Submitting My PhD Thesis: 4 Years of Energy Neutral Sensors

The moment I submitted my PhD thesis, I went to the pub. This is not a remarkable statement for anyone who’s done a PhD in the UK. What was remarkable was that I genuinely couldn’t remember the last time I’d been to a pub without a laptop. Four years of evenings spent staring at LaTeX will do that to you.

The thesis was called “Promoting Energy Efficiency and Longevity in Energy Neutral Sensor Systems.” If you’ve already glazed over, don’t worry. Most people do too. The short version: I spent four years figuring out how to make wireless sensors that harvest their own energy last longer and waste less of it. Think tiny devices powered by solar cells or vibration harvesters, deployed in places where you can’t change batteries because the location is remote, dangerous, or just really inconvenient.

The Three Research Questions

Every PhD at Imperial needs to demonstrate a “novel contribution to knowledge,” which is the academic way of saying “figure out something nobody else has figured out, and prove it.” Mine broke down into three questions:

First, can we model energy availability accurately enough to predict when a sensor will run out of power? (Yes, but it’s harder than you’d think because weather is involved and weather is chaos.)

Second, can we adapt the sensor’s behaviour in real time to match available energy? (Yes, and this is where it gets interesting. The sensor basically learns to be lazy when energy is scarce and productive when it’s abundant.)

Third, can we do all of this without making the sensor so complicated that the overhead eats the savings? (Mostly yes, with caveats that filled about 40 pages of the thesis.)

The total word count was somewhere around 65,000. I generated about 200 figures. The bibliography had 247 entries, of which I’d read approximately 190 with genuine attention and skimmed the rest while telling myself I’d come back to them. I never came back to them.

What a PhD at Imperial Is Actually Like

Here’s the tangent: people outside academia imagine PhD students as brilliant minds working in well-funded labs, pushing the boundaries of human knowledge. The reality, at least in computing at Imperial, is more like being a freelancer who has one very demanding client (your supervisor), no salary negotiation power (the stipend was about £16,500 per year in London, which is an adventure in creative budgeting), and a deliverable that won’t be due for four years, which sounds generous until you realise you’ll spend the first year reading, the second year failing, the third year finally getting results, and the fourth year writing it all up while panicking.

My supervisor was brilliant and supportive, but supervisors are busy people. You learn to be self-directed very quickly, or you don’t finish. I saw both outcomes among my cohort.

The department culture was good. There’s a reason Imperial consistently ranks in the top 10 globally for computing. The people around you are intimidatingly smart, and the seminars expose you to research across the full spectrum. I sat through talks on everything from formal verification to computational neuroscience to privacy-preserving machine learning. Most of it was only tangentially related to my work, but all of it made me a better thinker. I genuinely believe that.

The Viva

The viva voce examination is the final hurdle. Two examiners (one internal, one external) read your entire thesis and then question you on it for two to three hours. Mine lasted about two and a half hours. The internal examiner asked detailed technical questions about my energy models. The external examiner asked broader questions about real-world applicability.

The worst moment was when the external examiner pointed to a graph on page 147 and asked why the error bars were asymmetric. I knew the answer (the distribution was skewed because energy harvesting follows weather patterns, not Gaussian ones) but in the moment my brain decided to present me with a blank screen for about eight seconds. Eight seconds doesn’t sound long. In a viva, it’s geological.

I passed with minor corrections, which is the most common outcome and still felt like winning the lottery. The corrections took about three weeks. Then I was Dr Greg Jackson, which mainly means I can be insufferable at hotel check-in desks.

What I’d Do Differently

I’d write more, earlier. The biggest mistake I made was treating writing as something you do after the research, rather than alongside it. Every supervisor says this. Every PhD student ignores it. I was no exception.

I’d also collaborate more broadly. I spent too long in my own problem space and not enough time working with people in adjacent fields. Some of my best ideas came from conversations with people working on completely different problems.

Would I do a PhD again? Yes, without hesitation. But I’d negotiate a higher stipend. Or at least live further from South Kensington, where a pint costs £6.50 and a flat costs your entire sense of financial security.

The pub after submission was in Fulham. I had a Guinness. It tasted like freedom and hops.