Wireless Fully Passive Package-Embedded Seismocardiogram With RF Backscattering

Miniaturized fully passive wireless seismocardiogram (SCG) cardiac monitoring devices are demonstrated with heterogenous integration of sensor and telemetry components. The novelty stems from its minimal obtrusiveness on the skin, operation at zero power, and disposability because of its low cost. The key innovation is the passive wireless module comprising of a dual-band antenna, antiparallel diode, a bypass capacitor, and a piezoelectric polyvinylidene fluoride (PVDF) thin-film sensor for sensing the mechanical activity of the heart. The piezoelectric film is micropatterned to enhance compliance, match skin stiffness, provide stretchability, and convert mechanical vibrations into electrical signals (<inline-formula> <tex-math notation="LaTeX">${f} _{\text {SCG}}$ </tex-math></inline-formula>). A 2.4 GHz signal is transmitted from an interrogator to the wireless passive module, which upconverts and mixes the signal (4.8 ± <inline-formula> <tex-math notation="LaTeX">${f}_{\text {SCG}}$ </tex-math></inline-formula> GHz) and retransmits it to the interrogator. The system components are embedded in a liquid crystal polymer (LCP) to realize planar interconnections and minimize electrical parasitics and total thickness. The wireless passive module is <inline-formula> <tex-math notation="LaTeX">$8.5\times 9.5\times0.4$ </tex-math></inline-formula> mm3 whereas the thin, stretchable, and highly compliant piezotransducer is <inline-formula> <tex-math notation="LaTeX">$30.92\times 22.31\times0.028$ </tex-math></inline-formula> mm3. Thus, our approach leads to the smallest SCG cardiac monitoring device reported until now.