Quantitative supply of collected energy: wireless sensor node power consumption limit

Quantitative supply of collected energy: wireless sensor node power consumption limit

If the system around us can detect and react to changes in its environment by itself, it will undoubtedly change our lives completely. A wireless sensor network is such a system. Some distributed sensor implementations (nodes) in the system communicate with each other wirelessly and jointly respond to physical stimuli. This article outlines some of the latest developments in nodes to help you understand system-level design methods.

picture 1 Shows an example network and the subsystems of each node. Based on considerations of ease of deployment and lower installation costs, each node is required to be able to communicate wirelessly. In order to reduce communication overhead and shorten response time, we hope that nodes can process sensor data locally and control actuators. Routine maintenance (for example, battery replacement, etc.) for a large number of nodes may be extremely costly. The ideal situation is that only relying on the storage/collection energy sensor can continue to work for several years.
Quantitative supply of collected energy: wireless sensor node power consumption limit
picture 1 Sensor nodes collect energy to supply power, independently judge their environmental changes, and can communicate using multiple protocols.
The choice of sensor, radio and microcontroller (MCU) depends on the nature of the specific application. This article focuses on the sensor network in the office environment, and its applications include energy management, security, or resource planning.
Energy and storage
Light energy is usually the most common form of environmental energy in indoor environments.Some modern solar cells (made of amorphous silicon) can produce about5 uW/cm2.surface 1The estimated value of the rate of energy harvesting is listed, which indicates that a 10 cm2Solar cells can generate 70–120 uW.
surface 1 Approximate value of energy acquisition rate under general indoor fluorescent lighting environment
Room
strength (lux)
Power density(uW/cm2)
meeting room
300
7.5
desk
500
12.5
corridor
400
10.0
Micro thermal generators use a certain temperature gradient to generate electrical energy. But to generate 15 uW/cm3Power density, the heat collector needs about 10oThermal gradient of C. Many application environments, especially indoor environments, do not have large temperature fluctuations. Therefore, the applicability of heat collectors is limited in these environments.
Some of today’s vibration energy harvesters require an acceleration of about 1.75–2.00 g (indoor environments generally do not have such a large magnitude) to generate 60 Microwatts of power.
The board capacity of energy storage is very limited, and the opportunity to collect environmental energy is also very limited, so the sensor is required to use energy very economically.For example, if a solar cell with a battery capacity of 100 mAh gets 70 uW, it can be 10 The node life span of one year provides half the time of power supply. The node must allow its various subsystems to work, and the average power consumption must not be higher than 39 uW.
Node subsystem
MCUs, radios, sensors, and actuators have very different power consumption/performance characteristics. To meet the system power budget, sensor nodes are required to manage their subsystems in the best way.picture 1 Shows some subsystems used to implement a node.
Some modern low power consumption MCU Work on appointment 1MHz At the clock frequency, its peak power consumption is about 345 uW. Assuming that the sensor data processing requirements are generally moderate, the duty cycle of the MCU can be extremely small (for example: less than 1%) to reduce the average power consumption.
Sensor nodes usually transmit information such as physical phenomena and related control messages at a relatively low rate.surface 2 Summarized the salient characteristics of some important low-power wireless communication technologies.
surface 2 Comparison of some low-power communication architectures
Bluetooth [5]
IEEE 802.15.4a UWB [6]
Zigbee [5]
wirelessLAN [7]
frequency (GHz)
2.4
3.1–10.6
2.4
2.4
Data rate (Mb/s)
1
1–27
0.25
54
Nominal range(m)
1–10
1–30
10–100
100
Peak power consumption (mW)
92.4
<10
29.7
851
energy/bit (nJ/b)
92
~ 1
119
15
surface 2 The power consumption listed is only a general guideline for system design. With the development of transceiver design, its power consumption is getting lower and lower. When choosing a certain transceiver architecture, it is important to consider all aspects of the design. Wireless local area network (LAN) transceivers consume less energy/bit than Zigbee® transceivers, but they are optimized for higher data rates and have higher peak power consumption.
Some examples of sensors related to indoor applications include: thermometers, temperature sensors, microphones, and passive infrared sensors. Some current temperature and humidity sensors and microphones have peak power consumption of about 70-80 uW. The peak power consumption of some passive infrared sensors that can detect human activity is generally 100–500 uW. Temperature and humidity sensors monitor the phenomenon of slow changes, and work at a low duty cycle, while other sensors used to detect motion are turned off to reduce detection performance. In many applications, sensors require more energy than data processing or wireless communication. Therefore, meeting the system power budget requires innovative methods to manage sensors.
in conclusion
Although there have been tremendous advances in computing, communication, and sensing, the lack of sufficient power and energy sources is still a serious challenge facing the realization of wireless sensor networks. Some technological advances in energy harvesting and storage are constantly alleviating the power bottleneck, but some requirements for end applications are also pushing up their requirements. If you want to close this continuing power-demand gap, a system-level design method is required to achieve the best compromise between performance to achieve energy-saving purposes while ensuring the minimum quality of service. Future wireless sensor nodes will autonomously adapt to the changing application requirements and energy supply over time.

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