A Technology Review of Smart

Sensors With Wireless Networks

for Applications in Hazardous

Work Environments

IC 9496

INFORMATION CIRCULAR/2007

Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Information Circular 9496 

A Technology Review of Smart Sensors With Wireless Networks 

for Applications in Hazardous Work Environments 

By John J. Sammarco, Ph.D., P.E., Robert Paddock, Edward F. Fries, 

 and Vijia K. Karra, Ph.D.

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

April 2007
This document is in the public domain and may be freely copied 

or reprinted. 

DISCLAIMER 

The information presented in this document is for guidance and illustrative purposes only. 

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external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations 

or their programs or products. Furthermore, NIOSH is not responsible for the content of 

these Web sites. 

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DHHS (NIOSH) Publication No. 2007–114 

April 2007 

SAFER • HEALTHIER • PEOPLETM
CONTENTS 

Page 

Glossary ........................................................................................................................................... i 

Abstract............................................................................................................................................1 

Introduction......................................................................................................................................2 

Technical approach ..........................................................................................................................2 

Sensors .............................................................................................................................................4 

 Smart sensors .............................................................................................................................5 

 Smart sensor standard ................................................................................................................5 

 Body sensors ..............................................................................................................................5 

 BodyMedia system description..................................................................................................6 

 Sensor nodes and smart environments.......................................................................................7 

 Commercial sensor nodes and networks..................................................................................11 

Human interfaces ...........................................................................................................................11 

 Wearable digital displays.........................................................................................................11 

 Display technology ..................................................................................................................12 

 Commercially available wearable displays..............................................................................12 

 MicroOptical Corp.............................................................................................................12 

 Icuiti Corp. .........................................................................................................................13 

Wireless infrastructure...................................................................................................................15 

 Introduction..............................................................................................................................16 

 Network composition...............................................................................................................17 

 Machine-to-machine (M2M) ...................................................................................................20 

 Network data movement..........................................................................................................20 

 Light-based networks...............................................................................................................21 

 Radio-based networks..............................................................................................................21 

 Spread spectrum.......................................................................................................................22 

 Ultrawide band (UWB)............................................................................................................22 

 Why use spread spectrum or UWB?........................................................................................23

 Wireless sensor networks.........................................................................................................23 

 Power .................................................................................................................................24 

 Event-driven.......................................................................................................................24 

 Operating systems..............................................................................................................24 

 Off-the-shelf hardware.......................................................................................................25 

 Protocols ............................................................................................................................26 

 Bluetooth......................................................................................................................26 

 Digital-enhanced cordless telecommunications (DECT).............................................26 

 EnOcean.......................................................................................................................26 

 Ensation........................................................................................................................27 

 IEEE P1902.1TM standard for long wavelength wireless network protocol (RuBeeTM)...27 

 Millennial Net, Inc.......................................................................................................27 

 Near-field communication (NFC)................................................................................28 

 RFID-RadarTM..............................................................................................................28 

 Wi-Fi / WiFi / Wireless fidelity...................................................................................29 

 Wireless personal area network (WPAN) / 802.15.4...................................................29 
CONTENTS—Continued 

Page 

 Wireless USB (Atmel Corp., Cypress Semiconductor Corp.).....................................30 

 Wireless USB (USB forum).........................................................................................30 

 Worldwide interoperability for microwave access (WiMax) ......................................30 

 ZigBee..........................................................................................................................30 

 Z-WaveTM ....................................................................................................................31 

 Radio frequency identification (RFID)....................................................................................31 

 Blocker tags .............................................................................................................................33 

 Location awareness..................................................................................................................33 

Future research...............................................................................................................................34 

 Injured miner (person-down) detection ...................................................................................34 

 Sensor.................................................................................................................................36 

 Microcontroller ..................................................................................................................36 

 System operation................................................................................................................37 

 Wearable wireless remote viewer ............................................................................................38 

 Wireless camera.................................................................................................................40 

 IP camera viewer software.................................................................................................41 

 Wearable display................................................................................................................42 

 Wireless router...................................................................................................................42 

 UWB smart environment .........................................................................................................43 

 Commercial UWB systems................................................................................................44 

 Related research.................................................................................................................44 

Concluding remarks.......................................................................................................................45 

Acknowledgments..........................................................................................................................45 

References......................................................................................................................................45 

Appendix A.—List of useful Web sites.........................................................................................48

ILLUSTRATIONS 

 1. The system model .....................................................................................................................3 

 2. An information-processing model for sensor-based situational awareness..............................3 

 3. Sensors incorporated into the SenseWear® PRO2 armband.....................................................6 

 4. A mesh network of wireless sensor nodes can be used to create a smart mine environment 

 to protect the health and safety of miners during operation and in emergency situations....7 

 5. A sensor node is composed of a sensor(s) and a mote..............................................................8 

 6. The MICAz mote specification.................................................................................................8 

 7. The next-generation mote from Crossbow Technology, Inc. ...................................................9 

 8. Highly specialized motes such as the “Spec” can be used as an advanced RFID tag ............10 

 9. MEMS sensors can be extremely small..................................................................................10 

10. The Kopin CyberDisplay ........................................................................................................12 

11. The SV–6 PC viewer mounted to safety glasses ....................................................................13 

12. The M920–CF does not obstruct the user’s frontal or peripheral line of sight.......................14 

13. The Icuiti M920–CF interfaces to pocket PCs........................................................................15 

14. Star network topology.............................................................................................................18 
CONTENTS—Continued 

Page 

15. Ring network topology ...........................................................................................................18 

16. Mesh network topology ..........................................................................................................19 

17. Radio energy concentration ....................................................................................................22 

18. RFID tags can be very small...................................................................................................32 

19. An emergency stop system concept that uses an RFID ..........................................................32 

20. Basic block diagram of a person-down system.......................................................................35 

21. A wearable accelerometer (MEMSIC model MXD2020GL).................................................36 

22. The BASIC Stamp microcontroller ........................................................................................37 

23. Wayne State University cerebral concussion tolerance curve ................................................38 

24. The locations of 24 remote-control mining fatalities during 1988–2004 ...............................39 

25. This system enables a person to remotely view people or objects in blind spots...................40 

26. The pocket PC buttons are used for controlling the IP camera...............................................42 

27. The Netgear WPN824 RangeMax wireless router..................................................................43 

TABLES 

 1. The key specifications of the BASIC Stamp microcontroller ................................................36 

 2. Detailed specifications of the DCS–5300G IP camera...........................................................41 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

 A ampere 

 bps bits per second 

 cm centimeter 

 cm3

 cubic centimeter 

 fps frames per second 

 ft foot 

 ft2

 square foot 

 g acceleration of gravity 

 GHz gigahertz 

 Hz hertz 

 in inch 

 lb pound 

 kbps thousand bits per second 

 Kbyte kilobyte 

 kHz kilohertz 

 km kilometer 

 km/h kilometers per hour 

 lb pound 

 m meter 

 mA milliamp 

 MB megabyte 

 Mbps million bits per second 

 MHz megahertz 

 mm millimeter 

 mm3

 cubic millimeter 

 mph miles per hour 

 ms millisecond 

 mW milliwatt 

 nA nanoamp 

 oz ounce 

 sec second 

 V volt 

 V ac volt, alternating current 

 V dc volt, direct current 

 μA microamp 
i

GLOSSARY 

 Accelerometer: A sensor that measures acceleration. Acceleration can be due to gravity 

or changing motion. Acceleration is measured in units of Earth’s gravity (g) or meters per second 

squared.

 Bluetooth: A technical industry standard that facilitates communication between wireless 

devices such as mobile phones, personal digital assistants (PDAs), and handheld computers, and 

wireless enabled laptop or desktop computers and peripherals. 

Internet Protocol (IP): The method by which data are sent from one computer to another 

on the Internet. Each IP-based device has at least one IP address that uniquely identifies it from 

all other devices. 

Internet Protocol Security (IPSec): A security protocol that provides for confidentiality 

and authentication. 

Local area network (LAN): A computer network that spans a relatively small area. Most 

LANs are confined to a single building or group of buildings. However, one LAN can be 

connected to other LANs over any distance via telephone lines and radio waves. A system of 

LANs connected in this way is called a wide area network (WAN). 

Machine-to-machine (M2M): Data communications between machines that generally 

refer to telemetry that is accomplished using networks and wireless networks.

Micro-electro-mechanical systems (MEMS): The integration of mechanical elements, 

sensors, actuators, and electronics on a common silicon substrate through microfabrication 

technology. While the electronics are fabricated using integrated circuit process sequences (e.g., 

CMOS, Bipolar, or BiCMOS processes), the micromechanical components are fabricated using 

compatible “micromachining” processes that selectively etch away parts of the silicon wafer or 

add new structural layers to form the mechanical and electromechanical devices [MEMS and 

Nanotechnology Clearinghouse 2007]. 

MIMO (multi-in, multi-out): An advanced technology that uses multiple smart antennas 

to increase range and speeds. The smart antennas constantly survey the environment for physical 

barriers and interference and adjust the wireless signal to compensate for these performance 

inhibitors. 

Network IP camera: A stand-alone camera with a built-in Web server allowing users to 

view live, full-motion video over a computer network or the Internet. The camera also contains a 

CPU and embedded operating system (OS). 

Radio frequency identification (RFID): A transponder technology for the contactless 

recognition of objects. The technology uses an RFID tag—a small computer chip with 

a miniature antenna. When the chip receives the radio signal from a reading device, 

it automatically transmits the stored data wirelessly. 

Sensor: A device or system that responds to a physical, chemical, electrical, or optical 

quality to produce an output that is a measure of that quality. 

Sensor mote: A small, wireless hardware platform that enables sensors to be wireless. 

Typically, motes are battery-powered. 

Sensor node: A fundamental element (node) of a sensor network that consists of a sensor 

mote and sensors. A node typically consists of on-board sensors, memory, wireless connectivity, 

processing power, and a power source. 
ii

Smart sensor: A sensor with built-in intelligence, whether apparent to the user or not. 

The intelligence is partially or fully integrated on a single chip. Smart sensors provide added 

functionality beyond the primary function of producing an output representing a sensed quantity. 

Transducer: A device converting energy from one domain into another and calibrated to 

minimize the errors in the conversion process. 

Ultrawide band (UWB): A radio modulation technique based on transmitting very-shortduration pulses, often on the order of nanoseconds or less, whereby the occupied bandwidth goes 

to very large values. “Ultrawide band” may also refer to anything with a very large bandwidth. 

USB (universal serial bus): A standard interface commonly used to connect peripheral 

devices to computers. 

Wireless fidelity (WiFi): A set of standards for wireless local area networks (WLAN) 

currently based on the IEEE 802.11 specifications. Also known as WiFi, Wi-fi, Wifi, wifi. 

Wireless personal area network (WPAN): A wireless network that serves only the 

individual wireless user. This type of wireless network usually relates to the Bluetooth 

technology, a personal network. 

ZigBee: A proprietary set of high-level communication protocols designed to use small, 

low-power digital radios based on the IEEE 802.15.4 standard for wireless personal area 

networking. 
A TECHNOLOGY REVIEW OF SMART SENSORS 

WITH WIRELESS NETWORKS 

FOR APPLICATIONS IN HAZARDOUS WORK ENVIRONMENTS 

By John J. Sammarco, Ph.D., P.E.,1 Robert Paddock,2 Edward F. Fries,3 and Vijia K. Karra, Ph.D.4

ABSTRACT 

 Workers in hazardous environments such as mining are constantly exposed to the health 

and safety hazards of dynamic and unpredictable conditions. One approach to enable them 

to manage these hazards is to provide them with situational awareness: real-time data (environmental, physiological, and physical location data) obtained from wireless, wearable, smart sensor 

technologies deployed at the work area. The scope of this approach is limited to managing the 

hazards of the immediate work area for prevention purposes; it does not include technologies 

needed after a disaster. Three critical technologies emerge and converge to support this technical 

approach: smart-wearable sensors, wireless sensor networks, and low-power embedded 

computing. The major focus of this report is on smart sensors and wireless sensor networks. 

