Sensors and Actuators A 202 (2013) 147–154 Contents lists available at ScienceDirect Sensors and Actuators A: Physical jo ur nal homepage: www.elsevier.com/locate/sna Multi-sensor system with Bluetooth connectivity for non-invasive measurements of human body physical parameters A. Depari ∗ , A. Flammini, S. Rinaldi, A. Vezzoli Department of Information Engineering, University of Brescia, Via Branze 38, 25123 Brescia, Italy a r t i c l e i n f o Article history: Received 27 October 2012 Received in revised form 30 April 2013 Accepted 1 May 2013 Available online 18 May 2013 Keywords: Photoplethysmographic sensor Tissue impedance measurement Wireless sensor Portable smart sensor Non-invasive measurement a b s t r a c t In the last few years, the availability of powerful personal computing devices, like smartphones, has opened new scenarios to the so called “Body Area Network” (BAN), i.e., sensor networks specifically designed to monitor physical conditions of the user. The traditional methods adopted to monitor physical parameters, like heart beat rate or exertion level, are not suitable for real-time measurements. However, a continuous monitoring of such kind of parameters would allow the athletes to constantly control their physical conditions, furnishing useful information to prevent overstrain and to improve their perfor- mance. In this work, a simple, portable and low-cost system for non-invasive and real-time measurement of physical parameters is proposed and experimentally characterized. It is composed of three units: the sensor apparatus, electronic interface circuit, and the data transmission unit. Two different sensors are combined in a unique structure to be placed in a clip-like fashion on the earlobe or other body part of a person. A photoplethysmographic sensor is used to optically measure the changes of blood volume in the arteries, thus to acquire information about heart beat, blood pressure, and arrhythmias. The second sensor is composed of two electrodes, hence an impedance measurement of the tissue is carried out. The impedance estimation can be used to monitor the dielectric properties of biological tissues and fluids, like blood flow. A commercial battery-operated Bluetooth earphone is used both to transmit sensor data and to provide the power supply for the sensors and the first conditioning electronics. Data transmission is operated by the standard Bluetooth Hands-Free profile; therefore, sensor data can be easily acquired, elaborated and visualized by a broad range of commercial devices. In fact, Hands-Free is the only Blue- tooth data communication profile supported by any smartphone, from the low-cost ones to the high-end devices. The experimental characterization of the prototype, performed by using a specifically designed application for Android smartphone systems, has demonstrated the validity of the proposed approach. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Monitoring physical data, particularly during sport activities, can provide athletes with useful information about the body response to fatigue. If the information was given in real-time, the athlete could immediately recognize potential serious hazards for his health, for example due to overstrain, thus reducing or inter- rupting the activity. Moreover, training programs tailored to the athlete characteristics may take advantage of the real-time infor- mation, by suggesting him how to adjust the activity in order to improve his performance. A system able to acquire such data from the human body must be compact, light and portable, non-invasive and low-power, in order to be battery-operated during outdoor use. Several devices are today available on the market for such pur- poses; for instance heart rate belts are used to collect information ∗ Corresponding author. Tel.: +39 0303715899; fax: +39 030380014. E-mail address: alessandro.depari@ing.unibs.it (A. Depari). from athlete body and to transmit data to smartphones or dedi- cated devices. However, such systems are usually rather invasive and require a careful positioning of the sensitive elements, in order to provide meaningful results. In addition, the connection of these sensing devices to a smartphone for data visualization requires the use of external dongle, since typically their communication pro- tocol is not natively supported. In [1], a new approach has been proposed to improve the comfort and the quality of the provided heart rate measurements. The sensor is placed on the user earlobe and the acquired data are transmitted with wireless technology to an end-device for data processing and visualization. Therefore, the complexity and the cost of the sensor apparatus can be maintained low, whereas the power consumption is comparable to the one of the wireless transmission unit. The purpose of the present work is to improve the system in [1], in order to collect additional phys- ical information from the athlete’s body; in particular, beside the photoplethysmographic (PPG) sensor of [1], the measurement of the earlobe tissue impedance has been considered [2]. Data from both sensors are transmitted by the same audio Bluetooth interface, 0924-4247/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sna.2013.05.001