Low-noise ultrasonic wave focusing apparatus
The present invention reduces noise generated by a phase change in an ultrasonic wave focusing apparatus that changes an ultrasonic wave focal point within a space by changing the phase of vibration of a plurality of ultrasonic transducers. When inputted position coordinates within a three-dimensional space are changed, the ultrasonic wave focusing apparatus calculates a target time lag Tnew that allows ultrasonic waves outputted from the ultrasonic transducers to form a focal point at the changed position coordinates X1, Y1, Z1. The ultrasonic wave focusing apparatus then examines the ultrasonic transducers to locate a particular ultrasonic transducer that outputs an ultrasonic wave whose time lag Ttmp differs from the target time lag Tnew, and changes the phase of the outputted ultrasonic wave to a target phase in multiple steps (steps 140 and 150 ).
1. An ultrasonic wave focusing apparatus comprising:
a transducer array having a plurality of ultrasonic transducers; and
a control device to which position coordinates within a space are inputted, the control device causing the ultrasonic transducers to generate ultrasonic waves having phases based on the position coordinates in such a manner that the ultrasonic waves of the ultrasonic transducers form a focal point at the position coordinates,
wherein, when the inputted position coordinates within the space are changed discretely in a trajectory from a first position to a second position that is adjacent to the first position, the control device calculates a target value for each target phase necessary for the ultrasonic waves outputted from the ultrasonic transducers to form a focal point at the second position, locates an ultrasonic transducer whose current value for a current phase of an outputted ultrasonic wave is different from the target value, and changes a phase of an ultrasonic wave outputted from the ultrasonic transducer to its target phase in multiple steps.
2. The ultrasonic wave focusing apparatus according to claim 1 , wherein, when the inputted position coordinates within the space are changed, the control device calculates a target value for each target phase necessary for the ultrasonic waves outputted from the ultrasonic transducers to form a focal point at the changed position coordinates, locates an ultrasonic transducer whose current value for a current phase of an outputted ultrasonic wave is different from the target value, and changes a phase of an ultrasonic wave outputted from the located ultrasonic transducer to its target phase in multiple steps by one step at intervals of multiple cycles of ultrasonic vibration outputted from the located ultrasonic transducer.
3. The ultrasonic wave focusing apparatus according to claim 2 , wherein the multiple cycles are not more than 50 μs in length.
4. The ultrasonic wave focusing apparatus according to claim 1 , wherein, when the inputted position coordinates within the space are changed, the control device locates an ultrasonic transducer whose current value is different from the target value and changes a phase of an ultrasonic wave outputted from the located ultrasonic transducer to its target phase in multiple steps in either a phase advance mode or a phase retard mode based on whether the phase advance mode or the phase retard mode provides the target phase through a smaller number of steps.
5. The ultrasonic wave focusing apparatus according to claim 1 , wherein, when the inputted position coordinates within the space are changed from an initial position to a target position, the control device locates an ultrasonic transducer whose current value is different from the target value and changes the phase of an ultrasonic wave outputted from the located ultrasonic transducer to its target phase in multiple steps or continuously in order to gradually decrease a sound pressure at the initial position while fixing the focal point at the initial position, and at the same time, gradually increase a sound pressure at the target position while fixing the new focal point at the target position.
6. The ultrasonic wave focusing apparatus according to claim 1 , wherein, when the inputted position coordinates within the space are changed, the control device locates an ultrasonic transducer whose current value is different from the target value and changes a phase of an ultrasonic wave outputted from the located ultrasonic transducer to the target phase in multiple steps or continuously while ensuring that the average amount of phase change per cycle of the outputted ultrasonic wave is not larger than π/4 [rad].
7. The ultrasonic wave focusing apparatus according to claim 1 , wherein, when the inputted position coordinates within the space are changed, the control device locates an ultrasonic transducer whose current value is different from the target value and changes a phase of an ultrasonic wave outputted from the located ultrasonic wave outputted from the located ultrasonic transducer to consistently become closer to the target phase.
8. The ultrasonic wave focusing apparatus according to claim 1 , wherein
the control device changes the phase of the ultrasonic wave outputted from the located ultrasonic transducer to its target phase in multiple steps by one step at intervals of multiple cycles of ultrasonic vibration outputted from the located ultrasonic transducer, and
the control device changes the phase of the ultrasonic wave outputted from the located ultrasonic transducer to its target phase in multiple steps in order to gradually decrease a sound pressure at the initial position while fixing the focal point at the initial position, and at the same time, gradually increase a sound pressure at the target position while fixing the new focal point at the target position.
9. The ultrasonic wave focusing apparatus according to claim 8 , wherein the multiple cycles are not more than 50 μs in length.
10. The ultrasonic wave focusing apparatus according to claim 9 , wherein the control device changes the phase of the ultrasonic wave outputted from the located ultrasonic transducer to its target phase in multiple steps in either a phase advance mode or a phase retard mode based on whether the phase advance mode or the phase retard mode provides the target phase through a smaller number of steps.