ES2421321B2 - EMPLOYMENT OF PSEUDO-ORTOGONAL SEQUENCES IN PHASED ARRAY SYSTEMS FOR SIMULTANEOUS EXPLORATION IN MULTIPLE DIRECTIONS - Google Patents

Abstract

We propose the use of phased array techniques with an encoded excitation from a set of pseudo-orthogonal sequences, such as those derived from pseudo-random or CSS sequences (Complementary Sets of Sequences), as well as their subsequent process stage, all of which allows to obtain images of the environment with high resolution from a single emission that simultaneously covers multiple differentiated directions of the environment, unlike the classic phased array systems that require an emission for each sector to be inspected. This invention introduces a new method of excitation of the array elements and post-processing of the received echoes that increases the speed of image generation, as well as the maximum distance to be inspected while maintaining the image quality.

Description

Use of pseudo-orthogonal sequences in phased array systems for simultaneous multi-direction scanning

Technical sector

The invention belongs to the technical area of electronic technology and within this area, and according to its application, falls within the field of sensory systems that use the phased array technique for exploration (for example ultrasonic scanners, radar, or type Similary).

State of the art

Conventional phased array (pa) technology is widespread in the field of medical imaging and non-destructive testing (end) to obtain high resolution images [kisslo, j .; vonramm, or .; & thurstone, f., "cardiac imaging using a phased array ultrasound system", ii. Clinical technique and application. Circulation, vol.53 (2), pp. 262267, February 1976.] [m. Grill, p. Snowy, a. Ibañez, j. Camacho, j. Brizuela, and c. Fritsch, "ultrasonic imaging of solid railway wheels", in proceedings of the ieee ultrasonics symposium, pp. 414-417. Beijing, China, November 2008.]. This technique allows to obtain images with millimeter resolution, but with penetration depth of a few centimeters. However, the development of 3D imaging systems, as well as the need to represent systems with movement such as the heartbeat, generates the need to increase the imaging rate.

In order to improve the image rate, synthetic opening systems (sa) [lockwood, g.r .; talman, j.r .; brunke, s.s .; "real-time 3-d ultrasound imaging using sparse synthetic aperture beamforming," ieee t ultrasonic ferr, vol.45, no.4, pp. 980-988, July 1998]. Despite the notable increase in speed compared to conventional pa techniques, more than one emission is still necessary to generate the image. On the other hand, the signal-to-noise ratio and therefore the depth of penetration obtained with sa techniques, is deteriorated since each emission is made with a single element.

This invention proposes to increase the image rate and penetration depth in ultrasonic imaging systems, or others that use pa, combining pa technology with pseudo-orthogonal sequences used in cdma (code division for multiple access) systems. The coding of the emitted cdma signal has been a very effective resource, along with the frequency division for multiple access multiplexing, to work in multi-user environments allowing everyone to broadcast at the same time. [m. Peca, "ultrasonic localization of mobile robot using active beacons and code correlation," eurobot, vol.82, pp.63-70, 2009.] [jörg, k.-w., & berg, m., "Mobile robot sonar sensing with pseudo-random codes ", in proceedings of the ieee internationalconference on robotics and automation leuven, belgium 1998.] [pérez, m. From c., J. Urena, á. Hernandez, f. J Alvarez,

to. Jiménez, and c. De marziani, "efficient correlator for ls codes generated from orthogonal css", ieee communications letters, vol.12 (10), pp. 764-766, October 2008.] [hernández, á., J. Urena, m. Gavel, j. J. García, a.Jiménez, j. A. Jiménez, m. From c. Pérez, f. J. Álvarez, c. From Marziani, j. P. Derutin, et al., "Advanced adaptive sonar for mapping applications", journal of intelligent & robotic systems., Vol.55, pp. 81-106, October 2009.]. As the previous works demonstrate, in order to achieve simultaneous emission and reception of the different elements that form the sensory structure, each of them is assigned a pseudo-orthogonal sequence that uniquely identifies it. Therefore, the sequences used must comply with pseudo-orthogonality properties, such as kasami codes, complementary sequence sets (css) and derived codes. Pseudo-orthogonality is understood when the self-correlation (ac) of any of the sequences considered has a very marked maximum for zero displacement in relation to the rest of the values, and the cross correlation

(cc) has very low values for any displacement in relation to the maximum auto-correlation.

