If I were searching through biographies looking for lesser-known electronics innovators of the mid-twentieth century, I would instinctively expect to find middle-aged men working at places like Bell Labs or MIT. These would be studious, cerebral individuals of somewhat prosaic character and unremarkable appearance. Artistic pursuits would be secondary—or tertiary, or quaternary—concerns in their lives. Most would have “MS” or “PhD” after their names. And they probably wore browline spectacles.

But life is full of surprises. Hedy Lamarr had no formal education in engineering or related fields.

Lamarr in 1940. Image used courtesy of MGM/Clarence Bull

Her research lab was a place called Hollywood, where she plied her trade as an actress and specialized in captivating audiences with her astonishing beauty. And she holds a patent for a frequency-hopping radio communication system intended for jam-resistant torpedo control. 

An Expansive Mind

Though Lamarr never went to college and was already a film actress at age 16, she was a brilliant young woman whose interest in technology had been cultivated from a young age by her father.

Though her young adulthood was occupied far more with movie sets than with STEM experiments, Lamarr’s naturally creative and exploratory mind was nourished by various activities that were interwoven with her artistic career: she was briefly married to a munitions dealer and thereby acquired some knowledge of weapons technology; she had access to equipment that allowed her to tinker in her spare time; her relationship with Howard Hughes (of Hughes Aircraft Company fame) connected her with aerospace technology and professional engineers; and she crossed paths with George Antheil, whose inventive spirit and familiarity with player pianos would be crucial in the elaboration of her most famous innovation.

Samson and Delilah was one of Lamarr’s most successful films. Image used courtesy of Wikimedia Commons

The Player-Piano Torpedo

The year was 1940, and Lamarr was eager to contribute to the war effort. She knew that radio-controlled torpedoes were potentially decisive weapons in naval combat but were also seriously susceptible to jamming—i.e., to intentionally generated RF interference.

In order to produce an effective jamming signal, the enemy must broadcast sufficient RF energy at the target equipment’s carrier frequency. This task could be rather easy or rather difficult depending on the circumstances, but it will always become much more difficult if the target’s carrier frequency is continually changing. Lamarr realized this and formulated her idea for a frequency-hopping radio system, which is aptly summarized by the following excerpt from the patent issued jointly to her and Antheil:

Our system as adapted for radio control of a remote craft, employs a pair of synchronous records, one at the transmitting station and one at the receiving station, which change the tuning of the transmitting and receiving apparatus from time to time, so that without knowledge of the records an enemy would be unable to determine at what frequency a controlling impulse would be sent. Furthermore, we contemplate employing records of the type used for many years in player pianos, and which consist of long rolls of paper having perforations variously positioned in a plurality of longitudinal rows along the records.

Thus, the craft’s control signal “hops” from one carrier frequency to another according to a sequence that is known to the transmitter and receiver but (hopefully) not to the enemy. Even if the enemy succeeds in jamming one of the frequencies, the other frequencies will enable enough communication for successful remote-control functionality.

This ingenious adaptation of player-piano technology to dirigible torpedoes is surely a milestone in the history of low-budget, hobbyist-style engineering. The United States Navy didn’t initially implement the design, but Lamarr sowed a seed that would grow and bear fruit in the decades to come.

Lamarr’s patent shows familiar building blocks of RF systems. Image used courtesy of Free Patents Online

From Torpedoes to Wi-Fi and Beyond

Frequency hopping and other forms of spread-spectrum technology were eventually incorporated into numerous RF protocols and systems, including IEEE 802.11 (commonly known as Wi-Fi), Bluetooth, GPS, and cellular networks. Without the pioneering work of Hedy Lamarr and other twentieth-century innovators, the current landscape of fast, reliable, easily accessible wireless communication would not exist.

This diagram depicts the manner in which direct-sequence spread spectrum (DSSS) modulation makes an RF link resistant to interference.  

Lamarr’s work is a case study in the harmonious convergence of art and science, and a homage to the variegated and adaptive brilliance of the human mind. She is an inspiration to those who pursue knowledge and accomplishment outside their sphere of professional or academic expertise.

This piece is part of a series of articles that All About Circuits will publish throughout Women's History Month, celebrating key female figures in electrical engineering. Stay tuned for more feature stories. You can find what we've already covered below. 

• Kicking Off Women’s History Month with the “Queen of Carbon Science”