Wireless networks form the infrastructure to support the realization of situational awareness; 

therefore, there is a significant focus on wireless networks. Lastly, the “Future Research” section 

pulls together the three critical technologies by proposing applications that are relevant to 

mining. The applications are injured miner (person-down) detection; a wireless, wearable remote 

viewer; and an ultrawide band smart environment that enables localization and tracking of 

humans and resources. The smart environment could provide location data, physiological data, 

and communications (video, photos, graphical images, audio, and text messages). 

 

 1Electrical engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

 2President, The Designer-III Co., Franklin, PA. 

 3

General engineer, Pittsburgh Research Laboratory (now with the National Personal Protective Technology 

Laboratory), National Institute for Occupational Safety and Health, Pittsburgh, PA. 

 4

Supervisory general engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and 

Health, Pittsburgh, PA. 
2

INTRODUCTION 

 Workers in hazardous environments such as mining are continually exposed to dynamic 

and unpredictable hazardous conditions. For instance, slipping and tripping hazards are created 

by mine conditions such as water, mud, uneven floors, and mine floor obstacles. Moving 

machinery in the confined mine environment creates pinning and striking hazards. These 

environments also have limited visibility due to line-of-sight restrictions, poor lighting, airborne 

dust, and smoke. Workers must be able to constantly monitor their hazardous environments in 

real time so they can be aware of impending and existing dangers. 

 This report details the current state of the art in smart sensors and wireless sensor network 

technology and some potential applications for situational awareness in harsh, dynamic environments such as mining. The objective is to enable miners to safely manage the hazards produced 

by an ever-changing, unpredictable, dangerous work environment by providing them with realtime environmental and physiological data obtained from wireless, wearable, smart sensor 

technologies. Miners will be able to better manage hazards because smart-wearable sensors 

could provide the key information needed for early warning of potential and existing hazards. 

Thus, these technologies could be useful for preventing injuries and disasters. This report 

does not address in specific detail the topics of intrinsic safety, tracking and locating trapped 

miners, or communication with trapped miners. 

 Numerous technologies and references are presented to help create awareness and common 

understanding of the pros, cons, and application requirements of these technologies. Specifically, 

a glossary of terms is presented at the beginning of the report, followed by sections on sensors, 

wireless networking, and wireless sensor networks. Lastly, the “Future Research” section pulls 

together the technical information by proposing applications that are relevant to mining and that 

could also potentially cross over to other workers such as firefighters, emergency rescue 

workers, and other first responders. The applications for future research are injured miner 

(person-down) detection; a wireless, wearable remote viewer; and ultrawide band localization 

and tracking of humans and resources. 

TECHNICAL APPROACH 

 As stated earlier, the objective is to enable situational awareness of potential and current 

health and safety hazards produced by an ever-changing, unpredictable, dangerous work 

environment. Workers must first be aware of these hazards if they are to safely manage them. 

Safety must be from a system viewpoint. Safety cannot be assured if efforts are focused on parts 

of the system because safety is an emergent property of the entire system. Safety emerges once 

all the parts and interfaces of the system have been identified and integrated. 

 One of the first steps to safety is defining the system. The system model used in the technical approach is shown in Figure 1, where a system is the collection of a human, machine, and the 

environment interconnected to perform a desired function. In the context of this report, the 

system provides a worker with the functionality of situational awareness. The system functionality is depicted by an information-processing model (Figure 2). The key parts of this model are: 

sensing through the use of sensors that measure key attributes of the machine, environment, and 

human; information processing (monitoring, collecting, and displaying) through the use of 

embedded computers; and decision-making and action as done by humans. 
3

Figure 1.—The system model. 

Monitor Process Collect

Display

Decision making

Action

Sense 

Figure 2.—An information-processing model for sensor-based situational awareness. 
4

 Three critical technologies emerge and converge to support this information-processing 

model. They are wireless networks for sensors, low-power embedded computing, and smart 

sensors. Computer and smart sensor technologies have advanced rapidly; they are relatively 

mature technologies. Wireless networks for sensors are still emerging. Robust wireless networks 

are the key part of an infrastructure to support the realization of wireless smart sensor networks 

that provide users with situational awareness of their environment. Therefore, this report has 

placed the greatest focus on wireless networks for sensors. The second major focus is on smart 

sensors that range in size from a “spec” to a matchbox. Lastly, the “Future Research” section ties 

together all three technologies by proposing multiple applications that could improve the health 

and safety of workers in hazardous, dynamic environments. 

SENSORS 

 A sensor is a device or system that responds to a physical, chemical, electrical, or optical 

quality to produce an output that is a measure of that quality. A simple sensor has two parts: 

a sensing element and a transducer that converts the sensed quality to a representative signal. 

 Sensor technology plays a key role in situational awareness. Sensors are needed to measure 

the critical parameters of the environment, machines, and the human. In this report, sensors are 

grouped into five classifications: 

 • Chemical 

 • Electric, magnetic, electromagnetic wave 

 • Heat, temperature 

 • Physical (mechanical displacement) 

 • Optical 

 Sensors, regardless of the classification, are characterized by the specification of various 

parameters. The parameters of importance largely depend on the application. These parameters 

include: 

 • Sensitivity 

 • Stability 

 • Accuracy 

 • Hysteresis 

 • Drift 

 • Cost, size, weight 

 • Range (span) 

 • Resolution 

 • Linearity 

 • Environmental (temperature, shock, vibration, etc.) 
5

SMART SENSORS 

 A sensor with built-in intelligence, whether apparent to the user or not, can be referred to 

as a “smart” sensor. The intelligence is partially or fully integrated on a single chip. Smart 

sensors provide added functionality beyond the primary function of producing an output 

representing a sensed quantity. 

 Typically, a smart sensor contains a physical transducer, a network interface, a processor, 

and a memory core that can all be fabricated on a single die [Kovacs 1998; Frank 2000]. The 

physical transducer can be made very small because silicon micromachining technology that is 

used to make integrated circuits is now being used to create micro-electro-mechanical systems 

(MEMS) that can be an integral part of a smart sensor. 

 It is anticipated that the cost and functionality of smart sensors will progress at rates 

similar to those experienced by other integrated circuits, such as microprocessors and memory, 

because smart sensors use much of the same technology [Frank 2000]. Smart sensor growth 

should also increase now that a smart sensor standard is in place. 

SMART SENSOR STANDARD 

 The smart sensor standard, Institute of Electrical and Electronics Engineers (IEEE) 

1451.2–1997, was developed to define a flexible, standard interface that would enable any smart 

sensor from any manufacturer to connect to a multinode network of smart sensors [IEEE 1998]. 

The standard defines a standard transducer interface module (STIM) that includes the sensor 

interface, signal conditioning and conversion, calibration, linearization, and network 

communication. In essence, IEEE 1451.2–1997 enables plug and play functionality for smart 

sensors that connect to smart sensor networks. 

BODY SENSORS 

 Wearable body sensor systems are available to continuously measure and monitor the 

physiological conditions of workers in real time. BodyMedia has produced a wearable body 

sensor system (Figure 3) that acquires, analyzes, transmits, and stores physiological data such as 

energy expenditure, duration of physical activity, number of steps, distanced traveled, 

sleep/wake states, movement, heat flux, skin temperature, and galvanic skin response. 

 The system is used mainly as a health and safety research tool. For instance, PPG 

Industries used the BodyMedia system to monitor the activity level and energy expenditure 

trends of their shift workers. The data obtained were used to reduce job-related fatigue and 

improve the ergonomic design of equipment. Fatigue is a significant health and safety hazard for 

shift workers in general, but it is of special concern for miners who must keep alert to recognize 

moving machinery hazards, trip/slip hazards, and potential falls of ground from the roof, ribs, 

and back areas. 

 The BodyMedia system has applications beyond that of a research tool. For instance, the 

system can monitor workers and alert them of potentially dangerous physiologic conditions from 

overexertion. This same application crosscuts to first responders such as firefighters who, while 

wearing protective equipment, expend large amounts of energy for sustained periods in 

hazardous atmospheres of heat and smoke. The BodyMedia system can also be used in persondown applications. The physiological data can be used to indicate that a person has become 

incapacitated because of an accident or a health condition. The system would then wirelessly 

alert other workers or rescue personnel of the worker’s condition. 
6

Figure 3.—Sensors incorporated into the SenseWear® PRO2 armband. (Image courtesy of BodyMedia.) 

BODYMEDIA SYSTEM DESCRIPTION 

 The major features include the following: 

 • Can be worn up to 14 days continuously without changing the battery 

 • Stores up to 14 days of continuous physiological data 

 • Allows users to time-stamp specific events 

 • Compatible with BodyMedia InnerViewTM software 

 • Eliminates the need to apply cumbersome sensors to research subjects 

 The heart of the system is the SenseWear® PRO2 armband that is worn on the back of the 

upper right arm. The battery-powered device contains a dedicated sensor ensemble that is useful 

for the direct and indirect measurement of physiological data. The sensors for direct measurements (Figure 3) are listed below: 

 • Accelerometer (two-axis) 

 • Heat flux 

 • Galvanic skin response 

 • Skin surface temperature 

 • Near-body temperature 
7

 The sensor data can be used for indirect measurements. This is possible via the use of 

virtual sensors, sensor fusion, digital signal processing, and Kalman filtering. Derived measurements include: 

 • Total calories burned 

 • Duration of physical activity 

 • Number of steps 

 • Resting energy expenditure 

 • Active energy expenditure 

SENSOR NODES AND SMART ENVIRONMENTS 

 Sensor nodes are critical elements of a smart environment to protect the health and safety 

of miners during operation and in emergency situations. Figure 4 depicts a smart mine 

environment that can provide interactivity and situational awareness of the mine environment, 

machinery, and people. Sensor nodes are used in this smart mine environment to provide 

communication and to acquire data about mining machine postion, mine roof and rib conditions, 

crosscut traffic, the location and status of miners, and the mine atmosphere such that the data can 

be used to alert miners of health and safety hazards during operation. For instance, the smart 

environment would automatically provide an alert that a miner has been struck by falling roof 

even though the miner is incapacitated. This application is detailed later in this report. The 

functionality of this smart environment could be expanded to help miners find the best escape 

route or find other miners in emergency situations, especially when smoke obscures visibility. 

 Limited or even zero visibility environments are also common to firefighters. A smart 

building environment could provide health and safety functions similar to that of a smart mine 

environment. Firefighters could find escape routes even under zero visibiltiy, or they could 

locate fallen firefighters who are unable to communicate their condition or location. 

 Figure 4.—A mesh network of wireless sensor nodes can be used to create a smart mine environment to 

protect the health and safety of miners during operation and in emergency situations. 
8

 A sensor node consists of a mote and sensors, as shown in Figure 5. Nodes typically have 

on-board processing power, on-board memory, wireless connectivity, sensors, and a small 

battery power source. A mote is a small, wireless hardware platform that enables sensors to be 

wireless. Motes can be highly specialized or general purpose; they can be of low bandwidth to 

support the transfer of limited data or high bandwidth to support the transfer of streaming video, 

graphics, and audio. 

 The MICAz (Figure 6) is a commercially available, high-bandwidth sensor mote from 

Crossbow Technology, Inc. It enables the creation of low-powered, wireless sensor networks that 

can collect data on physical and environmental properties such as temperature, acceleration, and 

vibration. The mote is small and battery-operated for use in wearable sensor applications. The 

power requirements are very low, making the motes a good choice for use in hazardous 

environments. The MICAz mote with its associated software also complies with the ZigBee 

protocol standard. 

 

 Figure 5.—A sensor node is composed of a sensor(s) and a mote. (Image copyrighted by Crossbow 

Technology, Inc., and reprinted with permission.) 

Name and size 

Applications 

Radio data rate 

MIPS 

Flash 

RAM 

Energy usage (typ.) 

Sleep energy (typ.) 

Duty cycle (typ.) 

