JPH04344459A - Acoustic receiving unit - Google Patents

Abstract

PURPOSE:To enhance the S/N of received acoustic signals even if there is noise having regularity and/or noise which is difficult to separate using gates. CONSTITUTION:An acoustic receiving unit is comprised of a receiving element 1 and a receiver 2 for receiving acoustic signals, switches 4-6 for switching signal lines, delay circuits 7-9 for delaying received signals, memories 3, 10-12 for storing the received signals, an adding circuit 14 for adding (m+1) signals together, an addition time setting circuit 13 for setting the number m of times of the addition, and an outputter 15 for outputting the added signals. First, the receiver 2 is connected to each of the delay circuits 7-9 by the switches 4-6. The acoustic signals received by the receiving element 1 are stored in the memory 3 and the signals delayed by each delay circuit are stored in the memories 10-12. The (m+1) signals stored in the memories are added together by the adding circuit 14 and the result of the addition is output to the outputter 15.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a device for nondestructively inspecting structures, etc., and a device for detecting the position of a sound source, etc. and obstacles using sound, and in particular, the present invention relates to a device for nondestructively inspecting structures, etc., using sound, and a device for detecting the position of a sound source, etc., and an obstacle. The present invention relates to a device suitable for improving.

0002

2. Description of the Related Art There are two main conventional methods for improving the signal-to-noise ratio.

[0003] For random noise with irregular generation time and generation intensity, a sensor that receives sound (hereinafter referred to as a receiver) is fixed and receives a signal m times, and the m
Add signals. In this case, the target signal S is always received at the same time on the time axis, so it is multiplied by m. However, since the random noise N is not always received at the same time, even if it is added m times, it will only be multiplied by √m. Therefore, the S/N ratio becomes m/√m=√m times (Automatic Processing of Analysis Information, Nikkan Kogyo Shimbun, 1970). Another method is to separate signals that are received at the same time on the time axis but are not of interest, unlike random noise. Specifically, the signals are separated by providing a gate on the time axis into which only the target signal enters and extracting only the signal inside the gate. Thereby, the SN ratio can be improved.

0004

In reality, there are regular noises that are not random noises, and signals that are difficult to separate from a target signal using a gate. There are also signals that are a combination of these. If it is difficult to separate signals using a gate, it may be difficult to separate them in the first place because the signals overlap or because the signals move on the time axis (that is, the distance between the receiver and the signal source changes). However, it is conceivable that the desired signal may come out of the gate, or that a signal other than the desired signal may enter the gate. In such a case, even if the conventional technology is applied, S
It is difficult to improve the N ratio.

An object of the present invention is to provide a means and apparatus for improving the SN ratio even in the presence of such noise.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the acoustic signals received with the receiver fixed are delayed or advanced by arbitrary time intervals on the time axis and then added together. As a result, the strength of the non-target signal N can be reduced,
As a result, the SN ratio can be improved.

[0007]

[Operation] Since the distance attenuation rate of acoustic intensity differs depending on the frequency, the frequency distribution of the received acoustic signal varies depending on the distance between the receiver and the acoustic source. Furthermore, the frequency distribution of the received signals differs due to the overlap between the received signals. This means that on the time axis, the period of the target signal (hereinafter, this signal is simply referred to as signal S) and the period of the non-target signal (
Hereinafter, this signal will be referred to as noise N). Therefore, when the received signals are moved by arbitrary time intervals on the time axis and added, the received strength of each signal becomes zero when one cycle of the signal and the noise are added. Therefore, when one cycle of noise is added, the intensity of the noise becomes zero, so the S/N ratio becomes infinite, and the S/N ratio can be improved.

[0008] Hereinafter, the relationship between the number of additions and the S/N ratio when the signals are added by moving at arbitrary time intervals on the time axis will be explained in detail.

FIG. 7 shows a schematic diagram of the received acoustic signal.

When the received signal is divided into signal S and noise N, the signal voltage Es(t) and the noise voltage En(t) are expressed by Equations 1 and 2.

[0011]

[Math 1]

0012

[Math 2]

##EQU1## where As is the amplitude of the signal, An is the amplitude of the noise, Ts is the period of the signal, and Tn is the period of the noise.

When these signals are moved by Δt on the time axis and added, Equations 1 and 2 become Equations 3 and 4.

[0015]

[Math 3]

[0016]

[Math 4]

[0017] However, m is the number of additions. That is, m
When m = 0, the received signal is the same as it is, and when m = 1, the result of Equations 3 and 4 is a signal obtained by adding the received signal and a signal obtained by shifting the signal by a time Δt.

