CN114814790A

CN114814790A - Low-cost high-resolution laser radar

Info

Publication number: CN114814790A
Application number: CN202210491420.9A
Authority: CN
Inventors: 李雨晗; 江钧屹
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2022-05-07
Filing date: 2022-05-07
Publication date: 2022-07-29

Abstract

The invention provides a low-cost high-resolution laser radar, which realizes the dynamic control of resolution by independently controlling a VCSEL transmitting dot matrix, and reduces the requirement on a receiver, thereby reducing the system cost. VCSELs typically consist of hundreds or even thousands of emission points, and more advanced VCSELs can achieve independent control of the lattice. Based on the method, the VCSEL can divide the whole emission array surface into N according to requirements ₁ ×M ₁ The emitting units irradiate the detection target in a time-sharing manner, and the detector receives and senses the detection target at the same time, and each independent emitting unit can obtain the resolution ratio N ₂ ×M ₂ Thereby obtaining the sensing result finally after all the transmitting units complete sensingResolution is (N) ₁ ×N ₂ )×(M ₁ ×M ₂ ) Thereby greatly improving the resolution.

Description

Low-cost high-resolution laser radar

Technical Field

The invention relates to the technical field of laser radars, in particular to a low-cost high-resolution laser radar.

Background

The lidar generally emits laser light of 905nm or 1050nm wavelength, receives the laser light by an avalanche photodiode or CMOS, and determines the distance to a detection object by calculating its time of flight (TOF). Laser radar has been widely studied and applied in the fields of automatic driving and space modeling due to its outstanding angle, speed and distance resolution.

However, when using a photodiode array as the receive sensing, existing solutions often use a single transmitter as the signal transmitting part, so that the final system resolution is equal to the receiver array resolution, but only the system resolution can be increased by increasing the number of receiver sensing arrays. However, the avalanche diode array detector is usually high in cost, the improvement of the resolution is very limited, the number of received signals is greatly increased, and the difficulty of signal processing is increased.

Disclosure of Invention

In view of the above-mentioned problems in the prior art, the present application proposes a low-cost high-resolution lidar comprising a transmit array, a plurality of metamaterial elements forming a lens, the array configured to transmit radar range frequency electromagnetic waves; an exciter configured to excite the metamaterial element so as to generate electromagnetic waves that illuminate the target with sub-wavelength sized illumination; and a control part configured to control a focal point of the lens.

Preferably, the control means for controlling the focus of the lens is further configured to control the focus of the lens using a time delay.

Preferably, the stimulator is selected from a near field probe, a port, an antenna or a combination thereof.

Preferably, the control component is selected from a tunable resonant component and a tunable resonant sub-circuit.

Preferably, the frequency of the electromagnetic wave is less than about 1 MHz.

The features mentioned above can be combined in various suitable ways or replaced by equivalent features as long as the object of the invention is achieved.

Compared with the prior art, the low-cost high-resolution laser radar provided by the invention at least has the following beneficial effects:

1. the detection resolution ratio is dynamically controlled, and the radar detection efficiency is improved. The radar signal processing complexity and the signal resolution ratio are in positive correlation, if the radar resolution ratio is far higher than the scene requirement, the processing complexity is easily caused to be higher, so that waste is caused, and on the contrary, if the radar resolution ratio cannot meet the scene requirement, the radar signal processing complexity cannot be used. According to the scheme, the radar resolution ratio is dynamically controlled, the calculation efficiency of the radar system can be improved, the calculation waste is reduced, and the resolution ratio requirements of different scenes are met.

2. The system cost is reduced, and the resolution is maximized. In lidar systems, the price of the receiver is often higher than that of the VCSEL, and in order to achieve the required resolution, a relatively expensive receiver is usually used. The resolution is improved at the transmitting end by the scheme, and the cost of the radar system is greatly reduced. In addition, based on a final resolution calculation formula in the technical scheme, the number of the VCSELs and the receivers can be reasonably selected according to the cost of the VCSELs and the cost of the receivers, so that the system resolution is maximized, and the cost performance is improved.

Drawings

The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

FIG. 1 shows a schematic diagram of the basic principle of a lidar of the present invention;

FIG. 2 shows a schematic diagram of a VCSEL of the present invention;

fig. 3 shows a schematic diagram of the resolution calculation of the radar system of the present invention.

Detailed Description

The invention will be further explained with reference to the drawings.

As shown in fig. 1, the present invention may include at least one component or circuit that performs the following operations. Far-field tuning is used to optimize power transfer between the antenna array and the RF front-end, control the antenna array's direction, beam width, bandwidth, center frequency, modulation, squint, polarization, front-to-back ratio, etc. characteristics to optimize far-field reception and transmission.

