Abstract—In this paper， the problem of wireless communications in human tissue is addressed for biosensor network applications. Today’s offered solutions involve the usage of RF communication systems， which have shown to provide adequate performance to ensure proper network functionality. Yet they do not ensure that human tissue is not harmfully affected. In order to overcome this issue， we propose the use of ultrasonic waves for wireless communications in biosensor networks， motivated by the fact that， in contrast to electromagnetic waves， ultrasound has been used for almost a century now for medical purposes without any reported side effects. A simple propagation model is used to evaluate ultrasonic waves as a communication medium， study the feasibility of our proposal， the effective bit rates that may be achieved， the power efficiency of the scheme， as well as other system issues. Index Terms—Biosensor networks， body area networks， channel model， implanted sensors， ultrasonic communications. I. INTRODUCTION T HE SCIENTIFIC field of wireless biosensor networks has been developing extensively in the last few years， promising a significant upgrade in the quality of healthcare services provided to users. The vision for future biosensory systems includes the development of networks of devices implanted in the human body， which will be used for real-time health monitoring， diagnostics， or as prosthetic devices （i.e.， ［1］–［5］）。 The challenges involved in meeting this vision are still a great many， including the development of implantable material， sensing devices， algorithms， and protocols for communication. In the field of sensor communications in particular， there has been a large amount of technology transfer from the ad hoc and sensor networks fields of research， where RF communications are dominating ［6］。 For biosensor networks， research on RF communications focuses on the challenges involved with the way that the human body behaves as a communication medium as well as how RF waves affect the health of human tissues. This research has not been conducted solely for biosensor network applications， but for the general case of electromagnetic emissions from any device that resides in the vicinity of the human body. The human tissue is very vulnerable to heat absorption. If this is done over a specific limit， then the tissue can either be damaged or infected by bacteria that otherwise could not grow in population due to lack of heat ［4］。 This fact further limit