blockchain History of engineering & technology 11 Technology: general issues 11 machine learning 7 artificial intelligence 6 sustainability 5 COVID-19 4 Ethereum 4 IoT 4 circular economy 4 classification 4 internet of things 4 smart contract 4 supply chain 4 3D printing 3 Industry 4.0 3 additive manufacturing 3 blockchain technology 3 cyber-physical systems 3 cybersecurity 3 distributed ledger 3 electric vehicle 3 electric vehicles 3 emissions 3 healthcare 3 microgrid 3 optimization 3 power quality 3 regulation 3 renewable energy 3