Power/Performance Bits: Sept. 29

Implantable transmitter
Researchers from Purdue University developed a fully implantable, wirelessly powered 2.4GHz radio-frequency transmitter chip for wireless sensor nodes and biomedical devices.

The team says the transmitter chip consumes the lowest amount of energy per digital bit published to date, consuming an active-mode power of 70 μW at 10 Mbps while radiating -33 dBm of power, resulting in an energy efficiency of 7 pJ/bit. It is small enough that it can be implanted into an eye to monitor pressure for a glaucoma patient or into another part of the body to measure data related to heart functions.

“A transmitter is an integral part of these kinds of devices,” said Hansraj Bhamra, a research and development scientist who created the technology while he was a graduate student at Purdue. “It facilitates a wireless communication between the sensor node or biomedical device and a smart phone application. The user can simply operate the device through a smart phone application and receive the biophysiological data in real-time. The transmitter in this case enables a 24-hour intraocular pressure monitoring for glaucoma patients.”

A fully implantable transmitter chip for wireless sensor nodes and biomedical devices. (Source: Purdue University)

The transmitter comprises a voltage-controlled power oscillator (VCPO) and a loop antenna which is patterned over a flexible Parylene C substrate to achieve biocompatibility. Acting as both a radiator and an inductive element for the VCPO, the loop antenna removes the need for a power amplifier stage and bulky off-chip matching network.

“In addition to being low power, our transmitter operates on wireless power to replace the conventional batteries,” said Pedro Irazoqui, professor of biomedical engineering and professor of electrical and computer engineering at Purdue. “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.”

Spray-on smart windows
Researchers at RMIT University, La Trobe University, and Queensland University of Technology produced a spray-on clear coating that could enable cheaper smart windows. The coating can block heat and conduct electricity, plus they rival the performance of current industry standards for transparent electrodes, according to the team.

Transparent electrodes are most commonly based on indium, which is expensive, applied through vacuum deposition methods. Instead, the researchers turned to tin oxide, which is much cheaper, doped with antimony to enhance conductivity and transparency.

The scientists used a process called “ultrasonic spray pyrolysis” to fabricate smooth, uniform coatings. A precursor solution is nebulized, using commercially available technology to create a fine spray mist that forms ultra-small and uniformly-sized droplets. This solution is sprayed on a heated support layer, such as glass.

When the solution hits the hot layer a chemical reaction is triggered, decomposing the precursor into a solid residue that is deposited as an ultra-thin coating. All the by-products of the reaction are eliminated as vapors, leaving a pure coating with the desired composition.

The ultra-thin clear coatings are made with a new spray-on method that is fast, cost-effective and scalable. (Source: RMIT University)

“Smart windows and low-emissivity glass can help regulate temperatures inside a building, delivering major environmental benefits and financial savings, but they remain expensive and challenging to manufacture,” said Della Gaspera, a senior lecturer and Australian Research Council DECRA Fellow at RMIT. “We’re keen to collaborate with industry to further develop this innovative type of coating. The ultimate aim is to make smart windows much more widely accessible, cutting energy costs and reducing the carbon footprint of new and retrofitted buildings.”

The coatings transmit between 80% and 90% of visible light and have sheet resistances of 10–20 Ω/sq⁻¹. It also blocks both UV light and infrared radiation.

The next steps in the research were developing precursors that will decompose at lower temperatures, allowing the coatings to be deposited on plastics and used in flexible electronics, as well as producing larger prototypes by scaling up the deposition, said Jaewon Kim, a PhD researcher in Applied Chemistry at RMIT. “The spray coater we use can be automatically controlled and programmed, so fabricating bigger proof-of-concept panels will be relatively simple.”