The application relates to an ingestible capsule (102) for delivery of a substance e.g. a pharmaceutical drug, to a human or animal. The ingestible capsule comprises a capsule wall structure (202) forming a substantially sealed reservoir or lumen holding the substance (204). An electrical resonance structure, responsive to microwave electromagnetic radiation, is attached to a first wall portion of the capsule wall structure which comprises a lossy dielectric material. At least a predetermined segment of the first wall portion is heated by received microwave electromagnetic radiation to trigger a release mechanism of the ingestible capsule.