Design engineers are always trying to make their devices smaller, and it is in the area of medical technology where this is given perhaps more priority than any other. After all, the human body has limited space to (or in) which things can be attached or implanted, and the smaller, more ergonomic, and less intrusive a device is, the better it is for a patient and their outcome.
Now, researchers at Purdue University (PU) say they have developed a wireless RF (radio frequency) transmitter that consumes “the lowest amount of energy per digital bit published to date”. The transmitter is implantable and can be used with wireless sensor nodes and biomedical devices.
How the RF Transmitter Works
According to research published in the journal, IEEE Transactions on Circuits and Systems II, the PU researchers’ transmitter chip works similarly to the communication technologies found in smartphones and watches; where it’s different, however, is where it has an unprecedented level of miniaturisation and low energy consumption. This means it can be implanted into the body to measure data related to heart functions or into an eye (for example, to monitor the eyeball pressure of a glaucoma patient).
Designed to work with wireless sensors, the transmitter collects and then relays continuous data to sensory receivers within biomedical devices. With the use of connected apps, this enables 24/7 patient-led health monitoring. It also contains no battery. Instead, the transmitter obtains power wirelessly from other connected devices by using a resonance cavity.
A close-up of the transmitter made by the research team at Purdue University. Annotated is its polymer substrate: ‘Parylene C’. Image Credit: Purdue University.
“Batteries are undesirable since they increase the device size and weight and make it uncomfortable for patients. In addition, the batteries are built of toxic material and require frequent recharging or replacement surgeries,” said Pedro Irazoqul, a professor of PU’s School of Electrical and Computer Engineering.
The 2.4GHz narrowband transmitter uses 434MHz of power, and the power is harvested using an inductive loop antenna that radiates a signal. It has a continuous data mode (70 microwatts) and a sleep mode (128 picowatts) for on-and-off data capture, which reduces power consumption when continuous data capture isn’t necessary.
The transmitter is built using a complementary metal-oxide-semiconductor technology, which reduces power dissipation and is highly efficient. As for the materials used, Purdue’s transmitter is made from an inorganic material that is then coated by a substrate made up of Parylene C (annotated in the above picture)—which is biologically compatible with human tissue—to prevent the triggering of the patient’s immune response.
Whether the transmitter works in real-world applications remains to be seen. The human body is a tricky application and there are many things that could get in the way of the transmitter carrying out its function, particularly at times when it needs to communicate with sensory receptors some distance away. The team at Purdue University plans to continue its work to address these and other potential limitations.