{
    "title": "Crystal Radio Circuits",
    "inventor_name": null,
    "publication_year": null,
    "device_name": "Crystal Radio",
    "goal": "Provide a low-cost, self-powered radio receiver that can demodulate broadcast signals without an external power source.",
    "problem_addressed": "Need for inexpensive, portable radio reception in situations where batteries or mains power are unavailable.",
    "concept_summary": "A crystal radio uses a passive resonant LC circuit to select a broadcast frequency, a crystal detector (often a galena diode) to rectify the signal, and high-impedance headphones to convert the demodulated audio into sound. The entire system is powered by the energy of the incoming radio waves.",
    "detailed_description": null,
    "category": "Electromagnetism & Magnetism",
    "principles": [
        "Resonant LC tuning",
        "Crystal (semiconductor) detection",
        "Passive energy harvesting from RF fields"
    ],
    "scientific_domains": [
        "Electrical Engineering",
        "Physics"
    ],
    "mechanisms_of_action": [
        "Radiofrequency energy induces a current in the antenna",
        "LC circuit selects the desired carrier frequency",
        "Crystal detector rectifies the carrier, extracting the audio modulation",
        "High-impedance headphones convert the low-level audio current into sound"
    ],
    "materials": [
        "Galena (PbS) crystal or germanium diode",
        "Copper wire for antenna and coil",
        "Paper or cardboard for chassis",
        "Wooden or plastic housing",
        "Earphones/headphones"
    ],
    "energy_sources": [
        "Ambient radiofrequency electromagnetic waves"
    ],
    "inputs": [
        "Radiofrequency broadcast signals (AM, shortwave, etc.)"
    ],
    "outputs": [
        "Audio signal delivered to headphones"
    ],
    "claimed_performance": "Receives AM broadcast stations without any external power; audio output sufficient for headphones.",
    "experimental_evidence": "Numerous construction guides and test reports listed in the article (e.g., \"High Power Crystal Set\", \"Sun-Powered Radio\", \"Super-Sensitive Vestpocket Crystal Radio\") describe successful builds and listening tests.",
    "replication_status": "Multiple independent builds reported across decades; many hobbyist publications document functional receivers.",
    "keywords": [
        "crystal radio",
        "passive receiver",
        "galena detector",
        "LC resonant circuit",
        "free energy"
    ],
    "related_technologies": [
        "AM broadcast receivers",
        "shortwave radios",
        "diode detectors"
    ],
    "controversy_level": "low",
    "confidence_score": 0.9,
    "practicability_score": 0.8,
    "fringe_score": 0.1,
    "evidence_strength": 0.6,
    "risk_score": 0.1,
    "trl_estimate": 7,
    "source_urls": [
        "http://rexresearch.com/",
        "http://www.crystalradio.net/crystalplans/coolplans/"
    ],
    "organizations": [
        "Rexresearch"
    ],
    "applications": [
        "Emergency communication",
        "Educational demonstrations",
        "Low-cost hobby radio"
    ],
    "limitations": [
        "Very low audio power; requires sensitive headphones",
        "Limited reception range, depends on antenna size and signal strength",
        "Performance varies with crystal quality"
    ],
    "open_questions": [
        "How to improve detector sensitivity without external power?",
        "Optimal antenna designs for urban environments",
        "Materials that can replace galena for more consistent performance"
    ],
    "red_flags": [],
    "evidence_quotes": [
        "\"High Power Crystal Set\" (Electronic Experimenter's Handbook, 1951) demonstrates a functional high-gain receiver.",
        "\"Sun-Powered Radio\" (Science & Mechanics, June 1956) shows operation using only ambient RF energy.",
        "\"Super-Sensitive Vestpocket Crystal Radio\" (Oct. 1952) reports audible reception with a pocket-size antenna.",
        "\"A Simple Radiophone Receiver\" (Science & Invention, Apr. 1922) provides a step-by-step build that was successfully tested.",
        "\"Crystal Detectors & How They Work\" (detectors.pdf) explains the physics of the crystal diode used in all listed circuits."
    ]
}