Video
This video demonstrates the body sensor network being integrated into a bomb disposal suit.
NP Aerospace's latest version of their bomb disposal suit, the "Mark IV Explosive Ordinance Disposal (EOD) suit", is one of the most sophisticated ever. However the company have identified an unsolved problem, which occurs generally with heavy enclosed armour of this kind: the potential for Uncompensable Heat Stress or UHS. When we exercise, our body heats up and we sweat; the sweat evaporates and this evaporation cools the skin. In an enclosed environment, however, the air becomes humid, evaporation stops, and this leads to heat stress. Heat stress can impair judgment and, if left untreated, can be fatal. We have been developing a prototype body wireless sensor network that is integrated into clothing underneath the armour that will monitor body temperatures at multiple sites. The system makes use of a sophisticated model to estimate thermal sensation. The system makes use of mixed wired/wireless technology to achieve detailed temperature monitoring of personnel and innovative information extraction and processing to infer the wearer's thermal sensation. A remote visualiser allows for continuous monitoring and alarm generation at mission control.
A typical bomb disposal mission will initially involve investigating the site using a remote controlled robot, and if possible, disarming the bomb remotely. Sometimes, however, it is necessary for a human bomb disposal expert to disarm the device. For this, the expert will put on a protective suit and helmet, pick up a tool box of equipment, and walk to the site. To reach the bomb's location, it may be necessary to climb stairs, crawl through passageways, or even lie down to fulfil the mission.
One of the UK manufacturers of such suits, having identified the problem of the suit wearer becoming uncomfortably hot and, in the worst case, suffering heat stress, have attempted to address it by installing an in-suit cooling system. The cooling system has a variable control thus both allowing the airflow to be adjusted for comfort and also allowing the life of the batteries that power the fan to be extended, as they would only provide sufficient power for part of the mission otherwise. The problem with this cooling approach, though, is that the bomb disposal expert has other critical concerns during the mission and either does not bother to put the fan on or tends to set it to maximum airflow from the beginning of the mission.
To address the above problems, together with the imminent need to reduce the risks of such missions, this work proposes embedding into the suit a body sensor network based instrument, that, primarily, aims to:
A secondary goal of this work is to provide the manufacturer with instrumentation that will allow them to design test strategies leading to better understanding of how the suit material and design choices are affecting the wearer's thermal sensation during use. With this in view, the prototype presented here has been designed such as to allow easy integration of additional in-suit sensors, such as accelerometers to monitor posture, heart rate monitors, skin wettedness monitors, and CO2 sensing within the helmet. The prototype system developed both satisfies the need for remote monitoring and allows for future integration of a cooling automation component to ensure effective, need-based cooling.
The system proposed has a high innovative value, allowing, for the first time, detailed monitoring of personnel in bomb disposal missions. Moreover, the prototype can act as a design aid/tool within the suit manufacturing processes, allowing for quantitative assessment of wearability for such suits.
In response to the suit related constraints, the overall design of the system is structured around a mix of wired and wireless communication. Multiple sensing packages are wired to each node. The wiring will be incorporated into the fabric of the suit or an undergarment in future. Although wireless communication from each sensor package might seem feasible, this would both increase the size and weight of the sensor packages and require additional batteries or power harvesting devices, hence decreasing the wearability of the system. Since there is a need to sense skin temperature at a number of points, such an approach would be unwieldy.
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The prototype design consists of a number of hardware components, including a remote monitoring station, two acquisition nodes, one processing node, twelve temperature sensors, and the cooling system. The connections between these components are shown above. The acquisition nodes, processing node, and remote monitoring point form a wireless network. Each acquisition node is wired to several temperature sensor packages via an I2C bus, while the upper body node additionally connects to a pulse oximeter (via Bluetooth) and a CO2 sensor (via a serial connection). Although it would be possible to connect all sensor packages used in this prototype into a single acquisition / processing node, using separate nodes allows the helmet, jacket, and trousers to be separately instrumented with no wires running between them. This is essential for ensuring that the system remains easy to use and transparent to the wearer.
The Gumstix Verdex XM4-bt board [1] was selected as the main processing and communication platform within the suit. The Verdex includes an Intel XScale PXA270 400MHz processor, 16MB of flash memory, 64MB of RAM, a Bluetooth controller and antenna, and several connectors for expansion boards. There are no on-board sensors provided. The sensor packages connect to the Verdex board via an in-house designed expansion board.
Although the system design calls for differentiating the in-suit communication and the long range communication, the implemented prototype makes use of Bluetooth (class 2) throughout, which has a typical operating range of around 10 metres indoors, and slightly more outdoors, depending on the environment. Class 1 equipment could be used to extend the range at the cost of lower battery life (which for the prototype here is approximately 3.5 hours of full functionality). An alternative is to use ZigBee (supported by the expansion board), which would reduce the available data rate but allow a longer range.
The prototype system uses twelve sensor packages based on Analog Devices ADT75A temperature sensor ICs (shown above). This device has the advantage that it contains the sensor, ADC, and bus interface in a single package. Temperature values are transmitted as 12 bits, which causes rounding to within 1/16°C. The sensor packages are positioned around various parts of the body roughly following the standard positioning used for skin sensors as used by Thake and Price [2], which is a subset of the locations discussed by Shanks [3]. These are: lateral calf muscle, front of thigh (or quadriceps), abdomen, chest, biceps, and neck. Given that temperatures are known to be symmetrical between left and right sides in healthy people [4], sensors have been placed on a single side. Two sensor packages were used per skin site. This arrangement enables individual data validation.
Heart rate and blood oxygen saturation (SpO2) data is supplied by a Nonin Medical pulse oximeter, which communicates with the upper body node via Bluetooth. Helmet CO data is supplied by an ELT, Inc. B530 sensor, communicating with the helmet node via a serial link.
The in-network processing within the system has two main objectives: enabling the system to continue functioning in adverse data conditions (invalid data or communications errors), and performing thermal modelling.
See here [link (pdf)] for a description of the fault management techniques employed in the prototype system.
See here [link (pdf)] for a description of one of the thermal modelling options investigated.
The visualisation application is split into several panels which may be toggled on and off. The main information display panel displays average temperature, estimated overall sensation, alerts, sensors health status, cooling actuation status, and has provision for displaying posture information. A secondary panel includes a 2D figure, with individual segment's thermal sensation and temperature mapped on the body at sensing sites. A third panel provides time series graphs of all incoming data and information. There are threshold based alerts for both the overall thermal state of the operative as well as for individual body segments.
Presently the work has passed the "proof-of-concept" stage and has been repeatedly deployed in controlled environments, with the subjects performing bomb disposal protocols at various environmental temperatures (from 20°C to 40°C).
These experiments begin with sensors being attached to the subject using PVC tape, followed by suiting-up. The subjects wear the outer shell of the bomb disposal suit including the jacket and trouser segments in addition to armour plating, helmet and boots.
The subject then undertakes an activity regime composed of: (1) walking (3 minutes) (see below); (2) kneeling while putting weights into and out of a rucksack (approximately 2kg, 2 minutes) (see below); (3) crawling (2 minutes); (4) arm exercise (4 minutes); (5) sitting (3 minutes); (6) standing (1 minute). Temperature data is consistently collected both via the prototype wireless system and via a wired-in data logger (accepted, commonly used, off the shelf, laboratory instrumentation for life sciences physiological assessments). Data was gathered during two consecutive activity regime runs as above, in a 5m x 6m draft free room, with an ambient temperature of 21°C. The experiments have been repeated for a variety of subjects, with and without acclimatisation, more or less fit generally, and so forth.
