for Harvesting Energy!
By Mohammad Honarparvar
Every electrical and electronic system needs a proper power supply to work perfectly. It is obvious that a television does not work without electricity. Your cellphone has a limited battery life and it will die if you don’t recharge the battery. At the first sight, it does not seem very important in the mentioned examples. However, just think about the devices which directly impact on the human health and quality of the human hearth such as pacemakers, hearing aid devices, implantable biomedical devices etc. an external battery has been using for the device outside the body and an external connection is made for the implantable device to recharge the battery. In the first case, due to the size of the battery the device size is undesirable even if the size of electronic part is small and in the second, the patient probably needs and extra surgery to check the implantable device and recharge it.
To tackle the afore mentioned problem, self-powered devices have been suggested. In such systems, the required power supply can be harvested from the available power resources in our surroundings, e.g. solar, wind, vibrations. Therefore, for proper utilization of the energy harvester, the available energy must be captured with extreme efficiency over the entire available power range. Designing the energy harvester in an integrated circuit (IC) requires effective architecture and appropriate control to achieve the required efficiency.
One of the interesting rich sources of energy is the human body. It is worth noting that the average adults consume about 2000 kcal per day which equals to 100W. The total available power associated with everybody activities for a 68kg adult is shown in the following picture. Since most of this power is lost as a body heat and vibration, it could be recovered to feed the biomedical devices. As you can see from the picture 67 µW powers is available from footfalls while about 2% of this power is quite sufficient to run many implantable devices. Blood pressure and lung motion are also fantastic source of energy with up to 1.5 µW power. Having had such a source of energy, patients can get rid of the extra surgeries for pacemaker battery replacement.
Having discussed a single source power harvester, capturing the power from multiple sources of energy is a hot topic and ongoing research. However, it should be mentioned that combining the power from the variable sources of energy needs a complicated control system. In such way the most reliable system can be achieved to avoid blacking out the device.
In conclusion, we are approaching to human implantable devices to monitor human body activities to send live feedback to the doctors. Moreover, wearable gadgets such smart watches and bracelets, smart eye wear, etc. could be supplied by ambient energy sources. Energy harvesting will commence to play a significant role in the development of such self-powered systems.