MICAz, 1–10 cm3

High bandwidth sensing such as 

image transfer, audio, and vibration 

<500 kbps 

<50 

<10 MB 

<128 kB 

3 V × 60 mA 

3 V × 100 μA 

5%–10% 

 Figure 6.—The MICAz mote specification. (Image copyrighted by Crossbow Technology, Inc., and reprinted 

with permission.) 
9

 Sensor motes are rapidly developing in terms of size and cost reduction, and increasing 

functionality. For instance, the next-generation MICAz mote will be offered in a much smaller 

physical package. Figure 7 depicts this new mote, which is about the size of a postage stamp, 

yet it has the same functionality as the MICAz mote and lower power requirements. Smaller 

motes such as the “Spec” shown in Figure 8, also called smart dust, are available now; however, 

these motes are extremely limited in terms of functionality and bandwidth. The Spec can be used 

as an advanced, low-cost, radio frequency identification (RFID) tag. The small size enables these 

motes to be embedded virtually anywhere; the low cost makes them a disposable item that can be 

left behind. Size and cost reductions will drive its widespread usage. Some of the key features 

include the following: 

 • Lifetime longer than 3 years 

 • Size smaller than 1 mm3

 • Price less than 15 cents 

 Sensors are the other part of a sensor node. They too are rapidly developing in terms of 

size, cost, and functionality. For instance, a MEMS dual-axis acceleration sensor, shown in 

Figure 9, is featured in a “person-down” application described later in this report. 

 Figure 7.—The next-generation mote from Crossbow Technology, Inc. (Image copyrighted by Crossbow 

Technology, Inc., and reprinted with permission.) 
10

Name and size 

Applications 

Radio data rate 

MIPS 

Flash 

RAM 

Energy usage (typ.) 

Sleep energy (typ.) 

Duty cycle (typ.)

“Spec”, mm3

Specialized, single-purpose sensor, 

or advanced RFID tag 

<50 kbps 

<5 

<0.1 MB 

<4 kB 

1.8 V × 10 to 18 mA 

1.8 V × 1 μA 

0.1%–0.5%

 Figure 8.—Highly specialized motes such as the "Spec" can be used as an advanced RFID tag. The small 

size makes wearable sensor nodes practical. (Image copyrighted by Crossbow Technology, Inc., and 

reprinted with permission.)

MEMS Sensor Wireless Node

Figure 9.—MEMS sensors can be extremely small. This sensor measures acceleration. 
11

COMMERCIAL SENSOR NODES AND NETWORKS 

 Commercial wireless sensor nodes and networks are becoming available and will also 

continue as an area for research [Culler et al. 2004]. Sensor nodes can be purchased as part of 

complete wireless sensing systems that contain tools for development and prototyping. Crossbow 

Technology, Inc., offers an extensive line of wireless sensing systems, kits, nodes, and motes. 

Other systems include: 

 • Ambient Systems μNode 

 • Intel iMote 

 • Microstrain X-link 

 • Caiser from Cambridge Silicon Radio 

 • Ember motes 

 • Lynx Technologies motes 

HUMAN INTERFACES 

 Wearable wireless sensor ensembles can be used to provide a wealth of continuous, realtime data that can be used to communicate the health and safety of people, the location and 

identification of people and critical assets, and the state of the environment. All the data acquired 

and processed by wearable wireless sensor ensembles can be useless unless the data can be 

quickly and richly conveyed to people without encumbering those people to obtain and view the 

data. Therefore, the human interface is a vital part of the system. 

WEARABLE DIGITAL DISPLAYS 

 Wearable digital displays can provide the equivalent of a desktop monitor or a personal 

digital assistant (PDA) screen, yet they are small, lightweight devices that can be worn. For 

instance, the M920–CF video display by Icuiti Corp. weighs only 3.5 oz, yet it provides a video 

display equivalent to a 1-in color monitor. 

 Wearable digital displays are also known as head-mounted displays, helmet-mounted 

displays, and personal monitors. These displays are grouped into three categories: 

 • See-around displays – Provide visual information without obstructing the user’s view of 

 the surroundings or task at hand. 

 • See-through displays – Superimpose images onto the user’s panoramic view. 

 Applications include entertainment, military operations, and maintenance support. 

 • Immersive displays – Typically used for training and entertainment applications, such as 

 for simulators and virtual reality. 

 The see-around displays are the most practical for people working in hazardous 

environments. These displays allow hands-free operation and they do not obstruct the user’s 

view; thus, see-around displays are the primary focus here. 
12

DISPLAY TECHNOLOGY 

 Kopin Corp. is a leading developer and manufacturer of ultrasmall, high-density imaging 

devices for consumer, industrial, and defense systems. The Kopin CyberDisplay (Figure 10) is a 

rugged, robust display that is well suited for harsh, demanding environments such as those found 

in mining and first-responder applications. This is the microdisplay standardized for the U.S. 

military.

 The color and monochrome CyberDisplays use nanotechnology to make active-matrix 

liquid crystal displays (AMLCDs). This technology helps enable the highest resolution and 

performance available today for AMLCDs. The CyberDisplay is incorporated in numerous 

commercially available wearable display products. 

Figure 10.—The Kopin CyberDisplay. (Image courtesy of Kopin Corp.) 

COMMERCIALLY AVAILABLE WEARABLE DISPLAYS 

 There are many commercially available wearable display products available today; 

however, those from MicroOptical Corp. and Icuiti Corp. seem well suited to harsh environment 

applications because they are used for harsh and rugged military applications as opposed to other 

displays used for home entertainment and commercial products such as cameras, cell phones, 

and video recorders. 

MicroOptical Corp. 

 MicroOptical Corp. offers two categories of wearable displays: VGA viewers (Figure 11) 

and video viewers [MicroOptical 2007]. Both viewers can be mounted directly to existing 

eyewear such as prescription glasses or safety glasses. The viewers can be mounted for left-eye 

or right-eye viewing. 
13

 The SV–6 PC is a VGA viewer. The key specifications are as follows: 

 • Display: 

 – VGA LCD panel 

 – 640 × 480 resolution in true color 

 – Field of view: 16o horizontal, 20o diagonal 

 – Image appears as if projected at a distance of up to 15 ft 

 – Independent focus of 2–15 ft 

 • Weight: 2.5 oz 

 • Display interfaces: 

 – Compact Flash Type II 

 – PCMCIA via optional adapter 

 – Windows® Pocket PC® 2000–2003 

 • Video input formats: 

 – VGA, SVGA, XVGA 

 – 18-bit color 

Figure 11.—The SV–6 PC viewer mounted to safety glasses. (Image courtesy of MicroOptical Corp.) 

Icuiti Corp. 

 Icuiti Corp. also offers a VGA display, the Icuiti M920–CF, and a digital video display, the 

Icuiti M920–VIDEO. Both displays are see-around displays that can be worn with protective 

equipment such as safety glasses and hardhats (Figure 12). Both interface to a wide variety of 

devices such as pocket PCs, laptop PCs, portable media players, and video cameras (Figure 13). 

Currently, the displays use a single-wire connection. Future plans by Icuiti are to provide a 

wireless model. 
14

 The key specifications of the Icuiti M920–CF are as follows: 

 • Display: 

 – VGA LCD panel (920,000 pixels) 

 – 640 × 480 resolution in true color 

 – 26° field of view 

 – Image appears as if projected at a distance of 11 ft 

 – Independent focus 

 • Weight: 3.5 oz 

 • Display interfaces: 

 – Compact Flash Type II 

 – PCMCIA Via optional adapter 

 – Windows® Pocket PC® 2000–2003 

 • Video input formats: 

 – VGA 

 – 16-bit color 

Figure 12.—The M920–CF does not obstruct the user’s frontal or peripheral line of sight. 
15

Figure 13.—The Icuiti M920–CF interfaces to pocket PCs. 

WIRELESS INFRASTRUCTURE 

 This section gives an overview of wireless technologies and wireless sensor networks. 

Wireless devices are constructed with three major sections: (1) data acquisition, (2) data 

transportation, and (3) data presentation. Data acquisition is the acquiring of data of interest. The 

data may be physiological data, such as a person’s heart rate, or data on the environment, such as 

gas level concentrations. Data transportation is moving data items of interest from a source 

device, such as a gas sensor, to a destination device, such as a display or database. Data 

presentation is the displaying or annunciation of the acquired data in some usable form. 

 The focus in this section is on data transportation. The underlying networking topologies 

are addressed, as well as the tradeoffs of each wireless technology with respect to physical size, 

data rate, and power consumption. Also addressed are a brief introduction to RFID and the 

problems of location awareness, i.e., the ability to know the location of an object in threedimensional (3–D) space. 
16

INTRODUCTION 

 Emerging wireless networking technologies are opening up opportunities for new systems, 

achieving significant cost savings in equipment design and maintenance, as well as significant 

reductions in time-lost incidents due to injuries, in mining operations. 

 When a machine operator uses a wired control pendant, he or she must be constantly aware 

of the tangle and tripping hazards presented by the wires. Full concentration is not focused on the 

task at hand. By removing the wires from the proximity of operators, the tripping and tangle 

hazards are removed, allowing the operator to fully concentrate on the task at hand, thereby 

increasing productivity. Also, data transmitters worn by the operators can act as personal 

“shield” devices that automatically shut down equipment when the operator enters an unsafe 

location, such as a pinch or pinning area. Emerging ultrawide band (UWB) technology now 

allows for personal/asset tracking applications that were impossible to implement less than 

2 years ago. 

 Significant reductions in maintenance downtime can be achieved by replacing the 

notoriously weak links of cables and connectors with wireless devices. Once the connectors are 

removed from equipment, it becomes easier to seal, leading to less downtime. 

 Device costs may be significantly reduced by removing displays from equipment that are 

often hard to read and in dangerous locations. The displays are replaced by a single display 

device, such as a PDA-style device, carried by the operator. Virtual displays allow for easy-touse operator interfaces, while keeping the device node cost low. This is because each device no 

longer has to include the cost of the physical display and related packaging issues. The PDA-like 

device becomes an easy-to-update diagnostic/control device, while simultaneously removing the 

need to continually update the wireless device nodes throughout the mine. 

 A network of wireless sensors can gather environmental data during mine operations to 

demonstrate compliance and real-time status information, as well as during and after mine 

reclamation processes. 

 In the ideal world, it would be possible to transmit an infinite amount of data in zero 

amount of time while consuming no energy to accomplish the task. In the real world, there are 

tradeoffs that must be made among data rates, energy consumption, physical size, security, and 

costs of units. These tradeoffs have resulted in a number of different, usually incompatible, 

network systems that optimize certain attributes at the expense of the others. 

 Conceptually, networks are constructed of physical and logical layers, typically seven. 

Most commonly used is the Open Systems Interconnection Seven-layer Reference Model 

[Wetteroth 2002]. Layer 1 of the reference model deals with the physical real world, with 

physical hardware such as wires, radio hardware, or optical systems. The remaining layers 

implement a protocol stack. A protocol stack is two or more layers of software and hardware that 

build upon each other to form a system that manages the data flow of a communication channel 

according to the rules of a particular protocol. 

 A number of different protocol stacks have been created to solve different problem 

domains. Some stacks have been optimized for lower power/low data rates; others have been 

optimized for high data rates with no consideration to energy consumption. Later in this report, 

a number of wireless protocol stacks will be summarized and their application to wireless sensor 

networks in a mining environment described. 
17

NETWORK COMPOSITION 

 Networks are composed of a number of devices called nodes. The nodes are arranged in 

various configurations, such as master/slave networks, mesh networks, peer-to-peer networks, 

star networks, or ring networks. 

 There are two general types of networks or combination of the two types: peer-to-peer 

networks and master/slave networks. In a peer-to-peer network, all nodes are equal in terms of 

priorities; they will negotiate with each other to determine which gets control of the network at 

any given moment. In the master/slave topology, the master node directs all network activity. 

It directs which slave may access the network at any given time. 

 In a star network (Figure 14), the slave nodes are connected solely to a fixed master node 

that directs slave node communication. The master will relay messages between the slave nodes 

as required. Star networks are the easiest to set up and manage; however, they have a singlepoint failure problem in that if the master node goes down, the entire network goes down. 

 In a ring network (Figure 15), the master is not a fixed node. Each node becomes a master 

by passing a “token.” The node that has the token is the master until it relinquishes the token to 

the next node in the ring. In a single-direction ring topology, a break in two sections of the 

network disables the network. In a bidirectional ring topology, the token may flow in both 

directions, clockwise or counterclockwise. This gives redundancy to the network even if both 

connections are down between two adjacent nodes because one node can loopback the clockwise 

traffic toward the counterclockwise connection and the other node can loopback the other way 

around. Therefore, the logical ring remains intact and the network remains functional. However, 

the network speed may be reduced as the time it takes the token to transverse all of the nodes 

increases. For instance, it would take one “hop” to go from node 1 to 2 in an intact bidirectional 

ring topology; however, multiple hops are needed if there is a break between nodes 1 and 2. 

