mdr for law enforcement

8/12/2019 MDR for Law Enforcement

1/4

h c US Dcp ar tmen t of

Defense (DoD) has funded a

dazzling array of high tech

solutions for military prob-

lems. W hile typically effective for

long range mass destruction, these

solutions generally are not useful in

combatting civilian crime.

Our

goal

is to convert high tech Doll) capa-

bilities into cost effective tools that

help law enforce ment agencies.

For example , a new sensor has

been designed based on technology

developed for missile warhead fusing.

This

small,

light weight, low power

radar exploits the fact that opti-

mized radio waves can penetrate non-

me ta l l i c ma te r i a l s . Th i s n ew

surveillance capability can help pro-

vide information about what is in a

wall, ceiling, floor, on the other side

of

a

door or even a c oncrete wall.

generally line-of-sight

LOS)

devices.

They must have a clear visual view of

the surveillance area. This obviously

places a major limitation on police

field operations. It is o ften difficult to

set up this typ e of surveillance without

being detected.

Whats more, visual surveillance,

even with a TV, can be tedious and

hstraling.

A person watching a TV

screen showing an area w here nothing

is going on soon loses interest. As a

result, other distractions or drowsi-

ness can cause important activities to

be missed. A signal, such as a tone or

flashing light, that operates only when

there is activity would help.

T h e M o t io n D e t e c t i o n R a d a r

(MDR) adds

a

new dimension to sur-

veillance. MDR can be effective even

through wooden doors and concrete

walls, It requires very little setup and

P ;emote

Monitor I

I Body Dielectric

Concrete Constant - 80

Wall Dielectric

Constant - 8

-12

.

he

Human Body Contains -65 Water

. ater Has A High Dielectric Constant

Walls Have A

Low

Dielectric Constant

~

Fig

Wd / sare opaque the body

i s a good

reflector.

Law enforcement agency surveil-

lance typically incl udea; television

(TV) cameras, infra-red

(IR)

sensors

and hidden microphones, often with

remote transmitters. These sensors

have greatly enhanced the surveillance

capabilities of the law enforcement

agencies. However, these sensors are

does not have any ext em d wires con-

nected to it. Unlike TV cameras and

IR

sensors that must be con cealed, the

MDR can be placed in

a

safe loca-

hidden in a container with non-metal-

l i c wa l l s . Th e MDR p r o v id es an

effective and timely alert even if the

tion

on

the other side of a wall or

person doing the surveillance is pre-

occupied, distracted or inadvertently

nods off due to fatigue.

The basic premise is that radio

waves will penetrate most non-metal-

lic materials. However,

a

number of

factors must be conside red to properly

exploit this phmorriena. The cornpo-

sition and thickness of the m aterial to

be penetrated

is a

prime factor in the

initial design. Likewise, the reflectivi-

ty and uniquenes s of the actual targets

on the other side of the wall must also

be co nsidered. Radio waves both pen-

etrate and reflect off

of

surfaces of

a

non-metall ic material . The surface

roughness, dielectr ic constant and

angle of incidence all affect the pene-

tration characteristics.

In

Fig.

1,

the radar waves

are

pene-

trating a dry concrete wall with

a

dielectric constant between

8

and 12.

The primary target on the other side

of

th e wa l l i s

a

mo v in g p e r so n .

Because the human body has a high

concentration of water, which has

a

dielectric constant of

80

(distilled),

the expected reflectivity

is

quite rea-

sonable compared to other objects in

view. While other metallic objects

have greater reflectance, the radars

abili ty to scnse motion makes the

moving target unique and relatively

easy to detect in this highly cluttered

environment.

The ef fec ts

of

ve l oc i t y change

ubsorption,

refraction and reflection

all must be considered as shown in

Fig.

2.

The radio waves velocity is

s lowed by the square roo t o f the

dielectric constant of the non-metallic

materials (Fig. 2a .

A

material with a

d ie l ec t r i c co n s t an t o f 4 wo u ld

decrease the velocity of the radio

wave

by a

factor o f

2.