In fact, the relationship between the signal S and the noise N can be roughly divided into two. One is when the signal S and the noise N overlap (Fig. 8(a)), and the second is when the signal S and the noise N do not overlap on the time axis (Fig. 8(a)).
(b)). These two received signals E(t) are expressed by Equations 5 and 6.

[0019]

[Math 5]

[0020]

[Math 6]

Therefore, SN corresponding to Equations 5 and 6
The ratio is the maximum value Emax of the received signal E(t) to the noise En
This is the value divided by the maximum value Enmax of (t).

[0022]

[Math 7]

[0023]

[Math. 8]

FIG. 9 schematically shows the relationship between the number of additions and the SN ratio.

Specifically, an example of calculation with As=An is shown in FIGS. 10 and 11. The squares in Figures 10 and 11 are
The value obtained by normalizing the periods Ts and Tn by Δt is (Ts/Δt=
20, Tn/Δt=19), and plus is an example of (Ts/Δt=20, Tn/Δt=21). When the number of additions m is (Tw/Δt)-1, Esmax
= 0, so the SN ratio becomes minimum, and (Tn/Δt)−
When it is 1, Enmax=0, so the SN ratio becomes infinite.

FIG. 12 shows the results of an experimental study of this relationship. The squares in FIG. 12 are experimental values, and the diamonds are (T
s/Δt=17, Tn/Δt=16). In the experiment, as shown in FIG. 13, frequency 2.
The reflected waves from the welded portion 202 are processed using a 25 MHz surface wave 210. The difference between the experimental value and the calculated value is Δt=0.033 μs in the experiment, whereas
This is because Ts=0.567 μs and Tn=0.533 μs, which are not divisible by Δt. Even in this case, the signal-to-noise ratio was improved by 35% in experimental results by signal addition.

[0027]

EXAMPLES The present invention will be explained below using examples.

FIG. 1 is a block diagram of a first embodiment of the present invention. In FIG. 1, 1 is a receiver, 2 is a receiver, 3
, 10 to 12 are memories, 4 to 6 are switchers, 7 to 9 are delay circuits, 13 is an addition number setting circuit, 14 is an addition circuit, 15
is an output device.

Next, the operation will be explained using FIGS. 1 and 2. In advance, the number of additions m is set in the addition number setting circuit 13 and the contents of the memory are cleared. When the set number of times m is zero, the switches 4 to 6 disconnect the receiver 2 from the delay circuits 7 to 9. When the number of additions m is a positive integer other than zero, the receiver 2 and the delay circuits 7 to 9 are connected in m switchers in order from the switch 4. Further, delay times Δt1 to Δtm are set in the delay circuits 7 to 9, respectively. For example, each delay time is Δt2=2×Δt1, Δt3=3×Δt1...Δ
It is set as tm=m×Δt1. In this situation, when receiver 1 receives the acoustic signal shown in FIG. 2(a),
The memory 3 stores the signal a. At the same time, the received signal a is sent to the delay circuits 7 to 9 via the switches 4 to 6. The delay circuits 7 to 9 delay the received signal a by a preset delay time. Therefore, the memory 10 stores a signal obtained by delaying the received signal a by Δt1 time, as shown in FIG. 2(b). Similarly, the signals stored in the memory 11 are shown in FIG. 2(c), and the signals stored in the memory 12 are shown in FIG. 2(d). The signals stored in these memories 3 to 12 are sent to an adding circuit 14 and added. As a result of this addition, a received signal with an improved SN ratio is output to the output device 15.

In the embodiment shown in FIG. 1, the delay time is set to an integral multiple of Δt1, but the delay time is not limited to this. Further, although m switchers are selected in order from switch 4, any m switchers may be selected.

