Measuring and testing – Vibration – By mechanical waves
Utility Patent
1998-10-23
2001-01-02
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
Utility Patent
active
06167758
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to a method and an apparatus for generating ultrasonic pulses with a precisely specified waveform shape.
2. Description of Prior Art
Ultrasound imaging devices are widely used in medicine and industry for non-destructive
on-invasive study of interior of objects.
These devices produce a beam of ultrasonic energy, which travels through the object under investigation. An echosignal is formed by reflections resulting from inhomohenities or interfaces within the object.
Lateral resolution of a pulsed-echo ultrasound imaging system depends on the ultrasonic beam width. Axial resolution depends on the ultrasonic pulse duration.
The lateral resolution is improved by means of static or dynamic focusing using acoustic lenses or electronically focused transducer arrays. The width of the focused ultrasonic beam is proportional to its wavelength.
The axial resolution is improved by using high frequency ultrasound or making the ultrasonic pulses shorter. However the high frequency ultrasound limits depth of penetration due to attenuation, increasing as some power of the pulse frequency.
Normally a transducer is excited by a sharp voltage spike. In this case the length of the transducer impulse response function limits the duration of the ultrasonic pulse. Mechanical damping of the transducer allows reducing the impulse response function length by the cost of sacrificing the transducer sensitivity. This is often unacceptable since in most cases the same transducer is used for transmission and reception of ultrasonic signals.
Thus in order to overcome this problem different excitation voltage waveform must be applied to the transducer. The shape of the excitation voltage waveform ultimately determines the shape and duration of the transmitted ultrasonic pulse.
Attempts to control the transmitted ultrasonic pulse waveform can be traced in the following patents: in U.S. Pat. No. 4,222,274 to Steven A. Johnson (1978) an apparatus is proposed capable of transmitting ultrasonic beams of two predetermined shapes; in U.S. Pat. No. 4,520,670 to Göran Salomonsson et. al. (1982) a method and an apparatus is proposed for generating short ultrasonic pulses by means of an excitation signal shaped as a weighted least squares filter; a complex beamformer is described in U.S. Pat. No. 5,675,554 to Christopher R. Cole et al. (1996) which is capable of producing focused ultrasonic beams having a specified carrier frequency and envelope.
Nevertheless it is still desirable to be able to produce ultrasonic pulses having a variety of precisely specified waveforms including those which can not be specified in terms of carrier frequency and envelope.
The specified waveform will determine the frequency spectrum and the wavelength of the transmitted ultrasonic pulse thus enabling the use of the same transducer for different applications such as near field and far field examinations. The precise shape of the transmitted ultrasonic pulse can be selected to facilitate image reconstruction techniques such as deconvolution or wavelet transform resulting in the improved lateral and axial resolution and superior image quality.
OBJECTS AND ADVANTAGES
The key advantage of the present invention is the means of precise control over the transmitted ultrasonic pulse waveform and frequency.
Another advantage of this invention is the ability to transmit ultrasonic pulses, which can not be specified in terms of carrier frequency and envelope.
Yet another advantage of this invention is the simplicity of the method and the apparatus implementation.
REFERENCES:
patent: 4080660 (1978-03-01), Constant
patent: 4164740 (1979-08-01), Constant
patent: 4222274 (1980-09-01), Johnson
patent: 4228517 (1980-10-01), Constant
patent: 4243935 (1981-01-01), McCool et al.
patent: 4387597 (1983-06-01), Brandestini
patent: 4520670 (1985-06-01), Salomousson
patent: 5675554 (1997-10-01), Cole
Miller Rose M.
Williams Hezron
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