Th u s . t h e

dielectric constant and the thickness

of the material determine how much

the apparent range to the target is

DECEMBER

97IJANUARY 98 0278-6648/97/$10.00 1997

IEEE

23


2/4

Transmission Speed

Non-Metallic Material Slows Waves

(4

Absorption

The Wall Absorbs

(c)

Refraction Loss

Lar e Particles Cause The

Ra jar Beam To Break

Up

Refraction

Waves Bend Through Dielectrics

b)

Reflection

The Wall Reflects

(4

Diffraction

Waves Diffract

Around Edges

Fig

2

Considerations when

RF is

penetrating non-metall ic maferials.

Fig. 3

Measured one way

oss: 4- 140GHz

modif ied each t ime the s ignal goes

through the mater ia l . For most th in

materials, this delay is insignificant;

but, for others, it can make a consider-

able difference.

The absorption of the radio energy,

while passing through the material, is

affected by the materials physical mak e

up (Fig. 2c). If sufficiently large, con-

ductive, dissipative particles (such as

ca r b o n ) a r e i n t h e ma te r i a l , t h en

depending upon the signal frequency,

ohmic attenuation may cause sufficient

loss to make the system unusable. If the

dielectric particle size of the structures

material is large with respect to the sig-

nals wavelength, there will be intemal

reflections and refraction. These will

distort the signal wave front and cause

excessive a t tenuat ion (Fig . 2e) . For

example, concrete with large internal

stone aggregate will have far greater

loss at 10 GHz than the same thickness

of concrete made with fine sand.

The refraction of the wave passing

through the material (Fig. 2b) is also a

function of the dielectric constant and

thickness. The effect of refraction is

small for homogeneous materials with

particle sizes much smaller than on e

quarter wavelength. For construction

concrete, the effect can be significant at

higher frequencies. The radar designer

must consider

the loss

through the mate-

rial (which should be small) compared

to the normal two way radar range loss

(one over range to

the

fourth power).

Diffraction (Fig. 2f) is caused by

radio waves striking an objects edge

and producing a scattering of the radio

waves. This effect

is

predominant when

metal objects are inside the wall the

radar beam is penetrating.

The refection of the radio wave is

also influenced by the angle of incidence

between the wave and the wall, as well

as the distance between the radar anten-

na and the wall (Fig. 2d). When the

antenna is pointed directly at the wall,

the maximum direct return from the wall

is received back

at

the radar.

When

the

antenna beam

is

pointed at an angle to

the wall, the

reflection

from the wall

back to the radar rapidly decreas es.

Reflections

off walls that go back to

objects on the radars side of the wall

can becom e quite strong. All large flat

surfaces act as mirrors to the radar sig-

nal. The consequences of this charac-

teristic are difficult to predict. This can

l e a d

to

s ig n i f i can t an g le e r r o r s i n

assessing the location of the moving

person at certain frequencies with cer-

tain types of walls. The effect is

also

modified by the texture of the walls

su r f ace : t h e smo o th e r t h e wa l l , t h e

greater the effective reflection and the

smal ler

the

penetra t ion .

A

poten t ia l

radar system limitation is the ratio of

the power received off the close wall

relative to the power received off a dis-

tant moving target.

The loss of radio frequency energy

as the beam passes through materials

varies greatly with different conditions.

The se conditions include: age, chemical

as well as mechanical construction, and

the am ount of metallic contaminates.

24

IEEE

POTENTIAL


3/4

Figure 3 shows a comparison

of

the

measured m e w a y

losses

versus fre-

quency for various common wall and

building materials. The concrete blocks

were standard

6

inches thick by

6

inches

high by 12 inches long blocks with two

holes in the middle. This left about 1

and 1/2 inches of concrete on each side

of the holes.

A

number of these blocks

were stacked to prevent direct energy

radiation around the wall . The same

setup was used for the boards and other

ma te r i a l s measu r ed . Th e r e was n o

attempt to maintain uniform thickness

for these tests; however, the distance

between the antennas was constant.

The concrete blocks presented the

greatest loss of the m aterials tested. The

initial tests concentrated on the effects

at the higher frequencies. While there is

a temptation to directly convert lhe one

way loss to two way losses, this may

lead to erroneous results. While the loss

alone may be translatable, the angle of

incidence and the distance from the tar-

get to the wall can have a greater effect

than just the one way loss factor. Com-

mon window glass, for example, can

cause large signal losses at certain offset

angles.