While the number of nodes remains fixed, the number of hops changes with damage to the ring, 

thus decreasing performance.

 A new standard of networking is beginning to emerge for wireless sensor networks known 

as mesh network (also called multihop networks) (Figure 16). It is so named because it appears 

as a mesh fishing net when lines are drawn between each node to the neighboring nodes. Unlike 

a conventional network, a mesh network does not have a central computer that orchestrates 

communication with the nodes. Each node acts as a router for the neighboring nodes. The 

concept would be like having a cell phone network with no towers. As long as there are cell 

phones between the phone placing the call and the destination phone, each phone along the way 

passes on the phone call data. 
18

Figure 14.—Star network topology. 

Figure 15.—Ring network topology. 
19

Figure 16.—Mesh network topology. 

 Mesh networking is particularly suited to machine-to-machine (M2M) and wireless 

networks, allowing for instant growth in an unpredictable, constantly changing environment such 

as a mine. 

 Typically, nodes are as small as the technologies will allow, but in Portsmouth, U.K., the 

city buses comprise the nodes of the network that allow passengers to check arrival times at the 

bus stop [Rupley 2004]. Mining vehicles acting as nodes can act as relay stations for smaller 

nodes, as well as report on their own position to a central control system. Data gathered from 

position reports may be analyzed to locate traffic bottlenecks, which, once removed, lead to 

increased production. 

 A mesh network has two subdivisions: full-mesh topology and partial-mesh topology. In 

the full-mesh topology, each node is connected directly to each of the others. In the partial-mesh 

topology, some nodes are connected to all the others, but some of the nodes are connected only 

to other nodes with which they exchange the most data. 

 It would be a waste of bandwidth for each node to talk to each of its adjacent nodes for 

every data transaction, so each node keeps some sort of routing table that tells it to which of its 

neighbors a packet with a particular address should be forwarded. Networks can be either fixed, 

where the number and connection of the individual nodes are generally static, or fixed in place. 

However, the connections and number of nodes can change if a node is switched off. An ad hoc 

network differs in that the routing will dynamically change or adapt as its nodes experience 

changes, such as being physically moved. 

 Mesh networks have the capability to provide: 

 • Effortless installation of a communications infrastructure 

 • Enhanced reliability via route redundancy 

 • Extended distance and communication speed 

 • Extensions of network coverage without increasing transmit power or receive sensitivity 

 • Increased speed 

 • Low power 

 • Resiliency, with no single point of failure 

 • Self-configuration, self-diagnostics, and self-healing 
20

 Interference and other factors that lead to the loss of data increase as distance increases. 

Mesh networks increase bandwidth and robustness of the network using multiple short hops. 

Also, little power is required to transmit signals over short distances, allowing for the overall 

network power to exceed the Federal Communications Commission (FCC) limitations on the 

maximum transmission power levels of a single transmitter. The analogy is the difference 

between a shout and a whisper. 

 Mesh networks can perform multihop firmware field upgrades either over the air or 

through other nodes within a logical mesh network. This is crucial in maintaining the firmware 

integrity of large networks. This upgrade feature is particularly useful in mining environments 

where the unit must remain sealed and may be in locations difficult to access. However, the 

ability to do over-the-air upgrades also opens the network up to potential compromise by viruses 

unless security issues are considered as part of the system safety design. 

 Currently, there are no standards governing mesh networks, which means you have to stick 

with one mesh vendor or construct bridges between the different mesh networks. The Internet 

Engineering Task Force (http://www.ietf.org) is evaluating two ad hoc mesh network standards: 

the Mobile Ad hoc Networking (MANet, http://www.ietf.org/html.charters/manet-charter.html) 

and Ad hoc On-demand Distance Vector published by the National Institute of Standards and 

Technology. 

 Of all topologies, mesh networks are the best suited to the mine environment due to the 

constantly changing mine environment. 

MACHINE-TO-MACHINE (M2M) 

 SensorLogic has published the M2MXML protocol and put it in the public domain at: 

http://www.m2mxml.org. The purpose of the M2MXML project is to develop an open-standard 

Extensible Markup Language (XML) based protocol for machine-to-machine (M2M) 

communications. The primary design philosophy of M2MXML is simplicity. Other attempts to 

develop protocols for M2M communications have resulted in protocols that are difficult to 

understand and too verbose to be used in small devices with limited communications bandwidth. 

 One of the goals of M2MXML is to establish an open standard that can be adopted by 

device manufacturers and M2M application developers, thus allowing some interoperability that 

does not exist today. 

 By using M2M communication standards each manufacturer can concentrate on its core 

markets while interoperating with other manufacturers. When wireless connection standards are 

used, even issues of different styles of connectors and cabling are removed. 

NETWORK DATA MOVEMENT 

 Regardless of the protocol stack or network topology, there are two styles of data movement in networking: datagrams and virtual circuits. 

 Datagrams contain all source and destination information in their message packet and are 

conceptually similar to mailing a letter at the post office. The envelope contains the desired 

address and the return address, making the data packets larger. Each node in the network only 

needs to know how to route the envelope to the next node along the way. No knowledge of 

previous nodes is retained or needed, but effort is expended at each node to get the envelope to 

its destination. Datagram networks are robust in one sense because nodes could be shut down or 
21

fail after the envelope has been passed to the next node with no consequence to the delivery of 

the envelope. However, datagram networks are unreliable in the sense that there is no guarantee 

that the envelop will be delivered. 

 Virtual circuits are conceptually similar to making a phone call. It takes a bit of effort to 

initiate the call via establishing the best route through the network, but virtually no effort to 

maintain the call, leading to a significant energy savings. Once the connection between the caller 

and the destination is established, that route is maintained until the connection is terminated or 

the equipment fails. 

 At the physical layer, there are two broad classifications of data networks: (1) those that 

use wire, or fiber optics, to move data from point to point, and (2) those that do not use wire, but 

instead use wireless media such as light or radio waves. 

LIGHT-BASED NETWORKS 

 Light-based systems may use visible light or invisible infrared light. Point-to-point lightbased wireless technology is commonly found on computers, PDAs, and cell phones. The 

Infrared Data Association (IrDA) defines specifications for infrared wireless communications 

typically used for distances of less than 2 m (6.6 ft). However, light-based systems may be used 

over significant distances and for many-to-many point transfers. 

 Networks based on diffuse infrared light saturate a confined space rather than requiring 

directional orientation, as do IrDA-based systems. Diffuse networks are used in areas where 

security is paramount because, unlike radio waves, the light waves do not penetrate walls. 

Diffuse networks can work in dusty environments as each dust particle acts as a diffuser, but the 

overall distance range will be somewhat reduced. 

 Light-based systems will always use an error-checking or correction system because of 

the prevalence of infrared sources in the environment. For example, a spider building a web on 

the front of an infrared motion sensor would look like a 6-ft-tall person walking past the sensor 

10 ft away. 

RADIO-BASED NETWORKS 

 Radio transmissions occupy a particular frequency or range of frequencies (Figure 17). The 

style of transmission, such as AM or FM, will occupy a certain width of frequencies centered 

around (on) a particular frequency. The occupied frequency width around the center frequency is 

known as bandwidth. A typical analog voice signal sent using frequency modulation (FM) will 

occupy up to 30 kHz. As frequencies are a limited resource, means for sharing the frequencies 

simultaneously by different devices and users have been developed. In radio-based networks, 

Spread spectrum and UWB are the most common of the frequency-sharing methods. 
22

 Figure 17.—Radio energy concentration. (Image courtesy of Loop Start Consulting Group, Leesburg, VA.) 

SPREAD SPECTRUM 

 In continuing with the FM voice transmission example, when using spread spectrum 

techniques the 30-kHz voice signal will have the radio energy of 30 kHz divided up into a 

bandwidth of 5 MHz. (Spread spectrum signals may use more or less than 5 MHz depending on 

the FCC frequency allocations.) The overall energy of the radio transmission remains the same, 

but the radio energy at any given frequency within the 5-MHz bandwidth is now approximately 

1,000 times smaller. The signal is so small, in fact, that it appears as radio background noise to 

non-spread-spectrum receivers. Special processing is required by the receiver to separate the 

signal of interest from the background noise and to reconstruct the 30-kHz signal. 

ULTRAWIDE BAND (UWB) 

 A new form of radio signal is just now emerging from the research labs into real-world 

products known as ultrawide band (UWB) signaling. It is similar in concept to spread spectrum 

except that instead of being spread across a few million frequencies (5 million in our spread 

spectrum example), the signal of interest is now spread across billions of frequencies at power 

levels so low they are hard to comprehend. 

 UWB has unique properties due to the extremely short and fast pulses used to comprise the 

UWB signal. It does not use a radio carrier as all conventional radio frequency devices would. 

Short pulses allow for accurately pinpointing the location of people and objects. This cannot be 

done using longer signal wavelengths. UWB radar signals are also being used in x-ray visionlike applications, so that even behind-the-wall movements of terrorist suspects may be seen. 

Applications to mining are numerous. Examples include locating trapped miners after a 

hazardous event and looking into the coal face to assess depth of coal/rock interface. 

 UWB signals are digitally based rather than analog-based as all radio technology has been 

in the past. UWB technologies are designed to cost significantly less than current radio 

technology. Current radio technologies rely on expensive selection filters and tuning processes to 

pass only the signals of interest. By the very nature of UWB, such expensive filters are not 

needed. 
23

WHY USE SPREAD SPECTRUM OR UWB? 

 Through the use of spread spectrum or UWB techniques, the radio spectrum may be shared 

by simultaneous users and devices. If narrow band signals are used, there are a limited number of 

frequencies that can be used simultaneously before signals start to interfere with each other. 

Spread spectrum and UWB offer numerous advantages that are especially important for 

applications in hazardous environments. Major advantages of spread spectrum are: reduced 

crosstalk interference, very good data integrity with less static noise, less susceptibility to 

multipath fading, and very good coexistence with other systems such that it doesn’t create severe 

interference with other systems. UWB advantages include: high data rates, low power (suitable 

for battery-powered applications), very good coexistence with other systems, relative immunity 

to multipath problems, and precise ranging or distance measurements that can be used for 

location identification. 

WIRELESS SENSOR NETWORKS 

 A combination of factors (recent catastrophic natural disasters, terrorist activities, rapidly 

deteriorating infrastructure, and increasing costs for new construction) point to the need for a 

robust, low-cost, low-power, and high-performance autonomous wireless monitoring system for 

the health and safety of workers in mines, in buildings, on bridges, and on other civil structures. 

Wireless sensor networks enable the remote monitoring and management of critical devices 

while providing data to enable more informed decision-making, better control, and increased 

revenue opportunities. 

 In the past, wired networks made many ideas economically or physically impossible to 

consider. Wireless sensor networks are opening the door to a new world of opportunities in 

supply chain logistics, data collection, system monitoring, and control applications. Actuators, 

gauges, and sensors can now be monitored and controlled wirelessly, obviating the expensive 

installation and maintenance of copper or fiber-optic cables. 

 The basic goals of a wireless ad hoc sensor network generally depend on the application. 

However, the following tasks and examples are common to many networks: 

 1. Determine the value of some parameter at a given location: In an environmental 

network, one might want to know the temperature, atmospheric pressure, gas concentrations, and 

the relative humidity at a number of locations. This example shows that a given sensor node may 

be connected to different types of sensors, each with a different sampling rate and range of 

allowed values. 

 2. Detect the occurrence of events of interest and estimate parameters of the detected 

event or events: Has someone entered a restricted area or area with a high risk of injury (e.g., 

a pinch point), has a ground fault been detected, etc.? 

 3. Classify a detected object: Make decisions based on the quality of the coal or ore, 

i.e., its disposition while in motion. 