Next, a second embodiment will be explained using FIG. 3. In the configuration of FIG. 3, 16 to 18 are switchers, 19 is an addition count detection circuit, and 20 is a comparator. Next, the operation of FIG. 3 will be explained. In advance, the number of additions m is set in the number of additions setting circuit 13, and the contents of the memory and the number of times detected by the number of additions detection circuit 19 are cleared. The switch 16 connects the receiver 2 and the memory 3, and the switch 18 connects the receiver 2 and the delay circuit 7. When the number of additions m is zero, the number of additions m and the number of detections by the addition number detection circuit 19 are the same (zero), so the switch 17 connects the memory 3 and the output device 15. Therefore, in this case, the received signal is sent directly to the output device 1.
Output from 5. Consider the case where the number of additions m in the addition number detection circuit is a positive integer other than zero. The switch 17 is
The memory 16 and the adder circuit 14 are connected. The acoustic signal received by the receiver 1 is stored in the memory 3 via the receiver 2 and the switch 16. At the same time, the received signal is
The signal is sent to the delay circuit 7 via. Received signal is switch 1
6, the switch 16 switches the connection between the adder circuit 14 and the memory 3. Further, the delay circuit 7 delays the received signal by a set delay time Δt, and sends it to the memory 10, which stores this signal. The signal stored in the memory 10 is sent to the addition count detection circuit 19 and at the same time is sent again to the delay circuit 7 via the switch 18. A signal further delayed by Δt in the delay circuit 7 (a signal obtained by delaying the received signal by (2×Δt) time) is sent to the memory 10.
is memorized. The number of additions detection circuit 19 calculates the number of additions based on the number of times the signal passes through this circuit, and sends the detected number of additions to the comparator 20. In the adder circuit 14, the memory 3
and the contents of the memory 10, and the result is stored in the memory 3 via the switch 16. The comparator 20 compares the number of additions m set by the number of additions setting circuit 13 with the number detected by the number of additions detection circuit 19, and if the two values are different, nothing is done. If they are the same, the connection of the switch 17 is switched to the connection between the memory 3 and the output device 15. As a result, the received signal with improved S/N ratio is transmitted to the output device 1.
5 is output.

The embodiment of FIG. 3 has the advantage that the number of switches, delay circuits, memories, etc. can be reduced.

The above two embodiments are cases in which one acoustic signal received by the receiver 1 is used. FIG. 4 shows a schematic diagram of a third embodiment, in which m acoustic signals are used. In the configuration of FIG. 4, 21 is a delay circuit. Next, the operation in FIG. 4 will be explained. In advance, the number of additions m is set in the number of additions setting circuit 13, and the contents of the memory and the number of detections by the number of additions detector 19 are cleared. The switch 16 connects the receiver 2 and the memory 3, and the switch 18 disconnects the receiver 2 and the memory 10. Addition count setting circuit 13
If the number of additions m is zero, the number of additions m and the number of detections by the addition number detection circuit 19 are the same (zero), so the switch 1
7 connects the memory 3 and the output device 15. therefore,
In this case, the received signal is output from the output device 15 as it is. Next, the addition number setting circuit 13 sets the number of additions to m.
Consider the case where The switch 17 is connected to the memory 16
and the adder circuit 14 are connected. The acoustic signal received by the receiver 1 is stored in the memory 3 via the receiver 2 and the switch 16. Thereafter, the switch 16 switches the connection between the delay circuit 21 and the memory 3. The signal stored in the memory 3 is sent to the adder circuit 14 via the switch 17. The adder circuit 14 adds the signal in the memory 3 and the memory 10 (all zeros at this stage), and sends the added signal to the delay circuit 21.
send to In the delay circuit 21, the output signal of the adder circuit 14 is delayed by a set time Δt and stored in the memory 3 via the switch 16. Further, the addition circuit 14 sends an addition completion signal to the switch 18 at the same time as the addition is completed. On the other hand, in the comparator 20, the number of additions m set by the number of additions setting circuit 13 and the number of additions m detected by the number of additions detecting circuit 19 (
(in this case zero). If the two values are different, the connection of the switch 17 is left as is. When the switch 18 receives the addition end signal from the addition circuit 14, it connects the receiver 2 and the memory 10, and sends the newly received acoustic signal to the memory 10. Next, 1 is added to the number of detections by the addition number detection circuit 19, and the contents of the memory 10 are transferred to the addition circuit 14.
send to The adder circuit 14 adds the signal to the contents of the memory 3 (the signal added once before and delayed by Δt time). At the same time as sending the result to the delay circuit 21, an addition end signal is sent to the receiver 2. The comparator 20 compares the number of additions m set by the number of additions setting circuit 13 with the number detected by the number of additions detection circuit 19. If the two values are different, switch 1
Leave connection 7 as is. The above operation is repeated until the number of additions detected by the addition number detection circuit 19 matches the number of additions m set in the addition number setting circuit 13. If the two values match, the connection of the switch 17 is switched to the connection between the memory 3 and the output device 15. As a result, the received waveform signal is output to the received waveform signal output device 15 with an improved SN ratio.

In the embodiment shown in FIG. 4, since (m+1) received signals having different reception times are added, random noise with irregular occurrence times and occurrence strengths can be reliably reduced to 1/√(m+
1) has the advantage of being possible.

In the above embodiment, the received signals are delayed and added using a delay circuit, but the same result can be obtained even if the received signals are advanced by Δt and added.

