Multi-Channel Real-Time Phase Modulation for EMI Reduction in an Ultrasound Device

A method of reducing electromagnetic interference arising from a set of ultrasound transducers that are part of an array of ultrasound transducers in a thermal therapy apparatus, the set comprising N transducers, each transducer in the set corresponding to an active channel and being electrically driven with a driving signal at an amplitude, a frequency and a phase angle, the frequencies of the driving signals being the same for all transducers in the set, the method comprising a determination and setting of the phase angles Θ1, Θ2, . . . , ΘN of each driving signal, the determination and setting of such phase angles comprising:

• determining the amplitudes A1, A2, . . . , AN of the respective driving signals of each transducer, each amplitude being a nonnegative real number;
• determining whether one of the amplitudes Am is greater than the sum of all the amplitudes other than Am, A1+A2+ . . . Am−1+Am+1+ . . . +AN;
• if Am is greater than or equal to the sum of such other amplitudes, setting Θm=180° and setting Θi=0° for all i not equal to m;
• if Am is less than the sum of such other amplitudes:
• determining a vector P, such vector comprising N elements, each such element being either 1 or −1, such that the scalar product of P and the vector [A1, A2, . . . , AN] comprising all of the amplitudes is nonnegative and is not greater in magnitude than the magnitude of the scalar product of any other possible vector comprising N elements, each such element being either 1 or −1, and the vector [A1, A2, . . . , AN] comprising all of the amplitudes;
• defining a vector Ō comprising N elements, such that each element Oi is equal to the product of Pi and Ai, for i=1, 2, . . . , N;
• determining a first positive element of Ō, Oa, that is not less than any other element of Ō;
• determining a second positive element of Ō, Ob, that is not less than any other element of Ō save Oa;
• defining a quantity γ as the absolute value of the sum of all elements of Ō save Oa and Ob;
• and
• setting Θa and Θb as:
• Θ
• a
• =
• -
• cos
• -
• 1
• ⁢
• O
• a
• 2
• +
• γ
• 2
• -
• O
• b
• 2
• 2
• ⁢
• O
• a
• ⁢
• γ
• Θ
• b
• =
• -
• cos
• -
• 1
• ⁢
• O
• b
• 2
• +
• γ
• 2
• -
• O
• a
• 2
• 2
• ⁢
• O
• b
• ⁢
• γ
• and for all Θi, other than Θa and Θb, setting Θi=cos−1 Oi.