 4. Track an object: Direct a battery hauler to the next free dumping station, return it to the 

next machine ready to unload, etc. 
24

Power 

 The key to an effective wireless sensor network is power. An iPod or cell phone can be 

recharged every night, but what about items that can never be recharged? Pacemakers, 

implantable physiological monitors, and mine environmental sensors in physically inaccessible 

or dangerous locations are examples of devices that must function for years without the power 

source ever being replaced. 

 In the application of wireless sensor networks, called a smart sensor network, the 

conservation of power is paramount. The average inactive (sleep) current consumption goal of 

each independent node is to be as low as possible. Current technologies place this in the 200-nA 

to 10-μA range. There are two different schools of thought on power consumption by network 

nodes. The first is that when a task needs to be executed, get the work done as fast as possible 

even if it means high peak currents into the hundreds of milliamps, so that the node can return to 

sleep as fast as possible. The opposing school of thought is that the average current consumption 

should be kept low, taking as long as needed to do the job at the slowest speed acceptable, as 

current consumption is proportional to speed. When the task is completed, return to sleep. 

 At the extreme low-power end of the energy consumption spectrum are some switches and 

sensors that require no power at all because they use piezoelectric generators as switch elements 

or gather energy by small changes in environmental pressure. The mechanical act of pressing the 

button generates enough power for the switch to power the wireless node transmitter long 

enough to transmit the state of the switch. Handheld remote controls with up to eight single 

pushbuttons or up to four rocker switches with medial positions can be constructed. Issues of 

batteries or power supply wires are completely eliminated. However, there are many safety 

issues to consider if these switches are used for emergency stop applications [Sammarco 2005]. 

 Startup EnOcean GmbH (Oberhaching, Germany) has introduced a solar-powered wireless 

sensor module. The STM100 unit includes three analog and four digital sensor connections, but 

not the sensors themselves, and integrates them with a controlling microprocessor, an RF 

transceiver, and light energy capture and storage in a module measuring 20 mm by 40 mm by 

10 mm. The two-stage solar cell reservoir system will operate in lighting levels as low as a 

typical hallway light. The energy storage is sufficient for the module to operate continuously for 

up to 5 days in complete darkness. These solar-powered wireless sensor modules would be 

applicable to surface mining applications or could be recharged with a simply flash of a caplamp 

light every few days. 

Event-driven 

 To conserve energy, wireless sensors are event-driven, i.e., they sleep until some stimuli 

causes them to wake up and take action. The stimuli may be a periodic timer expiring, a change 

in a monitored environmental condition, or direct user interaction. An operating system is 

required to handle such events and coordinate network traffic. 

Operating Systems 

 Considerable work has been done by the academic community to create an operating 

system that will run on small low-cost, low-power systems. Initially funded by the Defense 

Advanced Research Projects Agency (DARPA), an operating system specifically designed for 
25

wireless sensor networks was created at the University of California, Berkeley [Hill 2003]. The 

wireless sensor operating system known as TinyOS has become the premier operating system for 

sensor network research. 

 TinyOS is an open-source operating system designed for wireless embedded sensor 

networks. It features a component-based architecture that enables rapid innovation and 

implementation while minimizing code size as required by the severe memory constraints 

inherent in sensor networks. TinyOS’s component library includes network protocols, distributed 

services, sensor drivers, and data acquisition tools, all of which can be used as is or be further 

refined for a custom application. TinyOS’s event-driven execution model enables fine-grained 

power management, yet allows the scheduling flexibility made necessary by the unpredictable 

nature of wireless communication and physical world interfaces. 

 TinyOS has been ported to over a dozen platforms and numerous sensor boards. A large 

community uses it in simulation to develop and test various algorithms and protocols. More than 

500 research groups and companies are using TinyOS on the Berkeley/Crossbow motes. 

Numerous groups are actively contributing code to the site “http://sourceforge.net/projects/

tinyos” and are working together to establish standard interoperable network services built from 

a base of direct experience and honed through competitive analysis in an open environment. 

 TinyOS programs are compiled with a C language-like compiler called “nesC.” TinyOS 

and nesC are now supported on the Gentoo Linux (http://www.gentoo.org) development 

platform. 

 An alternative to TinyOS is SOS (https://projects.nesl.ucla.edu/public/sos-2x) from the 

Networked and Embedded Systems Laboratory at the University of California, Los Angeles 

(UCLA). SOS is a dynamic operating system for sensor networks that relies on conventional 

C compilers for code creation, removing one step from the learning curve for those new to 

wireless sensor networks. SOS uses a common kernel that implements messaging, dynamic 

memory, module loading and unloading, and other services. SOS uses dynamically loaded 

software modules to create a system supporting dynamic addition, modification, and removal of 

network services. 

Off-the-shelf Hardware 

 The hardware platform consists of processor/radio boards commonly referred to as 

“motes.” A mote runs the TinyOS to provide low-level event and task management. Crossbow 

Technology, Inc., is the major supplier of off-the-shelf motes running TinyOS. Crossbow offers 

XMesh, a self-forming, micropower, networking stack. Cogent Computer Systems, Inc., is the 

major supplier of off-the-shelf motes running SOS based on the XYZ Sensor Node wireless 

sensing platform developed at Embedded Networks and Applications Laboratory, Yale 

University (http://www.eng.yale.edu/enalab). 
26

Protocols 

 Pros and cons for each protocol relative to mining applications are summarized below, 

along with a basic overview of data transfer rate(s), distance, and frequency range(s). Distances 

listed are those for an unobstructed line-of-sight path. 

Bluetooth

Pros: Bluetooth is the oldest of the wireless-based protocols discussed in this report. 

As such, it is found in millions of cell phones and PDAs. The primary application of a Bluetoothenabled device is in virtual displays. Nodes, referred to as “headless,” contain no display of their 

own, but transfer data to an external viewer to present the node data. 

Cons: As the oldest wireless method discussed here, Bluetooth is the most attacked. 

Numerous security breaches have been documented [Biever 2005; Bluetooth 2005]. Also, it 

consumes more energy than newer protocols, limiting its usefulness in sensor nodes. 

Data rate: Up to 723.1 kbps. Bluetooth Enhanced Data Rate – 2.1 Mbps. 

Range: 10 m (33 ft). 

Frequencies: The protocol operates in the license-free ISM band at 2.45 GHz. In order to 

avoid interfering with other protocols that use the 2.45-GHz band, the Bluetooth protocol divides 

the band into 79 channels (each 1 MHz wide) and changes channels up to 1,600 times per 

second. 

Comments: Bluetooth devices can have groups of up to eight devices (one master and 

seven slaves). They are called piconets. 

Digital-enhanced Cordless Telecommunications (DECT) 

 DECT was developed mainly for use by European cordless phones, but is now starting to 

be used as a general data transmission method. 

Pros: Wide acceptance in Europe. Nodes are designed to operate while in motion up to 

20 km/h (12 mph). 

Cons: Limited support in the United States. This may change, as the FCC approved the 

use of DECT in the 1,920–1,930 MHz band in the spring of 2005. Currently no known support 

for sensor systems. 

Data rate: 552 kbps and 1.15 Mbps. 

Range: 100 m (328 ft). 

Frequencies: 1.80–1.93 GHz. 

EnOcean 

Pros: Ultralow power, scavenges minute amounts of energy from the environment. Gas 

sensors for several gases are already on the market. Already in use for environmental monitoring 

systems in car parking garages. Used for lighting control in building automation. 

Cons: Limited public availability of technical details. 

Data rate: Unknown. 

Range: Unknown. 

Frequencies: Unknown, presumed to be ISM spread spectrum-based. 

Comments: MSR-Electronic supplies EnOcean-compatible wireless sensor technology 

monitors for gases such as CO, CO2, NOx, NH3, EX, and O2. 
27

Ensation 

 Pros: For use in headphones and hearing protection devices in high-noise mine 

environments. 

Cons: Ensation was formally announced while this report was in preparation. No devices 

that use it are on the market yet. Long-term support and market penetration is therefore 

unknown. 

Data rate: 150–500 kbps. 

Range: Indoor distances of 30 m (98 ft) at a transmit power level of 10 mW. 

Frequencies: 863–865 MHz for Europe and 902–928 MHz for the United States. 

Comments: Ensation’s main usage is point-to-multipoint low-latency audio, such as a 

single transmitter communicating with multiple headphones. The protocol may be useful for 

control pendants due to the low-latency data transfer. Latency is the time between an action, such 

as a button press, and a result, such as the startup of a haulage motor. Latency time is less than 

20 ms. 

IEEE P1902.1TM Standard for Long Wavelength Wireless Network Protocol (RuBeeTM) 

Pros: RuBee networks and tags are distinguished from most RFID tags in that they are 

unaffected by liquids and can be used underwater and underground. Being magnetic-based rather 

than radio-based allows them to operate in and near areas of high metal content. 

Cons: Limited public availability of technical details, as the P1902.1TM standardizations 

process has just began. 

Data rate: 300–9,600 bps. 

Range: 3–15 m (10–50 ft). 

Frequencies: Below 450 kHz. 

Comments: RuBee tags maintain performance around steel, which removes a key 

obstacle for low-cost deployment of RFID in industrial item-level tracking environments. 

Millennial Net, Inc. 

Pros: Ultralow power will run for years on a 3-V coin-sized battery. 

Cons: Limited public availability of technical details. 

Data rate: Unknown. 

Range: Unknown. 

Frequencies: 916 MHz, 2.45 GHz. 

Comments: Millennial Net devices can operate with an extremely low rate of power 

consumption on the energy of a 3-V coin-sized battery for years at a time as part of a scalable, 

self-organizing wireless sensor networking system. Millennial Net supplies the Wireless Sensor 

Networking Source Book [Rhee and Liu 2005], which is a must-read for anyone considering a 

wireless sensor network system. 

 A unique feature of Millennial Net is Persistent Dynamic Routing. This provides a 

mechanism for the network to ensure reliable data transmission without dropping data packets. 

Combined with the technique of dynamic route discovery, which discovers the best route for 

packet delivery on the fly, Persistent Dynamic Routing enables a level of scalability and power 

efficiency that other networking systems have not yet achieved. Standard reference kits are 

available. 
28

Near-field Communication (NFC) 

Pros: Intended for short distances, such as for transferring configuration information or as 

a connector replacement. Used in many new cell phones and electronic cards. NFC uses very low 

power. NFC devices can serve as connector replacements and as replacements to IrDA infrared 

devices. 

Cons: Limited public availability of technical details, must become a member of the 

NFC Forum to obtain them. However, off-the-shelf modules are available from Philips 

Semiconductors. 

Data rate: Up to 424 kbps. 

Range: 20 cm (8 in). 

Frequencies: 13.56 MHz. 

Comments: A radio wave is a combination of an electric wave and a magnetic wave. 

When these waves leave the antenna, they are offset by 90°. By the time the electric and 

magnetic waves have traveled about a half-wavelength from the transmitting antenna, the phase 

offset has decreased to almost zero. NFC technology operates by using magnetic field induction. 

 NFC is already standardized according to globally accepted standardization bodies, such as 

the International Organization for Standardization (ISO 18092), Ecma International (ECMA–

340) and the European Telecommunications Standards Institute (ETSI TS 102 190). NFC is 

compatible with Philips’ MIFARE® (ISO 14443 A) and Sony Corp.’s FeliCaTM smart card 

protocols. 

 NFC may be used to configure and initiate other wireless network connections, such as 

Bluetooth, via transferring the hard-to-set-up Bluetooth address. NFC may also be used in 

address training modes where a particular receiver has to be told to listen to a particular 

transmitter, in situations where multiple transmitters may be in operation in close proximity to 

each other at the coal face, completely removing the need for teach/learn connectors. 

 There are many similarities between NFC and RFID, as they both operate very much in the 

contactless connections arena and share the same frequency spectrum. 

RFID-RadarTM

Pros: Achieves millimeter precision for monitoring movement. RFID-radar has the ability 

to measure the radio path length, which is the signal distance from the transponder to a reader. 

RFID readers can handle up to 800 transponders in a zone at a time with speeds up to 300 km/h 

(186 mph), while the radar will give accurate location information for up to 50 transponders in a 

zone at a time at low speeds. Due to low spectrum utilization, multiple readers and radars can 

operate in close proximity with minimal interaction. 

Cons: Antenna system(s) being used are currently a work in progress. A large-scale, highvolume manufacturer is currently being sought. 