In order to remove random noise in the first and second embodiments, a random noise removal circuit 101 shown in FIG.
It is also possible to add times. The random noise removal circuit 101 is installed immediately after the receiver 2, and its operation is as follows. In advance, an addition number j (different from the addition number m) is set in the addition number setting circuit 107, and the contents of the memory and the detection number of the addition number detector are cleared. Switcher 1
03 connects the adder circuit 102 and the memory 104. The received signal is added to the contents of memory 104 by addition circuit 102, and the result is stored in memory 104. Addition circuit 1
When the addition at step 02 is completed, the addition end signal is sent to the receiver 2.
and receive it again. The comparator 106 calculates the number j set by the addition number setting circuit 107 and the addition number detection circuit 105.
Compare the number of times detected with , and repeat the addition until both values are the same. When both values become the same, the switch 103 connects the adder circuit 102 to the signal line immediately after the receiver 2 of the first and second embodiments.

FIG. 6 is a schematic diagram of the fourth embodiment. FIG. 6 shows a system equipped with the acoustic receiving device shown in the above embodiment.
This is a sound source position detection device. 201 is a test piece, 202 is an acoustic source (welded part), 203 is a transmitter and receiver, 204 is a transmitter, 205 is an acoustic receiver, 206 is a detector, 207 is a propagation distance measuring circuit, and 208 is an acoustic source position detection circuit, 20
9 is a display. Next, the operation in FIG. 6 will be explained. It transmits based on a signal from a transmitter 204, and an acoustic signal (surface wave) 210 is transmitted from a receiver to an acoustic source (welding part) 202. The acoustic signal (surface wave) 210 is reflected by the welding part 202, returns to the transmitter/receiver 202, and is received. The received acoustic signal has an S/N ratio improved by an acoustic receiving device 505 and is sent to a detector 206. The detected acoustic signal is sent to the propagation distance measuring device 207, and the propagation distance measuring device 20
In step 7, the propagation distance from transmission to reception is determined and the result is sent to the acoustic position detection circuit 208. Acoustic position detection circuit 20
8, the acoustic position is detected from the propagation distance, and the result is sent to the display 209 and displayed.

[0038]

According to the present invention, even when regular noise or unintended signals (noise N) are present, by shifting the received signals on the time axis and adding them,
Since the intensity of this noise N can be reduced, the SN ratio, which is the ratio between the target signal S and the noise N, can be improved. For example, when a surface wave with a frequency of 2.25 MHz was applied to a reflected wave from a weld, the S/N ratio was improved by 35%.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of signal waveforms.

FIG. 3 is a block diagram of a second embodiment of the invention.

FIG. 4 is a block diagram of a third embodiment of the present invention.

FIG. 5 is a block diagram of a random noise removal circuit.

FIG. 6 is a block diagram of a sound source position detection device including a sound receiving device.

FIG. 7 is a schematic diagram of a received acoustic signal.

FIG. 8 is a timing chart showing the relationship between signals and noise.

FIG. 9 is a characteristic diagram of the relationship between the number of additions and the SN ratio.

FIG. 10 is an explanatory diagram showing a calculation example of the relationship between the number of additions and the SN ratio.

FIG. 11 is an explanatory diagram showing a calculation example of the relationship between the number of additions and the SN ratio.

FIG. 12 is an explanatory diagram showing an example of experimental results regarding the relationship between the number of additions and the SN ratio.

FIG. 13 is an explanatory diagram of the experimental system.

[Explanation of symbols]

1...Receiver, 2...Receiver, 3, 10-12...Memory, 4
~6...Switcher, 7~9...Delay circuit, 13...Addition count setting circuit, 14...Addition circuit, 15...Output device.

Claims (5)

[Claims] Claim 1: An acoustic receiving device comprising a receiver and a receiver for receiving an acoustic signal, and outputting the received acoustic signal,
An acoustic receiving device comprising: means for shifting the received acoustic signal by an arbitrary amount of time; and means for adding a plurality of the acoustic signals. 2. The acoustic receiving device according to claim 1, comprising switching means for distributing the received acoustic signal, addition number setting means for selecting the switching means, and a memory for storing the acoustic signal. 3. In claim 1, a switching means for switching the flow of the acoustic signal, a means for detecting the number of additions, a means for setting the number of additions, and a number of additions set by the means for setting the number of additions. An acoustic receiving device comprising means for comparing the number of additions detected by the means for detecting the number of additions, and a memory for storing the acoustic signal. 4. According to claim 1, switching means for switching the flow of the acoustic signal, switching means for passing the acoustic signal based on an addition completion signal from the means for adding the acoustic signal, and detecting the number of additions. means for setting the number of additions, means for comparing the number of additions set by the means for setting the number of additions and the number of additions detected by the means for detecting the number of additions, and storing the acoustic signal. An acoustic receiving device comprising a memory for 5. A sound source position detection device comprising the sound receiving device according to claim 1.