MUHD: A Multi-channel Ultrasound Prototype for Remote Heartbeat Detection Topics: Biomedical Equipment & Instrumentation; Biomedical Sensors; Diagnostic devices; Electrocardiography and Heart Monitoring; Health Monitoring Devices; Wearable and Mobile Devices In Proceedings of the 13th International Joint Conference on Biomedical Engineering Systems and Technologies - Volume 1: BIOSTEC, 57-63, 2020 , Valletta, Malta