As described above, the front-end stage is used to combine, synchronize and convert received RF frequencies into a lower frequency signal that can be more easily processed by a Digital Signal Processor (DSP) and/or other analog and digital circuitry.

Near field and far field processing refer to analog or digital signal processing as is well known to those skilled in the art.

Since the resolution is maximized when both the far field and the near field are used to generate an image of the object, a composite signal must be generated. The composite signal is a combination of near-field and far-field features, resulting in maximum resolution.

In one embodiment, the composite signal is generated from a plurality of signal samples. Most likely, one scanning system, or an equivalent scanning system via two or more antennas, is required as with conventional radar imagers (e.g., SNOM applications).

Another way to obtain improved radar resolution is to partially overlap the antenna patterns of the transmit and receive arrays, as shown in fig. 1, in such a way that the resolution is improved, but at the cost of power. Scanning the receive array focus (or peak gain) relative to the transmit array focus is similar to the techniques used to improve image resolution in certain types of optical sensors. An additional benefit of this approach is to optimize the focus of the array in a closed-loop manner.

In another embodiment, a "superlens" like system may be used, where the composite signal is generated from only one sample, rather than by scanning. By using the proposed new techniques, a superlens can be created that is not subject to standard superlens geometry requirements (e.g., sensing through a near-field probe or port, and generating a composite image by software).

Due to temperature, vibration, and circuit variations caused by operational and environmental factors (e.g., temperature, humidity, etc.), it may be desirable to implement a control loop to ensure that both the metamaterial and the conventional array have the desired characteristics. For example, the control loop may ensure that the metamaterial filter is centered on the transmit signal and that the filter rejects the returned far field.

In some embodiments, the invention may also include circuitry in communication with the metamaterial transmit array, and in some cases with a patch antenna or other antenna array. The circuit is designed to adjust/combine/control the array level the adjust/combine/control array level is a circuit for detecting near field signals from a near field probe, a high impedance probe or other type of touch probe. It may also be used to excite metamaterial elements using near-field probes. Furthermore, the adjustment/combination/control array stage may be used to steer the angle, beam width, bandwidth, center frequency, modulation, squint, polarization, focus of the main beam of the metamaterial array by using ports or probes or separate patches or other antenna arrays for reception or transmission. It may provide appropriate signals to a patch or other antenna array. It may be possible to control the center frequency, bandwidth and/or possible order of the metamaterial filter by using tuning elements such as varactors, gyroscopes, PIN diode switching elements, load/impedance pulling, saturable magnets, modulation/frequency control, or other tunable resonator components or sub-circuits, or combinations thereof. Also, it can be used to optimize power transfer between the sensing/stimulation array and the control circuitry.

In some embodiments, the invention may be used for improved metal penetrating radar. Electromagnetic frequencies from hertz (Hz) to several MHz effectively penetrate metal.

Also, in some embodiments, the invention may be used for clutter suppression. Far field return produces near field waves and far field waves upon diffraction. Rocks, soil changes and other buried objects having features with dimensions smaller than the wavelength of the incident wave are located between the desired object (or area) of interest and the radar system, adding noise to any radar returns. These far-field components will appear as clutter noise to conventional Ground Penetrating Radar (GPR).

However, these noise components of the far-field return are similar to the return produced by the metamaterial. By placing a metamaterial element (e.g., a resonator) with known electromagnetic properties near the object to be imaged, the return noise is better defined, allowing a large portion of the return noise to be subtracted from the far-field return. After the noise is subtracted, the far-field returns may be processed to improve the imaging resolution of the object of interest. These far-field components will appear as clutter noise to conventional Ground Penetrating Radar (GPR).

In some embodiments, clutter noise may be suppressed by "seeding" with a sub-wavelength sized resonator for controlling diffraction effects. The resonator may be dispersed in the ground on or near the object to be imaged. The resonator is preferably optimized to enable detection of echoes reflected from the object, wherein the echoes include dimensional information of the object that is smaller than the incident wavelength.

Sowing is also effective in detecting positional changes in the ground by determining the seed position at the start of sowing and detecting their positional changes. The baseline is determined by measuring radar images or features of the area immediately after seed placement. By re-measuring the image or feature and comparing it to the original radar image or feature, any disturbance or change in the conditions in the seed region can be determined. It is apparent that seeding has many important applications, including detection of buried mines, unexploded detonators (UXO), tunnels, utility lines and temporary explosion devices (IEDs)

In some embodiments, a seed subwavelength resonator is used to perform near-field to far-field conversion to enhance GPR imaging resolution.

In other embodiments, clutter suppression is achieved by narrowband, narrow beam, modulation techniques and time domain techniques. Although broadband metamaterials have been demonstrated, most metamaterials are narrowband. Due to its resonant structure, the metamaterial can be designed to provide its unique characteristics over a relatively narrow bandwidth and a relatively narrow angle of incidence.

