Why SWaP is not just for defence applications

Neil Oliver debunks the idea that size, weight and power (SWaP) are engineering considerations specific to defence applications. He why these are crucial in other high-precision applications, such as medical technology.

Achieving the optimum balance of size, weight and power (SWaP) has been crucial in the development of portable electronic devices for the military (MilTech), as well as the battery packs that power them, for decades. On the battlefield, calculating how much to reduce size and weight whilst maintaining sufficient power is essential.

SWaP originated in the military and aerospace sectors to address the need for portable electronic devices that were more compact, lighter, and energy efficient. Reducing the size and weight of each component inside the device, including the battery pack or single-cell battery, plays an important role in reducing the overall size and weight.

When it comes to meeting the power needs, the battery takes centre stage. That is why battery manufacturers were heavily involved in the soldier modernisation projects that resulted in the multiple electronic devices worn by a dismounted soldier being powered by a single battery pack, drastically reducing the weight the soldier needed to carry whilst still being able to sufficiently power all the equipment.

These projects have been so successful that the focus on SWaP has expanded into various other industries, including medical devices, where optimising these factors has enhanced portability and performance.

Medical applications

Most medical device designers will factor SWaP into their specifications for a battery pack or single-cell battery for different reasons, such as to reduce the size and weight of the end device to take up less space at the patient’s bedside, to improve transportability and manoeuvrability of the end device or to make patient-worn devices more comfortable. However, it is essential that medical devices still have enough power to perform reliably, as they play a vital role in treating patients.

Taking up less space is especially key for large medical equipment such as ventilators, defibrillators and infusion pumps. In recent years, improvements in the energy density of rechargeable battery packs have enabled these devices to perform with high reliability without adding excessive size and weight. In these applications, factors other than SWaP should also be considered, such as the ability to replace the battery packs when components (such as cells) reach end of life, especially bearing in mind that many of these devices have a service life exceeding 15 years.

The second reason medical device engineers consider SWaP (to aid transportability and manoeuvrability) is key for medical carts. Starting with the power demands, workstations may carry computers, monitors, printers and scanners, so it is vital to ensure that the portable power source delivers enough energy.

With regards to size and weight, these mobile workstations are pushed along hospital corridors and between different patient beds for hours at a time, so a heavy cart that is difficult to manoeuvre would be impractical and could result in an accident or injury. Reducing the size and weight of the battery pack and power system can help to alleviate that.

Finally, as previously mentioned, SWaP is an important consideration for medical wearables, which must be compact so as not to irritate the patients wearing them. Size and weight-wise, the innovative Thin Cell range of non-rechargeable single-cell batteries measure as thin as 1.1mm and have a 50% better gravimetric energy density than lithium coin cells. Power-wise, Thin Cells outperform coin cells at higher discharge rates, provide a stable voltage, and operate safely within a wide temperature range of between -20°C and +60°C.

The medical device sector is a perfect example of why the concept of SWaP isn’t just applicable to military applications. However, there are many other sectors where it is also a key consideration.

In consumer electronics, devices such as smartphones, tablets and wearables prioritise compactness and long battery life, pushing innovations in lithium-ion and solid-state battery technology. In aerospace, reducing weight is critical as lighter batteries contribute to fuel efficiency and longer flight durations. In the industrial and robotics sectors, autonomous systems and robotics depend on lightweight, high-capacity power sources to extend operational efficiency without frequent recharges.

The right balance

Achieving the right balance between size, weight and power presents several challenges. A smaller device may be more portable but may not accommodate a large enough battery to meet runtime requirements. Designers must weigh the need for compactness against the necessity for extended operation.

There is also the contest between aesthetics and functionality to consider. Product designers aim to create sleek, visually appealing devices, while engineers and regulatory experts must ensure the battery delivers sufficient power in a reliable way. Striking a balance between form and function is key.

To address these challenges, early collaboration between designers, engineers, regulatory experts and suppliers is essential. By understanding requirements from the outset, battery manufacturers can develop a product that meets all stakeholders’ needs without unnecessary compromises.

SWaP is not just a concern for military engineers. It is critical for designing efficient, high-performance portable devices across multiple industries.

Neil Oliver is, technical marketing manager at military, medical, and industrial battery manufacturer, Accutronics.