A METHOD FOR COMPENSATING A HARMONIC COMPONENT OF AN EMITTED ULTRASOUND WAVE.

A method for compensating a harmonic component of an emitted ultrasound wave .

FIELD OF THE INVENTION The invention concerns a method for compensating a harmonic component of an emitted ultrasound wave from an electrostatic ultrasonic transducer.

BACKGROUND OF THE INVENTION The invention particularly concerns a method for compensating a harmonic component of an emitted ultrasound wave, comprising an excitation step wherein an excitation signal is generated, the excitation signal comprising at least a first signal having a first harmonic component at a first fundamental frequency and being applied to an ultrasound transducer for transmitting the emitted ultrasound wave in a volume towards a target object, and said emitted ultrasound wave comprises at least the harmonic component at a harmonic frequency higher than said first fundamental frequency and being a natural number multiple of said first fundamental frequency, said excitation signal further comprises a second signal added to said first signal, comprising parameters at least one of which is tuned so that the harmonic component at the harmonic frequency of the emitted ultrasound wave has a minimal amplitude, said parameters comprising at least a predetermined frequency, a predetermined amplitude, a predetermined phase with respect to said first signal, and a predetermined bandwidth. The document US-6 461 299 discloses a method for imaging reflected ultrasound echo signals from a target object, wherein the predetermined frequency is equal to said harmonic frequency. Unfortunately, using this method, the amplitude of the first harmonic component of the first signal is modified. OBJECTS AND SUMMARY OF THE INVENTION

The following invention tends to offer an alternative to the prior art method, without having the drawbacks of the prior method. For this purpose, the method is characterized in that said predetermined frequency is different than said harmonic frequency.

Thanks to this predetermined frequency inside the second signal different than said harmonic frequency, the first harmonic component at the first fundamental frequency of the first signal is not influenced by said second signal .

In various embodiments of the method, one may further use one and / or other of the following dispositions:

- the predetermined frequency is higher than said harmonic frequency;

- the emitted ultrasound wave transmitted by the ultrasound transducer from the second signal comprises a low harmonic component at a frequency equal to said predetermined frequency minus said first fundamental frequency, this low harmonic component being produced by the non linearity of the ultrasound transducer, and

- said frequency being substantially equal to said harmonic frequency to minimise the amplitude of said harmonic component; the harmonic frequency is twice the first fundamental frequency;

- the ultrasound transducer which is used in the excitation step is a capacitive micromachined ultrasonic transducer;

- the predetermined amplitude minimising the amplitude of the harmonic component is searched into an interval of plus and minus 10 percent of the amplitude of the second signal producing a low harmonic component equal to the amplitude of the harmonic component to be minimised without the second signal;

- the predetermined phase minimising the amplitude of the harmonic component is searched into an interval of - 180 degrees to +180 degrees relative to said first signal; - the predetermined amplitude and the predetermined phase are determined by using a frequency response function of the ultrasound transducer.

Another object of the invention is a device comprising an ultrasound transducer for transmitting an emitted ultrasound wave in a volume towards a target object and for receiving a received ultrasound wave reflected by the target object from said emitted ultrasound wave. The device is designed for implementing a method as defined above and is either producing images of the volume or transmitting the emitted ultrasound wave to modify the target object.