Millimeter-Wave Pulse Radar Scattering Measurements on the Human Hand

We investigate the backscattering of low-power millimeter-wave pulses (wavelets) on the human hand in order to determine the detection limit of scattering features. Using an in-house wavelet radar setup with a nominal spatial resolution of 2.29 cm, we measure a hand in three different postures: a flat hand, a fist, and a hand with raised index finger. For the latter, we are able to resolve backscattering from at least two different scattering centers, attributed to the heel of the hand and the finger. The effective radar cross section in the measurements was in the range from $-\text{29.5}$  to  $-\text{35.1}$  dBsm. We demonstrate that detecting scattering features from the hand with an equivalent isotropically radiated power spectral density of $-$ 68.5 dBm/MHz is possible. This shows that, compared to most conventional radar systems operating close to the regulatory emission limits (13 dBm/MHz), the energy of the transmitted waveform can be significantly reduced. The result shows that low-power radar systems for gesture recognition are feasible using pulsed systems with ultrashort pulses and low duty cycles. This is key for integration in battery-powered devices.