Data rate: Currently limited to preprogrammed serial numbers of the tags. 

Range: Up to 40 m (131 ft). Manufacturer’s tests indicated that a target of 0.2-m (8-in) 

accuracy would be achievable out to 100 m (328 ft). 

Frequencies: 860–960 MHz. 

Comments: Besides identifying RFID transponders in its zone, the RFID-radar system is 

able to measure the range and direction of those transponders from the reader antennas. The 

system operates at UHF frequencies in the bands allocated for RFID using electric coupled 
29

propagation properties to transfer energy from the reader to the transponder and from the 

transponder back to the reader. The RFID-radar measures the path length for signals traveling 

from the transponder to the reader to determine range. By comparing signals arriving at two 

identical receivers with closely spaced antennas, the reader is able to determine the angle of 

arrival of the signals from the transponder and thus the direction of that transponder from the 

reader. A third receiver channel can be added to give 3–D coverage rather than two-dimensional 

(2–D) coverage. 

Wi-Fi / WiFi / Wireless Fidelity 

 Wi-Fi is a wireless networking technology based on the IEEE 802.11b/802.11g standards. 

IEEE’s 802.11g standard defines the way in which wireless gear communicates at up to 54 Mbps 

while remaining backward-compatible with 11 Mbps 802.11b. 

Pros: Found virtually everywhere, such as laptop computers. 

Cons: Power-hungry. Not suited for long-term battery-powered usage. Not designed for 

low data transfer applications such as sensors. 

Data rate: 802.11b has a maximum raw data rate of 11 Mbps, but network overhead 

limits the maximum usable data rate to less than 7 Mbps. 802.11g has a data rate up to 54 Mbps. 

Range: Line-of-sight distances up to about 100 m (328 ft). 

Frequencies: 16 channels in the 2.4-GHz ISM band, 10 channels in the 915-MHz ISM 

band, and 1 channel in the 868-MHz band. 

Wireless Personal Area Network (WPAN) / 802.15.4

 The IEEE 802.15 TG4 was chartered to investigate a low data rate solution with 

multimonth to multiyear battery life and very low complexity. 802.15.4 is not usually used 

directly; however, it forms the lower layers of other protocols such as ZigBee. 

Pros: Designed from the start to be low-power, with sensor applications in mind. Many 

subfeatures such as network time synchronization (all nodes in the network show the same time). 

Time synchronization is important in data logging and location features. 

Cons: Overwhelming amount of publicly available technical details. The 802.15.4 

protocol document is 679 pages long. Such complexity requires reliance on semiconductor 

suppliers to implement the protocol in hardware correctly. 

Data rate: 20 kbps, 40 kbps, 250 kbps. 

Range: Dependent on system design. Up to 10-m (33-ft) radius. 

Frequencies: Dependent on system design. 

Comments: Incorporates a variety of features to ensure reliable operation. These include a 

quality assessment, receiver energy detection, and clear channel assessment. Data transfers have 

a maximum payload of 104 bytes, with 16-bit or 64-bit address. 

 Support exists for critical latency devices, such as joysticks. There is an automatic network 

establishment by the coordinator and a full handshake protocol for transfer reliability. Power 

management ensures low power consumption. 
30

Wireless USB (Atmel Corp., Cypress Semiconductor Corp.) 

Pros: All modern computers contain human interface device drivers, so that no custom 

software is required to be written when used with laptop or desktop computers. 

Cons: None known. 

Data rate: 62.5 kbps. 

Range: 10 m (32 ft) for the short-range version, 50 m (164 ft) for long-range version. 

Frequencies: 2.45 GHz. 

Comments: WirelessUSB N:1 is based on a wireless star topology consisting of multiple 

nodes connected to a central aggregator or hub. The hub ties directly to the controller through 

either a serial connection or an existing wired control system. Wireless nodes use the 

WirelessUSB N:1 multipoint-to-point protocol to receive and send data to the hub. Wireless USB 

has received several industry awards for outstanding interference avoidance, high-node density 

(up to 65,000 nodes), and long-range wireless capabilities, all of which contribute to a costeffective, simple, yet highly reliable wireless sensor environment. 

 WirelessUSB N:1 is optimized for low power. The hardware is fully off until an event 

occurs. Because a wireless USB sensor node can be asleep for a majority of the time, the radio is 

transmitting and/or receiving less than 0.1% of the time. Thus, the average current consumption 

is very low (in microamps). A wireless USB sensor node can achieve 5+ years of battery life 

using typical batteries. Further details may be obtained at: http://www.atmel.com, and 

http://www.cypress.com. 

 

Wireless USB (USB Forum) 

Pros: A pro cannot be established at this time, as this technology was released while this 

report was in preparation. Wireless USB is expected to be widely used within a few years. 

Cons: Overwhelming amount of publicly available technical details of the protocol, but 

lacking details in frequency range and distance. The Wireless USB Forum protocol document is 

303 pages long. Such complexity requires reliance on semiconductor suppliers to implement the 

protocol in hardware correctly. Further details may be obtained at: http://www.usb.org/wusb. 

Worldwide Interoperability for Microwave Access (WiMax) 

 802.16 [Eklund et al. 2006] provides up to 50 km (31 miles) of linear service area range 

and allows users connectivity without a direct line of sight to a base station. Note that this should 

not be taken to mean that users 50 km (31 miles) away without line of sight will have 

connectivity. The technology also provides shared data rates up to 70 Mbps. 

 Not relevant to data collection devices such as sensors; however, may be useful for linking 

mine campuses. 

ZigBee 

 ZigBee is a wireless networking technology based on the newly defined IEEE 802.15.4 

Low-rate Wireless Personal Area Network (WPAN) standard. ZigBee adds the upper protocol 

layers of the ISO stack where the logical network, security, and application software reside. 
31

Pros: ZigBee provides static and dynamic, star, cluster tree, and mesh networking 

structures to create large-area scalable networks with single point-of-failure avoidance. Many 

manufacturers are about to bring ZigBee-based products and semiconductors to the market. 

Cons: There is limited availability of off-the-shelf devices at this time. 

Data rate: 20 kbps in the 868-MHz band, 40 kbps per channel in the 915-MHz band, 

250 kbps per channel in the 2.4-GHz band. 

Range: 10–75 m (33–246 ft). 

Frequencies: Operation in the unlicensed 868-MHz, 915-MHz, and 2.4-GHz bands. 

Comments: ZigBee shows the most long-term promise to a ubiquitous mine-wide 

deployment of sensors on equipment and worn by personnel. 

 ZigBee has an optional method for time synchronization, which is important in mine-wide 

data logging and location applications. In addition, it is recognized that some messages need to 

be given a high priority. To achieve this, a guaranteed time slot mechanism has been 

incorporated into the specification. This enables these high-priority messages to be sent across 

the network as swiftly as possible. This has applications such as automatic and emergency 

shutdowns. 

Z-WaveTM 

Pros: Z-WaveTM generally costs less and has a smaller code size footprint than ZigBee. 

Z-WaveTM-enabled end-user products are now available from commercial retailers, while 

ZigBee-enabled end-user products were not available at the time this report was in preparation. 

Cons: Limited public availability of technical details. Not as many features as ZigBee. 

Data rate: Unknown at this time. 

Range: Unknown at this time. 

Frequencies: 868/915-MHz bands. 

Comments: Z-WaveTM is a wireless RF-based communications technology designed for 

residential and light commercial control and for status reading applications such as meter 

reading, lighting and appliance control, HVAC, access control, intruder and fire detection, etc. ZWaveTM is the de facto standard for wireless home controls using mesh networking. Further 

details may be obtained at: http://www.zen-sys.com. 

RADIO FREQUENCY IDENTIFICATION (RFID) 

 Radio frequency identification (RFID) is an emerging subset of wireless technology. 

RFID devices are known as tags, as they “tag” an object or person with a small device containing 

a large binary number, typically 48 bits or 2.8 × 1014 different numbers. A few styles of tags 

allow a small amount of information to be written to the tag. 

 Figure 18 shows a common “pet implant.” This is a very common form of RFID in use 

today by consumers. 

 Some RFID systems are designed to handle reading multiple tags clustered into a small 

space, such as a shopping cart, or a number of personnel standing near a piece of equipment. 

A potential mining application would be an “automatic” emergency stop system that would 

protect miners from machine striking or pinning accidents. An emergency stop system could be 

constructed to shut down a machine if an RFID tag worn by a miner came in view of a tag reader 

(Figure 19). 
32

Figure 18.—RFID tags can be very small. An implantable pet tag is shown. 

Figure 19.—An emergency stop system concept that uses an RFID. (Image courtesy of Intersoft Corp). 

 Due to the small size of tags, they rarely contain their own power source. Rather, they 

receive their power from a magnetic field supplied by a device known as a reader, as it reads the 

binary number from the tag. A tag that contains its own power source, such as a battery, is 

known as an active tag. Tags that do not contain their own power source are known as passive 

tags. The magnetic power system used by passive tags may not work well in areas containing a 

lot of metal. 

 The typical operating frequency of RFID systems are 125 kHz, 13.56 MHz for older 

legacy systems, and the 400-MHz / 2.4-GHz / 5-GHz regions for newer systems. 

 RFID has been used for the tagging of coal [Lauf 2001]. In other applications of RFID, 

there is a movement to replace the ubiquitous UPC bar codes with RFID tags. 

 Opponents to RFID tags fear that there maybe a loss of privacy associated with widespread 

RFID usage. One possible scenario is that you buy an item of clothing, such as a shirt or dress, 

and pay with your credit card. There is now a link between a piece of personal identification, 

your credit card number, and the RFID tag used for inventory management. If the RFID tag is 

not disabled at the point of sale, it is hypothetically possible that the next time you enter the store 

wearing the item of clothing, you could be targeted with ads specifically directed at you. 
33

BLOCKER TAGS 

 A special class of RFID tags has been created known as blocker tags. An individual tag is 

identified out of a cluster of tags by a process known as singulation. Singulation is where the tag 

reader breaks down each of the individual tag addresses, trying to identify a unique tag. In the 

shopping scenario, this would be multiple people passing through the entrance of the store 

simultaneously. Blocker tags interfere with the singulation process by generating all possible 

RFID identification numbers, which confuses the tag reader. Blocker tag technology can be 

countered by using “tags talk first” (TTF), as they do not rely on the singulation process. 

LOCATION AWARENESS 

 Location awareness is the ability to know the location of an object or person in 3–D space 

and in real time. Contrary to what one might expect, the wider the area that an object or person 

needs to be tracked within, the easier the tracking can be done. It is tracking of objects or 

personnel within an area of a few meters that is the most difficult. However, emerging UWB 

techniques are enabling asset and personnel tracking at ranges of 600 ft to a resolution of 10 in. 

 By using a global positioning satellite system, it is comparatively easy to locate objects on 

a global scale. The Automatic Position Reporting System (APRS) (http://www.aprs.org) is one 

such example. APRS, in conjunction with “findU” (http://www.findu.com), is a live, real-time 

example of location awareness on a global scale. From findU, a properly tagged object, such as a 

vehicle, is shown with a satellite image and a local street map. APRS is a real-time tactical 

digital communications protocol for exchanging information among a large number of stations 

covering a large area. APRS integrates maps and other data displays to organize and display data 

by using a one-to-many protocol to update the network in real time. 

 A more regional location problem is that of locating a cell phone user dialing “911” 

emergency services. On June 12, 1996, the FCC adopted a Report and Order known as 

Enhanced 911, or E911, which will eventually require all cell phone operators to provide 

identification of the wireless caller’s phone number and physical location. 

 One challenge is that of locating a person or object inside of a building or underground 

mine, where GPS and systems requiring outside signals do not function. 

 There are eight fundamental ways to do base location awareness, which may be used alone 

or in conjunction with each other. The carrier of the information may be a radio wave, light 

wave, sound wave (ultrasonic), or magnetic wave (near-field inductive coupling). All systems 

require more than one point of reference. 

 • Angle of arrival (AOA): Uses multiple antennas at a reference point to determine the 

incident angle of an arriving signal. 

 • Time difference of arrival (TDOA): Uses the time it takes for a signal to travel as an 

indirect method of calculating distance. Precisely synchronized time between units and/or 

reference points is required. 