In systems for medical imaging, encoded sequences have also been used together with phased array systems, but with the aim of improving the signal to noise ratio snr without increasing the power emitted to the patient. [m. O'donnell, "coded excitation system for improving the penetration of real-time phased array imaging systems", ieee ultrasound ferr, vol.39, pp.341–351, May 1992] [t. Toosi and h. Behnam, "combined pulse compression and adaptive beamforming in coded excitation ultrasound medical imaging", in proceedings of the international conference on signal processing systems, pp. 210-214, May 2009]. Also, in [and. Avrithis, a. Delopoulos and g. Papageorgiou, "ultrasonic array imaging using cdma techniques", in proceedings of the ix european signal processing conference (eusipco '98), pp.681-684, greece, september 1998] proposes a pa system combined with m-sequences to acquire in Parallel signals from several directions. However, in this work it is not possible to inspect all directions with a single emission, but it requires several emissions as there are not enough pseudo-orthogonal sequences with low cross correlation with each other. Thus, the technique used to finally inspect the different directions of the environment is tdma (time division for multiple access).

This invention minimizes the number of sequential emissions necessary to generate the image, a single emission is sufficient for scanning the entire desired angular sector while maintaining the number of image scanning lines. The possibility of directing or deflecting the beam at multiple angles is described.

simultaneously thanks to the pseudo-orthogonality properties of the emitted sequences. Thus, it is possible to inspect the environment and obtain an image of it with a single emission, improving the signal to noise ratio of the snr system and the image generation rate; while maintaining the number of scan lines.

Explanation

Phased arrays allow deflecting the beam or changing the direction of the main lobe of the sensory system by modifying the activation delays of each of the elements that constitute the array. The calculation of delays for deflection is defined by equation (1) [smith, s .; pavy, h.g.jr .; von ramm, o.t., "high-speed ultrasound volumetric imaging system. I. Transducer design and beam steering", ieee t ultrason ferr, vol.38, no.2, pp. 100-108, March 1991]. Being c the speed of sound, ot (n, 8i) the delay in the emission, which is a function of the distance between the elements or pitch (d) and the angle of deflection 8i, where i = [1, ..., l] represent the different directions or angular sectors of the environment to be scanned. The variable n takes values n = [0, ± 1, ± 2,…, ± n / 2] for the array elements equi-spaced in both directions to the central element. Equation (1) includes an initial delay t0 to avoid negative delays.

Lt (n, 8i) = n · d · Sin 8i + T0

C

(one)

In conventional systems each of the elements is excited by a pulse with the delay ot (n, 8i) corresponding to the angle of deflection (8i) and the element (n), obtaining a wavefront whose direction of propagation is 8i. This process is carried out by each of the addresses that you want to scan 8i and that give rise to the lines (a-scan) that make up the image of the environment (b-scan). For each line of the image it is necessary to make an emission with all the elements of the array, therefore the time required to obtain an image with the lines is given by (2). Where rmax is the maximum inspection distance, l the number of lines that make up the image, tpulso the time needed to emit the pulse used for the excitation of the elements and c the propagation speed of the emitted signal (sound, radio frequency, ...) .

rmax

Timagen = l · (tpulso + 2 ·)

C (2)

In the proposed system, instead of pulses, different pseudo-orthogonal sequences are used to excite the array elements. The coding of the signal (ultrasonic or other) allows the entire environment to be inspected with a single emission, deflecting the beam at the angles simultaneously. For this, a pseudo-orthogonal sequence is assigned to each of the angular sectors (l = k). Thanks to its auto-correlation (ac) and cross-correlation (cc) properties, it is possible to discern the angular sector from which the echoes come after a correlation process that takes place at the reception stage.

