Clara Vance pressed the small brass disc of her bone-conduction transducer flat against the boiling green flank of Master Transformer #00.
The steel skin of the hundred-ton tank vibrated with thirty thousand amperes of circulating magnetic flux. The heat radiating from the cooling fins was so intense that Clara’s bangs clung wetly to her forehead, but her hand never slipped. Her thumb adjusted the gain potentiometer on the side of her acoustic receiver, tuning the carrier frequency until the forty-two-hundred-hertz tone in Julian’s right ear locked into absolute phase.
“Julian,” Clara whispered, her gray eyes widening in the dim orange emergency light. “It’s not an echo. It’s a magnetic induction loop.
Dad wired his own voice into the silicon steel core laminations.”
“How is that even possible?” Mac Cole asked, keeping his back pressed against the catwalk safety railing while watching the corridor behind them.
“Magnetostriction,” Clara explained, her fingers gently tracing the microscopic vibration along the steel seam. “When thousands of amperes of alternating current surge through an iron core, the metal grains physically expand and contract sixty times a second. In nineteen ninety-six, Dad didn’t just inspect this transformer with an ammeter.
He used an acoustic recording transducer -- the same model I have right here. He pulsed his own voice through the auxiliary excitation winding, permanently aligning the magnetic domains in the center steel core. As long as this transformer has power flowing through it, his words are trapped inside the metal.”