As

stated previously, this is not

necessarily predictable, but must b e con -

sidered in the system de sign and setup.

To determine the possibil i t ies for

practical radar operation through con-

crete, tests were conducted at the lower

frequencies, Figure 4a shows the one

way loss measurements through com-

mon

8

inch, pre-stressed, reinforced

concrete walls for both horizontal

(H)

and vertical

(V)

antenna orientations.

The typical one w ay

loss

of only

2

to 4

dB at

900

MH z was quite acceptable for

radar penetration.

Figure 4b shows the one way

H-H

loss

measurements through a three foot

thick reinforced concrete wall in the fre-

q u en cy r an g e of

500

M H z t o 2 5 0 0

MHz. t 900 MH z, the loss increased to

6

to 8 dB, which was still quite accept-

able.

A

number of different measure-

ments at different locations along the

wal l were taken , whi le keep ing the

transmit and receive antennas

of

the bi-

static radar at

a

constant 12 inch dis-

tance from the wall. The losses were

quite consistent when the antennas were

both placed horizontally.

Figure 4c shows the var ia t ion in

attenuation when the antennas

were

placed vertically. Some of the variation

in the data was caused by the vertical

steel reinforcing bars m ounted every

12

inches in the concrete. The distance

of

the receive antenna

from

the wall also

caused wide variations in the one way

received energy levels. This also may

have been caused by the reinforcing

steel, or by the interference of reflec-

tions between the wall and the antenna .

x

The M otion Detection Radar, shown

in Fig. 5(pg. 26), is contained ina high

impact carrying case. The antenna is a

flat plate

13

inches

x

13inches

33

cm x

33

cm) located in the lid of the case.

The antenna radiates a

+/- 45

degree

conical beam out of the case 's r ight

side. The transmitter and receiver mod-

ules are mounted on the antenna. They

also fit into the lid of the carrying case.

The con trol unit is visible in the left side

oi

the case.

Two

high current recharge-

able NI-CAD (nickel-cadmium) batter-

i e s a r e l o ca t ed u n d e r t h e f o am

partitions.

The V HF radio transmitter is mount-

ed in the

left

front of the case (not visi-

b le) . I t can be removed for remote

operation or it can be replaced by the

audio amplifier shown below the case.

The two remote VHF radio receivers

are used to receive the target detection

tones that are generated by the radar.

The receivers can pick up the tones up

to a

mile from

the

radar. The three bat-

tery chargers are shown just below the

receivers,

A 50 foot

extension cable

allows the antenna, and transmitter and

receiver units to be remote up to that

distance from the carrying case.

Th e h ig h ly sen s i t i v e co n t in u o u s

wave CW) phase detection radar has

been approved by the Federal Commu-

nications Commission

FCC)

for opera-

tion in the 902 to 928

MHz

frequency

band. There are restrictions imposed by

the FCC which limit the power radiated

from the antenna and signal harmonic

content of any commercially sold prod-

uct using this frequency band. While

this is not necessarily the best frequency

for material penetration, it is

a

reason-

able compromise. This

iq

hecauqe

i t

can

be sold and used commercially, and has

proven to be effective.

A

block d iagram

of

the system is

shown in Fig.

6

There are two different

W kl & V-V

Qne

Way LossThrough

8 Concrete Wall

(a)

H4-I

b n e Way

Loss Through 3

Concrete b}

V-v oneW&

toss

TfIrough

Concrete (c)

%Lo

7 so 4 4 l i a o

;Do

4 2100 A *&lo

FreauencvMHz = Receive Antenna fromW

Fig. 4 One

wa y

loss through 8 inch and

36

inch reinforced concrete

DECEMBER

'97IJANUARY

'98

25


4/4

Fig.

5

The highly porfable

MDR

antenna types used with this system.

One is a high gain directional anten-

na with approximately 9 dB gain. I t

produces a cone shaped pattern that is

+/- 45

degrees wide at the

-3

dB point.

This antenna radiates from the r ight

edge of the thin, 13 inch (33 cm ) square

antenna. It has a front to back ratio of

better than 10:1.