In classical techniques, to be able to deflect the beam in a given angular sector, all the elements of the array must be activated, each in its corresponding moment according to (1). In the proposed case it is desired to deflect the beam simultaneously in l = k angular sectors, assigning a different sequence to each angular sector. Therefore, each element of the emitting array emits the sum of k different sequences; each of them with the delay corresponding to the angular sector assigned ot (n, 8i). If each sector 8i is assigned the sequence yes, the nth element of the array will emit the signal sen (3). In this emission scheme, hereinafter referred to as scheme 1, there is a different sequence for each angular sector l = k, so that the number of available pseudo-orthogonal sequences will limit the number of angular lines or sectors that constitute the image. Said sequences can be modulated to adapt the emitted signal to the available bandwidth.

k

Sen = L si (t-Lt (n, 8i))

I = 1

(3)

Bearing in mind that the pseudo-orthogonality of the sequences is applicable to both the emission process and the reception process, a more elaborate emission process is proposed that improves the image quality, hereinafter Scheme 2. This improvement is supported by a post -processing of the received signal in an array of nrx receiver elements that allows to divide the reception also into p sectors sfj [j = 1, ..., p], as will be explained below. The main difference with scheme 1 is that in scheme 2 it is possible to assign the same sequence if to different angular emission sectors, which are 8i, 8i + k, 8i + 2k,… provided that these emission sectors to which they have The repeated sequences have been assigned within different reception sectors. Therefore in scheme 2, each element will emit l signals (the k sequences repeated p times), each with a different delay ot (n, 8i), according to the angular sector 8i corresponding to [i = 1,…, l] and l = k · p, according to (4).

l = p · k

Sen = Lsi (t-Lt (n, 8i))

I = 1

(4)

Scheme 2 allows to increase the number of lines of the image, which means that the image quality is superior to that obtained with scheme 1. In this case, l> k is fulfilled, that is, the number of pseudo-orthogonal sequences available in the set considered k, will not limit the number of scanned lines or angular sectors that constitute the image. Although the emission of sequences is repeated, as the repeated sequences belong to different reception sectors, the entire environment can be inspected with a single emission as in scheme 1. To distinguish between sectors with the same coding, in the scheme 2 it is necessary to use an array of nrx elements. Each of them will receive an echo rm to which a delay ot (m, fj) with [j = 1, ..., p] will be applied, for each angle of deflection considered in reception fj. The sum of the received nrx signals, with the p delays corresponding to each reception angle fj generate the p reception sectors s �j according to (5).

nrx

S �j = Lrm (t-Lt (m, � j))

M = 1

(5)

Each receiving sector sfj covers k broadcasting sectors, [8k · (j-1) + 1,…, 8k · j]. Therefore, the final image will have l = k · p a-scan lines. To generate the l-a-scan lines of the final image, the p reception sectors will be traversed, searching in each of them, the k lines that it covers through a bank of k correlators. All correlator banks will be made with the same k pseudo-orthogonal sequences used in emission, which are called sk where [k = 1, ..., k]. Thus, in order to generate the k-a-scan lines corresponding to the jth reception sector lj, k with [k = 1, ..., k], it is necessary to correlate said reception sector, sfj, with the k pseudo-orthogonal sequences according to (6). In this expression li refers to the ith line of the final b-scan image [i = 1,…, l].

L (k + (j-1) · k) = Lj, k = S �j (Sk with [k = 1,…, k] and [j = 1,…, p]

(6)

This process is repeated for the p reception sectors obtaining the l = k · p lines that make up the bscan image.

