Heart disease is the leading cause of death in the world, and any form of early warning system for heart attacks not only buys time, but potentially saves lives. On that front, a group of innovative engineering students from Lund University (Lund, Sweden), led by Georg Wolgast, put a unique antenna design to work with a smartphone as part of a wireless body area network (BAN). The wireless BAN works with a small-form-factor planar-inverted-F antenna (PIFA) for early detection of heart attacks. The system utilizes the user’s own smartphone for data processing and to send an alarm upon detection of a heart attack.
The proposed heart-monitoring/reporting wireless system includes an electrocardiogram (ECG) sensor with electrodes attached with adhesive tape to a user’s chest to measure an ECG signal. Measurements are transferred to a microprocessor and then to a Bluetooth transceiver, where data can be broadcast to a user’s smartphone via the PIFA. Software processes that data, which shows the ECG and the received signal strength of the signals. The heart-monitoring system was evaluated with an Android smartphone and Android application software to process the data.
To conserve costs for commercial use and restrict size to no larger than 30 × 30 × 5 mm, the PIFA for the Bluetooth transceiver was designed on PCB substrates limited to 3-mm thickness. In fact, the antenna was built on two layers of 1.5-mm-thick FR-4 substrates with dielectric constant of 2.92 in the z-axis (thickness) of the material. The antenna was fabricated on copper-laminated substrates; unneeded copper was removed by means of low-cost chemical etching. The antenna’s ground plane was significantly extended to shield the antenna from the large dielectric load of a human body.
The PIFA for the unique Bluetooth-based wireless BAN was simulated with the aid of CST Microwave Studio from Computer Simulation Technology. The antenna was designed to operate in the frequency range of 2.440 to 2.448 GHz even when mounted on a human body, which is a large dielectric load. Simulations show an increase in resonant frequency of the antenna when adding such a large dielectric load. The 10-dB bandwidths of the antenna in free space and on the body were simulated as 105 and 143 MHz, respectively.
The end results from testing a completed system in a normal room with no shielding were recorded through 1 m of free space, through a user’s front pocket, and through a user’s back pocket. Measurements were made using a commercial vector network analyzer (VNA). Readings strongly resembled a normal ECG signal, and emphasize that this prototype system, designed and constructed with low-cost components, has the potential to provide correct ECG readings for patients even when surrounded by many other wireless-technology users.
See “Wireless Body Area Network for Heart Attack Detection,” IEEE Antennas & Propagation Magazine, Vol. 58, No. 5, October, 2016, p. 84.