## 5 Applications of BSNs
### Trends and Challenges  
The scope of BSN applications is becoming wider and wider, which reflects not only in the broadening of the application domain, but also the improvement of service quality. Precisely, the improvements include three aspects: wearability, power consumption, and generality. Moreover, in the aspect of implementation, except for adopting normal sensors, bio-sensors, base stations and other hardware devices, more and more researchers are getting interested in mobile devices with embedded sensors such as mobile phones and smartphones. Wearability is one of the most important issues of BSNs. Researchers have done a lot of work on improving features like the volume, weight, wear resistance, softness, and biocompatibility of sensor nodes. In the process of sensor node design, reduction of volume and weight can be achieved by optimizing system hardware architecture and applying micro-electronic components. In order to enhance the wear resistance of sensors, highly abrasion-resistant materials are generally adopted to protect them. In the aspect of improving softness, P-FCB technique was proposed and is still under continuous study. Besides, flexible batteries can also improve softness, on condition that the problem of the great reduction of energy storage is solved. The improvement in biocompatibility could contribute to avoiding inflammation and allergy, as well as reducing the failure rate of devices. References [150] and [151] show how the defects of biofouling, hermeticity of encapsulation, electrode passivation and limited life of the immobilized enzymes can cause implanted sensor failure and affect patient health. Therefore, designing sensors with mild side effects is an important research topic to improve wearability. The power consumption problem, which is one of the major research directions now and in future, exists in any BSN system. Different from WSN ones, BSN sensors are small in size. They can only use compact batteries with limited capacity, which lead to short sensor node lifetimes [14]. At the same time, in many BSN applications, especially for those using implantable sensors, it is hard to prolong usage time by replacing the batteries. In view of these problems, how to reduce power consumption of sensor nodes, and increase the capacity of a battery in a limited volume, as well as prolong system life-span by energy acquisition from the surroundings are all potential development directions. In fact, the problems of power consumption are more than limited battery capacity and energy acquisition. In the aspects of circuit design, data processing algorithms and network communication protocols, a lot of work has been done and needs to be done sequentially and in depth in the future. In the future applications of BSNs, it is required that not only a system can work in any environment but also that data sharing and function cooperation can be achieved among different systems, therefore many studies focus on how to improve the universality of BSN applications. Universality mainly consists of algorithm universality and system universality. As for improving algorithm universality, further study is needed to explore the issues of signal processing applied to multiple non-standard data sets and finding the basic algorithms suited for many conditions. In order to improve system universality, research indicates that shaping an eventual data standard for data sharing can promote function cooperation among BSN applications. As mobile phones are becoming more and more popular in daily life, m-health technology has attracted extensive attention in medical field over the recent years. Existing research has implemented activity recognition, energy consumption monitoring and other functions. More and more functions will be gradually discovered in the future. In addition, the method of adopting mobile devices in BSN systems is not only suitable for the medical field, but also for other fields.