 • Time of arrival (TOA): Similar to the TDOA technique, this technology differs only in 

that it uses the absolute time of arrival at reference points rather than the difference between two 

stations. 
34

 • Enhanced observed time difference (E–OTD): E–OTD is an enhancement of TDOA, 

where the receiving unit, e.g., a cell phone, returns information back to the reference points for 

location calculations. 

 • Signal strength: The received signal strength is measured from a transmitter sending a 

known level of power. This is the oldest method used in classic direction-finding techniques. 

Multiple points of reference are still needed. A single measurement of signal strength is helpful 

for determining distance from the transmitter. 

 • Multipath fingerprint (MF): Waves of various types will have received a signal 

directly from a transmitter and receive indirect signals reflected off of objects in the 

environment. Multipath is a problem when the direct wave and the reflected waves cancel each 

other out so that no signal is received at the receiver. MF takes advantage of what is normally 

considered to be a problem. It requires knowledge of the environment; if the environment 

changes, new fingerprints have to be created. 

 • Smart antennas or smart optics: Antennas are rotated mechanically or electronically 

to locate the strongest signal. 

 • Near-field electromagnetic ranging (NFER): The physics behind NFER technology is 

relatively easy to grasp. Radio signals are electromagnetic waves. A radio wave is a combination 

of an electric wave and a magnetic wave. When these waves leave the antenna, they are offset 

by 90°. By the time the electric and magnetic waves have traveled about a half-wavelength from 

the transmitting antenna, the phase offset has decreased to almost zero. By measuring the angle 

between the electric wave and the magnetic wave, distance may be calculated. 

 An unstructured environment is one that has not, or cannot, be prepared in advance, such 

as a train wreck or a mine collapse. Structured environments can unexpectedly become 

unstructured due to outside influences such as earthquakes or explosions. 

 The major problem in location awareness that has not yet been solved is knowledge of 

the vertical z-axis, or height. It is easy to locate a player in contact with the basketball court, 

but extremely difficult to determine the player location in 3–D while making a jump shot in 

real time. A practical problem would be to locate an injured person lying on the floor in a highrise building. It can be hard to distinguish a tall person standing on the second floor from an 

injured person lying on the third floor. 

FUTURE RESEARCH 

INJURED MINER (PERSON-DOWN) DETECTION 

 Miners, as well as firefighters and first responders, work in dynamic, hazardous 

environments. Miners can become incapacitated from falls of ground (i.e., roof, rib, and back 

falls); from slips, trips, or falls; or from being struck or pinned by moving machinery. In all of 

these mishaps, a miner will be subjected to bodily impact hazards that can be detected by using 

accelerometers to measure the force of impact. Alternately, the lack of bodily movement can be 

measured using the accelerometers; this lack of movement indicates that the miner has been 

incapacitated (“person down”). Commercial systems with person-down functions are available 

for firefighters. For instance, the TPASS–3 EVACUATETM system uses a solid-state 
35

accelerometer for “lack of motion sensing.” An alarm signal indicating a person-down situation 

is sent to a central command base if body motion is not detected after 18–23 sec. 

 A wearable accelerometer would play a key role in a person-down system designed to alert 

other miners that a mishap has occurred. Such a person-down system for mining could save 

valuable time so that medical attention could be more quickly administered. This is especially 

important for situations where a worker is alone. This is common in mining because miners walk 

down entries to retrieve tools or materials or to inspect or repair a piece of equipment. A persondown system could also be very useful for situations when the miner is not alone. Mines are 

often characterized as dark, dusty, and noisy environments, so it is quite conceivable that a miner 

could be injured without the immediate knowledge of other miners in the vicinity. For instance, 

a remotely controlled continuous miner could strike a worker positioned in one of the machine’s 

blind spots. This mishap could go unnoticed because of noise and the absence of a line of sight to 

the worker; thus, the extent of injury could become more severe as the machine advances. Also, 

precious time would be lost until the injured worker was seen. 

 The wearable person-down system (Figure 20) is composed of just a few simple 

components. Thus, the system is small enough to be wearable and cost-effective to be used by 

every miner. Each component is described below. 

MEMSIC

Accelerometer

Basic Stamp

processor

Visual 

alarm

Audible

alarm

Wireless 

link

Figure 20.—Basic block diagram of a person-down system. 
36

Sensor 

 The sensor (Figure 21) is the MEMSIC model MXD2020GL accelerometer. The major 

features of this sensor include: 

 • Dual-axis accelerometer fabricated on a monolithic CMOS IC 

 • No moving parts 

 • Less than 2 milli-g resolution 

 • No sensitivity or zero g bias hysteresis 

 • 50,000-g shock survival rating 

 • 35-Hz bandwidth expandable to >100 Hz 

 • Low-height (2-mm) surface mount package 

 • Continuous self-test for failures 

 • Low cost (about $5.00) 

Figure 21.—A wearable accelerometer (MEMSIC model MXD2020GL). 

Microcontroller 

 The BASIC Stamp microcontroller (Table 1 and Figure 22) is a computer on a chip 

optimized for monitoring and controlling specific systems or devices such as switches, timers, 

motors, sensors, relays, and valves. It is self-sufficient and has a processor, RAM and EPROM 

memory, clock, and interface (via 16 input/output (I/O) pins). The microcontroller software is 

PBASIC. This programming language is very similar to BASIC. The PBASIC language is 

relatively simple and has only 42 commands. 

Table 1.—The key specifications of the BASIC Stamp microcontroller 

(adapted from Parallax [2006])

Processor speed ............................ 20 MHz

Program execution speed .............. ~4,000 instructions per second

RAM ............................................... 32 bytes (6 I/O, 26 variable)

EEPROM........................................ 2 Kbytes, ~500 instructions

Input/output (I/O) ............................ 16 + 2 dedicated serial

Voltage requirements ..................... 5–15 V dc

Current draw at 5 V ........................ 3 mA run / 50 μA sleep

Physical size................................... 1.2 in × 0.6 in × 0.4 in

Cost ................................................ ~$49 single; $39 each for 1,000
37

Figure 22.—The BASIC Stamp microcontroller. (Image courtesy of Parallax, Inc.) 

System Operation 

 The basic operation of a wearable person-down system centers on two hazardous states: 

the lack of motion and excessive bodily impact [MEMSIC 2007]. If one of these situations 

occurs, other miners are wirelessly alerted by using an ad hoc wireless mesh sensor network 

based on the ZigBee standard. 

 This MEMS sensor is sampled by the BASIC Stamp microcontroller. Data are periodically 

sampled and compared to the previous sample. The microcontroller provides the logic to 

ascertain if one of the hazardous states is present. The sensitivity and sampling frequency is 

software-programmable such that jitter and false signals are rejected. If a hazardous state is 

detected, the microcontroller activates a visual and audible alarm locally and wirelessly to other 

miners. 

 The logic to detect a high-impact hazardous state is based on the ability of humans to 

sustain impacts without incurring a concussion injury. This is dependent on the average 

acceleration and the duration of the acceleration as defined by the Wayne State University 

concussion tolerance curve (Figure 23). The area above the curve defines impact hazards that can 

cause injury, while the area below the curve is defined as safe. A person can be subjected to a 

high average acceleration, yet not incur a concussion if the exposure time is very small. 

Therefore, the microcontroller logic is programmed to activate the alarm when the impact 

exceeds the safe area of average acceleration and time duration. 
38

Figure 23.—Wayne State University cerebral concussion tolerance curve. (Adapted from SAE [1980]).

WEARABLE WIRELESS REMOTE VIEWER 

 The objective of this application is to mitigate striking and pinning injuries associated with 

remote-controlled mining machinery. There are two basic hazardous conditions: (1) workers are 

injured or killed because they are in a blind spot with respect to the machine operator; and 

(2) machine operators are injured or killed because they followed the unsafe work practice of 

placing themselves in unsafe areas to better see the task at hand. 

 The use of remote-controlled mining machinery subjects miners to injuries from the 

striking and pinning hazards of moving machinery. The Mine Safety and Health Administration 

reported that there were 167 remote-control incidents in mining during 1988–2004; of these, 

there were 24 fatalities [Dransite and Huntley 2004]. The most hazardous job function for remote 

control was tramming to a new location (76 incidents). Poor work practices were listed as the 

main cause because the operators placed themselves in dangerous areas near the machine. 

Operators often place themselves in dangerous areas because these areas afford the best vantage 

points to operate the machine (Figure 24). 

INJURY 

SAFE 
39

 Figure 24.—The locations of 24 remote-control mining fatalities during 1988–2004. Circles represent the 

operator, squares represent other workers, and gray background indicates accidents during maintenance. 

The locations are categorized into three areas: A, the tail area; B, the cab area; and C, the cutter head area. 

(Adapted from Dransite and Huntley [2004].) 

 This application employs wearable display technology and wireless sensor technologies to 

enable operators to see blind spots and to see well enough to tram to new locations without 

positioning themselves in dangerous areas near the machine (Figure 25). Until recently, the 

technologies to display video (CRT monitors) were large and bulky, were visually and physically 

restrictive, and required significant power such that they were not intrinsically safe. Wearable 

display technology overcomes these limitations. This innovative technology uses a small, single 

eyepiece that weighs just 2 oz, yet it appears as if you’re looking at a 17-in monitor from 3 ft 

away. The display doesn’t restrict the user’s field of vision; thus, the wearer can maintain 

awareness of his or her surroundings. The display is not physically restrictive because it is worn 

by the user, thus giving the flexibility to use the system without sitting in the operator’s cab. 

 A second major benefit of wearable display technology can be achieved by combining it 

with remote control. This can afford the operator with all the visual information needed to 

control the machine and to see the machine’s blind spots without having to sit in the machine’s 

cab, which can reduce striking and pinning hazards. 
40

Wireless

LAN

Pocket 

PC

Wireless

camera

Wearable

display

Figure 25.—This system enables a person to remotely view people or objects in blind spots. 

Wireless Camera 

 The video camera is a wireless, networked IP camera that directly connects to a network or 

the Internet without the need of cabling. It enables users to remotely view live, full-motion video 

over a computer network or the Internet. It supports multiple users and can be viewed using any 

Web browser. Therefore, for the mining environment, the IP camera gives unmatched flexibility 

in terms of mobility, mounting locations, and the number of cameras and users. 

 An IP camera differs from a Web camera (WebCam), which needs to connect to a host 

computer that supports only one user at a time. The IP camera has a built-in CPU, embedded 

operating system, and Web server. Both the IP camera and WebCam are digital and differ from 

traditional analog video cameras that use a single analog video signal sent through a dedicated 

coaxial cable. Each analog camera needs a dedicated coaxial cable. The digital cameras digitize 

the images, and the video stream data are sent over the network. Therefore, multiple cameras can 

be used by multiple users at the same time. 

 The IP camera used in this application is the DCS–5300G from D-Link [2006]. It has pan, 

tilt, and zoom functions that can be remotely controlled from the Web interface or from the 

included remote control. The camera pans up to 270° horizontally and vertically tilts up to 90°. 

The complete camera specifications are listed in Table 2. 
41

Table 2.—Detailed specifications of the DCS–5300G IP camera 

(adapted from D-Link [2006])

Camera specification..................... 1/4-in color CCD sensor

Electronic shutter: 1/60–1/15,000 sec

Fixed focus glass lens, F2.0, 1 lux

Ports .............................................. 10/100 Mbps Fast Ethernet

Audio/video output

External microphone input

External I/O

Connectivity................................... Wireless 802.11g

10/100 Mbps Fast Ethernet

Audio ............................................. Built-in omnidirectional microphone

Video resolution............................. Up to 30 fps at 160×120

Up to 30 fps at 320×240

Up to 10 fps at 640×480

Pan, tilt, and zoom control............. Auto pan and auto patrol mode with preconfigured stops

Pan: range 270°

Tilt: range 90°

4× digital zoom

Networking protocols..................... TCP/IP, HTTP, SMTP, FTP, Telnet, NTP, DNS, and DHCP

General I/O.................................... 1 opto-isolated sensor input (max. 12 V dc 50 mA)

1 relay output (max. 24 V dc 1 A, 125 V ac 0.5 A)

Operating system .......................... Microsoft Windows® XP, 2000, Me

Power input.................................... External power supply; 12 V dc 1.5 A

Dimensions.................................... 4.0 in long × 4.1 in wide × 4.4 in high

Weight ........................................... 12.2 oz (0.76 lb)

IP Camera Viewer Software 

 Viewer software is needed to display video on a pocket PC. ViewCommander-Mobile 

software enables you to remotely view the live streaming video output from multiple IP cameras 

on a pocket PC. The software includes the following major features: 

 • Connect to up to 16 video cameras or 16 video servers (with each server supporting up to 

 32 cameras, totaling 512 cameras) 

 • View video from Motion JPEG (M–JPEG) video streams 

 • Take snapshots and save to local device 

 • Pan/tilt/zoom controls 

 • Digital zoom: digitally zoom in on objects 

 The ViewCommander-Mobile software also configures the pocket PC buttons for 

pan/tilt/zoom controls, as shown in Figure 26. The controls are as follows: 

 • Zoom Fully Out: Use this button to zoom the camera to its widest field of view. 

