Senior / Staff Power Electronics Engineer

About the Company  Until is a moonshot company building a “pause button” for biology. Our near-term focus is organ-scale reversible cryopreservation: preserving donated organs at subzero temperatures without ice formation, then rewarming them uniformly for transplant. By solving this grand challenge, we’re laying the foundation for whole-body reversible cryopreservation, giving patients a bridge to future cures. To achieve our goal, we are assembling an interdisciplinary team to develop perfusion systems, cryoprotectant formulations, and vitrification and rewarming hardware. We envision a future where no transplantable organ is lost to logistics, and no terminal diagnosis is final because patients can safely wait for future medicine to arrive. About the Role One of the key unsolved challenges in cryopreservation is the rewarming problem: how do we rapidly and uniformly rewarm whole organs and, ultimately, whole bodies to restart cryopreserved biology? Solving this requires MHz-frequency energy delivery into complex biological loads, involving high-voltage resonant power conversion, very high circulating currents, demanding insulation and safety constraints, and RF behavior that pushes well beyond conventional power electronics design.  We are building an elite team of electrical engineers and physicists with high autonomy, strong first-principles thinking, and a desire to build technology that feels impossible until it works.  This role is for someone who can own the architecture of extreme power electronics hardware from first principles, as comfortable deriving a back-of-the-envelope model from circuit laws, electromagnetics, and thermal physics as they are running simulation tools and wiring up hardware in the lab. What You'd Do: • Fully own power electronics hardware development for rewarming systems with unprecedented performance, from architecture through modeling, prototyping, validation, and iteration. • Architect novel power converter topologies, high-Q resonant networks, impedance matching systems, and electromagnetic structures • Drive system-level tradeoff studies across topology, frequency, voltage, current, insulation, thermal management, manufacturability, and safety. • Roll up your sleeves in the lab to prototype, test, and debug hardware and instrumentation setups methodically using rigorous engineering best practices • Design, build, and safely operate advanced laboratory infrastructure for validating high-voltage, high-current, MHz-frequency systems. • Collaborate closely with engineers, scientists, physicists, and cryobiologists to design and validate whole-organ and whole-body rewarming systems. About You: • Deep understanding of power electronics, electromagnetics, and analog circuit design, both first-principles theory and practical design. • 7+ years of hands-on experience (or equivalent advanced degree + track record) designing, building, and validating high-reliability, high-energy power systems. • Proven experience with high-frequency, high-voltage power converter design, including device-level modeling, semiconductor selection (SiC/GaN), layout parasitic mitigation, impedance matching, shielding, and EMI/EMC. • Strong lab skills with high-voltage, high-current, and high-bandwidth instrumentation; experience safely bringing up and debugging high-energy systems. • Proficiency with simulation tools (e.g., SPICE, PSIM, ANSYS Maxwell) to model power electronic, electromagnetic, and thermal behavior before fabrication. • Track record of exceptional engineering and a high degree of autonomy across the full hardware stack. • Desire to join a small, fast-paced team on an excellent adventure. Preferred Quailifications: • Experience developing first-of-its-kind high-energy hardware: RF power delivery and impedance matching for plasma processing, RF generators, EV power converters, induction heating, pulsed-power systems or similar. • Experience with medium-to-high voltage isolation systems, including creepage/clearance, dielectric materials, partial discharge mitigation, breakdown testing, and arc-flash safety. • Experience designing high-Q resonant tanks, matching networks, RF generators, or high-power MHz-frequency systems. • Experience with thermal design, liquid cooling, calorimetry, and multi-physics tradeoffs in high-power systems. • Experience leading or mentoring highly technical, multidisciplinary engineering teams. Benefits: Generous medical, dental and vision insurance coverage Flexible time off and paid holidays Competitive compensation package, including salary and equity Access to a 401(k) retirement savings plan FSA and commuter benefits Daily lunch and dinners, plus a variety of snacks  Monthly learning stipend On-site fitness center Quarterly team social budget