Modulated Excitation Imaging System for Near-Surface Anomaly Resolution

The patent employs periodic modulated excitation signals (such as sinusoidal or square wave modulations) applied continuously or in repeated cycles to the transducer. This periodic action allows the system to accumulate signal energy over multiple cycles while maintaining the effective pulse duration short enough to resolve near-surface anomalies. The modulation frequency is selected to match or exceed the resonant frequency of the transducer, maximizing energy transfer and detectable signal strength.

The system transitions from discrete short pulses to continuous or quasi-continuous modulated excitation. The modulated signal maintains continuous energy input to the medium, allowing the receiver to continuously detect reflected signals. This continuity ensures that sufficient energy is always available for detection while the modulation envelope controls the effective imaging pulse duration, resolving the contradiction between energy availability and resolution.

By using periodic modulation of the excitation signal, the system achieves high energy input over extended periods while the modulated envelope maintains sharp temporal transitions. The receiver detects signals at specific phases of the modulation cycle, effectively filtering out late-arriving reflections that would cause eclipsing. This allows long-duration energy input without sacrificing the resolution provided by short effective pulse duration.

The system applies a preliminary gating or windowing function to the received signals, selectively accepting reflections that arrive within a specific time window corresponding to the modulated excitation phase. This preliminary action filters out later reflections that would otherwise eclipse near-surface anomalies, allowing the system to use longer pulse durations for energy accumulation while maintaining resolution through selective signal acceptance.

The modulated excitation signal concentrates energy at specific frequencies and time phases, creating high peak amplitudes during active modulation cycles. Even though the average power is reduced, the peak amplitudes during each modulation cycle are sufficiently high to generate detectable reflections. The periodic nature allows the receiver to synchronize detection with these peak amplitude phases, maintaining signal detectability while reducing overall power consumption.

The system changes the temporal and spectral parameters of the excitation signal through modulation, transforming a simple high-power continuous wave into a modulated signal with optimized energy distribution. This parameter change allows the same equipment to operate at lower average power levels while maintaining or improving signal detectability through the enhanced temporal structure of the modulated waveform, which improves signal-to-noise ratio through coherent integration.