US Patent 11642084 Measurement of body fluid retention using inductive coupling

An apparatus includes a magnetic-field transducer, and circuitry. The magnetic-field transducer is configured to be coupled externally to a body of a patient. The circuitry is configured to generate and apply to the magnetic-field transducer a time-varying signal, so as to generate a time-varying magnetic field outside the body of the patient, for supplying electrical energy by inductive coupling to an electronic device that is positioned inside the body, to estimate an intensity of the magnetic field that reaches the electronic device, and to assess fluid retention in an organ of the patient based on the estimated intensity of the magnetic field.