultrasound allows us to reduce the errors in power measurements that arise due to lateral pressure on the rod of the sensitive element of the mass meter. The stands are made of durable and lightweight material (for example, aluminum), which makes it possible to reduce the LEL of the scales used, which also leads to a reduction in the cost of the entire meter, since scales with a large LEL are more expensive. Also, the high strength of the racks provides a more accurate result of power measurements, due to less deformation (deflection) during measurements.

The use of the proposed technical solution increases the reliability of ultrasonic power measurements, the ergonomics of ultrasonic radiation power meters built according to layout B with an absorbing target in accordance with GOST R IEC 61161-2019, and reduces the cost of servicing such meters.

Literature

IEC 61161:2013 Ultrasonics - Power measurements - Radiation force balance and performance requirements

GOST R IEC 61161-2019 State measurement system. Ultrasound power in liquids. General requirements for performing measurements using the radiation force balancing method

IEC 62555-2013 Ultrasonics - Power measurement - High intensity therapeutic ultrasound (HITU) transducers and systems.

Claims (6)

1. Ultrasonic radiation power meter, made in the form of a single measurement system, consisting of a measuring tank mounted on a mass meter, pressed into a metal case, characterized in that the measuring tank is made of transparent organic glass; there are holes in the body of the mass meter: one threaded hole - for installing the transducer holder stand, the other two - for installing the ultrasonic radiation force transmission device, made in the form of two target rocker arms, on which the target rocker arm with an absorbing target is fixed, made of ultrasound-absorbing polyurethane foam and having on one side a surface consisting from pyramidal projections. 2. Ultrasonic radiation power meter according to claim 1, characterized in that the absorbing target is made on one side in the form of a surface consisting of pyramidal protrusions 4-5 mm high with an inclination angle between the side surfaces of the pyramids of 60±2°. 3. The ultrasonic radiation power meter according to claim 1, characterized in that the mass meter is pressed into a metal case and can be removed from it without damage. 4. The ultrasonic radiation power meter according to claim 1, characterized in that the mass meter can be replaced without compromising its integrity with a mass meter with a larger or smaller maximum weighing limit, if necessary. 5. Ultrasonic radiation power meter according to claim 1, characterized in that the target rocker arms are made of aluminum. 6. Ultrasonic radiation power meter according to claim 1, characterized in that the target beam is made of stainless steel.