With this algorithm the time required to generate an image with the lines is given by (5). Where rmax is the maximum inspection distance, the time required to emit the pseudo-orthogonal sequences used to excite the elements, and c the speed of the signal used (sound, rf, ...).

rmaxT'imagen = Sequence + 2 · C

 (7)

Comparing equations (2) and (7) it is observed that, unlike conventional systems, in the proposed system the time needed to generate the image does not depend on the quality of it. By dividing equations (2) and (7) the relationship between the rates of image generation between the two systems (8) is obtained, where the approximation is obtained considering the time needed to emit the pulse in conventional techniques negligible. From (8) it is possible to conclude that, keeping the length of the sequence fixed, the greater the maximum distance to be inspected (rmax) and the quality of the required image (number of lines = l), the greater the speed of generation of Images will be obtained in comparison with classical techniques.

1 t · pulse

/) 2+

'L · (tpulso + 2 · rmax 1

= = = l · �L.

1 2+ c · tsequence 1+ c · tsequence

V'imagen timagen C Rmax

vimagen / Frequency + 2 · rmax

timagen 'C

Rmax 2.rmax

(8)

Description of the drawings

Figure 1 shows the block diagram of the emission stage, with the delay bank (1.1) that allows deflecting the beam in each of the angular sectors and the array of emitting elements [n = 1,…, n] ( 1.2). The two emission schemes considered are shown below, scheme 1 (1.3.a) and scheme 2 (1.3.b). In scheme 1 (1.3.a), pseudo-orthogonal sequences sk with [k = 1, ..., k] are emitted, assigning one to each of the angular sectors that are to be inspected 8i with [i = 1, ... , l]. In this case, the number of pseudo-orthogonal sequences emitted k and the number of sectors l in which the image is divided is considered to be the same (l = k).

In scheme 2 (1.3.b), the number of angular sectors l into which the image is divided is greater than the number of pseudo-orthogonal sequences emitted k (l> k). In this case the same sequence is assigned if to different angular sectors 8i, 8i + k, 8i + 2k, ... which are then made to coincide with different sectors of sfj reception.

Figure 2 shows the stage of reception and post-processing of the signal necessary to generate the b-scan image of the environment, using the emission scheme 2. In (2.1) the sfj reception sectors are shown with [j = 1, …, P], each reception sector covers k broadcast sectors [8k · (j-1) +1,…, 8k · j]. To generate said reception sectors, it is necessary to delay the received signals rm in the nrx elements of the receiver array (2.2) with a delay bank ot (m, fj) [m = 1,…, nrx] (2.3), one per each angle of deflection considered in reception fj, [j = 1,… p].

The sum of the received nrx signals, with the p delays corresponding to each reception angle fj generate the p reception sectors sfj. Finally, in (2.5) the b-scan image obtained after the correlator banks (2.4) is represented. Each of them provides, k a-scan lines for each sfj reception sector providing the l = k · p lines of the final image.

Embodiment

Figure 1 shows the emission stage, where k pseudo-orthogonal sequences sk are generated with [k = 1,…, k]. A delay bank ot (n, 8i) (1.1) will then be applied for each angular sector that 8i is to be inspected. Each sector 8i is assigned the sequence if, so that each element of the emitter array (1.2) will emit the sum of the pseudo-orthogonal sequences, each with its corresponding delays. If the number of sectors to be inspected is equal to the number of available pseudo-orthogonal sequences (k = l), the emission scheme 1 (1.3.a) is obtained in which the image resolution will depend on the number of available pseudo-orthogonal sequences . If the number of sectors is greater than the number of sequences (l> k), based on the reception stage shown in Figure 2, the emission scheme 2 (1.3.b) is obtained. In scheme 2 the number of lines of the image l does not depend on the number of available sequences k, since thanks to the processing of the echoes received at the reception stage it is possible to repeat sequences, that is, assign the same sequence to several sectors 8i different inspection.