The optional antenna is a very broad

beam omni-directional antenna. The

omni-antenna is round, 114 inches (.63

cm> in diameter, 18 inches

45.75

cm)

long and has a gain of one. The omni-

antenna provides large volume cover-

age in an enclosed region, such as a

r o o m . A l t h o u g h i t p r o v i d e s m u c h

shorter range coverage than the high

gain antenna, it is aspect independent.

It can be placed into a small hole or

dropped into

an

isolated location to

observe motion.

A transmitter and receiver (TR) unit

is mounted on each antenna. A small

cable for power and signal is connected

from the radar control unit to the TR

unit. The length of this cable can be

extended to

100

feet (30.5 meters) or

more for remote antenna operation, or

when i t i s used in throw phones.

(These are ruggedized telephones that

can be thrown through a window or

door to encourage communications with

an uncooperative occupant.)

The si gnal processor restr icts the

sen s i t i v i ty

of the

radar to

motions

between 0.2 feet per second to 5 feet per

second. This covers the range of m otion

that could be expected from a human

being under most conditions.

There are two outputs from the radar.

The first is a relay closure which acti-

vates anytime there is motion detected

above the adjustable threshold setting.

The second is an audio tone which

varies in pitch in proportion to the rate

of motion being detec ted. The pilot tone

is 60 Hz when there is no motion. The

tone r i ses to approximate ly 300 H z

when motion is detected. The tone will

fluctuate in pitch with the motion. This

gives a relative indication of the distance

to the radar and the persons speed.

A hand-held portable, commercial

band (VHF) radio

is

controlled by the

MDR relay. When motion is detected,

th e r ad io t r an smi t t e r i s k ey ed . Th e

MDR audio tone is applied to the mike

jack of the radio. One or more similar

por tab le rad io rece ivers are used to

pickup the transmitted signal at ranges

of up to one mile from the MDR.

Th e develo pmen t of the NLDR system

has been completely an in-house com-

mercial activity. Other hardw are using

similar technology has been developed

for several

US

government organiza-

tions to meet their unique needs.

A number

of

three dimensional

imaging radars have been delivered to

the

US government. These can produce

a three dimensional (3D) image

of

a

person or object in the field of view

with better than

2

inch three dimension-

al image resolution. The very portable

3D system

has

been used in

a

number of

field operations while operating with

portable power.

A modification of the 3D imaging

radar is the two dimensional

2D)

sys-

tem. This system can provide range and

angle to targets through concrete walls

with better than

6

inch range resolution.

T h e 2D system

uses

the same signal

processors and display as the 3D system.

It can be installed on the 3D system in

a

few minutes. Because of the frequencies

and bandwidths required for these more

sophisticated systems, it is not possible

to obtain FCC approval for commercial

applications under the present regula-

tions How ever, the US government is

m ng them available

to

local enforce-

ment agencies w ith prior approval.

Applications for

ground penetration

are being tested and evaluated The key

l im i t a t io n has b een th e n o n - u n iq u e

nature of buried materials and the fact

they

are

not moving It is difficult to tell

the difference between

a

mine and

a

dead tree limb, or pop-bottle, just below

the surface Both can

be

detected by

radar, but there are not enough unique

features to clearly identify the objects.

W e have been researching techniques

that will greatly enhance both the range

and the angle accuracies. The goal is to

obtain enough resolution to automati-

cally extract salient unique features of

objects below the ground.

Frazier, L. M ., Surveillance Through

Walls and Other Opaque Materials,

presented at the IEEE 1996 ational

Radar

Conference,

Ann Arbor Michi-

gan, 13-16 May 1996.

Mr Frazier has been with Hughes/

General Dynamics for 40 years His

experience includes design and field

testing of many different types

of

radar

and sign al processing systems. This

includes both pulsed and continuous

wave radar systems for mono-static

and bi-static radar applications. Over

the past six years, he has developed a

field portable, high resolution three-

dimensional imaging radar which pro-

vides isometric images

of

RF reflective

targets . He has developed the hand

held, motion detection, concrete pene-

trating radar that fits in a briefcase. He

is presently working on new concepts

for ground and wall penetration and

mapping radars.

Fig.

6

Motion detection radar block diagram

26

IEEE POTENTIALS

mdr for law enforcement

Documents