NGHIEN CUTU - TRAO B6\
N C H I E N COU T H r E T KE V A CHi T A O B p T A O XUNC HEP CHO HE THONC RADAR X U Y ^ N O A T
DESIGN AND IMPLEMENTATION OF A NARROW IMPULSE GENERATOR APPLYING TO GROUND PENETRATING RADAR SYSTEMS
Bill HOu Phii', Au Ng9C Due', Nguyen Trung Hieu', Nguyen Thanh TuS H i Minh TSn^
'PTN DCSELAB, Truang Dai hpc Bach khoa TP H6 Chi Minh -Trucmg Dai hpc Khoa hgc Ty nhien TP. Ho Chi Minh
^Tnrong Dai hpc Nguyen Tat Thanh
TOM TAT
He thdng radar xuyen ddt (GPR) dang dug'c nghien ciru rong rai tren the giai bod tinh ung dung da dgng cua nd trong nhieu ITnh vuc khdc nhau nhu trong qudn doi, xdy dung, dia vdt ly,... Trong bdi bdo ndy, chiing Idi trinh bdy viec nghien ciru thiet ke vd che tqo bg tgo xung hep cua chiing tdi dua tren cdc Iinh kien dan gidn vd phd bien. Cdc ket qud mo phong va do dgc cho thdy cdc xung tgo ra Id chinh xdc vd de ddng dieu khien thay doi dp rong va chu AT xung.
Til khda: Radar xuyen ddt (GPR), bg tgo xung hep ABSTRACT
Ground penetrating radar (GPR) systems have been studying widely over the world due to their various applications such as military, constructions, geophysics, etc. In this paper, we will present our design and implementation of a narrow impulse generator based on lumped distributed elements and common ICs. The measured results show that stable impules can be exactly generated and the width and duration of the impulses can easily controlled.
Keywords: Ground Penetrating Radar (GPR), narrow impulse genertor.
mi TAP CHi GO KHl VIETNAM V S6 6 (Thang 6 nam 2012)
NGHIEN CUfU-TRAO D 6 |
1. GlOfI THIEU
He thdng radar xuyen ddt ngay cang dupc nghien cijru va phat tri^n cho nhiSu muc dich ung dung khac nhau nhu do tim bom min, trSc dia, do tim khoang san, khao sat cau dudng va c^ khao c6 hpc... Nguyen ly hoat dpng ciia he thdng nay la phat ra mpt tin hieu nang lupng dien tir truang vao trong long dat va thu lai tin hieu phan xa tra v8, sau do xu Iy tin hieu va hien thi hinh anli ciia muc tieu duai long dat can khao sat, nhu bi^u dien trong hinh 1.
tren thi triidng. Sd d6 nguyen ly c i a mach nay dupc bieu dien trong hinh 2.
Hinh 2: Phtlcftig phap tao xung bang transistor avalanche Trong bai bao nay, chiing t6i xin trinh bay phUdng phap tao x u i ^ hep ddn gian hdn vcfi n h i ^ Uu diem noi bat hdn nhii kha nang thay doi do rpng xung ^ chu ky xung tiiy y bang each ling dung nhiJi^
thanh tiiu cua ky thuat thiet ke vl mach (VLSI) ngay nay, ma cu the se dUpc trinh bay d phSn sau.
Hinh 1: Sa do khoi ciia he thong radar xuyen ddt 2. MACH TAO XUNG HEP
\^ec tao xung trong radar xuyen d& co vai tro anh hUcfng rat 16n doi vdi viec hien thi hinh anh va dp phan giai cua rauc tieu, xung cang hep tiic ling vdi tan so cang cao se cho ta hinh anh cua muc tieu co dp phan giai cang cao. Tuy nhien, n^u ta sfi dung dd rpng xung cang hep (tan so cang cao) thi ta se co dp xuy^n sau thlip hdn so vdi dp r6ng xung ldn hdn, do moi quan he ty le giiJa tan so va suy hao tin hieu trong moi trUdng truyen.
Chinh vl the ma iing vdi nhfing nhu cia ve iing dung khac nhau thi viec thi^t ke he thong radar xuyen dat ciing da dang va khac nhau.
PhUdng phap thong diing triidc diy la sit dung kha nang ng.p xa tdc thdi nang liipng lUu trji tren mdt dUdng truyin ngan bang each dung tranistor avalanche d che dp huy thac (break- down) nhu mpt bd chuyen mach nhanh va dUdng truyen sdng ciic ngan. Tuy nhien, phUdng phap nay lai phiic tap, ddi hdi phai tinh toan cd dp chinh xac cao, ngoai ra cdn cd van di linh kien di^n tii si( dyng cho phUdng phap nay khd tim
Y tiidng thiic hien cua mach tao xung hep dUa tren sU phat trien noi bat cua ky thuat thiet ke vi mach (VLSI) khi ma cac mach tich hpp (IC) cd kha nang dap dng tSn so cao va thdi gian canh len va canh xudng ciia xung chi vao khoang vai ns den vai tram ps. Y tiidng cua phUdng phap nay dUpc the hien nhii trong hinh 3.