To avoid confusion between the sectors that have the same sequences, it is necessary to assign them to different reception sectors (2.1). To generate said reception sectors, it is necessary to delay the received signals rm in each of the elements of the receiving array [m = 1,…, nrx] (2.2), by means of a delay bank ot (m, fj) (2.3). To generate the signal from each receiving sector sfj [j = 1,… p], the received signal rm in each element of the receiving array will be delayed according to the angle fj of the corresponding receiving sector and then the delayed nrx signals will be added. Thus a signal will be obtained for each sector of sfj reception. In (2.4) a correlator bank is applied to each of the p signals of the sfj reception sectors, the correlator bank will be made up of the available pseudo-orthogonal sequences that were included within said reception sector. In this way, the l = k · p a-scan lines that make up the final b-scan image (2.5) are obtained.

As an example, an airborne ultrasonic system (with c = 340m / s) with a maximum distance of rmax = 1m and l = 32 lines is considered, so that the time required for a line corresponds to line = 5.9 ms , assuming the duration of the pulse is negligible, and therefore the time to obtain the image of 32 timagen lines = 32 · line = 189 ms. With the proposed system, four reception sectors will be assumed. Thus, with k = 8 ls pseudo-orthogonal sequences of length 2303 bits it would be enough to encode the emissions in 8 + 8 + 8 + 8 = 32 sectors. In the reception a sampling frequency fs = 1.6 mhz is used and an oversampling factor, sb = 20, that is, working at a central frequency of f0 = 80 khz. The time required to issue a sequence is tsequence = 28.8 ms, so the time required to obtain the image is t’imagen = tsequence + line = 34.7 ms. In this case it is concluded that the speed obtained using coding is multiplied by a factor greater than 5 compared to conventional techniques. In the same example, using 8 pseudo-orthogonal kasami sequences of 63 bits, the imaging rate is multiplied by 28.

This increase in the generation rate is especially interesting with 2d arrays that have a very high number of elements. On the other hand, in addition to increasing the rate of image generation, an increase in the signal-to-noise ratio will be possible and with it the penetration depth.

Industrial application

Ultrasonic imaging systems for medical imaging, non-destructive evaluation systems, systems for detecting obstacles in the air, radar applications, detection of signal arrival angles and applications in communications with various antennas.

Claims (10)

one.

A method of generating B-Scan images with L environment lines, using an array of N transmitters and another of NRX receivers from a single signal emission without the need to multiplex in time or frequency.

2.

The method according to the first claim, characterized in that N emitters and a single receiver are used, combining the deflection of the characteristic beam of the PA techniques in the emitter array with a coding with K pseudo-orthogonal sequences derived from pseudo-random sequences or complementary sets of sequences or derived codes.

3.

The method described in claims 1 and 2, characterized by the processing of the reception in a single element with a bank of K correlator filters, capable of giving L = K sectors or lines of the environment.

Four.

The method described in claims 1, 2 and 3, characterized by the combination of the coding and processing technique described with others based on time or frequency multiplexing.

5.

The method described in claims 1, 2, 3 and 4, characterized by the use of other types of orthogonal or pseudo-orthogonal sequences, as well as by modulations of the signal sent in phase or frequency, which allow discriminating between the different sectors analyzed .

6.

The method described in the first claim characterized by the use of N transmitters and NRX receivers, extended to a coding with K pseudo-orthogonal sequences, repeated by each of the P sectors in which the signal is then divided into reception from the array of NRX receiving elements.

7.

The method described in claims 1 and 6 characterized by the processing in reception with K correlators in each of the P reception sectors, obtaining a total of L = K · P sectors or lines of the environment without the need to multiplex in time or frequency.

8.

The method described in claims 1, 6, and 7, characterized by the combination of the coding and processing technique described with others based on time or frequency multiplexing.

9.

The method described in claims 1, 6, 7 and 8, characterized by the use of other types of orthogonal or pseudo-orthogonal sequences, as well as by modulations of the signal sent in phase or frequency, which allow discriminating between the different sectors analyzed .

