Structural Health Monitoring using Wireless Sensor Networks - Mobile and Pervasive Computing in Construction - page 219

11.2 How to realize long-term monitoring with WSNs using
battery-powered wireless sensor nodes

In traditional wire-based SHM systems, power management is of little concern,
since the deployed sensors are all AC powered. However, considering the
availability of AC power access, the cost of cables and the convenience of
deployment, wireless sensor nodes in most of the WSN-based SHM systems are
battery powered.
Limited power supply is one of the most critical issues of WSN-based SHM
systems. Table 11.3 lists the power consumption of some prototypes of wireless
sensor nodes, some of which are academic developed and others of which are
commercial off-the-shelf prototypes. It can be seen that most of the wireless sensor
nodes used in SHM are energy consuming when working in a full load condition.
Taking the Jingdo Bridge as an example, the maximum current drawn by the sensor
nodes developed by UIUC is 184mA. The battery can only support about five hours
of continuous work. Considering the potential cost of the constant maintenance
and battery replacement, particularly when access to the sensors is difficult, some
measures need to be taken to extend the lifetime of the system.
Solutions proposed to solve this problem can be largely classified into three
categories: sleep and wakeup, in-network processing, and energy harvesting.

11.2.1 Sleep and wakeup

A common approach to achieving energy savings in wireless sensor networks is to
put the sensor nodes into the sleep mode if they are not working. Almost all the
types of wireless sensor nodes working in the sleep mode consume much less energy
than in the working status. For example, in the wireless sensor node designed by
UIUC, the current draw of the node is only 0.5mA at sleep mode, whereas it can
reach more than 150mA in full load working status such as sampling and data
transmission (Nagayama and Spencer, 2008). Putting the sensor nodes into sleep
mode as long as possible can significantly extend the system lifetime.
Putting a sensor node into sleep mode is a trivial task, but when and how to wake
it up needs a careful design. Since SHM applications require synchronized

Table 11.3 Some wireless sensor nodes and their power consumptions

Prototypes Power consumption at full load Battery used

Dual-core mote 100mA @ 3.5V (CPU) 7.5V battery pack

(MPC555 Atmel AT90S8515 190mA @ 5V (Wireless mote)

þ

RangeLAN2)

þ

(UM)
MicaZ sensor board 44mA @ 9 V Four lantern batteries 9V

(11 Ah)

þ

(UC Berkeley)
ISM400 56mA @ 3.3 V (Imote2 @ 13MHz) 3 V AAA (1000mAh)

(Imote2 þ sensor board) 184mA @ 3.3V (Imote2 @ 104MHz)

(UIUC)