JHL
Hinh 3: Mo hinh f tiidng thiic hien mach tao xung hep diing 2 IC toe dp cao
Ngoai viec phai tao ra xung vudng cd chu ky 1 |is va khoang thdi gian giiia canh len va canh xuong la deu nhau thi dieu quan trpng nhat trong mach tao xung nay, dd la sd dung phan td truyen'^
TAP CHI CO KHl VlfiT NAM V Sd 6 (Thang 6 nam 2012)
NGHIEN C U T U - T R A O D O I
eham, nd yeu cdu ngudi thik kk ph^i tinh to^n sao K^t qud md phdng ciia h^ thdng ciia mach cho sau khi qua phdn tii truySn ch^m nhu phdn tir t^o xung h?p tren proteus 7 cho ta y nghia rat ro phan bd hay cdc phan tir thy dpng L, C sao cho tin
hi?u tren vd tin hipu dudi cd dp tre Id 5ns, dc sau dd qua m^ch XOR vdi ddp ling thdi gian cgnh ISn vd thdi gian cgnh xuong cao s5 Idm cho dau ra cd dp rpng xung Id 5ns vd chu ky Id I ps. M^ch t^o xung toe dp !MHz dupc bieu dien trong hinh 4.
rdng gifla IC td dd cao vd nhflng d^ng IC thdng thudng.
Hinh 4- Mo hinh mach tao xung vudng 1 Mhz bdng th^ch anh 8Mhz
Phan tfl truyen eham ta cd the sfl dyng cap dong tryc de thfle hien, ta ed edng thfle tinh todn van tdc truyen cua cap ddng true nhfl sau:
If = . = 2e8(m / s) -jL.C
Nhfl vay, neu flng vdi tan sd trung tdm 200Mhz tfle tao dp tre 5ns ta cd the tinh todn chi^u ddi cua cap dong true nhfl sau:
l = v^.t,= l(m)
Vl theo nhfl y tfldng thiet ke thi dp rpng xung vudng vao eae cong IC toe dp eao se quyet dinh ehu ky xung vd cac phan tfl truyen chdm quyet djnh den dd rdng xung h?p, do dd de thay ddi ehu ky xung ta chi can thay doi dp rpng xung vudng bang each diing bien trd tang hoac gidm tan sd cfla thach anh.
3. KET QUA
Hinh 5: Sd do maeh tao xung tren testboard Dp tin cay ket qua md phdng tren se edng eao hdn khi cho mpt sd ket qua thfl nghi?m thiic te nhfl trong hinh sau.
Hinh 6: D^ng xung cua m?ch t?io xung hep iing v6i tu C = 5pF va lOpF (mpt 1 vudng flng vdi 50ns)
Nhfl hinh tren ta thay ro dp rdng xung da cd sfl thay doi ddng ke khi thay gid tri tu dien til 5pF len lOpF. Cy th^ d day la 5ns vd 22ns (gid tri cdng cao dp rdng xung edng khd chinh xae do anh hfldng sai sd cang Idn).
Ngoai ra, chu ky giiia eae xung hep cua maeh cung rdt deu nhau vd cd kha nang thay d6i chu ky xung cua m^ch mdt edch rat de dang nhd vdo bien trd t?o dp tre cua m^ch tao xung vudng.
TAP CHI CO KHl VlfiT NAM • S6 6 (Thang 6 nam 2012)
NGHIEN CUfU-TRAO D 6 |
Hinh 7: Chu ky giiia cdc xung ciia m^ch t?o xung hep img vdi bien trd R = 2KQ. va 2.5Kn
4. TONG KET
Mach tao xung hep trong bdi bao hoan todn khdp vdi nhu cdu sir dung cua radar xuyen ddt.
Tuy nhien, vi mach sir dung phan tir truyen chdm gdm phdn di phan bd vd phdn tu thu ddng cd nhimg nhupc diem la cdng kenh vd kich thudc Idn, ngodi ra khd thay ddi khi cd nhu cau thay ddi dp rpng va chu ky xung. Thuc te, phuang phap dung cac phan tir thu dpng L,C se giup cho mach nhd gpn ban. •
Ngirol phan Men: TS. Ho Pham Huy Anh
Tai li§u tham khao:
[1]. David.J.Damels, "Ground Penetrating Radar 2nd Edition", Hpc vien Ky thuat Dien tu, trang 13-35.
[2]. Devendra K. Misra, "Radio-Frequency and Microwave Communication Circuit", Tap chi A Wiley-Inter- science, trang 25-101.
[3]. ht^://www.edaboard.com. High Frequency Pulse Generator.
[4]. http://www.edaboard.com, R, C delay network.
[5], "Passive Delay Network Design Considerations", Tap doan Rhombuslndustnes.
TAP CHf CO KHf VlfiT NAM V Sd 6 (Thdng 6 nam 2012)