Figure 1 Figure 2 SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 201230295 SPAIN Date of submission of the application: 02.28.2012 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: See Additional Sheet RELEVANT DOCUMENTS

Category

56 Documents cited Claims Affected

A A A A

US 2007242567 A1 (DAFT CHRISTOPHER M et al.) 18.10.2007 EP 2305123 A1 (FUJIFILM CORP) 06.04.2011 US 2006241454 A1 (USTUNER KUTAY F et al.) 26.10.2006 US 5976089 A (CLARK DAVID W) 02.11.1999 1 1 1 1

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 29.10.2013

Examiner M. C. González Vasserot Page 1/4

REPORT OF THE STATE OF THE TECHNIQUE Application number: 201230295 CLASSIFICATION OBJECT OF THE APPLICATION H01Q3 / 26 (2006.01) G10K11 / 34 (2006.01) G01S7 / 52 (2006.01) Minimum documentation sought (classification system followed by classification symbols) G01S, G10K, A61B Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENTIONS, EPODOC, WPI State of the Art Report Page 2/4  WRITTEN OPINION Application number: 201230295 Date of Completion of Written Opinion: 29.10.2013 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims Claims 1-9 IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 1-9 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 201230295  1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

US 2007242567 A1 (DAFT CHRISTOPHER M et al.) 18.10.2007

D02

EP 2305123 A1 (FUJIFILM CORP) 06.04.2011

D03

US 2006241454 A1 (USTUNER KUTAY F et al.) 10.26.2006

D04

US 5976089 A (CLARK DAVID W) 02.11.1999

 2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement The documents cited only show the general state of the art, and are not considered of particular relevance. Thus, the claimed invention is considered to meet the requirements of novelty, inventive activity and industrial application. 1.-The object of the present patent application belongs to the technical area of electronic technology and within this area, and according to its application, it falls within the field of sensory systems that use the phased array technique for exploration (by example ultrasonic scanners, radar, or similar type). Conventional phased array (PA) technology is widespread in the field of medical imaging and non-destructive testing (NDT) to obtain high resolution images. 2.-The problem posed by the applicant is to minimize the number of sequential emissions necessary to generate the image, a single emission is sufficient for scanning the entire desired angular sector while maintaining the number of scan lines of the image. The possibility of directing or deflecting the beam at multiple angles is described simultaneously thanks to the pseudo-orthogonality properties of the emitted sequences. Thus, it is possible to inspect the environment and obtain an image of it with a single emission, improving the signal-to-noise ratio of the SNR system and the image generation rate; while maintaining the number of scan lines. For this purpose, the use of phased array techniques with an encoded excitation from a set of pseudo-orthogonal sequences is proposed, such as those derived from pseudo-random sequences or CSS (Complementary Sets of Sequences), as well as their subsequent stage of process, all of which allows to obtain images of the environment with high resolution from a single emission that simultaneously covers multiple directions differentiated from the environment, unlike the classic phased array systems that require an emission for each sector to be inspected. This invention introduces a new method of excitation of the array elements and post-processing of the received echoes that increases the speed of image generation, as well as the maximum distance to be inspected while maintaining the image quality. Document D1 can be considered as the representative of the closest state of the art since most of the claimed technical characteristics converge in this document.  Analysis of the independent claims The state of the art closest to the object of the invention is represented by document D01, which discloses: Methods, systems and matrix of transducers and receivers to generate information for medical diagnosis with ultrasound. It does not disclose and differs in that: It is not a method of generating B-Scan images with L environment lines using an array of N emitters and another of NRX receivers from a single signal emission without the need to multiplex in time or frequency. Claim 1 is new (Art. 6.1 LP 11/1986) and has inventive activity (Art. 8.1 LP11 / 1986).  Analysis of the rest of the documents Thus, neither document D1, nor any of the rest of the documents cited in the State of the Art Report, taken alone or in combination, reveal the invention under study as defined in the independent claims, so that The documents cited only show the general state of the art, and are not considered of particular relevance. In addition, there are no suggestions in the cited documents that direct the person skilled in the art to a combination that could make the invention defined by these claims evident and it is not obvious for a person skilled in the art to apply the features included in the cited documents and reach the invention as revealed therein. State of the Art Report Page 4/4