A benefit of narrow band radar is that the radar becomes less susceptible to interference. The narrowband antenna/lens is also less susceptible to noise pickup, ringing caused by antenna-ground bounce, produces less interference, and is better matched to optimize transmit and receive power, thereby providing a wider dynamic range than is possible with wideband systems. Generating a transmission signal for a narrow band radar has proven to be prior art. However, it is novel and inventive to improve the resolution of GPR and Building Penetrating Radar (BPR) as well as Metal Penetrating Radar (MPR) using the near field techniques proposed here.

It is desirable to achieve GPR/BPR resolution in centimeters. To achieve centimeter resolution with standard radar, many gigahertz of bandwidth are required. The prior art sub-wavelength techniques have achieved sub-wavelength resolution improvements of about 3-700 times beyond the diffraction limit. For narrow band radars using sub-wavelength techniques with resolution increased by a factor of 100, an operating frequency of about 300MHz may be used. This is the frequency at which soil attenuation begins to increase, but the attenuation is low enough that significant soil penetration can occur at reasonable transmit power levels. Another benefit of using lower frequencies is that free space path loss is reduced, optimizing the return power of the near and far field signals.

Reducing the effective beamwidth of the GPR (i.e., the narrow beam) also reduces received artificial and ambient interference signals and noise, reduces clutter and facilitates scanning typically required for near field techniques.

Narrow-band modulation techniques (e.g., unmodulated waves, gaussian decay periods, monocycles, etc.) may be used in conjunction with knowledge of the focal and ultra-wideband like techniques (e.g., time-correlation) to reduce overall system noise, including suppression of clutter.

In some embodiments of the invention, sub-wavelength illumination may be used for metal penetrating radar. Although sub-wavelength illumination is not required for metal penetration, as previously described, sub-wavelength illumination does improve the resolution of metal penetrating radar. Achieving optimal resolution at the metal penetration frequency would require a combination of techniques such as sub-wavelength illumination and near field sensing components and feedback techniques such as scanning the receive lens focus across the transmit lens focus to detect and fine tune the sub-wavelength.

In some embodiments of the invention, sub-wavelength illumination may be used as a directed energy weapon. Directed energy weapons using sub-wavelength illumination techniques are advantageous over laser systems because they have lower path loss, are resistant to cloud cover, are resistant to obscuration by the combustion process, and offer new capabilities for directing electromagnetic damage. Directional electromagnetic damage includes the generation of electromagnetic pulses (EMPs) and simply the generation of successively higher local field strengths. With EMP or high field strength, the electronics in the target can be damaged (including the case where the target is shielded by EMI/EMP) without damaging the electronics of nearby electronic systems, and without requiring the emission power to be as high as that required to burn through the walls of the target system.

In at least one embodiment of the invention, sub-wavelength illumination may be used for clutter suppression. By focusing the energy of the incident radiation over a region of sub-wavelength size, the signal-to-noise ratio of the return signal from the sub-wavelength region is increased. The above-described techniques for clutter suppression may be used in conjunction with sub-wavelength illumination.

By independently controlling the VCSEL emitting lattice, the dynamic control of the resolution is realized, and the requirement on a receiver is reduced, so that the system cost is reduced.

VCSELs typically consist of hundreds or even thousands of emission points, and more advanced VCSELs can achieve independent control of the lattice. Based on the method, the VCSEL can divide the whole emission array surface into N according to requirements ₁ ×M ₁ The emitting units irradiate the detection target in a time-sharing manner, and the detector receives and senses the detection target at the same time, and each independent emitting unit can obtain the resolution ratio N ₂ ×M ₂ Thereby obtaining a resolution of (N) after all the transmitting units have finished sensing ₁ ×N ₂ )×(M ₁ ×M ₂ ) Thereby greatly improving the resolution.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.

Claims

1. A low cost high resolution lidar comprising a transmit array, a plurality of metamaterial elements forming a lens, the array configured to transmit radar range frequency electromagnetic waves; an exciter configured to excite the metamaterial element so as to generate electromagnetic waves that illuminate the target with sub-wavelength sized illumination; and a control part configured to control a focal point of the lens.

2. The low cost high resolution lidar of claim 1, wherein the control component that controls the focus of the lens is further configured to control the focus of the lens using a time delay.

3. The low cost high resolution lidar of claim 1, wherein the stimulator is selected from a near field probe, a port, an antenna, or combinations thereof.

4. The low-cost high-resolution lidar of claim 1, wherein the control component is selected from the group consisting of a tunable resonant component and a tunable resonant subcircuit.

5. The low-cost high-resolution lidar of claim 1, wherein the frequency of the electromagnetic wave is less than about 1 MHz.