Artifact on 3d objects in threejs

Whenever I add a narrow 3d object like the one below to the scene, I encounter some unwanted artifacts like a repeating texture on the object's surface. It worth mentioning that everything looks fine until I switch the receive shadow property of the object to true.

to be more precise, I created a box geometry with the size of (0.35, 0.02, 0.15) then I made a MeshStandardMaterial and feed both geometry and material to a THREE.Mesh. the lightning consists of ambient light and a directional light

ideally, the object should look like this:

Here is the code for lightning, object, and material

let ambientLight = new THREE.AmbientLight(0xffffff, 0.5);
let directionalLight = new THREE.DirectionalLight(0xffffff, 0.5);
directionalLight.castShadow = true;
this.directionalLight.position.set(-20, 20, 32);

scene.add(this.ambientLight);
scene.add(this.directionalLight);

let box = new THREE.BoxGeometry(0.02, 0.15, 
0.35)
let material = new THREE.MeshStandardMaterial({color: 'white', 
shadowSide: THREE.FrontSide, side: THREE.DoubleSide})
let mesh = new THREE.Mesh(box, material)
mesh.receiveshadow = true
mesh.castshadow = true

scene.add(mesh)

This is known as shadow acne. It happens when light hits a surface at a shallow angle. You'll probably need to make small modifications to the LightShadow.bias property. Quoting from the documentation:

Shadow map bias, how much to add or subtract from the normalized depth when deciding whether a surface is in shadow. The default is 0. Very tiny adjustments here (in the order of 0.0001) may help reduce artifacts in shadows.

Try something like: directionalLight.shadow.bias = 0.0001; and start from there, making small adjustments until the shadow acne isn't noticeable.

There's also a second parameter named LightShadow.normalBias that you could tweak.