Coded signals are widely used in ultrasound microscopy and they can improve signal to noise ratio and imaging quality. However, so far all reported solutions has limited bandwidth under 135 MHz. We present a solution for ultrasonic microscopy that is capable of dealing with coded GHz signals.
The ultrasound microscope features a high frequency arbitrary signal source, a solid state switch, a microcontroller trigger device, and a preamplifier. Our signal source based on quadrature I-Q modulator modulates a high frequency signal with low frequency arbitrary signals and produces a high frequency arbitrary signal. This signal source gives more than 200 MHz bandwidth in center frequency range of 0.2 - 1 GHz that can be used for coded signals. For pulse echo operation we use commercial 3 GHz solid state switches that handle 15 Vpp signals and that are controlled by an Atmel microcontroller. The preamplifier is a custom built low noise preamplifier (3.3 dB noise figure) with broadband, 0.01 - 1.2 GHz. Originally the components was developed for wireless networking.
We performed electric tests on our devices with several signals whose frequency range was 0.1 - 1.1 GHz. We also validated our device with a custom built ultrasound immersion microscope by imaging a 5 µm tall MEMS step structure using 100 - 300 MHz, 3 µs, 10.5 Vpp linear and non-linear chirp excitation. This device allows one to use high frequency coded signals and it advances the state-of-art of ultrasonic microscopy.
