Medical Electronics
rechargeable battery. This is because of patient compliance with regards to recharging: patients may forget to recharge the battery or the battery charger may become faulty. This impacts product design since primary batteries are much bigger than secondary ones because they must contain, from day one, all the energy required by the device for many years. In a conventional pacemaker, for example, the battery takes up about two thirds of the device’s volume.
There are signs that this could change. The examples of next generation AIMD described above have one thing in common: they have been miniaturised to the extent that they can be placed directly onto nerves, inside the heart, inside joints and implanted into arteries by catheters. All these devices need a small, energy dense battery. Primary batteries will not work: they will not contain enough energy to power the devices for years, hence rechargeable batteries are the only solution to enable the promise of these new medical technologies. A new conversation will have to happen, however, with the patients and approval authorities, in terms of deploying more rechargeable solutions. At the same time, several technologies have been developed that may yield energy dense miniature secondary batteries.
Cylindrical batteries, similar in shape to the batteries used for example in TV remote controls, can be miniaturised to become
almost needle-like. These specialised medical batteries can be as small as ~2 mm in diameter and 1 cm in length. Miniaturising
to this level however is tricky: at some point, the battery volume is dominated by that of the metallic packaging, and the proportion of active battery material diminishes. Solid state batteries are a novel type of rechargeable battery, made uniquely from solid ceramic and metallic materials. With no liquid inside, they need little packaging and can be miniaturised more effectively, down to a few mm3 in volume. The technology for producing these batteries is more akin to semi-conductor techniques than battery manufacturing methods, and their form factor and usability similar to integrated chips. Solid state batteries consist of stacked, thin (micron- level) layers of cathodes and anodes, which provide them with relatively higher power and fast charge capability, down to 10-15 min. It is likely that this latter feature will go some way to alleviating the problem of patient compliance with regards to regular recharging. Whilst not yet deployed in AIMD, medical device designers Cirtec Medical and solid state battery developers Ilika Technologies (this author’s company) have now joined forces to industrialise and commercialise this new battery technology. Watch this space!
https://www.ilika.com/
www.cieonline.co.uk.
Components in Electronics
October 2023 41
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