JPH0348789A - Cw doppler device - Google Patents

Abstract

PURPOSE:To reduce CW-like interference disturbance that the Doppler device receives as much as possible by providing a wobbler oscillator which generates a signal varying in voltage periodically at a constant variation rate. CONSTITUTION:The wobbler oscillator 1 generates a saw-tooth wave. An FM oscillator 2 is modulated with the output of the oscillator 1 to generate an FM wave-which increases linearly in frequency. The output is amplified 3 and sent from an ultrasonic probe 4. An echo signal reflected by a reflection body is received by the probe 4, amplifed 5, and inputted to a beat signal generator 6. The signal from the FM oscillator 2 is also inputted to the generator 6 to generate beats of the difference between the two signals. Then a band-pass filter(BPF) 7 removes an unnecessary high frequency signal and a low frequency signal from the beat signal. Then the output is amplified by a low frequency amplifier 8 and converted by an AD converter 9 into a digital signal, which is processed by the Fourier transform of an FFT 10. Consequently, the CW-like interference disturbance that the device receives can be reduced as much as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a CW Doppler apparatus for various uses, and more particularly to a CW Doppler apparatus in which interference caused by CW from the outside is made less noticeable.

(Prior art) Medical ultrasonic diagnostic equipment, speed measurement devices for vehicles, etc. transmit ultrasonic CW signals from a transducer and receive Doppler-shifted echoes from moving objects. Information such as the direction in which the stream is flowing and the speed in the line of sight direction is obtained.

(Problem to be Solved by the Invention) By the way, since the transmitted signal in this case is CW, it is devised to prevent it from being input to the receiving circuit and interfering with reception. From the perspective of how to prevent damage, no special measures have been taken so far other than strict shielding. It has been difficult to implement a strict shield to completely eliminate this interference. In particular, it has been difficult to implement this method for ultra-small devices with telemeters, etc., and for inexpensive devices that can be carried by individuals.

In addition, conventional devices do not use ultrasonic CW that enters through the sound field.
It is completely powerless to interfere.

The present invention has been made in view of the above points, and its purpose is to realize a CW Doppler device that can minimize CW interference received by the CW Doppler device.

(Means for Solving the Problems) In order to solve the above problems, in the present invention, the carrier frequency of the system is wobbled. This wobbling is almost harmless to the observation and analysis of the Doppler shift component of the observation target, and is caused by the beat formed by the fixed reflections (clutter) returning from the surrounding sensitive area including the observation target and the carrier of the system. is carried out to the extent that it can be effectively removed by a clutter removal filter (Doppler filter). The purpose of this carrier wobbling is that the beats formed by constant frequency (i.e., CW) external interference and the carrier are dispersed over the frequency spectrum, so that the beats that would otherwise have occurred are The object of this invention is to make the emission line spectral interference inconspicuous in a dispersed form in the frequency analysis results of Doppler signals.

The most preferred embodiment of the present invention for carrying out the above method includes a wobbler oscillator that generates a signal whose voltage periodically changes at a constant rate of change, and an FM signal modulated by the output signal of the wobbler oscillator. The FM oscillator is characterized by comprising an FM oscillator that generates an FM oscillator, and a beat signal generator that generates a beat signal having a frequency difference between a received signal and an output signal of the FM oscillator.

(Function) Since the carrier of the system is wobbling, external CW interference no longer becomes a constant frequency in the beat signal generator, and is dispersed and becomes unnoticeable in the frequency analysis results, so it is effectively an interference. It will no longer be.

(Embodiment f!'1) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention using ultrasound as an example. In the figure, 1 is a wobbler oscillator that generates a signal whose voltage changes at a constant rate of change, such as a sawtooth wave, and 2 is an FM wave whose frequency changes in proportion to the voltage waveform of the wobbler oscillator. It is an FM oscillator. The output signal of the FM oscillator 2 is power-amplified by the transmission amplifier 3, converted into an ultrasound signal from the transmission oscillator of the ultrasound probe 4, and transmitted. The ultrasonic probe 4 is composed of a transmitting transducer exclusively used for transmission and a receiving transducer exclusively used for receiving. The transmitted signal is reflected from the reflectors A, B, C, etc., returns to the ultrasound probe 4, and is converted into an electrical signal by the receiving transducer.

5 is a reception amplifier that amplifies the reception signal from the ultrasound probe 4. 6 is a beat signal generator (demodulator) that receives the received signal from the receiving amplifier 5 and the signal from the FM oscillator 2 and generates a beat signal that is the difference between the two signals; 7 is an unnecessary high-frequency signal among the beat signals; and a bandpass filter (hereinafter referred to as BPF) that removes low-frequency signals. Thereafter, this output is amplified by a low frequency amplifier 8, converted to a digital signal by an AD converter 9, and subjected to Fourier transform and signal processing by FFT10.

The circuit after this low frequency amplifier 8 is similar to a normal Doppler device.