 • Zoom Fully In: Use this button to zoom the camera to its maximum zoom level. 

 • Zoom Step Out: Use this button to zoom out one step. 

 • Zoom Step In: Use this button to zoom in one step. 

 • Up, Down, Left, and Right: Use this button to move the camera in the desired direction. 
42

Figure 26.—The pocket PC buttons are used for controlling the IP camera. 

Wearable Display 

 The wearable display is the model M920–CF by Icuiti Corp. A technical description is 

provided in the earlier “Icuiti Corp.” section. 

Wireless Router 

 The Netgear WPN824 RangeMax wireless router (Figure 27) is a key device for setting up 

the wireless network of this application. This router is well suited for the mine environment 

given its sleek physical design, excellent range, and strong resistance to interference, yet it is 

relatively inexpensive (about $130). The RangeMax does not have external antennas that can be 

damaged in the dynamic, hazardous mine environment. Instead, seven internal antennas are 

mounted inside the top cover. These antennas are part of the multi-in, multi-out (MIMO) 

technology employed by the RangeMax to increase the wireless range and speeds. The unit’s 

seven antennas help the router counteract the negative impact of interference by dynamically 

reconfiguring themselves to changing conditions. For instance, if the signal of one of the 

transceiving antennas becomes weak, the unit automatically searches for a better signal from the 

other antennas. This dynamic reconfiguration of antennas is especially important given the 

dynamic mine environment of mobile machinery, changing physical geometries of the mine face 

and entries, and the presence of high-voltage electrical sources that can cause interference. The 

MIMO technology will also be useful to optimize the antennas given other wireless challenges 

such as large metallic machines, signal occlusions, and multipath effects. 
43

 The key specifications for the RangeMax are as follows: 

 • Connectivity: Wired or wireless 

 • Data transfer rate: Up to 108 Mbps 

 • Data protocols: Ethernet, IEEE 802.11b, 802.11g, and 802.11 Super G 

 • Transport protocol: Internet Protocol Security (IPSec) 

 • Weight: 1.1 lb 

 • Features: Firewall protection, DoS attack prevention, Smart MIMO technology, 

 Intrusion Detection System (IDS) 

 • Bandwidth: 2.4 GHz 

 • Compatibility: PC, Mac 

Figure 27.—The Netgear WPN824 RangeMax wireless router. 

UWB SMART ENVIRONMENT 

 This application uses UWB to help create a smart environment that enables localization 

and tracking of first responders and resources. The smart environment provides location data, 

physiological data, and communications (video, photos, graphical images, audio, and text 

messages). 

 UWB technology has many advantages for a smart environment. It uses extremely short 

and fast pulses. This reduces multipath cancellation problems encountered from signal 

reflections off of walls, ceilings, and large objects. These short waves can also penetrate walls. 

Other advantages include the following: 
44

 • Time-of-flight properties that can be used for precision distance and positioning 

 measurements 

 • Relative immunity to multipath problems 

 • Extremely high data rates 

 • Well suited for mobile wireless applications 

 • UWB transceivers can be made very small with MEMS technology 

Commercial UWB Systems 

 Commercial UWB systems are emerging for indoor location and tracking of people and 

assets in smart environments [Fontana et al. 2003]. For instance, Ubisence offers a system and 

the associated development tools. Multispectral Solutions, Inc. (MSSI), offers multiple systems 

and associated development tools. MSSI’s Sapphire UWB Precision Asset Location SystemTM 

(PALTM) has been approved to meet UL1604 safety standards for operation in hazardous 

locations. Some research has been conducted for first responder applications. The PAL650TM is 

another system by MSSI. The specifications follow: 

 • Typical indoor range: 300 ft 

 • Measurement accuracy: ±1 ft 

 • Transmission power: FCC §15.517 

 • Operating frequency: 6.2 GHz 

 • Coverage area: Up to 90,000 ft2

 Commercial UWB systems for indoor location and tracking of people and assets are 

intended for applications within a building. The efficacy of commercial UWB systems for 

underground mining applications has not been rigorously established. 

Related Research 

 The Center for Advanced Integrated Radio Navigation (CAIRN) at Worcester Polytechnic 

Institute is conducting research to integrate communication and navigation system technologies 

in order to create systems for infrastructure-based and ad hoc-based networks [CAIRN 2007]. 

A location system for first responders is an active area of research for CAIRN. 

 Commonwealth Scientific and Industrial Research Organisation (CSIRO) Exploration and 

Mining in Australia has taken the lead in wireless technologies for localization of mobile 

equipment operating in an underground coal mining environment [Ralston et al. 2005]. 

CSIRO research involves the use of IEEE 802.11b Wireless Ethernet and uses the signal strength 

received from several wireless access points for the real-time localization. 

 A local positioning system (LPS) for outdoor applications such as construction, 

agriculture, and marine safety has been developed by the National Institute for Occupational 

Safety and Health [Lee et al. 2005]. In essence, the LPS is a smart environment for health and 

safety assessment of tasks conducted by multiple workers. The system is able to track the 

locations of multiple workers via a global positioning system and through integrated position 

data and assessment data obtained from real-time monitoring systems. Field testing of the LPS 

was conducted in order to evaluate noise levels for a highway paving project. The LPS enabled 

researchers to successfully measure, log, map, and analyze worker exposure to noise in order to 

pinpoint the primary source of noise. 
45

CONCLUDING REMARKS 

 This report presents an overview of the technologies that could be used to supply miners 

and first responders with real-time situational data (environmental, physiological, and physical 

location data) needed for early warnings of health and safety hazards. Secondly, the same 

situational data can be useful to assist injured miners. This report does not address in specific 

detail the topics of intrinsic safety, tracking and locating trapped miners, or communication with 

trapped miners. 

 Three critical technologies emerge and converge to support this technical approach: 

wireless networks, low-power embedded computing, and smart microsensors. Computer and 

MEMS technologies have rapidly advanced; they are relatively mature technologies. Numerous 

inexpensive, commercial, off-the-shelf MEMS sensors, sensor motes and nodes, and embedded 

microcontrollers exist. However, wireless technologies are rapidly changing. While this report 

was being prepared, one new “standard” emerged—the Wireless USB from the USB Forum, 

which was in conflict with the de facto standard of the day, Wireless USB from Atmel Corp. and 

Cypress Semiconductor Corp., and two wireless methodologies merged. 

 This report does not address the realities of using the technologies to construct devices that 

are practical and certifiable for use in coal mines. It is unlikely that one could simply go out and 

purchase off-the-shelf technology and directly install it in an underground mine. The scope of 

this report was to highlight the technology that is available upon which products could be 

developed not only for coal mining, but also for other hazardous environments. 

ACKNOWLEDGMENTS 

 The authors acknowledge the National Personal Protective Technology Laboratory’s 

Technology Research Branch under the direction of Ronald Shaffer (Branch Chief) for 

supporting this research effort. The authors also thank Robert J. Tuchman, Technical WriterEditor, Centers for Disease Control and Prevention, for his contributions to improving the clarity 

and quality of this report. 

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736–742. 

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48

APPENDIX A.—LIST OF USEFUL WEB SITES

1. Designing wireless interfaces for patient monitoring equipment. [http://rfdesign.com/mag/

504rfdf4b.pdf]. 

2. Medical usability: how to kill patients through bad design. [http://www.useit.com/alertbox/

20050411.html]. 

3. Virtual Network Computing (VNC) software makes it possible to view and fully interact 

with one computer from any other computer or mobile device. [http://www.realvnc.com]. 

4. The Open Systems Interconnection Seven-layer Reference Model. [http://www.answers.com/

topic/osi-model]. 

5. Introduction to Mesh Network routing issues. [ftp://ieee:wireless@ftp.802wirelessworld.com/

15/03/15-03-0393-00-0030-mesh-network-outline.doc]. 

6. Building a Wireless World With Mesh Networking Technology. [http://www.intel.com/

technology/magazine/communications/nc11032.pdf]. 

7. RFC 3561 – Ad hoc On-demand Distance Vector (AODV). [http://www.faqs.org/rfcs/

rfc3561.html]. 

8. Simulation Model for the AODV MANET Routing Protocol. [http://www.antd.nist.gov/

wctg/manet/prd_aodvfiles.html]. 

9. Wireless Ad Hoc Networks homepage. [http://www.antd.nist.gov/wahn_home.shtml]. 

10. Distributed Detection for Smart Sensor Networks. [http://w3.antd.nist.gov/wctg/

smartsensors/sensornetworks.html]. 

11. RFC 3684 – Topology Dissemination Based on Reverse-path Forwarding (TBRPF). 

[http://www.faqs.org/rfcs/rfc3684.html]. 

12. Ronja: Reasonable Optical Near Joint Access, optical point-to-point data link. 

[http://ronja.twibright.com]. 

13. An Introduction to Optical Wireless. [http://www.eng.ox.ac.uk/optcomm/research/Intro/

optical%20wireless%20introduction.htm]. 

14. UWB Archive: Ultra Wideband (UWB) Frequently Asked Questions (FAQ). 

[http://www.multispectral.com]. 

15. Propagated Reference Design Provides Portable Ultra-wideband (UWB) Personnel Tracking 

System. [http://www.eetimes.com/showArticle.jhtml?articleID=20300709]. 
49

16. Run for your life: Ultra low-power systems designed for the long haul. [http://www.edn.com/

article/CA601827.html?industryid=2817&text=]. 

17. The DARPA-sponsored SensIT program. [http://www.sainc.com/sensit]. 

18. IEEE Begins Wireless, Long-wavelength Standard for Healthcare, Retail and Livestock 

Visibility Networks. [http://standards.ieee.org/announcements/pr_p19021Rubee.html]. 

19. Near-field Electromagnetic Ranging (NFER). [http://www.q-track.com]. 

20. Near-field Communication (NFC) Forum. [http://www.nfc-forum.org]. 

21. Near field or far field? How do we define the far field of an antenna system, and what 

criteria define the boundary between it and the near field? The answer depends on your 

perspective and your design’s tolerances. [http://www.edn.com/article/CA150828.html]. 

22. Trolley Scan (Pty.) Ltd., RFID-RadarTM. [http://www.rfid-radar.com]. 

23. IEEE 802.15 WPANTM Task Group 4 (TG4). [http://ieee802.org/15/pub/TG4.html]. 

24. IEEE 802.16 LAN/MAN Broadband Wireless LANS standards. [http://standards.ieee.org/

getieee802/802.16.html]. 

25. Electronic ID, Inc. [http://www.electronicidinc.com]. 

26. Wal-Mart Suppliers Discuss RFID. [http://www.rfidjournal.com/article/articleview/956/1/1]. 

27. RFID Blocker Tags. [http://www.ddj.com/dept/architect/184405806]. 
SAFER HEALTHIER PEOPLE tm

● ●

DHHS (NIOSH) Publication No. 2007–114

Delivering on the Nation’s promise:

Safety and health at work for all people

through research and prevention

To receive documents or more information about occupational safety and health topics,

contact NIOSH at

1 800 35 NIOSH (1 800 356 4674)

Fax: 513 533 8573

E-mail: pubstaft@cdc.gov

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or visit the NIOSH Web site at www.cdc.gov/niosh

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