Next, the operation of the embodiment configured as described above will be explained. The wobbler oscillator 1 generates, for example, a sawtooth wave. This period is determined based on the assumption of the distance to the farthest target of the device. If the period is T and the distance to the farthest target is D, the period is T -2D/c where C: The sonic FM oscillator 2 is an FM whose frequency increases linearly by being modulated by the output of the wobbler oscillator 1. generate waves. This output is amplified by the transmission amplifier 3 and transmitted from the transmission transducer of the ultrasound probe 4. The echo signal reflected from the reflector is received by the receiving transducer of the ultrasonic probe 4, amplified by the receiving amplifier 5, and input to the beat signal generator 6. The beat signal generator 6 also receives the signal from the FM oscillator 2, and generates a beat that is the difference between the two signals. This beat varies depending on the distance to the reflector, and the beat due to the echo signal from reflector C at distance d has a higher frequency than the beat due to the echo signal from reflector B at distance d2. The beat due to the signal has a higher frequency than the beat due to the echo signal from reflector A at distance d. Therefore, it is only necessary that the clutter caused by the reflector near the target C at the farthest distance can be distinguished from the Doppler shift component that is the object of measurement.

This will be explained using numerical values. Set the frequency increase rate of the sawtooth wave to 0. 51 (z/μS). If the return time from the farthest clutter is 300 μs (depth 22.5 cm assuming sound speed of 1500 m/s), the FM signal will have a difference of about 150 Hz during this return time. occurs, thus producing a 150 Hz beat for clutter. However,
This frequency is cut off by BPF7. On the other hand, echoes with a Doppler shift from blood flow, etc., which is the original target for observation, have a Doppler shift much higher than this frequency, so they pass unhindered by BPF7, which removes clutter up to 1.50 Hz. . In this way, the target Doppler-shifted echo signal reaches the low frequency amplifier 8, where it is amplified, digitized by the AD converter 9, Fourier transformed by FFT 1.0, and then subjected to normal signal processing. be done.

By the way, considering the case where there is CW interference from the outside,
The rate of rise of the above sawtooth wave is 0.5Hz/μs or 500
KHz/s, and the above-mentioned CW interference component remains as it is as a total energy, but in terms of frequency, if the analysis data collection time width is set as a unit of 5 to 10 m5, as a result of wobbling oscillation within that time, 2. 5KHz~5
A distribution on the frequency axis occurs over a width of KHz. In other words, the interference signal, which was originally CW, is chirped and appears in a dispersed form at the stage of the Doppler signal or analysis output of this system. Therefore, when the ultrasonic frequency is changed by wobbling, even if a CW interference wave comes in, the interference wave is not concentrated on the observed Doppler shift frequency axis, but is generated in a dispersed form, and is scattered and becomes less noticeable. Specifically, the noise floor only appears to be raised slightly, and it no longer interferes with diagnosis and measurement. This will be explained with reference to FIG. (A) is a diagram showing the spectrum 11 of CW interference waves in a conventional Doppler device,
(b) is a diagram showing a spectrum 12 of dispersed CW interference waves in the device of the embodiment.

In the figure, 13 is a Doppler shift signal. The total energy amount of the CW interference wave spectrum 11 and the dispersed CW interference wave 12 is equal, but the dispersed CW interference wave 1
2 shows that the amplitude is small and almost unnoticeable. 14 is a slightly raised noise floor.

Note that the present invention is not limited to the above embodiments.

The waveform of the wobbler oscillator is a linearly varying sawtooth wave, which is the easiest and most reliable method, but the waveform of the subsequent FFTl
If you are doing work such as periodically cutting out data frames and performing FFT processing on them, it is better to repeat rising FM (up chirp) and falling FM (down chirp) for each frame. FIG. 3 shows the waveform in that case. The waveform shown in the figure is a wobbling FM waveform of a triangular waveform in which rising FM and falling FM alternately repeat.

23 is an inflection point from a rise to a fall or from a fall to a rise in the wobbling FM waveform 21, and 22 is a data analysis section. If there is such an inflection point, the Doppler signal will be unpleasant to listen to, so it may be better to modulate it with a sine wave as shown in FIG. 4. In the figure, 22 is a data analysis section, and 25 is a wolving FM waveform with a sine wave.

Such a method is applicable not only to CW Doppler but also to pulsed Doppler.

(Effects of the Invention) As described in detail above, according to the present invention, CW interference can be reduced and rendered harmless by a simple method, and the practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a CW
Figures illustrating the effects of interference, (a) is a diagram showing the case using the conventional device, (b) is a diagram showing the case according to this embodiment, Fig. 3 is a diagram showing the case when different wobbling waveforms are used, and Fig. 4 The figure shows a case where a different wobbling waveform is used. 1... Wobbling oscillator 2... FM oscillator 4... Ultrasonic probe 6... Beat signal generator 7... BPF

Claims (1)

[Claims] A wobbler oscillator (1) that generates a signal whose voltage periodically changes at a constant rate of change, and an F modulated by the output signal of the wobbler oscillator (1).
The FM oscillator (2) outputs an M signal, and the beat signal generator (6) generates a beat signal having a frequency difference between the received signal and the output signal of the FM oscillator (2). Characteristics of CW Doppler equipment.